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Login FH, Dam VS, Nejsum LN. Following the cellular itinerary of renal aquaporin-2 shuttling with 4.5x expansion microscopy. Am J Physiol Cell Physiol 2024; 326:C194-C205. [PMID: 38047301 DOI: 10.1152/ajpcell.00397.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 11/21/2023] [Accepted: 11/22/2023] [Indexed: 12/05/2023]
Abstract
The shuttling of renal collecting duct aquaporin-2 (AQP2) between intracellular vesicles and the apical plasma membrane is paramount for regulation of renal water reabsorption. The binding of the circulating antidiuretic hormone arginine vasopressin (AVP) to the basolateral AVP receptor increases intracellular cAMP, which ultimately leads to AQP2 plasma membrane accumulation via a dual effect on AQP2 vesicle fusion with the apical plasma membrane and reduced AQP2 endocytosis. This AQP2 plasma membrane accumulation increases water reabsorption and consequently urine concentration. Conventional fluorescent microscopy provides a lateral resolution of ∼250 nm, which is insufficient to resolve the AQP2-containing endosomes/vesicles. Therefore, detailed information regarding the AQP2 vesicular population is still lacking. Newly established 4.5x Expansion Microscopy (ExM) can increase resolution to 60-70 nm. Using 4.5x ExM, we detected AQP2 vesicles/endosomes as small as 79 nm considering an average expansion factor of 4.3 for endosomes. Using different markers of the endosomal system provided detailed information of the cellular AQP2 itinerary upon changes in endogenous cAMP levels. Before cAMP elevation, AQP2 colocalized with early and recycling, but not late endosomes. Forskolin-induced cAMP increase was characterized by AQP2 insertion into the plasma membrane and AQP2 withdrawal from large perinuclear endosomes as well as some localization to lysosomal compartments. Forskolin washout promoted AQP2 endocytosis where AQP2 localized to not only early and recycling endosomes but also late endosomes and lysosomes indicating increased AQP2 degradation. Thus, our results show that 4.5 ExM is an attractive approach to obtain detailed information regarding AQP2 shuttling.NEW & NOTEWORTHY Renal aquaporin-2 (AQP2) imaged by expansion microscopy provides unprecedented 3-D information regarding the AQP2 itinerary in response to changes in cellular cAMP.
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Affiliation(s)
- Frédéric H Login
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Vibeke S Dam
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Lene N Nejsum
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
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2
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Zhao X, Liang B, Li C, Wang W. Expression Regulation and Trafficking of Aquaporins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1398:39-51. [PMID: 36717485 DOI: 10.1007/978-981-19-7415-1_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Aquaporins (AQPs) mediate the bidirectional water flow driven by an osmotic gradient. Either gating or trafficking allows for rapid and specific AQP regulation in a tissue-dependent manner. The regulatory mechanisms of AQP2 are discussed mainly in this chapter, as the mechanisms controlling the regulation and trafficking of AQP2 have been very well studied. The targeting of AQP2 to the apical plasma membrane of collecting duct principal cells is mainly regulated by the action of arginine vasopressin (AVP) on the type 2 AVP receptor (V2R), which cause increased intracellular cAMP or elevated intracellular calcium levels. Activation of these intracellular signaling pathways results in vesicles bearing AQP2 transport, docking and fusion with the apical membrane, which increase density of AQP2 on the membrane. The removal of AQP2 from the membrane requires dynamic cytoskeletal remodeling. AQP2 is degraded through the ubiquitin proteasome pathway and lysosomal proteolysis pathway. Finally, we review updated findings in transcriptional and epigenetic regulation of AQP2.
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Affiliation(s)
- Xiaoduo Zhao
- Department of Pathophysiology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China
| | - Baien Liang
- Department of Pathophysiology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China
| | - Chunling Li
- Department of Physiology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China.
| | - Weidong Wang
- Department of Pathophysiology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China.
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3
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Liu CCS, Cheung PW, Dinesh A, Baylor N, Paunescu TC, Nair AV, Bouley R, Brown D. Actin-related protein 2/3 complex plays a critical role in the aquaporin-2 exocytotic pathway. Am J Physiol Renal Physiol 2021; 321:F179-F194. [PMID: 34180716 PMCID: PMC8424666 DOI: 10.1152/ajprenal.00015.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The trafficking of proteins such as aquaporin-2 (AQP2) in the exocytotic pathway requires an active actin cytoskeleton network, but the mechanism is incompletely understood. Here, we show that the actin-related protein (Arp)2/3 complex, a key factor in actin filament branching and polymerization, is involved in the shuttling of AQP2 between the trans-Golgi network (TGN) and the plasma membrane. Arp2/3 inhibition (using CK-666) or siRNA knockdown blocks vasopressin-induced AQP2 membrane accumulation and induces the formation of distinct AQP2 perinuclear patches positive for markers of TGN-derived clathrin-coated vesicles. After a 20°C cold block, AQP2 formed perinuclear patches due to continuous endocytosis coupled with inhibition of exit from TGN-associated vesicles. Upon rewarming, AQP2 normally leaves the TGN and redistributes into the cytoplasm, entering the exocytotic pathway. Inhibition of Arp2/3 blocked this process and trapped AQP2 in clathrin-positive vesicles. Taken together, these results suggest that Arp2/3 is essential for AQP2 trafficking, specifically for its delivery into the post-TGN exocytotic pathway to the plasma membrane.NEW & NOTEWORTHY Aquaporin-2 (AQP2) undergoes constitutive recycling between the cytoplasm and plasma membrane, with an intricate balance between endocytosis and exocytosis. By inhibiting the actin-related protein (Arp)2/3 complex, we prevented AQP2 from entering the exocytotic pathway at the post-trans-Golgi network level and blocked AQP2 membrane accumulation. Arp2/3 inhibition, therefore, enables us to separate and target the exocytotic process, while not affecting endocytosis, thus allowing us to envisage strategies to modulate AQP2 trafficking and treat water balance disorders.
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Affiliation(s)
- Chen-Chung Steven Liu
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Pui Wen Cheung
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Anupama Dinesh
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Noah Baylor
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Theodor C. Paunescu
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Anil V. Nair
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Richard Bouley
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Dennis Brown
- Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
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Chlorpromazine Induces Basolateral Aquaporin-2 Accumulation via F-Actin Depolymerization and Blockade of Endocytosis in Renal Epithelial Cells. Cells 2020; 9:cells9041057. [PMID: 32340337 PMCID: PMC7226349 DOI: 10.3390/cells9041057] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 04/13/2020] [Accepted: 04/19/2020] [Indexed: 12/11/2022] Open
Abstract
We previously showed that in polarized Madin-Darby canine kidney (MDCK) cells, aquaporin-2 (AQP2) is continuously targeted to the basolateral plasma membrane from which it is rapidly retrieved by clathrin-mediated endocytosis. It then undertakes microtubule-dependent transcytosis toward the apical plasma membrane. In this study, we found that treatment with chlorpromazine (CPZ, an inhibitor of clathrin-mediated endocytosis) results in AQP2 accumulation in the basolateral, but not the apical plasma membrane of epithelial cells. In MDCK cells, both AQP2 and clathrin were concentrated in the basolateral plasma membrane after CPZ treatment (100 µM for 15 min), and endocytosis was reduced. Then, using rhodamine phalloidin staining, we found that basolateral, but not apical, F-actin was selectively reduced by CPZ treatment. After incubation of rat kidney slices in situ with CPZ (200 µM for 15 min), basolateral AQP2 and clathrin were increased in principal cells, which simultaneously showed a significant decrease of basolateral compared to apical F-actin staining. These results indicate that clathrin-dependent transcytosis of AQP2 is an essential part of its trafficking pathway in renal epithelial cells and that this process can be inhibited by selectively depolymerizing the basolateral actin pool using CPZ.
