Selective Assembly of V-ATPase Subunit Isoforms in Mouse Kidney

The kidney plays vital roles in acid–base homeostasis, and the reabsorption of water, ions, and proteins. These processes are achieved through acidification of urine and endosomes of proximal tubule epithelial cells. Multisubunit vacuolar-type proton ATPase (V-ATPase) is one of the major acidification-machinery proteins that localizes to the apical or basolateral plasma membranes of intercalated cells in collecting ducts and the endosomal region at the base of brush border microvilli in proximal tubules. Multiple subunit isoforms of V-ATPase, which are expressed in kidney, have been identified. One obvious question is whether the pumps at different locations in the kidney have their own unique subunit identities. We have used a combination of methods to study this enzyme in kidney including immunocytochemical staining and immunoprecipitation analyses. The subunit isoforms of V-ATPase exhibited selective association/assembly in kidney: kidney-specific isoforms predominantly formed the intercalated cell proton pump, whereas the pump located in the brush border comprised ubiquitously expressed counterparts.     

Immunofluorescent localization of the Rab-GAP protein TBC1D4 (AS160) in mouse kidney

TBC1D4 (or AS160) was identified as a Rab-GTPase activating protein (Rab-GAP) that controls insulin-dependent trafficking of the glucose transporter GLUT4 in skeletal muscle cells and in adipocytes. Recent in vitro cell culture studies suggest that TBC1D4 may also regulate the intracellular trafficking of kidney proteins such as the vasopressin-dependent water channel AQP2, the aldosterone-regulated epithelial sodium channel ENaC, and the Na(+)-K(+)-ATPase. To study the possible role of TBC1D4 in the kidney in vivo, we raised a rabbit polyclonal antibody against TBC1D4 to be used for immunoblotting and immunohistochemical studies. In immunoblots on mouse kidney homogenates, the antibody recognizes specific bands at the expected size of 160 kDa and at lower molecular weights, which are absent in kidneys of TBC1D4 deficient mice. Using a variety of nephron-segment-specific marker proteins, immunohistochemistry reveals TBC1D4 in the cytoplasm of the parietal epithelial cells of Bowman's capsule, the thin and thick limbs of Henle's loop, the distal convoluted tubule, the connecting tubule, and the collecting duct. In the latter, both principal as well as intercalated cells are TBC1D4-positive. Thus, with the exception of the proximal tubule, TBC1D4 is highly expressed along the nephron and the collecting duct, where it may interfere with the intracellular trafficking of many renal transport proteins including AQP2, ENaC and Na(+)-K(+)-ATPase. Hence, TBC1D4 may play an important role for the control of renal ion and water handling and hence for the control of extracellular fluid homeostasis.     

Differential expression and targeting of endogenous Arf1 and Arf6 small GTPases in kidney epithelial cells in situ

ADP-ribosylation factors (Arfs) are small GTPases that regulate vesicular trafficking in exo- and endocytotic pathways. As a first step in understanding the role of Arfs in renal physiology, immunocytochemistry and Western blotting were performed to characterize the expression and targeting of Arf1 and Arf6 in epithelial cells in situ. Arf1 and Arf6 were associated with apical membranes and subapical vesicles in proximal tubules, where they colocalized with megalin. Arf1 was also apically expressed in the distal tubule, connecting segment, and collecting duct (CD). Arf1 was abundant in intercalated cells (IC) and colocalized with V-ATPase in A-IC (apical) and B-IC (apical and/or basolateral). In contrast, Arf6 was associated exclusively with basolateral membranes and vesicles in the CD. In the medulla, basolateral Arf6 was detectable mainly in A-IC. Expression in principal cells became weaker throughout the outer medulla, and Arf6 was not detectable in principal cells in the inner medulla. In some kidney epithelial cells Arf1 but not Arf6 was also targeted to a perinuclear patch, where it colocalized with TGN38, a marker of the trans-Golgi network. Quantitative Western blotting showed that expression of endogenous Arf1 was 26–180 times higher than Arf6. These data indicate that Arf GTPases are expressed and targeted in a cell- and membrane-specific pattern in kidney epithelial cells in situ. The results provide a framework on which to base and interpret future studies on the role of Arf GTPases in the multitude of cellular trafficking events that occur in renal tubular epithelial cells. protein trafficking; immunofluorescence microscopy; Western blotting; endocytosis     

