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Characterization of different G protein coupling properties of CB1 and CB2 cannabinoid receptors and GPR55 receptor using BRET

Background

CB1 and CB2 cannabinoid receptors are G protein-coupled receptors which have been described to couple mainly to the Gi/o subfamily of G proteins. However, in some cell types and upon stimulation with certain cannabinoid agonists, activation of other G protein subtypes has also been observed. GPR55 is an orphan G protein-coupled receptor which has been suggested to be a novel member of the cannabinoid receptor family.

Methods

In this study we wanted to characterize the G protein activation properties of the two known cannabinoid receptors and GPR55 following stimulation with different cannabinoid ligands, using bioluminescence resonance energy transfer (BRET). We monitored the activation of different G protein subtypes (Go, Gq, Gs or G12) using Renilla luciferase-tagged wild type or chimeric Gαo subunits (i.e. Gαo with the C-terminal 5 amino acids replaced with those of Gαq, Gαs or Gα12, respectively) co-expressed with EYFP-tagged α1α11 subunit and the receptor in CHO cells.

Results

We found that CB1 was able to activate all four subtypes of G proteins, with different pharmacokinetic properties, following stimulation by non-selective (WIN55 and 2-AG) or CB1-selective (ACEA) cannabinoid agonists. Basal activity of CB1 could also be detected with Go and G12 subtypes, as the CB1 inverse agonist AM251 caused significant BRET increase (i.e. G protein subunit association) when tested with these G proteins. In contrast, CB2 showed no G protein activation other than Go, upon either WIN55 or 2-AG stimuli. Stimulation of GPR55 with WIN55, 2-AG or AM251 did not alter the activity of the tested G proteins even at considerably high ligand concentrations.

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Correspondence to László Hunyady.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/2.0 ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Gyombolai, P., Turu, G. & Hunyady, L. Characterization of different G protein coupling properties of CB1 and CB2 cannabinoid receptors and GPR55 receptor using BRET. BMC Pharmacol 9, A43 (2009). https://doi.org/10.1186/1471-2210-9-S2-A43

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Keywords

  • Inverse Agonist
  • Protein Coupling
  • Coupling Property
  • GPR55 Receptor
  • High Ligand