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Salari A, Zhou K, Nikolovska K, Seidler U, Amiri M. Human Colonoid-Myofibroblast Coculture for Study of Apical Na +/H + Exchangers of the Lower Cryptal Neck Region. Int J Mol Sci 2023; 24:ijms24054266. [PMID: 36901695 PMCID: PMC10001859 DOI: 10.3390/ijms24054266] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Revised: 02/17/2023] [Accepted: 02/18/2023] [Indexed: 02/25/2023] Open
Abstract
Cation and anion transport in the colonocyte apical membrane is highly spatially organized along the cryptal axis. Because of lack of experimental accessibility, information about the functionality of ion transporters in the colonocyte apical membrane in the lower part of the crypt is scarce. The aim of this study was to establish an in vitro model of the colonic lower crypt compartment, which expresses the transit amplifying/progenitor (TA/PE) cells, with accessibility of the apical membrane for functional study of lower crypt-expressed Na+/H+ exchangers (NHEs). Colonic crypts and myofibroblasts were isolated from human transverse colonic biopsies, expanded as three-dimensional (3D) colonoids and myofibroblast monolayers, and characterized. Filter-grown colonic myofibroblast-colonic epithelial cell (CM-CE) cocultures (myofibroblasts on the bottom of the transwell and colonocytes on the filter) were established. The expression pattern for ion transport/junctional/stem cell markers of the CM-CE monolayers was compared with that of nondifferentiated (EM) and differentiated (DM) colonoid monolayers. Fluorometric pHi measurements were performed to characterize apical NHEs. CM-CE cocultures displayed a rapid increase in transepithelial electrical resistance (TEER), paralleled by downregulation of claudin-2. They maintained proliferative activity and an expression pattern resembling TA/PE cells. The CM-CE monolayers displayed high apical Na+/H+ exchange activity, mediated to >80% by NHE2. Human colonoid-myofibroblast cocultures allow the study of ion transporters that are expressed in the apical membrane of the nondifferentiated colonocytes of the cryptal neck region. The NHE2 isoform is the predominant apical Na+/H+ exchanger in this epithelial compartment.
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Affiliation(s)
- Azam Salari
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, 30625 Hannover, Germany
| | - Kunyan Zhou
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, 30625 Hannover, Germany
- Department of Thyroid Surgery, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310027, China
| | - Katerina Nikolovska
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, 30625 Hannover, Germany
| | - Ursula Seidler
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, 30625 Hannover, Germany
- Correspondence: (U.S.); (M.A.); Tel.: +49-511-532-9427 (U.S.); Fax: +49-511-532-8428 (U.S.)
| | - Mahdi Amiri
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, 30625 Hannover, Germany
- Correspondence: (U.S.); (M.A.); Tel.: +49-511-532-9427 (U.S.); Fax: +49-511-532-8428 (U.S.)
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Nikolovska K, Seidler UE, Stock C. The Role of Plasma Membrane Sodium/Hydrogen Exchangers in Gastrointestinal Functions: Proliferation and Differentiation, Fluid/Electrolyte Transport and Barrier Integrity. Front Physiol 2022; 13:899286. [PMID: 35665228 PMCID: PMC9159811 DOI: 10.3389/fphys.2022.899286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 04/19/2022] [Indexed: 12/11/2022] Open
Abstract
The five plasma membrane Na+/H+ exchanger (NHE) isoforms in the gastrointestinal tract are characterized by distinct cellular localization, tissue distribution, inhibitor sensitivities, and physiological regulation. NHE1 (Slc9a1) is ubiquitously expressed along the gastrointestinal tract in the basolateral membrane of enterocytes, but so far, an exclusive role for NHE1 in enterocyte physiology has remained elusive. NHE2 (Slc9a2) and NHE8 (Slc9a8) are apically expressed isoforms with ubiquitous distribution along the colonic crypt axis. They are involved in pHi regulation of intestinal epithelial cells. Combined use of a knockout mouse model, intestinal organoid technology, and specific inhibitors revealed previously unrecognized actions of NHE2 and NHE8 in enterocyte proliferation and differentiation. NHE3 (Slc9a3), expressed in the apical membrane of differentiated intestinal epithelial cells, functions as the predominant nutrient-independent Na+ absorptive mechanism in the gut. The new selective NHE3 inhibitor (Tenapanor) allowed discovery of novel pathophysiological and drug-targetable NHE3 functions in cystic-fibrosis associated intestinal obstructions. NHE4, expressed in the basolateral membrane of parietal cells, is essential for parietal cell integrity and acid secretory function, through its role in cell volume regulation. This review focuses on the expression, regulation and activity of the five plasma membrane Na+/H+ exchangers in the gastrointestinal tract, emphasizing their role in maintaining intestinal homeostasis, or their impact on disease pathogenesis. We point to major open questions in identifying NHE interacting partners in central cellular pathways and processes and the necessity of determining their physiological role in a system where their endogenous expression/activity is maintained, such as organoids derived from different parts of the gastrointestinal tract.
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Donowitz M. Has a physiologic function for NHE2 finally been identified? Acta Physiol (Oxf) 2022; 234:e13792. [PMID: 35094506 PMCID: PMC11283681 DOI: 10.1111/apha.13792] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 01/22/2022] [Accepted: 01/24/2022] [Indexed: 11/29/2022]
Affiliation(s)
- Mark Donowitz
- Department of Medicine and Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Han Y, Yun CC. Ubiquitin-specific peptidase 7 (USP7) and USP10 mediate deubiquitination of human NHE3 regulating its expression and activity. FASEB J 2020; 34:16476-16488. [PMID: 33095475 DOI: 10.1096/fj.202001875r] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 09/21/2020] [Accepted: 10/06/2020] [Indexed: 12/19/2022]
Abstract
Na+ /H+ exchanger NHE3 of human or primates differs from NHE3 of other animals by having a PY motif, which mediates interaction with the E3 ubiquitin (Ub) ligase Nedd4-2. Ub-conjugation of human NHE3 by Nedd4-2 regulates endocytosis of NHE3 but does not affect its cellular expression. Because Ub-conjugation is a reversible process, the aim of this study is to identify deubiquitinating enzyme (DUB) regulating the post-endosomal fate of human NHE3. Using an activity-based chemical screening, we identified ubiquitin specific protease-7 (USP7) and USP10 that bind NHE3. The roles of DUBs in regulation of NHE3 were studied by determining the effects of silencing of USP7 and USP10. Knockdown of USP7 or USP10 resulted in increased NHE3 ubiquitination and decreased NHE3 expression at the surface membrane and cellular level. The endocytic retrieval of NHE3 was promoted by depletion of USP7 or USP10, with increased association of NHE3 with Rab5a and Rab7. Inhibition of USP7 and USP10 by chemical inhibitors or knockdown had an additive effect on NHE3. In addition, NHE3 half-life was reduced accounting for decreased NHE3 protein abundance. NHE3 is inhibited by protein kinase A. Activation of PKA by forskolin decreased the binding of USP7 and USP10 to NHE3, while increasing ubiquitination of NHE3. Knockdown of USP10 had an additive effect on PKA-dependent inhibition of NHE3. These findings demonstrate that USP7 and USP10 are DUBs that regulate NHE3 ubiquitination and expression, and reveal a new mechanism of NHE3 inhibition involving DUBs.
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Affiliation(s)
- Yiran Han
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA.,Gastroenterology Research, Atlanta VA Medical Center, Decatur, GA, USA
| | - C Chris Yun
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA.,Gastroenterology Research, Atlanta VA Medical Center, Decatur, GA, USA.,Cell and Molecular Biology Research Program, Winship Cancer Institute, Emory University School of Medicine, Atlanta, GA, USA
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Pedersen SF, Counillon L. The SLC9A-C Mammalian Na +/H + Exchanger Family: Molecules, Mechanisms, and Physiology. Physiol Rev 2019; 99:2015-2113. [PMID: 31507243 DOI: 10.1152/physrev.00028.2018] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Na+/H+ exchangers play pivotal roles in the control of cell and tissue pH by mediating the electroneutral exchange of Na+ and H+ across cellular membranes. They belong to an ancient family of highly evolutionarily conserved proteins, and they play essential physiological roles in all phyla. In this review, we focus on the mammalian Na+/H+ exchangers (NHEs), the solute carrier (SLC) 9 family. This family of electroneutral transporters constitutes three branches: SLC9A, -B, and -C. Within these, each isoform exhibits distinct tissue expression profiles, regulation, and physiological roles. Some of these transporters are highly studied, with hundreds of original articles, and some are still only rudimentarily understood. In this review, we present and discuss the pioneering original work as well as the current state-of-the-art research on mammalian NHEs. We aim to provide the reader with a comprehensive view of core knowledge and recent insights into each family member, from gene organization over protein structure and regulation to physiological and pathophysiological roles. Particular attention is given to the integrated physiology of NHEs in the main organ systems. We provide several novel analyses and useful overviews, and we pinpoint main remaining enigmas, which we hope will inspire novel research on these highly versatile proteins.
