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Kasahara Y, Narukawa M, Takeuchi A, Tominaga M, Abe K, Asakura T. Molecular logic of salt taste reception in special reference to transmembrane channel-like 4 (TMC4). J Physiol Sci 2022; 72:31. [DOI: 10.1186/s12576-022-00856-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Accepted: 11/13/2022] [Indexed: 12/05/2022]
Abstract
AbstractThe taste is biologically of intrinsic importance. It almost momentarily perceives environmental stimuli for better survival. In the early 2000s, research into taste reception was greatly developed with discovery of the receptors. However, the mechanism of salt taste reception is not fully elucidated yet and many questions still remain. At present, next-generation sequencing and genome-editing technologies are available which would become pivotal tools to elucidate the remaining issues. Here we review current mechanisms of salt taste reception in particular and characterize the properties of transmembrane channel-like 4 as a novel salt taste-related molecule that we found using these sophisticated tools.
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2
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Shabbir W, Topcagic N, Aufy M. Activation of autosomal recessive Pseudohypoaldosteronism1 ENaC with aldosterone. Eur J Pharmacol 2021; 901:174090. [PMID: 33831414 DOI: 10.1016/j.ejphar.2021.174090] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 03/26/2021] [Accepted: 03/31/2021] [Indexed: 11/28/2022]
Abstract
The mineralocorticoid hormone aldosterone stimulates sodium reabsorption in the collecting ducts by increasing the activity of the epithelial sodium channel (ENaC). Being a rate-liming channel the loss of function mutations caused Pseudohypoaldosteronism 1 (PHA1). Despite elevated plasma aldosterone in PHA 1 patients the modulation of PHA 1 causing ENaC mutants with hormone has never been studied. After recording control ENaC current in PHA1 causing ENaC stop codon mutants we demonstrated the activation of aldosterone in the whole cell as well as single channel patch clamp assays. Single channel recoding experiments demonstrated that aldosterone can increase the open probability of all analyzed PHA 1 stop codon mutants and WT. Additionally, we demonstrated by western blot experiments that aldosterone can increase the expression of WT and PHA 1 stop codon mutants. Extensive whole cell patch clamp experiments demonstrated that C-terminal γ ENaC domain is necessary for aldosterone to activate whole cell current in HEK-293 cells. This novel finding of γ ENaC C-terminus dependent activation of whole cell current by aldosterone could alter our understanding of ENaC-mediated sodium reabsorption in the aldosterone-sensitive distal nephron (ASDN).
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Affiliation(s)
- Waheed Shabbir
- Institute for Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria.
| | - Nermina Topcagic
- Institute for Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
| | - Mohammed Aufy
- Institute for Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
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3
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Guo Y, Yan B, Gui Y, Tang Z, Tai S, Zhou S, Zheng XL. Physiology and role of PCSK9 in vascular disease: Potential impact of localized PCSK9 in vascular wall. J Cell Physiol 2020; 236:2333-2351. [PMID: 32875580 DOI: 10.1002/jcp.30025] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 08/12/2020] [Accepted: 08/16/2020] [Indexed: 12/26/2022]
Abstract
Proprotein convertase subtilisin/kexin type-9 (PCSK9), a member of the proprotein convertase family, is an important drug target because of its crucial role in lipid metabolism. Emerging evidence suggests a direct role of localized PCSK9 in the pathogenesis of vascular diseases. With this in our consideration, we reviewed PCSK9 physiology with respect to recent development and major studies (clinical and experimental) on PCSK9 functionality in vascular disease. PCSK9 upregulates low-density lipoprotein (LDL)-cholesterol levels by binding to the LDL-receptor (LDLR) and facilitating its lysosomal degradation. PCSK9 gain-of-function mutations have been confirmed as a novel genetic mechanism for familial hypercholesterolemia. Elevated serum PCSK9 levels in patients with vascular diseases may contribute to coronary artery disease, atherosclerosis, cerebrovascular diseases, vasculitis, aortic diseases, and arterial aging pathogenesis. Experimental models of atherosclerosis, arterial aneurysm, and coronary or carotid artery ligation also support PCSK9 contribution to inflammatory response and disease progression, through LDLR-dependent or -independent mechanisms. More recently, several clinical trials have confirmed that anti-PCSK9 monoclonal antibodies can reduce systemic LDL levels, total nonfatal cardiovascular events, and all-cause mortality. Interaction of PCSK9 with other receptor proteins (LDLR-related proteins, cluster of differentiation family members, epithelial Na+ channels, and sortilin) may underlie its roles in vascular disease. Improved understanding of PCSK9 roles and molecular mechanisms in various vascular diseases will facilitate advances in lipid-lowering therapy and disease prevention.
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Affiliation(s)
- Yanan Guo
- Department of Cardiology, The Second Xiangya Hospital of Central South University, Changsha, China.,Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Physiology & Pharmacology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada
| | - Binjie Yan
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Physiology & Pharmacology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Pathophysiology, Institute of Cardiovascular Disease, Key Lab for Arteriosclerology of Hunan Province, University of South China, Hengyang, Hunan, China
| | - Yu Gui
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Physiology & Pharmacology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada
| | - Zhihan Tang
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Physiology & Pharmacology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Pathophysiology, Institute of Cardiovascular Disease, Key Lab for Arteriosclerology of Hunan Province, University of South China, Hengyang, Hunan, China
| | - Shi Tai
- Department of Cardiology, The Second Xiangya Hospital of Central South University, Changsha, China.,Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Physiology & Pharmacology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada
| | - Shenghua Zhou
- Department of Cardiology, The Second Xiangya Hospital of Central South University, Changsha, China
| | - Xi-Long Zheng
- Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada.,Department of Physiology & Pharmacology, Libin Cardiovascular Institute of Alberta, Cumming School of Medicine, The University of Calgary, Calgary, Alberta, Canada
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4
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Bukhari AAS, Zhang X, Li M, Zhao A, Dong H, Liang X. Cofilin participates in regulating alpha-epithelial sodium channel by interaction with 14-3-3 isoforms. J Biomed Res 2020; 34:351-360. [PMID: 32981895 PMCID: PMC7540242 DOI: 10.7555/jbr.34.20190155] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Renal epithelial sodium channel (ENaC) plays a crucial role in maintaining homeostasis and sodium absorption. While insulin participates in controlling sodium transport across the renal epithelium, the underlying molecular mechanism remain unclear. In this study, we found that insulin increased the expression and function of alpha-epithelial sodium channel (α-ENaC) as well as phosphorylation of cofilin, a family of actin-binding proteins which disassembles actin filaments, in mouse cortical collecting duct (mpkCCDc14) cells. The wild-type (WT) cofilin and its constitutively phosphorylated form (S3D), but not its constitutively non-phosphorylable form (S3A), contributed to the elevated expression on α-ENaC. Overexpression of 14-3-3ε, β, or γ increased the expression of α-ENaC and cofilin phosphorylation, which was blunted by knockdown of 14-3-3ε, β, or γ. Moreover, it was found that insulin increased the interaction between cofilin and 14-3-3 isoforms, which indicated relevance of 14-3-3 isoforms with cofilin. Furthermore, LIMK1/SSH1 pathway was involved in regulation of cofilin and α-ENaC expression by insulin. The results from this work indicate that cofilin participates in the regulation of α-ENaC by interaction with 14-3-3 isoforms.
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Affiliation(s)
| | | | | | | | | | - Xiubin Liang
- Department of Pathophysiology;Department of Nephrology, the Affiliated Sir Run Run Hospital of Nanjing Medical University, Nanjing, Jiangsu 211166, China
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5
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Garcia-Caballero A, Gandini MA, Huang S, Chen L, Souza IA, Dang YL, Stutts MJ, Zamponi GW. Cav3.2 calcium channel interactions with the epithelial sodium channel ENaC. Mol Brain 2019; 12:12. [PMID: 30736831 PMCID: PMC6368719 DOI: 10.1186/s13041-019-0433-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 02/04/2019] [Indexed: 11/10/2022] Open
Abstract
This study describes the functional interaction between Cav3.2 calcium channels and the Epithelial Sodium Channel (ENaC). β-ENaC subunits showed overlapping expression with endogenous Cav3.2 calcium channels in the thalamus and hypothalamus as detected by immunostaining. Moreover, β- and γ-ENaC subunits could be co-immunoprecipitated with Cav3.2 calcium channels from brain lysates, dorsal horn and lumbar dorsal root ganglia. Mutation of a cluster of lysines present in the intracellular N-terminus region of β-ENaC (K4R/ K5R/ K9R/ K16R/ K23R) reduced interactions with Cav3.2 calcium channels. Αβγ-ENaC channels enhanced Cav3.2 calcium channel trafficking to the plasma membrane in tsA-201 cells. This effect was reciprocal such that Cav3.2 channel expression also enhanced β-ENaC trafficking to the cell surface. T-type current density was increased when fully assembled αβγ-ENaC channels were transiently expressed in CAD cells, a neuronal derived cell line. Altogether, these findings reveal ENaC as an interactor and potential regulator of Cav3.2 calcium channels expressed in neuronal tissues.
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Affiliation(s)
- Agustin Garcia-Caballero
- Molecular Neuroscience, Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada
| | - Maria A Gandini
- Molecular Neuroscience, Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada
| | - Shuo Huang
- Molecular Neuroscience, Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada
| | - Lina Chen
- Molecular Neuroscience, Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada
| | - Ivana A Souza
- Molecular Neuroscience, Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada
| | - Yan L Dang
- Cystic Fibrosis Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - M Jackson Stutts
- Cystic Fibrosis Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Gerald W Zamponi
- Molecular Neuroscience, Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada.
