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Abtahi S, Turner JR. Exploiting Alternative Brush Border Trafficking Routes to Treat Microvillous Inclusion Disease. Gastroenterology 2020; 159:1233-1235. [PMID: 32777279 DOI: 10.1053/j.gastro.2020.08.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 08/03/2020] [Indexed: 12/02/2022]
Affiliation(s)
- Shabnam Abtahi
- Laboratory of Mucosal Barrier Pathobiology, Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
| | - Jerrold R Turner
- Laboratory of Mucosal Barrier Pathobiology, Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
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Abstract
The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, Los Angeles, CA; Brain Research Institute, UCLA, Los Angeles, CA
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3
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Zhu XC, Sarker R, Horton JR, Chakraborty M, Chen TE, Tse CM, Cha B, Donowitz M. Nonsynonymous single nucleotide polymorphisms of NHE3 differentially decrease NHE3 transporter activity. Am J Physiol Cell Physiol 2015; 308:C758-66. [PMID: 25715704 DOI: 10.1152/ajpcell.00421.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 02/23/2015] [Indexed: 12/24/2022]
Abstract
Genetic determinants appear to play a role in susceptibility to chronic diarrhea, but the genetic abnormalities involved have only been identified in a few conditions. The Na⁺/H⁺ exchanger 3 (NHE3) accounts for a large fraction of physiologic intestinal Na⁺ absorption. It is highly regulated through effects on its intracellular COOH-terminal regulatory domain. The impact of genetic variation in the NHE3 gene, such as single nucleotide polymorphisms (SNPs), on transporter activity remains unexplored. From a total of 458 SNPs identified in the entire NHE3 gene, we identified three nonsynonymous mutations (R474Q, V567M, and R799C), which were all in the protein's intracellular COOH-terminal domain. Here we evaluated whether these SNPs affect NHE3 activity by expressing them in a mammalian cell line that is null for all plasma membrane NHEs. These variants significantly reduced basal NHE3 transporter activity through a reduction in intrinsic NHE3 function in variant R474Q, abnormal trafficking in variant V567M, or defects in both intrinsic NHE3 function and trafficking in variant R799C. In addition, variants NHE3 R474Q and R799C failed to respond to acute dexamethasone stimulation, suggesting cells with these mutant proteins might be defective in NHE3 function during postprandial stimulation and perhaps under stressful conditions. Finally, variant R474Q was shown to exhibit an aberrant interaction with calcineurin B homologous protein (CHP), an NHE3 regulatory protein required for basal NHE3 activity. Taken together, these results demonstrate decreased transport activity in three SNPs of NHE3 and provide mechanistic insight into how these SNPs impact NHE3 function.
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Affiliation(s)
- Xinjun Cindy Zhu
- Department of Medicine, Division of Gastroenterology and Hepatology, Center of Cardiovascular Sciences, Albany Medical Center, Albany, New York; Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Rafiquel Sarker
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - John R Horton
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia
| | - Molee Chakraborty
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Tian-E Chen
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - C Ming Tse
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Boyoung Cha
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Mark Donowitz
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
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4
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Zhu X, Cha B, Zachos NC, Sarker R, Chakraborty M, Chen TE, Kovbasnjuk O, Donowitz M. Elevated calcium acutely regulates dynamic interactions of NHERF2 and NHE3 proteins in opossum kidney (OK) cell microvilli. J Biol Chem 2011; 286:34486-96. [PMID: 21799002 DOI: 10.1074/jbc.m111.230219] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The brush border (BB) Na(+)/H(+) exchanger NHE3 is rapidly activated or inhibited by changes in trafficking, which mimics renal and intestinal physiology. However, there is a paradox in that NHE3 has limited mobility in the BB due to its binding to the multi-PDZ domain containing the NHERF family. To allow increased endocytosis, as occurs with elevated intracellular Ca(2+), we hypothesized that NHE3 had to be, at least transiently, released from the BB cytoskeleton. Because NHERF1 and -2 are localized at the BB, where they bind NHE3 as well as the cytoskeleton, we tested whether either or both might dynamically interact with NHE3 as part of Ca(2+) signaling. We employed FRET to study close association of NHE3 and these NHERFs and fluorescence recovery after photobleaching to monitor NHE3 mobility in the apical domain in polarized opossum kidney cells. Under basal conditions, NHERF2 and NHE3 exhibited robust FRET signaling. Within 1 min of A23187 (0.5 μm) exposure, the NHERF2-NHE3 FRET signal was abolished, and BB NHE3 mobility was transiently increased. The dynamics in FRET signal and NHE3 mobility correlated well with a change in co-precipitation of NHE3 and NHERF2 but not NHERF1. We conclude the following. 1) Under basal conditions, NHE3 closely associates with NHERF2 in opossum kidney cell microvilli. 2) Within 1 min of elevated Ca(2+), the close association of NHE3-NHERF2 is abolished but is re-established in ∼60 min. 3) The change in NHE3-NHERF2 association is accompanied by an increased BB mobile fraction of NHE3, which contributes to inhibition of NHE3 transport activity via increased endocytosis.
