title: Acute hypertonicity alters aquaporin-2 trafficking and induces a MAPK-dependent accumulation at the plasma membrane of renal epithelial cells.
abstract: The unique phenotype of renal medullary cells allows them to survive and functionally adapt to changes of interstitial osmolality/tonicity. We investigated the effects of acute hypertonic challenge on AQP2 (aquaporin-2) water channel trafficking. In the absence of vasopressin, hypertonicity alone induced rapid (<10 min) plasma membrane accumulation of AQP2 in rat kidney collecting duct principal cells in situ, and in several kidney epithelial lines. Confocal microscopy revealed that AQP2 also accumulated in the trans-Golgi network (TGN) following hypertonic challenge. AQP2 mutants that mimic the Ser(256)-phosphorylated and -nonphosphorylated state accumulated at the cell surface and TGN, respectively. Hypertonicity did not induce a change in cytosolic cAMP concentration, but inhibition of either calmodulin or cAMP-dependent protein kinase A activity blunted the hypertonicity-induced increase of AQP2 cell surface expression. Hypertonicity increased p38, ERK1/2, and JNK MAPK activity. Inhibiting MAPK activity abolished hypertonicity-induced accumulation of AQP2 at the cell surface but did not affect either vasopressin-dependent AQP2 trafficking or hypertonicity-induced AQP2 accumulation in the TGN. Finally, increased AQP2 cell surface expression induced by hypertonicity largely resulted from a reduction in endocytosis but not from an increase in exocytosis. These data indicate that acute hypertonicity profoundly alters AQP2 trafficking and that hypertonicity-induced AQP2 accumulation at the cell surface depends on MAP kinase activity. This may have important implications on adaptational processes governing transcellular water flux and/or cell survival under extreme conditions of hypertonicity.
authors.affiliation: Massachusetts General Hospital Center for Systems Biology, Program in Membrane Biology and Nephrology Division, Massachusetts General Hospital, Boston, Massachusetts 02114-2790, USA. Udo.Hasler@medecine.unige.ch
authors.forename: Udo
authors.initials: U
authors.lastname: Hasler
authors.forename: Paula
authors.initials: P
authors.lastname: Nunes
authors.forename: Richard
authors.initials: R
authors.lastname: Bouley
authors.forename: Hua A J
authors.initials: HA
authors.lastname: Lu
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsuzaki
authors.forename: Dennis
authors.initials: D
authors.lastname: Brown
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology; D000818:Animals; D050034:Antidiuretic Agents / Q000494:pharmacology; D051399:Aquaporin 2 / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006056:Golgi Apparatus / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009997:Osmotic Pressure / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011910:Rats, Brattleboro; D014667:Vasopressins / Q000494:pharmacology; D014867:Water / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D050034:Antidiuretic Agents; C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D014867:Water; D014667:Vasopressins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases