1
|
Sure F, Einsiedel J, Gmeiner P, Duchstein P, Zahn D, Korbmacher C, Ilyaskin AV. The small molecule activator S3969 stimulates the epithelial sodium channel by interacting with a specific binding pocket in the channel's β-subunit. J Biol Chem 2024; 300:105785. [PMID: 38401845 PMCID: PMC11065748 DOI: 10.1016/j.jbc.2024.105785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 01/13/2024] [Accepted: 02/19/2024] [Indexed: 02/26/2024] Open
Abstract
The epithelial sodium channel (ENaC) is essential for mediating sodium absorption in several epithelia. Its impaired function leads to severe disorders, including pseudohypoaldosteronism type 1 and respiratory distress. Therefore, pharmacological ENaC activators have potential therapeutic implications. Previously, a small molecule ENaC activator (S3969) was developed. So far, little is known about molecular mechanisms involved in S3969-mediated ENaC stimulation. Here, we identified an S3969-binding site in human ENaC by combining structure-based simulations with molecular biological methods and electrophysiological measurements of ENaC heterologously expressed in Xenopus laevis oocytes. We confirmed a previous observation that the extracellular loop of β-ENaC is essential for ENaC stimulation by S3969. Molecular dynamics simulations predicted critical residues in the thumb domain of β-ENaC (Arg388, Phe391, and Tyr406) that coordinate S3969 within a binding site localized at the β-γ-subunit interface. Importantly, mutating each of these residues reduced (R388H; R388A) or nearly abolished (F391G; Y406A) the S3969-mediated ENaC activation. Molecular dynamics simulations also suggested that S3969-mediated ENaC stimulation involved a movement of the α5 helix of the thumb domain of β-ENaC away from the palm domain of γ-ENaC. Consistent with this, the introduction of two cysteine residues (βR437C - γS298C) to form a disulfide bridge connecting these two domains prevented ENaC stimulation by S3969 unless the disulfide bond was reduced by DTT. Finally, we demonstrated that S3969 stimulated ENaC endogenously expressed in cultured human airway epithelial cells (H441). These new findings may lead to novel (patho-)physiological and therapeutic concepts for disorders associated with altered ENaC function.
Collapse
Affiliation(s)
- Florian Sure
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Jürgen Einsiedel
- Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Peter Gmeiner
- Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Patrick Duchstein
- Theoretical Chemistry/Computer Chemistry Center (CCC), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Dirk Zahn
- Theoretical Chemistry/Computer Chemistry Center (CCC), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Alexandr V Ilyaskin
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
| |
Collapse
|
2
|
Ahmad T, Ertuglu LA, Masenga SK, Kleyman TR, Kirabo A. The epithelial sodium channel in inflammation and blood pressure modulation. Front Cardiovasc Med 2023; 10:1130148. [PMID: 37123470 PMCID: PMC10132033 DOI: 10.3389/fcvm.2023.1130148] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 03/24/2023] [Indexed: 05/02/2023] Open
Abstract
A major regulator of blood pressure and volume homeostasis in the kidney is the epithelial sodium channel (ENaC). ENaC is composed of alpha(α)/beta(β)/gamma(γ) or delta(δ)/beta(β)/gamma(γ) subunits. The δ subunit is functional in the guinea pig, but not in routinely used experimental rodent models including rat or mouse, and thus remains the least understood of the four subunits. While the δ subunit is poorly expressed in the human kidney, we recently found that its gene variants are associated with blood pressure and kidney function. The δ subunit is expressed in the human vasculature where it may influence vascular function. Moreover, we recently found that the δ subunit is also expressed human antigen presenting cells (APCs). Our studies indicate that extracellular Na+ enters APCs via ENaC leading to inflammation and salt-induced hypertension. In this review, we highlight recent findings on the role of extra-renal ENaC in inflammation, vascular dysfunction, and blood pressure modulation. Targeting extra-renal ENaC may provide new drug therapies for salt-induced hypertension.
Collapse
Affiliation(s)
- Taseer Ahmad
- Department of Pharmacology, College of Pharmacy, University of Sargodha, Sargodha, Pakistan
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, United States
| | - Lale A. Ertuglu
- Division of Nephrology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, United States
| | - Sepiso K. Masenga
- Department of Physiological Sciences, School of Medicine and Health Sciences, Mulungushi University, Livingstone, Zambia
| | - Thomas R. Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA, United States
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Annet Kirabo
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, United States
| |
Collapse
|
3
|
Zhang L, Wang X, Chen J, Kleyman TR, Sheng S. Accessibility of ENaC extracellular domain central core residues. J Biol Chem 2022; 298:101860. [PMID: 35339489 PMCID: PMC9052164 DOI: 10.1016/j.jbc.2022.101860] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 03/16/2022] [Accepted: 03/21/2022] [Indexed: 11/20/2022] Open
Abstract
The epithelial Na+ channel (ENaC)/degenerin family has a similar extracellular architecture, where specific regulatory factors interact and alter channel gating behavior. The extracellular palm domain serves as a key link to the channel pore. In this study, we used cysteine-scanning mutagenesis to assess the functional effects of Cys-modifying reagents on palm domain β10 strand residues in mouse ENaC. Of the 13 ENaC α subunit mutants with Cys substitutions examined, only mutants at sites in the proximal region of β10 exhibited changes in channel activity in response to methanethiosulfonate reagents. Additionally, Cys substitutions at three proximal sites of β and γ subunit β10 strands also rendered mutant channels methanethiosulfonate-responsive. Moreover, multiple Cys mutants were activated by low concentrations of thiophilic Cd2+. Using the Na+ self-inhibition response to assess ENaC gating behavior, we identified four α, two β, and two γ subunit β10 strand mutations that changed the Na+ self-inhibition response. Our results suggest that the proximal regions of β10 strands in all three subunits are accessible to small aqueous compounds and Cd2+ and have a role in modulating ENaC gating. These results are consistent with a structural model of mouse ENaC that predicts the presence of aqueous tunnels adjacent to the proximal part of β10 and with previously resolved structures of a related family member where palm domain structural transitions were observed with channels in an open or closed state.
Collapse
Affiliation(s)
- Lei Zhang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Xueqi Wang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Jingxin Chen
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Thomas R Kleyman
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
| | - Shaohu Sheng
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| |
Collapse
|
4
|
Reihill JA, Douglas LEJ, Martin SL. Modulation of Ion Transport to Restore Airway Hydration in Cystic Fibrosis. Genes (Basel) 2021; 12:genes12030453. [PMID: 33810137 PMCID: PMC8004921 DOI: 10.3390/genes12030453] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Revised: 03/11/2021] [Accepted: 03/19/2021] [Indexed: 12/11/2022] Open
Abstract
Cystic fibrosis (CF) is a life-limiting genetic disorder caused by loss-of-function mutations in the gene which codes for the CF transmembrane conductance regulator (CFTR) Cl- channel. Loss of Cl- secretion across the apical membrane of airway lining epithelial cells results in dehydration of the airway surface liquid (ASL) layer which impairs mucociliary clearance (MCC), and as a consequence promotes bacterial infection and inflammation of the airways. Interventions that restore airway hydration are known to improve MCC. Here we review the ion channels present at the luminal surface of airway epithelial cells that may be targeted to improve airway hydration and MCC in CF airways.
Collapse
|
5
|
Hartati YW, Komala DR, Hendrati D, Gaffar S, Hardianto A, Sofiatin Y, Bahti HH. An aptasensor using ceria electrodeposited-screen-printed carbon electrode for detection of epithelial sodium channel protein as a hypertension biomarker. R Soc Open Sci 2021; 8:202040. [PMID: 33972878 PMCID: PMC8074578 DOI: 10.1098/rsos.202040] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 01/20/2021] [Indexed: 06/02/2023]
Abstract
Epithelial sodium channel (ENaC) is a transmembrane protein that has an essential role in maintaining the levels of sodium in blood plasma. A person with a family history of hypertension has a high enough amount of ENaC protein in the kidneys or other organs, so that the ENaC protein acts as a marker that a person is susceptible to hypertension. An aptasensor involves aptamers, which are oligonucleotides that function similar to antibodies, as sensing elements. An electrochemical aptasensor for the detection of ENaC was developed using a screen-printed carbon electrode (SPCE) which was modified by electrodeposition of cerium oxide (CeO2). The aptamer immobilization was via the streptavidin-biotin system. The measurement of changes in current of the active redox [Fe(CN)6]3-/4- was carried out by differential pulse voltammetry. The surfaces of SPCE and SPCE/CeO2 were characterized using scanning electron microscopy, voltammetry and electrochemical impedance spectroscopy. The Box-Behnken experimental optimization design revealed the streptavidin incubation time, aptamer incubation time and streptavidin concentrations were 30 min, 30 min and 10.8 µg ml-1, respectively. Various concentrations of ENaC were used to obtain the linearity range of 0.05-3.0 ng ml-1, and the limits of detection and quantification were 0.012 ng ml-1 and 0.038 ng ml-1, respectively. This aptasensor method has the potential to measure the ENaC protein levels in urine samples as well as to be a point-of-care device.
Collapse
Affiliation(s)
- Yeni Wahyuni Hartati
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia
| | - Dina Ratna Komala
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia
| | - Diana Hendrati
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia
| | - Shabarni Gaffar
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia
| | - Ari Hardianto
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia
| | - Yulia Sofiatin
- Department of Public Health, Faculty of Medicine, Universitas Padjadjaran, Bandung, Indonesia
| | - Husein Hernandi Bahti
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Bandung, Indonesia
| |
Collapse
|
6
|
Shabbir W, Topcagic N, Aufy M, Oz M. CRISPR/Cas9 Mediated Knock Down of δ-ENaC Blunted the TNF-Induced Activation of ENaC in A549 Cells. Int J Mol Sci 2021; 22:1858. [PMID: 33673381 DOI: 10.3390/ijms22041858] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2021] [Revised: 02/02/2021] [Accepted: 02/09/2021] [Indexed: 11/16/2022] Open
Abstract
Tumor necrosis factor (TNF) is known to activate the epithelial Na+ channel (ENaC) in A549 cells. A549 cells are widely used model for ENaC research. The role of δ-ENaC subunit in TNF-induced activation has not been studied. In this study we hypothesized that δ-ENaC plays a major role in TNF-induced activation of ENaC channel in A549 cells which are widely used model for ENaC research. We used CRISPR/Cas 9 approach to knock down (KD) the δ-ENaC in A549 cells. Western blot and immunofluorescence assays were performed to analyze efficacy of δ-ENaC protein KD. Whole-cell patch clamp technique was used to analyze the TNF-induced activation of ENaC. Overexpression of wild type δ-ENaC in the δ-ENaC KD of A549 cells restored the TNF-induced activation of whole-cell Na+ current. Neither N-linked glycosylation sites nor carboxyl terminus domain of δ-ENaC was necessary for the TNF-induced activation of whole-cell Na+ current in δ-ENaC KD of A549 cells. Our data demonstrated that in A549 cells the δ-ENaC plays a major role in TNF-induced activation of ENaC.
Collapse
|
7
|
Ilyaskin AV, Korbmacher C, Diakov A. Inhibition of the epithelial sodium channel (ENaC) by connexin 30 involves stimulation of clathrin-mediated endocytosis. J Biol Chem 2021; 296:100404. [PMID: 33577799 PMCID: PMC7973139 DOI: 10.1016/j.jbc.2021.100404] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 02/05/2021] [Accepted: 02/08/2021] [Indexed: 01/16/2023] Open
Abstract
Mice lacking connexin 30 (Cx30) display increased epithelial sodium channel (ENaC) activity in the distal nephron and develop salt-sensitive hypertension. This indicates a functional link between Cx30 and ENaC, which remains incompletely understood. Here, we explore the effect of Cx30 on ENaC function using the Xenopus laevis oocyte expression system. Coexpression of human Cx30 with human αβγENaC significantly reduced ENaC-mediated whole-cell currents. The size of the inhibitory effect on ENaC depended on the expression level of Cx30 and required Cx30 ion channel activity. ENaC inhibition by Cx30 was mainly due to reduced cell surface ENaC expression resulting from enhanced ENaC retrieval without discernible effects on proteolytic channel activation and single-channel properties. ENaC retrieval from the cell surface involves the interaction of the ubiquitin ligase Nedd4-2 with PPPxY-motifs in the C-termini of ENaC. Truncating the C- termini of β- or γENaC significantly reduced the inhibitory effect of Cx30 on ENaC. In contrast, mutating the prolines belonging to the PPPxY-motif in γENaC or coexpressing a dominant-negative Xenopus Nedd4 (xNedd4-CS) did not significantly alter ENaC inhibition by Cx30. Importantly, the inhibitory effect of Cx30 on ENaC was significantly reduced by Pitstop-2, an inhibitor of clathrin-mediated endocytosis, or by mutating putative clathrin adaptor protein 2 (AP-2) recognition motifs (YxxФ) in the C termini of β- or γ-ENaC. In conclusion, our findings suggest that Cx30 inhibits ENaC by promoting channel retrieval from the plasma membrane via clathrin-dependent endocytosis. Lack of this inhibition may contribute to increased ENaC activity and salt-sensitive hypertension in mice with Cx30 deficiency.
