, Volume 53, Issue 1, pp 10-21
Date: 22 Nov 2013

Delineation of Domains Within the Cannabinoid CB1 and Dopamine D2 Receptors That Mediate the Formation of the Heterodimer Complex

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Both the cannabinoid CB1 receptor (CB1) and dopamine D2 receptor (D2R) are G protein-coupled receptors that are linked to inhibitory Gαi/o protein, whereby activation of the receptor leads to the inhibition of cAMP production. Moreover, previous findings have shown evidence of cross-talk between the dopamine and endocannabinoid systems. In this report, we confirm the interaction of CB1 and D2R with co-immunoprecipitation experiments using human embryonic kidney 293T (HEK-293T) cells co-expressing both receptors. We also generated GST and His-tagged fusion proteins of the D2R and CB1 and conducted affinity purification assays and in vitro binding experiments to show that the CB1–D2R complex can be formed by a direct protein–protein interaction. This interaction is mediated by the carboxyl terminus of the CB1 receptor and the third intracellular loop of the D2 receptor. Co-transfection of an inhibitory mini-gene resulted in decreased levels of the CB1–D2R complex. Using a cAMP biosensor, we show that activation of D2R or CB1 alone in HEK-293T cells co-expressing both receptors leads to an inhibition of forskolin-stimulated cAMP accumulation. However, co-activation of both receptors resulted in a loss of this inhibition on cAMP accumulation. Our findings characterize the physical interaction between CB1 and D2R as well as demonstrate the potential functional outcome of the receptor complex.