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Affiliation(s)
- Xinjun Zhu
- Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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5
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Murtazina R, Kovbasnjuk O, Chen TE, Zachos NC, Chen Y, Kocinsky HS, Hogema BM, Seidler U, de Jonge HR, Donowitz M. NHERF2 is necessary for basal activity, second messenger inhibition, and LPA stimulation of NHE3 in mouse distal ileum. Am J Physiol Cell Physiol 2011; 301:C126-36. [PMID: 21430287 DOI: 10.1152/ajpcell.00311.2010] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To test the hypothesis that Na(+)/H(+) exchanger (NHE) regulatory factor 2 (NHERF2) is necessary for multiple aspects of acute regulation of NHE3 in intact mouse small intestine, distal ileal NHE3 activity was determined using two-photon microscopy/SNARF-4F in a NHERF2-null mouse model. The NHERF2-null mouse ileum had shorter villi, deeper crypts, and decreased epithelial cell number. Basal rates of NHE3 activity were reduced in NHERF2-null mice, which was associated with a reduced percentage of NHE3 in the apical domain and an increase in intracellular NHE3 amount but no change in total level of NHE3 protein. cAMP, cGMP, and elevated Ca(2+) due to apical exposure to UTP all inhibited NHE3 activity in wild-type mouse ileum but not in NHERF2-null mice, while inhibition by hyperosmolarity occurred normally. The cAMP-increased phosphorylation of NHE3 at aa 552; levels of PKAIIα and cGMP-dependent protein kinase II (cGKII); and elevation of Ca(2+) were similar in wild-type and NHERF2-null mouse ileum. Luminal lysophosphatidic acid (LPA) stimulated NHE3 in wild-type but not in NHERF2-null ileum. In conclusion, 1) there are subtle structural abnormalities in the small intestine of NHERF2-null mouse which include fewer villus epithelial cells; 2) the decreased basal NHE3 activity and reduced brush border NHE3 amount in NHERF2-null mice show that NHERF2 is necessary for normal basal trafficking or retention of NHE3 in the apical domain; 3) hyperosmolar inhibition of NHE3 occurs similarly in wild-type and NHERF2-null ileum, demonstrating that some inhibitory mechanisms of NHE3 are not NHERF2 dependent; 4) cAMP inhibition of NHE3 is NHERF2 dependent at a step downstream of cAMP/PKAII phosphorylation of NHE3 at aa 552; 5) cGMP- and UTP-induced inhibition of NHE3 are NHERF2 dependent at steps beyond cGKII and the UTP-induced increase of intracellular Ca(2+); and 6) LPA stimulation of NHE3 is also NHERF2 dependent.
