Abstract
Heteromerization of opioid receptors has been shown to alter opioid receptor pharmacology. However, how receptor heteromerization affects the processes of endocytosis and postendocytic sorting has not been closely examined. This question is of particular relevance for heteromers of the μ-opioid receptor (MOR) and δ-opioid receptor (DOR), because the MOR is recycled primarily after endocytosis and the DOR is degraded in the lysosome. Here, we examined the endocytic and postendocytic fate of MORs, DORs, and DOR/MOR heteromers in human embryonic kidney 293 cells stably expressing each receptor alone or coexpressing both receptors. We found that the clinically relevant MOR agonist methadone promotes endocytosis of MOR but also the DOR/MOR heteromer. Furthermore, we show that DOR/MOR heteromers that are endocytosed in response to methadone are targeted for degradation, whereas MORs in the same cell are significantly more stable. It is noteworthy that we found that the DOR-selective antagonist naltriben mesylate could block both methadone- and [d-Ala2,NMe-Phe4,Gly-ol5]-enkephalin-induced endocytosis of the DOR/MOR heteromers but did not block signaling from this heteromer. Together, our results suggest that the MOR adopts novel trafficking properties in the context of the DOR/MOR heteromer. In addition, they suggest that the heteromer shows “biased antagonism,” whereby DOR antagonist can inhibit trafficking but not signaling of the DOR/MOR heteromer.
Footnotes
This study was supported by a Schrödinger fellowship from the Austrian Science Fund [Fellowship J 2967-B09] (to L.M.-L.); the National Institutes of Health National Institute on Drug Abuse [Grant DA015232] (to J.L.W.); and funds provided by the State of California for medical research through the University of California, San Francisco (to J.L.W.).
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.111.179093.
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- DOR
- δ-opioid receptor
- MOR
- μ-opioid receptor
- GPCR
- G-protein coupled receptor
- HEK
- human embryonic kidney
- PBS
- phosphate-buffered saline
- ANOVA
- analysis of variance
- RFU
- relative fluorescence units
- PAGE
- polyacrylamide gel electrophoresis
- DPDPE
- [d-Pen2,d-Pen5]-enkephalin
- BNTX
- 7-benzylidene naltrexone maleate
- NTB
- naltriben mesylate
- NTI
- naltrindole hydrochloride
- DAMGO
- [d-Ala2,NMe-Phe4,Gly-ol5]-enkephalin
- HA
- hemagglutinin.
- Received January 7, 2011.
- Accepted March 18, 2011.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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