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6
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Reus-Chavarría E, Martínez-Vieyra I, Salinas-Nolasco C, Chávez-Piña AE, Méndez-Méndez JV, López-Villegas EO, Sosa-Peinado A, Cerecedo D. Enhanced expression of the Epithelial Sodium Channel in neutrophils from hypertensive patients. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1861:387-402. [DOI: 10.1016/j.bbamem.2018.11.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 10/29/2018] [Accepted: 11/08/2018] [Indexed: 12/17/2022]
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7
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Wu NC, Cramp RL, Ohmer MEB, Franklin CE. Epidermal epidemic: unravelling the pathogenesis of chytridiomycosis. ACTA ACUST UNITED AC 2019; 222:jeb.191817. [PMID: 30559300 DOI: 10.1242/jeb.191817] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 12/05/2018] [Indexed: 12/18/2022]
Abstract
Chytridiomycosis, a lethal fungal skin disease of amphibians, fatally disrupts ionic and osmotic homeostasis. Infected amphibians increase their skin shedding rate (sloughing) to slow pathogen growth, but the sloughing process also increases skin permeability. Healthy amphibians increase active ion uptake during sloughing by increasing ion transporter abundance to offset the increased skin permeability. How chytridiomycosis affects the skin function during and between sloughing events remains unknown. Here, we show that non-sloughing frogs with chytridiomycosis have impaired cutaneous sodium uptake, in part because they have fewer sodium transporters in their skin. Interestingly, sloughing was associated with a transient increase in sodium transporter activity and abundance, suggesting that the newly exposed skin layer is initially fully functional until the recolonization of the skin by the fungus again impedes cutaneous function. However, the temporary restoration of skin function during sloughing does not restore ionic homeostasis, and the underlying loss of ion uptake capacity is ultimately detrimental for amphibians with chytridiomycosis.
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Affiliation(s)
- Nicholas C Wu
- School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Rebecca L Cramp
- School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Michel E B Ohmer
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Craig E Franklin
- School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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8
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Chapter Five - Ubiquitination of Ion Channels and Transporters. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2016; 141:161-223. [DOI: 10.1016/bs.pmbts.2016.02.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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9
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Christmann J, Azer L, Dörr D, Fuhr GR, Bastiaens PIH, Wehner F. Adaptive responses of cell hydration to a low temperature arrest. J Physiol 2015; 594:1663-76. [PMID: 26593308 DOI: 10.1113/jp271245] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Accepted: 11/04/2015] [Indexed: 01/24/2023] Open
Abstract
Slow cooling leads to a passive dehydration of cells, whereas rehydration during warming reflects the active regain of functionality. The ability to modulate such an energy demanding process could be instrumental in optimizing the cryo-arrest of living systems. In the present study, various levels of hypertonic stress were used to disturb the water content of cells and to define the energy profiles of aquaporins and (Na(+) conducting) cation channels during rehydration. Na(+) import was found to be the rate-limiting step in water restoration, whereas aquaporins merely played a permissive role. Indeed, regulated Na(+) import was increased 2-fold following cryo-arrests, thus facilitating the osmotic rehydration of cells. Freezing temperatures increased cell viscosity with a remarkable hysteresis and viscosity was a trigger of cation channels. The peptide hormone vasopressin was a further activator of channels, increasing the viability of post-cryo cells considerably. Hence, the hormone opens the path for a novel class of cryo-protectants with an intrinsic biological activity.
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Affiliation(s)
- Jens Christmann
- Max Planck Institute of Molecular Physiology, Department of Systemic Cell Biology, Dortmund, Germany
| | - Lale Azer
- Max Planck Institute of Molecular Physiology, Department of Systemic Cell Biology, Dortmund, Germany
| | - Daniel Dörr
- Fraunhofer Institute for Biomedical Engineering, St Ingbert, Germany
| | - Günter R Fuhr
- Fraunhofer Institute for Biomedical Engineering, St Ingbert, Germany
| | - Philippe I H Bastiaens
- Max Planck Institute of Molecular Physiology, Department of Systemic Cell Biology, Dortmund, Germany
| | - Frank Wehner
- Max Planck Institute of Molecular Physiology, Department of Systemic Cell Biology, Dortmund, Germany
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10
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Wang Y, O’Bryant Z, Wang H, Huang Y. Regulating Factors in Acid-Sensing Ion Channel 1a Function. Neurochem Res 2015; 41:631-45. [DOI: 10.1007/s11064-015-1768-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2015] [Revised: 11/04/2015] [Accepted: 11/08/2015] [Indexed: 12/11/2022]
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11
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Control of ENaC-mediated sodium reabsorption in the distal nephron by Bradykinin. VITAMINS AND HORMONES 2015. [PMID: 25817868 DOI: 10.1016/bs.vh.2014.12.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Abstract
Kinins, such as Bradykinin (BK), are peptide hormones of the kallikrein-kinin system. Apart from being a vasodilator, BK also increases urinary sodium excretion to reduce systemic blood pressure. It is becoming appreciated that BK modulates function of the epithelial Na(+) channel in the distal part of the renal nephron to affect tubular sodium reabsorption. In this chapter, we outline the molecular details, as well as discuss the physiological relevance of this regulation for the whole organism sodium homeostasis and setting chronic blood pressure.
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12
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Butler PL, Staruschenko A, Snyder PM. Acetylation stimulates the epithelial sodium channel by reducing its ubiquitination and degradation. J Biol Chem 2015; 290:12497-503. [PMID: 25787079 DOI: 10.1074/jbc.m114.635540] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Indexed: 12/29/2022] Open
Abstract
The epithelial Na(+) channel (ENaC) functions as a pathway for Na(+) absorption in the kidney and lung, where it is crucial for Na(+) homeostasis and blood pressure regulation. ENaC is regulated in part through signaling pathways that control the ubiquitination state of ENaC lysines. A defect in ubiquitination causes Liddle syndrome, an inherited form of hypertension. Here we determined that α-, β-, and γENaC are also substrates for lysine acetylation. Trichostatin A (TSA), a histone deacetylase inhibitor, enhanced ENaC acetylation and increased ENaC abundance in the total cell lysate and at the cell surface. Moreover, TSA increased ENaC current in Fischer rat thyroid and kidney collecting duct epithelia. We found that HDAC7 is expressed in the kidney collecting duct, supporting a potential role for this histone deacetylase in ENaC regulation. HDAC7 overexpression reduced ENaC abundance and ENaC current, whereas ENaC abundance and current were increased by silencing of HDAC7. ENaC and HDAC7 form a complex, as detected by coimmunoprecipitation. We observed a reciprocal relationship between acetylation and ubiquitination; TSA reduced ENaC ubiquitination, whereas HDAC7 increased ubiquitination. By reducing ENaC ubiquitination, TSA decreased the rate of ENaC degradation. Thus, acetylation increases epithelial Na(+) absorption by antagonizing ENaC ubiquitination. This stabilizes ENaC, and hence, increases its abundance at the cell surface.
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Affiliation(s)
- Phillip L Butler
- From the Departments of Internal Medicine and Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | | | - Peter M Snyder
- From the Departments of Internal Medicine and Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, the Iowa City Veterans Affairs Healthcare System, Iowa City, Iowa 52246, and
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Chen MX, Gatfield K, Ward E, Downie D, Sneddon HF, Walsh S, Powell AJ, Laine D, Carr M, Trezise D. Validation and optimization of novel high-throughput assays for human epithelial sodium channels. ACTA ACUST UNITED AC 2014; 20:242-53. [PMID: 25278498 DOI: 10.1177/1087057114552399] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The epithelial sodium channel (ENaC) plays a crucial role in salt and water homeostasis and is primarily involved in sodium reabsorption in the kidney and lung. Modulators of ENaC function, particularly within lung epithelia, could offer potential treatments for a number of diseases. As a constitutively active sodium channel, ENaC expression at the cell membrane is highly regulated through rapid turnover. This short half-life of the channel at the membrane and cytotoxicity from overexpression pose a problem for reagent generation and assay development in drug discovery. We have generated an HEK293 stable cell line expressing ENaC β and γ subunits containing the PY motif trafficking mutations found in Liddle's syndrome to overcome rapid channel turnover at the membrane. A BacMam virus was used to transiently express the ENaC α subunit to reconstitute channel function to reduce the toxicity associated with long-term overexpression. We have configured a 384-well FLIPR membrane potential antagonist assay for high-throughput screening and an IonWorks Quattro electrophysiology antagonist assay that is predictive of potency values derived from primary lung epithelial cell short-circuit measurements. The triage strategy for compound screening and profiling against this target using these assays has resulted in the discovery of novel chemotypes.
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Affiliation(s)
- Mao Xiang Chen
- Biological Sciences, GlaxoSmithKline R&D, Stevenage, Herts, UK
| | - Kelly Gatfield
- Biological Sciences, GlaxoSmithKline R&D, Stevenage, Herts, UK
| | - Emma Ward
- Biological Sciences, GlaxoSmithKline R&D, Stevenage, Herts, UK
| | - David Downie
- Biological Sciences, GlaxoSmithKline R&D, Stevenage, Herts, UK
| | - Helen F Sneddon
- Green Chemistry Performance Unit, GlaxoSmithKline R&D, Stevenage, Herts, UK
| | - Stacey Walsh
- Target and Pathway Validation, GlaxoSmithKline R&D, Upper Providence, Philadelphia, PA, USA
| | - Andrew J Powell
- Biological Sciences, GlaxoSmithKline R&D, Stevenage, Herts, UK
| | - Dramane Laine
- Neurobiology DPU, GlaxoSmithKline R&D, Upper Merion, Philadelphia, PA, USA
| | - Michael Carr
- Neurobiology DPU, GlaxoSmithKline R&D, Upper Merion, Philadelphia, PA, USA
| | - Derek Trezise
- Biological Sciences, GlaxoSmithKline R&D, Stevenage, Herts, UK
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14
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Direct regulation of ENaC by bradykinin in the distal nephron. Implications for renal sodium handling. Curr Opin Nephrol Hypertens 2014; 23:122-9. [PMID: 24378775 DOI: 10.1097/01.mnh.0000441053.81339.61] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
PURPOSE OF REVIEW Locally produced peptide hormones kinins, such as bradykinin, are thought to oppose many of the prohypertensive actions of the renin-angiotensin-aldosterone system. In the kidney, bradykinin, via stimulation of B2 receptors (B2R), favors natriuresis mostly due to the inhibition of tubular Na reabsorption. Recent experimental evidence identifies the epithelial Na channel (ENaC) as a key end effector of bradykinin actions in the distal tubular segments. The focus of this review is the physiological relevance and molecular details of the bradykinin signal to ENaC. RECENT FINDINGS The recent epidemiological GenSalt study demonstrated that genetic variants of the gene encoding B2R show significant associations with the salt sensitivity of blood pressure. Bradykinin was shown to have an inhibitory effect on the distal nephron sodium transport via stimulation of B2 receptor-phospholipase C (B2R-PLC) cascade to decrease ENaC open probability. Genetic ablation of bradykinin receptors in mice led to an augmented ENaC function, particularly during elevated sodium intake, likely contributing to the salt-sensitive hypertensive phenotype. Furthermore, augmentation of bradykinin signaling in the distal nephron was demonstrated to be an important component of the natriuretic and antihypertensive effects of angiotensin converting enzyme inhibition. SUMMARY Salt-sensitive inhibition of ENaC activity by bradykinin greatly advances our understanding of the molecular mechanisms that are responsible for shutting down distal tubule sodium reabsorption during volume expanded conditions to avoid salt-sensitive hypertension.
