Constitutive activity of the cannabinoid CB1 receptor regulates the function of co-expressed Mu opioid receptors

Canals Buj, M. and Milligan, G. (2008) Constitutive activity of the cannabinoid CB1 receptor regulates the function of co-expressed Mu opioid receptors. Journal of Biological Chemistry, 283(17), pp. 11424-11434. (doi:10.1074/jbc.M710300200)

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Publisher's URL: http://dx.doi.org/10.1074/jbc.M710300200

Abstract

The human mu opioid receptor was expressed stably in Flp-In T-REx HEK293 cells. Occupancy by the agonist DAMGO (Tyr-D-Ala-Gly-N-methyl-Phe-Gly-ol) resulted in phosphorylation of the ERK1/2 MAP kinases, which was blocked by the opioid antagonist naloxone but not the cannabinoid CB1 receptor inverse agonist SR141716A. Expression of the human cannabinoid CB1 receptor in these cells from the inducible Flp-In T-REx locus did not alter expression levels of the mu opioid receptor. This allowed the cannabinoid CB1 agonist WIN55212-2 to stimulate ERK1/2 phosphorylation but resulted in a large reduction in the capacity of DAMGO to activate these kinases. Although lacking affinity for the mu opioid receptor, co-addition of SR141716A caused recovery of the effectiveness of DAMGO. In contrast co-addition of the CB1 receptor neutral antagonist O-2050 did not. Induction of the CB1 receptor also resulted in an increase of basal [<sup>35</sup>S]guanosine 5′-3-O-(thio)triphosphate (GTPγS) binding and thereby a greatly reduced capacity of DAMGO to further stimulate [<sup>35</sup>S]GTPγS binding. CB1 inverse agonists attenuated basal [<sup>35</sup>S]GTPγS binding and restored the capacity of DAMGO to stimulate. Flp-In T-REx HEK293 cells were generated, which express the human mu opioid receptor constitutively and harbor a modified D163N cannabinoid CB1 receptor that lacks constitutive activity. Induction of expression of the modified cannabinoid CB1 receptor did not limit DAMGO-mediated ERK1/2 MAP kinase phosphorylation and did not allow SR141716A to enhance the function of DAMGO. These data indicate that it is the constitutive activity inherent in the cannabinoid CB1 receptor that reduces the capacity of co-expressed mu opioid receptor to function.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Milligan, Professor Graeme and Canals Buj, Dr Meritxell
Authors: Canals Buj, M., and Milligan, G.
Subjects:Q Science > QH Natural history > QH345 Biochemistry
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Journal Name:Journal of Biological Chemistry
Journal Abbr.:J Biol Chem.
Publisher:American Society for Biochemistry and Molecular Biology, Inc.
ISSN:0021-9258
ISSN (Online):1083-351X
Published Online:04 March 2008
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