Collapse
Affiliation(s)
- Alexandr V Ilyaskin
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
| | - Alexei Diakov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| |
Collapse
|
8
|
Archer CR, Enslow BT, Carver CM, Stockand JD. Phosphatidylinositol 4,5-bisphosphate directly interacts with the β and γ subunits of the sodium channel ENaC. J Biol Chem 2020; 295:7958-7969. [PMID: 32341072 PMCID: PMC7278353 DOI: 10.1074/jbc.ra120.012606] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 04/22/2020] [Indexed: 12/18/2022] Open
Abstract
The plasma membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) regulates the activity of diverse ion channels to include the epithelial Na+ channel ENaC. Whether PIP2 regulation of ENaC is due to a direct phospholipid-protein interaction, remains obscure. To date, possible interaction of PIP2 with ENaC primarily has been tested indirectly through assays of channel function. A fragment-based biochemical analysis approach is used here to directly quantify possible PIP2-ENaC interactions. We find using the CIBN-CRY2 optogenetic dimerization system that the phosphoryl group positioned at carbon 5 of PIP2 is necessary for interaction with ENaC. Previous studies have implicated conserved basic residues in the cytosolic portions of β- and γ-ENaC subunits as being important for PIP2-ENaC interactions. To test this, we used synthetic peptides of these regions of β- and γ-ENaC. Steady-state intrinsic fluorescence spectroscopy demonstrated that phosphoinositides change the local conformation of the N terminus of β-ENaC, and two sites of γ-ENaC adjacent to the plasma membrane, suggesting direct interactions of PIP2 with these three regions. Microscale thermophoresis elaborated PIP2 interactions with the N termini of β- (Kd ∼5.2 μm) and γ-ENaC (Kd ∼13 μm). A weaker interaction site within the carboxyl terminus of γ-ENaC (Kd ∼800 μm) was also observed. These results support that PIP2 regulates ENaC activity by directly interacting with at least three distinct regions within the cytoplasmic domains of the channel that contain conserved basic residues. These interactions are probably electrostatic in nature, and are likely to bear a key structural role in support of channel activity.
Collapse
Affiliation(s)
- Crystal R Archer
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Benjamin T Enslow
- Division of Nephrology, Department of Medicine, University of Texas Health Science Center, San Antonio, Texas, United States
| | - Chase M Carver
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center, San Antonio, Texas, United States
| | - James D Stockand
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center, San Antonio, Texas, United States
| |
Collapse
|
9
|
Shi S, Montalbetti N, Wang X, Rush BM, Marciszyn AL, Baty CJ, Tan RJ, Carattino MD, Kleyman TR. Paraoxonase 3 functions as a chaperone to decrease functional expression of the epithelial sodium channel. J Biol Chem 2020; 295:4950-4962. [PMID: 32079677 DOI: 10.1074/jbc.ra119.011789] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 02/17/2020] [Indexed: 01/11/2023] Open
Abstract
The paraoxonase (PON) family comprises three highly conserved members: PON1, PON2, and PON3. They are orthologs of Caenorhabditis elegans MEC-6, an endoplasmic reticulum-resident chaperone that has a critical role in proper assembly and surface expression of the touch-sensing degenerin channel in nematodes. We have shown recently that MEC-6 and PON2 negatively regulate functional expression of the epithelial Na+ channel (ENaC), suggesting that the chaperone function is conserved within this family. We hypothesized that other PON family members also modulate ion channel expression. Pon3 is specifically expressed in the aldosterone-sensitive distal tubules in the mouse kidney. We found here that knocking down endogenous Pon3 in mouse cortical collecting duct cells enhanced Na+ transport, which was associated with increased γENaC abundance. We further examined Pon3 regulation of ENaC in two heterologous expression systems, Fisher rat thyroid cells and Xenopus oocytes. Pon3 coimmunoprecipitated with each of the three ENaC subunits in Fisher rat thyroid cells. As a result of this interaction, the whole-cell and surface abundance of ENaC α and γ subunits was reduced by Pon3. When expressed in oocytes, Pon3 inhibited ENaC-mediated amiloride-sensitive Na+ currents, in part by reducing the surface expression of ENaC. In contrast, Pon3 did not alter the response of ENaC to chymotrypsin-mediated proteolytic activation or [2-(trimethylammonium)ethyl]methanethiosulfonate-induced activation of αβS518Cγ, suggesting that Pon3 does not affect channel open probability. Together, our results suggest that PON3 regulates ENaC expression by inhibiting its biogenesis and/or trafficking.
Collapse
Affiliation(s)
- Shujie Shi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Nicolas Montalbetti
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Xueqi Wang
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Nephrology, Second Xiangya Hospital of Central South University, Changsha 410011, Hunan, China
| | - Brittney M Rush
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Allison L Marciszyn
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Catherine J Baty
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Roderick J Tan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Marcelo D Carattino
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
10
|
Fujikawa H, Kawakami T, Nakashima R, Nasu A, Kamei S, Nohara H, Eto Y, Ueno-Shuto K, Takeo T, Nakagata N, Suico MA, Kai H, Shuto T. Azithromycin Inhibits Constitutive Airway Epithelial Sodium Channel Activation in Vitro and Modulates Downstream Pathogenesis in Vivo. Biol Pharm Bull 2020; 43:725-730. [PMID: 32009028 DOI: 10.1248/bpb.b19-01091] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epithelial sodium channel (ENaC) is an amiloride-sensitive sodium ion channel that is expressed in epithelial tissues. ENaC overexpression and/or hyperactivation in airway epithelial cells cause sodium over-absorption and dysregulated ciliary movement for mucus clearance; however, the agents that suppress constitutive airway ENaC activation are yet to be clinically available. Here, we focused on macrolides, which are widely used antibiotics that have many potential immunomodulatory effects. We examined whether macrolides could modulate constitutive ENaC activity and downstream events that typify cystic fibrosis (CF) and chronic obstructive pulmonary diseases (COPD) in in vitro and in vivo models of ENaC overexpression. Treatment of ENaC-overexpressing human bronchial epithelial cells (β/γENaC-16HBE14o- cells) with three macrolides (erythromycin, clarithromycin, azithromycin) confirmed dose-dependent suppression of ENaC function. For in vivo studies, mice harboring airway specific βENaC overexpression (C57BL/6J-βENaC-transgenic mice) were treated orally with azithromycin, a well-established antimicrobial agent that has been widely prescribed. Azithromycin treatment modulated pulmonary mechanics, emphysematous phenotype and pulmonary dysfunction. Notably, a lower dose (3 mg kg-1) of azithromycin significantly increased forced expiratory volume in 0.1 s (FEV0.1), an inverse indicator of bronchoconstriction. Although not statistically significant, improvement of pulmonary obstructive parameters such as emphysema and lung dysfunction (FEV0.1%) was observed. Our results demonstrate that macrolides directly attenuate constitutive ENaC function in vitro and may be promising for the treatment of obstructive lung diseases with defective mucociliary clearance, possibly by targeting ENaC hyperactivation.
Collapse
Affiliation(s)
- Haruka Fujikawa
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University.,Program for Leading Graduate Schools "HIGO (Health life science: Interdisciplinary and Glocal Oriented) Program," Kumamoto University
| | - Taise Kawakami
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University
| | - Ryunosuke Nakashima
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University
| | - Aoi Nasu
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University
| | - Shunsuke Kamei
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University.,Program for Leading Graduate Schools "HIGO (Health life science: Interdisciplinary and Glocal Oriented) Program," Kumamoto University.,Center for Inflammation, Immunity & Infection, Institute for Biomedical Sciences, Georgia State University
| | - Hirofumi Nohara
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University.,Program for Leading Graduate Schools "HIGO (Health life science: Interdisciplinary and Glocal Oriented) Program," Kumamoto University
| | - Yuka Eto
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University
| | - Keiko Ueno-Shuto
- Laboratory of Pharmacology, Division of Life Science, Faculty of Pharmaceutical Sciences, Sojo University
| | - Toru Takeo
- Division of Reproductive Engineering, Center for Animal Resources and Development (CARD), Kumamoto University
| | - Naomi Nakagata
- Division of Reproductive Engineering, Center for Animal Resources and Development (CARD), Kumamoto University
| | - Mary Ann Suico
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University.,Global Center for Natural Resources Sciences, Faculty of Life Sciences, Kumamoto University
| | - Hirofumi Kai
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University.,Global Center for Natural Resources Sciences, Faculty of Life Sciences, Kumamoto University
| | - Tsuyoshi Shuto
- Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University.,Global Center for Natural Resources Sciences, Faculty of Life Sciences, Kumamoto University
| |
Collapse
|
11
|
Bohnert BN, Daiminger S, Wörn M, Sure F, Staudner T, Ilyaskin AV, Batbouta F, Janessa A, Schneider JC, Essigke D, Kanse S, Haerteis S, Korbmacher C, Artunc F. Urokinase-type plasminogen activator (uPA) is not essential for epithelial sodium channel (ENaC)-mediated sodium retention in experimental nephrotic syndrome. Acta Physiol (Oxf) 2019; 227:e13286. [PMID: 31006168 DOI: 10.1111/apha.13286] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/10/2019] [Accepted: 04/15/2019] [Indexed: 12/17/2022]
Abstract
AIM In nephrotic syndrome, aberrantly filtered plasminogen (plg) is converted to active plasmin by tubular urokinase-type plasminogen activator (uPA) and thought to lead to sodium retention by proteolytic activation of the epithelial sodium channel (ENaC). This concept predicts that uPA is an important factor for sodium retention and that inhibition of uPA might be protective in nephrotic syndrome. METHODS Activation of amiloride-sensitive currents by uPA and plg were studied in Xenopus laevis oocytes expressing murine ENaC. In doxorubicin-induced nephrotic mice, uPA was inhibited pharmacologically by amiloride and genetically by the use of uPA-deficient mice (uPA-/- ). RESULTS Experiments in Xenopus laevis oocytes expressing murine ENaC confirmed proteolytic ENaC activation by a combination of plg and uPA which stimulated amiloride-sensitive currents with concomitant cleavage of the ENaC γ-subunit at the cell surface. Treatment of nephrotic wild-type mice with amiloride inhibited urinary uPA activity, prevented urinary plasmin formation and sodium retention. In nephrotic mice lacking uPA (uPA-/- ), urinary plasmin formation from plg was suppressed and urinary uPA activity absent. However, in nephrotic uPA-/- mice, sodium retention was not reduced compared to nephrotic uPA+/+ mice. Amiloride prevented sodium retention in nephrotic uPA-/- mice which confirmed the critical role of ENaC in sodium retention. CONCLUSION uPA is responsible for the conversion of aberrantly filtered plasminogen to plasmin in the tubular lumen in vivo. However, uPA-dependent plasmin generation is not essential for ENaC-mediated sodium retention in experimental nephrotic syndrome.