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15
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Collier DM, Tomkovicz VR, Peterson ZJ, Benson CJ, Snyder PM. Intersubunit conformational changes mediate epithelial sodium channel gating. ACTA ACUST UNITED AC 2014; 144:337-48. [PMID: 25225551 PMCID: PMC4178938 DOI: 10.1085/jgp.201411208] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Residues forming interfaces between the three ENaC subunits participate in conformational changes required for transition between open and closed states. The epithelial Na+ channel (ENaC) functions as a pathway for Na+ absorption in the kidney and lung, where it is crucial for Na+ homeostasis and blood pressure regulation. However, the basic mechanisms that control ENaC gating are poorly understood. Here we define a role in gating for residues forming interfaces between the extracellular domains of the three ENaC subunits. Using cysteine substitution combined with chemical cross-linking, we determined that residues located at equivalent positions in the three subunits (αK477, βE446, and γE455) form interfaces with residues in adjacent subunits (βV85, γV87, and αL120, respectively). Cross-linking of these residues altered ENaC activity in a length-dependent manner; long cross-linkers increased ENaC current by increasing its open probability, whereas short cross-linkers reduced ENaC open probability. Cross-linking also disrupted ENaC gating responses to extracellular pH and Na+, signals which modulate ENaC activity during shifts in volume status. Introduction of charged side chains at the interfacing residues altered ENaC activity in a charge-dependent manner. Current increased when like charges were present at both interfacing residues, whereas opposing charges reduced current. Together, these data indicate that conformational changes at intersubunit interfaces participate in ENaC transitions between the open and closed states; movements that increase intersubunit distance favor the open state, whereas the closed state is favored when the distance is reduced. This provides a mechanism to modulate ENaC gating in response to changing extracellular conditions that threaten Na+ homeostasis.
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Affiliation(s)
- Daniel M Collier
- Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | - Vivian R Tomkovicz
- Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | - Zerubbabel J Peterson
- Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | - Christopher J Benson
- Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Iowa City VA Health Care System, Iowa City, IA 52246
| | - Peter M Snyder
- Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Department of Internal Medicine and Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242 Iowa City VA Health Care System, Iowa City, IA 52246
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Abstract
The apical membrane epithelial Na(+) channel subunit (ENaC) in series with the basolateral Na(+)/K(+)-adenosine triphosphatase mediates collecting duct Na(+) reabsorption. Aldosterone induces αENaC gene transcription, which appears to be rate limiting for ENaC activity in this segment. Although this response has long been assumed to be solely the result of liganded nuclear hormone receptors trans-activating αENaC, epigenetic controls of basal and aldosterone-induced transcription of αENaC in the collecting duct recently were described. These epigenetic pathways involve dynamic nuclear repressor complexes targeted to specific subregions of the αENaC promoter and consisting of the histone methyltransferase disrupter of telomeric silencing (Dot)1a together with the transcriptional factor Af9 or the nicotinamide adenine dinucleotide (NAD)-dependent protein deacetylase Sirt1, key co-regulatory proteins, including serum- and glucocorticoid-induced kinase-1 and the putative transcription factor Af17, and targeted chromatin modifications. The complexes, through the action of Dot1a, maintain chromatin associated with the αENaC promoter in a stable hypermethylated state, constraining αENaC transcription under basal conditions. Aldosterone and serum- and glucocorticoid-induced kinase-1, itself, activate αENaC transcription in large part by disrupting or diminishing the Dot1a-Af9 and Dot1a-Sirt1 complexes and their effects on chromatin. Mouse models indicate potential roles of the Dot1a pathways in renal salt excretion and hypertension.
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Affiliation(s)
- Bruce C Kone
- Division of Renal Diseases and Hypertension, Department of Internal Medicine, The University of Texas Medical School, Houston, TX.
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17
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Bao HF, Thai TL, Yue Q, Ma HP, Eaton AF, Cai H, Klein JD, Sands JM, Eaton DC. ENaC activity is increased in isolated, split-open cortical collecting ducts from protein kinase Cα knockout mice. Am J Physiol Renal Physiol 2014; 306:F309-20. [PMID: 24338818 PMCID: PMC3920049 DOI: 10.1152/ajprenal.00519.2013] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 12/04/2013] [Indexed: 11/22/2022] Open
Abstract
The epithelial Na channel (ENaC) is negatively regulated by protein kinase C (PKC) as shown using PKC activators in a cell culture model. To determine whether PKCα influences ENaC activity in vivo, we examined the regulation of ENaC in renal tubules from PKCα⁻/⁻ mice. Cortical collecting ducts were dissected and split open, and the exposed principal cells were subjected to cell-attached patch clamp. In the absence of PKCα, the open probability (P₀) of ENaC was increased three-fold vs. wild-type SV129 mice (0.52 ± 0.04 vs. 0.17 ± 0.02). The number of channels per patch was also increased. Using confocal microscopy, we observed an increase in membrane localization of α-, β-, and γ-subunits of ENaC in principal cells in the cortical collecting ducts of PKCα⁻/⁻ mice compared with wild-type mice. To confirm this increase, one kidney from each animal was perfused with biotin, and membrane protein was pulled down with streptavidin. The nonbiotinylated kidney was used to assess total protein. While total ENaC protein did not change in PKCα⁻/⁻ mice, membrane localization of all the ENaC subunits was increased. The increase in membrane ENaC could be explained by the observation that ERK1/2 phosphorylation was decreased in the knockout mice. These results imply a reduction in ENaC membrane accumulation and P₀ by PKCα in vivo. The PKC-mediated increase in ENaC activity was associated with an increase in blood pressure in knockout mice fed a high-salt diet.
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Affiliation(s)
- Hui-Fang Bao
- Emory Univ. School of Medicine, Dept. of Physiology, Whitehead Biomedical Research Bldg., 615 Michael St., Atlanta, GA 30322.
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18
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Christensen EI, Wagner CA, Kaissling B. Uriniferous tubule: structural and functional organization. Compr Physiol 2013; 2:805-61. [PMID: 23961562 DOI: 10.1002/cphy.c100073] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.
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19
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Mamenko M, Zaika O, Prieto MC, Jensen VB, Doris PA, Navar LG, Pochynyuk O. Chronic angiotensin II infusion drives extensive aldosterone-independent epithelial Na+ channel activation. Hypertension 2013; 62:1111-1122. [PMID: 24060890 DOI: 10.1161/hypertensionaha.113.01797] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The inability of mineralocorticoid receptor (MR) blockade to reduce hypertension associated with high angiotensin (Ang) II suggests direct actions of Ang II to regulate tubular sodium reabsorption via the epithelial Na(+) channel (ENaC) in the aldosterone-sensitive distal nephron. We used freshly isolated aldosterone-sensitive distal nephron from mice to delineate the synergism and primacy between aldosterone and Ang II in controlling functional ENaC activity. Inhibition of MR specifically prevented the increased number of functionally active ENaC, but not ENaC open probability elicited by a low sodium diet. In contrast, we found no functional role of glucocorticoid receptors in the regulation of ENaC activity by dietary salt intake. Simultaneous inhibition of MR and Ang II type 1 receptors ameliorated the enhanced ENaC activity caused by low dietary salt intake and produced significantly greater natriuresis than either inhibitor alone. Chronic systemic Ang II infusion induced more than 2 times greater increase in ENaC activity than observed during dietary sodium restriction. Importantly, ENaC activity remained greatly above control levels during maximal MR inhibition. We conclude that during variations in dietary salt intake both aldosterone and Ang II contribute complementarily to the regulation of ENaC activity in the aldosterone-sensitive distal nephron. In contrast, in the setting of Ang II-dependent hypertension, ENaC activity is upregulated well above the physiological range and is not effectively suppressed by inhibition of the aldosterone-MR axis. This provides a mechanistic explanation for the resistance to MR inhibition that occurs in hypertensive subjects having elevated intrarenal Ang II levels.
