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ORIGINAL ARTICLE

Concurrent Stimulation of Cannabinoid CB1 and Dopamine D2 Receptors Enhances Heterodimer Formation: A Mechanism for Receptor Cross-Talk?

Departments of Anesthesiology (C.S.K., K.M.) and Physiology and Biophysics (K.M.), University of Washington, Seattle, Washington; and Department of Pharmacology, University of Auckland, Auckland, New Zealand (K.B.-P., E.D., M.G.)

Abstract

Dopamine and endogenous cannabinoids display complex interactions in the basal ganglia. One possible level of interaction is between CB1 cannabinoid and D2 dopamine receptors. Here, we demonstrate that a regulated association of CB1 and D2 receptors profoundly alters CB1 signaling. This provides the first evidence that CB1/D2 receptor complexes exist, are dynamic, and are agonist-regulated with highest complex levels detected when both receptors are stimulated with subsaturating concentrations of agonist. The consequence of this interaction is a differential preference for signaling through a "nonpreferred" G protein. In this case, D2 receptor activation, simultaneously with CB1 receptor stimulation, results in the receptor complex coupling to Gs protein in preference to the expected Gi/o proteins. The result of this interaction is an increase in the second messenger cAMP, reversing an initial synergistic inhibition of adenylyl cyclase activity seen at subthreshold concentrations of cannabinoid agonist. Additionally, a pertussis toxin insensitive component in the activation of extracellular signal-regulated kinase (ERK) 1/2 kinases by the cannabinoid agonist CP 55,940 [(1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol] is revealed in cells stably expressing both CB1 and D2 receptors. Thus, concurrent receptor stimulation promotes a heterooligomeric receptor complex and an apparent shift of CB1 signaling from a pertussis toxin-sensitive inhibition to a partly pertussis toxin-insensitive stimulation of adenylyl cyclase and ERK 1/2 phosphorylation.

Address correspondence to: Dr. Michelle Glass, Department of Pharmacology, University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: m.glass{at}auckland.ac.nz

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