pH-dependent cargo sorting from the Golgi

The vacuolar proton-translocating ATPase (V-ATPase) plays a major role in organelle acidification and works together with other ion transporters to maintain pH homeostasis in eukaryotic cells. We analyzed a requirement for V-ATPase activity in protein trafficking in the yeast secretory pathway. Deficiency of V-ATPase activity caused by subunit deletion or glucose deprivation results in missorting of newly synthesized plasma membrane proteins Pma1 and Can1 directly from the Golgi to the vacuole. Vacuolar mislocalization of Pma1 is dependent on Gga adaptors although no Pma1 ubiquitination was detected. Proper cell surface targeting of Pma1 was rescued in V-ATPase-deficient cells by increasing the pH of the medium, suggesting that missorting is the result of aberrant cytosolic pH. In addition to mislocalization of the plasma membrane proteins, Golgi membrane proteins Kex2 and Vrg4 are also missorted to the vacuole upon loss of V-ATPase activity. Because the missorted cargos have distinct trafficking routes, we suggest a pH dependence for multiple cargo sorting events at the Golgi.     

Aldolase directly interacts with ARNO and modulates cell morphology and acidic vesicle distribution

Previously, we demonstrated that the vacuolar-type H(+)-ATPase (V-ATPase) a2-subunit functions as an endosomal pH sensor that interacts with the ADP-ribosylation factor (Arf) guanine nucleotide exchange factor, ARNO. In the present study, we showed that ARNO directly interacts not only with the a2-subunit but with all a-isoforms (a1-a4) of the V-ATPase, indicating a widespread regulatory interaction between V-ATPase and Arf GTPases. We then extended our search for other ARNO effectors that may modulate V-ATPase-dependent vesicular trafficking events and actin cytoskeleton remodeling. Pull-down experiments using cytosol of mouse proximal tubule cells (MTCs) showed that ARNO interacts with aldolase, but not with other enzymes of the glycolytic pathway. Direct interaction of aldolase with the pleckstrin homology domain of ARNO was revealed by pull-down assays using recombinant proteins, and surface plasmon resonance revealed their high avidity interaction with a dissociation constant: K(D) = 2.84 × 10(-10) M. MTC cell fractionation revealed that aldolase is also associated with membranes of early endosomes. Functionally, aldolase knockdown in HeLa cells produced striking morphological changes accompanied by long filamentous cell protrusions and acidic vesicle redistribution. However, the 50% knockdown we achieved did not modulate the acidification capacity of endosomal/lysosomal compartments. Finally, a combination of small interfering RNA knockdown and overexpression revealed that the expression of aldolase is inversely correlated with gelsolin levels in HeLa cells. In summary, we have shown that aldolase forms a complex with ARNO/Arf6 and the V-ATPase and that it may contribute to remodeling of the actin cytoskeleton and/or the trafficking and redistribution of V-ATPase-dependent acidic compartments via a combination of protein-protein interaction and gene expression mechanisms.     

a4, a unique kidney-specific isoform of mouse vacuolar H+-ATPase subunit a

The vacuolar-type H+ -ATPase (V-ATPase) translocates protons across membranes. Here, we have identified a mouse cDNA coding for a fourth isoform (a4) of the membrane sector subunit a of V-ATPase. This isoform was specifically expressed in kidney, but not in the heart, brain, spleen, lung, liver, muscle, or testis. Immunoprecipitation experiments, together with sequence similarities for other isoforms (a1, a2, and a3), indicate that the a4 isoform is a component of V-ATPase. Moreover, histochemical studies show that a4 is localized in the apical and basolateral plasma membranes of cortical alpha- and beta-intercalated cells, respectively. These results suggest that the V-ATPase, with the a4 isoform, is important for renal acid/base homeostasis.     

V-ATPase B1-subunit promoter drives expression of EGFP in intercalated cells of kidney, clear cells of epididymis and airway cells of lung in transgenic mice