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Affiliation(s)
- Mykola Mamenko
- Department of Integrative Biology and Pharmacology; The University of Texas Health Science Center at Houston, USA
| | - Oleg Zaika
- Department of Integrative Biology and Pharmacology; The University of Texas Health Science Center at Houston, USA
| | - Minolfa C Prieto
- Department of Physiology and Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, LA, USA
| | - V Behrana Jensen
- Center for Laboratory Animal Medicine and Care The University of Texas Health Science Center at Houston, USA
| | - Peter A Doris
- Institute of Molecular Medicine, The University of Texas Health Science Center at Houston, USA
| | - L Gabriel Navar
- Department of Physiology and Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, LA, USA
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology; The University of Texas Health Science Center at Houston, USA
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20
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Yu L, Al-Khalili O, Duke BJ, Stockand JD, Eaton DC, Bao HF. The inhibitory effect of Gβγ and Gβ isoform specificity on ENaC activity. Am J Physiol Renal Physiol 2013; 305:F1365-73. [PMID: 23863469 DOI: 10.1152/ajprenal.00009.2013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial Na(+) channel (ENaC) activity, which determines the rate of renal Na(+) reabsorption, can be regulated by G protein-coupled receptors. Regulation of ENaC by Gα-mediated downstream effectors has been studied extensively, but the effect of Gβγ dimers on ENaC is unclear. A6 cells endogenously contain high levels of Gβ1 but low levels of Gβ3, Gβ4, and Gβ5 were detected by Q-PCR. We tested Gγ2 combined individually with Gβ1 through Gβ5 expressed in A6 cells, after which we recorded single-channel ENaC activity. Among the five β and γ2 combinations, β1γ2 strongly inhibits ENaC activity by reducing both ENaC channel number (N) and open probability (Po) compared with control cells. In contrast, the other four β-isoforms combined with γ2 have no significant effect on ENaC activity. By using various inhibitors to probe Gβ1γ2 effects on ENaC regulation, we found that Gβ1γ2-mediated ENaC inhibition involved activation of phospholipase C-β and its enzymatic products that induce protein kinase C and ERK1/2 signaling pathways.
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Affiliation(s)
- Ling Yu
- College of Resources and Environmental Sciences, Nanjing Agricultural Univ., Nanjing 210095, China.
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21
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Abstract
Angiotensin II (Ang II) is the principal effector of the renin-angiotensin-aldosterone system (RAAS). It initiates myriad processes in multiple organs integrated to increase circulating volume and elevate systemic blood pressure. In the kidney, Ang II stimulates renal tubular water and salt reabsorption causing antinatriuresis and antidiuresis. Activation of the RAAS is known to enhance activity of the epithelial Na(+) channel (ENaC) in the aldosterone-sensitive distal nephron. In addition to its well described stimulatory actions on aldosterone secretion, Ang II is also capable of directly increasing ENaC activity. In this brief review, we discuss recent findings about non-classical Ang II actions on ENaC and speculate about its relevance for renal sodium handling.
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22
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Kline CF, Mohler PJ. Defective interactions of protein partner with ion channels and transporters as alternative mechanisms of membrane channelopathies. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:723-30. [PMID: 23732236 DOI: 10.1016/j.bbamem.2013.05.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 05/15/2013] [Accepted: 05/21/2013] [Indexed: 01/27/2023]
Abstract
The past twenty years have revealed the existence of numerous ion channel mutations resulting in human pathology. Ion channels provide the basis of diverse cellular functions, ranging from hormone secretion, excitation-contraction coupling, cell signaling, immune response, and trans-epithelial transport. Therefore, the regulation of biophysical properties of channels is vital in human physiology. Only within the last decade has the role of non-ion channel components come to light in regard to ion channel spatial, temporal, and biophysical regulation in physiology. A growing number of auxiliary components have been determined to play elemental roles in excitable cell physiology, with dysfunction resulting in disorders and related manifestations. This review focuses on the broad implications of such dysfunction, focusing on disease-causing mutations that alter interactions between ion channels and auxiliary ion channel components in a diverse set of human excitable cell disease. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé
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Affiliation(s)
- Crystal F Kline
- The Dorothy M. Davis Heart and Lung Research Institute, Department of Internal Medicine, Division of Cardiovascular Medicine, Department of Physiology & Cell Biology, The Ohio State University Wexner Medical Center, USA
| | - Peter J Mohler
- The Dorothy M. Davis Heart and Lung Research Institute, Department of Internal Medicine, Division of Cardiovascular Medicine, Department of Physiology & Cell Biology, The Ohio State University Wexner Medical Center, USA.
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23
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Zhou R, Tomkovicz VR, Butler PL, Ochoa LA, Peterson ZJ, Snyder PM. Ubiquitin-specific peptidase 8 (USP8) regulates endosomal trafficking of the epithelial Na+ channel. J Biol Chem 2013; 288:5389-97. [PMID: 23297398 DOI: 10.1074/jbc.m112.425272] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ubiquitination plays a key role in trafficking of the epithelial Na(+) channel (ENaC). Previous work indicated that ubiquitination enhances ENaC endocytosis and sorting to lysosomes for degradation. Moreover, a defect in ubiquitination causes Liddle syndrome, an inherited form of hypertension. In this work, we identified a role for USP8 in the control of ENaC ubiquitination and trafficking. USP8 increased ENaC current in Xenopus oocytes and collecting duct epithelia and enhanced ENaC abundance at the cell surface in HEK 293 cells. This resulted from altered endocytic sorting; USP8 abolished ENaC degradation in the endocytic pathway, but it had no effect on ENaC endocytosis. USP8 interacted with ENaC, as detected by co-immunoprecipitation, and it deubiquitinated ENaC. Consistent with a functional role for deubiquitination, mutation of the cytoplasmic lysines of ENaC reduced the effect of USP8 on ENaC cell surface abundance. In contrast to USP8, USP2-45 increased ENaC surface abundance by reducing endocytosis but not degradation. Thus, USP8 and USP2-45 selectively modulate ENaC trafficking at different steps in the endocytic pathway. Together with previous work, the data indicate that the ubiquitination state of ENaC is critical for the regulation of epithelial Na(+) absorption.
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Affiliation(s)
- Ruifeng Zhou
- Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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24
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Abstract
Ion channels play key roles in physiology. They function as protein transducers able to transform stimuli and chemical gradients into electrical signals. They also are critical for cell signaling and play a particularly important role in epithelial transport acting as gateways for the movement of electrolytes across epithelial cell membranes. Experimental limitations, though, have hampered the recording of ion channel activity in many types of tissue. This has slowed progress in understanding the cellular and physiological function of these channels with most function inferred from in vitro systems and cell culture models. In many cases, such inferences have clouded rather than clarified the picture. Here, we describe a contemporary method for isolating and patch-clamping renal tubules for ex vivo analysis of ion channel function in native tissue. Focus is placed on quantifying the activity of the epithelial Na(+) channel (ENaC) in the aldosterone--sensitive distal nephron (ASDN). This isolated, split-open tubule preparation enables recording of renal ion channels in the close-to-native environment under the control of native cell signaling pathways and receptors. When combined with complementary measurements of organ and system function, and contemporary molecular genetics and pharmacology used to manipulate function and regulation, patch-clamping renal channels in the isolated, split-open tubule enables understanding to emerge about the physiological function of these key proteins from the molecule to the whole animal.
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25
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Wang Q, Dai XQ, Li Q, Tuli J, Liang G, Li SS, Chen XZ. Filamin interacts with epithelial sodium channel and inhibits its channel function. J Biol Chem 2012; 288:264-73. [PMID: 23161538 DOI: 10.1074/jbc.m112.396408] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Epithelial sodium channel (ENaC) in the kidneys is critical for Na(+) balance, extracellular volume, and blood pressure. Altered ENaC function is associated with respiratory disorders, pseudohypoaldosteronism type 1, and Liddle syndrome. ENaC is known to interact with components of the cytoskeleton, but the functional roles remain largely unclear. Here, we examined the interaction between ENaC and filamins, important actin filament components. We first discovered by yeast two-hybrid screening that the C termini of ENaC α and β subunits bind filamin A, B, and C, and we then confirmed the binding by in vitro biochemical assays. We demonstrated by co-immunoprecipitation that ENaC, either overexpressed in HEK, HeLa, and melanoma A7 cells or natively expressed in LLC-PK1 and IMCD cells, is in the same complex with native filamin. Furthermore, the biotinylation and co-immunoprecipitation combined assays showed the ENaC-filamin interaction on the cell surface. Using Xenopus oocyte expression and two-electrode voltage clamp electrophysiology, we found that co-expression of an ENaC-binding domain of filamin substantially reduces ENaC channel function. Western blot and immunohistochemistry experiments revealed that the filamin A C terminus (FLNAC) modestly reduces the expression of the ENaC α subunit in oocytes and A7 cells. After normalizing the current by plasma membrane expression, we found that FLNAC results in ~50% reduction in the ENaC channel activity. The inhibitory effect of FLNAC was confirmed by lipid bilayer electrophysiology experiments using purified ENaC and FLNAC proteins, which showed that FLNAC substantially reduces ENaC single channel open probability. Taken together, our study demonstrated that filamin reduces ENaC channel function through direct interaction on the cell surface.
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Affiliation(s)
- Qian Wang
- Membrane Protein Disease Research Group, Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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26
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Collier DM, Peterson ZJ, Blokhin IO, Benson CJ, Snyder PM. Identification of extracellular domain residues required for epithelial Na+ channel activation by acidic pH. J Biol Chem 2012; 287:40907-14. [PMID: 23060445 DOI: 10.1074/jbc.m112.417519] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A growing body of evidence suggests that the extracellular domain of the epithelial Na(+) channel (ENaC) functions as a sensor that fine tunes channel activity in response to changes in the extracellular environment. We previously found that acidic pH increases the activity of human ENaC, which results from a decrease in Na(+) self-inhibition. In the current work, we identified extracellular domain residues responsible for this regulation. We found that rat ENaC is less sensitive to pH than human ENaC, an effect mediated in part by the γ subunit. We identified a group of seven residues in the extracellular domain of γENaC (Asp-164, Gln-165, Asp-166, Glu-292, Asp-335, His-439, and Glu-455) that, when individually mutated to Ala, decreased proton activation of ENaC. γ(E455) is conserved in βENaC (Glu-446); mutation of this residue to neutral amino acids (Ala, Cys) reduced ENaC stimulation by acidic pH, whereas reintroduction of a negative charge (by MTSES modification of Cys) restored pH regulation. Combination of the seven γENaC mutations with β(E446A) generated a channel that was not activated by acidic pH, but inhibition by alkaline pH was intact. Moreover, these mutations reduced the effect of pH on Na(+) self-inhibition. Together, the data identify eight extracellular domain residues in human β- and γENaC that are required for regulation by acidic pH.
