Structural requirements for V2 vasopressin receptor proteolytic cleavage.

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The ligand-induced proteolytic cleavage of the V2 vasopressin receptor transiently expressed in COS cells was investigated. After incubation of the cell membranes with a photoreactive ligand possessing full agonistic properties for V2 receptors, approximately 90% of the porcine and bovine V2 vasopressin receptors were cleaved in the upper part of transmembrane helix 2 at a heptapeptide sequence conserved in both vasopressin and oxytocin receptors. The oxytocin receptor was completely resistant to proteolysis after binding the same photoreactive ligand, which is only a partial agonist for this receptor. Chimeric V2/oxytocin receptors obtained by transfer of extracellular domains of the oxytocin receptor into the V2 receptor showed an increase in binding affinity for oxytocin versus vasopressin and a diminished cleavage. The proteolysis-resistant chimeric V2/oxytocin receptor, which contains the first three extracellular domains of the oxytocin receptor, stimulated cAMP accumulation to a larger extent in response to vasopressin than the wild-type receptor and showed impaired desensitization of the adenylate cyclase system. Our data indicate that the proteolytic cleavage of the V2 receptor requires a defined conformation, especially of the first two extracellular domains that is induced by agonist binding. Furthermore, the results suggest that the proteolytic V2 receptor cleavage might play a role in signal termination at elevated hormone concentrations.