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  • Title: Acute hypertonicity alters aquaporin-2 trafficking and induces a MAPK-dependent accumulation at the plasma membrane of renal epithelial cells.
    Author: Hasler U, Nunes P, Bouley R, Lu HA, Matsuzaki T, Brown D.
    Journal: J Biol Chem; 2008 Sep 26; 283(39):26643-61. PubMed ID: 18664568.
    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.
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