The kidney, epididymis, and lungs are complex organs with considerable epithelial cell heterogeneity. This has limited the characterization of pathophysiological transport processes that are specific for each cell type in these epithelia. The purpose of the present study was to develop new tools to study cell-specific gene and protein expression in such complex tissues and organs. We report the production of a transgenic mouse that expresses enhanced green fluorescent protein (EGFP) in a subset of epithelial cells that express the B1 subunit of vacuolar H⁺-ATPase (V-ATPase) and are actively involved in proton transport. A 6.5-kb portion of the V-ATPase B1 promoter was used to drive expression of EGFP. In two founders, quantitative real-time RT-PCR demonstrated expression of EGFP in kidney, epididymis, and lung. Immunofluorescence labeling using antibodies against the B1 and E subunits of V-ATPase and against carbonic anhydrase type II (CAII) revealed specific EGFP expression in all renal type A and type B intercalated cells, some renal connecting tubule cells, all epididymal narrow and clear cells, and some nonciliated airway epithelial cells. No EGFP expression was detected in collecting duct principal cells (identified using an anti-AQP2 antibody) or epididymal principal cells (negative for V-ATPase or CAII). This EGFP-expressing mouse model should prove useful in future studies of gene and protein expression and their physiological and/or developmental regulation in distinct cell types that can now be separated using fluorescence-assisted microdissection, fluorescence-activated cell sorting, and laser capture microdissection. collecting duct; enhanced green fluorescent protein     

New insights into the dynamic regulation of water and acid-base balance by renal epithelial cells

Maintaining tight control over body fluid and acid-base homeostasis is essential for human health and is a major function of the kidney. The collecting duct is a mosaic of two cell populations that are highly specialized to perform these two distinct processes. The antidiuretic hormone vasopressin (VP) and its receptor, the V2R, play a central role in regulating the urinary concentrating mechanism by stimulating accumulation of the aquaporin 2 (AQP2) water channel in the apical membrane of collecting duct principal cells. This increases epithelial water permeability and allows osmotic water reabsorption to occur. An understanding of the basic cell biology/physiology of AQP2 regulation and trafficking has informed the development of new potential treatments for diseases such as nephrogenic diabetes insipidus, in which the VP/V2R/AQP2 signaling axis is defective. Tubule acidification due to the activation of intercalated cells is also critical to organ function, and defects lead to several pathological conditions in humans. Therefore, it is important to understand how these "professional" proton-secreting cells respond to environmental and cellular cues. Using epididymal proton-secreting cells as a model system, we identified the soluble adenylate cyclase (sAC) as a sensor that detects luminal bicarbonate and activates the vacuolar proton-pumping ATPase (V-ATPase) via cAMP to regulate tubular pH. Renal intercalated cells also express sAC and respond to cAMP by increasing proton secretion, supporting the hypothesis that sAC could function as a luminal sensor in renal tubules to regulate acid-base balance. This review summarizes recent advances in our understanding of these fundamental processes.     

Use of the Ramsay Assay to Measure Fluid Secretion and Ion Flux Rates in the Drosophila melanogaster Malpighian Tubule

Modulation of renal epithelial ion transport allows organisms to maintain ionic and osmotic homeostasis in the face of varying external conditions. The Drosophila melanogaster Malpighian (renal) tubule offers an unparalleled opportunity to study the molecular mechanisms of epithelial ion transport, due to the powerful genetics of this organism and the accessibility of its renal tubules to physiological study. Here, we describe the use of the Ramsay assay to measure fluid secretion rates from isolated fly renal tubules, with the use of ion-specific electrodes to measure sodium and potassium concentrations in the secreted fluid. This assay allows study of transepithelial fluid and ion fluxes of ~20 tubules at a time, without the need to transfer the secreted fluid to a separate apparatus to measure ion concentrations. Genetically distinct tubules can be analyzed to assess the role of specific genes in transport processes. Additionally, the bathing saline can be modified to examine the effects of its chemical characteristics, or drugs or hormones added. In summary, this technique allows the molecular characterization of basic mechanisms of epithelial ion transport in the Drosophila tubule, as well as regulation of these transport mechanisms.     

PIP2 signaling,an integrator of cell polarity and vesicle trafficking in directionally migrating cells

Cell migration is a fundamental cellular process required for embryonic development to wound healing and also plays a key role in tumor metastasis and atherosclerosis. Migration is regulated at multiple strata, from cytoskeletal reorganization to vesicle trafficking. In migrating cells, signaling pathways are integrated with vesicle trafficking machineries in a highly coordinated fashion to accomplish the recruitment and trafficking of the trans-membrane proteins toward the leading edge. Different signaling molecules regulate cell migration in different physio-pathological contexts, among them, phosphatidylinositol-4,5-biphosphate (PIP2) is an integral component of the plasma membrane and pleiotropic lipid signaling molecule modulating diverse biological processes, including actin cytoskeletal dynamics and vesicle trafficking required for cell migration. In this commentary, we provide a brief overview of our current understandings on the phosphoinositide signaling and its implication in regulation of cell polarity and vesicle trafficking in migrating cells. In addition, we highlight the coordinated role of PIPKIγi2, a focal adhesion-targeted enzyme that synthesizes PIP2, and the exocyst complex, a PIP2-effector, in the trafficking of E-cadherin in epithelial cells and integrins in migrating cancer cells.     

