Kinase-inactive G-protein-coupled receptor kinases ave able to attenuate follicle-stimulating hormone-induced signaling

Homologous desensitization of G-protein-coupled receptors (GPCR) is thought to occur in several steps: binding of G-protein-coupled receptor kinases ( GRKs) to receptors, receptor phosphorylation, kinase dissociation, and fina lly binding of beta -arrestin to phosphorylated receptors and functional un coupling of the associated Ga protein. It has recently been reported that G RKs can inhibit Gag-mediated signaling in the absence of phosphorylation of some GPCRs. Whether or not comparable phosphorylation-independent effects are also possible with G alphas-coupled receptors remains unclear. In the p resent study, using the tightly G alphas-coupled FSR receptor (FSH-R) as a model, we observed inhibition of the cAMP-dependent signaling pathway using kinase-inactive mutants of GRK2, 5, and 6. These negative effects occur up stream of adenylyl cyclase activation and are likely independent of GRK int eraction with G protein alpha or beta/gamma subunits. Moreover, we demonstr ated that, when overexpressed in Cos 7 cells, mutated GRK2 associates with the FSH activated FSH-R. We hypothesize that phosphorylation-independent da mpening of the FSH-R-associated signaling could be attributable to physical association between GRKs and the receptor, subsequently inhibiting G; prot ein activation. (C) 2001 Academic Press.