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Affiliation(s)
- Rakhilya Murtazina
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA
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Donowitz M, Singh S, Singh P, Chakraborty M, Chen Y, Murtazina R, Gucek M, Cole RN, Zachos NC, Salahuddin FF, Kovbasnjuk O, Broere N, Smalley-Freed WG, Reynolds AB, Hubbard AL, Seidler U, Weinman E, de Jonge HR, Hogema BM, Li X. Alterations in the proteome of the NHERF2 knockout mouse jejunal brush border membrane vesicles. Physiol Genomics 2011; 43:674-84. [PMID: 21427361 DOI: 10.1152/physiolgenomics.00258.2010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To identify additional potential functions for the multi-PDZ domain containing protein Na+/H+ exchanger regulatory factor 2 (NHERF2), which is present in the apical domain of intestinal epithelial cells, proteomic studies of mouse jejunal villus epithelial cell brush border membrane vesicles compared wild-type to homozygous NHERF2 knockout FVB mice by a two-dimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS)-iTRAQ approach. Jejunal architecture appeared normal in NHERF2 null in terms of villus length and crypt depth, Paneth cell number, and microvillus structure by electron microscopy. There was also no change in proliferative activity based on BrdU labeling. Four brush border membrane vesicles (BBMV) preparations from wild-type mouse jejunum were compared with four preparations from NHERF2 knockout mice. LC-MS/MS identified 450 proteins in both matched wild-type and NHERF2 null BBMV; 13 proteins were changed in two or more separate BBMV preparations (9 increased and 4 decreased in NHERF2 null mice), while an additional 92 proteins were changed in a single BBMV preparation (68 increased and 24 decreased in NHERF2 null mice). These proteins were categorized as 1) transport proteins (one increased and two decreased in NHERF2 null); 2) signaling molecules (2 increased in NHERF2 null); 3) cytoskeleton/junctional proteins (4 upregulated and 1 downregulated in NHERF2 null); and 4) metabolic proteins/intrinsic BB proteins) (2 upregulated and 1 downregulated in NHERF2 null). Immunoblotting of BBMV was used to validate or extend the findings, demonstrating increase in BBMV of NHERF2 null of MCT1, coronin 3, and ezrin. The proteome of the NHERF2 null mouse small intestinal BB demonstrates up- and downregulation of multiple transport proteins, signaling molecules, cytoskeletal proteins, tight junctional and adherens junction proteins, and proteins involved in metabolism, suggesting involvement of NHERF2 in multiple apical regulatory processes and interactions with luminal contents.
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Affiliation(s)
- M Donowitz
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2195, USA.
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Cha B, Zhu XC, Chen W, Jones M, Ryoo S, Zachos NC, Chen TE, Lin R, Sarker R, Kenworthy AK, Tse M, Kovbasnjuk O, Donowitz M. NHE3 mobility in brush borders increases upon NHERF2-dependent stimulation by lyophosphatidic acid. J Cell Sci 2010; 123:2434-43. [PMID: 20571054 DOI: 10.1242/jcs.056713] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The epithelial brush border (BB) Na(+)/H(+) exchanger NHE3 is associated with the actin cytoskeleton by binding both directly and indirectly to ezrin; indirect binding is via attachment to NHERF family proteins. NHE3 mobility in polarized epithelial cell BBs is restricted by the actin cytoskeleton and NHERF binding such that only approximately 30% of NHE3 in the apical domain of an OK cell line stably expressing NHERF2 is mobile, as judged by FRAP analysis. Given that levels of NHE3 are partially regulated by changes in trafficking, we investigated whether the cytoskeleton association of NHE3 was dynamic and changed as part of acute regulation to allow NHE3 trafficking. The agonist studied was lysophosphatidic acid (LPA), an inflammatory mediator, which acutely stimulates NHE3 activity by increasing the amount of NHE3 on the BBs by stimulated exocytosis. LPA acutely stimulated NHE3 activity in OK cells stably expressing NHERF2. Two conditions that totally prevented LPA stimulation of NHE3 activity only partially prevented stimulation of NHE3 mobility: the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, and the NHE3F1 double mutant which has minimal direct binding of NHE3 to ezrin. These results show that LPA stimulation of NHE3 mobility occurs in two parts: (1) PI3K-dependent exocytic trafficking to the BB and (2) an increase in surface mobility of NHE3 in BBs under basal conditions. Moreover, the LPA stimulatory effect on NHE3 mobility required NHERF2. Although NHE3 and NHERF2 co-precipitated under basal conditions, they failed to co-precipitate 30 minutes after addition of LPA, whereas the physical association was re-established by 50-60 minutes. This dynamic interaction between NHERF2 and NHE3 was confirmed by acceptor photobleaching Förster Resonance energy Transfer (FRET). The restricted mobility of NHE3 in BBs under basal conditions as a result of cytoskeleton association is therefore dynamic and is reversed as part of acute LPA stimulation of NHE3. We suggest that this acute but transient increase in NHE3 mobility induced by LPA occurs via two processes: addition of NHE3 to the BB by exocytosis, a process which precedes binding of NHE3 to the actin cytoskeleton via NHERF2-ezrin, and by release of NHERF2 from the NHE3 already localized in the apical membrane, enabling NHE3 to distribute throughout the microvilli. These fractions of NHE3 make up a newly identified pool of NHE3 called the 'transit pool'. Moreover, our results show that there are two aspects of LPA signaling involved in stimulation of NHE3 activity: PI3K-dependent stimulated NHE3 exocytosis and the newly described, PI3K-independent dissociation of microvillar NHE3 from NHERF2.
