Rho inhibits cAMP-induced translocation of aquaporin-2 into the apical membrane of renal cells

We have recently demonstrated that actin depolymerization is a prerequisite for cAMP-dependent translocation of the water channel aquaporin-2 (AQP2) into the apical membrane in AQP2-transfected renal CD8 cells (29). The Rho family of small GTPases, including Cdc42, Rac, and Rho, regulates the actin cytoskeleton. In AQP2-transfected CD8 cells, inhibition of Rho GTPases with Clostridium difficile toxin B or with C. limosum C3 fusion toxin, as well as incubation with the Rho kinase inhibitor, Y-27632, caused actin depolymerization and translocation of AQP2 in the absence of the cAMP- elevating agent forskolin. Both forskolin and C3 fusion toxin-induced AQP2 translocation were associated with a similar increase in the osmotic water permeability coefficient. Expression of constitutively active RhoA induced formation of stress fibers and abolished AQP2 translocation in response to forskolin. Cytochalasin D induced both depolymerization of F-actin and AQP2 translocation, suggesting that depolymerization of F-actin is sufficient to induce AQP2 translocation. Together, these data indicate that Rho inhibits cAMP-dependent translocation of AQP2 into the apical membrane of renal principal cells by controlling the organization of the actin cytoskeleton.