Cross-communication between G and G 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 (AR or AR) can form AR-AR heteromers (A-AHet), and their activation leads to canonical G-protein-dependent (adenylate cyclase mediated) and -independent (β-arrestin mediated) signaling. Adenosine has different affinities for AR and AR, allowing the heteromeric receptor to detect its concentration by integrating the downstream G- and G-dependent signals. cAMP accumulation and β-arrestin recruitment assays have shown that, within the complex, activation of AR impedes signaling via AR.

RESULTS

We examined the mechanism by which A-AHet integrates G- and G-dependent signals. AR blockade by AR in the A-AHet is not observed in the absence of AR activation by agonists, in the absence of the C-terminal domain of AR, or in the presence of synthetic peptides that disrupt the heteromer interface of A-AHet, indicating that signaling mediated by AR and AR is controlled by both G and G proteins.

CONCLUSIONS

We identified a new mechanism of signal transduction that implies a cross-communication between G and G proteins guided by the C-terminal tail of the AR. This mechanism provides the molecular basis for the operation of the A-AHet as an adenosine concentration-sensing device that modulates the signals originating at both AR and AR.