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Kovesdy CP, Adebiyi A, Rosenbaum D, Jacobs JW, Quarles LD. Novel Treatments from Inhibition of the Intestinal Sodium-Hydrogen Exchanger 3. Int J Nephrol Renovasc Dis 2021; 14:411-420. [PMID: 34880650 PMCID: PMC8646223 DOI: 10.2147/ijnrd.s334024] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Accepted: 11/11/2021] [Indexed: 12/31/2022] Open
Abstract
Plasma membrane sodium–hydrogen exchangers (NHE) transport Na+ into cells in exchange for H+. While there are nine isoforms of NHE in humans, this review focuses on the NHE3 isoform, which is abundantly expressed in the gastrointestinal tract, where it plays a key role in acid–base balance and water homeostasis. NHE3 inhibition in the small intestine results in luminal sodium and water retention, leading to a general decrease in paracellular water flux and diffusional driving force, reduced intestinal sodium absorption, and increased stool sodium excretion. The resulting softer and more frequent stools are the rationale for the development of tenapanor as a novel, first-in-class NHE3 inhibitor to treat irritable bowel syndrome with constipation. NHE3 also has additional therapeutic implications in nephrology. Inhibition of intestinal NHE3 also lowers blood pressure by reducing intestinal sodium absorption. Perhaps, the most novel effect is its ability to decrease intestinal phosphate absorption by inhibiting the paracellular phosphate absorption pathway. Therefore, selective pharmacological inhibition of NHE3 could be a potential therapeutic strategy to treat not only heart failure and hypertension but also hyperphosphatemia. This review presents an overview of the molecular and physiological functions of NHE3 and discusses how these functions translate to potential clinical applications in nephrology.
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Affiliation(s)
- Csaba P Kovesdy
- Division of Nephrology, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Adebowale Adebiyi
- Department of Physiology, University of Tennessee Health Science Center, Memphis, TN, USA
| | | | | | - L Darryl Quarles
- Division of Nephrology, University of Tennessee Health Science Center, Memphis, TN, USA
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2
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Yanda MK, Cha B, Cebotaru CV, Cebotaru L. Pharmacological reversal of renal cysts from secretion to absorption suggests a potential therapeutic strategy for managing autosomal dominant polycystic kidney disease. J Biol Chem 2019; 294:17090-17104. [PMID: 31570523 DOI: 10.1074/jbc.ra119.010320] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 09/26/2019] [Indexed: 12/19/2022] Open
Abstract
Autosomal-dominant polycystic kidney disease (ADPKD) induces a secretory phenotype, resulting in multiple fluid-filled cysts. We have previously demonstrated that VX-809, a corrector of the cystic fibrosis transmembrane conductance regulator (CFTR), reduces cyst growth. Here, we show that in normal mice CFTR is located within the cells and also at the apical and basolateral membranes. However, in polycystic kidney disease (pkd1)-knockout mice, CFTR was located at the plasma membrane, consistent with its role in cAMP-dependent fluid secretion. In cystic mice, VX-809 treatment increased CFTR levels at the apical membrane and reduced its association with the endoplasmic reticulum. Surprisingly, VX-809 treatment significantly increased CFTR's co-localization with the basolateral membrane in cystic mice. Na+/H+ exchanger 3 (NHE3) is present in pkd1-knockout and normal mice and in proximal tubule-derived, cultured pkd1-knockout cells. VX-809 increased the expression, activity, and apical plasma membrane localization of NHE3. Co-localization of epithelial sodium channel (ENaC) with the plasma membrane was reduced in cysts in pkd1-knockout mice, consistent with an inability of the cysts to absorb fluid. Interestingly, in the cystic mice, VX-809 treatment increased ENaC levels at the apical plasma membrane consistent with fluid absorption. Thus, VX-809 treatment of pkd1-null mouse kidneys significantly affected CFTR, NHE3, and ENaC, altering the cyst phenotype from one poised toward fluid secretion toward one more favorable for absorption. VX-809 also altered the location of CFTR but not of NHE3 or ENaC in normal mice. Given that VX-809 administration is safe, it may have potential utility for treating patients with ADPKD.
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Affiliation(s)
- Murali K Yanda
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Boyoung Cha
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Cristina V Cebotaru
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Liudmila Cebotaru
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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3
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Singh V, Yang J, Yin J, Cole R, Tse M, Berman DE, Small SA, Petsko G, Donowitz M. Cholera toxin inhibits SNX27-retromer-mediated delivery of cargo proteins to the plasma membrane. J Cell Sci 2018; 131:jcs.218610. [PMID: 30030371 DOI: 10.1242/jcs.218610] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Accepted: 06/22/2018] [Indexed: 12/14/2022] Open
Abstract
Cholera toxin (CT) causes severe diarrhea by increasing intracellular cAMP leading to a PKA-dependent increase in Cl- secretion through CFTR and decreased Na+ absorption through inhibition of Na+/H+ exchanger 3 (NHE3; also known as SLC9A3). The mechanism(s) by which CT inhibits NHE3 is partially understood, although no drug therapy has been successful at reversing this inhibition. We now describe that CT phosphorylates an amino acid in the PDZ domain of SNX27, which inhibits SNX27-mediated trafficking of NHE3 from the early endosomes to the plasma membrane (PM), and contributes to reduced basal NHE3 activity through a mechanism that involves reduced PM expression and reduced endocytic recycling. Importantly, mutagenesis studies (Ser to Asp) showed that the effect of this phosphorylation of SNX27 phenocopies the effects seen upon loss of SNX27 function, affecting PM trafficking of cargo proteins that bind SNX27-retromer. Additionally, CT destabilizes retromer function by decreasing the amount of core retromer proteins. These effects of CT can be partially rescued by enhancing retromer stability by using 'pharmacological chaperones'. Moreover, pharmacological chaperones can be used to increase basal and cholera toxin-inhibited NHE3 activity and fluid absorption by intestinal epithelial cells.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Varsha Singh
- Departments of Medicine and Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | - Jianbo Yang
- Departments of Medicine and Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | - Jianyi Yin
- Departments of Medicine and Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | - Robert Cole
- Department of Biological Chemistry, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | - Ming Tse
- Departments of Medicine and Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | - Diego E Berman
- The Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Department of Pathology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
| | - Scott A Small
- The Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Department of Pathology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
| | - Gregory Petsko
- Helen and Robert Appel Alzheimer's Disease Research Institute and Department of Neurology, Weill Cornell Medical College, New York, NY 10021, USA
| | - Mark Donowitz
- Departments of Medicine and Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
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4
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Rajkumar P, Cha B, Yin J, Arend LJ, Păunescu TG, Hirabayashi Y, Donowitz M, Pluznick JL. Identifying the localization and exploring a functional role for Gprc5c in the kidney. FASEB J 2018; 32:2046-2059. [PMID: 29196502 DOI: 10.1096/fj.201700610rr] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The investigation of orphan GPCRs (GPRs) has the potential to uncover novel insights into whole animal physiology. In this study, our goal was to determine the renal localization of Gprc5c, a receptor that we previously reported to be highly expressed in murine whole kidney, and to examine physiologic parameters in Gprc5c knockout (KO) mice to gain insight into function. Gprc5c localized to the apical membrane of renal proximal tubules (PTs) in mice, rats, and humans. With the comparison of Gprc5c wild-type (WT) and KO mice, we found that Gprc5c KO mice have altered acid-base homeostasis. Specifically, Gprc5c KO mice have lower blood pH and higher urine pH compared with WT mice, with a reduced level of titratable acids in their urine. In an in vitro GPCR internalization assay, we observed that Gprc5c internalization (an index of activation) was triggered by alkaline extracellular pH. Furthermore, with the use of an in vitro BCECF assay, we observed that Gprc5c increases Na+/H+ exchanger 3 (NHE3) activity at alkaline pH. We also find that the NHE3 activity is reduced in Gprc5c KO mice by 2 photon imaging in seminaphthorhodafluors (SNARF)-4F-loaded kidney sections. NHE3 is a primary contributor to apical transport of H+ in the renal PT. Together, these data imply that Gprc5c modulates the renal contribution to systemic pH homeostasis, at least in part, by taking part in the regulation of NHE3.-Rajkumar, P., Cha, B., Yin, J., Arend, L. J., Păunescu, T. G., Hirabayashi, Y., Donowitz, M., Pluznick, J. L. Identifying the localization and exploring a functional role for Gprc5c in the kidney.
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Affiliation(s)
- Premraj Rajkumar
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Boyoung Cha
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Jianyi Yin
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Lois J Arend
- Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Teodor G Păunescu
- Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Yoshio Hirabayashi
- Laboratory for Molecular Membrane Neuroscience, RIKEN Brain Science Institute, Saitama, Japan
| | - Mark Donowitz
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Jennifer L Pluznick
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Engevik AC, Goldenring JR. Trafficking Ion Transporters to the Apical Membrane of Polarized Intestinal Enterocytes. Cold Spring Harb Perspect Biol 2018; 10:cshperspect.a027979. [PMID: 28264818 DOI: 10.1101/cshperspect.a027979] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Epithelial cells lining the gastrointestinal tract require distinct apical and basolateral domains to function properly. Trafficking and insertion of enzymes and transporters into the apical brush border of intestinal epithelial cells is essential for effective digestion and absorption of nutrients. Specific critical ion transporters are delivered to the apical brush border to facilitate fluid and electrolyte uptake. Maintenance of these apical transporters requires both targeted delivery and regulated membrane recycling. Examination of altered apical trafficking in patients with Microvillus Inclusion disease caused by inactivating mutations in MYO5B has led to insights into the regulation of apical trafficking by elements of the apical recycling system. Modeling of MYO5B loss in cell culture and animal models has led to recognition of Rab11a and Rab8a as critical regulators of apical brush border function. All of these studies show the importance of apical membrane trafficking dynamics in maintenance of polarized epithelial cell function.
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Affiliation(s)
- Amy Christine Engevik
- Section of Surgical Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232.,Epithelial Biology Center, Vanderbilt University Medical Center, Nashville, Tennessee 37232
| | - James R Goldenring
- Section of Surgical Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232.,Epithelial Biology Center, Vanderbilt University Medical Center, Nashville, Tennessee 37232.,Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37232.,Nashville VA Medical Center, Nashville, Tennessee 37232
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Sarker R, Cha B, Kovbasnjuk O, Cole R, Gabelli S, Tse CM, Donowitz M. Phosphorylation of NHE3-S 719 regulates NHE3 activity through the formation of multiple signaling complexes. Mol Biol Cell 2017; 28:1754-1767. [PMID: 28495796 PMCID: PMC5491184 DOI: 10.1091/mbc.e16-12-0862] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 03/09/2017] [Accepted: 05/04/2017] [Indexed: 12/02/2022] Open
Abstract
CK2 regulates NHE3 by phosphorylating a single C-terminal amino acid, which, when mutated, reduces basal NHE3 activity and its acute stimulation and inhibition. It also is necessary for binding of proteins throughout the C-terminus, which means that it determines the C-terminal structure. Casein kinase 2 (CK2) binds to the NHE3 C-terminus and constitutively phosphorylates a downstream site (S719) that accounts for 40% of basal NHE3 activity. The role of CK2 in regulation of NHE3 activity in polarized Caco-2/bbe cells was further examined by mutation of NHE3-S719 to A (not phosphorylated) or D (phosphomimetic). NHE3-S719A but not -S719D had multiple changes in NHE3 activity: 1) reduced basal NHE3 activity—specifically, inhibition of the PI3K/AKT-dependent component; 2) reduced acute stimulation of NHE3 activity by LPA/LPA5R stimulation; and 3) reduced acute inhibition of NHE3 activity—specifically, elevated Ca2+ related (carbachol/Ca2+ ionophore), but there was normal inhibition by forskolin and hyperosmolarity. The S719A mutant had reduced NHE3 complex size, reduced expression in lipid rafts, increased BB mobile fraction, and reduced binding to multiple proteins that bind throughout the NHE3 intracellular C-terminus, including calcineurin homologous protein, the NHERF family and SNX27 (related PDZ domains). These studies show that phosphorylation of the NHE3 at a single amino acid in the distal part of the C-terminus affects multiple aspects of NHE3 complex formation and changes the NHE3 lipid raft distribution, which cause changes in specific aspects of basal as well as acutely stimulated and inhibited Na+/H+ exchange activity.