Collapse
Affiliation(s)
- Bernhard N. Bohnert
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| | - Sophie Daiminger
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Matthias Wörn
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Florian Sure
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Tobias Staudner
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Alexandr V. Ilyaskin
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Firas Batbouta
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Andrea Janessa
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Jonas C. Schneider
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Daniel Essigke
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Sandip Kanse
- Institute of Basic Medical Sciences University of Oslo Oslo Norway
| | - Silke Haerteis
- Institute of Anatomy University of Regensburg Regensburg Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Ferruh Artunc
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| |
Collapse
|
12
|
Bikard Y, Viviano J, Orr MN, Brown L, Brecker M, Jeger JL, Grits D, Suaud L, Rubenstein RC. The KDEL receptor has a role in the biogenesis and trafficking of the epithelial sodium channel (ENaC). J Biol Chem 2019; 294:18324-18336. [PMID: 31653700 DOI: 10.1074/jbc.ra119.008331] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Revised: 10/21/2019] [Indexed: 11/06/2022] Open
Abstract
Endoplasmic reticulum protein of 29 kDa (ERp29) is a thioredoxin-homologous endoplasmic reticulum (ER) protein that regulates the biogenesis of cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial sodium channel (ENaC). ERp29 may promote ENaC cleavage and increased open probability by directing ENaC to the Golgi via coat complex II (COP II) during biogenesis. We hypothesized that ERp29's C-terminal KEEL ER retention motif, a KDEL variant that is associated with less robust ER retention, strongly influences its regulation of ENaC biogenesis. As predicted by our previous work, depletion of Sec24D, the cargo recognition component of COP II that we previously demonstrated to interact with ENaC, decreases ENaC functional expression without altering β-ENaC expression at the apical surface. We then tested the influence of KDEL ERp29, which should be more readily retrieved from the proximal Golgi by the KDEL receptor (KDEL-R), and a KEEL-deleted mutant (ΔKEEL ERp29), which should not interact with the KDEL-R. ENaC functional expression was decreased by ΔKEEL ERp29 overexpression, whereas KDEL ERp29 overexpression did not significantly alter ENaC functional expression. Again, β-ENaC expression at the apical surface was unaltered by either of these manipulations. Finally, we tested whether the KDEL-R itself has a role in ENaC forward trafficking and found that KDEL-R depletion decreases ENaC functional expression, again without altering β-ENaC expression at the apical surface. These results support the hypothesis that the KDEL-R plays a role in the biogenesis of ENaC and in its exit from the ER through its association with COP II. The cleavage of the extracellular loops of the epithelial sodium channel (ENaC) α and γ subunits increases the channel's open probability and function. During ENaC biogenesis, such cleavage is regulated by the novel 29-kDa chaperone of the ER, ERp29. Our data here are consistent with the hypothesis that ERp29 must interact with the KDEL receptor to exert its regulation of ENaC biogenesis. The classically described role of the KDEL receptor is to retrieve ER-retained species from the proximal Golgi and return them to the ER via coat complex I machinery. In contrast, our data suggest a novel and important role for the KDEL receptor in the biogenesis and forward trafficking of ENaC.
Collapse
Affiliation(s)
- Yann Bikard
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Jeffrey Viviano
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Melissa N Orr
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Lauren Brown
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Margaret Brecker
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Jonathan Litvak Jeger
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Daniel Grits
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Laurence Suaud
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Ronald C Rubenstein
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104; Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104.
| |
Collapse
|
13
|
Yanda MK, Cha B, Cebotaru CV, Cebotaru L. Pharmacological reversal of renal cysts from secretion to absorption suggests a potential therapeutic strategy for managing autosomal dominant polycystic kidney disease. J Biol Chem 2019; 294:17090-17104. [PMID: 31570523 DOI: 10.1074/jbc.ra119.010320] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 09/26/2019] [Indexed: 12/19/2022] Open
Abstract
Autosomal-dominant polycystic kidney disease (ADPKD) induces a secretory phenotype, resulting in multiple fluid-filled cysts. We have previously demonstrated that VX-809, a corrector of the cystic fibrosis transmembrane conductance regulator (CFTR), reduces cyst growth. Here, we show that in normal mice CFTR is located within the cells and also at the apical and basolateral membranes. However, in polycystic kidney disease (pkd1)-knockout mice, CFTR was located at the plasma membrane, consistent with its role in cAMP-dependent fluid secretion. In cystic mice, VX-809 treatment increased CFTR levels at the apical membrane and reduced its association with the endoplasmic reticulum. Surprisingly, VX-809 treatment significantly increased CFTR's co-localization with the basolateral membrane in cystic mice. Na+/H+ exchanger 3 (NHE3) is present in pkd1-knockout and normal mice and in proximal tubule-derived, cultured pkd1-knockout cells. VX-809 increased the expression, activity, and apical plasma membrane localization of NHE3. Co-localization of epithelial sodium channel (ENaC) with the plasma membrane was reduced in cysts in pkd1-knockout mice, consistent with an inability of the cysts to absorb fluid. Interestingly, in the cystic mice, VX-809 treatment increased ENaC levels at the apical plasma membrane consistent with fluid absorption. Thus, VX-809 treatment of pkd1-null mouse kidneys significantly affected CFTR, NHE3, and ENaC, altering the cyst phenotype from one poised toward fluid secretion toward one more favorable for absorption. VX-809 also altered the location of CFTR but not of NHE3 or ENaC in normal mice. Given that VX-809 administration is safe, it may have potential utility for treating patients with ADPKD.
Collapse
Affiliation(s)
- Murali K Yanda
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Boyoung Cha
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Cristina V Cebotaru
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Liudmila Cebotaru
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| |
Collapse
|
14
|
Wang X, Chen J, Shi S, Sheng S, Kleyman TR. Analyses of epithelial Na + channel variants reveal that an extracellular β-ball domain critically regulates ENaC gating. J Biol Chem 2019; 294:16765-16775. [PMID: 31551351 DOI: 10.1074/jbc.ra119.010001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 09/19/2019] [Indexed: 11/06/2022] Open
Abstract
Epithelial Na+ channel (ENaC)-mediated Na+ transport has a key role in the regulation of extracellular fluid volume, blood pressure, and extracellular [K+]. Among the thousands of human ENaC variants, only a few exist whose functional consequences have been experimentally tested. Here, we used the Xenopus oocyte expression system to investigate the functional roles of four nonsynonymous human ENaC variants located within the β7-strand and its adjacent loop of the α-subunit extracellular β-ball domain. αR350Wβγ and αG355Rβγ channels exhibited 2.5- and 1.8-fold greater amiloride-sensitive currents than WT αβγ human ENaCs, respectively, whereas αV351Aβγ channels conducted significantly less current than WT. Currents in αH354Rβγ-expressing oocytes were similar to those expressing WT. Surface expression levels of three mutants (αR350Wβγ, αV351Aβγ, and αG355Rβγ) were similar to that of WT. However, three mutant channels (αR350Wβγ, αH354Rβγ, and αG355Rβγ) exhibited a reduced Na+ self-inhibition response. Open probability of αR350Wβγ was significantly greater than that of WT. Moreover, other Arg-350 variants, including αR350G, αR350L, and αR350Q, also had significantly increased channel activity. A direct comparison of αR350W and two previously reported gain-of-function variants revealed that αR350W increases ENaC activity similarly to αW493R, but to a much greater degree than does αC479R. Our results indicate that αR350W along with αR350G, αR350L, and αR350Q, and αG355R are novel gain-of-function variants that function as gating modifiers. The location of these multiple functional variants suggests that the αENaC β-ball domain portion that interfaces with the palm domain of βENaC critically regulates ENaC gating.
Collapse
Affiliation(s)
- Xueqi Wang
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Nephrology, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, China.,The Third Xiangya Hospital of Central South University, Changsha, Hunan 410013, China
| | - Jingxin Chen
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shujie Shi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shaohu Sheng
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
15
|
Wang XP, Im SJ, Balchak DM, Montalbetti N, Carattino MD, Ray EC, Kashlan OB. Murine epithelial sodium (Na +) channel regulation by biliary factors. J Biol Chem 2019; 294:10182-10193. [PMID: 31092599 PMCID: PMC6664190 DOI: 10.1074/jbc.ra119.007394] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 05/15/2019] [Indexed: 01/01/2023] Open
Abstract
The epithelial sodium channel (ENaC) mediates Na+ transport in several epithelia, including the aldosterone-sensitive distal nephron, distal colon, and biliary epithelium. Numerous factors regulate ENaC activity, including extracellular ligands, post-translational modifications, and membrane-resident lipids. However, ENaC regulation by bile acids and conjugated bilirubin, metabolites that are abundant in the biliary tree and intestinal tract and are sometimes elevated in the urine of individuals with advanced liver disease, remains poorly understood. Here, using a Xenopus oocyte-based system to express and functionally study ENaC, we found that, depending on the bile acid used, bile acids both activate and inhibit mouse ENaC. Whether bile acids were activating or inhibiting was contingent on the position and orientation of specific bile acid moieties. For example, a hydroxyl group at the 12-position and facing the hydrophilic side (12α-OH) was activating. Taurine-conjugated bile acids, which have reduced membrane permeability, affected ENaC activity more strongly than did their more membrane-permeant unconjugated counterparts, suggesting that bile acids regulate ENaC extracellularly. Bile acid-dependent activation was enhanced by amino acid substitutions in ENaC that depress open probability and was precluded by proteolytic cleavage that increases open probability, consistent with an effect of bile acids on ENaC open probability. Bile acids also regulated ENaC in a cortical collecting duct cell line, mirroring the results in Xenopus oocytes. We also show that bilirubin conjugates activate ENaC. These results indicate that ENaC responds to compounds abundant in bile and that their ability to regulate this channel depends on the presence of specific functional groups.
Collapse
Affiliation(s)
- Xue-Ping Wang
- From the Renal-Electrolyte Division, Department of Medicine
| | | | | | | | - Marcelo D Carattino
- From the Renal-Electrolyte Division, Department of Medicine
- the Department of Cell Biology and Molecular Physiology, and
| | - Evan C Ray
- From the Renal-Electrolyte Division, Department of Medicine
| | - Ossama B Kashlan
- From the Renal-Electrolyte Division, Department of Medicine,
- the Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
16
|
Wichmann L, Dulai JS, Marles-Wright J, Maxeiner S, Szczesniak PP, Manzini I, Althaus M. An extracellular acidic cleft confers profound H +-sensitivity to epithelial sodium channels containing the δ-subunit in Xenopus laevis. J Biol Chem 2019; 294:12507-12520. [PMID: 31248986 DOI: 10.1074/jbc.ra119.008255] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2019] [Revised: 06/27/2019] [Indexed: 11/06/2022] Open
Abstract
The limited sodium availability of freshwater and terrestrial environments was a major physiological challenge during vertebrate evolution. The epithelial sodium channel (ENaC) is present in the apical membrane of sodium-absorbing vertebrate epithelia and evolved as part of a machinery for efficient sodium conservation. ENaC belongs to the degenerin/ENaC protein family and is the only member that opens without an external stimulus. We hypothesized that ENaC evolved from a proton-activated sodium channel present in ionocytes of freshwater vertebrates and therefore investigated whether such ancestral traits are present in ENaC isoforms of the aquatic pipid frog Xenopus laevis Using whole-cell and single-channel electrophysiology of Xenopus oocytes expressing ENaC isoforms assembled from αβγ- or δβγ-subunit combinations, we demonstrate that Xenopus δβγ-ENaC is profoundly activated by extracellular acidification within biologically relevant ranges (pH 8.0-6.0). This effect was not observed in Xenopus αβγ-ENaC or human ENaC orthologs. We show that protons interfere with allosteric ENaC inhibition by extracellular sodium ions, thereby increasing the probability of channel opening. Using homology modeling of ENaC structure and site-directed mutagenesis, we identified a cleft region within the extracellular loop of the δ-subunit that contains several acidic amino acid residues that confer proton-sensitivity and enable allosteric inhibition by extracellular sodium ions. We propose that Xenopus δβγ-ENaC can serve as a model for investigating ENaC transformation from a proton-activated toward a constitutively-active ion channel. Such transformation might have occurred during the evolution of tetrapod vertebrates to enable bulk sodium absorption during the water-to-land transition.
Collapse
Affiliation(s)
- Lukas Wichmann
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom; Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University Giessen, 35390 Giessen, Germany
| | - Jasdip Singh Dulai
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Jon Marles-Wright
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Stephan Maxeiner
- Institute of Anatomy and Cell Biology, Saarland University, 66421 Homburg, Germany
| | - Pawel Piotr Szczesniak
- Department of Medicine, Haematology/Oncology, Johann-Wolfgang-Goethe University Frankfurt, 60323 Frankfurt, Germany
| | - Ivan Manzini
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University Giessen, 35390 Giessen, Germany
| | - Mike Althaus
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom.
| |
Collapse
|
17
|
Sheng S, Chen J, Mukherjee A, Yates ME, Buck TM, Brodsky JL, Tolino MA, Hughey RP, Kleyman TR. Thumb domains of the three epithelial Na + channel subunits have distinct functions. J Biol Chem 2018; 293:17582-17592. [PMID: 30228189 PMCID: PMC6231141 DOI: 10.1074/jbc.ra118.003618] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 09/13/2018] [Indexed: 01/10/2023] Open
Abstract
The epithelial Na+ channel (ENaC) possesses a large extracellular domain formed by a β-strand core enclosed by three peripheral α-helical subdomains, which have been dubbed thumb, finger, and knuckle. Here we asked whether the ENaC thumb domains play specific roles in channel function. To this end, we examined the characteristics of channels lacking a thumb domain in an individual ENaC subunit (α, β, or γ). Removing the γ subunit thumb domain had no effect on Na+ currents when expressed in Xenopus oocytes, but moderately reduced channel surface expression. In contrast, ENaCs lacking the α or β subunit thumb domain exhibited significantly reduced Na+ currents along with a large reduction in channel surface expression. Moreover, channels lacking an α or γ thumb domain exhibited a diminished Na+ self-inhibition response, whereas this response was retained in channels lacking a β thumb domain. In turn, deletion of the α thumb domain had no effect on the degradation rate of the immature α subunit as assessed by cycloheximide chase analysis. However, accelerated degradation of the immature β subunit and mature γ subunit was observed when the β or γ thumb domain was deleted, respectively. Our results suggest that the thumb domains in each ENaC subunit are required for optimal surface expression in oocytes and that the α and γ thumb domains both have important roles in the channel's inhibitory response to external Na+ Our findings support the notion that the extracellular helical domains serve as functional modules that regulate ENaC biogenesis and activity.
