|Eur J Pharmacol. 2017 Jul 19. pii: S0014-2999(17)30491-0. doi: 10.1016/j.ejphar.2017.07.034. [Epub ahead of print]|
Bidirectional allosteric interactions between cannabinoid receptor 1 (CB1) and dopamine receptor 2 long (D2L) heterotetramers.
Bagher AM1, Laprairie RB2, Toguri JT3, Kelly MEM4, Denovan-Wright EM5.
Department of Pharmacology, Dalhousie University, Halifax NS, Canada; Department of Pharmacology and Toxicology, King AbdulAziz University, Jeddah, KSA.
College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon SK, Canada.
Department of Pharmacology, Dalhousie University, Halifax NS, Canada.
Department of Pharmacology, Dalhousie University, Halifax NS, Canada; Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax NS, Canada.
Department of Pharmacology, Dalhousie University, Halifax NS, Canada. Electronic address: email@example.com.
Type 1 cannabinoid (CB1) and dopamine 2 long form (D2L) receptors can physically interact to form heteromers that display unique pharmacology in vitro compared to homomeric complexes. Co-expression of CB1 and D2L and co-application of CB1 and D2 agonists increases cAMP levels while administration of either agonist alone decreases cAMP levels. To understand the observed co-agonist response, our first goal of the current study was to define the stoichiometry of CB1/D2L/Ga protein complexes. Using bioluminescence resonance energy transfer 2 (BRET2), we confirmed that, CB1 homodimers, D2L homodimers, and CB1/D2L heteromers are formed. By using sequential energy transfer 2 (SRET2) combined with bimolecular fluorescence complementation (BiFC), we were able to demonstrate that CB1/D2L form heterotetramers consisting of CB1 and D2L homodimers. We demonstrated that CB1/D2L heterotetramers are coupled to at least two Ga proteins. The second aim of the study was to investigate allosteric effects of a D2L agonist (quinpirole) on CB1 receptor function and to investigate the effects of a CB1 agonist [arachidonyl-2-chloroethylamide (ACEA)] on D2L receptor function within CB1/D2L heterotetramers. Treating cells co-expressing CB1 and D2L with both ACEA and quinpirole switched CB1 and D2L receptor coupling and signaling from Gai to Gas proteins, enhanced ß-arrestin1 recruitment and receptor co-internalization. The concept of bidirectional allosteric interaction within CB1/D2 heterotetramers has important implications for understanding the activity of receptor complexes in native tissues and under pathological conditions.