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Affiliation(s)
- S F Pedersen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark; and Université Côte d'Azur, CNRS, Laboratoire de Physiomédecine Moléculaire, LP2M, France, and Laboratories of Excellence Ion Channel Science and Therapeutics, Nice, France
| | - L Counillon
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark; and Université Côte d'Azur, CNRS, Laboratoire de Physiomédecine Moléculaire, LP2M, France, and Laboratories of Excellence Ion Channel Science and Therapeutics, Nice, France
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Yu Y, Seidler A, Zhou K, Yuan Z, Yeruva S, Amiri M, Yun CC, Nikolovska K, Seidler U. Expression, Localization and Functional Activity of the Major Na⁺/H⁺ Exchange Isoforms Expressed in the Intestinal Cell Line Caco-2BBe. Cell Physiol Biochem 2019; 52:1017-1038. [PMID: 30977986 PMCID: PMC7104346 DOI: 10.33594/000000070] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 02/25/2019] [Indexed: 12/15/2022] Open
Abstract
Background/Aims Enterocytes express a number of NHE isoforms with presumed localization in the apical (NHE2, 3 and 8) or basolateral (NHE1) membrane. Functional activity and localization of enterocyte NHE isoforms were assessed using fully differentiated Caco-2BBe cells, whose genetic expression profile closely resembles mature enterocytes. Methods The activity of the different NHEs was analyzed by fluorometric pHi-metry in a perfusion chamber with separate apical and basolateral perfusion, using specific inhibitors and shRNA knockdown of NHE2. The expression of the NHEs and of other relevant acid extrusion transporters was quantified by qPCR. Results Quantitative comparison of the mRNA expression levels of the different NHE isoforms in 14 day-differentiated Caco-2BBe cells showed the following order: NHE2>NHE8>NHE3>NHE1. Acid-activated NHE exchange rates in the basolateral membrane were >6-fold higher than in the apical membrane. 79 ± 3 % of the acid-activated basolateral Na+/H+ exchange rate displayed a NHE1-typical inhibitor profile, and no NHE2/3/8 typical activity could be observed. Analysis of the apical Na+/H+ exchange rates revealed that approximately 51 ± 3 % of the total apical activity displayed a NHE2/8-typical inhibitor profile and 31 ± 6 % a NHE3-typical inhibitor profile. Because no selective NHE2 inhibitor is available, a stable NHE2 knockdown cell line (C2NHE2KD) was generated. C2NHE2KD displayed a reduced NHE2-typical apical Na+/H+ exchange rate and maintained a lower steady-state pHi, despite high expression levels of other acid extruders, in particular NBCn1 (Slc4a7). Conclusion Differentiated Caco-2BBe cells display particularly high mRNA expression levels of NHE2, which can be functionally identified in the apical membrane. Although at low intracellular pH, NHE2 transport rate was far lower than that of NHE1. NHE2 activity was nevertheless essential for the maintenance of the steady-state pHi of these cells.
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Affiliation(s)
- Yan Yu
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Anna Seidler
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Kunyan Zhou
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Zhenglin Yuan
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Sunil Yeruva
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Mahdi Amiri
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany
| | - Chris C Yun
- Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, GA, USA
| | | | - Ursula Seidler
- Department of Gastroenterology, Hannover Medical School, Hannover, Germany,
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Flinck M, Kramer SH, Schnipper J, Andersen AP, Pedersen SF. The acid-base transport proteins NHE1 and NBCn1 regulate cell cycle progression in human breast cancer cells. Cell Cycle 2018; 17:1056-1067. [PMID: 29895196 DOI: 10.1080/15384101.2018.1464850] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Precise acid-base homeostasis is essential for maintaining normal cell proliferation and growth. Conversely, dysregulated acid-base homeostasis, with increased acid extrusion and marked extracellular acidification, is an enabling feature of solid tumors, yet the mechanisms through which intra- and extracellular pH (pHi, pHe) impact proliferation and growth are incompletely understood. The aim of this study was to determine the impact of pH, and specifically of the Na+/H+ exchanger NHE1 and Na+, HCO3- transporter NBCn1, on cell cycle progression and its regulators in human breast cancer cells. Reduction of pHe to 6.5, a common condition in tumors, significantly delayed cell cycle progression in MCF-7 human breast cancer cells. The NHE1 protein level peaked in S phase and that of NBCn1 in G2/M. Steady state pHi changed through the cell cycle, from 7.1 in early S phase to 6.8 in G2, recovering again in M phase. This pattern, as well as net acid extrusion capacity, was dependent on NHE1 and NBCn1. Accordingly, knockdown of either NHE1 or NBCn1 reduced proliferation, prolonged cell cycle progression in a manner involving S phase prolongation and delayed G2/M transition, and altered the expression pattern and phosphorylation of cell cycle regulatory proteins. Our work demonstrates, for the first time, that both NHE1 and NBCn1 regulate cell cycle progression in breast cancer cells, and we propose that this involves cell cycle phase-specific pHi regulation by the two transporters.
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Affiliation(s)
- Mette Flinck
- a Section for Cell Biology and Physiology, Department of Biology , University of Copenhagen , Copenhagen Ø , Denmark
| | - Signe Hoejland Kramer
- a Section for Cell Biology and Physiology, Department of Biology , University of Copenhagen , Copenhagen Ø , Denmark
| | - Julie Schnipper
- a Section for Cell Biology and Physiology, Department of Biology , University of Copenhagen , Copenhagen Ø , Denmark
| | - Anne Poder Andersen
- a Section for Cell Biology and Physiology, Department of Biology , University of Copenhagen , Copenhagen Ø , Denmark
| | - Stine Falsig Pedersen
- a Section for Cell Biology and Physiology, Department of Biology , University of Copenhagen , Copenhagen Ø , Denmark
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Olesen CW, Vogensen J, Axholm I, Severin M, Schnipper J, Pedersen IS, von Stemann JH, Schrøder JM, Christensen DP, Pedersen SF. Trafficking, localization and degradation of the Na +,HCO 3- co-transporter NBCn1 in kidney and breast epithelial cells. Sci Rep 2018; 8:7435. [PMID: 29743600 PMCID: PMC5943355 DOI: 10.1038/s41598-018-25059-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Accepted: 04/13/2018] [Indexed: 01/28/2023] Open
Abstract
The Na+;HCO3− co-transporter NBCn1 (SLC4A7) is a major regulator of intracellular pH yet its trafficking and turnover are essentially unstudied. Here, we used MDCK-II and MCF-7 cells to investigate these processes in epithelial cells. GFP-NBCn1 membrane localization was abolished by truncation of the full NBCn1 C-terminal tail (C-tail) yet did not require the C-terminal PDZ-binding motif (ETSL). Glutathione-S-Transferase-pulldown of the C-tail followed by mass spectrometry analysis revealed putative interactions with multiple sorting-, degradation- and retention factors, including the scaffolding protein RACK1. Pulldown of FLAG-tagged deletion constructs mapped the RACK1 interaction to the proximal NBCn1 C-tail. Proximity Ligation Assay and co-immunoprecipitation confirmed that native NBCn1 interacts with RACK1 in a cellular context. Consistent with a functional role of this complex, RACK1 knockdown reduced NBCn1 membrane localization without affecting total NBCn1 expression. Notably, only non-confluent cells exhibited detectable NBCn1-RACK1 plasma membrane co-localization, suggesting that RACK1 regulates the trafficking of NBCn1 to the membrane. Whereas total NBCn1 degradation was slow, with a half-life of more than 24 h, one-third of surface NBCn1 was constitutively endocytosed from the basolateral membrane within 60 min. This suggests that a fraction of NBCn1 exhibits recycling between the basolateral membrane and intracellular compartment(s). Our findings have important implications for understanding NBCn1 regulation as well as its dysregulation in disease.
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Affiliation(s)
- Christina Wilkens Olesen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Jens Vogensen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Ida Axholm
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Marc Severin
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Julie Schnipper
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Isabella Skandorff Pedersen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Jakob Hjorth von Stemann
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Jacob Morville Schrøder
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Dan Ploug Christensen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark.
| | - Stine Falsig Pedersen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark.