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Affiliation(s)
- Boyoung Cha
- Departments of Physiology and Medicine, Gastroenterology Division, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Baltimore, MD 212052, USA
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8
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LIN SONGBAI, YERUVA SUNIL, HE PEIJIAN, SINGH ANURAGKUMAR, ZHANG HUANCHUN, CHEN MINGMIN, LAMPRECHT GEORG, DE JONGE HUGOR, TSE MING, DONOWITZ MARK, HOGEMA BORISM, CHUN JEROLD, SEIDLER URSULA, YUN CCHRIS. Lysophosphatidic acid stimulates the intestinal brush border Na(+)/H(+) exchanger 3 and fluid absorption via LPA(5) and NHERF2. Gastroenterology 2010; 138:649-58. [PMID: 19800338 PMCID: PMC2976485 DOI: 10.1053/j.gastro.2009.09.055] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2009] [Revised: 08/24/2009] [Accepted: 09/23/2009] [Indexed: 01/08/2023]
Abstract
BACKGROUND & AIMS Diarrhea results from reduced net fluid and salt absorption caused by an imbalance in intestinal absorption and secretion. The bulk of sodium and water absorption in the intestine is mediated by Na(+)/H(+) exchanger 3 (NHE3), located in the luminal membrane of enterocytes. We investigated the effect of lysophosphatidic acid (LPA) on Na(+)/H(+) exchanger activity and Na(+)-dependent fluid absorption in the intestine. METHODS We analyzed the effects of LPA on fluid absorption in intestines of wild-type mice and mice deficient in Na(+)/H(+) exchanger regulatory factor 2 (NHERF2; Nherf2(-/-)) or LPA(2) (Lpa(2)(-/-)). Roles of LPA(5) and NHERF2 were determined by analysis of heterologous expression. RESULTS Under basal conditions, LPA increased fluid absorption in an NHE3-dependent manner and restored the net fluid loss in a mouse model of acute diarrhea. Expression of the LPA receptor LPA(5) was necessary for LPA-induced stimulation of NHE3 activity in colonic epithelial cells. Stimulation of NHE3 by the LPA-LPA(5) signaling required coexpression of NHERF2, which interacted with LPA(5). LPA-mediated intestinal fluid absorption was impaired in Nherf2(-/-) mice, demonstrating the requirement for NHERF2 in LPA(5) activity. However, fluid absorption was unaltered in Lpa(2)(-/-) mice. LPA stimulated NHE3 and fluid absorption in part by increasing NHE3 protein abundance at the brush border membrane of intestinal epithelial cells. CONCLUSIONS LPA is a potent stimulant of NHE3 and fluid absorption in the intestine, signaling through LPA(5). Regulation by LPA(5) depends on its interaction with NHERF2. LPA might be useful in the treatment of certain diarrheal diseases.