PIP2 signaling,an integrator of cell polarity and vesicle trafficking in directionally migrating cells

Cell migration is a fundamental cellular process required for embryonic development to wound healing and also plays a key role in tumor metastasis and atherosclerosis. Migration is regulated at multiple strata, from cytoskeletal reorganization to vesicle trafficking. In migrating cells, signaling pathways are integrated with vesicle trafficking machineries in a highly coordinated fashion to accomplish the recruitment and trafficking of the trans-membrane proteins toward the leading edge. Different signaling molecules regulate cell migration in different physio-pathological contexts, among them, phosphatidylinositol-4,5-biphosphate (PIP2) is an integral component of the plasma membrane and pleiotropic lipid signaling molecule modulating diverse biological processes, including actin cytoskeletal dynamics and vesicle trafficking required for cell migration. In this commentary, we provide a brief overview of our current understandings on the phosphoinositide signaling and its implication in regulation of cell polarity and vesicle trafficking in migrating cells. In addition, we highlight the coordinated role of PIPKIγi2, a focal adhesion-targeted enzyme that synthesizes PIP2, and the exocyst complex, a PIP2-effector, in the trafficking of E-cadherin in epithelial cells and integrins in migrating cancer cells.     

Vesicular transport and kidney development.

Vesicular transport processes play crucial roles in the biogenesis of cellular membranes and in the polarized transport functions of epithelial cells. During the 1990's we have witnessed major progress in elucidation of the machineries responsible for the intracellular membrane trafficking. The components of these machineries are abundant in tissues with a high content of epithelial cells, such as the kidney. However, the developmental role of the membrane trafficking apparatus in higher eukaryotes has been addressed hardly at all. We summarize here data on the presence and the functional role of vesicle transport proteins in the kidney, and describe work addressing the developmentally regulated expression and localization of three molecules suggested to be involved in polarized trafficking in kidney epithelia, Rab17, syntaxin 3, and Munc-18-2. The results show that specialized transport machinery is induced during differentiation of renal epithelia. However, the expression levels of the components under study are highest in the mature structures, indicating that the proteins are predominantly required for the function of mature epithelia and possibly for the maintenance of the polarized phenotype of specific epithelial cells. The proteins are, however, detected at low levels already in earlier, differentiating structures, and could thus also be involved in the differentiation of kidney epithelia.     

Interaction between aldolase and vacuolar H+-ATPase: evidence for direct coupling of glycolysis to the ATP-hydrolyzing proton pump

Vacuolar H(+)-ATPases (V-ATPases) are essential for acidification of intracellular compartments and for proton secretion from the plasma membrane in kidney epithelial cells and osteoclasts. The cellular proteins that regulate V-ATPases remain largely unknown. A screen for proteins that bind the V-ATPase E subunit using the yeast two-hybrid assay identified the cDNA clone coded for aldolase, an enzyme of the glycolytic pathway. The interaction between E subunit and aldolase was confirmed in vitro by precipitation assays using E subunit-glutathione S-transferase chimeric fusion proteins and metabolically labeled aldolase. Aldolase was isolated associated with intact V-ATPase from bovine kidney microsomes and osteoclast-containing mouse marrow cultures in co-immunoprecipitation studies performed using an anti-E subunit monoclonal antibody. The interaction was not affected by incubation with aldolase substrates or products. In immunocytochemical assays, aldolase was found to colocalize with V-ATPase in the renal proximal tubule. In osteoclasts, the aldolase-V-ATPase complex appeared to undergo a subcellular redistribution from perinuclear compartments to the ruffled membranes following activation of resorption. In yeast cells deficient in aldolase, the peripheral V(1) domain of V-ATPase was found to dissociate from the integral membrane V(0) domain, indicating direct coupling of glycolysis to the proton pump. The direct binding interaction between V-ATPase and aldolase may be a new mechanism for the regulation of the V-ATPase and may underlie the proximal tubule acidification defect in hereditary fructose intolerance.     

