Protein phosphatase 2C is responsible for VP-induced dephosphorylation of AQP2 serine 261

Aquaporin 2 (AQP2) trafficking is regulated by phosphorylation and dephosphorylation of serine residues in the AQP2 COOH terminus. Vasopressin (VP) binding to its receptor (V2R) leads to a cascade of events that result in phosphorylation of serine 256 (S256), S264, and S269, but dephosphorylation of S261. To identify which phosphatase is responsible for VP-induced S261 dephosphorylation, we pretreated cells with different phosphatase inhibitors before VP stimulation. Sanguinarine, a specific protein phosphatase (PP) 2C inhibitor, but not inhibitors of PP1, PP2A (okadaic acid), or PP2B (cyclosporine), abolished VP-induced S261 dephosphorylation. However, sanguinarine and VP significantly increased phosphorylation of ERK, a kinase that can phosphorylate S261; inhibition of ERK by PD98059 partially decreased baseline S261 phosphorylation. These data support a role of ERK in S261 phosphorylation but suggest that, upon VP treatment, increased phosphatase activity overcomes the increase in ERK activity, resulti...