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Affiliation(s)
- Rafiquel Sarker
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Boyoung Cha
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Olga Kovbasnjuk
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Robert Cole
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Sandra Gabelli
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Chung Ming Tse
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Mark Donowitz
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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7
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Cha B, Yang J, Singh V, Zachos NC, Sarker RI, Chen TE, Chakraborty M, Tse CM, Donowitz M. PDZ domain-dependent regulation of NHE3 protein by both internal Class II and C-terminal Class I PDZ-binding motifs. J Biol Chem 2017; 292:8279-8290. [PMID: 28283572 DOI: 10.1074/jbc.m116.774489] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Revised: 03/06/2017] [Indexed: 12/16/2022] Open
Abstract
NHE3 directly binds Na+/H+ exchanger regulatory factor (NHERF) family scaffolding proteins that are required for many aspects of NHE3 regulation. The NHERFs bind both to an internal region (amino acids 586-660) of the NHE3 C terminus and to the NHE3 C-terminal four amino acids. The internal NHERF-binding region contains both putative Class I (-592SAV-) and Class II (-595CLDM-) PDZ-binding motifs (PBMs). Point mutagenesis showed that only the Class II motif contributes to NHERF binding. In this study, the roles in regulation of NHE3 activity of these two PBMs were investigated, revealing the following findings. 1) Interaction occurred between these binding sites because mutation of either removed nearly all NHERF binding. 2) Mutations in either significantly reduced basal NHE3 activity. Total and percent plasma membrane (PM) NHE3 protein expression was reduced in the C-terminal but not in the internal PBD mutation. 3) cGMP- and Ca2+-mediated inhibition of NHE3 was impaired in both the internal and the C-terminal PBM mutations. 4) There was a significant reduction in half-life of the PM pool of NHE3 in only the internal PBM mutation but no change in total NHE3 half-life in either. 5) There were some differences in NHE3-associating proteins in the two PBM mutations. In conclusion, NHE3 binds to NHERF proteins via both an internal Class II PBM and C-terminal Class I PBM, which interact. The former determines NHE3 stability in the PM, and the latter determines total expression and percent PM expression.
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Affiliation(s)
- Boyoung Cha
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Jianbo Yang
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Varsha Singh
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Nicholas C Zachos
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Rafiquel I Sarker
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Tian-E Chen
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Molee Chakraborty
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Chung-Ming Tse
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Mark Donowitz
- Departments of Physiology and Medicine, Gastroenterology Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
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Han Y, Ding C, Zhou J, Tian Y. Single Probe for Imaging and Biosensing of pH, Cu(2+) Ions, and pH/Cu(2+) in Live Cells with Ratiometric Fluorescence Signals. Anal Chem 2015; 87:5333-9. [PMID: 25898074 DOI: 10.1021/acs.analchem.5b00628] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
It is very essential to disentangle the complicated inter-relationship between pH and Cu in the signal transduction and homeostasis. To this end, reporters that can display distinct signals to pH and Cu are highly valuable. Unfortunately, there is still no report on the development of biosensors that can simultaneously respond to pH and Cu(2+), to the best of our knowledge. In this work, we developed a single fluorescent probe, AuNC@FITC@DEAC (AuNC, gold cluster; FITC, fluorescein isothiocyanate; DEAC, 7-diethylaminocoumarin-3-carboxylic acid), for biosensing of pH, Cu(2+), and pH/Cu(2+) with different ratiometric fluorescent signals. First, 2,2',2″-(2,2',2″-nitrilotris(ethane-2,1-diyl)tris((pyridin-2-yl-methyl)azanediyl))triethanethiol (TPAASH) was designed for specific recognition of Cu(2+), as well as for organic ligand to synthesize fluorescent AuNCs. Then, pH-sensitive molecule, FITC emitting at 518 nm, and inner reference molecule, DEAC with emission peak at 472 nm, were simultaneously conjugated on the surface of AuNCs emitting at 722 nm, thus, constructing a single fluorescent probe, AuNC@FITC@DEAC, to sensing pH, Cu(2+), and pH/Cu(2+) excited by 405 nm light. The developed probe exhibited high selectivity and accuracy for independent determination of pH and Cu(2+) against reactive oxygen species (ROS), other metal ions, amino acids, and even copper-containing proteins. The AuNC-based inorganic-organic probe with good cell-permeability and high biocompatibility was eventually applied in monitoring both pH and Cu(2+) and in understanding the interplaying roles of Cu(2+) and pH in live cells by ratiometric multicolor fluorescent imaging.
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Affiliation(s)
- Yingying Han
- †Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, People's Republic of China
| | - Changqin Ding
- †Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, People's Republic of China
| | - Jie Zhou
- †Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, People's Republic of China
| | - Yang Tian
- †Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, People's Republic of China.,‡Department of Chemistry, School of Chemistry and Molecular Engineering, East China Normal University, North Zhongshan Road 3663, Shanghai 200062, People's Republic of China
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Singh V, Yang J, Cha B, Chen TE, Sarker R, Yin J, Avula LR, Tse M, Donowitz M. Sorting nexin 27 regulates basal and stimulated brush border trafficking of NHE3. Mol Biol Cell 2015; 26:2030-43. [PMID: 25851603 PMCID: PMC4472014 DOI: 10.1091/mbc.e14-12-1597] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 04/01/2015] [Indexed: 12/21/2022] Open
Abstract
In polarized epithelial cells, SNX27 regulates PDZ domain–directed trafficking of NHE3 from endosomes to the plasma membrane and increases the stability of brush border NHE3. This establishes SNX27 as an important regulator of polarized sorting in epithelial cells. Sorting nexin 27 (SNX27) contains a PDZ domain that is phylogenetically related to the PDZ domains of the NHERF proteins. Studies on nonepithelial cells have shown that this protein is located in endosomes, where it regulates trafficking of cargo proteins in a PDZ domain–dependent manner. However, the role of SNX27 in trafficking of cargo proteins in epithelial cells has not been adequately explored. Here we show that SNX27 directly interacts with NHE3 (C-terminus) primarily through the SNX27 PDZ domain. A combination of knockdown and reconstitution experiments with wild type and a PDZ domain mutant (GYGF → GAGA) of SNX27 demonstrate that the PDZ domain of SNX27 is required to maintain basal NHE3 activity and surface expression of NHE3 in polarized epithelial cells. Biotinylation-based recycling and degradation studies in intestinal epithelial cells show that SNX27 is required for the exocytosis (not endocytosis) of NHE3 from early endosome to plasma membrane. SNX27 is also required to regulate the retention of NHE3 on the plasma membrane. The findings of the present study extend our understanding of PDZ-mediated recycling of cargo proteins from endosome to plasma membrane in epithelial cells.
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Affiliation(s)
- Varsha Singh
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Jianbo Yang
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Boyoung Cha
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Tiane-e Chen
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Rafiquel Sarker
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Jianyi Yin
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Leela Rani Avula
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Ming Tse
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Mark Donowitz
- Gastroenterology Division, Departments of Physiology and Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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10
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Zhu XC, Sarker R, Horton JR, Chakraborty M, Chen TE, Tse CM, Cha B, Donowitz M. Nonsynonymous single nucleotide polymorphisms of NHE3 differentially decrease NHE3 transporter activity. Am J Physiol Cell Physiol 2015; 308:C758-66. [PMID: 25715704 DOI: 10.1152/ajpcell.00421.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 02/23/2015] [Indexed: 12/24/2022]
Abstract
Genetic determinants appear to play a role in susceptibility to chronic diarrhea, but the genetic abnormalities involved have only been identified in a few conditions. The Na⁺/H⁺ exchanger 3 (NHE3) accounts for a large fraction of physiologic intestinal Na⁺ absorption. It is highly regulated through effects on its intracellular COOH-terminal regulatory domain. The impact of genetic variation in the NHE3 gene, such as single nucleotide polymorphisms (SNPs), on transporter activity remains unexplored. From a total of 458 SNPs identified in the entire NHE3 gene, we identified three nonsynonymous mutations (R474Q, V567M, and R799C), which were all in the protein's intracellular COOH-terminal domain. Here we evaluated whether these SNPs affect NHE3 activity by expressing them in a mammalian cell line that is null for all plasma membrane NHEs. These variants significantly reduced basal NHE3 transporter activity through a reduction in intrinsic NHE3 function in variant R474Q, abnormal trafficking in variant V567M, or defects in both intrinsic NHE3 function and trafficking in variant R799C. In addition, variants NHE3 R474Q and R799C failed to respond to acute dexamethasone stimulation, suggesting cells with these mutant proteins might be defective in NHE3 function during postprandial stimulation and perhaps under stressful conditions. Finally, variant R474Q was shown to exhibit an aberrant interaction with calcineurin B homologous protein (CHP), an NHE3 regulatory protein required for basal NHE3 activity. Taken together, these results demonstrate decreased transport activity in three SNPs of NHE3 and provide mechanistic insight into how these SNPs impact NHE3 function.
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Affiliation(s)
- Xinjun Cindy Zhu
- Department of Medicine, Division of Gastroenterology and Hepatology, Center of Cardiovascular Sciences, Albany Medical Center, Albany, New York; Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Rafiquel Sarker
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - John R Horton
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia
| | - Molee Chakraborty
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Tian-E Chen
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - C Ming Tse
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Boyoung Cha
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Mark Donowitz
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
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11
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Chen T, Kocinsky HS, Cha B, Murtazina R, Yang J, Tse CM, Singh V, Cole R, Aronson PS, de Jonge H, Sarker R, Donowitz M. Cyclic GMP kinase II (cGKII) inhibits NHE3 by altering its trafficking and phosphorylating NHE3 at three required sites: identification of a multifunctional phosphorylation site. J Biol Chem 2014; 290:1952-65. [PMID: 25480791 DOI: 10.1074/jbc.m114.590174] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The epithelial brush-border Na(+)/H(+) exchanger NHE3 is acutely inhibited by cGKII/cGMP, but how cGKII inhibits NHE3 is unknown. This study tested the hypothesis that cGMP inhibits NHE3 by phosphorylating it and altering its membrane trafficking. Studies were carried out in PS120/NHERF2 and in Caco-2/Bbe cells overexpressing HA-NHE3 and cGKII, and in mouse ileum. NHE3 activity was measured with 2',7'-bis(carboxyethyl)-S-(and 6)carboxyfluorescein acetoxy methylester/fluorometry. Surface NHE3 was determined by cell surface biotinylation. Identification of NHE3 phosphorylation sites was by iTRAQ/LC-MS/MS with TiO2 enrichment and immunoblotting with specific anti-phospho-NHE3 antibodies. cGMP/cGKII rapidly inhibited NHE3, which was associated with reduced surface NHE3. cGMP/cGKII increased NHE3 phosphorylation at three sites (rabbit Ser(554), Ser(607), and Ser(663), equivalent to mouse Ser(552), Ser(605), and Ser(659)), all of which had to be present at the same time for cGMP to inhibit NHE3. NHE3-Ser(663) phosphorylation was not necessary for cAMP inhibition of NHE3. Dexamethasone (4 h) stimulated wild type NHE3 activity and increased surface expression but failed to stimulate NHE3 activity or increase surface expression when NHE3 was mutated to either S663A or S663D. We conclude that 1) cGMP inhibition of NHE3 is associated with phosphorylation of NHE3 at Ser(554), Ser(607), and Ser(663), all of which are necessary for cGMP/cGKII to inhibit NHE3. 2) Dexamethasone stimulates NHE3 by phosphorylation of a single site, Ser(663). The requirement for three phosphorylation sites in NHE3 for cGKII inhibition, and for phosphorylation of one of these sites for dexamethasone stimulation of NHE3, is a unique example of regulation by phosphorylation.
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Affiliation(s)
- Tiane Chen
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | | | - Boyoung Cha
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | - Rakhilya Murtazina
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | - Jianbo Yang
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | - C Ming Tse
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | - Varsha Singh
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | - Robert Cole
- the Biological Chemistry Department, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Peter S Aronson
- Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, and
| | - Hugo de Jonge
- the GI Division, Erasmus Medical Center, 3015CN Rotterdam, Netherlands
| | - Rafiquel Sarker
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
| | - Mark Donowitz
- From the Departments of Physiology and Medicine, Gastroenterology Division, and
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Wu YX, Zhang XB, Li JB, Zhang CC, Liang H, Mao GJ, Zhou LY, Tan W, Yu RQ. Bispyrene–Fluorescein Hybrid Based FRET Cassette: A Convenient Platform toward Ratiometric Time-Resolved Probe for Bioanalytical Applications. Anal Chem 2014; 86:10389-96. [DOI: 10.1021/ac502863m] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Yong-Xiang Wu
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Xiao-Bing Zhang
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Jun-Bin Li
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Cui-Cui Zhang
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Hao Liang
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Guo-Jiang Mao
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Li-Yi Zhou
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Weihong Tan
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
| | - Ru-Qin Yu
- Molecular Science and Biomedicine Laboratory, State Key
Laboratory of Chemo/Biosensing and Chemometrics, College
of Chemistry and Chemical Engineering, College of Biology, Hunan University, Changsha 410082, China
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13
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Castellanos-Mendoza A, Castro-Acosta RM, Olvera A, Zavala G, Mendoza-Vera M, García-Hernández E, Alagón A, Trujillo-Roldán MA, Valdez-Cruz NA. Influence of pH control in the formation of inclusion bodies during production of recombinant sphingomyelinase-D in Escherichia coli. Microb Cell Fact 2014; 13:137. [PMID: 25213001 PMCID: PMC4177172 DOI: 10.1186/s12934-014-0137-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Accepted: 09/04/2014] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Inclusion bodies (IBs) are aggregated proteins that form clusters when protein is overexpressed in heterologous expression systems. IBs have been considered as non-usable proteins, but recently they are being used as functional materials, catalytic particles, drug delivery agents, immunogenic structures, and as a raw material in recombinant therapeutic protein purification. However, few studies have been made to understand how culture conditions affect the protein aggregation and the physicochemical characteristics that lead them to cluster. The objective of our research was to understand how pH affects the physicochemical properties of IBs formed by the recombinant sphingomyelinase-D of tick expressed in E. coli BL21-Gold (DE3) by evaluating two pH culture strategies. RESULTS Uncontrolled pH culture conditions favored recombinant sphingomyelinase-D aggregation and IB formation. The IBs of sphingomyelinase-D produced under controlled pH at 7.5 and after 24 h were smaller (<500 nm) than those produced under uncontrolled pH conditions (>500 nm). Furthermore, the composition, conformation and β-structure formation of the aggregates were different. Under controlled pH conditions in comparison to uncontrolled conditions, the produced IBs presented higher resistance to denaturants and proteinase-K degradation, presented β-structure, but apparently as time passes the IBs become compacted and less sensitive to amyloid dye binding. CONCLUSIONS The manipulation of the pH has an impact on IB formation and their physicochemical characteristics. Particularly, uncontrolled pH conditions favored the protein aggregation and sphingomyelinase-D IB formation. The evidence may lead to find methodologies for bioprocesses to obtain biomaterials with particular characteristics, extending the application possibilities of the inclusion bodies.
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Cha B, Chen T, Sarker R, Yang J, Raben D, Tse CM, Kovbasnjuk O, Donowitz M. Lysophosphatidic acid stimulation of NHE3 exocytosis in polarized epithelial cells occurs with release from NHERF2 via ERK-PLC-PKCδ signaling. Am J Physiol Cell Physiol 2014; 307:C55-65. [PMID: 24760985 PMCID: PMC4080180 DOI: 10.1152/ajpcell.00045.2014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 04/03/2014] [Indexed: 01/19/2023]
Abstract
The Na(+)/H(+) exchanger 3 (NHE3) is a brush border (BB) Na(+)/H(+) antiporter that accounts for the majority of physiologic small intestinal and renal Na(+) absorption. It is regulated physiologically and in disease via changes in endocytosis/exocytosis. Paradoxically, NHE3 is fixed to the microvillar (MV) actin cytoskeleton and has little basal mobility. This fixation requires NHE3 binding to the multi-PDZ domain scaffold proteins Na(+)/H(+) exchanger regulatory factor (NHERF)1 and NHERF2 and to ezrin. Coordinated release of NHE3 from the MV cytoskeleton has been demonstrated during both stimulation and inhibition of NHE3. However, the signaling molecules involved in coordinating NHE3 trafficking and cytoskeletal association have not been identified. This question was addressed by studying lysophosphatidic acid (LPA) stimulation of NHE3 in polarized renal proximal tubule opossum kidney (OK) cells that occurs via apical LPA5 receptors and is NHERF2 dependent and mediated by epidermal growth factor receptor (EGFR), Rho/Rho-associated kinase (ROCK), and ERK. NHE3 activity was determined by BCECF/fluorometry and NHE3 microvillar mobility by FRAP/confocal microscopy using NHE3-EGFP. Apical LPA (3 μM)/LPA5R stimulated NHE3 activity, increased NHE3 mobility, and decreased the NHE3/NHERF2 association. The LPA stimulation of NHE3 was also PKCδ dependent. PKCδ was necessary for LPA stimulation of NHE3 mobility and NHE3/NHERF2 association. Moreover, the LPA-induced translocation to the membrane of PKCδ was both ERK and phospholipase C dependent with ERK acting upstream of PLC. We conclude that LPA stimulation of NHE3 exocytosis includes a signaling pathway that regulates fixation of NHE3 to the MV cytoskeleton. This involves a signaling module consisting of ERK-PLC-PKCδ, which dynamically and reversibly releases NHE3 from NHERF2 to contribute to the changes in NHE3 MV mobility.
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Affiliation(s)
- Boyoung Cha
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Tiane Chen
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Rafiquel Sarker
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Jianbo Yang
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Daniel Raben
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - C Ming Tse
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Olga Kovbasnjuk
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Mark Donowitz
- Departments of Physiology and Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and
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Zachos NC, Alamelumangpuram B, Lee LJ, Wang P, Kovbasnjuk O. Carbachol-mediated endocytosis of NHE3 involves a clathrin-independent mechanism requiring lipid rafts and Cdc42. Cell Physiol Biochem 2014; 33:869-81. [PMID: 24713550 PMCID: PMC4052452 DOI: 10.1159/000358659] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/10/2014] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND In intestinal epithelial cells, acute regulation of the brush border Na(+)/H(+) exchanger, NHE3, usually occurs by changes in endocytosis and/or exocytosis. Constitutive NHE3 endocytosis involves clathrin. Carbachol (CCH), which elevates intracellular Ca(2+) ([Ca(2+)]i), decreases NHE3 activity and stimulates endocytosis; however, the mechanism involved in calcium-mediated endocytosis of NHE3 is unclear. A pool of NHE3 resides in lipid rafts, which contributes to basal, but not cAMP-mediated, NHE3 trafficking, suggesting that an alternative mechanism exists for NHE3 endocytosis. Cdc42 was demonstrated to play an integral role in some cases of cholesterol-sensitive, clathrin-independent endocytosis. Therefore, the current study was designed to test the hypotheses that (1) clathrin-mediated endocytosis (CME) is involved in constitutive, but not CCH-mediated, endocytosis of NHE3, and (2) CCH-mediated endocytosis of NHE3 occurs through a lipid raft, activated Cdc42-dependent pathway that does not involve clathrin. METHODS The role of Cdc42 and lipid rafts on NHE3 activity and endocytosis were investigated in polarized Caco-2/BBe cells using pharmacological and shRNA knockdown approaches. RESULTS Basal NHE3 activity was increased in the presence of CME blockers (chlorpromazine; K(+) depletion) supporting previous reports that constitutive NHE3 endocytosis is clathrin dependent. In contrast, CCH-inhibition of NHE3 activity was abolished in Caco-2/BBe cells treated with MβCD (to disrupt lipid rafts) as well as in Cdc42 knockdown cells but was unaffected by CME blockers. CONCLUSION CCH-mediated inhibition of NHE3 activity is not dependent on clathrin and involves lipid rafts and requires Cdc42.
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Affiliation(s)
- Nicholas C Zachos
- Department of Medicine/Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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16
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Sodium/proton exchanger 3 (NHE3) and sudden infant death syndrome (SIDS). Int J Legal Med 2014; 128:939-43. [PMID: 24590378 DOI: 10.1007/s00414-014-0978-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Accepted: 02/04/2014] [Indexed: 01/26/2023]
Abstract
The sodium/proton exchanger protein 3 (NHE3) is located in chemosensitive areas of the medulla oblongata and plays an important role in the central control of respiration. Overexpression of NHE3 is correlated with lower respiration and might therefore contribute to the vulnerability of infants dying suddenly and unexpected (sudden infant death syndrome, SIDS). Our aim in this study was to verify already reported genetic variations in the NHE3 gene in an independent SIDS cohort from Switzerland. Two single nucleotide polymorphisms (SNPs) in the promoter region (G1131A and C1197T) and one variation in the coding sequence of exon 16 (C2405T) in the NHE3 gene were analyzed in 160 Caucasian SIDS infants and 192 Swiss adult controls by using a single base extension method (SNaPshot multiplex). No significant differences were detected in the allelic frequencies of the three NHE3 polymorphisms between SIDS cases and controls. We conclude that the three investigated NHE3 SNPs are unlikely to play a major role in the pathogenesis of SIDS in Caucasian infants. However, further genetic investigations in different ethnicities are required to determine whether variations in NHE3 are associated with an increased SIDS risk.
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17
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Singh V, Lin R, Yang J, Cha B, Sarker R, Tse CM, Donowitz M. AKT and GSK-3 are necessary for direct ezrin binding to NHE3 as part of a C-terminal stimulatory complex: role of a novel Ser-rich NHE3 C-terminal motif in NHE3 activity and trafficking. J Biol Chem 2014; 289:5449-61. [PMID: 24398676 DOI: 10.1074/jbc.m113.521336] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Basal activity of the BB Na(+)/H(+) exchanger NHE3 requires multiprotein complexes that form on its C terminus. One complex stimulates basal NHE3 activity and contains ezrin and phosphoinositides as major components; how it stimulates NHE3 activity is not known. This study tested the hypothesis that ezrin dynamically associates with this complex, which sets ezrin binding. NHE3 activity was reduced by an Akti. This effect was eliminated if ezrin binding to NHE3 was inhibited by a point mutant. Recombinant AKT phosphorylated NHE3 C terminus in the domain ezrin directly binds. This domain (amino acids 475-589) is predicted to be α-helical and contains a conserved cluster of three serines (Ser(515), Ser(522), and Ser(526)). Point mutations of two of these (S515A, S515D, or S526A) reduced basal NHE3 activity and surface expression and had no Akti inhibition. S526D had NHE3 activity equal to wild type with normal Akti inhibition. Ezrin binding to NHE3 was regulated by Akt, being eliminated by Akti. NHE3-S515A and -S526D did not bind ezrin; NHE3-S515D had reduced ezrin binding; NHE3-S526D bound ezrin normally. NHE3-Ser(526) is predicted to be a GSK-3 kinase phosphorylation site. A GSK-3 inhibitor reduced basal NHE3 activity as well as ezrin-NHE3 binding, and this effect was eliminated in NHE3-S526A and -S526D mutants. The conclusions were: 1) NHE3 basal activity is regulated by a signaling complex that is controlled by sequential effects of two kinases, Akt and GSK-3, which act on a Ser cluster in the same NHE3 C-terminal domain that binds ezrin; and 2) these kinases regulate the dynamic association of ezrin with NHE3 to affect basal NHE3 activity.