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Affiliation(s)
- SONGBAI LIN
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
| | - SUNIL YERUVA
- Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Hannover, Germany
| | - PEIJIAN HE
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
| | - ANURAG KUMAR SINGH
- Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Hannover, Germany
| | - HUANCHUN ZHANG
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
| | - MINGMIN CHEN
- Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Hannover, Germany
| | - GEORG LAMPRECHT
- Department of Medicine, University of Tübingen, Tübingen, Germany
| | - HUGO R. DE JONGE
- Department of Biochemistry, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - MING TSE
- Departments of Medicine and Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - MARK DONOWITZ
- Departments of Medicine and Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - BORIS M. HOGEMA
- Department of Biochemistry, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - JEROLD CHUN
- Department of Molecular Biology, Scripps Research Institute, La Jolla, California
| | - URSULA SEIDLER
- Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Hannover, Germany
| | - C. CHRIS YUN
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
,Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
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Di Sole F, Babich V, Moe OW. The calcineurin homologous protein-1 increases Na(+)/H(+) -exchanger 3 trafficking via ezrin phosphorylation. J Am Soc Nephrol 2009; 20:1776-86. [PMID: 19556366 DOI: 10.1681/asn.2008121255] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The Na(+)/H(+)-exchanger 3 (NHE3) is essential for regulation of Na(+) transport in the renal and intestinal epithelium. Although changes in cell surface abundance control NHE3 function, the molecular signals that regulate NHE3 surface expression are not well defined. We found that overexpression of the calcineurin homologous protein-1 (CHP1) in opossum kidney cells increased NHE3 transport activity, surface protein abundance, and ezrin phosphorylation. CHP1 knockdown by small interfering RNA had the opposite effects. Overexpression of wild-type ezrin increased both NHE3 transport activity and surface protein abundance, confirming that NHE3 is downstream of ezrin. Expression of a pseudophosphorylated ezrin enhanced these effects, whereas expression of an ezrin variant that could not be phosphorylated prevented the downstream effects on NHE3. Furthermore, CHP1 knockdown reversed the activation of NHE3 by wild-type ezrin but not by the pseudophosphorylated ezrin. Taken together, these results demonstrate that CHP1 increases NHE3 abundance and constitutive function in a manner dependent on ezrin phosphorylation.
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Affiliation(s)
- Francesca Di Sole
- Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390-8885, USA.
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10
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Alexander RT, Grinstein S. Tethering, recycling and activation of the epithelial sodium–proton exchanger, NHE3. J Exp Biol 2009; 212:1630-7. [DOI: 10.1242/jeb.027375] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
NHE3 is a sodium–proton exchanger expressed predominantly in the apical membrane of renal and intestinal epithelia, where it plays a key role in salt and fluid absorption and pH homeostasis. It performs these functions through the exchange of luminal sodium for cytosolic protons. Acute regulation of NHE3 function is mediated by altering the total number of exchangers in the plasma membrane as well as their individual activity. Traffic between endomembrane and plasmalemmal pools of NHE3 dictates the density of exchangers available at the cell surface. The activity of the plasmalemmal pool, however,is not fixed and can be altered by the association with modifier proteins, by post-translational alterations (such as cAMP-mediated phosphorylation) and possibly also via interaction with specific plasmalemmal phospholipids. Interestingly, association with cytoskeletal components affects both levels of regulation, tethering NHE3 molecules at the surface and altering their intrinsic activity. This paper reviews the role of proteins and lipids in the modulation of NHE3 function.
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Affiliation(s)
- R. Todd Alexander
- Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada,T6G 2R7
| | - Sergio Grinstein
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada,M5G 1X8
- Department of Biochemistry, University of Toronto, Ontario, Canada
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11
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Bobulescu IA, Moe OW. Luminal Na(+)/H (+) exchange in the proximal tubule. Pflugers Arch 2009; 458:5-21. [PMID: 18853182 PMCID: PMC2878283 DOI: 10.1007/s00424-008-0595-1] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/26/2008] [Indexed: 12/11/2022]
Abstract
The proximal tubule is critical for whole-organism volume and acid-base homeostasis by reabsorbing filtered water, NaCl, bicarbonate, and citrate, as well as by excreting acid in the form of hydrogen and ammonium ions and producing new bicarbonate in the process. Filtered organic solutes such as amino acids, oligopeptides, and proteins are also retrieved by the proximal tubule. Luminal membrane Na(+)/H(+) exchangers either directly mediate or indirectly contribute to each of these processes. Na(+)/H(+) exchangers are a family of secondary active transporters with diverse tissue and subcellular distributions. Two isoforms, NHE3 and NHE8, are expressed at the luminal membrane of the proximal tubule. NHE3 is the prevalent isoform in adults, is the most extensively studied, and is tightly regulated by a large number of agonists and physiological conditions acting via partially defined molecular mechanisms. Comparatively little is known about NHE8, which is highly expressed at the lumen of the neonatal proximal tubule and is mostly intracellular in adults. This article discusses the physiology of proximal Na(+)/H(+) exchange, the multiple mechanisms of NHE3 regulation, and the reciprocal relationship between NHE3 and NHE8 at the lumen of the proximal tubule.
