ALLOSTERIC INTERACTIONS WITHIN CANNABINOID RECEPTOR 1 (CB1) AND DOPAMINE RECEPTOR 2 LONG (D2L) HETEROMERS
Date
2017-08-23T12:50:57Z
Authors
Bagher, Amina Mustafa
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Abstract
receptors mediating a vast array of functions in eukaryotes. GPCRs have more
complex signaling than originally envisioned due to the fact that GPCRs can associate to
form homomeric complexes or associate with other GPCRs to form heteromeric complexes.
Allosteric communication within complexes influences the range of receptor function.
Cannabinoid receptor 1 (CB1) and dopamine receptor 2 long (D2L) are GPCRs that are colocalized
in specific neuronal populations in the basal ganglia. These receptors play crucial
roles in the coordination of movement. I hypothesized that CB1 and D2L receptors associate
in heteromeric complexes and that CB1 and D2L ligands promote bidirectional allosteric
interactions within heteromeric complexes. I confirmed that CB1 and D2L receptors form
homodimers and that each homodimer was coupled to a Gαi protein. CB1 and D2L receptors
formed higher order oligomeric complexes; the minimum functional heteromeric complex
was composed of a CB1 and D2L homodimer each coupled to a Gαi protein. Activation of
either CB1 or D2L receptors by the agonists, arachidonyl-2-chloroethylamide (ACEA) or
quinpirole, respectively, resulted in fast and transient conformational changes among CB1,
D2L and Gαi proteins indicative of receptor activation. Treating cells co-expressing CB1 and
D2L receptors with both ACEA and quinpirole switched CB1 and D2L receptors coupling and
signaling from Gαi to Gαs, enhanced β-arrestin1 recruitment and co-internalization. The
high-affinity D2L receptor antagonist, haloperidol, was also able to switch CB1 coupling from
Gαi to Gαs but, unlike D2 agonists, haloperidol inhibited β-arrestin1 recruitment to CB1 and
inhibited complex internalization. Allosteric interactions within CB1/D2L heteromeric
complexes were ligand dose-dependent and bidirectional. CB1/D2L heteromers were detected
in the globus pallidus of C57BL/6J mice. Chronic exposure to the cannabinoid CP 55,940
increased CB1/D2L heteromers while the D2 antagonist haloperidol reduced CB1/D2L
heteromers in the globus pallidus of C57BL/6J mice indicating that functional heteromers
existed in vivo and were affected by chronic drug exposure. The concept of bidirectional
allosteric interaction within CB1/D2 heterotetramers has significant implication for the
understanding of the complex physiology and pharmacology of CB1 and D2L receptors.
Description
Keywords
CB1, D2L, BRET2, SRET2, G protein coupling, Receptor heteromerization