Cross-communication between Gi and Gs in a G-protein-coupled receptor heterotetramer guided by a receptor C-terminal domain

Background: G-protein-coupled receptor (GPCR) heteromeric complexes have distinct properties from homomeric GPCRs, giving rise to new receptor functionalities. Adenosine receptors (A(1)R or A(2A)R) can form A(1)R-A(2A)R heteromers (A(1)-A(2A)Het), and their activation leads to canonical G-protein-dependent (adenylate cyclase mediated) and -independent (beta-arrestin mediated) signaling. Adenosine has different affinities for A(1)R and A(2A)R, allowing the heteromeric receptor to detect its concentration by integrating the downstream G(i)- and G(s)-dependent signals. cAMP accumulation and beta-arrestin recruitment assays have shown that, within the complex, activation of A(2A)R impedes signaling via A(1)R. Results: We examined the mechanism by which A(1)-A(2A)Het integrates G(i)- and G(s)-dependent signals. A(1)R blockade by A(2A)R in the A(1)-A(2A)Het is not observed in the absence of A(2A)R activation by agonists, in the absence of the C-terminal domain of A(2A)R, or in the presence of synthetic peptides that disrupt the heteromer interface of A(1)-A(2A)Het, indicating that signaling mediated by A(1)R and A(2A)R is controlled by both G(i) and G(s) proteins. Conclusions: We identified a new mechanism of signal transduction that implies a cross-communication between G(i) and G(s) proteins guided by the C-terminal tail of the A(2A)R. This mechanism provides the molecular basis for the operation of the A(1)-A(2A)Het as an adenosine concentration-sensing device that modulates the signals originating at both A(1)R and A(2A)R.