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5
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Basolateral cholesterol depletion alters Aquaporin-2 post-translational modifications and disrupts apical plasma membrane targeting. Biochem Biophys Res Commun 2018; 495:157-162. [DOI: 10.1016/j.bbrc.2017.11.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 11/01/2017] [Indexed: 11/22/2022]
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6
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Umejiego EN, Wang Y, Knepper MA, Chou CL. Roflumilast and aquaporin-2 regulation in rat renal inner medullary collecting duct. Physiol Rep 2017; 5:5/2/e13121. [PMID: 28108651 PMCID: PMC5269416 DOI: 10.14814/phy2.13121] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 11/29/2016] [Accepted: 12/12/2016] [Indexed: 12/23/2022] Open
Abstract
Roflumilast is a cyclic nucleotide phosphodiesterase inhibitor that is FDA‐approved for treatment of chronic obstructive pulmonary disease. With a view toward possible use for treatment of patients with X‐linked nephrogenic diabetes insipidus (NDI) due to hemizygous mutations in the V2 vasopressin receptor, this study sought to determine the effect of roflumilast on aquaporin‐2 (AQP2) phosphorylation, AQP2 trafficking, and water permeability in the rat inner medullary collecting duct (IMCD). In the presence of the vasopressin analog dDAVP (0.1 nmol/L), both roflumilast and its active metabolite roflumilast N‐oxide (RNO) significantly increased phosphorylation at S256, S264, and S269, and decreased phosphorylation at S261 (immunoblotting) in IMCD suspensions in a dose‐dependent manner (3–3000 nmol/L). Another commonly used phosphodiesterase inhibitor, IBMX, affected phosphorylation only at the highest concentration in this range. However, neither roflumilast nor RNO had an effect on AQP2 phosphorylation in the absence of vasopressin. Furthermore, roflumilast alone did not increase AQP2 trafficking to the plasma membrane (immunofluorescence) or increase water permeability in freshly microdissected perfused IMCD segments. We conclude that roflumilast can be used to enhance vasopressin's action on AQP2 activity in the renal collecting duct, but has no detectable effect in the absence of vasopressin. These findings suggest that roflumilast may not have a beneficial effect in X‐linked NDI, but could find useful application in acquired NDI.
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Affiliation(s)
- Ezigbobiara N Umejiego
- Epithelial Systems Biology Laboratory, Systems Biology Center NHLBI National Institutes of Health, Bethesda, Maryland, 20892-1603
| | - Yanhua Wang
- Renal Division, Department of Medicine, Emory University, Atlanta, Georgia, 30322
| | - Mark A Knepper
- Epithelial Systems Biology Laboratory, Systems Biology Center NHLBI National Institutes of Health, Bethesda, Maryland, 20892-1603
| | - Chung-Lin Chou
- Epithelial Systems Biology Laboratory, Systems Biology Center NHLBI National Institutes of Health, Bethesda, Maryland, 20892-1603
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Rahman SS, Moffitt AEJ, Trease AJ, Foster KW, Storck MD, Band H, Boesen EI. EHD4 is a novel regulator of urinary water homeostasis. FASEB J 2017; 31:5217-5233. [PMID: 28778975 DOI: 10.1096/fj.201601182rr] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 07/25/2017] [Indexed: 01/08/2023]
Abstract
The Eps15-homology domain-containing (EHD) protein family comprises 4 members that regulate endocytic recycling. Although the kidney expresses all 4 EHD proteins, their physiologic roles are largely unknown. This study focused on EHD4, which we found to be expressed differentially across nephron segments with the highest expression in the inner medullary collecting duct. Under baseline conditions, Ehd4-/- [EHD4-knockout (KO)] mice on a C57Bl/6 background excreted a higher volume of more dilute urine than control C57Bl/6 wild-type (WT) mice while maintaining a similar plasma osmolality. Urine excretion after an acute intraperitoneal water load was significantly increased in EHD4-KO mice compared to WT mice, and although EHD4-KO mice concentrated their urine during 24-h water restriction, urinary osmolality remained significantly lower than in WT mice, suggesting that EHD4 plays a role in renal water handling. Total aquaporin 2 (AQP2) and phospho-S256-AQP2 (pAQP2) protein expression in the inner medulla was similar in the two groups in baseline conditions. However, localization of both AQP2 and pAQP2 in the renal inner medullary principal cells appeared more dispersed, and the intensity of apical membrane staining for AQP2 was reduced significantly (by ∼20%) in EHD4-KO mice compared to WT mice in baseline conditions, suggesting an important role of EHD4 in trafficking of AQP2. Together, these data indicate that EHD4 play important roles in the regulation of water homeostasis.-Rahman, S. S., Moffitt, A. E. J., Trease, A. J., Foster, K. W., Storck, M. D., Band, H., Boesen, E. I. EHD4 is a novel regulator of urinary water homeostasis.
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Affiliation(s)
- Shamma S Rahman
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Alexandra E J Moffitt
- The Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Andrew J Trease
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Kirk W Foster
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Matthew D Storck
- The Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Hamid Band
- The Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska, USA; .,Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska, USA.,Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.,Department of Genetics, Cell Biology, and Anatomy, University of Nebraska Medical Center, Omaha, Nebraska, USA.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska, USA; and.,Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Erika I Boesen
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska, USA;
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8
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Chen L, Higgins PJ, Zhang W. Development and Diseases of the Collecting Duct System. Results Probl Cell Differ 2017; 60:165-203. [PMID: 28409346 DOI: 10.1007/978-3-319-51436-9_7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The collecting duct of the mammalian kidney is important for the regulation of extracellular volume, osmolarity, and pH. There are two major structurally and functionally distinct cell types: principal cells and intercalated cells. The former regulates Na+ and water homeostasis, while the latter participates in acid-base homeostasis. In vivo lineage tracing using Cre recombinase or its derivatives such as CreGFP and CreERT2 is a powerful new technique to identify stem/progenitor cells in their native environment and to decipher the origins of the tissue that they give rise to. Recent studies using this technique in mice have revealed multiple renal progenitor cell populations that differentiate into various nephron segments and collecting duct. In particular, emerging evidence suggests that like principal cells, most of intercalated cells originate from the progenitor cells expressing water channel Aquaporin 2. Mutations or malfunctions of the channels, pumps, and transporters expressed in the collecting duct system cause various human diseases. For example, gain-of-function mutations in ENaC cause Liddle's syndrome, while loss-of-function mutations in ENaC lead to Pseudohypoaldosteronism type 1. Mutations in either AE1 or V-ATPase B1 result in distal renal tubular acidosis. Patients with disrupted AQP2 or AVPR2 develop nephrogenic diabetes insipidus. A better understanding of the function and development of the collecting duct system may facilitate the discovery of new therapeutic strategies for treating kidney disease.
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Affiliation(s)
- Lihe Chen
- Epithelial Systems Biology Laboratory, Systems Biology Center, NHLBI, Bethesda, MD, 20892-1603, USA
| | - Paul J Higgins
- Department of Regenerative and Cancer Cell Biology, Albany Medical College, MC-165, 47 New Scotland Avenue, Albany, NY, 12208, USA
| | - Wenzheng Zhang
- Department of Regenerative and Cancer Cell Biology, Albany Medical College, MC-165, 47 New Scotland Avenue, Albany, NY, 12208, USA.
