Allelic Variation S268P of the Human μ-Opioid Receptor Affects Both Desensitization and G Protein Coupling1
- Thomas Koch2,
- Thomas Kroslak2,
- Marco Averbeck,
- Peter Mayer,
- Helmut Schröder,
- Evelyn Raulf and
- Volker Höllt
Abstract
The decrease in μ-opioid receptor activity after chronic agonist exposure (1 μM [d-Ala2,N-MePhe4,Gly-ol5]-enkephalin) is largely due to kinase-mediated phosphorylation of intracellular receptor domains. We have recently shown that the substitution of two putative Ca2+/calmodulin-dependent protein kinase II (CaMK II) phosphorylation sites, S261 and S266, by alanines in the third intracellular loop of the rat μ-opioid receptor (rMOR1) confers resistance to CaMK II-induced receptor desensitization. In the present study, we show that the injection of active CaMK II inXenopus laevis oocytes led to the desensitization of S261A but not S266A receptor mutant, indicating that S266 is the primary CaMK II phosphorylation site of the rMOR1. For the corresponding phosphorylation site in the human μ-opioid receptor (hMOR), an allelic variation S268P has been recently identified. After expression in X. laevis oocytes and human embryonic kidney 293 cells, this human S268P receptor and a corresponding rat S266P receptor mutant revealed a loss of CaMK II-induced receptor desensitization and a decreased G protein coupling compared with the wild-type receptors. Our results suggest that serines 266 (rMOR1) and 268 (hMOR) play crucial role in receptor desensitization and signaling and that the allelic variation S268P results in a human receptor type with a weaker but persistent G protein coupling after agonist treatment.
Footnotes
-
Send reprint requests to: Dr. Volker Höllt, Department of Pharmacology and Toxicology, Otto-von-Guericke University, Leipziger Str. 44, 39120 Magdeburg, Germany. E-mail:Volker.Hoellt{at}Medizin.Uni-Magdeburg.de
-
↵1 This study was supported by Grant 1895A/0025 (to T.K.) from the Land Sachsen-Anhalt, SFB 426 (V.H.), and Fonds der Chemischen Industrie (V.H.).
-
↵2 These authors contributed equally to this work.
- Abbreviations:
- rMOR1
- rat μ-opioid receptor isoform 1
- hMOR
- human μ-opioid receptor
- CaMK II
- Ca2+/calmodulin-dependent protein kinase II
- DAMGO
- [d-Ala2,N-MePhe4,Gly-ol5]-enkephalin
- GTPγS
- guanosine-5′-O-(3-thio)triphosphate
- GIRK
- G protein-gated, inwardly rectifying K+ channel
- HEK
- human embryonic kidney
- PCR
- polymerase chain reaction
-
- Received February 3, 2000.
- Accepted April 10, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