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Affiliation(s)
- I. Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
| | - Orson W. Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA,
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
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12
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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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13
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He P, Zhang H, Yun CC. IRBIT, inositol 1,4,5-triphosphate (IP3) receptor-binding protein released with IP3, binds Na+/H+ exchanger NHE3 and activates NHE3 activity in response to calcium. J Biol Chem 2008; 283:33544-53. [PMID: 18829453 DOI: 10.1074/jbc.m805534200] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium (Ca2+) is a highly versatile second messenger that regulates various cellular processes. Previous studies showed that elevation of intracellular Ca2+ regulates the activity of Na+/H+ exchanger 3 (NHE3). However, the effect of Ca2+-dependent signaling on NHE3 activity varies depending on cell types. In this study, we report the identification of IP3 receptor-binding protein released with IP3 (IRBIT) as a NHE3 interacting protein and its role in regulation of NHE3 activity. IRBIT bound to the carboxyl-terminal domain of NHE3, which is necessary for acute regulation of NHE3. Ectopic expression of IRBIT resulted in Ca2+-dependent activation of NHE3 activity, whereas silencing of endogenous IRBIT resulted in inhibition of NHE3 activity. Ca2+-dependent stimulation of NHE3 activity was dependent on the binding of IRBIT to NHE3. Previously Ca2+-dependent inhibition of NHE3 was demonstrated in the presence of NHERF2. Co-expression of IRBIT was able to reverse the NHERF2-dependent inhibition of NHE3. We also showed that IRBIT-dependent activation of NHE3 involves exocytic trafficking of NHE3 to the plasma membrane and this activation was blocked by inhibition of calmodulin (CaM) or CaM-dependent kinase II. These results suggest that the overall effect of Ca2+ on NHE3 activity is balanced by IRBIT-dependent activation and NHERF2-dependent inhibition.
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Affiliation(s)
- Peijian He
- Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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14
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Pradère JP, Gonzalez J, Klein J, Valet P, Grès S, Salant D, Bascands JL, Saulnier-Blache JS, Schanstra JP. Lysophosphatidic acid and renal fibrosis. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1781:582-7. [PMID: 18455518 DOI: 10.1016/j.bbalip.2008.04.001] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 04/01/2008] [Accepted: 04/01/2008] [Indexed: 02/07/2023]
Abstract
The development of fibrosis involves a multitude of events and molecules. Until now the majority of these molecules were found to be proteins or peptides. But recent data show significant involvement of the phospholipid lysophosphatidic acid (LPA) in the development of pulmonary, liver and renal fibrosis. The latest data on the role of LPA and the G-protein-coupled LPA1 receptor in the development of renal fibrosis will be discussed. LPA1-receptor activation was found to be associated with increased vascular leakage and increased fibroblast recruitment in pulmonary fibrosis. Furthermore, in renal fibrosis LPA1-receptor activation stimulates macrophage recruitment and connective tissue growth factor expression. The observations make this receptor an interesting alternative and new therapeutic target in fibrotic diseases.
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Affiliation(s)
- Jean-Philippe Pradère
- Inserm, U858/I2MR, Department of Metabolism and Obesity, Team #3, 1 Avenue Jean Poulhès, BP 84225, 31432 Toulouse Cedex 4, France
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15
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Orlowski J, Grinstein S. Emerging roles of alkali cation/proton exchangers in organellar homeostasis. Curr Opin Cell Biol 2007; 19:483-92. [PMID: 17646094 PMCID: PMC5021530 DOI: 10.1016/j.ceb.2007.06.001] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2007] [Revised: 05/31/2007] [Accepted: 06/08/2007] [Indexed: 11/28/2022]
Abstract
The regulated movement of monovalent cations such as H(+), Li(+), Na(+) and K(+) across biological membranes influences a myriad of cellular processes and is fundamental to all living organisms. This is accomplished by a multiplicity of ion channels, pumps and transporters. Our insight into their molecular, cellular and physiological diversity has increased greatly in the past few years with the advent of genome sequencing, genetic manipulation and sophisticated imaging techniques. One of the revelations from these studies is the emergence of novel alkali cation/protons exchangers that are present in endomembranes, where they function to regulate not only intraorganellar pH but also vesicular biogenesis, trafficking and other aspects of cellular homeostasis.
