Characterization of the interaction of the dopamine D2 receptor and the cannabinoid CB1 receptor and its effects on signal transduction pathways

Activation of either the cannabinoid CB1 receptor CB1 or dopamine D2 receptor D2R inhibits cAMP production since both are Gαi/o linked G protein-coupled receptors. This study confirms the interaction of CB1 and D2R with co-immunoprecipitation experiments using HEK-293T cells co-expressing both receptors. Moreover, GST and His-tagged fusion proteins of CB1 and D2R were generated and used in affinity purification assays to show that the carboxyl terminus of the CB1 receptor interacts with the third intracellular loop of the D2 receptor to form the CB1-D2R complex. Additionally, the CB1-D2R complex is formed by a direct protein-protein interaction. Furthermore, the activation of either D2R or CB1 in HEK-293T cells co-expressing both receptors leads to inhibition of forskolin stimulated cAMP accumulation. However, co-activation of both receptors results in a loss of cAMP inhibition. This study characterizes the interaction between CB1 and D2R as well as demonstrates the functional outcomes of the receptor complex.