Phosphatidylinositol 3-kinase-mediated effects of glucose on vacuolar H+-ATPase assembly, translocation, and acidification of intracellular compartments in renal epithelial cells

Vacuolar H+-ATPases (V-ATPases) are a family of ATP-driven proton pumps. They maintain pH gradients between intracellular compartments and are required for proton secretion out of the cytoplasm. Mechanisms of extrinsic control of V-ATPase are poorly understood. Previous studies showed that glucose is an important regulator of V-ATPase assembly in Saccharomyces cerevisiae. Human V-ATPase directly interacts with aldolase, providing a coupling mechanism for glucose metabolism and V-ATPase function. Here we show that glucose is a crucial regulator of V-ATPase in renal epithelial cells and that the effect of glucose is mediated by phosphatidylinositol 3-kinase (PI3K). Glucose stimulates V-ATPase-dependent acidification of the intracellular compartments in human proximal tubular cells HK-2 and porcine renal epithelial cells LLC-PK1. Glucose induces rapid ATP-independent assembly of the V1 and Vo domains of V-ATPase and extensive translocation of the V-ATPase V1 and Vo domains between different membrane pools and between membranes and the cytoplasm. In HK-2 cells, glucose stimulates polarized translocation of V-ATPase to the apical plasma membrane. The effects of glucose on V-ATPase trafficking and assembly can be abolished by pretreatment with the PI3K inhibitor LY294002 and can be reproduced in glucose-deprived cells by adenoviral expression of the constitutively active catalytic subunit p110alpha of PI3K. Taken together these data provide evidence that, in renal epithelial cells, glucose plays an important role in the control of V-ATPase-dependent acidification of intracellular compartments and V-ATPase assembly and trafficking and that the effects of glucose are mediated by PI3K-dependent signaling.     

Tissue and cell distribution of the multidrug resistance-associated protein (MRP) in mouse intestine and kidney.

The multidrug resistance-associated protein (MRP) that is involved in drug resistance and the export of glutathione-conjugated substrates may not have the same epithelial cell membrane distribution as the P-glycoprotein encoded by the MDR gene. Because intestinal and kidney epithelial cells are polarized cells endowed distinct secreting and absorptive ion and protein transport capacities, we investigated the tissue and cell distribution of MRP in adult mouse small intestine, colon, and kidney by immunohistochemistry. Western blot analyses revealed the 190-kD MRP protein in these tissues. MRP was found in the basolateral membranes of intestinal crypt cells, mainly Paneth cells, but not in differentiated enterocytes. All the cells lining the crypt-villous axis of the colon wall contained MRP. MRP was found in the glomeruli, ascending limb cells, and basolateral membranes of the distal and collecting tubule cells of the kidney but not in proximal tubule cells. Cultured mouse intestinal m-ICcl2 cells and renal distal mpkDCT cells that have retained the features typical of intestinal crypt and renal distal epithelial cells, respectively, also possess MRP in their basolateral membranes. The patterns of subcellular and cellular distribution indicate that MRP may have a specific role in the basolateral transport of endogenous compounds in Paneth, renal distal, and collecting tubule cells.     

Modifications of the genital kidney proximal and distal tubules for sperm transport in Notophthalmus viridescens (Amphibia,Urodela, Salamandridae)

Male salamanders use nephrons from the genital kidney to transport sperm from the testicular lobules to the Wolffian duct. The microstructure of the epithelia of the genital kidney proximal tubule and distal tubule was studied over 1 year in a population of Notophthalmus viridescens from Crawford and Pike counties in central Missouri. Through ultrastructural analysis, we were able to support the hypothesis that the genital kidney nephrons are modified to aid in the transportation of sperm. A lack of folding of the basal plasma membrane, in both the genital kidney proximal and distal tubules when compared to the pelvic kidney proximal and distal tubules, reduces the surface area and thus likely decreases the efficiency of reabsorption in these nephron regions of the genital kidney. Ciliated epithelial cells are also present along the entire length of the genital kidney proximal tubule, but are lacking in the epithelium of the pelvic kidney proximal tubule. The exact function of these cilia remains unknown, but they may aid in mixing of seminal fluids or the transportation of immature sperm through the genital kidney nephrons. Ultrastructural analysis of proximal and distal tubules of the genital kidney revealed no seasonal variation in cellular activity and no mass production of seminal fluids throughout the reproductive cycle. Thus, we failed to support the hypothesis that the cellular activity of the epithelia lining the genital kidney nephrons is correlated to specific events in the reproductive cycle. The cytoplasmic contents and overall structure of the genital and pelvic kidney epithelial cells were similar to recent observations in Ambystoma maculatum, with the absence of abundant dense bodies apically in the epithelial cells lining the genital kidney distal tubule. J. Morphol. 275:914–922, 2014. © 2014 Wiley Periodicals, Inc.     

