Agonist-Dependent Coupling of the Promiscuous Adenosine A 2B Receptor to Gα Protein Subunits.

The adenosine A 2B receptor (A 2B AR) belongs to the rhodopsin-like G protein-coupled receptor (GPCR) family. It is upregulated under hypoxic conditions, in inflammation and cancer. Previous studies indicated the coupling of the A 2B AR to different G proteins, mainly G s , but in some cases G q/11 or G i , depending on the cell type. We have now utilized novel technologies, (i) heterologous expression of individual members of the Gα q/11 protein family (Gα q , Gα 11 , Gα 14 , and Gα 15 ) in Gα q/11 knockout cells, and (ii) the TRUPATH platform, allowing the direct observation of Gα protein activation for each of the Gα subunits by bioluminescence resonance energy transfer (BRET) measurements. Three structurally diverse A 2B AR agonists were studied: the cognate agonist adenosine, its metabolically stable analog NECA, and the non-nucleosidic partial agonist BAY 60-6583. Adenosine and NECA activated most members of all four Gα protein families (Gα s , Gα q/11 , Gα i , and Gα 12/13 ). Significant differences in potencies and efficacies were observed; the highest efficacies were determined at the Gα 15 , Gα s , and Gα 12 proteins, and for NECA additionally at the Gα i2 protein. In contrast, the partial agonist BAY 60-6583 only activated Gα 15 , Gα s , and Gα 12 proteins. Adenosine deaminase, an allosteric modulator of ARs, selectively increased the potency and efficacy of NECA and BAY 60-6583 at the Gα 15 protein, while it had no effect or decreased efficacy at the other Gα proteins. We conclude that the A 2B AR is preferably coupled to the Gα 15 , Gα s , and Gα 12 proteins. Upon upregulation of receptor or Gα protein expression, coupling to further Gα proteins likely occurs. Importantly, different agonists can display different activation profiles.