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9
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Mamuya FA, Xie D, Lei L, Huang M, Tsuji K, Capen DE, Yang B, Weissleder R, Păunescu TG, Lu HAJ. Deletion of β1-integrin in collecting duct principal cells leads to tubular injury and renal medullary fibrosis. Am J Physiol Renal Physiol 2017; 313:F1026-F1037. [PMID: 28701310 DOI: 10.1152/ajprenal.00038.2017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 06/19/2017] [Accepted: 07/11/2017] [Indexed: 11/22/2022] Open
Abstract
The renal collecting duct (CD) contains two major cell types, intercalated (ICs) and principal cells (PCs). A previous report showed that deletion of β1-integrin in the entire renal CD causes defective CD morphogenesis resulting in kidney dysfunction. However, subsequent deletion of β1-integrin specifically in ICs and PCs, respectively, did not cause any morphological defects in the CDs. The discrepancy between these studies prompts us to reinvestigate the role of β1-integrin in CD cells, specifically in the PCs. We conditionally deleted β1-integrin in mouse CD PCs using a specific aquaporin-2 (AQP2) promoter Cre-LoxP system. The resulting mutant mice, β-1f/fAQP2-Cre+, had lower body weight, failed to thrive, and died around 8-12 wk. Their CD tubules were dilated, and some of them contained cellular debris. Increased apoptosis and proliferation of PCs were observed in the dilated CDs. Trichrome staining and electron microscopy revealed the presence of peritubular and interstitial fibrosis that is associated with increased production of extracellular matrix proteins including collagen type IV and fibronectin, as detected by immunoblotting. Further analysis revealed a significantly increased expression of transforming growth factor-β (TGF-β)-induced protein, fibronectin, and TGF-β receptor-1 mRNAs and concomitantly increased phosphorylation of SMAD-2 that indicates the activation of the TGF-β signaling pathway. Therefore, our data reveal that normal expression of β1-integrin in PCs is a critical determinant of CD structural and functional integrity and further support the previously reported critical role of β1-integrin in the development and/or maintenance of the CD structure and function.
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Affiliation(s)
- Fahmy A Mamuya
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts
| | - Dongping Xie
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts.,Department of Physiology, Tongji University School of Medicine, Shanghai, China; and
| | - Lei Lei
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Ming Huang
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Kenji Tsuji
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts
| | - Diane E Capen
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts
| | - BaoXue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Ralph Weissleder
- Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts
| | - Teodor G Păunescu
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts.,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts
| | - Hua A Jenny Lu
- Program in Membrane Biology and Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts; .,Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts
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Abstract
Aquaporins (AQPs ) are a family of membrane water channels that basically function as regulators of intracellular and intercellular water flow. To date, thirteen AQPs , which are distributed widely in specific cell types in various organs and tissues, have been characterized in humans. Four AQP monomers, each of which consists of six membrane-spanning alpha-helices that have a central water-transporting pore, assemble to form tetramers, forming the functional units in the membrane. AQP facilitates osmotic water transport across plasma membranes and thus transcellular fluid movement. The cellular functions of aquaporins are regulated by posttranslational modifications , e.g. phosphorylation, ubiquitination, glycosylation, subcellular distribution, degradation, and protein interactions. Insight into the molecular mechanisms responsible for regulated aquaporin trafficking and synthesis is proving to be fundamental for development of novel therapeutic targets or reliable diagnostic and prognostic biomarkers.
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Affiliation(s)
- Chunling Li
- Institute of Hypertension, Zhongshan School of Medicine, Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China
| | - Weidong Wang
- Institute of Hypertension, Zhongshan School of Medicine, Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China.
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Mamuya FA, Cano-Peñalver JL, Li W, Rodriguez Puyol D, Rodriguez Puyol M, Brown D, de Frutos S, Lu HAJ. ILK and cytoskeletal architecture: an important determinant of AQP2 recycling and subsequent entry into the exocytotic pathway. Am J Physiol Renal Physiol 2016; 311:F1346-F1357. [PMID: 27760768 DOI: 10.1152/ajprenal.00336.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Revised: 09/29/2016] [Accepted: 10/11/2016] [Indexed: 12/20/2022] Open
Abstract
Within the past decade tremendous efforts have been made to understand the mechanism behind aquaporin-2 (AQP2) water channel trafficking and recycling, to open a path toward effective diabetes insipidus therapeutics. A recent study has shown that integrin-linked kinase (ILK) conditional-knockdown mice developed polyuria along with decreased AQP2 expression. To understand whether ILK also regulates AQP2 trafficking in kidney tubular cells, we performed in vitro analysis using LLCPK1 cells stably expressing rat AQP2 (LLC-AQP2 cells). Upon treatment of LLC-AQP2 cells with ILK inhibitor cpd22 and ILK-siRNA, we observed increased accumulation of AQP2 in the perinuclear region, without any significant increase in the rate of endocytosis. This perinuclear accumulation did not occur in cells expressing a serine-256-aspartic acid mutation that retains AQP2 in the plasma membrane. We then examined clathrin-mediated endocytosis after ILK inhibition using rhodamine-conjugated transferrin. Despite no differences in overall transferrin endocytosis, the endocytosed transferrin also accumulated in the perinuclear region where it colocalized with AQP2. These accumulated vesicles also contained the recycling endosome marker Rab11. In parallel, the usual vasopressin-induced AQP2 membrane accumulation was prevented after ILK inhibition; however, ILK inhibition did not measurably affect AQP2 phosphorylation at serine-256 or its dephosphorylation at serine-261. Instead, we found that inhibition of ILK increased F-actin polymerization. When F-actin was depolymerized with latrunculin, the perinuclear located AQP2 dispersed. We conclude that ILK is important in orchestrating dynamic cytoskeletal architecture during recycling of AQP2, which is necessary for its subsequent entry into the exocytotic pathway.
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Affiliation(s)
- Fahmy A Mamuya
- Division of Nephrology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
| | - Jose Luis Cano-Peñalver
- Department of Systems Biology, Physiology Unit, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain; Instituto Reina Sofia de Investigación Renal and Red de Investigación Renal (REDinREN), Instituto de Salud Carlos III, Madrid, Spain; and
| | - Wei Li
- Division of Nephrology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
| | - Diego Rodriguez Puyol
- Biomedical Research Foundation and Nephrology Department, Hospital Príncipe de Asturias, Alcalá de Henares, and Instituto Reina Sofia de Investigación Renal and REDinREN from Instituto de Salud Carlos III, Madrid, Spain
| | - Manuel Rodriguez Puyol
- Department of Systems Biology, Physiology Unit, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain; Instituto Reina Sofia de Investigación Renal and Red de Investigación Renal (REDinREN), Instituto de Salud Carlos III, Madrid, Spain; and
| | - Dennis Brown
- Division of Nephrology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
| | - Sergio de Frutos
- Department of Systems Biology, Physiology Unit, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain; Instituto Reina Sofia de Investigación Renal and Red de Investigación Renal (REDinREN), Instituto de Salud Carlos III, Madrid, Spain; and
| | - Hua Ann Jenny Lu
- Division of Nephrology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts;
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12
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Sands JM, Klein JD. Physiological insights into novel therapies for nephrogenic diabetes insipidus. Am J Physiol Renal Physiol 2016; 311:F1149-F1152. [PMID: 27534996 DOI: 10.1152/ajprenal.00418.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 08/16/2016] [Indexed: 12/11/2022] Open
Abstract
Fundamental kidney physiology research can provide important insight into how the kidney works and suggest novel therapeutic opportunities to treat human diseases. This is especially true for nephrogenic diabetes insipidus (NDI). Over the past decade, studies elucidating the molecular physiology and signaling pathways regulating water transport have suggested novel therapeutic possibilities. In patients with congenital NDI due to mutations in the type 2 vasopressin receptor (V2R) or acquired NDI due to lithium (or other medications), there are no functional abnormalities in the aquaporin-2 (AQP2) water channel, or in another key inner medullary transport protein, the UT-A1 urea transporter. If it is possible to phosphorylate and/or increase the apical membrane accumulation of these proteins, independent of vasopressin or cAMP, one may be able to treat NDI. Sildenifil (through cGMP), erlotinib, and simvastatin each stimulate AQP2 insertion into the apical plasma membrane. Some recent human data suggest that sildenafil and simvastatin may improve urine concentrating ability. ONO-AE1-329 (ONO) stimulates the EP4 prostanoid receptor (EP4), which stimulates kinases that in turn phosphorylate AQP2 and UT-A1. Clopidogrel is a P2Y12-R antagonist that potentiates the effect of vasopressin and increases AQP2 abundance. Metformin stimulates AMPK to phosphorylate and activate AQP2 and UT-A1, and it increases urine concentrating ability in two rodent models of NDI. Since metformin, sildenafil, and simvastatin are commercially available and have excellent safety records, the potential for rapidly advancing them into clinical trials is high.
