β-arrestin-dependent and -independent endosomal G protein activation by the vasopressin type 2 receptor.

The vasopressin type 2 receptor (VR) is an essential GPCR in renal regulation of water homeostasis. Upon stimulation, the VR activates Gα and Gα, which is followed by robust recruitment of β-arrestins and receptor internalization into endosomes. Unlike canonical GPCR signaling, the β-arrestin association with the VR does not terminate Gα activation, and thus, Gα-mediated signaling is sustained while the receptor is internalized. Here, we demonstrate that this VR ability to co-interact with G protein/β-arrestin and promote endosomal G protein signaling is not restricted to Gα, but also involves Gα. Furthermore, our data implies that β-arrestins potentiate Gα/Gα activation at endosomes rather than terminating their signaling. Surprisingly, we found that the VR internalizes and promote endosomal G protein activation independent of β-arrestins to a minor degree. These new observations challenge the current model of endosomal GPCR signaling and suggest that this event can occur in both β-arrestin-dependent and -independent manners.