Characterizing the Effect of A2AR-D2R Heteromeric Complex Formation on Homomeric A2AR and D2R Signaling

Abstract

G protein-coupled receptors (GPCRs) are the targets of many drugs used in clinical practice because G proteins mediate a plethora of physiological functions. Appreciation of the existence of oligomeric GPCR complexes with distinct signaling properties from their monomeric counterparts is growing. Yet, the effect of heteromerization on the pharmacology and signaling of many GPCR monomers remains unknown. We have undertaken the task to examine the effect of heteromerization on the Gs signaling through the adenosine 2A receptor (A2AR) and Gi signaling through the dopamine receptor type 2 (D2R). Signaling through the A2AR-D2R heteromeric complex is of great interest as this heteromer is a pharmacological target for pathologies associated with dysfunctional dopaminergic signaling, such as in Parkinson's disease. In order to analyze A2AR-D2R heterocomplex cross signaling through Gi, we are using an electrophysiological assay with heterologously expressed channels serving as reporters for GPCR signaling. Preliminary data suggest that heteromer formation decreases the dopamine elicited Gi signaling through the D2R. We are in the process of assessing the effect of D2R on the Gs signaling of the A2AR, using a tritiated cAMP assay. We hypothesize that Gs and Gi signaling through the A2AR-D2R heterocomplex are inversely coupled, in a manner similar to the serotonin 2A- metabotropic glutamate type 2 receptor heteromer (Fribourg et al. 2011). Thus, if our hypothesis is correct, heteromerization is expected to increase adenosine elicited Gs signaling through the A2AR. Furthermore, we expect that dominant agonists and inverse agonists for the A2AR and D2R can be used to manipulate the Gi and Gs signaling through the heteromer. Characterization of the signaling pathway through the A2AR-D2R heteromer could lead to novel therapeutics for Parkinson's disease.