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Pedersen AK, Mendes Lopes de Melo J, Mørup N, Tritsaris K, Pedersen SF. Tumor microenvironment conditions alter Akt and Na +/H + exchanger NHE1 expression in endothelial cells more than hypoxia alone: implications for endothelial cell function in cancer. BMC Cancer 2017; 17:542. [PMID: 28806945 PMCID: PMC5556346 DOI: 10.1186/s12885-017-3532-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 08/03/2017] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Chronic angiogenesis is a hallmark of most tumors and takes place in a hostile tumor microenvironment (TME) characterized by hypoxia, low nutrient and glucose levels, elevated lactate and low pH. Despite this, most studies addressing angiogenic signaling use hypoxia as a proxy for tumor conditions. Here, we compared the effects of hypoxia and TME conditions on regulation of the Na+/H+ exchanger NHE1, Ser/Thr kinases Akt1-3, and downstream effectors in endothelial cells. METHODS Human umbilical vein endothelial cells (HUVEC) and Ea.hy926 endothelial cells were exposed to simulated TME (1% hypoxia, low serum, glucose, pH, high lactate) or 1% hypoxia for 24 or 48 h, with or without NHE1 inhibition or siRNA-mediated knockdown. mRNA and protein levels of NHE1, Akt1-3, and downstream effectors were assessed by qPCR and Western blotting, vascular endothelial growth factor (VEGF) release by ELISA, and motility by scratch assay. RESULTS Within 24 h, HIF-1α level and VEGF mRNA level were increased robustly by TME and modestly by hypoxia alone. The NHE1 mRNA level was decreased by both hypoxia and TME, and NHE1 protein was reduced by TME in Ea.hy926 cells. Akt1-3 mRNA was detected in HUVEC and Ea.hy926 cells, Akt1 most abundantly. Akt1 protein expression was reduced by TME yet unaffected by hypoxia, while Akt phosphorylation was increased by TME. The Akt loss was partly reversed by MCF-7 human breast cancer cell conditioned medium, suggesting that in vivo, the cancer cell secretome may compensate for adverse effects of TME on endothelial cells. TME, yet not hypoxia, reduced p70S6 kinase activity and ribosomal protein S6 phosphorylation and increased eIF2α phosphorylation, consistent with inhibition of protein translation. Finally, TME reduced Retinoblastoma protein phosphorylation and induced poly-ADP-ribose polymerase (PARP) cleavage consistent with inhibition of proliferation and induction of apoptosis. NHE1 knockdown, mimicking the effect of TME on NHE1 expression, reduced Ea.hy926 migration. TME effects on HIF-1α, VEGF, Akt, translation, proliferation or apoptosis markers were unaffected by NHE1 knockdown/inhibition. CONCLUSIONS NHE1 and Akt are downregulated by TME conditions, more potently than by hypoxia alone. This inhibits endothelial cell migration and growth in a manner likely modulated by the cancer cell secretome.
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Affiliation(s)
- A K Pedersen
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Panum Institute, Blegdamsvej 3B, 2200, Copenhagen, Denmark
| | - J Mendes Lopes de Melo
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Panum Institute, Blegdamsvej 3B, 2200, Copenhagen, Denmark
| | - N Mørup
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Panum Institute, Blegdamsvej 3B, 2200, Copenhagen, Denmark
| | - K Tritsaris
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Panum Institute, Blegdamsvej 3B, 2200, Copenhagen, Denmark.
| | - S F Pedersen
- Section for Cell Biology and Physiology, Department of Biology, Faculty of Science, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen, Denmark.
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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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Paehler Vor der Nolte A, Chodisetti G, Yuan Z, Busch F, Riederer B, Luo M, Yu Y, Menon MB, Schneider A, Stripecke R, Nikolovska K, Yeruva S, Seidler U. Na + /H + exchanger NHE1 and NHE2 have opposite effects on migration velocity in rat gastric surface cells. J Cell Physiol 2017; 232:1669-1680. [PMID: 28019659 PMCID: PMC5396337 DOI: 10.1002/jcp.25758] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 12/21/2016] [Accepted: 12/22/2016] [Indexed: 12/13/2022]
Abstract
Following superficial injury, neighbouring gastric epithelial cells close the wound by rapid cell migration, a process called epithelial restitution. Na+/H+ exchange (NHE) inhibitors interfere with restitution, but the role of the different NHE isoforms expressed in gastric pit cells has remained elusive. The role of the basolaterally expressed NHE1 (Slc9a1) and the presumably apically expressed NHE2 (Slc9a2) in epithelial restitution was investigated in the nontransformed rat gastric surface cell line RGM1. Migration velocity was assessed by loading the cells with the fluorescent dye DiR and following closure of an experimental wound over time. Since RGM1 cells expressed very low NHE2 mRNA and have low transport activity, NHE2 was introduced by lentiviral gene transfer. In medium with pH 7.4, RGM1 cells displayed slow wound healing even in the absence of growth factors and independently of NHE activity. Growth factors accelerated wound healing in a partly NHE1‐dependent fashion. Preincubation with acidic pH 7.1 stimulated restitution in a NHE1‐dependent fashion. When pH 7.1 was maintained during the restitution period, migratory speed was reduced to ∼10% of the speed at pH 7,4, and the residual restitution was further inhibited by NHE1 inhibition. Lentiviral NHE2 expression increased the steady‐state pHi and reduced the restitution velocity after low pH preincubation, which was reversible by pharmacological NHE2 inhibition. The results demonstrate that in RGM1 cells, migratory velocity is increased by NHE1 activation, while NHE2 activity inhibit this process. A differential activation of NHE1 and NHE2 may therefore, play a role in the initiation and completion of the epithelial restitution process.
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Affiliation(s)
- Anja Paehler Vor der Nolte
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Giriprakash Chodisetti
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Zhenglin Yuan
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Florian Busch
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Brigitte Riederer
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Min Luo
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Yan Yu
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Manoj B Menon
- Departments of Biochemistry, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Andreas Schneider
- Departments of Hematology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Renata Stripecke
- Departments of Hematology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Katerina Nikolovska
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Sunil Yeruva
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
| | - Ursula Seidler
- Departments of Gastroenterology, Hemostatsis, Oncology and Stem Cell Transplantation, Medical School of Hannover, Germany
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Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges. Clin Microbiol Rev 2015; 27:823-69. [PMID: 25278576 DOI: 10.1128/cmr.00036-14] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.
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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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14
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Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule. Cell Mol Life Sci 2015; 72:2061-74. [PMID: 25680790 DOI: 10.1007/s00018-015-1848-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 01/28/2015] [Accepted: 01/29/2015] [Indexed: 01/17/2023]
Abstract
The ubiquitously expressed plasma membrane Na(+)-H(+) exchanger NHE1 is a 12 transmembrane-spanning protein that directs important cell functions such as homeostatic intracellular volume and pH control. The 315 amino acid cytosolic tail of NHE1 binds plasma membrane phospholipids and multiple proteins that regulate additional, ion-translocation independent functions. This review focuses on NHE1 structure/function relationships, as well as the role of NHE1 in kidney proximal tubule functions, including pH regulation, vectorial Na(+) transport, cell volume control and cell survival. The implications of these functions are particularly critical in the setting of progressive, albuminuric kidney diseases, where the accumulation of reabsorbed fatty acids leads to disruption of NHE1-membrane phospholipid interactions and tubular atrophy, which is a poor prognostic factor for progression to end stage renal disease. This review amplifies the vital role of the proximal tubule NHE1 Na(+)-H(+) exchanger as a kidney cell survival factor.
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Antisecretory factor peptide AF-16 inhibits the secreted autotransporter toxin-stimulated transcellular and paracellular passages of fluid in cultured human enterocyte-like cells. Infect Immun 2014; 83:907-22. [PMID: 25534938 DOI: 10.1128/iai.02759-14] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Both the endogenous antisecretory factor (AF) protein and peptide AF-16, which has a sequence that matches that of the active N-terminal region of AF, inhibit the increase in the epithelial transport of fluid and electrolytes induced by bacterial toxins in animal and ex vivo models. We conducted a study to investigate the inhibitory effect of peptide AF-16 against the increase of transcellular passage and paracellular permeability promoted by the secreted autotransporter toxin (Sat) in a cultured cellular model of the human intestinal epithelial barrier. Peptide AF-16 produced a concentration-dependent inhibition of the Sat-induced increase in the formation of fluid domes, in the mucosal-to-serosal passage of D-[1-(14)C]mannitol, and in the rearrangements in the distribution and protein expression of the tight junction (TJ)-associated proteins ZO-1 and occludin in cultured human enterocyte-like Caco-2/TC7 cell monolayers. In addition, we show that peptide AF-16 also inhibits the cholera toxin-induced increase of transcellular passage and the Clostridium difficile toxin-induced effects on paracellular permeability and TJ protein organization in Caco-2/TC7 cell monolayers. Treatment of cell monolayers by the lipid raft disorganizer methyl-β-cyclodextrin abolished the inhibitory activity of peptide AF-16 at the transcellular passage level and did not modify the effect of the peptide at the paracellular level.
