title: Delineation of domains within the cannabinoid CB1 and dopamine D2 receptors that mediate the formation of the heterodimer complex.
abstract: 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.
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada.
authors.forename: Shazina S
authors.initials: SS
authors.lastname: Khan
authors.forename: Frank J S
authors.initials: FJ
authors.lastname: Lee
mesh_terms: D057809:HEK293 Cells; D006801:Humans; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D043884:Receptor, Cannabinoid, CB1 / Q000737:chemistry / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D043884:Receptor, Cannabinoid, CB1; D017448:Receptors, Dopamine D2