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Affiliation(s)
- Daniel M Collier
- Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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27
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Mamenko M, Zaika O, Doris PA, Pochynyuk O. Salt-dependent inhibition of epithelial Na+ channel-mediated sodium reabsorption in the aldosterone-sensitive distal nephron by bradykinin. Hypertension 2012; 60:1234-41. [PMID: 23033373 DOI: 10.1161/hypertensionaha.112.200469] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We have documented recently that bradykinin (BK) directly inhibits activity of the epithelial Na(+) channel (ENaC) via the bradykinin B2 receptor (B2R)-G(q/11)-phospholipase C pathway. In this study, we took advantage of mice genetically engineered to lack bradykinin receptors (B1R, B2R(-/-)) to probe a physiological role of BK cascade in regulation of ENaC in native tissue, aldosterone-sensitive distal nephron. Under normal sodium intake (0.32% Na(+)), ENaC open probability (P(o)) was modestly elevated in B1R, B2R(-/-) mice compared with wild-type mice. This difference is augmented during elevated Na(+) intake (2.00% Na(+)) and negated during Na(+) restriction (<0.01% Na(+)). Saturation of systemic mineralocorticoid status with deoxycorticosterone acetate similarly increased ENaC activity in both mouse strains, suggesting that the effect of BK on ENaC is independent of aldosterone. It is accepted that angiotensin-converting enzyme represents the major pathway of BK degradation. Systemic inhibition of angiotensin-converting enzyme with captopril (30 mg/kg of body weight for 7 days) significantly decreases ENaC activity and P(o) in wild-type mice, but this effect is diminished in B1R, B2R(-/-) mice. At the cellular level, acute captopril (100 μmol/L) treatment sensitized BK signaling cascade and greatly potentiated the inhibitory effect of 100 nmol/L of BK on ENaC. We concluded that BK cascade has its own specific role in blunting ENaC activity, particularly under conditions of elevated sodium intake. Augmentation of BK signaling in the aldosterone-sensitive distal nephron inhibits ENaC-mediated Na(+) reabsorption, contributing to the natriuretic and antihypertensive effects of angiotensin-converting enzyme inhibition.
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Affiliation(s)
- Mykola Mamenko
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, 6431 Fannin, Houston, TX 77030, USA
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28
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Snyder PM. Intoxicated Na(+) channels. Focus on "ethanol stimulates epithelial sodium channels by elevating reactive oxygen species". Am J Physiol Cell Physiol 2012; 303:C1125-6. [PMID: 22992679 DOI: 10.1152/ajpcell.00301.2012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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29
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Sharotri V, Collier DM, Olson DR, Zhou R, Snyder PM. Regulation of epithelial sodium channel trafficking by proprotein convertase subtilisin/kexin type 9 (PCSK9). J Biol Chem 2012; 287:19266-74. [PMID: 22493497 DOI: 10.1074/jbc.m112.363382] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The epithelial Na(+) channel (ENaC) is critical for Na(+) homeostasis and blood pressure control. Defects in its regulation cause inherited forms of hypertension and hypotension. Previous work found that ENaC gating is regulated by proteases through cleavage of the extracellular domains of the α and γ subunits. Here we tested the hypothesis that ENaC is regulated by proprotein convertase subtilisin/kexin type 9 (PCSK9), a protease that modulates the risk of cardiovascular disease. PCSK9 reduced ENaC current in Xenopus oocytes and in epithelia. This occurred through a decrease in ENaC protein at the cell surface and in the total cellular pool, an effect that did not require the catalytic activity of PCSK9. PCSK9 interacted with all three ENaC subunits and decreased their trafficking to the cell surface by increasing proteasomal degradation. In contrast to its previously reported effects on the LDL receptor, PCSK9 did not alter ENaC endocytosis or degradation of the pool of ENaC at the cell surface. These results support a role for PCSK9 in the regulation of ENaC trafficking in the biosynthetic pathway, likely by increasing endoplasmic reticulum-associated degradation. By reducing ENaC channel number, PCSK9 could modulate epithelial Na(+) absorption, a major contributor to blood pressure control.
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Affiliation(s)
- Vikas Sharotri
- Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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30
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Abstract
The central goal of this overview article is to summarize recent findings in renal epithelial transport,focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD).Mammalian CCD and CNT are involved in fine-tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, for example, aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades.Recent studies shed new light on several key questions concerning the regulation of renal transport.Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will also be covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD.
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Affiliation(s)
- Alexander Staruschenko
- Department of Physiology and Kidney Disease Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
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31
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Olteanu D, Liu X, Liu W, Roper VC, Sharma N, Yoder BK, Satlin LM, Schwiebert EM, Bevensee MO. Increased Na+/H+ exchanger activity on the apical surface of a cilium-deficient cortical collecting duct principal cell model of polycystic kidney disease. Am J Physiol Cell Physiol 2012; 302:C1436-51. [PMID: 22301060 DOI: 10.1152/ajpcell.00063.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pathophysiological anomalies in autosomal dominant and recessive forms of polycystic kidney disease (PKD) may derive from impaired function/formation of the apical central monocilium of ductal epithelia such as that seen in the Oak Ridge polycystic kidney or orpk (Ift88(Tg737Rpw)) mouse and its immortalized cell models for the renal collecting duct. According to a previous study, Na/H exchanger (NHE) activity may contribute to hyperabsorptive Na(+) movement in cilium-deficient ("mutant") cortical collecting duct principal cell monolayers derived from the orpk mice compared with cilium-competent ("rescued") monolayers. To examine NHE activity, we measured intracellular pH (pH(i)) by fluorescence imaging with the pH-sensitive dye BCECF, and used a custom-designed perfusion chamber to control the apical and basolateral solutions independently. Both mutant and rescued monolayers exhibited basolateral Na(+)-dependent acid-base transporter activity in the nominal absence of CO(2)/HCO(3)(-). However, only the mutant cells displayed appreciable apical Na(+)-induced pH(i) recoveries from NH(4)(+) prepulse-induced acid loads. Similar results were obtained with isolated, perfused collecting ducts from orpk vs. wild-type mice. The pH(i) dependence of basolateral cariporide/HOE-694-sensitive NHE activity under our experimental conditions was similar in both mutant and rescued cells, and 3.5- to 4.5-fold greater than apical HOE-sensitive NHE activity in the mutant cells (pH(i) 6.23-6.68). Increased apical NHE activity correlated with increased apical NHE1 expression in the mutant cells, and increased apical localization in collecting ducts of kidney sections from orpk vs. control mice. A kidney-specific conditional cilium-knockout mouse produced a more acidic urine compared with wild-type littermates and became alkalotic by 28 days of age. This study provides the first description of altered NHE activity, and an associated acid-base anomaly in any form of PKD.
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Affiliation(s)
- Dragos Olteanu
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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32
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Campbell CR, Voyles J, Cook DI, Dinudom A. Frog skin epithelium: electrolyte transport and chytridiomycosis. Int J Biochem Cell Biol 2011; 44:431-4. [PMID: 22182598 DOI: 10.1016/j.biocel.2011.12.002] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 11/23/2011] [Accepted: 12/02/2011] [Indexed: 11/16/2022]
Abstract
One unique physiological characteristic of frogs is that their main route for intake of water is across the skin. In these animals, the skin acts in concert with the kidney and urinary bladder to maintain electrolyte homeostasis. Water absorption across the skin is driven by the osmotic gradient that develops as a consequence of solute transport. Our recent study demonstrated that chytridiomycosis, an infection of amphibian skin by the fungal pathogen, Batrachochytrium dendrobatidis, inhibits epithelial Na(+) channels, attenuating Na(+) absorption through the skin. In frogs that become severely affected by this fungus, systemic depletion of Na(+), K(+) and Cl(-) is thought to cause deterioration of cardiac electrical function, leading to cardiac arrest. Here we review the ion transport mechanisms of frog skin, and discuss the effect of chytridiomycosis on these mechanisms.
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Affiliation(s)
- Craig R Campbell
- Discipline of Physiology, Sydney Medical School and Bosch Institute, The University of Sydney, New South Wales 2006, Australia
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33
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Mamenko M, Zaika O, Ilatovskaya DV, Staruschenko A, Pochynyuk O. Angiotensin II increases activity of the epithelial Na+ channel (ENaC) in distal nephron additively to aldosterone. J Biol Chem 2011; 287:660-671. [PMID: 22086923 DOI: 10.1074/jbc.m111.298919] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Dietary salt intake controls epithelial Na+ channel (ENaC)-mediated Na+ reabsorption in the distal nephron by affecting status of the renin-angiotensin-aldosterone system (RAAS). Whereas regulation of ENaC by aldosterone is generally accepted, little is known about whether other components of RAAS, such as angiotensin II (Ang II), have nonredundant to aldosterone-stimulatory actions on ENaC. We combined patch clamp electrophysiology and immunohistochemistry in freshly isolated split-opened distal nephrons of mice to determine the mechanism and molecular signaling pathway of Ang II regulation of ENaC. We found that Ang II acutely increases ENaC Po, whereas prolonged exposure to Ang II also induces translocation of α-ENaC toward the apical membrane in situ. Ang II actions on ENaC Po persist in the presence of saturated mineralocorticoid status. Moreover, aldosterone fails to stimulate ENaC acutely, suggesting that Ang II and aldosterone have different time frames of ENaC activation. AT1 but not AT2 receptors mediate Ang II actions on ENaC. Unlike its effect in vasculature, Ang II did not increase [Ca2+]i in split-opened distal nephrons as demonstrated using ratiometric Fura-2-based microscopy. However, application of Ang II to mpkCCDc14 cells resulted in generation of reactive oxygen species, as probed with fluorescent methods. Consistently, inhibiting NADPH oxidase with apocynin abolished Ang II-mediated increases in ENaC Po in murine distal nephron. Therefore, we concluded that Ang II directly regulates ENaC activity in the distal nephron, and this effect complements regulation of ENaC by aldosterone. We propose that stimulation of AT1 receptors with subsequent activation of NADPH oxidase signaling pathway mediates Ang II actions on ENaC.