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16
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Hendus-Altenburger R, Kragelund BB, Pedersen SF. Structural dynamics and regulation of the mammalian SLC9A family of Na⁺/H⁺ exchangers. CURRENT TOPICS IN MEMBRANES 2014; 73:69-148. [PMID: 24745981 DOI: 10.1016/b978-0-12-800223-0.00002-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mammalian Na⁺/H⁺ exchangers of the SLC9A family are widely expressed and involved in numerous essential physiological processes. Their primary function is to mediate the 1:1 exchange of Na⁺ for H⁺ across the membrane in which they reside, and they play central roles in regulation of body, cellular, and organellar pH. Their function is tightly regulated through mechanisms involving interactions with multiple protein and lipid-binding partners, phosphorylations, and other posttranslational modifications. Biochemical and mutational analyses indicate that the SLC9As have a short intracellular N-terminus, 12 transmembrane (TM) helices necessary and sufficient for ion transport, and a C-terminal cytoplasmic tail region with essential regulatory roles. No high-resolution structures of the SLC9As exist; however, models based on crystal structures of the bacterial NhaAs support the 12 TM organization and suggest that TMIV and XI may form a central part of the ion-translocation pathway, whereas pH sensing may involve TMII, TMIX, and several intracellular loops. Similar to most ion transporters studied, SLC9As likely exist as coupled dimers in the membrane, and this appears to be important for the well-studied cooperativity of H⁺ binding. The aim of this work is to summarize and critically discuss the currently available evidence on the structural dynamics, regulation, and binding partner interactions of SLC9As, focusing in particular on the most widely studied isoform, SLC9A1/NHE1. Further, novel bioinformatic and structural analyses are provided that to some extent challenge the existing paradigm on how ions are transported by mammalian SLC9As.
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Affiliation(s)
- Ruth Hendus-Altenburger
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark; Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Birthe B Kragelund
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Stine Falsig Pedersen
- Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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17
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Li J, Xu L, Ye J, Li X, Zhang D, Liang D, Xu X, Qi M, Li C, Zhang H, Wang J, Liu Y, Zhang Y, Zhou Z, Liang X, Li J, Peng L, Zhu W, Chen YH. Aberrant dynamin 2-dependent Na(+) /H(+) exchanger-1 trafficking contributes to cardiomyocyte apoptosis. J Cell Mol Med 2013; 17:1119-27. [PMID: 23837875 PMCID: PMC4118171 DOI: 10.1111/jcmm.12086] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Accepted: 05/13/2013] [Indexed: 02/05/2023] Open
Abstract
Sarcolemmal Na+/H+ exchanger 1 (NHE1) activity is essential for the intracellular pH (pHi) homeostasis in cardiac myocytes. Emerging evidence indicates that sarcolemmal NHE1 dysfunction was closely related to cardiomyocyte death, but it remains unclear whether defective trafficking of NHE1 plays a role in the vital cellular signalling processes. Dynamin (DNM), a large guanosine triphosphatase (GTPase), is best known for its roles in membrane trafficking events. Herein, using co-immunoprecipitation, cell surface biotinylation and confocal microscopy techniques, we investigated the potential regulation on cardiac NHE1 activity by DNM. We identified that DNM2, a cardiac isoform of DNM, directly binds to NHE1. Overexpression of a wild-type DNM2 or a dominant-negative DNM2 mutant with defective GTPase activity in adult rat ventricular myocytes (ARVMs) facilitated or retarded the internalization of sarcolemmal NHE1, whereby reducing or increasing its activity respectively. Importantly, the increased NHE1 activity associated with DNM2 deficiency led to ARVMs apoptosis, as demonstrated by cell viability, terminal deoxynucleotidyl transferase–mediated dUTP nick-end labelling assay, Bcl-1/Bax expression and caspase-3 activity, which were effectively rescued by pharmacological inhibition of NHE1 with zoniporide. Thus, our results demonstrate that disruption of the DNM2-dependent retrograde trafficking of NHE1 contributes to cardiomyocyte apoptosis.
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Affiliation(s)
- Jun Li
- Key Laboratory of Arrhythmias of the Ministry of Education of China, East Hospital, Tongji University School of Medicine, Shanghai, China; Institute of Medical Genetics, Tongji University, Shanghai, China
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18
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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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19
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Hulikova A, Harris AL, Vaughan-Jones RD, Swietach P. Regulation of intracellular pH in cancer cell lines under normoxia and hypoxia. J Cell Physiol 2013; 228:743-52. [PMID: 22949268 DOI: 10.1002/jcp.24221] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 08/23/2012] [Indexed: 01/20/2023]
Abstract
Acid-extrusion by active transport is important in metabolically active cancer cells, where it removes excess intracellular acid and sets the intracellular resting pH. Hypoxia is a major trigger of adaptive responses in cancer, but its effect on acid-extrusion remains unclear. We studied pH-regulation under normoxia and hypoxia in eight cancer cell-lines (HCT116, RT112, MDA-MB-468, MCF10A, HT29, HT1080, MiaPaca2, HeLa) using the pH-sensitive fluorophore, cSNARF-1. Hypoxia responses were triggered by pre-incubation in low O(2) or with the 2-oxoglutarate-dependent dioxygenase inhibitor dimethyloxalylglycine (DMOG). By selective pharmacological inhibition or transport-substrate removal, acid-extrusion flux was dissected into components due to Na(+)/H(+) exchange (NHE) and Na(+)-dependent HCO(3)(-) transport. In half of the cell-lines (HCT116, RT112, MDA-MB-468, MCF10A), acid-extrusion on NHE was the dominant flux during an acid load, and in all of these, bar one (MDA-MB-468), NHE-flux was reduced following hypoxic incubation. Further studies in HCT116 cells showed that <4-h hypoxic incubation reduced NHE-flux reversibly with a time-constant of 1-2 h. This was not associated with a change in expression of NHE1, the principal NHE isoform. Following 48-h hypoxia, inhibition of NHE-flux persisted but became only slowly reversible and associated with reduced expression of the glycosylated form of NHE1. Acid-extrusion by Na(+)-dependent HCO(3)(-) transport was hypoxia-insensitive and comparable in all cell lines. This constitutive and stable element of pH-regulation was found to be important for setting and stabilizing resting pH at a mildly alkaline level (conducive for growth), irrespective of oxygenation status. In contrast, the more variable flux on NHE underlies cell-specific differences in their dynamic response to larger acid loads.
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Affiliation(s)
- Alzbeta Hulikova
- Department of Physiology, Anatomy, and Genetics, Oxford University, Oxford, UK
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20
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Estrogen-dependent regulation of sodium/hydrogen exchanger-3 (NHE3) expression via estrogen receptor β in proximal colon of pregnant mice. Histochem Cell Biol 2012; 137:575-87. [PMID: 22358497 DOI: 10.1007/s00418-012-0935-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/08/2012] [Indexed: 02/06/2023]
Abstract
Although constipation is very common during pregnancy, the exact mechanism is unknown. We hypothesized that the involvement of estrogen receptor (ER) in the regulation of electrolyte transporter in the colon leads to constipation. In this study, the intestines of normal female ICR mouse and pregnant mice were examined for the expression of ERα and ERβ by immunohistochemistry and in situ hybridization. ERβ, but not ERα, was expressed in surface epithelial cells of the proximal, but not distal, colon on pregnancy days 10, 15, and 18, but not day 5, and the number of ERβ-positive cells increased significantly during pregnancy. Expression of NHE3, the gene that harbors estrogen response element, examined by immunohistochemistry and western blotting, was localized in the surface epithelial cells of the proximal colon and increased in parallel with ERβ expression. In ovariectomized mice, NHE3 expression was only marginal and was up-regulated after treatment with 17β-estradiol (E(2)), but not E(2) + ICI 182,780 (estrogen receptor antagonist). Moreover, knock-down of ERβ expression by electroporetically transfected siRNA resulted in a significant reduction of NHE3 expression. These results indicate that ERβ regulates the expression of NHE3 in the proximal colon of pregnant mice through estrogen action, suggesting the involvement of increased sodium absorption by up-regulated NHE3 in constipation during pregnancy.
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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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22
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Nighot PK, Moeser A, Ali RA, Blikslager AT, Koci MD. Astrovirus infection induces sodium malabsorption and redistributes sodium hydrogen exchanger expression. Virology 2010; 401:146-54. [PMID: 20219227 DOI: 10.1016/j.virol.2010.02.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2009] [Revised: 11/03/2009] [Accepted: 02/03/2010] [Indexed: 01/04/2023]
Abstract
Astroviruses are known to be a leading cause of diarrhea in infants and the immunocompromised; however, our understanding of this endemic pathogen is limited. Histological analyses of astrovirus pathogenesis demonstrate clinical disease is not associated with changes to intestinal architecture, inflammation, or cell death. Recent studies in vitro have suggested that astroviruses induce actin rearrangement leading to loss of barrier function. The current study used the type-2 turkey astrovirus (TAstV-2) and turkey poult model of astrovirus disease to examine how astrovirus infection affects the ultrastructure and electrophysiology of the intestinal epithelium. These data demonstrate that infection results in changes to the epithelial ultrastructure, rearrangement of F-actin, decreased absorption of sodium, as well as redistribution of the sodium/hydrogen exchanger 3 (NHE3) from the membrane to the cytoplasm. Collectively, these data suggest astrovirus infection induces sodium malabsorption, possibly through redistribution of specific sodium transporters, which results in the development of an osmotic diarrhea.