Collapse
Affiliation(s)
- Shaohu Sheng
- From the Renal-Electrolyte Division, Department of Medicine and
| | - Jingxin Chen
- From the Renal-Electrolyte Division, Department of Medicine and
| | | | | | | | | | | | - Rebecca P Hughey
- From the Renal-Electrolyte Division, Department of Medicine and
- Cell Biology
- Microbiology and Molecular Genetics, and
| | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine and
- Cell Biology
- Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
18
|
Balchak DM, Thompson RN, Kashlan OB. The epithelial Na + channel γ subunit autoinhibitory tract suppresses channel activity by binding the γ subunit's finger-thumb domain interface. J Biol Chem 2018; 293:16217-16225. [PMID: 30131333 DOI: 10.1074/jbc.ra118.004362] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Revised: 08/21/2018] [Indexed: 01/11/2023] Open
Abstract
Epithelial Na+ channel (ENaC) maturation and activation require proteolysis of both the α and γ subunits. Cleavage at multiple sites in the finger domain of each subunit liberates their autoinhibitory tracts. Synthetic peptides derived from the proteolytically released fragments inhibit the channel, likely by reconstituting key interactions removed by the proteolysis. We previously showed that a peptide derived from the α subunit's autoinhibitory sequence (α-8) binds at the α subunit's finger-thumb domain interface. Despite low sequence similarity between the α and γ subunit finger domains, we hypothesized that a peptide derived from the γ subunit's autoinhibitory sequence (γ-11) inhibits the channel through an analogous mechanism. Using Xenopus oocytes, we found here that channels lacking a γ subunit thumb domain were no longer sensitive to γ-11, but remained sensitive to α-8. We identified finger domain sites in the γ subunit that dramatically reduced γ-11 inhibition. Using cysteines and sulfhydryl reactive cross-linkers introduced into both the peptide and the subunit, we also could cross-link γ-11 to both the finger domain and the thumb domain of the γ subunit. Our results suggest that α-8 and γ-11 occupy similar binding pockets within their respective subunits, and that proteolysis of the α and γ subunits activate the channel through analogous mechanisms.
Collapse
Affiliation(s)
| | | | - Ossama B Kashlan
- From the Department of Medicine, Renal-Electrolyte Division and .,the Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
19
|
Fang Q, You M, Xu W, Yang W, Gong Y, Dong X. pre-B cell colony enhancing factor negatively regulates Na + and fluid transport in lung epithelial cells. Am J Transl Res 2018; 10:2047-2054. [PMID: 30093942 PMCID: PMC6079128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 05/06/2018] [Indexed: 06/08/2023]
Abstract
UNLABELLED This study was undertaken to investigate the effect of pre-B cell colony enhancing factor (PBEF) on Na+ and fluid transport in lung epithelial cells. METHODS Type 1 and 2 cells were isolated from lung epithelium. After hypoxia reoxygenation treatment, the primary cell cultures were transfected with a plasmid over-expressing PBEF. Sodium-potassium ATPase (NKA), epithelial sodium channel (ENaC), type I cell marker rT140, surfactant protein (SP) and PBEF protein were analyzed at mRNA and protein levels using PCR and Western blot analysis. Immunofluorescence assays showed type 1 and 2 cells were successfully isolated. After the transfection with PBEF over-expression vector, PBEF and RTI40 levels were increased, while ENaC and SP as well as NKA, were decreased in both cells. It is clear that PBEF negatively regulates the expression of ENaC and NKA in the Na+ and fluid transport in lung epithelial cells.
Collapse
Affiliation(s)
- Qiao Fang
- Department of Cardiac Macrovascular Surgery, The Second Affiliated Hospital of Nanchang University Nanchang 330006, China
| | - Miaomiao You
- Department of Cardiac Macrovascular Surgery, The Second Affiliated Hospital of Nanchang University Nanchang 330006, China
| | - Weichang Xu
- Department of Cardiac Macrovascular Surgery, The Second Affiliated Hospital of Nanchang University Nanchang 330006, China
| | - Wei Yang
- Department of Cardiac Macrovascular Surgery, The Second Affiliated Hospital of Nanchang University Nanchang 330006, China
| | - Yi Gong
- Department of Cardiac Macrovascular Surgery, The Second Affiliated Hospital of Nanchang University Nanchang 330006, China
| | - Xiao Dong
- Department of Cardiac Macrovascular Surgery, The Second Affiliated Hospital of Nanchang University Nanchang 330006, China
| |
Collapse
|
20
|
Ho PY, Li H, Pavlov TS, Tuerk RD, Tabares D, Brunisholz R, Neumann D, Staruschenko A, Hallows KR. β 1Pix exchange factor stabilizes the ubiquitin ligase Nedd4-2 and plays a critical role in ENaC regulation by AMPK in kidney epithelial cells. J Biol Chem 2018; 293:11612-11624. [PMID: 29858246 DOI: 10.1074/jbc.ra118.003082] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Revised: 05/22/2018] [Indexed: 12/22/2022] Open
Abstract
Our previous work has established that the metabolic sensor AMP-activated protein kinase (AMPK) inhibits the epithelial Na+ channel (ENaC) by promoting its binding to neural precursor cell-expressed, developmentally down-regulated 4-2, E3 ubiquitin protein ligase (Nedd4-2). Here, using MS analysis and in vitro phosphorylation, we show that AMPK phosphorylates Nedd4-2 at the Ser-444 (Xenopus Nedd4-2) site critical for Nedd4-2 stability. We further demonstrate that the Pak-interacting exchange factor β1Pix is required for AMPK-mediated inhibition of ENaC-dependent currents in both CHO and murine kidney cortical collecting duct (CCD) cells. Short hairpin RNA-mediated knockdown of β1Pix expression in CCD cells attenuated the inhibitory effect of AMPK activators on ENaC currents. Moreover, overexpression of a β1Pix dimerization-deficient mutant unable to bind 14-3-3 proteins (Δ602-611) increased ENaC currents in CCD cells, whereas overexpression of WT β1Pix had the opposite effect. Using additional immunoblotting and co-immunoprecipitation experiments, we found that treatment with AMPK activators promoted the binding of β1Pix to 14-3-3 proteins in CCD cells. However, the association between Nedd4-2 and 14-3-3 proteins was not consistently affected by AMPK activation, β1Pix knockdown, or overexpression of WT β1Pix or the β1Pix-Δ602-611 mutant. Moreover, we found that β1Pix is important for phosphorylation of the aforementioned Nedd4-2 site critical for its stability. Overall, these findings elucidate novel molecular mechanisms by which AMPK regulates ENaC. Specifically, they indicate that AMPK promotes the assembly of β1Pix, 14-3-3 proteins, and Nedd4-2 into a complex that inhibits ENaC by enhancing Nedd4-2 binding to ENaC and its degradation.
Collapse
Affiliation(s)
- Pei-Yin Ho
- Division of Nephrology and Hypertension, Department of Medicine and USC/UKRO Kidney Research Center, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Hui Li
- Division of Nephrology and Hypertension, Department of Medicine and USC/UKRO Kidney Research Center, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Tengis S Pavlov
- the Division of Hypertension and Vascular Research, Henry Ford Health System, Detroit, Michigan 48202; Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Roland D Tuerk
- Department of Biology, Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Diego Tabares
- Division of Nephrology and Hypertension, Department of Medicine and USC/UKRO Kidney Research Center, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - René Brunisholz
- Functional Genomics Center, ETH Zurich, 8097 Zurich, Switzerland
| | - Dietbert Neumann
- Department of Biology, Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland; Department of Pathology, School for Cardiovascular Diseases, Maastricht University, 6200 MD Maastricht, The Netherlands
| | | | - Kenneth R Hallows
- Division of Nephrology and Hypertension, Department of Medicine and USC/UKRO Kidney Research Center, Keck School of Medicine, University of Southern California, Los Angeles, California 90033.
| |
Collapse
|
21
|
Shi S, Mutchler SM, Blobner BM, Kashlan OB, Kleyman TR. Pore-lining residues of MEC-4 and MEC-10 channel subunits tune the Caenorhabditis elegans degenerin channel's response to shear stress. J Biol Chem 2018; 293:10757-10766. [PMID: 29743244 DOI: 10.1074/jbc.ra118.002499] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 05/08/2018] [Indexed: 12/20/2022] Open
Abstract
The Caenorhabditis elegans MEC-4/MEC-10 channel mediates the worm's response to gentle body touch and is activated by laminar shear stress (LSS) when expressed in Xenopus oocytes. Substitutions at multiple sites within the second transmembrane domain (TM2) of MEC-4 or MEC-10 abolish the gentle touch response in worms, but the roles of these residues in mechanosensing are unclear. The present study therefore examined the role of specific MEC-4 and MEC-10 TM2 residues in the channel's response to LSS. We found that introducing mutations within the TM2 of MEC-4 or MEC-10 not only altered channel activity, but also affected the channel's response to LSS. This response was enhanced by Cys substitutions at selected MEC-4 sites (Phe715, Gly716, Gln718, and Leu719) between the degenerin and the putative amiloride-binding sites in this subunit. In contrast, the LSS response was largely blunted in MEC-10 variants bearing single Cys substitutions in the regions preceding and following the amiloride-binding site (Gly677-Leu681), as well as with four MEC-10 touch-deficient mutations that introduced charged residues into the TM2 domain. An enhanced response to LSS was observed with a MEC-10 mutation in the putative selectivity filter. Overall, MEC-4 or MEC-10 mutants that altered the channel's LSS response are primarily clustered between the degenerin site and the selectivity filter, a region that probably forms the narrowest portion of the channel pore. Our results suggest that pore-lining residues of MEC-4 and MEC-10 have important yet different roles in tuning the channel's response to mechanical forces.
Collapse
Affiliation(s)
- Shujie Shi
- From the Renal-Electrolyte Division, Department of Medicine
| | - Stephanie M Mutchler
- From the Renal-Electrolyte Division, Department of Medicine.,Department of Pharmacology and Chemical Biology, and
| | | | - Ossama B Kashlan
- From the Renal-Electrolyte Division, Department of Medicine.,Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine, .,Department of Pharmacology and Chemical Biology, and.,Department of Cell Biology
| |
Collapse
|
22
|
Puga Molina LC, Pinto NA, Torres NI, González-Cota AL, Luque GM, Balestrini PA, Romarowski A, Krapf D, Santi CM, Treviño CL, Darszon A, Buffone MG. CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC. J Biol Chem 2018; 293:9924-9936. [PMID: 29743243 DOI: 10.1074/jbc.ra118.003166] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Revised: 04/29/2018] [Indexed: 12/16/2022] Open
Abstract
To fertilize an egg, sperm must reside in the female reproductive tract to undergo several maturational changes that are collectively referred to as capacitation. From a molecular point of view, the HCO3--dependent activation of the atypical soluble adenylyl cyclase (ADCY10) is one of the first events that occurs during capacitation and leads to the subsequent cAMP-dependent activation of protein kinase A (PKA). Capacitation is also accompanied by hyperpolarization of the sperm plasma membrane. We previously reported that PKA activation is necessary for CFTR (cystic fibrosis transmembrane conductance regulator channel) activity and for the modulation of membrane potential (Em). However, the main HCO3- transporters involved in the initial transport and the PKA-dependent Em changes are not well known nor characterized. Here, we analyzed how the activity of CFTR regulates Em during capacitation and examined its relationship with an electrogenic Na+/HCO3- cotransporter (NBC) and epithelial Na+ channels (ENaCs). We observed that inhibition of both CFTR and NBC decreased HCO3- influx, resulting in lower PKA activity, and that events downstream of the cAMP activation of PKA are essential for the regulation of Em. Addition of a permeable cAMP analog partially rescued the inhibitory effects caused by these inhibitors. HCO3- also produced a rapid membrane hyperpolarization mediated by ENaC channels, which contribute to the regulation of Em during capacitation. Altogether, we demonstrate for the first time, that NBC cotransporters and ENaC channels are essential in the CFTR-dependent activation of the cAMP/PKA signaling pathway and Em regulation during human sperm capacitation.