Collective Cell Migration Drives Morphogenesis of the Kidney Nephron

Tissue organization in epithelial organs is achieved during development by the combined processes of cell differentiation and morphogenetic cell movements. In the kidney, the nephron is the functional organ unit. Each nephron is an epithelial tubule that is subdivided into discrete segments with specific transport functions. Little is known about how nephron segments are defined or how segments acquire their distinctive morphology and cell shape. Using live, in vivo cell imaging of the forming zebrafish pronephric nephron, we found that the migration of fully differentiated epithelial cells accounts for both the final position of nephron segment boundaries and the characteristic convolution of the proximal tubule. Pronephric cells maintain adherens junctions and polarized apical brush border membranes while they migrate collectively. Individual tubule cells exhibit basal membrane protrusions in the direction of movement and appear to establish transient, phosphorylated Focal Adhesion Kinase–positive adhesions to the basement membrane. Cell migration continued in the presence of camptothecin, indicating that cell division does not drive migration. Lengthening of the nephron was, however, accompanied by an increase in tubule cell number, specifically in the most distal, ret1-positive nephron segment. The initiation of cell migration coincided with the onset of fluid flow in the pronephros. Complete blockade of pronephric fluid flow prevented cell migration and proximal nephron convolution. Selective blockade of proximal, filtration-driven fluid flow shifted the position of tubule convolution distally and revealed a role for cilia-driven fluid flow in persistent migration of distal nephron cells. We conclude that nephron morphogenesis is driven by fluid flow–dependent, collective epithelial cell migration within the confines of the tubule basement membrane. Our results establish intimate links between nephron function, fluid flow, and morphogenesis.     

Molecular anatomy of a trafficking organelle

Membrane traffic in eukaryotic cells involves transport of vesicles that bud from a donor compartment and fuse with an acceptor compartment. Common principles of budding and fusion have emerged, and many of the proteins involved in these events are now known. However, a detailed picture of an entire trafficking organelle is not yet available. Using synaptic vesicles as a model, we have now determined the protein and lipid composition; measured vesicle size, density, and mass; calculated the average protein and lipid mass per vesicle; and determined the copy number of more than a dozen major constituents. A model has been constructed that integrates all quantitative data and includes structural models of abundant proteins. Synaptic vesicles are dominated by proteins, possess a surprising diversity of trafficking proteins, and, with the exception of the V-ATPase that is present in only one to two copies, contain numerous copies of proteins essential for membrane traffic and neurotransmitter uptake.     

Significance of the V-type ATPase for the adaptation to stressful growth conditions and its regulation on the molecular and biochemical level

Two electrogenic H(+)-pumps, the vacuolar type H(+)-ATPase (V-ATPase) and the vacuolar pyrophosphatase, coexist at membranes of the secretory pathway of plants. The V-ATPase is the dominant H(+)-pump at endomembranes of most plant cells, both in terms of protein amount and, frequently, also in activity. The V-ATPase is indispensable for plant growth under normal conditions due to its role in energizing secondary transport, maintenance of solute homeostasis and, possibly, in facilitating vesicle fusion. Under stress conditions such as salinity, drought, cold, acid stress, anoxia, and excess heavy metals in the soil, survival of the cells depends strongly on maintaining or adjusting the activity of the V-ATPase. Regulation of gene expression and activity are involved in adapting the V-ATPase on long- and short-term bases. The mechanisms known to regulate the V-ATPase are summarized in this paper with an emphasis on their implications for growth and development under stress.     

The V-type H+-ATPase in vesicular trafficking: targeting, regulation and function

Vacuolar-type H+-ATPase (V-ATPase)-driven proton pumping and organellar acidification is essential for vesicular trafficking along both the exocytotic and endocytotic pathways of eukaryotic cells. Deficient function of V-ATPase and defects of vesicular acidification have been recently recognized as important mechanisms in a variety of human diseases and are emerging as potential therapeutic targets. In the past few years, significant progress has been made in our understanding of function, regulation, and the cell biological role of V-ATPase. Here, we will review these studies with emphasis on novel direct roles of V-ATPase in the regulation of vesicular trafficking events.