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Affiliation(s)
- Jeff M Sands
- Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Janet D Klein
- Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
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Bonfrate L, Procino G, Wang DQH, Svelto M, Portincasa P. A novel therapeutic effect of statins on nephrogenic diabetes insipidus. J Cell Mol Med 2015; 19:265-82. [PMID: 25594563 PMCID: PMC4407600 DOI: 10.1111/jcmm.12422] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2014] [Accepted: 08/01/2014] [Indexed: 12/12/2022] Open
Abstract
Statins competitively inhibit hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase, resulting in reduced plasma total and low-density lipoprotein cholesterol levels. Recently, it has been shown that statins exert additional ‘pleiotropic’ effects by increasing expression levels of the membrane water channels aquaporin 2 (AQP2). AQP2 is localized mainly in the kidney and plays a critical role in determining cellular water content. This additional effect is independent of cholesterol homoeostasis, and depends on depletion of mevalonate-derived intermediates of sterol synthetic pathways, i.e. farnesylpyrophosphate and geranylgeranylpyrophosphate. By up-regulating the expression levels of AQP2, statins increase water reabsorption by the kidney, thus opening up a new avenue in treating patients with nephrogenic diabetes insipidus (NDI), a hereditary disease that yet lacks high-powered and limited side effects therapy. Aspects related to water balance determined by AQP2 in the kidney, as well as standard and novel therapeutic strategies of NDI are discussed.
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Affiliation(s)
- Leonilde Bonfrate
- Department of Biomedical Sciences and Human Oncology, Internal Medicine, University Medical School, Bari, Italy
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Abstract
PURPOSE OF REVIEW Aquaporin-2 (AQP2) water channels in principal cells of the kidney collecting duct are essential for urine concentration. Due to application of modern technologies, progress in our understanding of AQP2 has accelerated in recent years. In this article, we highlight some of the new insights into AQP2 function that have developed recently, with particular focus on the cell biological aspects of AQP2 regulation. RECENT FINDINGS AQP2 is subjected to a number of regulated modifications, including phosphorylation and ubiquitination, which are important for AQP2 function, cellular localization and degradation. AQP2 is likely internalized via clathrin and non-clathrin-mediated endocytosis. Regulation of AQP2 endocytosis, in addition to exocytosis, is a vital mechanism in determining overall AQP2 membrane abundance. AQP2 is associated with regulated membrane microdomains. Studies using membrane cholesterol depleting reagents, for example statins, have supported the role of membrane rafts in regulation of AQP2 trafficking. Noncanonical roles for AQP2, for example in epithelial cell migration, are emerging. SUMMARY AQP2 function and thus urine concentration is dependent on a variety of cell signalling mechanisms, posttranslational modification and interplay between AQP2 and its lipid environment. This complexity of regulation allows fine-tuning of AQP2 function and thus body water homeostasis.
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Combination of secretin and fluvastatin ameliorates the polyuria associated with X-linked nephrogenic diabetes insipidus in mice. Kidney Int 2014; 86:127-38. [PMID: 24522493 PMCID: PMC4080339 DOI: 10.1038/ki.2014.10] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 12/06/2013] [Accepted: 12/19/2013] [Indexed: 12/29/2022]
Abstract
X-linked nephrogenic diabetes insipidus (X-NDI) is a disease caused by inactivating mutations of the vasopressin (AVP) type 2 receptor (V2R) gene. Loss of V2R function prevents plasma membrane expression of the AQP2 water channel in the kidney collecting duct cells and impairs the kidney concentration ability. In an attempt to develop strategies to bypass V2R signaling in X-NDI, we evaluated the effects of secretin and fluvastatin, either alone or in combination, on kidney function in a mouse model of X-NDI. The secretin receptor was found to be functionally expressed in the kidney collecting duct cells. Based on this, X-NDI mice were infused with secretin for 14 days but urinary parameters were not altered by the infusion. Interestingly, secretin significantly increased AQP2 levels in the collecting duct but the protein primarily accumulated in the cytosol. Since we previously reported that fluvastatin treatment increased AQP2 plasma membrane expression in wild-type mice, secretin-infused X-NDI mice received a single injection of fluvastatin. Interestingly, urine production by X-NDI mice treated with secretin plus fluvastatin was reduced by nearly 90% and the urine osmolality was doubled. Immunostaining showed that secretin increased intracellular stores of AQP2 and the addition of fluvastatin promoted AQP2 trafficking to the plasma membrane. Taken together, these findings open new perspectives for the pharmacological treatment of X-NDI.
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Păunescu TG, Lu HAJ, Russo LM, Pastor-Soler NM, McKee M, McLaughlin MM, Bartlett BE, Breton S, Brown D. Vasopressin induces apical expression of caveolin in rat kidney collecting duct principal cells. Am J Physiol Renal Physiol 2013; 305:F1783-95. [PMID: 24133120 DOI: 10.1152/ajprenal.00622.2012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Caveolin (Cav)1 is expressed in the basolateral membrane domain of renal collecting duct (CD) principal cells (PCs), where it is associated with caveolae. To reveal any potential involvement of Cav1 in vasopressin signaling, we used specific monoclonal and polyclonal antibodies to examine its localization in CD PCs of Brattleboro (BB) rats treated with vasopressin (DDAVP). Compared with controls, immunofluorescence revealed a time-dependent increase in Cav1 expression in the apical membrane domain of PCs, where it overlapped with aquaporin-2 (AQP2). After 24 h of DDAVP treatment, Cav1 was visible as an increased number of small apical spots. The staining gradually became more extensive, and, after 2 wk of DDAVP, it occupied the majority of the apical membrane domain of many PCs. Cav1 also assumed an apical localization in PCs of DDAVP-treated Sprague-Dawley and Long-Evans rats. Similarly, Cav2 appeared at the apical pole of PCs after DDAVP treatment of BB, Sprague-Dawley, and Long-Evans rats. Immunogold electron microscopy confirmed bipolar Cav1 membrane expression in DDAVP-treated BB rats, whereas caveolae were only detected on the basolateral membrane. Immunoblot analysis of BB rat whole kidney homogenates revealed no significant increase in Cav1 levels in DDAVP-treated rats, suggesting that DDAVP induces Cav1 relocalization or modifies its targeting. We conclude that Cav1 and Cav2 trafficking and membrane localization are dramatically altered by the action of DDAVP. Importantly, the absence of apical caveolae indicates that while Cavs may have an as yet undetermined role in vasopressin-regulated signaling processes, this is probably unrelated to AQP2 internalization by caveolae.
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Affiliation(s)
- Teodor G Păunescu
- Program in Membrane Biology/Division of Nephrology, Massachusetts General Hospital, Simches Research Center, 185 Cambridge St., CPZN8150, Boston, MA 02114.
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17
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Regulation of aquaporin-2 in the kidney: A molecular mechanism of body-water homeostasis. Kidney Res Clin Pract 2013; 32:96-102. [PMID: 26877923 PMCID: PMC4714093 DOI: 10.1016/j.krcp.2013.07.005] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 06/29/2013] [Indexed: 11/22/2022] Open
Abstract
The kidneys play a key role in the homeostasis of body water and electrolyte balance. Aquaporin-2 (AQP2) is the vasopressin-regulated water-channel protein expressed at the connecting tubule and collecting duct, and plays a key role in urine concentration and body-water homeostasis through short-term and long-term regulation of collecting duct water permeability. The signaling transduction pathways resulting in the AQP2 trafficking to the apical plasma membrane of the collecting duct principal cells, including AQP2 phosphorylation, RhoA phosphorylation, actin depolymerization, and calcium mobilization, and the changes of AQP2 abundance in water-balance disorders have been extensively studied. Dysregulation of AQP2 has been shown to be importantly associated with a number of clinical conditions characterized by body-water balance disturbances, including hereditary nephrogenic diabetes insipidus (NDI), lithium-induced NDI, electrolytes disturbance, acute and chronic renal failure, ureteral obstruction, nephrotic syndrome, congestive heart failure, and hepatic cirrhosis. Recent studies exploiting omics technology further demonstrated the comprehensive vasopressin signaling pathways in the collecting ducts. Taken together, these studies elucidate the underlying molecular mechanisms of body-water homeostasis and provide the basis for the treatment of body-water balance disorders.
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18
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Sasaki S, Yui N, Noda Y. Actin directly interacts with different membrane channel proteins and influences channel activities: AQP2 as a model. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:514-20. [PMID: 23770358 DOI: 10.1016/j.bbamem.2013.06.004] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Revised: 06/01/2013] [Accepted: 06/06/2013] [Indexed: 11/26/2022]
Abstract
The interplay between actin and 10 membrane channel proteins that have been shown to directly bind to actin are reviewed. The 10 membrane channel proteins covered in this review are aquaporin 2 (AQP2), cystic fibrosis transmembrane conductance regulator (CFTR), ClC2, short form of ClC3 (sClC3), chloride intracellular channel 1 (CLIC1), chloride intracellular channel 5 (CLIC5), epithelial sodium channel (ENaC), large-conductance calcium-activated potassium channel (Maxi-K), transient receptor potential vanilloid 4 (TRPV4), and voltage-dependent anion channel (VDAC), with particular attention to AQP2. In regard to AQP2, most reciprocal interactions between actin and AQP2 occur during intracellular trafficking, which are largely mediated through indirect binding. Actin and the actin cytoskeleton work as cables, barriers, stabilizers, and force generators for motility. However, as with ENaC, the effects of actin cytoskeleton on channel gating should be investigated further. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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Affiliation(s)
- Sei Sasaki
- Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
| | - Naofumi Yui
- Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8519, Japan
| | - Yumi Noda
- Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8519, Japan
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19
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Sasaki S. Aquaporin 2: From its discovery to molecular structure and medical implications. Mol Aspects Med 2012; 33:535-46. [DOI: 10.1016/j.mam.2012.03.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2012] [Revised: 03/12/2012] [Accepted: 03/29/2012] [Indexed: 10/28/2022]
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20
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Yui N, Lu HAJ, Chen Y, Nomura N, Bouley R, Brown D. Basolateral targeting and microtubule-dependent transcytosis of the aquaporin-2 water channel. Am J Physiol Cell Physiol 2012; 304:C38-48. [PMID: 23015545 DOI: 10.1152/ajpcell.00109.2012] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The aquaporin-2 (AQP2) water channel relocates mainly to the apical plasma membrane of collecting duct principal cells after vasopressin (VP) stimulation. AQP2 transport to this membrane domain is assumed to be a direct route involving recycling of intracellular vesicles. However, basolateral plasma membrane expression of AQP2 is observed in vivo in principal cells. Here, we asked whether there is a transcytotic pathway of AQP2 trafficking between apical and basolateral membranes. We used MDCK cells in which AQP2 normally accumulates apically after VP exposure. In contrast, both site-specific biotinylation and immunofluorescence showed that AQP2 is strongly accumulated in the basolateral membrane, along with the endocytic protein clathrin, after a brief cold shock (4°C). This suggests that AQP2 may be constitutively targeted to basolateral membranes and then retrieved by clathrin-mediated endocytosis at physiological temperatures. Rab11 does not accumulate in basolateral membranes after cold shock, suggesting that the AQP2 in this location is not associated with Rab11-positive vesicles. After rewarming (37°C), basolateral AQP2 staining is diminished and it subsequently accumulates at the apical membrane in the presence of VP/forskolin, suggesting that transcytosis can be followed by apical insertion of AQP2. This process is inhibited by treatment with colchicine. Our data suggest that the cold shock procedure reveals the presence of microtubule-dependent AQP2 transcytosis, which represents an indirect pathway of apical AQP2 delivery in these cells. Furthermore, our data indicate that protein polarity data obtained from biotinylation assays, which require cells to be cooled to 4°C during the labeling procedure, should be interpreted with caution.
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Affiliation(s)
- Naofumi Yui
- Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
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21
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Păunescu TG, Rodriguez S, Benz E, McKee M, Tyszkowski R, Albers MW, Brown D. Loss of the V-ATPase B1 subunit isoform expressed in non-neuronal cells of the mouse olfactory epithelium impairs olfactory function. PLoS One 2012; 7:e45395. [PMID: 23028982 PMCID: PMC3447883 DOI: 10.1371/journal.pone.0045395] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Accepted: 08/22/2012] [Indexed: 02/07/2023] Open
Abstract
The vacuolar proton-pumping ATPase (V-ATPase) is the main mediator of intracellular organelle acidification and also regulates transmembrane proton (H(+)) secretion, which is necessary for an array of physiological functions fulfilled by organs such as the kidney, male reproductive tract, lung, bone, and ear. In this study we characterize expression of the V-ATPase in the main olfactory epithelium of the mouse, as well as a functional role for the V-ATPase in odor detection. We report that the V-ATPase localizes to the apical membrane microvilli of olfactory sustentacular cells and to the basolateral membrane of microvillar cells. Plasma membrane V-ATPases containing the B1 subunit isoform are not detected in olfactory sensory neurons or in the olfactory bulb. This precise localization of expression affords the opportunity to ascertain the functional relevance of V-ATPase expression upon innate, odor-evoked behaviors in B1-deficient mice. This animal model exhibits diminished innate avoidance behavior (revealed as a decrease in freezing time and an increase in the number of sniffs in the presence of trimethyl-thiazoline) and diminished innate appetitive behavior (a decrease in time spent investigating the urine of the opposite sex). We conclude that V-ATPase-mediated H(+) secretion in the olfactory epithelium is required for optimal olfactory function.
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Affiliation(s)
- Teodor G Păunescu
- MGH Center for Systems Biology, Division of Nephrology, Massachusetts General Hospital, Boston, Massachusetts, United States of America.
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22
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Cell biology of vasopressin-regulated aquaporin-2 trafficking. Pflugers Arch 2012; 464:133-44. [DOI: 10.1007/s00424-012-1129-4] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2012] [Revised: 06/10/2012] [Accepted: 06/11/2012] [Indexed: 01/03/2023]
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23
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Brown D, Bouley R, Păunescu TG, Breton S, Lu HAJ. New insights into the dynamic regulation of water and acid-base balance by renal epithelial cells. Am J Physiol Cell Physiol 2012; 302:C1421-33. [PMID: 22460710 DOI: 10.1152/ajpcell.00085.2012] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
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.
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Affiliation(s)
- Dennis Brown
- MGH Center for Systems Biology, Program in Membrane Biology and Division of Nephrology, Simches Research Center, Massachusetts General Hospital, Boston, MA 02114, USA.
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24
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Rice WL, Zhang Y, Chen Y, Matsuzaki T, Brown D, Lu HAJ. Differential, phosphorylation dependent trafficking of AQP2 in LLC-PK1 cells. PLoS One 2012; 7:e32843. [PMID: 22403603 PMCID: PMC3293519 DOI: 10.1371/journal.pone.0032843] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Accepted: 01/31/2012] [Indexed: 01/02/2023] Open
Abstract
The kidney maintains water homeostasis by modulating aquaporin 2 (AQP2) on the plasma membrane of collecting duct principal cells in response to vasopressin (VP). VP mediated phosphorylation of AQP2 at serine 256 is critical for this effect. However, the role of phosphorylation of other serine residues in the AQP2 C-terminus is less well understood. Here, we examined the effect of phosphorylation of S256, S261 and S269 on AQP2 trafficking and association with recycling pathway markers. We used LLC-PK1 cells expressing AQP2(S-D) or (S-A) phospho mutants and a 20°C cold block, which allows endocytosis to continue, but prevents protein exit from the trans Golgi network (TGN), inducing formation of a perinuclear AQP2 patch. AQP2-S256D persists on the plasma membrane during cold block, while wild type AQP2, AQP2-S256A, S261A, S269A and S269D are internalized and accumulate in the patch. Development of this patch, a measure of AQP2 internalization, was most rapid with AQP2-S256A, and slowest with S261A and S269D. AQP2-S269D exhibited a biphasic internalization profile with a significant amount not internalized until 150 minutes of cold block. After rewarming to 37°C, wt AQP2, AQP2-S261A and AQP2-S269D rapidly redistributed throughout the cytoplasm within 20 minutes, whereas AQP2-S256A dissipated more slowly. Colocalization of AQP2 mutants with several key vesicular markers including clathrin, HSP70/HSC70, EEA, GM130 and Rab11 revealed no major differences. Overall, our data provide evidence supporting the role of S256 and S269 in the maintenance of AQP2 at the cell surface and reveal the dynamics of internalization and recycling of differentially phosphorylated AQP2 in cell culture.