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Affiliation(s)
- Prashant K Nighot
- Department of Clinical Sciences, North Carolina State University, Raleigh, NC, USA
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Cornejo I, Niemeyer MI, Zúñiga L, Yusef YR, Sepúlveda FV, Cid LP. Rapid recycling of ClC-2 chloride channels between plasma membrane and endosomes: role of a tyrosine endocytosis motif in surface retrieval. J Cell Physiol 2009; 221:650-7. [PMID: 19711355 DOI: 10.1002/jcp.21900] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
ClC-2 chloride channel is present in the brain and some transporting epithelia where its function is poorly understood. We have now demonstrated that the surface channels are rapidly internalised and approximately the 70% of the surface membrane protein recycles after 4- to 8-min internalisation. Endocytosis of ClC-2 was dependent upon tyrosine 179 located within an endocytic motif. Rapid recycling accompanied by an even faster internalisation could account for the abundant presence of ClC-2 in intracellular membranous structures. At least a proportion of ClC-2 resides in lipid rafts. Use of beta-cyclodextrin led to an increase in cell surface channel, but, surprisingly, a decrease in functionally active channels. We suggest that ClC-2 requires residing in beta-cyclodextrin sensitive clusters with other molecules in order to remain active. Regulation of ClC-2 trafficking to and within the membrane could be a means of modulating its activity.
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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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Moeser AJ, Nighot PK, Ryan KA, Simpson JE, Clarke LL, Blikslager AT. Mice lacking the Na+/H+ exchanger 2 have impaired recovery of intestinal barrier function. Am J Physiol Gastrointest Liver Physiol 2008; 295:G791-7. [PMID: 18719001 PMCID: PMC4838133 DOI: 10.1152/ajpgi.00538.2007] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Ischemic injury induces breakdown of the intestinal barrier. Recent studies in porcine postischemic tissues indicate that inhibition of NHE2 results in enhanced recovery of barrier function in vitro via a process involving interepithelial tight junctions. To further study this process, recovery of barrier function was assessed in wild-type (NHE2(+/+)) and NHE2(-/-) mice in vivo and wild-type mice in vitro. Mice were subjected to complete mesenteric ischemia in vivo, after which barrier function was measured by blood-to-lumen mannitol clearance over a 3-h recovery period or measurement of transepithelial electrical resistance (TER) in Ussing chambers immediately following ischemia. Tissues were assessed for expression of select junctional proteins. Compared with NHE2(+/+) mice, NHE2(-/-) mice had greater intestinal permeability during the postischemic recovery process. In contrast to prior porcine studies, pharmacological inhibition of NHE2 in postischemic tissues from wild-type mice also resulted in significant reductions in TER. Mucosa from NHE2(-/-) mice displayed a shift of occludin and claudin-1 expression to the Triton-X-soluble membrane fractions and showed disruption of occludin and claudin-1 localization patterns following injury. This was qualitatively and quantitatively recovered in NHE2(+/+) mice compared with NHE2(-/-) mice by the end of the 3-h recovery period. Serine phosphorylation of occludin and claudin-1 was downregulated in NHE2(-/-) postischemia compared with wild-type mice. These data indicate an important role for NHE2 in recovery of barrier function in mice via a mechanism involving tight junctions.
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26
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Schelling JR, Abu Jawdeh BG. Regulation of cell survival by Na+/H+ exchanger-1. Am J Physiol Renal Physiol 2008; 295:F625-32. [PMID: 18480176 DOI: 10.1152/ajprenal.90212.2008] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Na(+)/H(+) exchanger-1 (NHE1) is a ubiquitous plasma membrane Na(+)/H(+) exchanger typically associated with maintenance of intracellular volume and pH. In addition to the NHE1 role in electroneutral Na(+)/H(+) transport, in renal tubular epithelial cells in vitro the polybasic, juxtamembrane NHE1 cytosolic tail domain acts as a scaffold, by binding with ezrin/radixin/moesin (ERM) proteins and phosphatidylinositol 4,5-bisphosphate, which initiates formation of a signaling complex that culminates in Akt activation and opposition to initial apoptotic stress. With robust apoptotic stimuli renal tubular epithelial cell NHE1 is a caspase substrate, and proteolytic cleavage may permit progression to apoptotic cell death. In vivo, genetic or pharmacological NHE1 loss of function causes renal tubule epithelial cell apoptosis and renal dysfunction following streptozotocin-induced diabetes, ureteral obstruction, and adriamycin-induced podocyte toxicity. Taken together, substantial in vivo and in vitro data demonstrate that NHE1 regulates tubular epithelial cell survival. In contrast to connotations of NHE1 as an unimportant "housekeeping" protein, this review highlights that NHE1 activity is critical for countering tubular atrophy and chronic renal disease progression.
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Affiliation(s)
- Jeffrey R Schelling
- Rammelkamp Center for Education and Research, 2500 MetroHealth Drive, Cleveland, OH 44109-1998, USA.
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27
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Claiborne JB, Choe KP, Morrison-Shetlar AI, Weakley JC, Havird J, Freiji A, Evans DH, Edwards SL. Molecular detection and immunological localization of gill Na+/H+ exchanger in the dogfish (Squalus acanthias). Am J Physiol Regul Integr Comp Physiol 2007; 294:R1092-102. [PMID: 18094061 DOI: 10.1152/ajpregu.00718.2007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The dogfish (Squalus acanthias) can make rapid adjustments to gill acid-base transfers to compensate for internal acidosis/alkalosis. Branchial Na+/H+ exchange (NHE) has been postulated as one mechanism driving the excretion of H+ following acidosis. We have cloned gill cDNA that includes an open reading frame coding for a 770-residue protein most homologous (approximately 71%) to mammalian NHE2. RT-PCR revealed NHE2 transcripts predominantly in gill, stomach, rectal gland, intestine, and kidney. In situ hybridization with an antisense probe against NHE2 in gill sections revealed a strong mRNA signal from a subset of interlamellar and lamellae cells. We developed dogfish-specific polyclonal antibodies against NHE2 that detected a approximately 70-kDa protein in Western blots and immunologically recognized branchial cells having two patterns of protein expression. Cytoplasmic and apical NHE2 immunoreactivity were observed in cells coexpressing basolateral Na+-K+-ATPase. Other large ovoid cells more generally staining for NHE2 also were strongly positive for basolateral H+-ATPase. Gill mRNA levels for NHE2 and H+-ATPase did not change following systemic acidosis (as measured by quantitative PCR 2 h after a 1- or 2-meq/kg acid infusion). These data indicate that posttranslational adjustments of NHE2 and other transport systems (e.g., NHE3) following acidosis may be of importance in the short-term pH adjustment and net branchial H+ efflux observed in vivo. NHE2 may play multiple roles in the gills, involved with H+ efflux from acid-secreting cells, basolateral H+ reabsorption for pHi regulation, and in parallel with H+-ATPase for the generation of HCO3(-) in base-secreting cells.
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Affiliation(s)
- James B Claiborne
- Department of Biology, Georgia Southern University, Statesboro, GA 30460, USA.
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28
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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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Musch MW, Arvans DL, Walsh-Reitz MM, Uchiyama K, Fukuda M, Chang EB. Synaptotagmin I binds intestinal epithelial NHE3 and mediates cAMP- and Ca2+-induced endocytosis by recruitment of AP2 and clathrin. Am J Physiol Gastrointest Liver Physiol 2007; 292:G1549-58. [PMID: 17307723 DOI: 10.1152/ajpgi.00388.2006] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Apical membrane sodium hydrogen exchanger 3 (NHE3), a major pathway for non-nutrient-dependent intestinal Na(+) absorption, is tightly regulated by second messenger systems that affect its functional activity and membrane trafficking. However, the events and components involved in NHE3 regulation are only partially understood. We report that the adaptor protein synaptotagmin I (Syt I) plays a pivotal role in cAMP- and Ca(2+)-induced cargo recognition of NHE3 and initiation of its endocytosis. Both mouse small intestine (jejunum) and Caco-2BBe Syt I coimmunoprecipitated with NHE3, particularly following increases in cellular cAMP or Ca(2+). Following short interfering RNA (siRNA) suppression of Syt I expression, cAMP- and Ca(2+)-induced inhibition of NHE3 activity were still observed but NHE3 endocytosis was blocked, as assessed by (22)Na influx and apical membrane biotin labeling, respectively. Similar effects on NHE3 inhibition and endocytosis were observed by siRNA suppression of either the mu-subunit of the adaptor protein 2 (AP2) complex or the heavy chain of clathrin. Coimmunoprecipitation analyses of NHE3 with these adaptor proteins revealed that cAMP- and Ca(2+)-induced NHE3-Syt I interaction preceded and was required for recruitment of AP2 and the clathrin complex. Confocal microscopy confirmed both the time sequence and protein associations of these events. We conclude that Syt I plays a pivotal role in mediating cAMP- and Ca(2+)-induced endocytosis of NHE3 (but not in inhibition of activity) through cargo recognition of NHE3 and subsequent recruitment of AP2-clathrin assembly required for membrane endocytosis.