Collapse
Affiliation(s)
- Lis C Puga Molina
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Nicolás A Pinto
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Nicolás I Torres
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Ana L González-Cota
- the Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Guillermina M Luque
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Paula A Balestrini
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Ana Romarowski
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Dario Krapf
- the Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET-UNR, Rosario 2000, Argentina, and
| | - Celia M Santi
- the Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Claudia L Treviño
- the Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, 62210 Morelos, México
| | - Alberto Darszon
- the Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, 62210 Morelos, México
| | - Mariano G Buffone
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina,
| |
Collapse
|
23
|
Wichmann L, Vowinkel KS, Perniss A, Manzini I, Althaus M. Incorporation of the δ-subunit into the epithelial sodium channel (ENaC) generates protease-resistant ENaCs in Xenopus laevis. J Biol Chem 2018; 293:6647-6658. [PMID: 29576549 DOI: 10.1074/jbc.ra118.002543] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 03/14/2018] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) is a critical regulator of vertebrate electrolyte homeostasis. ENaC is the only constitutively open ion channel in the degenerin/ENaC protein family, and its expression, membrane abundance, and open probability therefore are tightly controlled. The canonical ENaC is composed of three subunits (α, β, and γ), but a fourth δ-subunit may replace α and form atypical δβγ-ENaCs. Using Xenopus laevis as a model, here we found that mRNAs of the α- and δ-subunits are differentially expressed in different tissues and that δ-ENaC predominantly is present in the urogenital tract. Using whole-cell and single-channel electrophysiology of oocytes expressing Xenopus αβγ- or δβγ-ENaC, we demonstrate that the presence of the δ-subunit enhances the amount of current generated by ENaC due to an increased open probability, but also changes current into a transient form. Activity of canonical ENaCs is critically dependent on proteolytic processing of the α- and γ-subunits, and immunoblotting with epitope-tagged ENaC subunits indicated that, unlike α-ENaC, the δ-subunit does not undergo proteolytic maturation by the endogenous protease furin. Furthermore, currents generated by δβγ-ENaC were insensitive to activation by extracellular chymotrypsin, and presence of the δ-subunit prevented cleavage of γ-ENaC at the cell surface. Our findings suggest that subunit composition constitutes an additional level of ENaC regulation, and we propose that the Xenopus δ-ENaC subunit represents a functional example that demonstrates the importance of proteolytic maturation during ENaC evolution.
Collapse
Affiliation(s)
- Lukas Wichmann
- From the School of Natural and Environmental Sciences, Newcastle University, Ridley Building 2, Newcastle upon Tyne NE1 7RU, United Kingdom and.,the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Kirsty Sophia Vowinkel
- the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Alexander Perniss
- the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Ivan Manzini
- the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Mike Althaus
- From the School of Natural and Environmental Sciences, Newcastle University, Ridley Building 2, Newcastle upon Tyne NE1 7RU, United Kingdom and
| |
Collapse
|
24
|
Shobair M, Popov KI, Dang YL, He H, Stutts MJ, Dokholyan NV. Mapping allosteric linkage to channel gating by extracellular domains in the human epithelial sodium channel. J Biol Chem 2018; 293:3675-3684. [PMID: 29358325 DOI: 10.1074/jbc.ra117.000604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 01/08/2018] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) mediates sodium absorption in lung, kidney, and colon epithelia. Channels in the ENaC/degenerin family possess an extracellular region that senses physicochemical changes in the extracellular milieu and allosterically regulates the channel opening. Proteolytic cleavage activates the ENaC opening, by the removal of specific segments in the finger domains of the α- and γ ENaC-subunits. Cleavage causes perturbations in the extracellular region that propagate to the channel gate. However, it is not known how the channel structure mediates the propagation of activation signals through the extracellular sensing domains. Here, to identify the structure-function determinants that mediate allosteric ENaC activation, we performed MD simulations, thiol modification of residues substituted by cysteine, and voltage-clamp electrophysiology recordings. Our simulations of an ENaC heterotetramer, α1βα2γ, in the proteolytically cleaved and uncleaved states revealed structural pathways in the α-subunit that are responsible for ENaC proteolytic activation. To validate these findings, we performed site-directed mutagenesis to introduce cysteine substitutions in the extracellular domains of the α-, β-, and γ ENaC-subunits. Insertion of a cysteine at the α-subunit Glu557 site, predicted to stabilize a closed state of ENaC, inhibited ENaC basal activity and retarded the kinetics of proteolytic activation by 2-fold. Our results suggest that the lower palm domain of αENaC is essential for ENaC activation. In conclusion, our integrated computational and experimental approach suggests key structure-function determinants for ENaC proteolytic activation and points toward a mechanistic model for the allosteric communication in the extracellular domains of the ENaC/degenerin family channels.
Collapse
Affiliation(s)
- Mahmoud Shobair
- From the Program in Molecular and Cellular Biophysics.,Curriculum in Bioinformatics and Computational Biology.,Department of Biochemistry and Biophysics, and.,Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | | | - Yan L Dang
- Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Hong He
- Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - M Jackson Stutts
- Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Nikolay V Dokholyan
- From the Program in Molecular and Cellular Biophysics, .,Curriculum in Bioinformatics and Computational Biology.,Department of Biochemistry and Biophysics, and.,Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| |
Collapse
|
25
|
Blobner BM, Wang XP, Kashlan OB. Conserved cysteines in the finger domain of the epithelial Na + channel α and γ subunits are proximal to the dynamic finger-thumb domain interface. J Biol Chem 2018; 293:4928-4939. [PMID: 29425099 DOI: 10.1074/jbc.m117.819367] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Revised: 01/26/2018] [Indexed: 11/06/2022] Open
Abstract
The epithelial Na+ channel (ENaC) is a member of the ENaC/degenerin family of ion channels. In the structure of a related family member, the "thumb" domain's base interacts with the pore, and its tip interacts with the divergent "finger" domain. Between the base and tip, the thumb domain is characterized by a conserved five-rung disulfide ladder holding together two anti-parallel α helices. The ENaC α and γ subunits' finger domains harbor autoinhibitory tracts that can be proteolytically liberated to activate the channel and also host an ENaC-specific pair of cysteines. Using a crosslinking approach, we show that one of the finger domain cysteines in the α subunit (αCys-263) and both of the finger domain cysteines in the γ subunit (γCys-213 and γCys-220) lie near the dynamic finger-thumb domain interface. Our data suggest that the αCys-256/αCys-263 pair is not disulfide-bonded. In contrast, we found that the γCys-213/γCys-220 pair is disulfide-bonded. Our data also suggest that the γ subunit lacks the terminal rung in the thumb domain disulfide ladder, suggesting asymmetry between the subunits. We also observed functional asymmetry between the α and γ subunit finger-thumb domain interfaces; crosslinks bridging the α subunit finger-thumb interface only inhibited ENaC currents, whereas crosslinks bridging the γ subunit finger-thumb interface activated or inhibited currents dependent on the length of the crosslinker. Our data suggest that reactive cysteines lie at the dynamic finger-thumb interfaces of the α and γ subunits and may play a yet undefined role in channel regulation.
Collapse
Affiliation(s)
- Brandon M Blobner
- Departments of Medicine, Renal-Electrolyte Division, Pittsburgh, Pennsylvania 15261
| | - Xue-Ping Wang
- Departments of Medicine, Renal-Electrolyte Division, Pittsburgh, Pennsylvania 15261
| | - Ossama B Kashlan
- Departments of Medicine, Renal-Electrolyte Division, Pittsburgh, Pennsylvania 15261; Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
| |
Collapse
|
26
|
Zou L, Linck V, Zhai YJ, Galarza-Paez L, Li L, Yue Q, Al-Khalili O, Bao HF, Ma HP, Thai TL, Jiao J, Eaton DC. Knockout of mitochondrial voltage-dependent anion channel type 3 increases reactive oxygen species (ROS) levels and alters renal sodium transport. J Biol Chem 2017; 293:1666-1675. [PMID: 29180450 DOI: 10.1074/jbc.m117.798645] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/27/2017] [Indexed: 11/06/2022] Open
Abstract
It has been suggested that voltage-dependent anion channels (VDACs) control the release of superoxide from mitochondria. We have previously shown that reactive oxygen species (ROS) such as superoxide (O2̇̄) and hydrogen peroxide (H2O2) stimulate epithelial sodium channels (ENaCs) in sodium-transporting epithelial tissue, including cortical collecting duct (CCD) principal cells. Therefore, we hypothesized that VDACs could regulate ENaC by modulating cytosolic ROS levels. Herein, we find that VDAC3-knockout(KO) mice can maintain normal salt and water balance on low-salt and high-salt diets. However, on a high-salt diet for 2 weeks, VDAC3-KO mice had significantly higher systolic blood pressure than wildtype mice. Consistent with this observation, after a high-salt diet for 2 weeks, ENaC activity in VDAC3-KO mice was significantly higher than wildtype mice. EM analysis disclosed a significant morphological change of mitochondria in the CCD cells of VDAC3-KO mice compared with wildtype mice, which may have been caused by mitochondrial superoxide overload. Of note, compared with wildtype animals, ROS levels in VDAC3-KO animals fed a normal or high-salt diet were consistently and significantly increased in renal tubules. Both the ROS scavenger 1-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine (TEMPOL) and the mitochondrial ROS scavenger (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride (mito-TEMPO) could reverse the effect of high-salt on ENaC activity and systolic blood pressure in the VDAC3-KO mice. Mito-TEMPO partially correct the morphological changes in VDAC3-KO mice. Our results suggest that knocking out mitochondrial VDAC3 increases ROS, alters renal sodium transport, and leads to hypertension.
Collapse
Affiliation(s)
- Li Zou
- From the Department of Nephrology, the Second Affiliated Hospital of Harbin Medical University, Harbin 150086, China.,the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Valerie Linck
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Yu-Jia Zhai
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Laura Galarza-Paez
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Linda Li
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Qiang Yue
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Otor Al-Khalili
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Hui-Fang Bao
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - He-Ping Ma
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Tiffany L Thai
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| | - Jundong Jiao
- From the Department of Nephrology, the Second Affiliated Hospital of Harbin Medical University, Harbin 150086, China, .,the Institute of Nephrology, Harbin Medical University, Harbin, China
| | - Douglas C Eaton
- the Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, and
| |
Collapse
|
27
|
Yang XN, Niu YY, Liu Y, Yang Y, Wang J, Cheng XY, Liang H, Wang HS, Hu YM, Lu XY, Zhu MX, Xu TL, Tian Y, Yu Y. The nonproton ligand of acid-sensing ion channel 3 activates mollusk-specific FaNaC channels via a mechanism independent of the native FMRFamide peptide. J Biol Chem 2017; 292:21662-21675. [PMID: 29123030 DOI: 10.1074/jbc.m117.814707] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Revised: 11/07/2017] [Indexed: 12/13/2022] Open
Abstract
The degenerin/epithelial sodium channel (DEG/ENaC) superfamily of ion channels contains subfamilies with diverse functions that are fundamental to many physiological and pathological processes, ranging from synaptic transmission to epileptogenesis. The absence in mammals of some DEG/ENaCs subfamily orthologues such as FMRFamide peptide-activated sodium channels (FaNaCs), which have been identified only in mollusks, indicates that the various subfamilies diverged early in evolution. We recently reported that the nonproton agonist 2-guanidine-4-methylquinazoline (GMQ) activates acid-sensing ion channels (ASICs), a DEG/ENaC subfamily mainly in mammals, in the absence of acidosis. Here, we show that GMQ also could directly activate the mollusk-specific FaNaCs. Differences in ion selectivity and unitary conductance and effects of substitutions at key residues revealed that GMQ and FMRFamide activate FaNaCs via distinct mechanisms. The presence of two activation mechanisms in the FaNaC subfamily diverging early in the evolution of DEG/ENaCs suggested that dual gating is an ancient feature in this superfamily. Notably, the GMQ-gating mode is still preserved in the mammalian ASIC subfamily, whereas FMRFamide-mediated channel gating was lost during evolution. This implied that GMQ activation may be essential for the functions of mammalian DEG/ENaCs. Our findings provide new insights into the evolution of DEG/ENaCs and may facilitate the discovery and characterization of their endogenous agonists.