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Affiliation(s)
- John Orlowski
- Department of Physiology, McGill University, McIntyre Medical Science Bldg. 3655 Promenade Sir-William-Osler, Montreal, Quebec H3G 1Y6, Canada
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16
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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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Pepe GJ, Burch MG, Albrecht ED. Regulation of expression and localisation of the Na+/H+ exchanger (NHE) 3 and the NHE regulatory factor 2 in baboon placental syncytiotrophoblast by oestrogen. Placenta 2007; 28:878-88. [PMID: 17336377 PMCID: PMC1994787 DOI: 10.1016/j.placenta.2007.01.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 12/21/2006] [Accepted: 01/03/2007] [Indexed: 10/23/2022]
Abstract
Our understanding of the regulation of the expression of the sodium hydrogen exchangers (NHE) and their regulatory factors (NHERF), which play important roles in fetal-placental homeostasis, is incomplete. We previously showed that the expression and localisation of NHE3 and NHERF2 in the juxtanuclear compartment of the placental syncytiotrophoblast were markedly decreased between mid and late baboon pregnancy. In the current study, immunocytochemical fluorescence localisation and level of NHE3/NHE1 and NHERF1/NHERF2 proteins were determined in late gestation in baboons untreated or treated throughout the second half of gestation with an aromatase inhibitor CGS 20267 alone (reduced oestrogen levels by >95%) or with oestradiol to determine whether oestrogen regulated antiporter developmental expression. The immunocytochemical expression of NHE3 and NHERF2 in the juxtanuclear compartment was minimal in baboons untreated or treated with CGS 20267 plus oestradiol (i.e. oestrogen-replete) but extensive in oestrogen-suppressed animals. Moreover, the abundant expression of NHERF2 in fetal vascular endothelium of oestrogen-replete baboons was decreased in oestrogen-suppressed animals. In contrast, expression and localisation of NHE1 and NHERF1 in the placental syncytiotrophoblast were not altered by oestrogen deprivation in baboons. Based on our current and previous findings, we propose that oestrogen plays an important role in regulating localisation and expression of components of the NHE system within and consequently development and function of the primate placental syncytiotrophoblast.
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Affiliation(s)
- G J Pepe
- Department of Physiological Sciences, Eastern Virginia Medical School, P.O. Box 1980, Norfolk, VA 23501-1980, USA.
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Bobulescu IA, Dwarakanath V, Zou L, Zhang J, Baum M, Moe OW. Glucocorticoids acutely increase cell surface Na+/H+ exchanger-3 (NHE3) by activation of NHE3 exocytosis. Am J Physiol Renal Physiol 2005; 289:F685-91. [PMID: 15942046 PMCID: PMC2861571 DOI: 10.1152/ajprenal.00447.2004] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Glucocorticoids have important effects on renal function, including the modulation of renal acidification by the major proximal tubular Na(+)/H(+) exchanger, NHE3. While the chronic effect of glucocorticoids is considered to be primarily at the transcriptional level, with increases in NHE3 mRNA and protein expression driving increased transport activity, the mechanisms by which glucocorticoids activate NHE3 in an acute setting have not been investigated. Previous studies have shown that a glucocorticoid-stimulated increase in NHE3 activity can occur before any detectable change in NHE3 mRNA. The present study examines the acute effects of glucocorticoids on NHE3 using opossum kidney (OKP) cells as a cell model. In OKP cells, total NHE3 protein abundance was not changed by 3 h of treatment with dexamethasone (10(-6) M). However, the biotin-accessible fraction representing NHE3 at the apical membrane as well as Na(+)/H(+) exchange activity measured fluorimetrically using the pH-sensitive dye BCECF-AM were significantly increased. These effects were not prevented by the protein synthesis inhibitor cycloheximide. NHE3 insertion (biotinylatable NHE3 after sulfo-NHS-acetate blockade) was stimulated by dexamethasone incubation, with or without cycloheximide. The rate of NHE3 endocytic retrieval, assessed either by the avidin protection assay (early endocytosis) or by the sodium 2-mercaptoethane sulfonate (MesNa) cleavage assay (early and late endocytosis), was not affected by dexamethasone. These findings suggest that trafficking plays a key role in the acute stimulation of NHE3 by glucocorticoids, with exocytosis being the major contributor to the glucocorticoid-induced rapid increase in cell surface NHE3 protein abundance and Na(+)/H(+) exchange activity.
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Affiliation(s)
- I Alexandru Bobulescu
- Univ. of Texas Southwestern Medical Ctr., 5323 Harry Hines Blvd., Dallas, TX 75390-8856, USA
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