β-arrestin-independent endosomal cAMP signaling by a polypeptide hormone GPCR

Abstract

Many GPCRs are now recognized to initiate a second phase of G protein (Gs) -dependent signaling through the cAMP cascade after endocytosis. A prevailing current view is that endocytosis-promoted signaling from GPCRs is inherently {beta}-arrestin-dependent because {beta}-arrestin is necessary for receptors to internalize and, for some GPCRs, it also promotes Gs activation on endosomes. Here we revise this view by showing that the vasoactive intestinal peptide receptor 1 (VIPR1), a prototypic secretin-family polypeptide hormone receptor, remains bound to {beta}-arrestin after endocytosis but does not require {beta}-arrestin either to internalize or to generate an endosomal signal. {beta}-arrestin instead resolves the endosomal signal into a temporally separated cAMP peak, and it does so by attenuating signaling from the plasma membrane without detectably affecting the endosomal response. The mechanistic basis for this location-specific difference in {beta}-arrestin function is the formation of distinct VIPR1/{beta}-arrestin complexes at each location. The signal-attenuating complex formed at the plasma membrane does not require GRK-mediated phosphorylation of receptors, while the signaling-neutral complex present on the endosome membrane, in contrast, is GRK-dependent. To our knowledge, the present results provide the first direct demonstration that endosomal GPCR signaling can occur in the complete absence of {beta}-arrestin. They also reveal a discrete role of {beta}-arrestin in sculpting the spatiotemporal profile of cellular GPCR - G protein signaling through the location-specific formation or remodeling of GPCR/{beta}-arrestin complexes.