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Affiliation(s)
- Mark W Musch
- Dept. of Medicine, MC 6084, The Univ. of Chicago Hospitals, 5841 S. Maryland Ave., Chicago, IL 60637, USA
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Gens JS, Dou H, Tackett L, Kong SS, Chu S, Montrose MH. Different ionic conditions prompt NHE2 and NHE3 translocation to the plasma membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1023-35. [PMID: 17303069 PMCID: PMC1974857 DOI: 10.1016/j.bbamem.2007.01.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Revised: 12/31/2006] [Accepted: 01/04/2007] [Indexed: 11/29/2022]
Abstract
We tested whether NHE3 and NHE2 Na(+)/H(+) exchanger isoforms were recruited to the plasma membrane (PM) in response to changes in ion homeostasis. NHE2-CFP or NHE3-CFP fusion proteins were functional Na(+)/H(+) exchangers when transiently expressed in NHE-deficient PS120 fibroblasts. Confocal morphometry of cells whose PM was labeled with FM4-64 measured the fractional amount of fusion protein at the cell surface. In resting cells, 10-20% of CFP fluorescence was at PM and stable over time. A protocol commonly used to activate the Na(+)/H(+) exchange function (NH(4)-prepulse acid load sustained in Na(+)-free medium), increased PM percentages of PM NHE3-CFP and NHE2-CFP. Separation of cellular acidification from Na(+) removal revealed that only NHE3-CFP translocated when medium Na(+) was removed, and only NHE2-CFP translocated when the cell was acidified. NHE2/NHE3 chimeric proteins demonstrate that the Na(+)-removal response element resides predominantly in the NHE3 cytoplasmic tail and is distinct from the acidification response sequence of NHE2.
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Affiliation(s)
- J. Scott Gens
- Biocomplexity Institute, Indiana University, Bloomington, Indiana, 47405
| | - Hongwei Dou
- Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Lixuan Tackett
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
| | - Shen-Shen Kong
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
| | - Shaoyou Chu
- Eli Lilly and Company, Indianapolis, Indiana, 46225
| | - Marshall H. Montrose
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
- Corresponding Author: Marshall H. Montrose, Mail address: Department of Molecular and Cellular Physiology, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH 45267, Telephone number: (513)-558-5636, FAX number: (513)-558-5738, E-mail:
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Moeser AJ, Nighot PK, Ryan KA, Wooten JG, Blikslager AT. Prostaglandin-mediated inhibition of Na+/H+ exchanger isoform 2 stimulates recovery of barrier function in ischemia-injured intestine. Am J Physiol Gastrointest Liver Physiol 2006; 291:G885-94. [PMID: 16574991 DOI: 10.1152/ajpgi.00380.2005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Prostaglandins stimulate repair of the ischemia-injured intestinal barrier in the porcine ileum through a mechanism involving cAMP-dependent Cl- secretion and inhibition of electroneutral Na+/H+ exchanger (NHE) activity. In the present study, we focused on the role of individual NHE isoforms in the recovery of barrier function. Ischemia-injured porcine ileal mucosa was mounted on Ussing chambers. Short-circuit current (I(sc)), transepithelial electrical resistance (TER), and isotopic fluxes of 22Na were measured in response to PGE2 and selective inhibitors of epithelial NHE isoforms. Immunoassays were used to assess the expression of NHE isoforms. Forty-five minutes of intestinal ischemia resulted in a 45% reduction in TER (P < 0.01). Near-complete restitution occurred within 60 min. Inhibition of NHE2 with HOE-694 (25 microM) added to the mucosal surface of the injured ileum stimulated significant elevations in TER, independent of changes in I(sc) and histological evidence of restitution. Pharmacological inhibition of NHE3 or NHE1 with mucosal S-3226 (20 microM) or serosal cariporide (25 microM), respectively, had no effect. Ischemia-injured tissues treated with mucosal S-3226 or HOE-694 exhibited equivalent reductions in mucosal-to-serosal fluxes of 22Na+ (by approximately 35%) compared with nontreated ischemia-injured control tissues (P < 0.05). Intestinal ischemia resulted in increased expression of the cytoplasmic NHE regulatory factor EBP50 in NHE2 but not in NHE3 immunoprecipitates. Selective inhibition of NHE2, and not NHE3, induces recovery of barrier function in the ischemia-injured intestine.
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Affiliation(s)
- Adam J Moeser
- Department of Clinical Studies, College of Veterinary Medicine, North Carolina State University, NC 27606, USA
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32
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Hodges K, Gill R, Ramaswamy K, Dudeja PK, Hecht G. Rapid activation of Na+/H+ exchange by EPEC is PKC mediated. Am J Physiol Gastrointest Liver Physiol 2006; 291:G959-68. [PMID: 16782696 DOI: 10.1152/ajpgi.00274.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Enteropathogenic Escherichia coli (EPEC) increases sodium/hydrogen exchanger 2 (NHE2)-mediated sodium uptake by intestinal epithelial cells in a type III secretion-dependent manner. However, the mechanism(s) underlying these changes are not known. This study examines the role of a number of known secreted effector molecules and bacterial adhesins as well as the signaling pathways involved in this process. Deletion of the bacterial adhesins Tir and intimin had no effect on the increase in sodium/hydrogen exchanger (NHE) activity promoted by EPEC infection; however, there was a significant decrease upon deletion of the bundle-forming pili. Bacterial supernatant also failed to alter NHE activity, suggesting that direct interaction with bacteria is necessary. Analysis of the signal transduction cascades responsible for the increased NHE2 activity during EPEC infection showed that PLC increased Ca2+, as well as PKCalpha and PKCepsilon were involved in increasing NHE activity. The activation of PKCepsilon by EPEC has not been previously described nor has its role in regulating NHE2 activity. Because EPEC markedly increases NHE2 activity, this pathogen provides an exceptional opportunity to improve our understanding of this less-characterized NHE isoform.
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Affiliation(s)
- Kim Hodges
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois, Chicago, IL 60612, USA
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33
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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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Neuhoff S, Ungell AL, Zamora I, Artursson P. pH-Dependent passive and active transport of acidic drugs across Caco-2 cell monolayers. Eur J Pharm Sci 2005; 25:211-20. [PMID: 15911216 DOI: 10.1016/j.ejps.2005.02.009] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Revised: 12/20/2004] [Accepted: 02/17/2005] [Indexed: 10/25/2022]
Abstract
The aim of this study was to investigate pH-dependent passive and active transport of acidic drugs across Caco-2 cells. Therefore, the bidirectional pH-dependent transport of two acidic drugs, indomethacin and salicylic acid, across Caco-2 cells was studied in the physiological pH range of the gastrointestinal tract. The transport of both drugs decreased with increased pH, as expected from the pH-partition hypothesis. Net absorption occurred when the basolateral pH exceeded the apical pH. Concentration dependence and transporter inhibition studies indicated passive transport for indomethacin and a mixture of pH-dependent passive and active influx for salicylic acid. Unexpectedly, active and passive drug transport results were indistinguishable in temperature dependency studies. The transport of salicylic acid (apical pH 5.0; basolateral pH 7.4) was partly blocked by inhibitors of the proton-dependent transporters MCT1 (SLC16A1) and OATP-B (SLC21A9, SLCO2B1). This study shows that the asymmetry in bidirectional transport of acidic drugs is affected by both passive and active components in the presence of pH gradients across Caco-2 cells. Thus, combined studies of concentration-dependency and transport-inhibition are preferred when acidic drug transport is studied in a pH gradient. The findings of this in vitro study can be extrapolated to in vivo situations involving an acidic microclimate.
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Affiliation(s)
- Sibylle Neuhoff
- Department of Pharmacy, Division of Pharmaceutics, Uppsala University, Box 580, SE-751 23 Uppsala, Sweden.
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35
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Affiliation(s)
- John F Di Mari
- Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-1064, USA.
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Gonzalez-Gronow M, Misra UK, Gawdi G, Pizzo SV. Association of plasminogen with dipeptidyl peptidase IV and Na+/H+ exchanger isoform NHE3 regulates invasion of human 1-LN prostate tumor cells. J Biol Chem 2005; 280:27173-8. [PMID: 15911629 DOI: 10.1074/jbc.m500383200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Binding of plasminogen type II (Pg 2) to dipeptidyl peptidase IV (DPP IV) on the surface of the highly invasive 1-LN human prostate tumor cell line induces an intracellular Ca2+ ([Ca2+]i) signaling cascade accompanied by a rise in intracellular pH (pHi). In endothelial cells, Pg 2 regulates intracellular pH via Na+/H+ exchange (NHE) antiporters; however, this mechanism has not been demonstrated in any other cell type including prostate cancer cells. Because the Pg 2 receptor DPP IV is associated with NHE3 in kidney cell plasma membranes, we investigated a similar association in 1-LN human prostate cancer cells and a mechanistic explanation for changes in [Ca2+]i or pHi induced by Pg 2 in these cells. Our results suggest that the signaling cascade initiated by Pg 2 and its receptor proceeds via activation of phospholipase C, which promotes formation of inositol 3,4,5-trisphosphate, an inducer of Ca2+ release from endoplasmic reticulum stores. Furthermore, our results suggest that Pg 2 may regulate pHi via an association with NHE3 linked to DPP IV in these cells. These associations suggest that Pg has the potential to simultaneously regulate calcium signaling pathways and Na+/H+ exchanges necessary for tumor cell proliferation and invasiveness.