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Affiliation(s)
- Varsha Singh
- From the Departments of Physiology and Medicine, Gastroenterology Division, Johns, Hopkins University School of Medicine, Baltimore, Maryland 21205 and
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18
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Huang W, Lin W, Guan X. Development of ratiometric fluorescent pH sensors based on chromenoquinoline derivatives with tunable pKa values for bioimaging. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2013.10.130] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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19
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Zachos NC, Lee LJ, Kovbasnjuk O, Li X, Donowitz M. PLC-γ directly binds activated c-Src, which is necessary for carbachol-mediated inhibition of NHE3 activity in Caco-2/BBe cells. Am J Physiol Cell Physiol 2013; 305:C266-75. [PMID: 23703528 DOI: 10.1152/ajpcell.00277.2012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Elevated levels of intracellular Ca(2+) ([Ca(2+)]i) inhibit Na(+)/H(+) exchanger 3 (NHE3) activity in the intact intestine. We previously demonstrated that PLC-γ directly binds NHE3, an interaction that is necessary for [Ca(2+)]i inhibition of NHE3 activity, and that PLC-γ Src homology 2 (SH2) domains may scaffold Ca(2+) signaling proteins necessary for regulation of NHE3 activity. [Ca(2+)]i regulation of NHE3 activity is also c-Src dependent; however, the mechanism by which c-Src is involved is undetermined. We hypothesized that the SH2 domains of PLC-γ might link c-Src to NHE3-containing complexes to mediate [Ca(2+)]i inhibition of NHE3 activity. In Caco-2/BBe cells, carbachol (CCh) decreased NHE3 activity by ∼40%, an effect abolished with the c-Src inhibitor PP2. CCh treatment increased the amount of active c-Src as early as 1 min through increased Y(416) phosphorylation. Coimmunoprecipitation demonstrated that c-Src associated with PLC-γ, but not NHE3, under basal conditions, an interaction that increased rapidly after CCh treatment and occurred before the dissociation of PLC-γ and NHE3 that occurred 10 min after CCh treatment. Finally, direct binding to c-Src only occurred through the PLC-γ SH2 domains, an interaction that was prevented by blocking the PLC-γ SH2 domain. This study demonstrated that c-Src 1) activity is necessary for [Ca(2+)]i inhibition of NHE3 activity, 2) activation occurs rapidly (∼1 min) after CCh treatment, 3) directly binds PLC-γ SH2 domains and associates dynamically with PLC-γ under elevated [Ca(2+)]i conditions, and 4) does not directly bind NHE3. Under elevated [Ca(2+)]i conditions, PLC-γ scaffolds c-Src into NHE3-containing multiprotein complexes before dissociation of PLC-γ from NHE3 and subsequent endocytosis of NHE3.
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Affiliation(s)
- Nicholas C Zachos
- Department of Medicine/Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
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20
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Klaas M, Crocker PR. Sialoadhesin in recognition of self and non-self. Semin Immunopathol 2012; 34:353-64. [PMID: 22450957 DOI: 10.1007/s00281-012-0310-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Accepted: 03/05/2012] [Indexed: 11/28/2022]
Abstract
The immune system is tightly regulated to maintain an appropriate balance between immune activation and tolerance. Macrophages play a key role in this process since they express many pathogen recognition molecules as well as receptors for 'self'. Sialoadhesin is a major macrophage receptor that specifically recognizes sialic acid, an abundant component of host glycoconjugates but which can also be found on several human pathogens. In recent years, several studies have demonstrated that sialoadhesin can contribute to the uptake and processing of sialylated pathogens as well as playing an important role in regulating inflammatory and autoimmune responses via recognition of self.
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Affiliation(s)
- Mariliis Klaas
- Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, UK
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21
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Zizak M, Chen T, Bartonicek D, Sarker R, Zachos NC, Cha B, Kovbasnjuk O, Korac J, Mohan S, Cole R, Chen Y, Tse CM, Donowitz M. Calmodulin kinase II constitutively binds, phosphorylates, and inhibits brush border Na+/H+ exchanger 3 (NHE3) by a NHERF2 protein-dependent process. J Biol Chem 2012; 287:13442-56. [PMID: 22371496 DOI: 10.1074/jbc.m111.307256] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epithelial brush border (BB) Na(+)/H(+) exchanger 3 (NHE3) accounts for most renal and intestinal Na(+) absorption. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibits NHE3 activity under basal conditions in intact intestine, acting in the BB, but the mechanism is unclear. We now demonstrate that in both PS120 fibroblasts and polarized Caco-2BBe cells expressing NHE3, CaMKII inhibits basal NHE3 activity, because the CaMKII-specific inhibitors KN-93 and KN-62 stimulate NHE3 activity. This inhibition requires NHERF2. CaMKIIγ associates with NHE3 between aa 586 and 605 in the NHE3 C terminus in a Ca(2+)-dependent manner, with less association when Ca(2+) is increased. CaMKII inhibits NHE3 by an effect on its turnover number, not changing surface expression. Back phosphorylation demonstrated that NHE3 is phosphorylated by CaMKII under basal conditions. This overall phosphorylation of NHE3 is not affected by the presence of NHERF2. Amino acids downstream of NHE3 aa 690 are required for CaMKII to inhibit basal NHE3 activity, and mutations of the three putative CaMKII phosphorylation sites downstream of aa 690 each prevented KN-93 stimulation of NHE3 activity. These studies demonstrate that CaMKIIγ is a novel NHE3-binding protein, and this association is reduced by elevated Ca(2+). CaMKII inhibits basal NHE3 activity associated with phosphorylation of NHE3 by effects requiring aa downstream of NHE3 aa 690 and of the CaMKII-binding site on NHE3. CaMKII binding to and phosphorylation of the NHE3 C terminus are parts of the physiologic regulation of NHE3 that occurs in fibroblasts as well as in the BB of an intestinal Na(+)-absorptive cell.
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Affiliation(s)
- Mirza Zizak
- Division of Gastroenterology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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22
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Zhu X, Cha B, Zachos NC, Sarker R, Chakraborty M, Chen TE, Kovbasnjuk O, Donowitz M. Elevated calcium acutely regulates dynamic interactions of NHERF2 and NHE3 proteins in opossum kidney (OK) cell microvilli. J Biol Chem 2011; 286:34486-96. [PMID: 21799002 DOI: 10.1074/jbc.m111.230219] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The brush border (BB) Na(+)/H(+) exchanger NHE3 is rapidly activated or inhibited by changes in trafficking, which mimics renal and intestinal physiology. However, there is a paradox in that NHE3 has limited mobility in the BB due to its binding to the multi-PDZ domain containing the NHERF family. To allow increased endocytosis, as occurs with elevated intracellular Ca(2+), we hypothesized that NHE3 had to be, at least transiently, released from the BB cytoskeleton. Because NHERF1 and -2 are localized at the BB, where they bind NHE3 as well as the cytoskeleton, we tested whether either or both might dynamically interact with NHE3 as part of Ca(2+) signaling. We employed FRET to study close association of NHE3 and these NHERFs and fluorescence recovery after photobleaching to monitor NHE3 mobility in the apical domain in polarized opossum kidney cells. Under basal conditions, NHERF2 and NHE3 exhibited robust FRET signaling. Within 1 min of A23187 (0.5 μm) exposure, the NHERF2-NHE3 FRET signal was abolished, and BB NHE3 mobility was transiently increased. The dynamics in FRET signal and NHE3 mobility correlated well with a change in co-precipitation of NHE3 and NHERF2 but not NHERF1. We conclude the following. 1) Under basal conditions, NHE3 closely associates with NHERF2 in opossum kidney cell microvilli. 2) Within 1 min of elevated Ca(2+), the close association of NHE3-NHERF2 is abolished but is re-established in ∼60 min. 3) The change in NHE3-NHERF2 association is accompanied by an increased BB mobile fraction of NHE3, which contributes to inhibition of NHE3 transport activity via increased endocytosis.
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Affiliation(s)
- Xinjun Zhu
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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23
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Lin Z, Jin S, Duan X, Wang T, Martini S, Hulamm P, Cha B, Hubbard A, Donowitz M, Guggino SE. Chloride channel (Clc)-5 is necessary for exocytic trafficking of Na+/H+ exchanger 3 (NHE3). J Biol Chem 2011; 286:22833-45. [PMID: 21561868 DOI: 10.1074/jbc.m111.224998] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ClC-5, a chloride/proton exchanger, is predominantly expressed and localized in subapical endosomes of the renal proximal tubule. Mutations of the CLCN5 gene cause Dent disease. The symptoms of Dent disease are replicated in Clcn5 knock-out mice. Absence of ClC-5 in mice is associated with reduced surface expression of NHE3 in proximal tubules. The molecular basis for this change is not fully understood. In this study, we investigated the mechanisms by which ClC-5 regulates trafficking of NHE3. Whether ClC-5-dependent endocytosis, exocytosis, or both contributed to the altered distribution of NHE3 was examined. First, NHE3 activity in proximal tubules of wild type (WT) and Clcn5 KO mice was determined by two-photon microscopy. Basal and dexamethasone-stimulated NHE3 activity of Clcn5 KO mice was decreased compared with that seen in WT mice, whereas the degree of inhibition of NHE3 activity by increasing cellular concentration of cAMP (forskolin) or Ca(2+) (A23187) was not different in WT and Clcn5 KO mice. Second, NHE3-dependent absorption of HCO(3)(-), measured by single tubule perfusion, was reduced in proximal tubules of Clcn5 KO mice. Third, by cell surface biotinylation, trafficking of NHE3 was examined in short hairpin RNA (shRNA) plasmid-transfected opossum kidney cells. Surface NHE3 was reduced in opossum kidney cells with reduced expression of ClC-5, whereas the total protein level of NHE3 did not change. Parathyroid hormone decreased NHE3 surface expression, but the extent of decrease and the rate of endocytosis observed in both scrambled and ClC-5 knockdown cells were not significantly different. However, the rates of basal and dexamethasone-stimulated exocytosis of NHE3 were attenuated in ClC-5 knockdown cells. These results show that ClC-5 plays an essential role in exocytosis of NHE3.
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Affiliation(s)
- Zhihong Lin
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Alexander RT, Jaumouillé V, Yeung T, Furuya W, Peltekova I, Boucher A, Zasloff M, Orlowski J, Grinstein S. Membrane surface charge dictates the structure and function of the epithelial Na+/H+ exchanger. EMBO J 2011; 30:679-91. [PMID: 21245831 DOI: 10.1038/emboj.2010.356] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2010] [Accepted: 12/17/2010] [Indexed: 01/24/2023] Open
Abstract
The Na(+)/H(+) exchanger NHE3 plays a central role in intravascular volume and acid-base homeostasis. Ion exchange activity is conferred by its transmembrane domain, while regulation of the rate of transport by a variety of stimuli is dependent on its cytosolic C-terminal region. Liposome- and cell-based assays employing synthetic or recombinant segments of the cytosolic tail demonstrated preferential association with anionic membranes, which was abrogated by perturbations that interfere with electrostatic interactions. Resonance energy transfer measurements indicated that segments of the C-terminal domain approach the bilayer. In intact cells, neutralization of basic residues in the cytosolic tail by mutagenesis or disruption of electrostatic interactions inhibited Na(+)/H(+) exchange activity. An electrostatic switch model is proposed to account for multiple aspects of the regulation of NHE3 activity.
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Sarker R, Valkhoff VE, Zachos NC, Lin R, Cha B, Chen TE, Guggino S, Zizak M, de Jonge H, Hogema B, Donowitz M. NHERF1 and NHERF2 are necessary for multiple but usually separate aspects of basal and acute regulation of NHE3 activity. Am J Physiol Cell Physiol 2010; 300:C771-82. [PMID: 21191106 DOI: 10.1152/ajpcell.00119.2010] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Na(+)/H(+) exchanger 3 (NHE3) is expressed in the brush border (BB) of intestinal epithelial cells and accounts for the majority of neutral NaCl absorption. It has been shown that the Na(+)/H(+) exchanger regulatory factor (NHERF) family members of multi-PDZ domain-containing scaffold proteins bind to the NHE3 COOH terminus and play necessary roles in NHE3 regulation in intestinal epithelial cells. Most studies of NHE3 regulation have been in cell models in which NHERF1 and/or NHERF2 were overexpressed. We have now developed an intestinal Na(+) absorptive cell model in Caco-2/bbe cells by expressing hemagglutinin (HA)-tagged NHE3 with an adenoviral infection system. Roles of NHERF1 and NHERF2 in NHE3 regulation were determined, including inhibition by cAMP, cGMP, and Ca(2+) and stimulation by EGF, with knockdown (KD) approaches with lentivirus (Lenti)-short hairpin RNA (shRNA) and/or adenovirus (Adeno)-small interfering RNA (siRNA). Stable infection of Caco-2/bbe cells by NHERF1 or NHERF2 Lenti-shRNA significantly and specifically reduced NHERF protein expression by >80%. NHERF1 KD reduced basal NHE3 activity, while NHERF2 KD stimulated NHE3 activity. siRNA-mediated (transient) and Lenti-shRNA-mediated (stable) gene silencing of NHERF2 (but not of NHERF1) abolished cGMP- and Ca(2+)-dependent inhibition of NHE3. KD of NHERF1 or NHERF2 alone had no effect on cAMP inhibition of NHE3, but KD of both simultaneously abolished the effect of cAMP. The stimulatory effect of EGF on NHE3 was eliminated in NHERF1-KD but occurred normally in NHERF2-KD cells. These findings show that both NHERF2 and NHERF1 are involved in setting NHE3 activity. NHERF2 is necessary for cGMP-dependent protein kinase (cGK) II- and Ca(2+)-dependent inhibition of NHE3. cAMP-dependent inhibition of NHE3 activity requires either NHERF1 or NHERF2. Stimulation of NHE3 activity by EGF is NHERF1 dependent.
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Affiliation(s)
- Rafiquel Sarker
- Gastroenterology and Hepatology Division, Department of Medicine, Johns Hopkins Univ. School of Medicine, Baltimore, MD 21205-2195, USA
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26
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Mohan S, Tse CM, Gabelli SB, Sarker R, Cha B, Fahie K, Nadella M, Zachos NC, Tu-Sekine B, Raben D, Amzel LM, Donowitz M. NHE3 activity is dependent on direct phosphoinositide binding at the N terminus of its intracellular cytosolic region. J Biol Chem 2010; 285:34566-78. [PMID: 20736165 DOI: 10.1074/jbc.m110.165712] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The small intestinal BB Na(+)/H(+) antiporter NHE3 accounts for the majority of intestinal sodium and water absorption. It is highly regulated with both postprandial inhibition and stimulation sequentially occurring. Phosphatidylinositide 4,5-bisphosphate (PI(4,5)P(2)) and phosphatidylinositide 3,4,5-trisphosphate (PI(3,4,5)P(3)) binding is involved with regulation of multiple transporters. We tested the hypothesis that phosphoinositides bind NHE3 under basal conditions and are necessary for its acute regulation. His(6) proteins were made from the NHE3 C-terminal region divided into four parts as follows: F1 (amino acids 475-589), F2 (amino acids 590-667), F3 (amino acids 668-747), and F4 (amino acids 748-832) and purified by a nickel column. Mutations were made in the F1 region of NHE3 and cloned in pet30a and pcDNA3.1 vectors. PI(4,5)P(2) and PI(3,4,5)P(3) bound only to the NHE3 F1 fusion protein (amino acids 475-589) on liposomal pulldown assays. Mutations were made in the putative lipid binding region of the F1 domain and studied for alterations in lipid binding and Na(+)/H(+) exchange as follows: Y501A/R503A/K505A; F509A/R511A/R512A; R511L/R512L; R520/FR527F; and R551L/R552L. Our results indicate the following. 1) The F1 domain of the NHE3 C terminus has phosphoinositide binding regions. 2) Mutations of these regions alter PI(4,5)P(2) and PI(3,4,5)P(3) binding and basal NHE3 activity. 3) The magnitude of serum stimulation of NHE3 correlates with PI(4,5)P(2) and PI(3,4,5)P(3) binding of NHE3. 4) Wortmannin inhibition of PI3K did not correlate with PI(4,5)P(2) or PI(3,4,5)P(3) binding of NHE3. Two functionally distinct phosphoinositide binding regions (Tyr(501)-Arg(512) and Arg(520)-Arg(552)) are present in the NHE3 F1 domain; both regions are important for serum stimulation, but they display differences in phosphoinositide binding, and the latter but not the former alters NHE3 surface expression.
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Affiliation(s)
- Sachin Mohan
- Department of Physiology and Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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27
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Affiliation(s)
- Junyan Han
- Department of Chemistry, Texas A&M University, Box 30012, College Station, Texas 77841, USA
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28
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Tang B, Yu F, Li P, Tong L, Duan X, Xie T, Wang X. A near-infrared neutral pH fluorescent probe for monitoring minor pH changes: imaging in living HepG2 and HL-7702 cells. J Am Chem Soc 2010; 131:3016-23. [PMID: 19199620 DOI: 10.1021/ja809149g] [Citation(s) in RCA: 347] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A near-neutral pH near-infrared (NIR) fluorescent probe utilizing a fluorophore-spacer- receptor molecular framework that can modulate the fluorescence emission intensity through a fast photoinduced electron-transfer process was developed. Our strategy was to choose tricarbocyanine (Cy), a NIR fluorescent dye with high extinction coefficients, as a fluorophore, and 4'-(aminomethylphenyl)-2,2':6',2''-terpyridine (Tpy) as a receptor. The pH titration indicated that Tpy-Cy can monitor the minor physiological pH fluctuations with a pK(a) of approximately 7.10 near physiological pH, which is valuable for intracellular pH researches. The probe responds linearly and rapidly to minor pH fluctuations within the range of 6.70-7.90 and exhibits strong dependence on pH changes. As expected, the real-time imaging of cellular pH and the detection of pH in situ was achieved successfully in living HepG2 and HL-7702 cells by this probe. It is shown that the probe effectively avoids the influence of autofluorescence and native cellular species in biological systems and meanwhile exhibits high sensitivity, good photostability, and excellent cell membrane permeability.
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Affiliation(s)
- Bo Tang
- College of Chemistry, Chemical Engineering and Materials Science, Engineering Research Center of Pesticide and Medicine Intermediate Clean Production, Ministry of Education, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan 250014, People's Republic of China.
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29
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Cha B, Zhu XC, Chen W, Jones M, Ryoo S, Zachos NC, Chen TE, Lin R, Sarker R, Kenworthy AK, Tse M, Kovbasnjuk O, Donowitz M. NHE3 mobility in brush borders increases upon NHERF2-dependent stimulation by lyophosphatidic acid. J Cell Sci 2010; 123:2434-43. [PMID: 20571054 DOI: 10.1242/jcs.056713] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The epithelial brush border (BB) Na(+)/H(+) exchanger NHE3 is associated with the actin cytoskeleton by binding both directly and indirectly to ezrin; indirect binding is via attachment to NHERF family proteins. NHE3 mobility in polarized epithelial cell BBs is restricted by the actin cytoskeleton and NHERF binding such that only approximately 30% of NHE3 in the apical domain of an OK cell line stably expressing NHERF2 is mobile, as judged by FRAP analysis. Given that levels of NHE3 are partially regulated by changes in trafficking, we investigated whether the cytoskeleton association of NHE3 was dynamic and changed as part of acute regulation to allow NHE3 trafficking. The agonist studied was lysophosphatidic acid (LPA), an inflammatory mediator, which acutely stimulates NHE3 activity by increasing the amount of NHE3 on the BBs by stimulated exocytosis. LPA acutely stimulated NHE3 activity in OK cells stably expressing NHERF2. Two conditions that totally prevented LPA stimulation of NHE3 activity only partially prevented stimulation of NHE3 mobility: the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, and the NHE3F1 double mutant which has minimal direct binding of NHE3 to ezrin. These results show that LPA stimulation of NHE3 mobility occurs in two parts: (1) PI3K-dependent exocytic trafficking to the BB and (2) an increase in surface mobility of NHE3 in BBs under basal conditions. Moreover, the LPA stimulatory effect on NHE3 mobility required NHERF2. Although NHE3 and NHERF2 co-precipitated under basal conditions, they failed to co-precipitate 30 minutes after addition of LPA, whereas the physical association was re-established by 50-60 minutes. This dynamic interaction between NHERF2 and NHE3 was confirmed by acceptor photobleaching Förster Resonance energy Transfer (FRET). The restricted mobility of NHE3 in BBs under basal conditions as a result of cytoskeleton association is therefore dynamic and is reversed as part of acute LPA stimulation of NHE3. We suggest that this acute but transient increase in NHE3 mobility induced by LPA occurs via two processes: addition of NHE3 to the BB by exocytosis, a process which precedes binding of NHE3 to the actin cytoskeleton via NHERF2-ezrin, and by release of NHERF2 from the NHE3 already localized in the apical membrane, enabling NHE3 to distribute throughout the microvilli. These fractions of NHE3 make up a newly identified pool of NHE3 called the 'transit pool'. Moreover, our results show that there are two aspects of LPA signaling involved in stimulation of NHE3 activity: PI3K-dependent stimulated NHE3 exocytosis and the newly described, PI3K-independent dissociation of microvillar NHE3 from NHERF2.
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Affiliation(s)
- Boyoung Cha
- Departments of Physiology and Medicine, Gastroenterology Division, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Baltimore, MD 212052, USA
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30
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Poetsch M, Nottebaum BJ, Wingenfeld L, Frede S, Vennemann M, Bajanowski T. Impact of sodium/proton exchanger 3 gene variants on sudden infant death syndrome. J Pediatr 2010; 156:44-48.e1. [PMID: 19772970 DOI: 10.1016/j.jpeds.2009.07.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 05/21/2009] [Accepted: 07/07/2009] [Indexed: 10/20/2022]
Abstract
OBJECTIVE To determine the contribution of variations in the sodium/proton exchanger 3 (NHE3) gene in sudden infant death syndrome (SIDS). STUDY DESIGN Variations in the exons and promoter of the NHE3 gene were analyzed with direct sequencing analysis and mini sequencing (SNaPshot analysis) in 251 cases of SIDS, plus 50 infant control subjects who had died of other causes, and 170 healthy adults. RESULTS The C2405T variant (exon 16) and 2 polymorphisms in the promoter (G1131A and C1197T) were encountered significantly more frequently in cases of SIDS than in control subjects. At least 1 of these 3 variants was detected in 49% of SIDS cases, but only in 30% of control subjects. CONCLUSIONS Our findings suggest the involvement of polymorphisms in the NHE3 gene and promoter in cases of SIDS, which may result in an overexpression of NHE3 in the medulla oblongata and which possibly leads to a disturbance in breathing control. Furthermore, our results underline the heterogeneous character of SIDS.
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Affiliation(s)
- Micaela Poetsch
- Institute of Forensic Medicine, University Hospital Essen, Essen, Germany.
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Dynia DW, Steinmetz AG, Kocinsky HS. NHE3 function and phosphorylation are regulated by a calyculin A-sensitive phosphatase. Am J Physiol Renal Physiol 2009; 298:F745-53. [PMID: 20015946 DOI: 10.1152/ajprenal.00182.2009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Na+/H+ exchanger 3 (NHE3) is phosphorylated and regulated by multiple kinases, including PKA, SGK1, and CK2; however, the role of phosphatases in the dephosphorylation and regulation of NHE3 remains unknown. The purpose of this study was to determine whether serine/threonine phosphatases alter NHE3 activity and phosphorylation and, if so, at which sites. To this end, we first examined the effects of calyculin A [a combined protein phosphatase 1 (PP1) and PP2A inhibitor] and okadaic acid (a PP2A inhibitor) on general and site-specific NHE3 phosphorylation. Calyculin A induced a phosphorylation-dependent NHE3 gel mobility shift and increased NHE3 phosphorylation at serines 552 and 605. No change in NHE3 phosphorylation was detected after okadaic acid treatment. An NHE3 gel mobility shift was also evident in calyculin A-treated COS-7 cells transfected with either wild-type or mutant (S552A, S605G, S661A, S716A) rat NHE3. Since the NHE3 gel mobility shift occurred despite mutation of known phosphorylation sites, novel sites of phosphorylation must also exist. Next, we assayed NHE3 activity in response to calyculin A and okadaic acid and found that calyculin A induced a 24% inhibition of NHE3 activity, whereas okadaic acid had no effect. When all known NHE3 phosphorylation sites were mutated, calyculin A induced a stimulation of NHE3 activity, demonstrating a functional significance for the novel phosphorylation sites. Finally, we established that the PP1 catalytic subunit can directly dephosphorylate immunopurified NHE3 in vitro. In conclusion, our data demonstrate that a calyculin A-sensitive phosphatase, most likely PP1, is involved in the regulation and dephosphorylation of NHE3 at known and novel sites.
