Role of the human V-1 vasopressin receptor COOH terminus in internalization and mitogenic signal transduction

We studied the role played by the intracellular COOH-terminal region of the human arginine vasopressin (AVP) V-1-vascular receptor (V1R) in ligand bin ding, trafficking, and mitogenic signal transduction in Chinese hamster ova ry cells stably transfected with the human AVP receptor cDNA clones that we had isolated previously. Truncations, mutations, or chimeric alterations o f the V1R COOH terminus did not alter ligand binding, but agonist-induced V 1R internalization and recycling were reduced in the absence of the proxima l region of the V1R COOH terminus. Coupling to phospholipase C was altered as a function of the COOH-terminal length. Deletion of the proximal portion of the V1R COOH terminus or its replacement by the V-2-renal receptor COOH terminus prevented AVP stimulation of DNA synthesis and progression throug h the cell cycle. Mutation of a kinase consensus motif in the proximal regi on of the V1R COOH terminus also abolished the mitogenic response. Thus the V1R cytoplasmic COOH terminus is not involved in ligand specificity but is instrumental in receptor trafficking and facilitates the interaction betwe en the intracellular loops of the receptor, G protein, and phospholipase C. It is absolutely required for transmission of the mitogenic action of AVP, probably via a specific kinase phosphorylation site.