AQP2 is Necessary for Vasopressin- and Forskolin-Mediated Filamentous Actin Depolymerization in Renal Epithelial Cells

Abstract

Remodeling of the actin cytoskeleton is required for vasopressin (VP)‐induced aquaporin 2 (AQP2) trafficking. Here, we asked whether VP and forskolin (FK)‐mediated F‐actin depolymerization depends on AQP2 expression. Using various MDCK and LLC‐PK1 cell lines with different AQP2 expression levels, we performed F‐actin quantification and immunofluorescence staining after VP/FK treatment. In MDCK cells, in which AQP2 is delivered apically, VP/FK mediated F‐actin depolymerization was significantly correlated with AQP2 expression levels. A decrease of apical membrane associated F‐actin was observed upon VP/FK treatment in AQP2 transfected, but not in untransfected cells. There was no change in basolateral actin staining under these conditions. In LLC‐PK1 cells, which deliver AQP2 basolaterally, a significant VP/FK mediated decrease in F‐actin was also detected only in AQP2 transfected cells. This depolymerization response to VP/FK was significantly reduced by siRNA knockdown of AQP2. By immunofluorescence, an inverse relationship between plasma membrane AQP2 and membrane‐associated F‐actin was observed after VP/FK treatment again only in AQP2 transfected cells. This is the first report showing that VP/FK mediated F‐actin depolymerization is dependent on AQP2 protein expression in renal epithelial cells, and that this is not dependent on the polarity of AQP2 membrane insertion.