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Affiliation(s)
- Diane W Dynia
- Department of Pediatrics, Yale School of Medicine, New Haven, Connecticut, USA
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32
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Donowitz M, Mohan S, Zhu CX, Chen TE, Lin R, Cha B, Zachos NC, Murtazina R, Sarker R, Li X. NHE3 regulatory complexes. ACTA ACUST UNITED AC 2009; 212:1638-46. [PMID: 19448074 DOI: 10.1242/jeb.028605] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The epithelial brush border Na/H exchanger NHE3 is active under basal conditions and functions as part of neutral NaCl absorption in the intestine and renal proximal tubule, where it accounts for the majority of total Na absorbed. NHE3 is highly regulated. Both stimulation and inhibition occur post-prandially. This digestion related regulation of NHE3 is mimicked by multiple extracellular agonists and intracellular second messengers. The regulation of NHE3 depends on its C-terminal cytoplasmic domain, which acts as a scaffold to bind multiple regulatory proteins and links NHE3 to the cytoskeleton. The cytoskeletal association occurs by both direct binding to ezrin and by indirect binding via ezrin binding to the C-terminus of the multi-PDZ domain containing proteins NHERF1 and NHERF2. This is a review of the domain structure of NHE3 and of the scaffolding function and role in the regulation of NHE3 of the NHE3 C-terminal domain.
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Affiliation(s)
- Mark Donowitz
- Johns Hopkins University School of Medicine, 720 Rutland Avenue Baltimore, MD 21205, USA.
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Zachos NC, Li X, Kovbasnjuk O, Hogema B, Sarker R, Lee LJ, Li M, de Jonge H, Donowitz M. NHERF3 (PDZK1) contributes to basal and calcium inhibition of NHE3 activity in Caco-2BBe cells. J Biol Chem 2009; 284:23708-18. [PMID: 19535329 DOI: 10.1074/jbc.m109.012641] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Elevated intracellular Ca(2+) ([Ca(2+)](i)) inhibition of NHE3 is reconstituted by NHERF2, but not NHERF1, by a mechanism involving the formation of multiprotein signaling complexes. To further evaluate the specificity of the NHERF family in calcium regulation of NHE3 activity, the current study determined whether NHERF3 reconstitutes elevated [Ca(2+)](i) regulation of NHE3. In vitro, NHERF3 bound the NHE3 C terminus between amino acids 588 and 667. In vivo, NHE3 and NHERF3 associate under basal conditions as indicated by co-immunoprecipitation, confocal microscopy, and fluorescence resonance energy transfer. Treatment of PS120/NHE3/NHERF3 cells, but not PS120/NHE3 cells, with the Ca(2+) ionophore, 4-bromo-A23187 (0.5 mum): 1) inhibited NHE3 V(max) activity; 2) decreased NHE3 surface amount; 3) dissociated NHE3 and NHERF3 at the plasma membrane by confocal immunofluorescence and fluorescence resonance energy transfer. Similarly, in Caco-2BBe cells, NHERF3 and NHE3 colocalized in the BB under basal conditions but after elevation of [Ca(2+)](i) by carbachol, this overlap was abolished. NHERF3 short hairpin RNA knockdown (>50%) in Caco-2BBe cells significantly reduced basal NHE3 activity by decreasing BB NHE3 amount. Also, carbachol-mediated inhibition of NHE3 activity was abolished in Caco-2BBe cells in which NHERF3 protein expression was significantly reduced. In summary: 1) NHERF3 colocalizes and directly binds NHE3 at the plasma membrane under basal conditions; 2) NHERF3 reconstitutes [Ca(2+)](i) inhibition of NHE3 activity and dissociates from NHE3 in fibroblasts and polarized intestinal epithelial cells with elevated [Ca(2+)](i); 3) NHERF3 short hairpin RNA significantly reduced NHE3 basal activity and brush border expression in Caco-2BBe cells. These results demonstrate that NHERF3 reconstitutes calcium inhibition of NHE3 activity by anchoring NHE3 basally and releasing it with elevated Ca(2+).
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Affiliation(s)
- Nicholas C Zachos
- Department of Medicine, Hopkins Center for Epithelial Disorders, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195, USA
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34
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Alexander RT, Grinstein S. Tethering, recycling and activation of the epithelial sodium–proton exchanger, NHE3. J Exp Biol 2009; 212:1630-7. [DOI: 10.1242/jeb.027375] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
NHE3 is a sodium–proton exchanger expressed predominantly in the apical membrane of renal and intestinal epithelia, where it plays a key role in salt and fluid absorption and pH homeostasis. It performs these functions through the exchange of luminal sodium for cytosolic protons. Acute regulation of NHE3 function is mediated by altering the total number of exchangers in the plasma membrane as well as their individual activity. Traffic between endomembrane and plasmalemmal pools of NHE3 dictates the density of exchangers available at the cell surface. The activity of the plasmalemmal pool, however,is not fixed and can be altered by the association with modifier proteins, by post-translational alterations (such as cAMP-mediated phosphorylation) and possibly also via interaction with specific plasmalemmal phospholipids. Interestingly, association with cytoskeletal components affects both levels of regulation, tethering NHE3 molecules at the surface and altering their intrinsic activity. This paper reviews the role of proteins and lipids in the modulation of NHE3 function.
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Affiliation(s)
- R. Todd Alexander
- Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada,T6G 2R7
| | - Sergio Grinstein
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada,M5G 1X8
- Department of Biochemistry, University of Toronto, Ontario, Canada
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Zachos NC, van Rossum DB, Li X, Caraveo G, Sarker R, Cha B, Mohan S, Desiderio S, Patterson RL, Donowitz M. Phospholipase C-gamma binds directly to the Na+/H+ exchanger 3 and is required for calcium regulation of exchange activity. J Biol Chem 2009; 284:19437-44. [PMID: 19473983 DOI: 10.1074/jbc.m109.006098] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Multiple studies suggest that phospholipase C-gamma (PLC-gamma) contributes to regulation of sodium/hydrogen exchanger 3 (NHE3) in the small intestine, although the mechanism(s) for this regulation remain unknown. We demonstrate here that PLC-gamma binds directly to the C terminus of NHE3 and exists in similar sized multiprotein complexes as NHE3. This binding is dynamic and decreases with elevated [Ca(2+)](i). The PLC-gamma-binding site in NHE3 was identified (amino acids 586-605) and shown to be a critical regulatory domain for protein complex formation, because when it is mutated, NHE3 binding to PLC-gamma as well as NHERF2 is lost. An inhibitory peptide, which binds to the Src homology 2 domains contained in PLC-gamma without interrupting binding of PLC-gamma to NHE3, was used to probe a non-lipase-dependent role of PLC-gamma. In the presence of this peptide, carbachol-stimulated calcium inhibition of NHE3 was lost. These results mirror previous studies with the transient receptor potential channel and suggest that PLC-gamma may play a common role in regulating the cell-surface expression of ion transporters.
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Affiliation(s)
- Nicholas C Zachos
- Division of Gastroenterology and Hepatology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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36
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Lamprecht G, Hsieh CJ, Lissner S, Nold L, Heil A, Gaco V, Schäfer J, Turner JR, Gregor M. Intestinal anion exchanger down-regulated in adenoma (DRA) is inhibited by intracellular calcium. J Biol Chem 2009; 284:19744-53. [PMID: 19447883 DOI: 10.1074/jbc.m109.004127] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The Na/H exchanger 3 (NHE3) and the Cl/HCO(3) exchanger down-regulated in adenoma (DRA) together facilitate intestinal electroneutral NaCl absorption. Elevated Ca(2+)(i) inhibits NHE3 through mechanisms involving the PDZ domain proteins NHE3 kinase A regulatory protein (E3KARP) or PDZ kidney 1 (PDZK1). DRA also possesses a PDZ-binding motif, but the roles of interactions with E3KARP or PDZK1 and Ca(2+)(i) in DRA regulation are unknown. Wild type DRA and a mutant lacking the PDZ interaction motif (DRA-ETKFminus) were expressed constitutively in human embryonic kidney (HEK) and inducibly in Caco-2/BBE cells. DRA-mediated Cl/HCO(3) exchange was measured as intracellular pH changes. Ca(2+)(i) was assessed fluorometrically. DRA was induced 8-16-fold and was delivered to the apical surface of polarized Caco-2 cells. Putative anion transporter 1 and cystic fibrosis transmembrane regulator did not contribute to Cl/HCO(3) exchange in transfected Caco-2 cells. The calcium ionophore 4Br-A23187 inhibited DRA and DRA-ETKFminus in HEK cells, but only full-length DRA was inhibited in Caco-2 cells. In contrast, 100 microm UTP, which increased Ca(2+)(i), inhibited full-length DRA but not DRA-ETKFminus in Caco-2 and HEK cells. In HEK cells, which express little PDZK1, additional transfection of PDZK1 was required for UTP to inhibit DRA. As HEK cells do not express cystic fibrosis transmembrane regulator or NHE3, the data indicate that Ca(2+)(i)-dependent DRA inhibition is not because of modulation of other transport activities. In polarized epithelium, this inhibition requires interaction of DRA with PDZK1. Together with data from PDZK1(-/-) mice, these data underscore the prominent role of PDZK1 in Ca(2+)(i)-mediated inhibition of colonic NaCl absorption.
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Affiliation(s)
- Georg Lamprecht
- 1st Medical Department, University of Tübingen, 72076 Tübingen, Germany.
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37
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Zachos NC, Hodson C, Kovbasnjuk O, Li X, Thelin WR, Cha B, Milgram S, Donowitz M. Elevated intracellular calcium stimulates NHE3 activity by an IKEPP (NHERF4) dependent mechanism. Cell Physiol Biochem 2008; 22:693-704. [PMID: 19088451 DOI: 10.1159/000185553] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/24/2008] [Indexed: 01/09/2023] Open
Abstract
The ileal brush border (BB) contains four evolutionarily related multi-PDZ domain proteins including NHERF1, NHERF2, PDZK1 (NHERF3) and IKEPP (NHERF4). Why multiple related PDZ proteins are in a similar location in the same cell is unknown. However, some specificity in regulation of NHE3 activity has been identified. For example, elevated intracellular Ca(2+) ([Ca(2+)](i)) inhibition of NHE3 is reconstituted by NHERF2 but not NHERF1, and involves the formation of large NHE3 complexes. To further evaluate the specificity of the NHERF family in calcium regulation of NHE3 activity, the current study determined whether the four PDZ domain containing protein IKEPP reconstitutes elevated [Ca(2+)](i) regulation of NHE3. In vitro, IKEPP bound to the F2 region (aa 590-667) of NHE3 in overlay assays, which is the same region where NHERF1 and NHERF2 bind. PS120 cells lack endogenous NHE3 and IKEPP. Treatment of PS120/NHE3/IKEPP cells (stably transfected with NHE3 and IKEPP) with the Ca(2+) ionophore, 4-Br-A23187 (0.5 microM), stimulated NHE3 V(max) activity by approximately 40%. This was associated with an increase in plasma membrane expression of NHE3 by a similar amount. NHE3 activity and surface expression were unaffected by A23187 in PS120/NHE3 cells lacking IKEPP. Based on sucrose density gradient centrifugation, IKEPP was also shown to exist in large complexes, some of which overlap in size with NHE3, and the size of both NHE3 and IKEPP complexes decreased in parallel after [Ca(2+)](i) elevation. FRET experiments on fixed cells demonstrated that IKEPP and NHE3 directly associated at an intracellular site. Elevating [Ca(2+)](i) decreased this intracellular NHE3 and IKEPP association. In summary: (1) In the presence of IKEPP, elevated [Ca(2+)](i) stimulates NHE3 activity. This was associated with increased expression of NHE3 in the plasma membrane as well as a shift to smaller sizes of NHE3 and IKEPP containing complexes. (2) IKEPP directly binds NHE3 at its F2 C-terminal domain and directly associates with NHE3 in vivo (FRET). (3) Elevated [Ca(2+)](i) decreased the association of IKEPP and NHE3 in an intracellular compartment. Based on which NHERF family member is expressed in PS120 cells, elevated [Ca(2+)](i) stimulates (IKEPP), inhibits (NHERF2) or does not affect (NHERF1) NHE3 activity. This demonstrates that regulation of NHE3 depends on the nature of the NHERF family member associating with NHE3 and the accompanying NHE3 complexes.