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Affiliation(s)
- Mykola Mamenko
- Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center, Houston, Texas 77030
| | - Oleg Zaika
- Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center, Houston, Texas 77030
| | - Daria V Ilatovskaya
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226; Institute of Cytology, Russian Academy of Sciences, 194064 St. Petersburg, Russia
| | | | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center, Houston, Texas 77030.
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Purinergic activation of Ca2+-permeable TRPV4 channels is essential for mechano-sensitivity in the aldosterone-sensitive distal nephron. PLoS One 2011; 6:e22824. [PMID: 21850238 PMCID: PMC3151261 DOI: 10.1371/journal.pone.0022824] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Accepted: 07/03/2011] [Indexed: 11/19/2022] Open
Abstract
Mechanical forces are known to induce increases of [Ca2+]i in the aldosterone-sensitive distal nephron (ASDN) cells to regulate epithelial transport. At the same time, mechanical stress stimulates ATP release from ASDN cells. In this study, we combined ratiometric Fura-2 based monitoring of [Ca2+]i in freshly isolated split-opened ASDN with targeted deletion of P2Y2 and TRPV4 in mice to probe a role for purinergic signaling in mediating mechano-sensitive responses in ASDN cells. ATP application causes a reproducible transient Ca2+ peak followed by a sustained plateau. Individual cells of the cortical collecting duct (CCD) and the connecting tubule (CNT) respond to purinergic stimulation with comparative elevations of [Ca2+]i. Furthermore, ATP-induced Ca2+-responses are nearly identical in both principal (AQP2-positive) and intercalated (AQP2-negative) cells as was confirmed using immunohistochemistry in split-opened ASDN. UTP application produces elevations of [Ca2+]i similar to that observed with ATP suggesting a dominant role of P2Y2-like receptors in generation of [Ca2+]i response. Indeed, genetic deletion of P2Y2 receptors decreases the magnitude of ATP-induced and UTP-induced Ca2+ responses by more than 70% and 90%, respectively. Both intracellular and extracellular sources of Ca2+ appeared to contribute to the generation of ATP-induced Ca2+ response in ASDN cells. Importantly, flow- and hypotonic-induced Ca2+ elevations are markedly blunted in P2Y2 −/− mice. We further demonstrated that activation of mechano-sensitive TRPV4 channel plays a major role in the sustained [Ca2+]i elevation during purinergic stimulation. Consistent with this, ATP-induced Ca2+ plateau are dramatically attenuated in TRV4 −/− mice. Inhibition of TRPC channels with 10 µM BTP2 also decreased ATP-induced Ca2+ plateau whilst to a lower degree than that observed with TRPV4 inhibition/genetic deletion. We conclude that stimulation of purinergic signaling by mechanical stimuli leads to activation of TRPV4 and, to a lesser extent, TRPCs channels, and this is an important component of mechano-sensitive response of the ASDN.
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Ilatovskaya DV, Pavlov TS, Levchenko V, Negulyaev YA, Staruschenko A. Cortical actin binding protein cortactin mediates ENaC activity via Arp2/3 complex. FASEB J 2011; 25:2688-99. [PMID: 21536685 DOI: 10.1096/fj.10-167262] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Epithelial Na(+) channel (ENaC) activity is regulated, in part, by the cortical cytoskeleton. Here we demonstrate that cortactin is highly expressed in the kidney cortex and polarized epithelial cells, and is localized to the cortical collecting duct. Coexpression of cortactin with ENaC decreases ENaC activity, as measured in patch-clamp experiments. Biotinylation experiments and single-channel analysis reveal that cortactin decreases ENaC activity via affecting channel open probability (P(o)). Knockdown of cortactin in mpkCCD(c14) principal cells results in an increase in ENaC activity and sodium reabsorption. Coimmunoprecipitation analysis shows direct interactions between cortactin and all three ENaC subunits in cultured and native cells. To address the question of what mechanism underlies the action of cortactin on ENaC activity, we assayed the effects of various mutants of cortactin. The data show that only a cortactin mutant unable to bind Arp2/3 complex does not influence ENaC activity. Furthermore, inhibitor of the Arp2/3 complex CK-0944666 precludes the effect of cortactin. Depolymerization of the actin microfilaments and inhibition of the Arp2/3 complex does not result in the loss of association between ENaC and cortactin. Thus, these results indicate that cortactin is functionally important for ENaC activity and that Arp2/3 complex is involved in this mechanism.
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Affiliation(s)
- Daria V Ilatovskaya
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA
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Zaika O, Mamenko M, O'Neil RG, Pochynyuk O. Bradykinin acutely inhibits activity of the epithelial Na+ channel in mammalian aldosterone-sensitive distal nephron. Am J Physiol Renal Physiol 2011; 300:F1105-15. [PMID: 21325499 DOI: 10.1152/ajprenal.00606.2010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Activation of the renal kallikrein-kinin system results in natriuresis and diuresis, suggesting its possible role in renal tubular sodium transport regulation. Here, we used patch-clamp electrophysiology to directly assess the effects of bradykinin (BK) on the epithelial Na(+) channel (ENaC) activity in freshly isolated split-opened murine aldosterone-sensitive distal nephrons (ASDNs). BK acutely inhibits ENaC activity by reducing channel open probability (P(o)) in a dose-dependent and reversible manner. Inhibition of B2 receptors with icatibant (HOE-140) abolished BK actions on ENaC. In contrast, activation of B1 receptors with the selective agonist Lys-des-Arg(9)-BK failed to reproduce BK actions on ENaC. This is consistent with B2 receptors playing a critical role in mediating BK signaling to ENaC. BK has little effect on ENaC P(o) when G(q/11) was inhibited with Gp antagonist 2A. Moreover, inhibition of phospholipase C (PLC) with U73122, but not saturation of cellular cAMP levels with the membrane-permeable nonhydrolysable cAMP analog 8-cpt-cAMP, prevents BK actions on ENaC activity. This argues that BK stimulates B2 receptors with subsequent activation of G(q/11)-PLC signaling cascade to acutely inhibit ENaC activity. Activation of BK signaling acutely depletes apical PI(4,5)P(2) levels. However, inhibition of Ca(2+) pump SERCA of the endoplasmic reticulum with thapsigargin does not prevent BK signaling to ENaC. Furthermore, caffeine, while producing a similar rise in [Ca(2+)](i) as in response to BK stimulation, fails to recapitulate BK actions on ENaC. Therefore, we concluded that BK acutely inhibits ENaC P(o) in mammalian ASDN via stimulation of B2 receptors and following depletion of PI(4,5)P(2), but not increases in [Ca(2+)](i).
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Affiliation(s)
- Oleg Zaika
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, 77030, USA
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Edelheit O, Hanukoglu I, Dascal N, Hanukoglu A. Identification of the roles of conserved charged residues in the extracellular domain of an epithelial sodium channel (ENaC) subunit by alanine mutagenesis. Am J Physiol Renal Physiol 2011; 300:F887-97. [PMID: 21209000 DOI: 10.1152/ajprenal.00648.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial sodium channels (ENaC) are composed of three homologous subunits whose extracellular domains (ECD) form a funnel that directs ions from the lumen into the pore of ENaC. To examine the roles of conserved charged residues (Asp, Glu, Arg, and Lys) on ECD, we mutated 16 residues in human α-ENaC to alanine. The modified cRNAs were expressed in Xenopus laevis oocytes together with wild-type β- and γ-ENaC. The effect of each mutation was examined on three parameters: amiloride-sensitive Na(+) conductance (assayed by the two-electrode voltage-clamp method), Na(+)-dependent self-inhibition of ENaC, and oocyte cell surface expression of ENaC (quantitated by confocal microscopy of yellow fluorescent protein linked to γ-ENaC). Mutation of 13 of 16 residues reduced the ENaC Na(+) conductance (to 40-80% of WT). Mutation of only six residues showed a significant effect on the Na(+) self-inhibition time constant (τ). All 16 mutants showed a strong correlation between ENaC activity and oocyte surface expression (r = 0.62). Exclusion of four mutants showing the greatest effect on self-inhibition kinetics (Glu250 and Arg350 with τ = ~30% of WT, and Asp393 and Glu530 with τ = ~170% of WT) increased the correlation to r = 0.87. In the ASIC1 homotrimeric model, the homologs of α-ENaC Asp400 and Asp446 are exposed on the protein surface far from the other two chains. The mutations of these two residues showed the strongest effect on cell surface expression but had no effect on self-inhibition. Control mutations to a homologous charged residue (e.g., Asp to Glu) did not significantly affect ENaC activity. Changes in the two parameters, Na(+) self-inhibition and oocyte surface expression level, accounted for the magnitude of reduction in ENaC activity as a result of the mutation to Ala. These results establish that while some conserved charged residues are part of the structure responsible for Na(+) self-inhibition, most are essential for transport to the oocyte cell surface.