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Affiliation(s)
| | | | | | | | | | - Hua A. Jenny Lu
- Program in Membrane Biology, Division of Nephrology, Center for Systems Biology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
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25
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Moeller HB, Olesen ETB, Fenton RA. Regulation of the water channel aquaporin-2 by posttranslational modification. Am J Physiol Renal Physiol 2011; 300:F1062-73. [DOI: 10.1152/ajprenal.00721.2010] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The cellular functions of many eukaryotic membrane proteins, including the vasopressin-regulated water channel aquaporin-2 (AQP2), are regulated by posttranslational modifications. In this article, we discuss the experimental discoveries that have advanced our understanding of how posttranslational modifications affect AQP2 function, especially as they relate to the role of AQP2 in the kidney. We review the most recent data demonstrating that glycosylation and, in particular, phosphorylation and ubiquitination are mechanisms that regulate AQP2 activity, subcellular sorting and distribution, degradation, and protein interactions. From a clinical perspective, posttranslational modification resulting in protein misrouting or degradation may explain certain forms of nephrogenic diabetes insipidus. In addition to providing major insight into the function and dynamics of renal AQP2 regulation, the analysis of AQP2 posttranslational modification may provide general clues as to the role of posttranslational modification for regulation of other membrane proteins.
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Affiliation(s)
- Hanne B. Moeller
- The Water and Salt Research Center, Department of Anatomy, Aarhus University, Aarhus, Denmark
| | - Emma T. B. Olesen
- The Water and Salt Research Center, Department of Anatomy, Aarhus University, Aarhus, Denmark
| | - Robert A. Fenton
- The Water and Salt Research Center, Department of Anatomy, Aarhus University, Aarhus, Denmark
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26
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Li W, Zhang Y, Bouley R, Chen Y, Matsuzaki T, Nunes P, Hasler U, Brown D, Lu HAJ. Simvastatin enhances aquaporin-2 surface expression and urinary concentration in vasopressin-deficient Brattleboro rats through modulation of Rho GTPase. Am J Physiol Renal Physiol 2011; 301:F309-18. [PMID: 21511701 DOI: 10.1152/ajprenal.00001.2011] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Statins are 3-hydroxyl-3-methyglutaryl-CoA reductase inhibitors that are commonly used to inhibit cholesterol biosynthesis. Emerging data have suggested that they also have "pleotropic effects," including modulating actin cytoskeleton reorganization. Here, we report an effect of simvastatin on the trafficking of aquaporin-2 (AQP2). Specifically, simvastatin induced the membrane accumulation of AQP2 in cell cultures and kidneys in situ. The effect of simvastatin was independent of protein kinase A activation and phosphorylation at AQP2-Ser(256), a critical event involved in vasopressin (VP)-regulated AQP2 trafficking. Further investigation showed that simvastatin inhibited endocytosis in parallel with downregulation of RhoA activity. Overexpression of active RhoA attenuated simvastatin's effect, suggesting the involvement of this small GTPase in simvastatin-mediated AQP2 trafficking. Finally, the effect of simvastatin on urinary concentration was investigated in VP-deficient Brattleboro rats. Simvastatin acutely (3-6 h) increased urinary concentration and decreased urine output in these animals. In summary, simvastatin regulates AQP2 trafficking in vitro and urinary concentration in vivo via events involving downregulation of Rho GTPase activity and inhibition of endocytosis. Our study provides an alternative mechanism to regulate AQP2 trafficking, bypassing the VP-vasopressin receptor signaling pathway.
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Affiliation(s)
- Wei Li
- Center for Systems Biology, Program in Membrane Biology, Division of Nephrology, Dept. of Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
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27
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Gu R, Lu W, Xie J, Bai J, Xu B. Renalase deficiency in heart failure model of rats--a potential mechanism underlying circulating norepinephrine accumulation. PLoS One 2011; 6:e14633. [PMID: 21297953 PMCID: PMC3031511 DOI: 10.1371/journal.pone.0014633] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Accepted: 01/10/2011] [Indexed: 12/20/2022] Open
Abstract
Background Sympathetic overactivity and catecholamine accumulation are important characteristic findings in heart failure, which contribute to its pathophysiology. Here, we identify a potential mechanism underlying norepinephrine accumulation in a rat model of heart failure. Methodology/Principal Findings Initially, we constructed a rat model of unilateral renal artery stenosis (n = 16) and found that the expression of renalase, a previously identified secreted amine oxidase, was markedly reduced in the ischemic compared to the non-ischemic kidney (protein: 0.295±0.085 versus 0.765±0.171, p<0.05). Subsequently, we utilized an isolated perfused rat kidney model to demonstrate that the clearance rate of norepinephrine decreased with reduction of perfusion flow. On the basis of these findings, we hypothesized the reduced renal blood supply which occurs in heart failure would result in impaired synthesis of renalase by the kidney and consequently reduced degradation of circulating norepinephrine. To verify this, we used a rat model of infarction-induced heart failure (n = 12 per group). In these rats, the flow velocity of renal artery, when measured at four weeks, is obviously lower in the operation group. Renal expression of renalase was reduced (protein: 0.476±0.043 for control, 0.248±0.029 for operation versus 0.636±0.151 for sham-operation) and this was associated with an increase in circulating norepinephrine (0.168±0.016 ng/mL for control, 0.203±0.019 ng/mL for operation versus 0.138±0.008 ng/mL for sham-operation). Conclusions/Significance Renalase expression is influenced by renal blood flow and impaired synthesis of renalase by the kidney may represent a potential mechanism underlying circulating norepinephrine accumulation in heart failure.
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Affiliation(s)
- Rong Gu
- Department of Cardiology, Affiliated Drum Tower Hospital, Nanjing University Medical School, Nanjing, China
| | - Wen Lu
- Department of Cardiology, Affiliated Drum Tower Hospital, Nanjing University Medical School, Nanjing, China
| | - Jun Xie
- Department of Cardiology, Affiliated Drum Tower Hospital, Nanjing University Medical School, Nanjing, China
| | - Jian Bai
- Department of Cardiology, Affiliated Drum Tower Hospital, Nanjing University Medical School, Nanjing, China
| | - Biao Xu
- Department of Cardiology, Affiliated Drum Tower Hospital, Nanjing University Medical School, Nanjing, China
- * E-mail:
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Ares GR, Ortiz PA. Constitutive endocytosis and recycling of NKCC2 in rat thick ascending limbs. Am J Physiol Renal Physiol 2010; 299:F1193-202. [PMID: 20719977 DOI: 10.1152/ajprenal.00307.2010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The Na-K-2Cl cotransporter (NKCC2) mediates NaCl absorption by the thick ascending limb of Henle's loop (THAL). Exocytosis and endocytosis regulates surface expression of most transporters. However, little is known about the mechanism of NKCC2 trafficking in the absence of stimulating hormones and whether this mechanism contributes to regulation of steady-state surface expression of apical NKCC2 in the THAL. We tested whether NKCC2 undergoes constitutive endocytosis that regulates steady-state surface NKCC2 and NaCl reabsorption in THALs. We measured steady-state surface NKCC2 levels and the rate of NKCC2 endocytosis by surface biotinylation and Western blot and confocal microscopy of isolated perfused rat THALs. We observed constitutive NKCC2 endocytosis over 30 min that averaged 21.5 ± 2.7% of the surface pool. We then tested whether methyl-β-cyclodextrin (MβCD), a compound that inhibits endocytosis by chelating membrane cholesterol, blocked NKCC2 endocytic retrieval. We found that 30-min treatment with MβCD (5 mM) blocked NKCC2 endocytosis by 81% (P < 0.01). Blockade of endocytosis by MβCD induced accumulation of NKCC2 at the apical membrane as demonstrated by a 60 ± 16% (P < 0.05) increase in steady-state surface expression and enhanced apical surface NKCC2 immunostaining in isolated, perfused THALs. Acute treatment with MβCD did not change the total pool of NKCC2. MβCD did not affect NKCC2 trafficking when it was complexed with cholesterol before treatment. Inhibition endocytosis with MβCD enhanced NKCC2-dependent NaCl entry by 57 ± 16% (P < 0.05). Finally, we observed that a fraction of retrieved NKCC2 recycles back to the plasma membrane (36 ± 7%) over 30 min. We concluded that constitutive NKCC2 trafficking maintains steady-state surface NKCC2 and regulates NaCl reabsorption in THALs. These are the first data showing an increase in apical membrane NKCC2 in THALs by altering the rates of constitutive NKCC2 trafficking, rather than by stimulation of hormone-dependent signaling.