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Affiliation(s)
- Nicholas C Zachos
- Department of Medicine and Physiology, Hopkins Center for Epithelial Disorders, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2195, USA
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He P, Zhang H, Yun CC. IRBIT, inositol 1,4,5-triphosphate (IP3) receptor-binding protein released with IP3, binds Na+/H+ exchanger NHE3 and activates NHE3 activity in response to calcium. J Biol Chem 2008; 283:33544-53. [PMID: 18829453 DOI: 10.1074/jbc.m805534200] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium (Ca2+) is a highly versatile second messenger that regulates various cellular processes. Previous studies showed that elevation of intracellular Ca2+ regulates the activity of Na+/H+ exchanger 3 (NHE3). However, the effect of Ca2+-dependent signaling on NHE3 activity varies depending on cell types. In this study, we report the identification of IP3 receptor-binding protein released with IP3 (IRBIT) as a NHE3 interacting protein and its role in regulation of NHE3 activity. IRBIT bound to the carboxyl-terminal domain of NHE3, which is necessary for acute regulation of NHE3. Ectopic expression of IRBIT resulted in Ca2+-dependent activation of NHE3 activity, whereas silencing of endogenous IRBIT resulted in inhibition of NHE3 activity. Ca2+-dependent stimulation of NHE3 activity was dependent on the binding of IRBIT to NHE3. Previously Ca2+-dependent inhibition of NHE3 was demonstrated in the presence of NHERF2. Co-expression of IRBIT was able to reverse the NHERF2-dependent inhibition of NHE3. We also showed that IRBIT-dependent activation of NHE3 involves exocytic trafficking of NHE3 to the plasma membrane and this activation was blocked by inhibition of calmodulin (CaM) or CaM-dependent kinase II. These results suggest that the overall effect of Ca2+ on NHE3 activity is balanced by IRBIT-dependent activation and NHERF2-dependent inhibition.
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Affiliation(s)
- Peijian He
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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Sarker R, Grønborg M, Cha B, Mohan S, Chen Y, Pandey A, Litchfield D, Donowitz M, Li X. Casein kinase 2 binds to the C terminus of Na+/H+ exchanger 3 (NHE3) and stimulates NHE3 basal activity by phosphorylating a separate site in NHE3. Mol Biol Cell 2008; 19:3859-70. [PMID: 18614797 DOI: 10.1091/mbc.e08-01-0019] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Na(+)/H(+) exchanger 3 (NHE3) is the epithelial-brush border isoform responsible for most intestinal and renal Na(+) absorption. Its activity is both up- and down-regulated under normal physiological conditions, and it is inhibited in most diarrheal diseases. NHE3 is phosphorylated under basal conditions and Ser/Thr phosphatase inhibitors stimulate basal exchange activity; however, the kinases involved are unknown. To identify kinases that regulate NHE3 under basal conditions, NHE3 was immunoprecipitated; LC-MS/MS of trypsinized NHE3 identified a novel phosphorylation site at S(719) of the C terminus, which was predicted to be a casein kinase 2 (CK2) phosphorylation site. This was confirmed by an in vitro kinase assay. The NHE3-S719A mutant but not NHE3-S719D had reduced NHE3 activity due to less plasma membrane NHE3. This was due to reduced exocytosis plus decreased plasma membrane delivery of newly synthesized NHE3. Also, NHE3 activity was inhibited by the CK2 inhibitor 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole DMAT when wild-type NHE3 was expressed in fibroblasts and Caco-2 cells, but the NHE3-S(719) mutant was fully resistant to DMAT. CK2 bound to the NHE3 C-terminal domain, between amino acids 590 and 667, a site different from the site it phosphorylates. CK2 binds to the NHE3 C terminus and stimulates basal NHE3 activity by phosphorylating a separate single site on the NHE3 C terminus (S(719)), which affects NHE3 trafficking.
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Affiliation(s)
- Rafiquel Sarker
- Division of Gastroenterology and Hepatology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Walker JA, Smith KGC. Dependence of surface monoclonal antibody binding on dynamic changes in FcgammaRIIb expression. Immunology 2008; 124:412-8. [PMID: 18217946 PMCID: PMC2440835 DOI: 10.1111/j.1365-2567.2007.02791.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Receptors for the Fc region of immunoglobulin G (FcgammaRs) are expressed on a broad range of haematopoietic cell types and are responsible for regulating antibody production and linking the humoral and effector responses. In response to a number of stimuli, such as cytokine signals or inflammation, FcgammaR expression at the cell surface is dynamically regulated. On B cells, we observed what appeared to be a correlation between CD22 expression and FcgammaRIIb expression when the latter was varied in a number of models. Further investigation revealed that this was specific to a particular anti-CD22 monoclonal antibody, which appeared to require stabilization by interaction with FcgammaRIIb for optimal binding to CD22. Since alterations in the regulation of FcgammaR expression are important in controlling immune responses and have been associated with a number of immune-mediated disease states, we suggest that it might be prudent to confirm the expression of cell surface markers by two independent methods. Furthermore, because the efficacy of therapeutic antibodies may depend upon their interaction with FcgammaRs, our results are relevant to their design and assessment.
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Affiliation(s)
- Jennifer A Walker
- Department of Medicine, Cambridge Institute for Medical Research, Addenbrooke's Hospital, Cambridge, UK.
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41
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Abstract
CD22 is an inhibitory coreceptor of the B-cell receptor (BCR), and plays a critical role in establishing signalling thresholds for B-cell activation. Like other coreceptors, the ability of CD22 to modulate B-cell signalling is critically dependent upon its proximity to the BCR, and this in turn is governed by the binding of its extracellular domain to alpha2,6-linked sialic acid ligands. Manipulation of CD22 ligand binding in various experimental settings has profound effects on B-cell signalling, but as yet there is no complete model for how ligand binding in vivo controls normal CD22 function. Several elegant studies have recently shed light on this issue, although the results appear to suggest two mutually exclusive models for the role of ligand binding; in either promoting or inhibiting, CD22 function. We shall therefore discuss these results in detail, and suggest possible approaches by which these conflicting experimental findings might be reconciled. We shall also consider a second important issue in CD22 biology, which relates to the role that defects in this receptor might play in mediating autoimmune disease. We review the current evidence for this, and discuss the importance of genetic background in modifying CD22 function and predisposition to autoimmunity.
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Affiliation(s)
- Jennifer A Walker
- Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Cambridge CB2 0XY, United Kingdom.
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42
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Abstract
NHE3 is the brush-border (BB) Na+/H+exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na+absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.
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Affiliation(s)
- Mark Donowitz
- Department of Medicine, GI Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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Murtazina R, Kovbasnjuk O, Zachos NC, Li X, Chen Y, Hubbard A, Hogema BM, Steplock D, Seidler U, Hoque KM, Tse CM, De Jonge HR, Weinman EJ, Donowitz M. Tissue-specific regulation of sodium/proton exchanger isoform 3 activity in Na(+)/H(+) exchanger regulatory factor 1 (NHERF1) null mice. cAMP inhibition is differentially dependent on NHERF1 and exchange protein directly activated by cAMP in ileum versus proximal tubule. J Biol Chem 2007; 282:25141-51. [PMID: 17580307 DOI: 10.1074/jbc.m701910200] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The multi-PDZ domain containing protein Na(+)/H(+) Exchanger Regulatory Factor 1 (NHERF1) binds to Na(+)/H(+) exchanger 3 (NHE3) and is associated with the brush border (BB) membrane of murine kidney and small intestine. Although studies in BB isolated from kidney cortex of wild type and NHERF1(-/-) mice have shown that NHERF1 is necessary for cAMP inhibition of NHE3 activity, a role of NHERF1 in NHE3 regulation in small intestine and in intact kidney has not been established. Here a method using multi-photon microscopy with the pH-sensitive dye SNARF-4F (carboxyseminaphthorhodafluors-4F) to measure BB NHE3 activity in intact murine tissue and use it to examine the role of NHERF1 in regulation of NHE3 activity. NHE3 activity in wild type and NHERF1(-/-) ileum and wild type kidney cortex were inhibited by cAMP, whereas the cAMP effect was abolished in kidney cortex of NHERF1(-/-) mice. cAMP inhibition of NHE3 activity in these two tissues is mediated by different mechanisms. In ileum, a protein kinase A (PKA)-dependent mechanism accounts for all cAMP inhibition of NHE3 activity since the PKA antagonist H-89 abolished the inhibitory effect of cAMP. In kidney, both PKA-dependent and non-PKA-dependent mechanisms were involved, with the latter reproduced by the effect on an EPAC (exchange protein directly activated by cAMP) agonist (8-(4-chlorophenylthio)-2'O-Me-cAMP). In contrast, the EPAC agonist had no effect in proximal tubules in NHERF1(-/-) mice. These data suggest that in proximal tubule, NHERF1 is required for all cAMP inhibition of NHE3, which occurs through both EPAC-dependent and PKA-dependent mechanisms; in contrast, cAMP inhibits ileal NHE3 only by a PKA-dependent pathway, which is independent of NHERF1 and EPAC.
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Affiliation(s)
- Rakhilya Murtazina
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Murtazina R, Kovbasnjuk O, Donowitz M, Li X. Na+/H+ exchanger NHE3 activity and trafficking are lipid Raft-dependent. J Biol Chem 2006; 281:17845-55. [PMID: 16648141 DOI: 10.1074/jbc.m601740200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A previous study showed that approximately 25-50% of rabbit ileal brush border (BB) Na(+)/H(+) exchanger NHE3 is in lipid rafts (LR) (Li, X., Galli, T., Leu, S., Wade, J. B., Weinman E. J., Leung, G., Cheong, A., Louvard, D., and Donowitz, M. (2001) J. Physiol. (Lond.) 537, 537-552). Here, we examined the role of LR in NHE3 transport activity using a simpler system: opossum kidney (OK) cells (a renal proximal tubule epithelial cell line) containing NHE3. approximately 50% of surface (biotinylated) NHE3 in OK cells distributed in LR by density gradient centrifugation. Disruption of LR with methyl-beta-cyclodextrin (MbetaCD) decreased NHE3 activity and increased K'(H+)(i), but K(m)((Na+)) was not affected. The MbetaCD effect was completely reversed by repletion of cholesterol, but not by an inactive analog of cholesterol (cholestane-3beta,5alpha,6beta-triol). The MbetaCD effect was specific for NHE3 activity because it did not alter Na(+)-dependent l-Ala uptake. MbetaCD did not alter OK cell BB topology and did not change the surface amount of NHE3, but greatly reduced the rate of NHE3 endocytosis. The effects of inhibiting phosphatidylinositol 3-kinase and of MbetaCD on NHE3 activity were not additive, indicating a common inhibitory mechanism. In contrast, 8-bromo-cAMP and MbetaCD inhibition of NHE3 was additive, indicating different mechanisms for inhibition of NHE3 activity. Approximately 50% of BB NHE3 and only approximately 11% of intracellular NHE3 in polarized OK cells were in LR. In summary, the BB pool of NHE3 in LR is functionally active because MbetaCD treatment decreased NHE3 basal activity. The LR pool is necessary for multiple kinetic aspects of normal NHE3 activity, including V(max) and K'(H+)(i), and also for multiple aspects of NHE3 trafficking, including at least basal endocytosis and phosphatidylinositol 3-kinase-dependent basal exocytosis. Because the C-terminal domain of NHE3 is necessary for its regulation and because the changes in NHE3 kinetics with MbetaCD resemble those with second messenger regulation of NHE3, these results suggest that the NHE3 C terminus may be involved in the MbetaCD sensitivity of NHE3.
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Affiliation(s)
- Rakhilya Murtazina
- Departments of Physiology and Medicine, Division of Gastroenterology, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, Baltimore, MD 21205, USA
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Cha B, Tse M, Yun C, Kovbasnjuk O, Mohan S, Hubbard A, Arpin M, Donowitz M. The NHE3 juxtamembrane cytoplasmic domain directly binds ezrin: dual role in NHE3 trafficking and mobility in the brush border. Mol Biol Cell 2006; 17:2661-73. [PMID: 16540524 PMCID: PMC1474801 DOI: 10.1091/mbc.e05-09-0843] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Based on physiological studies, the epithelial brush-border (BB) Na+/H+ antiporter3 (NHE3) seems to associate with the actin cytoskeleton both by binding to and independently of the PDZ domain containing proteins NHERF1 and NHERF2. We now show that NHE3 directly binds ezrin at a site in its C terminus between aa 475-589, which is separate from the PSD95/dlg/zonular occludens-1 (PDZ) interacting domain. This is an area predicted to be alpha-helical, with a positive aa cluster on one side (K516, R520, and R527). Point mutations of these positively charged aa reduced (NHE3 double mutant [R520F, R527F]) or abolished (NHE3 triple mutant [K516Q, R520F, R 527F]) ezrin binding. Functional consequences of these NHE3 point mutants included the following. 1) A marked decrease in surface amount with a greater decrease in NHE3 activity. 2) Decreased surface expression due to decreased rates of exocytosis and plasma membrane delivery of newly synthesized NHE3, with normal total expression levels and slightly reduced endocytosis rates. 3) A longer plasma membrane half-life of mutant NHE3 with normal total half-life. 4) Decreased BB mobile fraction of NHE3 double mutant. These results show that NHE3 binds ezrin directly as well as indirectly and suggest that the former is related to 1) the exocytic trafficking of and plasma membrane delivery of newly synthesized NHE3, which determines the amount of plasma membrane NHE3 and partially determines NHE3 activity, and 2) BB mobility of NHE3, which may increase its delivery from microvilli to the intervillus clefts, perhaps for NHE3-regulated endocytosis.
