A role for G-proteins in directing G-protein-coupled receptor-caveolae localization

Abstract

Caveolae are membrane domains that may influence cell signaling by sequestering specific proteins such as G-protein-coupled receptors (GPCRs). While previous reports largely show that Gαq subunits, but not other G-proteins, interact strongly with the caveolae protein, Caveolin-1 (Cav1), the inclusion of GPCRs in caveolae is controversial. Here, we have used fluorescence methods to determine the effect of caveolae on the physical and functional properties of two GPCRs that have been reported to reside in caveolae, bradykinin receptor type 2 (B2R), which is coupled to Gαq, and the μ-opioid receptor (μOR), which is coupled to Gαi. While caveolae do not affect cAMP signals mediated by μOR, they prolong Ca2+ signals mediated by B2R. In A10 cells that endogenously express B2R and Cav1, downregulation of Cav1 ablates the prolonged recovery seen upon bradykinin stimulation in accord with the idea that the presence of caveolae prolongs Gαq activation. Immunofluorescence and Förster resonance energy transfer (FRET) studies show that a significant fraction of B2R resides at or close to caveolae domains while none or very little μOR resides in caveolae domains. The level of FRET between B2R and caveolae is reduced by downregulation of Gαq or by addition of a peptide that interferes with Gαq-Caveolin-1 interactions, suggesting that Gαq promotes localization of B2R to caveolae domains. Our results lead to the suggestion that Gαq can localize its associated receptors to caveolae domains to enhance their signals. © 2012 American Chemical Society.