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Affiliation(s)
- Gustavo R Ares
- Hypertension and Vascular Research Div., Dept. of Internal Medicine, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202, USA
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Păunescu TG, Ljubojevic M, Russo LM, Winter C, McLaughlin MM, Wagner CA, Breton S, Brown D. cAMP stimulates apical V-ATPase accumulation, microvillar elongation, and proton extrusion in kidney collecting duct A-intercalated cells. Am J Physiol Renal Physiol 2010; 298:F643-54. [PMID: 20053793 DOI: 10.1152/ajprenal.00584.2009] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Kidney proton-secreting A-intercalated cells (A-IC) respond to systemic acidosis by accumulating the vacuolar ATPase (V-ATPase) in their apical membrane and by increasing the length and number of apical microvilli. We show here that the cell-permeant cAMP analog CPT-cAMP, infused in vivo, results in an almost twofold increase in apical V-ATPase accumulation in AE1-positive A-IC within 15 min and that these cells develop an extensive array of apical microvilli compared with controls. In contrast, no significant change in V-ATPase distribution could be detected by immunocytochemistry in B-intercalated cells at the acute time point examined. To show a direct effect of cAMP on A-IC, we prepared cell suspensions from the medulla of transgenic mice expressing EGFP in IC (driven by the B1-subunit promoter of the V-ATPase) and exposed them to cAMP analogs in vitro. Three-dimensional reconstructions of confocal images revealed that cAMP induced a time-dependent growth of apical microvilli, starting within minutes after addition. This effect was blocked by the PKA inhibitor myristoylated PKI. These morphological changes were paralleled by increased cAMP-mediated proton extrusion (pHi recovery) by A-IC in outer medullary collecting ducts measured using the ratiometric probe BCECF. These results, and our prior data showing that the bicarbonate-stimulated soluble adenylyl cyclase (sAC) is highly expressed in kidney intercalated cells, support the idea that cAMP generated either by sAC, or by activation of other signaling pathways, is part of the signal transduction mechanism involved in acid-base sensing and V-ATPase membrane trafficking in kidney intercalated cells.
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Affiliation(s)
- Teodor G Păunescu
- MGH Center for Systems Biology, Program in Membrane Biology, and Division of Nephrology, Massachusetts General Hospital, and Harvard Medical School, Boston, Massachusetts 02114, USA
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Procino G, Barbieri C, Carmosino M, Rizzo F, Valenti G, Svelto M. Lovastatin-induced cholesterol depletion affects both apical sorting and endocytosis of aquaporin-2 in renal cells. Am J Physiol Renal Physiol 2009; 298:F266-78. [PMID: 19923410 DOI: 10.1152/ajprenal.00359.2009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Vasopressin causes the redistribution of the water channel aquaporin-2 (AQP2) from cytoplasmic storage vesicles to the apical plasma membrane of collecting duct principal cells, leading to urine concentration. The molecular mechanisms regulating the selective apical sorting of AQP2 are only partially uncovered. In this work, we investigate whether AQP2 sorting/trafficking is regulated by its association with membrane rafts. In both MCD4 cells and rat kidney, AQP2 preferentially associated with Lubrol WX-insoluble membranes regardless of its presence in the storage compartment or at the apical membrane. Block-and-release experiments indicate that 1) AQP2 associates with detergent-resistant membranes early in the biosynthetic pathway; 2) strong cholesterol depletion delays the exit of AQP2 from the trans-Golgi network. Interestingly, mild cholesterol depletion promoted a dramatic accumulation of AQP2 at the apical plasma membrane in MCD4 cells in the absence of forskolin stimulation. An internalization assay showed that AQP2 endocytosis was clearly reduced under this experimental condition. Taken together, these data suggest that association with membrane rafts may regulate both AQP2 apical sorting and endocytosis.
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Affiliation(s)
- G Procino
- Department of General and Environmental Physiology, University of Bari, Bari, Italy.
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31
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Phosphorylation events and the modulation of aquaporin 2 cell surface expression. Curr Opin Nephrol Hypertens 2009; 17:491-8. [PMID: 18695390 DOI: 10.1097/mnh.0b013e3283094eb1] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW This review highlights the role of phosphorylation in the trafficking and targeting of aquaporin 2. Current knowledge will be put into the context of modulating the cell surface expression of aquaporin 2 by vasopressin in renal epithelial cells, which is critical for regulation of urinary concentration and control of fluid and electrolyte homeostasis. RECENT FINDINGS In addition to previously identified phosphorylation sites on aquaporin 2, new data have revealed three other serine residues in the C-terminus whose phosphorylation is altered by vasopressin. Several steps in aquaporin 2 recycling, including exocytosis and endocytosis, are coordinated by phosphorylation and dephosphorylation to regulate cell surface accumulation. Aquaporin 2 phosphorylation on serine 256 regulates aquaporin 2 association with proteins that are involved in trafficking, including hsc/hsp70 and myelin and lymphocyte-associated protein. SUMMARY Aquaporin 2 trafficking is regulated by phosphorylation of serine 256 and other amino acid residues in its cytoplasmic domain. These events increase or decrease interaction of aquaporin 2 with key regulatory proteins to determine the cellular distribution and fate of aquaporin 2, both after vasopressin addition and under baseline conditions. Better understanding of these mechanisms may provide new therapeutic avenues for patients with X-linked nephrogenic diabetes insipidus, as well as providing basic cell biological information relevant to membrane trafficking processes in general.
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Affiliation(s)
- Tae-Hwan Kwon
- Water and Salt Research Center, Institute of Anatomy, University of Aarhus, 8000 Aarhus C, Denmark
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Bouley R, Hasler U, Lu HAJ, Nunes P, Brown D. Bypassing vasopressin receptor signaling pathways in nephrogenic diabetes insipidus. Semin Nephrol 2008; 28:266-78. [PMID: 18519087 DOI: 10.1016/j.semnephrol.2008.03.010] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Water reabsorption in the kidney represents a critical physiological event in the maintenance of body water homeostasis. This highly regulated process relies largely on vasopressin (VP) action and on the VP-sensitive water channel (AQP2) that is expressed in principal cells of the kidney collecting duct. Defects in the VP signaling pathway and/or in AQP2 cell surface expression can lead to an inappropriate reduction in renal water reabsorption and the development of nephrogenic diabetes insipidus, a disease characterized by polyuria and polydipsia. This review focuses on the major regulatory steps that are involved in AQP2 trafficking and function. Specifically, we begin with a discussion on VP-receptor-independent mechanisms of AQP2 trafficking, with special emphasis on the nitric oxide-cyclic guanosine monophosphate signaling pathway, followed by a review of the mechanisms that govern AQP2 endocytosis and exocytosis. We then discuss emerging data illustrating roles played by the actin cytoskeleton on AQP2 trafficking, and lastly we consider elements that affect AQP2 protein expression in cells. Recent advances in each topic are summarized and are presented in the context of their potential to serve as a basis for the development of novel therapies that may ultimately improve life quality of nephrogenic diabetes insipidus patients.
