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Interaction of the µ-Opioid Receptor with Synaptophysin Influences Receptor Trafficking and Signaling

Department of Pharmacology and Toxicology, Otto-von-Guericke University, Magdeburg, Germany

There is increasing evidence that the signal transduction of opioid receptors is modulated by receptor-associated proteins. In the search for proteins regulating µ-opioid receptor (MOPr) endocytosis, synaptophysin was found to bind to the rat µ-opioid receptor in yeast two-hybrid assay. Coimmunoprecipitation experiments and bioluminescence resonance energy transfer assays confirmed that the µ-opioid receptor constitutively interacts with synaptophysin in human embryonic kidney 293 cells overexpressing MOPr and synaptophysin. In this study, we show that overexpression of synaptophysin enhances the µ-opioid receptor endocytosis. One explanation for the observed effects is that synaptophysin recruits dynamin to the plasma membrane, facilitating fission of clathrin-coated vesicles. This suggestion is supported by our finding that overexpression of a synaptophysin truncation mutant, which breaks the interaction between synaptophysin and dynamin, prevents agonist-mediated µ-opioid receptor endocytosis. In addition, the synaptophysin-augmented µ-opioid receptor trafficking leads to attenuated agonist-induced receptor desensitization and faster receptor resensitization. Taken together, our findings strongly suggest that synaptophysin plays an important role in the regulation of µ-opioid receptor trafficking and signaling.

Address correspondence to: Thomas Koch, Department of Pharmacology and Toxicology, Otto-von-Guericke University, Leipziger Str. 44, 39120 Magdeburg, Germany. E-mail: thomas.koch{at}medizin.uni-magdeburg.de

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