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Affiliation(s)
- Mario Gonzalez-Gronow
- Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
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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, Kenworthy A, Murtazina R, Donowitz M. The lateral mobility of NHE3 on the apical membrane of renal epithelial OK cells is limited by the PDZ domain proteins NHERF1/2, but is dependent on an intact actin cytoskeleton as determined by FRAP. J Cell Sci 2005; 117:3353-65. [PMID: 15226406 DOI: 10.1242/jcs.01180] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The epithelial brush border (BB) Na+/H+ exchanger, NHE3, plays a major role in transcellular Na+ absorption in the renal proximal tubule. NHE3 activity is rapidly regulated by neurohumoral substances and growth factors via changes in its amount on the BB by a process partially involving vesicle trafficking. The PDZ domain-containing proteins, NHERF1/2, are scaffold proteins that link NHE3 to the actin cytoskeleton via their binding to both ezrin and NHE3. NHERF1/2 interact with both an internal C-terminal domain of NHE3 and the N-terminus of ezrin. We used fluorescence recovery after photobleaching (FRAP) to study the effect of NHERF1/2 on NHE3 mobility in the brush border of opossum kidney (OK) proximal tubule cells. A confocal microscope was used to allow the selective study of apical membrane versus intracellular NHE3. A chimera of NHE3-EGFP was transiently expressed in OK cells and its lateral diffusion in the apical membrane was measured with FRAP and confocal microscopy at 37 degrees C. The contribution of intracellular NHE3-EGFP to recovery on the OK surface not directly over the juxtanuclear area (non-JN) was negligible as exposure to the water soluble crosslinker BS3 (10 mM) at 4 degrees C resulted in no recovery of this component of surface NHE3-EGFP after photobleaching. The mobile fraction (Mf) of apical NHE3-EGFP was 47.5+/-2.2%; the effective diffusion coefficient (Deff) was (2.2+/-0.3) x10(-10) cm2/second. Overexpression of NHERF2 in OK cells decreased the Mf to 29.1+/-3.1% without changing Deff. In the truncation mutant, NHE3585-EGFP (aa 1-585), which lacks the NHERF1/2 binding domain, Mf increased to 66.4+/-2.2%, with no change in Deff, whereas NHE3660-EGFP, which binds NHERF1/2, had Mf (48.3+/-3.0%) and Deff both similar to full-length NHE3. These results are consistent with the PDZ domain proteins NHERF1 and NHERF2 scaffolding NHE3 in macromolecular complexes in the apical membrane of OK cells under basal conditions, which limits the lateral mobility of NHE3. It is probable that this is one of the mechanisms by which NHERF1/2 affects rapid regulation of NHE3 by growth factors and neurohumoral mediators. By contrast, disrupting the actin cytoskeleton by latrunculin B treatment (0.05 microM, 30 minutes) reduced the NHE3 Mf (21.9+/-4.5%) without altering the Deff. Therefore the actin cytoskeleton, independently of NHERF1/2 binding, is necessary for apical membrane mobility of NHE3.
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Affiliation(s)
- Boyoung Cha
- Department of Physiology, Gastroenterology Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Fuster D, Moe OW, Hilgemann DW. Lipid- and mechanosensitivities of sodium/hydrogen exchangers analyzed by electrical methods. Proc Natl Acad Sci U S A 2004; 101:10482-7. [PMID: 15240890 PMCID: PMC478595 DOI: 10.1073/pnas.0403930101] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2004] [Indexed: 11/18/2022] Open
Abstract
Sodium/hydrogen exchangers (NHEs) are ubiquitous ion transporters that serve multiple cell functions. We have studied two mammalian isoforms, NHE1 (ubiquitous) and NHE3 (epithelial-specific), by measuring extracellular proton (H+) gradients during whole-cell patch clamp with perfusion of the cell interior. Maximal Na(+)-dependent H+ fluxes (JH+) are equivalent to currents >20 pA for NHE1 in Chinese hamster ovary fibroblasts, >200 pA for NHE1 in guinea pig ventricular myocytes, and 5-10 pA for NHE3 in opossum kidney cells. The fluxes are blocked by an NHE inhibitor, ethylisopropylamiloride, and are absent in NHE-deficient AP-1 cells. NHE1 activity is stable with perfusion of nonhydrolyzable ATP [adenosine 5'-(beta,gamma-imido)triphosphate], is abolished by ATP depletion (2 deoxy-D-glucose with oligomycin or perfusion of apyrase), can be restored with phosphatidylinositol 4,5-bisphosphate, and is unaffected by actin cytoskeleton disruption (latrunculin or pipette perfusion of gelsolin). NHE3 (but not NHE1) is reversibly activated by phosphatidylinositol 3,4,5-trisphosphate. Both NHE1 and NHE3 activities are disrupted in giant patches during gigaohm seal formation. NHE1 (but not NHE3) is reversibly activated by cell shrinkage, even at neutral cytoplasmic pH without ATP, and inhibited by cell swelling. NHE1 in Chinese hamster ovary fibroblasts (but not NHE3 in opossum kidney cells) is inhibited by agents that thin the membrane (L-alpha-lysophosphatidylcholine and octyl-beta-D-glucopyranoside) and activated by cholesterol enrichment, which thickens membranes. Expressed in AP-1 cells, however, NHE1 is insensitive to these agents but remains sensitive to volume changes. Thus, changes of hydrophobic mismatch can modulate NHE1 but do not underlie its volume sensitivity.
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Affiliation(s)
- Daniel Fuster
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235, USA
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Bachmann O, Riederer B, Rossmann H, Groos S, Schultheis PJ, Shull GE, Gregor M, Manns MP, Seidler U. The Na+/H+ exchanger isoform 2 is the predominant NHE isoform in murine colonic crypts and its lack causes NHE3 upregulation. Am J Physiol Gastrointest Liver Physiol 2004; 287:G125-33. [PMID: 14962844 DOI: 10.1152/ajpgi.00332.2003] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The Na(+)/H(+) exchanger isoform NHE2 is highly expressed in the intestinal tract, but its physiological role has remained obscure. The aim of this study was to define its expression, location, and regulatory properties in murine colon and to look for the compensatory changes in NHE2 (-/-) colon that allow normal histology and absorptive function. To this end, we measured murine proximal colonic surface and crypt cell NHE1, NHE2, and NHE3 expression levels, transport rates in response to acid, hyperosmolarity and cAMP in murine proximal colonic crypts, as well as changes in transcript levels and acid-activated NHE activity in NHE2 (-/-) crypts. We found that NHE2 was expressed most abundantly in crypts, NHE1 equally in crypts and surface cells, and NHE3 much stronger in surface cells. NHE2, like NHE1, was activated by low intracellular pH (pH(i)), hyperosmolarity, and cAMP, whereas NHE3 was activated only by low pH(i). Crypts isolated from NHE2 (-/-) mice displayed increased acid-activated NHE1- and NHE3-attributable Na(+)/H(+) exchange activity, no change in NHE1 expression, and NHE3 expression levels twice as high as in normal littermates. No change in cellular ultrastructure was found in NHE2 (-/-) colon. Our results demonstrate high NHE2 expression in the crypts and suggest a role for NHE2 in cryptal pH(i) and volume homeostasis.
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Affiliation(s)
- O Bachmann
- Dept. of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30623 Hannover, Germany
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41
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Moreno-García ME, Partida-Sánchez S, Primack J, Sumoza-Toledo A, Muller-Steffner H, Schuber F, Oppenheimer N, Lund FE, Santos-Argumedo L. CD38 is expressed as noncovalently associated homodimers on the surface of murine B lymphocytes. ACTA ACUST UNITED AC 2004; 271:1025-34. [PMID: 15009214 DOI: 10.1111/j.1432-1033.2004.04006.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
CD38 is a transmembrane glycoprotein that functions as an ectoenzyme and as a receptor. Based on the structural similarity between CD38 and ADP-ribosyl cyclase from Aplysia californica, it was hypothesized that CD38 is expressed as a homodimer on the surface of cells. Indeed, CD38 dimers have been reported, however, the structural requirements for their stabilization on the plasma membrane are unknown. We demonstrate that the majority of CD38 is assembled as noncovalently associated homodimers on the surface of B cells. Analysis of CD38 mutants, expressed in Ba/F3 cells, revealed that truncation of the cytoplasmic region or mutation of a single amino acid within the alpha1-helix of CD38 decreased the stability of the CD38 homodimers when solubilized in detergent. Cells expressing the unstable CD38 homodimers had diminished expression of CD38 on the plasma membrane and the half-lives of these CD38 mutant proteins on the plasma membrane were significantly reduced. Together, these results show that CD38 is expressed as noncovalently associated homodimers on the surface of murine B cells and suggest that appropriate assembly of CD38 homodimers may play an important role in stabilizing CD38 on the plasma membrane of B cells.
