Agonist-induced formation of unproductive receptor-G12 complexes

G proteins are activated when they associate with G protein-coupled receptors (GPCRs), often in response to agonist-mediated receptor activation. It is generally thought that agonist-induced receptor-G protein association necessarily promotes G protein activation and, conversely, that activated GPCRs do not interact with G proteins that they do not activate. Here we show that GPCRs can form agonist-dependent complexes with G proteins that they do not activate. Using cell-based bioluminescence resonance energy transfer (BRET) and luminescence assays we find that vasopressin V-2 receptors (V2R) associate with both G(s) and G(12) heterotrimers when stimulated with the agonist arginine vasopressin (AVP). However, unlike V2R-G(s) complexes, V2R-G(12) complexes are not destabilized by guanine nucleotides and do not promote G(12) activation. Activating V2R does not lead to signaling responses downstream of G(12) activation, but instead inhibits basal G(12)-mediated signaling, presumably by sequestering G(12) heterotrimers. Overexpressing G(12) inhibits G protein receptor kinase (GRK) and arrestin recruitment to V2R and receptor internalization. Formyl peptide (FPR1 and FPR2) and Smoothened (Smo) receptors also form complexes with G(12) that are insensitive to nucleotides, suggesting that unproductive GPCR-G(12) complexes are not unique to V2R. These results indicate that agonist-dependent receptor-G protein association does not always lead to G protein activation and may in fact inhibit G protein activation.