Different regulation of human delta-opioid receptors by SNC-80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide] and endogenous enkephalins.
Among the different mechanisms underlying opioid tolerance, receptor desensitization would represent a major cellular adaptation process in which the role of receptor internalization is still a matter of debate. In the present study, we examined desensitization of the human delta-opioid receptor (hDOR) produced by endogenous opioid peptides Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) and Met-enkephalin (Tyr-Gly-Gly-Phe-Met), and the contribution of internalization in this process. Results obtained with natural peptides were compared with those produced by a synthetic opioid agonist, SNC-80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide). After a 30-min treatment, we observed a different regulation of hDOR between agonists. SNC-80 produced a stronger and faster desensitization and was associated with a loss of opioid binding sites by 50%. SNC-80 also caused a marked hDOR down-regulation by 30% as observed by Western blot. Immunocytochemistry revealed that SNC-80 induced a complete redistribution of hDOR from cell surface into intracellular compartments, whereas a partial internalization was visualized upon enkephalin exposure. In contrast, a stronger hDOR recycling and resensitization were measured after enkephalin treatment compared with SNC-80. These data strongly suggested a differential sorting of the internalized receptors caused by enkephalins and SNC-80 that was further confirmed by chloroquine as a lysosomal degradation blocker and monensin as a recycling endosome inhibitor. Finally, by preventing hDOR internalization with 0.5 M sucrose, we demonstrated that hDOR internalization contributes partially to desensitization. In conclusion, hDOR desensitization depends both on its internalization and its sorting either to the recycling pathway or to lysosomes.
Lecoq
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Laboratoire de Biochimie A, avenue Côte de Nacre, CHU de Caen, 14033 Caen Cedex, France.
Marie
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Jauzac
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Allouche
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D001549:Benzamides / Q000378:metabolism / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004745:Enkephalins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D010879:Piperazines / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000378:metabolism*
D001549:Benzamides; D004745:Enkephalins; D010879:Piperazines; D017465:Receptors, Opioid, delta; C088464:4-(alpha-(4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N,N-diethylbenzamide