Collapse
Affiliation(s)
- Xiao-Na Yang
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China.,Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - You-Ya Niu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China.,Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.,Department of Cell Biology and Genetics, Hunan University of Medicine, Huaihua, 418000, China
| | - Yan Liu
- Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yang Yang
- Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Jin Wang
- Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Xiao-Yang Cheng
- Discipline of Neuroscience, Department of Anatomy, Histology, and Embryology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Hong Liang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, School of Chemistry and Pharmacy, Guangxi Normal University, Guilin, 541004, China, and
| | - Heng-Shan Wang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, School of Chemistry and Pharmacy, Guangxi Normal University, Guilin, 541004, China, and
| | - You-Min Hu
- Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Xiang-Yang Lu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China
| | - Michael X Zhu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China.,Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas 77030
| | - Tian-Le Xu
- Discipline of Neuroscience, Department of Anatomy, Histology, and Embryology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yun Tian
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China,
| | - Ye Yu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China, .,Institute of Medical Sciences and Department of Pharmacology and Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| |
Collapse
|
28
|
Shi S, Buck TM, Kinlough CL, Marciszyn AL, Hughey RP, Chalfie M, Brodsky JL, Kleyman TR. Regulation of the epithelial Na + channel by paraoxonase-2. J Biol Chem 2017; 292:15927-15938. [PMID: 28768768 DOI: 10.1074/jbc.m117.785253] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 07/14/2017] [Indexed: 01/11/2023] Open
Abstract
Paraoxonase-2 (PON-2) is a membrane-bound lactonase with unique anti-oxidative and anti-atherosclerotic properties. PON-2 shares key structural elements with MEC-6, an endoplasmic reticulum-resident molecular chaperone in Caenorhabditis elegans MEC-6 modulates the expression of a mechanotransductive ion channel comprising MEC-4 and MEC-10 in touch-receptor neurons. Because pon-2 mRNA resides in multiple rat nephron segments, including the aldosterone-sensitive distal nephron where the epithelial Na+ channel (ENaC) is expressed, we hypothesized that PON-2 would similarly regulate ENaC expression. We observed PON-2 expression in aquaporin 2-positive principal cells of the distal nephron of adult human kidney. PON-2 also co-immunoprecipitated with ENaC when co-expressed in HEK293 cells. When PON-2 was co-expressed with ENaC in Xenopus oocytes, ENaC activity was reduced, reflecting a reduction in ENaC surface expression. MEC-6 also reduced ENaC activity when co-expressed in Xenopus oocytes. The PON-2 inhibitory effect was ENaC-specific, as PON-2 had no effect on functional expression of the renal outer medullary potassium channel. PON-2 did not alter the response of ENaC to extracellular Na+, mechanical shear stress, or α-chymotrypsin-mediated proteolysis, suggesting that PON-2 did not alter the regulation of ENaC by these factors. Together, our data suggest that PON-2 regulates ENaC activity by modulating its intracellular trafficking and surface expression.
Collapse
Affiliation(s)
- Shujie Shi
- From the Renal-Electrolyte Division, Department of Medicine
| | | | | | | | - Rebecca P Hughey
- From the Renal-Electrolyte Division, Department of Medicine.,Department of Cell Biology.,Department of Microbiology and Molecular Genetics, and
| | - Martin Chalfie
- the Department of Biological Sciences, Columbia University, New York, New York 10027
| | | | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine, .,Department of Cell Biology.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 and
| |
Collapse
|
29
|
Zaidman NA, Panoskaltsis-Mortari A, O'Grady SM. Large-conductance Ca 2+ -activated K + channel activation by apical P2Y receptor agonists requires hydrocortisone in differentiated airway epithelium. J Physiol 2017; 595:4631-4645. [PMID: 28481415 DOI: 10.1113/jp274200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 05/02/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Hydrocortisone (HC) is required for activation of large-conductance Ca2+ -activated K+ current (BK) by purinergic receptor agonists. HC reduces insertion of the stress-regulated exon (STREX) in the KCNMA1 gene, permitting protein kinase C (PKC)-dependent channel activation. Overlapping and unique purinergic signalling regions exist at the apical border of differentiated surface cells. BK channels localize in the cilia of surface cells. ABSTRACT In the present study we investigated the role of hydrocortisone (HC) on uridine-5'-triphosphate (UTP)-stimulated ion transport in differentiated, pseudostratified epithelia derived from normal human bronchial basal cells. The presence of a UTP-stimulated, paxilline-sensitive large-conductance Ca2+ -activated K+ (BK) current was demonstrated in control epithelia but was not stimulated in epithelia differentiated in the absence of HC (HC0). Addition of the BK channel opener NS11021 directly activated channels in control epithelia; however, under HC0 conditions, activation only occurred when UTP was added after NS11021. The PKC inhibitors GF109203x and Gö6983 blocked BK activation by UTP in control epithelia, suggesting that PKC-mediated phosphorylation plays a permissive role in purinoceptor-stimulated BK activation. Moreover, HC0 epithelia expressed significantly more KCNMA1 containing the stress-regulated exon (STREX), a splice-variant of the α-subunit that displays altered channel regulation by phosphorylation, compared to control epithelia. Furthermore, BK channels as well as purinergic receptors were shown to localize in unique and overlapping domains at the apical membrane of ciliated surface cells. These results establish a previously unrecognized role for glucocorticoids in regulation of BK channels in airway epithelial cells.
Collapse
Affiliation(s)
- Nathan A Zaidman
- Department of Integrative Biology and Physiology, University of Minnesota, 6-125 Jackson Hall, Minneapolis, MN, USA
| | - Angela Panoskaltsis-Mortari
- Department of Integrative Biology and Physiology, University of Minnesota, 6-125 Jackson Hall, Minneapolis, MN, USA.,Department of Pediatrics, University of Minnesota, 660E MCRB, Minneapolis, MN, USA
| | - Scott M O'Grady
- Department of Integrative Biology and Physiology, University of Minnesota, 6-125 Jackson Hall, Minneapolis, MN, USA.,Department of Animal Science, University of Minnesota, 480 Haecker Hall, St. Paul, Minneapolis, MN, USA
| |
Collapse
|
30
|
Mukherjee A, Wang Z, Kinlough CL, Poland PA, Marciszyn AL, Montalbetti N, Carattino MD, Butterworth MB, Kleyman TR, Hughey RP. Specific Palmitoyltransferases Associate with and Activate the Epithelial Sodium Channel. J Biol Chem 2017; 292:4152-4163. [PMID: 28154191 DOI: 10.1074/jbc.m117.776146] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) has an important role in regulating extracellular fluid volume and blood pressure, as well as airway surface liquid volume and mucociliary clearance. ENaC is a trimer of three homologous subunits (α, β, and γ). We previously reported that cytoplasmic residues on the β (βCys-43 and βCys-557) and γ (γCys-33 and γCys-41) subunits are palmitoylated. Mutation of Cys that blocked ENaC palmitoylation also reduced channel open probability. Furthermore, γ subunit palmitoylation had a dominant role over β subunit palmitoylation in regulating ENaC. To determine which palmitoyltransferases (termed DHHCs) regulate the channel, mouse ENaCs were co-expressed in Xenopus oocytes with each of the 23 mouse DHHCs. ENaC activity was significantly increased by DHHCs 1, 2, 3, 7, and 14. ENaC activation by DHHCs was lost when γ subunit palmitoylation sites were mutated, whereas DHHCs 1, 2, and 14 still activated ENaC lacking β subunit palmitoylation sites. β subunit palmitoylation was increased by ENaC co-expression with DHHC 7. Both wild type ENaC and channels lacking β and γ palmitoylation sites co-immunoprecipitated with the five activating DHHCs, suggesting that ENaC forms a complex with multiple DHHCs. RT-PCR revealed that transcripts for the five activating DHHCs were present in cultured mCCDcl1 cells, and DHHC 3 was expressed in aquaporin 2-positive principal cells of mouse aldosterone-sensitive distal nephron where ENaC is localized. Treatment of polarized mCCDcl1 cells with a general inhibitor of palmitoylation reduced ENaC-mediated Na+ currents within minutes. Our results indicate that specific DHHCs have a role in regulating ENaC.
Collapse
Affiliation(s)
| | | | | | | | | | | | | | | | - Thomas R Kleyman
- From the Departments of Medicine, .,Cell Biology, and.,Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | | |
Collapse
|
31
|
Jiang C, Kawabe H, Rotin D. The Ubiquitin Ligase Nedd4L Regulates the Na/K/2Cl Co-transporter NKCC1/SLC12A2 in the Colon. J Biol Chem 2017; 292:3137-3145. [PMID: 28087701 DOI: 10.1074/jbc.m116.770065] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 01/03/2017] [Indexed: 01/06/2023] Open
Abstract
The ubiquitin ligase Nedd4-like (Nedd4L, or Nedd4-2) binds to and regulates stability of the epithelial Na+ channel (ENaC) in salt-absorbing epithelia in the kidney, lung, and other tissues. Its role in the distal colon, which also absorbs salt and fluid and expresses ENaC, is unknown. Using a conditional knock-out approach to knock out Nedd4L in mice intestinal epithelium (Nedd4Lf/f ;Vil-CreERT2 ) we show here that Nedd4L depletion leads to a higher steady-state short circuit current (Isc) in mouse distal colon tissue relative to controls. This higher Isc was partially reduced by the addition of apical amiloride and strongly reduced by basolateral bumetanide as well as by depletion of basolateral Cl-, suggesting that Na+/K+/2Cl- (NKCC1/SLC12A2) co-transporter and ENaC are targets of Nedd4L in the colon. In accordance, NKCC1 (and γENaC) protein abundance in the colon of the Nedd4L knock-out animals was increased, indicating that Nedd4L normally suppresses these proteins. However, we did not observe co-immunoprecipitation between Nedd4L and NKCC1, suggesting that Nedd4L indirectly suppresses NKCC1 expression. Low salt diet resulted in a strong increase in β and γ (but not α) ENaC mRNA and protein expression and ENaC activity. Although salt restriction also increased NKCC1 protein and mRNA abundance, it did not lead to its elevated activity (Isc). These results identify NKCC1 as a novel target for Nedd4L-mediated down-regulation in vivo, which modulates ion and fluid transport in the distal colon together with ENaC.
Collapse
Affiliation(s)
- Chong Jiang
- Hospital for Sick Children and University of Toronto, Toronto, Ontario M5G 0A4, Canada
| | - Hiroshi Kawabe
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3D, 37075 Goettingen, Germany
| | - Daniela Rotin
- Hospital for Sick Children and University of Toronto, Toronto, Ontario M5G 0A4, Canada.
| |
Collapse
|
32
|
Klemens CA, Edinger RS, Kightlinger L, Liu X, Butterworth MB. Ankyrin G Expression Regulates Apical Delivery of the Epithelial Sodium Channel (ENaC). J Biol Chem 2016; 292:375-385. [PMID: 27895120 DOI: 10.1074/jbc.m116.753616] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 11/11/2016] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) is the limiting entry point for Na+ reabsorption in the distal kidney nephron and is regulated by numerous hormones, including the mineralocorticoid hormone aldosterone. Previously we identified ankyrin G (AnkG), a cytoskeletal protein involved in vesicular transport, as a novel aldosterone-induced protein that can alter Na+ transport in mouse cortical collecting duct cells. However, the mechanisms underlying AnkG regulation of Na+ transport were unknown. Here we report that AnkG expression directly regulates Na+ transport by altering ENaC activity in the apical membrane. Increasing AnkG expression increased ENaC activity while depleting AnkG reduced ENaC-mediated Na+ transport. These changes were due to a change in ENaC directly rather than through alterations to the Na+ driving force created by Na+/K+-ATPase. Using a constitutively open mutant of ENaC, we demonstrate that the augmentation of Na+ transport is caused predominantly by increasing the number of ENaCs at the surface. To determine the mechanism of AnkG action on ENaC surface number, changes in rates of internalization, recycling, and membrane delivery were investigated. AnkG did not alter ENaC delivery to the membrane from biosynthetic pathways or removal by endocytosis. However, AnkG did alter ENaC insertion from constitutive recycling pathways. These findings provide a mechanism to account for the role of AnkG in the regulation of Na+ transport in the distal kidney nephron.
