Sustained Gα signaling mediated by vasopressin type 2 receptors is ligand dependent but endocytosis and β-arrestin independent.

The canonical model of G protein-coupled receptor (GPCR) signaling comprises G protein activation at the plasma membrane, followed by receptor phosphorylation and β-arrestin recruitment, which leads to receptor desensitization and endocytosis. However, the activation of some GPCRs results in sustained G protein signaling from intracellular compartments in a manner reportedly dependent on β-arrestin and receptor endocytosis. The vasopressin type 2 receptor (VR) can be activated by two structurally similar hormones, arginine vasopressin and oxytocin, both of which stimulate the production of the second messenger cyclic adenosine monophosphate (cAMP). In this study, we showed that sustained VR signaling and endosomal Gα (stimulatory G protein alpha subunit) translocation could occur without β-arrestin-mediated receptor endocytosis and was primarily controlled by the residence time of the ligand on the receptor. β-Arrestin had opposing effects on sustained signaling: It facilitated receptor internalization into endosomes, where it activated Gα, and promoted cAMP production from this compartment. However, β-arrestin-mediated receptor endocytosis also induced ligand dissociation due to the acidic endosomal environment, thereby limiting the signal. Overall, our data suggest that signals originating at the plasma membrane play a dominant role in sustained VR signaling stimulated by arginine vasopressin.