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Affiliation(s)
- Boyoung Cha
- *Departments of Physiology and Medicine, Gastroenterology Division and
| | - Ming Tse
- *Departments of Physiology and Medicine, Gastroenterology Division and
| | - Chris Yun
- *Departments of Physiology and Medicine, Gastroenterology Division and
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322
| | - Olga Kovbasnjuk
- *Departments of Physiology and Medicine, Gastroenterology Division and
| | - Sachin Mohan
- *Departments of Physiology and Medicine, Gastroenterology Division and
| | - Ann Hubbard
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Monique Arpin
- Unite Mixte de Recherche 144, Centre National de la Recherche Scientifique/Institut Curie, 75248 Paris, France
| | - Mark Donowitz
- *Departments of Physiology and Medicine, Gastroenterology Division and
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Narins SC, Ramakrishnan R, Park EH, Bolno PB, Haggerty DA, Smith PR, Meyers WC, Abedin MZ. Protein kinase C-alpha regulation of gallbladder Na+ transport becomes progressively more dysfunctional during gallstone formation. ACTA ACUST UNITED AC 2005; 146:227-37. [PMID: 16194684 DOI: 10.1016/j.lab.2005.05.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2004] [Revised: 05/03/2005] [Accepted: 05/19/2005] [Indexed: 10/25/2022]
Abstract
Gallbladder Na+ absorption and biliary Ca2+ are both increased during gallstone formation and may promote cholesterol nucleation. Na+/H+ exchange (NHE) is a major pathway for gallbladder Na+ transport. Ca2+-dependent second messengers, including protein kinase C (PKC), inhibit basal gallbladder Na+ transport. Multiple PKC isoforms with species- and tissue-specific expression have been reported. In this study we sought to characterize Ca2+-dependent PKC isoforms in gallbladder and to examine their roles in Na+ transport during gallstone formation. Gallbladders were harvested from prairie dogs fed either nonlithogenic chow or 1.2% cholesterol-enriched diet for varying periods to induce various stages of gallstone formation. PKC was activated with the use of phorboldibutyrate, and we assessed gallbladder NHE regulation by measuring unidirectional Na+ flux and dimethylamiloride-inhibitable 22Na+ uptake. We measured gallbladder PKC activity with the use of histone III-S phosphorylation and used Gö 6976 to determine PKC-alpha contributions. Gallbladder PKC isoform messenger RNA and protein expression were examined with the use of Northern- and Western-blot analysis, respectively. Prairie dog and human gallbladder expresses PKC-alpha, betaII, and delta isoforms. The PKC activation significantly decreased gallbladder J(Na)(ms) and reduced baseline 22Na+ uptake by inhibiting NHE. PKC-alpha mediated roughly 42% of total PKC activity under basal conditions. PKC-alpha regulates basal gallbladder Na+ transport by way of stimulation of NHE isoform NHE-2 and inhibition of isoform NHE-3. PKC-alpha blockade reversed PKC-induced inhibition of J(Na)(ms) and 22Na+ uptake by about 45% in controls but was progressively less effective during gallstone formation. PKC-alpha contribution to total PKC activity is progressively reduced, whereas expression of PKC-alpha mRNA, and protein increases significantly during gallstone formation. We conclude that PKC-alpha regulation of gallbladder NHE becomes progressively more dysfunctional and may in part account for the increased Na+ absorption observed during gallstone formation.
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Affiliation(s)
- Seth C Narins
- Department of Surgery, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102-1192, USA
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Fouassier L, Nichols MT, Gidey E, McWilliams RR, Robin H, Finnigan C, Howell KE, Housset C, Doctor RB. Protein kinase C regulates the phosphorylation and oligomerization of ERM binding phosphoprotein 50. Exp Cell Res 2005; 306:264-73. [PMID: 15878350 DOI: 10.1016/j.yexcr.2005.02.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2004] [Revised: 02/08/2005] [Accepted: 02/14/2005] [Indexed: 11/18/2022]
Abstract
Ezrin-Radixin-Moesin (ERM) binding phosphoprotein 50 (EBP50, a.k.a. NHERF-1) is a scaffold protein essential for the localization and coordinated activity of apical transporters, enzymes and receptors in epithelial cells. EBP50 acts via multiple protein binding interactions, including oligomerization through interactions of its PSD95-Dlg-ZO1 (PDZ) domains. EBP50 can be phosphorylated on multiple sites and phosphorylation of specific sites modulates the extent of oligomerization. The aim of the present study was to test the capacity of protein kinase C (PKC) to phosphorylate EBP50 and to regulate its oligomerization. In vitro experiments showed that the catalytic subunit of PKC directly phosphorylates EBP50. In HEK-293 cells transfected with rat EBP50 cDNA, a treatment with 12 myristate 13-acetate (PMA) induced a translocation of PKCalpha and beta isoforms to the membrane and increased 32P incorporation into EBP50. In co-transfection/co-precipitation studies, PMA treatment stimulated EBP50 oligomerization. Mass spectrometry analysis of full-length EBP50 and phosphorylation analyses of specific domains, and of mutated or truncated forms of EBP50, indicated that PKC-induced phosphorylation of EBP50 occurred on the Ser337/Ser338 residue within the carboxyl-tail domain of the protein. Truncation of Ser337/Ser338 also diminished PKC-induced oligomerization of EBP50. These results suggest the PKC signaling pathway can impact EBP50-dependent cellular functions by regulating EBP50 oligomerization.
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Affiliation(s)
- Laura Fouassier
- Inserm U680, UPMC and Service de Biochimie et d'Hormonologie AP-HP, Hôpital Tenon, Faculté de Médecine Saint-Antoine, Paris, F-75012, France
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48
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Abstract
The sodium/hydrogen exchange (NHE) gene family plays an integral role in neutral sodium absorption in the mammalian intestine. The NHE gene family is comprised of nine members that are categorized by cellular localization (i.e., plasma membrane or intracellular). In the gastrointestinal (GI) tract of multiple species, there are resident plasma membrane isoforms including NHE1 (basolateral) and NHE2 (apical), recycling isoforms (NHE3), as well as intracellular isoforms (NHE6, 7, 9). NHE3 recycles between the endosomal compartment and the apical plasma membrane and functions in both locations. NHE3 regulation occurs during normal digestive processes and is often inhibited in diarrheal diseases. The C terminus of NHE3 binds multiple regulatory proteins to form large protein complexes that are involved in regulation of NHE3 trafficking to and from the plasma membrane, turnover number, and protein phosphorylation. NHE1 and NHE2 are not regulated by trafficking. NHE1 interacts with multiple regulatory proteins that affect phosphorylation; however, whether NHE1 exists in large multi-protein complexes is unknown. Although intestinal and colonic sodium absorption appear to involve at least NHE2 and NHE3, future studies are necessary to more accurately define their relative contributions to sodium absorption during human digestion and in pathophysiological conditions.
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Affiliation(s)
- Nicholas C Zachos
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195, USA.
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Cha B, Kim JH, Hut H, Hogema BM, Nadarja J, Zizak M, Cavet M, Lee-Kwon W, Lohmann SM, Smolenski A, Tse CM, Yun C, de Jonge HR, Donowitz M. cGMP inhibition of Na+/H+ antiporter 3 (NHE3) requires PDZ domain adapter NHERF2, a broad specificity protein kinase G-anchoring protein. J Biol Chem 2005; 280:16642-50. [PMID: 15722341 DOI: 10.1074/jbc.m500505200] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Electroneutral NaCl absorption mediated by Na+/H+ exchanger 3 (NHE3) is important in intestinal and renal functions related to water/Na+ homeostasis. cGMP inhibits NHE3 in intact epithelia. However, unexpectedly it failed to inhibit NHE3 stably transfected in PS120 cells, even upon co-expression of cGMP-dependent protein kinase type II (cGKII). Additional co-expression of NHERF2, the tandem PDZ domain adapter protein involved in cAMP inhibition of NHE3, restored cGMP as well as cAMP inhibition, whereas NHERF1 solely restored cAMP inhibition. In vitro conditions were identified in which NHERF2 but not NHERF1 bound cGKII. The NHERF2 PDZ2 C terminus, which binds NHE3, also bound cGKII. A non-myristoylated mutant of cGKII did not support cGMP inhibition of NHE3. Although cGKI also bound NHERF2 in vitro, it did not evoke inhibition of NHE3 unless a myristoylation site was added. These results show that NHERF2, acting as a novel protein kinase G-anchoring protein, is required for cGMP inhibition of NHE3 and that cGKII must be bound both to the plasma membrane by its myristoyl anchor and to NHERF2 to inhibit NHE3.
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Affiliation(s)
- Boyoung Cha
- Department of Physiology, GI Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Aires V, Hichami A, Moutairou K, Khan NA. Docosahexaenoic acid and other fatty acids induce a decrease in pHi in Jurkat T-cells. Br J Pharmacol 2004; 140:1217-26. [PMID: 14645139 PMCID: PMC1574148 DOI: 10.1038/sj.bjp.0705563] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. Docosahexaenoic acid (DHA) induced rapid (t1/2=33 s) and dose-dependent decreases in pHi in BCECF-loaded human (Jurkat) T-cells. Addition of 5-(N,N-dimethyl)-amiloride, an inhibitor of Na+/H+ exchanger, prolonged DHA-induced acidification as a function of time, indicating that the exchanger is implicated in pHi recovery. 2. Other fatty acids like oleic acid, arachidonic acid, eicosapentaenoic acid, but not palmitic acid, also induced a fall in pHi in these cells. 3. To assess the role of calcium in the DHA-induced acidification, we conducted experiments in Ca2+-free (0% Ca2+) and Ca2+-containing (100% Ca2+) buffer. We observed that there was no difference in the degree of DHA-induced transient acidification in both the experimental conditions, though pHi recovery was faster in 0% Ca2+ medium than that in 100% Ca2+ medium. 4. In the presence of BAPTA, a calcium chelator, a rapid recovery of DHA-induced acidosis was observed. Furthermore, addition of CaCl2 into 0% Ca2+ medium curtailed DHA-evoked rapid pHi recovery. In 0% Ca2+ medium, containing BAPTA, DHA did not evoke increases in [Ca2+]i, though this fatty acid still induced a rapid acidification in these cells. These observations suggest that calcium is implicated in the long-lasting DHA-induced acidosis. 5. DHA-induced rapid acidification may be due to its deprotonation in the plasma membrane (flip-flop model), as suggested by the following observations: (1) DHA with a -COOH group induced intracellular acidification, but this fatty acid with a -COOCH3 group failed to do so, and (2) DHA, but not propionic acid, -induced acidification was completely reversed by addition of fatty acid-free bovine serum albumin in these cells. 6. These results suggest that DHA induces acidosis via deprotonation and Ca2+ mobilization in human T-cells.
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Affiliation(s)
- Virginie Aires
- UPRES Lipides and Nutrition, Université de Bourgogne, Faculté des Sciences de la vie, 6, Boulevard Gabriel, Dijon 21000, France
| | - Aziz Hichami
- UPRES Lipides and Nutrition, Université de Bourgogne, Faculté des Sciences de la vie, 6, Boulevard Gabriel, Dijon 21000, France
| | - Kabirou Moutairou
- UPRES Lipides and Nutrition, Université de Bourgogne, Faculté des Sciences de la vie, 6, Boulevard Gabriel, Dijon 21000, France
| | - Naim Akhtar Khan
- UPRES Lipides and Nutrition, Université de Bourgogne, Faculté des Sciences de la vie, 6, Boulevard Gabriel, Dijon 21000, France
- Author for correspondence:
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