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Affiliation(s)
- Richard Bouley
- Massachusetts General Hospital-Center for Systems Biology, Program in Membrane Biology and Nephrology Division, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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Nunes P, Hasler U, McKee M, Lu HAJ, Bouley R, Brown D. A fluorimetry-based ssYFP secretion assay to monitor vasopressin-induced exocytosis in LLC-PK1 cells expressing aquaporin-2. Am J Physiol Cell Physiol 2008; 295:C1476-87. [PMID: 18799651 DOI: 10.1152/ajpcell.00344.2008] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vasopressin (VP)-induced exocytosis was dissected in native and aquaporin-2 (AQP2)-expressing renal LLC-PK(1) cells by a fluorimetric exocytosis assay based on soluble secreted yellow fluorescent protein (ssYFP). YFP was targeted to the secretory pathway by addition of an 18-amino acid signal peptide from hen egg white lysozyme. Immunofluorescence labeling, together with analysis of Alexa 555-dextran internalization, revealed that ssYFP is exclusively located in the secretory pathway. Immunofluorescence and immunogold electron microscopy showed significant colocalization of ssYFP and AQP2. Fluorimetry and Western blot analysis demonstrated similar constitutive ssYFP secretion in native LLC-PK(1) and AQP2-expressing cells. In AQP2-expressing cells, a twofold increase in ssYFP secretion was observed within 15 min of VP stimulation. This transient burst of ssYFP secretion was abolished by the PKA inhibitor H-89 and was not observed in native cells. The endocytotic inhibitor methyl-beta-cyclodextrin, which also promotes membrane accumulation of AQP2, had no effect on ssYFP secretion. Although cells expressing phosphorylation-deficient AQP2-S256A showed significantly lower baseline levels of constitutive secretion, VP induced a significant increase in exocytosis. Our data indicate that 1) this assay can monitor exocytosis in cultured epithelial cells, 2) VP has an acute stimulatory effect on ssYFP secretion in AQP2-expressing, but not native, cells, and 3) phosphorylation of AQP2 at S256 may be involved in the regulation of constitutive AQP2 exocytosis and play only a minor role in the VP-induced burst. These results support the idea that, in addition to its role in reducing AQP2 endocytosis, VP increases AQP2 exocytosis.
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Affiliation(s)
- Paula Nunes
- Massachusetts General Hospital, Boston, MA 02114, USA.
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Lu HJ, Matsuzaki T, Bouley R, Hasler U, Qin QH, Brown D. The phosphorylation state of serine 256 is dominant over that of serine 261 in the regulation of AQP2 trafficking in renal epithelial cells. Am J Physiol Renal Physiol 2008; 295:F290-4. [PMID: 18434387 DOI: 10.1152/ajprenal.00072.2008] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phosphorylation of serine 256 (S256) plays a critical role in vasopressin (VP)-mediated membrane accumulation of aquaporin-2 (AQP2). Recently, phosphorylation of serine 261 was also reported, raising the possibility that it has a role in AQP2 trafficking. We addressed this issue using transfected LLC-PK(1) cells that express point mutations of AQP2 S261 and S256, mimicking the phosphorylated (S to D) or dephosphorylated (S to A) states of these residues. Both AQP2 (S261A) and AQP2 (S261D) were located in the perinuclear cytoplasm without stimulation but, like wild-type AQP2, they both accumulated on the plasma membrane after 20-min exposure to VP or forskolin. Following membrane accumulation, S261A, S261D, and wild-type AQP2 reinternalization was complete over a similar time frame, between 30 and 60 min after VP washout. Using various combinations of point mutations, we showed that the phosphorylation state of S256 is dominant with respect to AQP2 behavior; AQP2 membrane accumulation and internalization were not detectably affected by the phosphorylation state of S261. Finally, blocking AQP2 endocytosis by methyl-beta-cyclodextrin caused membrane accumulation of AQP2 in cells expressing either a single S-A mutation or double mutations of S256 and S261, although as previously reported, the S256D mutation was always present at the cell surface. This suggests that constitutive recycling of AQP2 was not modified by the phosphorylation state of S261. Together, our data indicate that the phosphorylation state of AQP2 at S261 does not detectably affect regulated or constitutive trafficking of AQP2. The potential role of S261 phosphorylation/dephosphorylation in vasopressin action remains to be determined.
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Affiliation(s)
- Hua Jenny Lu
- Center for Systems Biology, Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
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Acute regulation of aquaporin-2 phosphorylation at Ser-264 by vasopressin. Proc Natl Acad Sci U S A 2008; 105:3134-9. [PMID: 18287043 DOI: 10.1073/pnas.0712338105] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
By phosphoproteome analysis, we identified a phosphorylation site, serine 264 (pS264), in the COOH terminus of the vasopressin-regulated water channel, aquaporin-2 (AQP2). In this study, we examined the regulation of AQP2 phosphorylated at serine 264 (pS264-AQP2) by vasopressin, using a phospho-specific antibody (anti-pS264). Immunohistochemical analysis showed pS264-AQP2 labeling of inner medullary collecting duct (IMCD) from control mice, whereas AQP2 knockout mice showed a complete absence of labeling. In rat and mouse, pS264-AQP2 was present throughout the collecting duct system, from the connecting tubule to the terminal IMCD. Immunogold electron microscopy, combined with double-labeling confocal immunofluorescence microscopy with organelle-specific markers, determined that the majority of pS264 resides in compartments associated with the plasma membrane and early endocytic pathways. In Brattleboro rats treated with [deamino-Cys-1, d-Arg-8]vasopressin (dDAVP), the abundance of pS264-AQP2 increased 4-fold over controls. Additionally, dDAVP treatment resulted in a time-dependent change in the distribution of pS264 from predominantly intracellular vesicles, to both the basolateral and apical plasma membranes. Sixty minutes after dDAVP exposure, a proportion of pS264-AQP2 was observed in clathrin-coated vesicles, early endosomal compartments, and recycling compartments, but not lysosomes. Overall, our results are consistent with a dynamic effect of AVP on the phosphorylation and subcellular distribution of AQP2.
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Abstract
PURPOSE OF REVIEW Aquaporin-2 is an aquaporin water channel protein present at the apical membrane of kidney collecting duct cells and plays a key role in urine concentrating ability. Like other membrane proteins, aquaporin-2 undergoes dynamic processes within the cells: synthesized, targeted to the subapical region, exocytosed to the apical membrane, endocytosed, recycled and finally degraded. The understanding of the molecular and cellular mechanisms of these events is advancing rapidly, and recent new findings characterizing such processes are reviewed. RECENT FINDINGS Hypertonicity itself stimulates aquaporin-2 expression through the tonicity-responsive enhancer and its transcription factors. Gene targeted mouse models for human nephrogenic diabetes insipidus show the importance of the C-terminus of aquaporin-2 in apical sorting and provide mechanistic insights. Evidence for the importance of actin cytoskelton in exocytosis of aquaporin-2 to the apical membrane is accumulating. Actin and other proteins bind to aquaporin-2 and make a multiprotein complex. New proteomic analyses indicate the involvement of a large series of proteins in aquaporin-2 dynamics. SUMMARY The protein-level understanding of aquaporin-2 dynamics has advanced considerably over the past few years, and continuing studies will open a new way in developing new manoeuvres or drugs to manipulate kidney water homeostasis.
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Affiliation(s)
- Sei Sasaki
- Department of Nephrology, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
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Current World Literature. Curr Opin Nephrol Hypertens 2007; 16:388-93. [PMID: 17565283 DOI: 10.1097/mnh.0b013e3282472fd5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Bichet DG. Lithium, cyclic AMP signaling, A-kinase anchoring proteins, and aquaporin-2. J Am Soc Nephrol 2006; 17:920-2. [PMID: 16540556 DOI: 10.1681/asn.2006020135] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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