Abstract
We have compared the ability of a number of μ-opioid receptor (MOPr) ligands to activate G proteins with their abilities to induce MOPr phosphorylation, to promote association of arrestin-3 and to cause MOPr internalization. For a model of G protein-coupled receptor (GPCR) activation where all agonists stabilize a single active conformation of the receptor, a close correlation between signaling outputs might be expected. Our results show that overall there is a very good correlation between efficacy for G protein activation and arrestin-3 recruitment, whereas a few agonists, in particular endomorphins 1 and 2, display apparent bias toward arrestin recruitment. The agonist-induced phosphorylation of MOPr at Ser375, considered a key step in MOPr regulation, and agonist-induced internalization of MOPr were each found to correlate well with arrestin-3 recruitment. These data indicate that for the majority of MOPr agonists the ability to induce receptor phosphorylation, arrestin-3 recruitment, and internalization can be predicted from their ability as agonists to activate G proteins. For the prototypic MOPr agonist morphine, its relatively weak ability to induce MOPr internalization can be explained by its low agonist efficacy.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the Medical Research Council UK [Grant G0600943]; the National Institutes of Health National Institute on Drug Abuse [Grant DA020836]; and the Biotechnology and Biochemical Sciences Research Council [Grant BB/D012902/1].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.066613.
-
ABBREVIATIONS:
- MOPr
- μ opioid receptor
- DAMGO
- [d-Ala2,N-MePhe4,Gly-ol]-enkephalin
- GPCR
- G protein-coupled receptor
- HEK
- human embryonic kidney
- EA
- enzyme acceptor
- FRET
- fluorescence resonance energy transfer
- CFP
- enhanced cyan fluorescent protein
- YFP
- enhanced yellow fluorescent protein
- HBBS
- Hanks' buffered saline solution
- ELISA
- enzyme-linked immunosorbent assay
- M6G
- morphine-6-glucuronide
- GRK2
- G protein-coupled receptor kinase 2
- GIRK
- G protein-gated K+ channel
- GTPγS
- guanosine 5′-O-(3-thio)triphosphate.
- Received May 26, 2010.
- Accepted July 20, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|