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Affiliation(s)
- Oded Edelheit
- Dept. of Molecular Biology, Ariel Univ. Center, Ariel 40700, Israel
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Garcia-Caballero A, Ishmael SS, Dang Y, Gillie D, Bond JS, Milgram SL, Stutts MJ. Activation of the epithelial sodium channel by the metalloprotease meprin β subunit. Channels (Austin) 2011; 5:14-22. [PMID: 20953144 DOI: 10.4161/chan.5.1.13759] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The Epithelial Na(+) Channel (ENaC) is an apical heteromeric channel that mediates Na(+) entry into epithelial cells from the luminal cell surface. ENaC is activated by proteases that interact with the channel during biosynthesis or at the extracellular surface. Meprins are cell surface and secreted metalloproteinases of the kidney and intestine. We discovered by affinity chromatography that meprins bind γ-ENaC, a subunit of the ENaC hetero-oligomer. The physical interaction involves NH(2)-terminal cytoplasmic residues 37-54 of γ-ENaC, containing a critical gating domain immediately before the first transmembrane domain, and the cytoplasmic COOH-terminal tail of meprin β (residues 679-704). This potential association was confirmed by co-expression and co-immunoprecipitation studies. Functional assays revealed that meprins stimulate ENaC expressed exogenously in Xenopus oocytes and endogenously in epithelial cells. Co-expression of ENaC subunits and meprin β or α/β in Xenopus oocytes increased amiloride-sensitive Na(+) currents approximately two-fold. This increase was blocked by preincubation with an inhibitor of meprin activity, actinonin. The meprin-mediated increase in ENaC currents in oocytes and epithelial cell monolayers required meprin β, but not the α subunit. Meprin β promoted cleavage of α and γ-ENaC subunits at sites close to the second transmembrane domain in the extracellular domain of each channel subunit. Thus, meprin β regulates the activity of ENaC in a metalloprotease-dependent fashion.
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Affiliation(s)
- Agustin Garcia-Caballero
- Cystic Fibrosis/Pulmonary Research and Treatment Center, Pennsylvania State University College of Medicine, Hershey, USA.
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Collier DM, Snyder PM. Identification of epithelial Na+ channel (ENaC) intersubunit Cl- inhibitory residues suggests a trimeric alpha gamma beta channel architecture. J Biol Chem 2010; 286:6027-32. [PMID: 21149458 DOI: 10.1074/jbc.m110.198127] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The extracellular domain of the epithelial Na(+) channel (ENaC) is exposed to a wide range of anion concentrations in the kidney. We have previously demonstrated that extracellular Cl(-) inhibits ENaC activity. To identify sites involved in Cl(-) inhibition, we mutated residues in the extracellular domain of α-, β-, and γENaC that are homologous to the Cl(-) binding site in acid-sensing ion channel 1a and tested the effect of Cl(-) on the activity of ENaC expressed in Xenopus oocytes. We identified two Cl(-) inhibitory sites in ENaC. One is formed by residues in the thumb domain of αENaC and the palm domain of βENaC. Mutation of residues at this interface decreased Cl(-) inhibition and decreased Na(+) self-inhibition. The second site is formed by residues at the interface of the thumb domain of βENaC and the palm domain of γENaC. Mutation of these residues also decreased Cl(-) inhibition yet had no effect on Na(+) self-inhibition. In contrast, mutations in the thumb domain of γENaC and palm of αENaC had little or no effect on Cl(-) inhibition or Na(+) self-inhibition. The data demonstrate that Cl(-) inhibits ENaC activity by two distinct Na(+)-dependent and Na(+)-independent mechanisms that correspond to the two functional Cl(-) inhibitory sites. Furthermore, based on the effects of mutagenesis on Cl(-) inhibition, the additive nature of mutations, and on differences in the mechanisms of Cl(-) inhibition, the data support a model in which ENaC subunits assemble in an αγβ orientation (listed clockwise when viewed from the top).
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Affiliation(s)
- Daniel M Collier
- Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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Epidermal growth factor-mediated proliferation and sodium transport in normal and PKD epithelial cells. Biochim Biophys Acta Mol Basis Dis 2010; 1812:1301-13. [PMID: 20959142 DOI: 10.1016/j.bbadis.2010.10.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 09/30/2010] [Accepted: 10/11/2010] [Indexed: 02/07/2023]
Abstract
Members of the epidermal growth factor (EGF) family bind to ErbB (EGFR) family receptors which play an important role in the regulation of various fundamental cell processes including cell proliferation and differentiation. The normal rodent kidney has been shown to express at least three members of the ErbB receptor family and is a major site of EGF ligand synthesis. Polycystic kidney disease (PKD) is a group of diseases caused by mutations in single genes and is characterized by enlarged kidneys due to the formation of multiple cysts in both kidneys. Tubule cells proliferate, causing segmental dilation, in association with the abnormal deposition of several proteins. One of the first abnormalities described in cell biological studies of PKD pathogenesis was the abnormal mislocalization of the EGFR in cyst lining epithelial cells. The kidney collecting duct (CD) is predominantly an absorptive epithelium where electrogenic Na(+) entry is mediated by the epithelial Na(+) channel (ENaC). ENaC-mediated sodium absorption represents an important ion transport pathway in the CD that might be involved in the development of PKD. A role for EGF in the regulation of ENaC-mediated sodium absorption has been proposed. However, several investigations have reported contradictory results indicating opposite effects of EGF and its related factors on ENaC activity and sodium transport. Recent advances in understanding how proteins in the EGF family regulate the proliferation and sodium transport in normal and PKD epithelial cells are discussed here. This article is part of a Special Issue entitled: Polycystic Kidney Disease.
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Zhou R, Kabra R, Olson DR, Piper RC, Snyder PM. Hrs controls sorting of the epithelial Na+ channel between endosomal degradation and recycling pathways. J Biol Chem 2010; 285:30523-30. [PMID: 20675381 DOI: 10.1074/jbc.m110.150755] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Epithelial Na(+) absorption is regulated by Nedd4-2, an E3 ubiquitin ligase that reduces expression of the epithelial Na(+) channel (ENaC) at the cell surface. Defects in this regulation cause Liddle syndrome, an inherited form of hypertension. Previous work found that Nedd4-2 functions through two distinct effects on trafficking, enhancing both ENaC endocytosis and ENaC degradation in lysosomes. To investigate the mechanism by which Nedd4-2 targets ENaC to lysosomes, we tested the role of hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), a component of the endosomal sorting complexes required for transport (ESCRT)-0 complex. We found that α-, β-, and γENaC each interact with Hrs. These interactions were enhanced by Nedd4-2 and were dependent on the catalytic function of Nedd4-2 as well as its WW domains. Mutation of ENaC PY motifs, responsible for inherited hypertension (Liddle syndrome), decreased Hrs binding to ENaC. Moreover, binding of ENaC to Hrs was reduced by dexamethasone/serum- and glucocorticoid-inducible kinase and cAMP, which are signaling pathways that inhibit Nedd4-2. Nedd4-2 bound to Hrs and catalyzed Hrs ubiquitination but did not alter Hrs protein levels. Expression of a dominant negative Hrs lacking its ubiquitin-interacting motif (Hrs-ΔUIM) increased ENaC surface expression and current. This occurred through reduced degradation of the cell surface pool of proteolytically activated ENaC, which enhanced its recycling to the cell surface. In contrast, Hrs-ΔUIM had no effect on degradation of uncleaved inactive channels. The data support a model in which Nedd4-2 induces binding of ENaC to Hrs, which mediates the sorting decision between ENaC degradation and recycling.
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Affiliation(s)
- Ruifeng Zhou
- Department of Internal Medicine, Roy J and Lucille A Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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Karpushev AV, Ilatovskaya DV, Staruschenko A. The actin cytoskeleton and small G protein RhoA are not involved in flow-dependent activation of ENaC. BMC Res Notes 2010; 3:210. [PMID: 20663206 PMCID: PMC2918634 DOI: 10.1186/1756-0500-3-210] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Accepted: 07/27/2010] [Indexed: 11/13/2022] Open
Abstract
Background Epithelial cells are exposed to a variety of mechanical stimuli. Epithelial Na+ channels (ENaC) mediate sodium transport across apical membranes of epithelial cells that line the distal nephron, airway and alveoli, and distal colon. Early investigations into stretch sensitivity of ENaC were controversial. However, recent studies are supportive of ENaC's mechanosensitivity. This work studied whether flow-dependent activation of ENaC is modulated by changes in the state of the actin cytoskeleton and whether small GTPase RhoA is involved in flow-mediated increase of ENaC activity. Findings Pretreatment with Cytochalasin D and Latrunculin B for 20 min and 1-2 hrs to disassemble F-actin had no effect on flow-mediated increase of amiloride-sensitive current. Overexpression of ENaC with constitutively active (G14V) or dominant negative (T19N) RhoA similarly had no effect on flow-dependent activation of ENaC activity. In addition, we did not observe changes when we inhibited Rho-kinase with Y27632. Conclusions Our results suggest that the flow-dependent activation of ENaC is not influenced by small GTPase RhoA and modifications in the actin cytoskeleton.
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Affiliation(s)
- Alexey V Karpushev
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd,, Milwaukee, WI 53226, USA.
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Regulation of ENaC-Mediated Sodium Reabsorption by Peroxisome Proliferator-Activated Receptors. PPAR Res 2010; 2010:703735. [PMID: 20613963 PMCID: PMC2896859 DOI: 10.1155/2010/703735] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/16/2010] [Accepted: 04/14/2010] [Indexed: 12/14/2022] Open
Abstract
Peroxisome proliferator-activated receptors (PPARs) are members of a steroid hormone receptor superfamily that responds to changes in lipid and glucose homeostasis. Peroxisomal proliferator-activated receptor subtype γ (PPARγ) has received much attention as the target for antidiabetic drugs, as well as its role in responding to endogenous compounds such as prostaglandin J2. However, thiazolidinediones (TZDs), the synthetic agonists of the PPARγ are tightly associated with fluid retention and edema, as potentially serious side effects. The epithelial sodium channel (ENaC) represents the rate limiting step for sodium absorption in the renal collecting duct. Consequently, ENaC is a central effector impacting systemic blood volume and pressure. The role of PPARγ agonists on ENaC activity remains controversial. While PPARγ agonists were shown to stimulate ENaC-mediated renal salt absorption, probably via Serum- and Glucocorticoid-Regulated Kinase 1 (SGK1), other studies reported that PPARγ agonist-induced fluid retention is independent of ENaC activity. The current paper provides new insights into the control and function of ENaC and ENaC-mediated sodium transport as well as several other epithelial channels/transporters by PPARs and particularly PPARγ. The potential contribution of arachidonic acid (AA) metabolites in PPAR-dependent mechanisms is also discussed.