Collapse
Affiliation(s)
- Christine A Klemens
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Robert S Edinger
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Lindsay Kightlinger
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Xiaoning Liu
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Michael B Butterworth
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
33
|
Lucas R, Yue Q, Alli A, Duke BJ, Al-Khalili O, Thai TL, Hamacher J, Sridhar S, Lebedyeva I, Su H, Tzotzos S, Fischer B, Gameiro AF, Loose M, Chakraborty T, Shabbir W, Aufy M, Lemmens-Gruber R, Eaton DC, Czikora I. The Lectin-like Domain of TNF Increases ENaC Open Probability through a Novel Site at the Interface between the Second Transmembrane and C-terminal Domains of the α-Subunit. J Biol Chem 2016; 291:23440-23451. [PMID: 27645999 DOI: 10.1074/jbc.m116.718163] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Indexed: 12/29/2022] Open
Abstract
Regulation of the epithelial sodium channel (ENaC), which regulates fluid homeostasis and blood pressure, is complex and remains incompletely understood. The TIP peptide, a mimic of the lectin-like domain of TNF, activates ENaC by binding to glycosylated residues in the extracellular loop of ENaC-α, as well as to a hitherto uncharacterized internal site. Molecular docking studies suggested three residues, Val567, Glu568, and Glu571, located at the interface between the second transmembrane and C-terminal domains of ENaC-α, as a critical site for binding of the TIP peptide. We generated Ala replacement mutants in this region of ENaC-α and examined its interaction with TIP peptide (3M, V567A/E568A/E571A; 2M, V567A/E568A; and 1M, E571A). 3M and 2M ENaC-α, but not 1M ENaC-α, displayed significantly reduced binding capacity to TIP peptide and to TNF. When overexpressed in H441 cells, 3M mutant ENaC-α formed functional channels with similar gating and density characteristics as the WT subunit and efficiently associated with the β and γ subunits in the plasma membrane. We subsequently assayed for increased open probability time and membrane expression, both of which define ENaC activity, following addition of TIP peptide. TIP peptide increased open probability time in H441 cells overexpressing wild type and 1M ENaC-α channels, but not 3M or 2M ENaC-α channels. On the other hand, TIP peptide-mediated reduction in ENaC ubiquitination was similar in cells overexpressing either WT or 3M ENaC-α subunits. In summary, this study has identified a novel site in ENaC-α that is crucial for activation of the open probability of the channel, but not membrane expression, by the lectin-like domain of TNF.
Collapse
Affiliation(s)
- Rudolf Lucas
- From the Vascular Biology Center, .,the Department of Pharmacology and Toxicology, and.,the Division of Pulmonary and Critical Care Medicine, Medical College of Georgia, Augusta, Georgia 30912
| | - Qiang Yue
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Abdel Alli
- the Department of Physiology, Emory University, Atlanta, Georgia 30322.,the Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida 32610
| | | | - Otor Al-Khalili
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Tiffany L Thai
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Jürg Hamacher
- the Department of Pulmonology, Saarland University, D-66421 Homburg, Germany
| | | | - Iryna Lebedyeva
- the Department of Chemistry, Augusta University, Augusta, Georgia 30912
| | - Huabo Su
- From the Vascular Biology Center
| | - Susan Tzotzos
- Apeptico Research and Development, 1150 Vienna, Austria
| | | | | | - Maria Loose
- the Institute for Medical Microbiology, Justus-Liebig University, 35390 Giessen, Germany, and
| | - Trinad Chakraborty
- the Institute for Medical Microbiology, Justus-Liebig University, 35390 Giessen, Germany, and
| | - Waheed Shabbir
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Mohammed Aufy
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Rosa Lemmens-Gruber
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Douglas C Eaton
- the Department of Physiology, Emory University, Atlanta, Georgia 30322,
| | | |
Collapse
|
34
|
Ilyaskin AV, Diakov A, Korbmacher C, Haerteis S. Activation of the Human Epithelial Sodium Channel (ENaC) by Bile Acids Involves the Degenerin Site. J Biol Chem 2016; 291:19835-47. [PMID: 27489102 DOI: 10.1074/jbc.m116.726471] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Indexed: 12/22/2022] Open
Abstract
The epithelial sodium channel (ENaC) is a member of the ENaC/degenerin ion channel family, which also includes the bile acid-sensitive ion channel (BASIC). So far little is known about the effects of bile acids on ENaC function. ENaC is probably a heterotrimer consisting of three well characterized subunits (αβγ). In humans, but not in mice and rats, an additional δ-subunit exists. The aim of this study was to investigate the effects of chenodeoxycholic, cholic, and deoxycholic acid in unconjugated (CDCA, CA, and DCA) and tauro-conjugated (t-CDCA, t-CA, t-DCA) form on human ENaC in its αβγ- and δβγ-configuration. We demonstrated that tauro-conjugated bile acids significantly stimulate ENaC in the αβγ- and in the δβγ-configuration. In contrast, non-conjugated bile acids have a robust stimulatory effect only on δβγENaC. Bile acids stimulate ENaC-mediated currents by increasing the open probability of active channels without recruiting additional near-silent channels known to be activated by proteases. Stimulation of ENaC activity by bile acids is accompanied by a significant reduction of the single-channel current amplitude, indicating an interaction of bile acids with a region close to the channel pore. Analysis of the known ASIC1 (acid-sensing ion channel) crystal structure suggested that bile acids may bind to the pore region at the degenerin site of ENaC. Substitution of a single amino acid residue within the degenerin region of βENaC (N521C or N521A) significantly reduced the stimulatory effect of bile acids on ENaC, suggesting that this site is critical for the functional interaction of bile acids with the channel.
Collapse
Affiliation(s)
- Alexandr V Ilyaskin
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Alexei Diakov
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Christoph Korbmacher
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Silke Haerteis
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| |
Collapse
|
35
|
Shi S, Luke CJ, Miedel MT, Silverman GA, Kleyman TR. Activation of the Caenorhabditis elegans Degenerin Channel by Shear Stress Requires the MEC-10 Subunit. J Biol Chem 2016; 291:14012-14022. [PMID: 27189943 DOI: 10.1074/jbc.m116.718031] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Indexed: 01/12/2023] Open
Abstract
Mechanotransduction in Caenorhabditis elegans touch receptor neurons is mediated by an ion channel formed by MEC-4, MEC-10, and accessory proteins. To define the role of these subunits in the channel's response to mechanical force, we expressed degenerin channels comprising MEC-4 and MEC-10 in Xenopus oocytes and examined their response to laminar shear stress (LSS). Shear stress evoked a rapid increase in whole cell currents in oocytes expressing degenerin channels as well as channels with a MEC-4 degenerin mutation (MEC-4d), suggesting that C. elegans degenerin channels are sensitive to LSS. MEC-10 is required for a robust LSS response as the response was largely blunted in oocytes expressing homomeric MEC-4 or MEC-4d channels. We examined a series of MEC-10/MEC-4 chimeras to identify specific domains (amino terminus, first transmembrane domain, and extracellular domain) and sites (residues 130-132 and 134-137) within MEC-10 that are required for a robust response to shear stress. In addition, the LSS response was largely abolished by MEC-10 mutations encoded by a touch-insensitive mec-10 allele, providing a correlation between the channel's responses to two different mechanical forces. Our findings suggest that MEC-10 has an important role in the channel's response to mechanical forces.
Collapse
Affiliation(s)
- Shujie Shi
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Cliff J Luke
- Department of Pediatrics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Mark T Miedel
- Department of Pediatrics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Gary A Silverman
- Department of Pediatrics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261; Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Thomas R Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261; Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261; Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
| |
Collapse
|
36
|
Abstract
Acid-sensing ion channels (ASICs) are cation-selective proton-gated channels expressed in neurons that participate in diverse physiological processes, including nociception, synaptic plasticity, learning, and memory. ASIC subunits contain intracellular N and C termini, two transmembrane domains that constitute the pore, and a large extracellular loop with defined domains termed the finger, β-ball, thumb, palm, and knuckle. Here we examined the contribution of the finger, β-ball, and thumb domains to activation and desensitization through the analysis of chimeras and the assessment of the effect of covalent modification of introduced Cys at the domain-domain interfaces. Our studies with ASIC1a-ASIC2a chimeras showed that swapping the thumb domain between subunits results in faster channel desensitization. Likewise, the covalent modification of Cys residues at selected positions in the β-ball-thumb interface accelerates the desensitization of the mutant channels. Studies of accessibility with thiol-reactive reagents revealed that the β-ball and thumb domains reside apart in the resting state but that they become closer to each other in response to extracellular acidification. We propose that the thumb domain moves upon continuous exposure to an acidic extracellular milieu, assisting with the closing of the pore during channel desensitization.
Collapse
Affiliation(s)
- Aram J Krauson
- From the Renal-Electrolyte Division, Department of Medicine, and
| | - Marcelo D Carattino
- From the Renal-Electrolyte Division, Department of Medicine, and Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| |
Collapse
|
37
|
Niu YY, Yang Y, Liu Y, Huang LD, Yang XN, Fan YZ, Cheng XY, Cao P, Hu YM, Li L, Lu XY, Tian Y, Yu Y. Exploration of the Peptide Recognition of an Amiloride-sensitive FMRFamide Peptide-gated Sodium Channel. J Biol Chem 2016; 291:7571-82. [PMID: 26867576 DOI: 10.1074/jbc.m115.710251] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2015] [Indexed: 12/22/2022] Open
Abstract
FMRFamide (Phe-Met-Arg-Phe-NH2)-activated sodium channel (FaNaC) is an amiloride-sensitive sodium channel activated by endogenous tetrapeptide in invertebrates, and belongs to the epithelial sodium channel/degenerin (ENaC/DEG) superfamily. The ENaC/DEG superfamily differs markedly in its means of activation, such as spontaneously opening or gating by mechanical stimuli or tissue acidosis. Recently, it has been observed that a number of ENaC/DEG channels can be activated by small molecules or peptides, indicating that the ligand-gating may be an important feature of this superfamily. The peptide ligand control of the channel gating might be an ancient ligand-gating feature in this superfamily. Therefore, studying the peptide recognition of FaNaC channels would advance our understanding of the ligand-gating properties of this superfamily of ion channels. Here we demonstrate that Tyr-131, Asn-134, Asp-154, and Ile-160, located in the putative upper finger domain ofHelix aspersaFaNaC (HaFaNaC) channels, are key residues for peptide recognition of this ion channel. Two HaFaNaC specific-insertion motifs among the ENaC/DEG superfamily, residing at the putative α4-α5 linker of the upper thumb domain and the α6-α7 linker of the upper knuckle domain, are also essential for the peptide recognition of HaFaNaC channels. Chemical modifications and double mutant cycle analysis further indicated that those two specific inserts and key residues in the upper finger domain together participate in peptide recognition of HaFaNaC channels. This ligand recognition site is distinct from that of acid-sensing ion channels (ASICs) by a longer distance between the recognition site and the channel gate, carrying useful information about the ligand gating and the evolution of the trimeric ENaC/DEG superfamily of ion channels.