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Bourgeois S, Rossignol P, Grelac F, Chalumeau C, Klein C, Laghmani K, Chambrey R, Bruneval P, Duong JP, Poggioli J, Houillier P, Paillard M, Kellermann O, Froissart M. Differentiated thick ascending limb (TAL) cultured cells derived from SV40 transgenic mice express functional apical NHE2 isoform: effect of nitric oxide. Pflugers Arch 2003; 446:672-83. [PMID: 12836026 DOI: 10.1007/s00424-003-1108-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2002] [Revised: 01/31/2003] [Accepted: 05/07/2003] [Indexed: 10/26/2022]
Abstract
Studying the apical Na/H exchanger NHE2 is difficult in the intact thick ascending limb (TAL) because of its weak expression and transport activity compared with the co-expressed NHE3. From a mouse transgenic for a recombinant plasmid adeno-SV(40) (PK4), we developed an immortalized TAL cell line, referred to as MKTAL, which selectively expresses NHE2 protein and activity. The immortalized cells retain the main properties of TAL cells. They have a stable homogeneous epithelial-like phenotype, express SV(40) T antigen and exhibit polarity with an apical domain bearing few microvilli and separated from lateral domains by typical epithelial-type junctional complexes expressing ZO1 protein. Tamm-Horsfall protein is present on the apical membrane. MKTAL cells express NHE2 and NHE1 proteins but not NHE3 and NHE4, whereby NHE2 protein is expressed selectively in the apical domain of the plasma membrane. NHE2 contributed about half of the total Na/H exchange activity. mRNAs for the Na-K-2Cl cotransporter-2 (NKCC2) and the anion exchangers AE2 and AE3 were also present. While acute exposure to NO donors did not alter NHE2 activity, chronic exposure inhibited NHE2 activity selectively and down-regulated NHE2 mRNA abundance. In conclusion, MKTAL cells retain structural and functional properties of their in vivo TAL counterparts and express functional NHE2 protein in the apical membrane, which may be inhibited by NO. Thus, MKTAL cells may be an appropriate model for studying the cellular mechanisms of NHE2 regulation.
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Affiliation(s)
- Soline Bourgeois
- INSERM Unité 356, IFR 58, Université Paris VI, Institut des Cordeliers, 15-21 rue de l'Ecole de Médecine, 75270, Paris Cedex 6, France.
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Wu KL, Khan S, Lakhe-Reddy S, Wang L, Jarad G, Miller RT, Konieczkowski M, Brown AM, Sedor JR, Schelling JR. Renal tubular epithelial cell apoptosis is associated with caspase cleavage of the NHE1 Na+/H+ exchanger. Am J Physiol Renal Physiol 2003; 284:F829-39. [PMID: 12453872 DOI: 10.1152/ajprenal.00314.2002] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Renal tubular epithelial cell (RTC) apoptosis causes tubular atrophy, a hallmark of renal disease progression. Apoptosis is generally characterized by reduced cell volume and cytosolic pH, but epithelial cells are relatively resistant to shrinkage due to regulatory volume increase, which is mediated by Na(+)/H(+) exchanger (NHE) 1. We investigated whether RTC apoptosis requires caspase cleavage of NHE1. Staurosporine- and hypertonic NaCl-induced RTC apoptosis was associated with cell shrinkage and diminished cytosolic pH, and apoptosis was potentiated by amiloride analogs, suggesting NHE1 activity opposes apoptosis. NHE1-deficient fibroblasts demonstrated increased susceptibility to apoptosis, which was reversed by NHE1 reconstitution. NHE1 expression was markedly decreased in apoptotic RTC due to degradation, and preincubation with peptide caspase antagonists restored NHE1 expression, indicating that NHE1 is degraded by caspases. Recombinant caspase-3 cleaved the in vitro-translated NHE1 cytoplasmic domain into five distinct peptides, identical in molecular weight to NHE1 degradation products derived from staurosporine-stimulated RTC lysates. In vivo, NHE1 loss-of-function C57BL/6.SJL-swe/swe mice with adriamycin-induced nephropathy demonstrated increased RTC apoptosis compared with adriamycin-treated wild-type controls, thereby implicating NHE1 inactivation as a potential mechanism of tubular atrophy. We conclude that NHE1 activity is critical for RTC survival after injury and that caspase cleavage of RTC NHE1 may promote apoptosis and tubular atrophy by preventing compensatory intracellular volume and pH regulation.
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Affiliation(s)
- Karen L Wu
- Department of Medicine, and Rammelkamp Center for Education and Research, Case Western Reserve University School of Medicine, Cleveland, Ohio 44109, USA
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Claiborne JB, Edwards SL, Morrison-Shetlar AI. Acid-base regulation in fishes: cellular and molecular mechanisms. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 2002; 293:302-19. [PMID: 12115903 DOI: 10.1002/jez.10125] [Citation(s) in RCA: 201] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The mechanisms underlying acid-base transfers across the branchial epithelium of fishes have been studied for more than 70 years. These animals are able to compensate for changes to internal pH following a wide range of acid-base challenges, and the gill epithelium is the primary site of acid-base transfers to the water. This paper reviews recent molecular, immunohistochemical, and functional studies that have begun to define the protein transporters involved in the acid-base relevant ion transfers. Both Na(+)/H(+) exchange (NHE) and vacuolar-type H(+)-ATPase transport H(+) from the fish to the environment. While NHEs have been thought to carry out this function mainly in seawater-adapted animals, these proteins have now been localized to mitochondrial-rich cells in the gill epithelium of both fresh and saltwater-adapted fishes. NHEs have been found in the gill epithelium of elasmobranchs, teleosts, and an agnathan. In several species, apical isoforms (NHE2 and NHE3) appear to be up-regulated following acidosis. In freshwater teleosts, H(+)-ATPase drives H(+) excretion and is indirectly coupled to Na(+) uptake (via Na(+) channels). It has been localized to respiratory pavement cells and chloride cells of the gill epithelium. In the marine elasmobranch, both branchial NHE and H(+)-ATPase have been identified, suggesting that a combination of these mechanisms may be utilized by marine elasmobranchs for acid-base regulation. An apically located Cl(-)/HCO(3)(-) anion exchanger in chloride cells may be responsible for base excretion in fresh and seawater-adapted fishes. While only a few species have been examined to date, new molecular approaches applied to a wider range of fishes will continue to improve our understanding of the roles of the various gill membrane transport processes in acid-base balance.
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Affiliation(s)
- James B Claiborne
- Department of Biology, Georgia Southern University, Statesboro, Georgia 30460, USA.
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Kim JH, Lee-Kwon W, Park JB, Ryu SH, Yun CHC, Donowitz M. Ca(2+)-dependent inhibition of Na+/H+ exchanger 3 (NHE3) requires an NHE3-E3KARP-alpha-actinin-4 complex for oligomerization and endocytosis. J Biol Chem 2002; 277:23714-24. [PMID: 11948184 DOI: 10.1074/jbc.m200835200] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two PDZ domain-containing proteins, NHERF and E3KARP are necessary for cAMP-dependent inhibition of Na(+)/H(+) exchanger 3 (NHE3). In this study, we demonstrate a specific role of E3KARP, which is not duplicated by NHERF, in Ca(2+)-dependent inhibition of NHE3 activity. NHE3 activity is inhibited by elevation of intracellular Ca(2+) ([Ca(2+)](i)) in PS120 fibroblasts stably expressing E3KARP but not those expressing NHERF. In addition, this Ca(2+)-dependent inhibition requires Ca(2+)-dependent association between alpha-actinin-4 and E3KARP. NHE3 is indirectly connected to alpha-actinin-4 in a protein complex through Ca(2+)-dependent interaction between alpha-actinin-4 and E3KARP, which occurs through the actin-binding domain plus spectrin repeat domain of alpha-actinin-4. Elevation of [Ca(2+)](i) results in oligomerization and endocytosis of NHE3 as well as in inhibition of NHE3 activity. Overexpression of alpha-actinin-4 potentiates the inhibitory effect of ionomycin on NHE3 activity by accelerating the oligomerization and endocytosis of NHE3. In contrast, overexpression of the actin-binding domain plus spectrin repeat domain acts as a dominant-negative mutant and prevents the inhibitory effect of ionomycin on NHE3 activity as well as the oligomerization and internalization of NHE3. From these results, we propose that elevated Ca(2+) inhibits NHE3 activity through oligomerization and endocytosis of NHE3, which occurs via formation of an NHE3-E3KARP-alpha-actinin-4 complex.
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Affiliation(s)
- Jae Ho Kim
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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