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Pavlov TS, Chahdi A, Ilatovskaya DV, Levchenko V, Vandewalle A, Pochynyuk O, Sorokin A, Staruschenko A. Endothelin-1 inhibits the epithelial Na+ channel through betaPix/14-3-3/Nedd4-2. J Am Soc Nephrol 2010; 21:833-43. [PMID: 20338996 DOI: 10.1681/asn.2009080885] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Epithelial Na+ channels (ENaCs) mediate sodium reabsorption in the cortical collecting duct (CCD), but the regulatory pathways that modulate the activity of these channels are incompletely understood. Here, we observed that endothelin-1 (ET-1) attenuates ENaC activity acutely by reducing the channel's open probability and chronically by decreasing the number of channels in the plasma membrane. To investigate whether beta1Pix, a signaling protein activated by ET-1, mediates ENaC activity, we reconstituted ENaC in CHO cells with or without coexpressed beta1Pix and found that beta1Pix negatively regulates ENaC. Knockdown of betaPix in native principal cells abolished the ET-1-induced decrease in ENaC channel number. Furthermore, we found that betaPix does not decrease ENaC activity through its guanine nucleotide exchange factor (GEF) activity for Rac1 and Cdc42. Instead, coexpression of beta1Pix mutant constructs revealed that beta1Pix affects ENaC activity through binding 14-3-3 proteins. Coimmunoprecipitation experiments supported a physical interaction between beta1Pix and 14-3-3beta in cultured principal cells. Coexpression of 14-3-3beta increased ENaC activity in CHO cells, but concomitant expression of beta1Pix attenuated this increase. Recruitment of 14-3-3beta by beta1Pix impaired the interaction of 14-3-3beta with the ubiquitin ligase Nedd4-2, thereby promoting ubiquitination and degradation of ENaC. Taken together, these results suggest that the inhibitory effects of chronic ET-1 on ENaC result from betaPix interacting with the 14-3-3/Nedd4-2 pathway.
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Affiliation(s)
- Tengis S Pavlov
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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Edelheit O, Hanukoglu I, Shriki Y, Tfilin M, Dascal N, Gillis D, Hanukoglu A. Truncated beta epithelial sodium channel (ENaC) subunits responsible for multi-system pseudohypoaldosteronism support partial activity of ENaC. J Steroid Biochem Mol Biol 2010; 119:84-8. [PMID: 20064610 DOI: 10.1016/j.jsbmb.2010.01.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2009] [Revised: 12/31/2009] [Accepted: 01/04/2010] [Indexed: 10/20/2022]
Abstract
Aldosterone regulated epithelial sodium channels (ENaC) are constructed of three homologous subunits. Mutations in the alpha-, beta- and gamma-ENaC subunit genes (SCNN1A, SCNN1B and SCNN1G) are associated with multi-system pseudohypoaldosteronism (PHA), and mutations in the PY motif of carboxy-terminal region of beta and gamma subunits are associated with Liddle syndrome of hereditary hypertension. In this study we identified two frameshift mutations in the SCNN1B alleles of a female infant diagnosed with multi-system PHA inherited from her parents. This is the first case of PHA in an Ashkenazi family in Israel. The p.Glu217fs (c.648dupA in exon 4) and p.Tyr306fs (c.915delC in exon 6) mutations produce shortened beta-ENaC subunits with 253 and 317 residues respectively instead of the 640 residues present in beta-ENaC subunit. Expression of cRNAs carrying these mutations in Xenopus oocytes showed that the mutations drastically reduce but do not eliminate ENaC activity. The findings reveal that truncated beta-ENaC subunits are capable of partially supporting intracellular transport of the other two subunits to the membrane and the final assembly of a weakly active channel together with normal alpha- and gamma-ENaC subunits. Moreover, these results enhance our understanding of the long-term consequences of these types of mutations in PHA patients.
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Affiliation(s)
- Oded Edelheit
- Department of Molecular Biology, Ariel University Center, Ariel, Israel
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Ben-Shahar Y, Lu B, Collier DM, Snyder PM, Schnizler M, Welsh MJ. The Drosophila gene CheB42a is a novel modifier of Deg/ENaC channel function. PLoS One 2010; 5:e9395. [PMID: 20195381 PMCID: PMC2827562 DOI: 10.1371/journal.pone.0009395] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Accepted: 02/04/2010] [Indexed: 11/18/2022] Open
Abstract
Degenerin/epithelial Na+ channels (DEG/ENaC) represent a diverse family of voltage-insensitive cation channels whose functions include Na+ transport across epithelia, mechanosensation, nociception, salt sensing, modification of neurotransmission, and detecting the neurotransmitter FMRFamide. We previously showed that the Drosophila melanogaster Deg/ENaC gene lounge lizard (llz) is co-transcribed in an operon-like locus with another gene of unknown function, CheB42a. Because operons often encode proteins in the same biochemical or physiological pathway, we hypothesized that CHEB42A and LLZ might function together. Consistent with this hypothesis, we found both genes expressed in cells previously implicated in sensory functions during male courtship. Furthermore, when coexpressed, LLZ coprecipitated with CHEB42A, suggesting that the two proteins form a complex. Although LLZ expressed either alone or with CHEB42A did not generate ion channel currents, CHEB42A increased current amplitude of another DEG/ENaC protein whose ligand (protons) is known, acid-sensing ion channel 1a (ASIC1a). We also found that CHEB42A was cleaved to generate a secreted protein, suggesting that CHEB42A may play an important role in the extracellular space. These data suggest that CHEB42A is a modulatory subunit for sensory-related Deg/ENaC signaling. These results are consistent with operon-like transcription of CheB42a and llz and explain the similar contributions of these genes to courtship behavior.
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Affiliation(s)
- Yehuda Ben-Shahar
- Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Beika Lu
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Daniel M. Collier
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Department of Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Peter M. Snyder
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Department of Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Mikael Schnizler
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Michael J. Welsh
- Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Department of Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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Intact cytoskeleton is required for small G protein dependent activation of the epithelial Na+ channel. PLoS One 2010; 5:e8827. [PMID: 20098689 PMCID: PMC2809106 DOI: 10.1371/journal.pone.0008827] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Accepted: 01/04/2010] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND The Epithelial Na(+) Channel (ENaC) plays a central role in control of epithelial surface hydration and vascular volume. Similar to other ion channels, ENaC activity is regulated, in part, by cortical cytoskeleton. Besides, the cytoskeleton is an established target for small G proteins signaling. Here we studied whether ENaC activity is modulated by changes in the state of the cytoskeleton and whether cytoskeletal elements are involved in small G protein mediated increase of ENaC activity. METHODS AND FINDINGS First, the functional importance of the cytoskeleton was established with whole-cell patch clamp experiments recording ENaC reconstituted in CHO cells. Pretreatment with Cytochalasin D (CytD; 10 microg/ml; 1-2 h) or colchicine (500 microM; 1-3 h) to disassembly F-actin and destroy microtubules, respectively, significantly decreased amiloride sensitive current. However, acute application of CytD induced rapid increase in macroscopic current. Single channel measurements under cell-attached conditions revealed similar observations. CytD rapidly increased ENaC activity in freshly isolated rat collecting duct, polarized epithelial mouse mpkCCD(c14) cells and HEK293 cells transiently transfected with ENaC subunits. In contrast, colchicine did not have an acute effect on ENaC activity. Small G proteins RhoA, Rac1 and Rab11a markedly increase ENaC activity. 1-2 h treatment with colchicine or CytD abolished effects of these GTPases. Interestingly, when cells were coexpressed with ENaC and RhoA, short-term treatment with CytD decreased ENaC activity. CONCLUSIONS We conclude that cytoskeleton is involved in regulation of ENaC and is necessary for small G protein mediated increase of ENaC activity.
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Sobczak K, Segal A, Bangel-Ruland N, Semmler J, Van Driessche W, Lindemann H, Heermann R, Weber WM. Specific inhibition of epithelial Na+ channels by antisense oligonucleotides for the treatment of Na+ hyperabsorption in cystic fibrosis. J Gene Med 2009; 11:813-23. [PMID: 19533590 DOI: 10.1002/jgm.1363] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Cystic fibrosis (CF) respiratory epithelia are characterized by a defect Cl(-) secretion and an increased Na(+) absorption through epithelial Na(+) channels (ENaC). The present study aimed to find an effective inhibitor of human ENaC with respect to replacing amiloride therapy for CF patients. Therefore, we developed specific antisense oligonucleotides (AON) that efficiently suppress Na(+) hyperabsorption by inhibiting the expression of the alpha-ENaC subunit. METHODS We heterologously expressed ENaC in oocytes of Xenopus laevis for mass screening of AON. Additionally, primary cultures of human nasal epithelia were transfected with AON and were used for Ussing chamber experiments, as well as biochemical and fluorescence optical analyses. RESULTS Screening of several AON by co-injection or sequential microinjection of AON and ENaC mRNA in X. laevis oocytes led to a sustained decrease in amiloride-sensitive current and conductance. Using primary cultures of human nasal epithelia, we show that AON effectively suppress amiloride-sensitive Na(+) absorption mediated by ENaC in CF and non-CF tissues. In western blot experiments, it could be shown that the amount of ENaC protein is effectively reduced after AON transfection. CONCLUSIONS Our data comprise an initial step towards a preclinical test with AON to reduce Na(+) hyperabsorption in CF epithelia.
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Affiliation(s)
- Katja Sobczak
- Institute of Animal Physiology, Westphalian Wilhelms-University Muenster, Muenster, Germany
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