Collapse
Affiliation(s)
- You-Ya Niu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China, Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yang Yang
- Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yan Liu
- Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Li-Dong Huang
- Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Xiao-Na Yang
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China, Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Ying-Zhe Fan
- Putuo District Center Hospital, Shanghai University of Chinese Traditional Medicine, Shanghai, 200062, China
| | - Xiao-Yang Cheng
- Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Peng Cao
- Hospital of Integrated Traditional Chinese and Western Medicine, Nanjing University of Chinese Medicine, Nanjing 210023, China, and Laboratory of Cellular and Molecular Biology, Jiangsu Province Academy of Traditional Chinese Medicine, Nanjing 210028, China
| | - You-Min Hu
- Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Lingyong Li
- Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030
| | - Xiang-Yang Lu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China
| | - Yun Tian
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China,
| | - Ye Yu
- From the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China, Institute of Medical Sciences and Departments of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China,
| |
Collapse
|
38
|
Thai TL, Yu L, Galarza-Paez L, Wu MM, Lam HYC, Bao HF, Duke BJ, Al-Khalili O, Ma HP, Liu B, Eaton DC. The Polarized Effect of Intracellular Calcium on the Renal Epithelial Sodium Channel Occurs as a Result of Subcellular Calcium Signaling Domains Maintained by Mitochondria. J Biol Chem 2015; 290:28805-11. [PMID: 26451045 DOI: 10.1074/jbc.m115.668293] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Indexed: 12/27/2022] Open
Abstract
The renal epithelial sodium channel (ENaC) provides regulated sodium transport in the distal nephron. The effects of intracellular calcium ([Ca(2+)]i) on this channel are only beginning to be elucidated. It appears from previous studies that the [Ca(2+)]i increases downstream of ATP administration may have a polarized effect on ENaC, where apical application of ATP and the subsequent [Ca(2+)]i increase have an inhibitory effect on the channel, whereas basolateral ATP and [Ca(2+)]i have a stimulatory effect. We asked whether this polarized effect of ATP is, in fact, reflective of a polarized effect of increased [Ca(2+)]i on ENaC and what underlying mechanism is responsible. We began by performing patch clamp experiments in which ENaC activity was measured during apical or basolateral application of ionomycin to increase [Ca(2+)]i near the apical or basolateral membrane, respectively. We found that ENaC does indeed respond to increased [Ca(2+)]i in a polarized fashion, with apical increases being inhibitory and basolateral increases stimulating channel activity. In other epithelial cell types, mitochondria sequester [Ca(2+)]i, creating [Ca(2+)]i signaling microdomains within the cell that are dependent on mitochondrial localization. We found that mitochondria localize in bands just beneath the apical and basolateral membranes in two different cortical collecting duct principal cell lines and in cortical collecting duct principal cells in mouse kidney tissue. We found that inhibiting mitochondrial [Ca(2+)]i uptake destroyed the polarized response of ENaC to [Ca(2+)]i. Overall, our data suggest that ENaC is regulated by [Ca(2+)]i in a polarized fashion and that this polarization is maintained by mitochondrial [Ca(2+)]i sequestration.
Collapse
Affiliation(s)
- Tiffany L Thai
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Ling Yu
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Laura Galarza-Paez
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Ming Ming Wu
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Ho Yin Colin Lam
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Hui Fang Bao
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Billie Jeanne Duke
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Otor Al-Khalili
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - He-Ping Ma
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Bingchen Liu
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Douglas C Eaton
- From the Department of Physiology, Emory University, Atlanta, Georgia 30322
| |
Collapse
|
39
|
Rajendran VM, Nanda Kumar NS, Tse CM, Binder HJ. Na-H Exchanger Isoform-2 (NHE2) Mediates Butyrate-dependent Na+ Absorption in Dextran Sulfate Sodium (DSS)-induced Colitis. J Biol Chem 2015; 290:25487-96. [PMID: 26350456 DOI: 10.1074/jbc.m115.654277] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Indexed: 12/13/2022] Open
Abstract
Diarrhea associated with ulcerative colitis (UC) occurs primarily as a result of reduced Na(+) absorption. Although colonic Na(+) absorption is mediated by both epithelial Na(+) channels (ENaC) and Na-H exchangers (NHE), inhibition of NHE-mediated Na(+) absorption is the primary cause of diarrhea in UC. As there are conflicting observations reported on NHE expression in human UC, the present study was initiated to identify whether NHE isoforms (NHE2 and NHE3) expression is altered and how Na(+) absorption is regulated in DSS-induced inflammation in rat colon, a model that has been used to study UC. Western blot analyses indicate that neither NHE2 nor NHE3 expression is altered in apical membranes of inflamed colon. Na(+) fluxes measured in vitro under voltage clamp conditions in controls demonstrate that both HCO3 (-)-dependent and butyrate-dependent Na(+) absorption are inhibited by S3226 (NHE3-inhibitor), but not by HOE694 (NHE2-inhibitor) in normal animals. In contrast, in DSS-induced inflammation, butyrate-, but not HCO3 (-)-dependent Na(+) absorption is present and is inhibited by HOE694, but not by S3226. These observations indicate that in normal colon NHE3 mediates both HCO3 (-)-dependent and butyrate-dependent Na(+) absorption, whereas DSS-induced inflammation activates NHE2, which mediates butyrate-dependent (but not HCO3 (-)-dependent) Na(+) absorption. In in vivo loop studies HCO3 (-)-Ringer and butyrate-Ringer exhibit similar rates of water absorption in normal rats, whereas in DSS-induced inflammation luminal butyrate-Ringer reversed water secretion observed with HCO3 (-)-Ringer to fluid absorption. Lumen butyrate-Ringer incubation activated NHE3-mediated Na(+) absorption in DSS-induced colitis. These observations suggest that the butyrate activation of NHE2 would be a potential target to control UC-associated diarrhea.
Collapse
Affiliation(s)
- Vazhaikkurichi M Rajendran
- From the Department of Biochemistry and Molecular Biology, West Virginia University School of Medicine, Morgantown, West Virginia 26506,
| | - Navalpur S Nanda Kumar
- From the Department of Biochemistry and Molecular Biology, West Virginia University School of Medicine, Morgantown, West Virginia 26506
| | - Chung M Tse
- the Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and
| | - Henry J Binder
- the Department of Internal Medicine, Yale University, New Haven, Connecticut 06520
| |
Collapse
|
40
|
Chen J, Ray EC, Yates ME, Buck TM, Brodsky JL, Kinlough CL, Winarski KL, Hughey RP, Kleyman TR, Sheng S. Functional Roles of Clusters of Hydrophobic and Polar Residues in the Epithelial Na+ Channel Knuckle Domain. J Biol Chem 2015; 290:25140-50. [PMID: 26306034 DOI: 10.1074/jbc.m115.665398] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Indexed: 12/21/2022] Open
Abstract
The extracellular regions of epithelial Na(+) channel subunits are highly ordered structures composed of domains formed by α helices and β strands. Deletion of the peripheral knuckle domain of the α subunit in the αβγ trimer results in channel activation, reflecting an increase in channel open probability due to a loss of the inhibitory effect of external Na(+) (Na(+) self-inhibition). In contrast, deletion of either the β or γ subunit knuckle domain within the αβγ trimer dramatically reduces epithelial Na(+) channel function and surface expression, and impairs subunit maturation. We systematically mutated individual α subunit knuckle domain residues and assessed functional properties of these mutants. Cysteine substitutions at 14 of 28 residues significantly suppressed Na(+) self-inhibition. The side chains of a cluster of these residues are non-polar and are predicted to be directed toward the palm domain, whereas a group of polar residues are predicted to orient their side chains toward the space between the knuckle and finger domains. Among the mutants causing the greatest suppression of Na(+) self-inhibition were αP521C, αI529C, and αS534C. The introduction of Cys residues at homologous sites within either the β or γ subunit knuckle domain resulted in little or no change in Na(+) self-inhibition. Our results suggest that multiple residues in the α subunit knuckle domain contribute to the mechanism of Na(+) self-inhibition by interacting with palm and finger domain residues via two separate and chemically distinct motifs.
Collapse
Affiliation(s)
- Jingxin Chen
- From the Renal-Electrolyte Division, Department of Medicine
| | - Evan C Ray
- From the Renal-Electrolyte Division, Department of Medicine
| | | | | | | | | | | | - Rebecca P Hughey
- From the Renal-Electrolyte Division, Department of Medicine, the Department of Cell Biology, the Department of Microbiology and Molecular Genetics, and
| | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine, the Department of Cell Biology, the Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shaohu Sheng
- From the Renal-Electrolyte Division, Department of Medicine
| |
Collapse
|
41
|
Abstract
A long isoform of the human Epithelial Sodium Channel (ENaC) α subunit has been identified, but little data exist regarding the properties or regulation of channels formed by α728. The baseline whole cell conductance of oocytes expressing trimeric α728βγ channels was 898.1±277.2 and 49.59±13.2 µS in low and high sodium solutions, respectively, and was 11 and 2 fold higher than the conductances of α669βγ in same solutions. α728βγ channels were also 2 to 5 fold less sensitive to activation by the serine proteases subtilisin and trypsin than α669βγ in low and high Na+ conditions. The long isoform exhibited lower levels of full length and cleaved protein at the plasma membrane and a rightward shifted sensitivity to inhibition by increases of [Na+]i. Both channels displayed similar single channel conductances of 4 pS, and both were activated to a similar extent by reducing temperature, altogether indicating that activation of baseline conductance of α728βγ was likely mediated by enhanced channel activity or open probability. Expression of α728 in native kidneys was validated in human urinary exosomes. These data demonstrate that the long isoform of αENaC forms the structural basis of a channel with different activity and regulation, which may not be easily distinguishable in native tissue, but may underlie sodium hyperabsorption and salt sensitive differences in humans.
Collapse
Affiliation(s)
- Jonathan M Berman
- a Department of Physiology and Biophysics ; State University of New York at Buffalo ; Buffalo , NY USA
| | | | | |
Collapse
|
42
|
Yang X, He J, Gu D, Hixson JE, Huang J, Rao DC, Shimmin LC, Chen J, Rice TK, Li J, Schwander K, Kelly TN. Associations of epithelial sodium channel genes with blood pressure changes and hypertension incidence: the GenSalt study. Am J Hypertens 2014; 27:1370-6. [PMID: 24735600 DOI: 10.1093/ajh/hpu060] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND We examined the associations of epithelial sodium channel (ENaC) genes with blood pressure (BP) changes and hypertension incidence in a longitudinal family study. METHODS A total of 2,755 Han Chinese participants of the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) baseline examination were eligible for this study. The associations of 43 tag single nucleotide polymorphisms (SNPs) in ENaC genes with BP changes and hypertension incidence were assessed using mixed models to account for the correlations of repeated measures among individuals and within families. A genotype by time interaction term was used to model differences in longitudinal BP change according to genotype over time. Gene-based analyses were conducted using the truncated product method. The Bonferroni method was used to adjust for multiple testing in all analyses. RESULTS During an average of 7.4 years follow-up, systolic BP (SBP) and diastolic BP (DBP) increased, and approximately 33% of participants developed hypertension. SCNN1A SNP rs11064153 and SCNN1G SNP rs4401050 were significantly associated with longitudinal changes in SBP after adjustment for multiple testing (P interaction = 5.8×10(-4) and 0.001, respectively). Similar but nonsignificant trends were observed for the associations between both rs11064153 and rs4401050 and DBP changes (P interaction = 0.024 and 0.005, respectively) and between rs11604153 and hypertension incidence (P = 0.02). Gene-based analyses also supported the overall association of SCNN1G with longitudinal changes in SBP (P = 2.0×10(-4)). CONCLUSIONS Our findings indicated that SCNN1A and SCNN1G may contribute to BP changes over time in the Han Chinese population. Replication of these findings is warranted.
Collapse
Affiliation(s)
- Xueli Yang
- Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana; State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center of Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Jiang He
- Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana; Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana
| | - Dongfeng Gu
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center of Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China;
| | - James E Hixson
- Department of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, Houston, Texas
| | - Jianfeng Huang
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center of Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Dabeeru C Rao
- Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri
| | - Lawrence C Shimmin
- Department of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, Houston, Texas
| | - Jichun Chen
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center of Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Treva K Rice
- Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri
| | - Jianxin Li
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center of Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Karen Schwander
- Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri
| | - Tanika N Kelly
- Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana
| |
Collapse
|
43
|
Rab A, Rowe SM, Raju SV, Bebok Z, Matalon S, Collawn JF. Cigarette smoke and CFTR: implications in the pathogenesis of COPD. Am J Physiol Lung Cell Mol Physiol 2013; 305:L530-41. [PMID: 23934925 DOI: 10.1152/ajplung.00039.2013] [Citation(s) in RCA: 115] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder consisting of chronic bronchitis and/or emphysema. COPD patients suffer from chronic infections and display exaggerated inflammatory responses and a progressive decline in respiratory function. The respiratory symptoms of COPD are similar to those seen in cystic fibrosis (CF), although the molecular basis of the two disorders differs. CF is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding a chloride and bicarbonate channel (CFTR), leading to CFTR dysfunction. The majority of COPD cases result from chronic oxidative insults such as cigarette smoke. Interestingly, environmental stresses including cigarette smoke, hypoxia, and chronic inflammation have also been implicated in reduced CFTR function, and this suggests a common mechanism that may contribute to both the CF and COPD. Therefore, improving CFTR function may offer an excellent opportunity for the development of a common treatment for CF and COPD. In this article, we review what is known about the CF respiratory phenotype and discuss how diminished CFTR expression-associated ion transport defects may contribute to some of the pathological changes seen in COPD.
Collapse
Affiliation(s)
- Andras Rab
- Dept. of Cell, Developmental and Integrative Biology, Univ. of Alabama at Birmingham, 1918 Univ. Blvd., MCLM 395, Birmingham, AL 35294.
| | | | | | | | | | | |
Collapse
|