The human type 1 cannabinoid (hCB1) receptor is expressed at high levels in the central nervous system. mRNA variants of the coding region of this receptor, human cannabinoid hCB1a and hCB1b receptors, have been identified, their biological function remains unclear. The present study demonstrated that the three human cannabinoid hCB1 coding region variants are expressed in the human and monkey (Macaca fascicularis) brain. Western blot analyses of homogenates from different regions of the monkey brain demonstrated that proteins with the expected molecular weights of the cannabinoid CB1, CB1a and CB1b receptors were co-expressed throughout the brain. Given the co-localization of these receptors, we hypothesized that physical interactions between the three splice variants may affect cannabinoid pharmacology. The human cannabinoid hCB1, hCB1a, and hCB1b receptors formed homodimers and heterodimers, as determined by BRET in transiently transfected HEK 293A cells. We found that the co-expression of the human cannabinoid hCB1 and each of the splice variants increased cell surface expression of the human cannabinoid hCB1 receptor and increased Gi/o-dependent ERK phosphorylation in response to cannabinoid agonists. Therefore, the human cannabinoid hCB1 coding region splice variants play an important physiological role in the activity of the endocannabinoid system.
Keywords: 2-AG; 2-arachidonyl glycerol; AEA; Bioluminescence resonance energy transfer (BRET); CB(1); CHO; CNR1; CNS; Chinese hamster ovary cells; D(2L); D(2Sh); Dimerization; Distribution; Function; G-protein coupled receptor; GFP(2); GPCR; HEK 293A; Human type 1 cannabinoid (hCB(1)) receptor coding region splice variants; PTx; Pertussis toxin; Renilla luciferase; Rluc; THC; UTR; anandamide; central nervous system; dopamine receptor 2 long isoform; dopamine receptor 2 short isoform; green fluorescent protein; hCB(1); hCB(1a); hCB(1b); human embryonic kidney 293A cells; human type 1 cannabinoid receptor; human type 1a cannabinoid receptor; human type 1b cannabinoid receptor; mRNA; type 1 cannabinoid receptor; type 1 cannabinoid receptor gene; untranslated region; ∆(9)-tetrahydrocannabinol.
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