title: Allosteric modulation of metabotropic glutamate receptor 5 affects phosphorylation, internalization, and desensitization of the micro-opioid receptor.
abstract: Recent evidence suggests that opioid analgesia and tolerance can be modulated by metabotropic glutamate receptors. Therefore, we studied the functional coupling and desensitization of the micro-opioid receptor (MOR) in human embryonic kidney (HEK) 293 cells which co-express metabotropic glutamate receptor 5 (mGluR5). As demonstrated by the D-Ala2,N-MePhe4,Gl-ol5-enkephalin (DAMGO)-induced inhibition of intracellular cAMP level and by binding studies, the co-expression of mGluR5 had no substantial effect on the agonist binding sites and functional coupling of the MOR. However, in MOR/ mGluR5 co-expressing cells, the non-competitive mGluR5 antagonist MPEP (2-methyl-6-(phenyl-ethynyl)-pyridine) decreases the DAMGO-induced MOR phosphorylation, internalization, and desensitization, whereas non-selective competitive mGluR antagonists or agonists had no effects. These findings indicate that an allosteric modulation of mGluR5 can affect the agonist-induced MOR signalling and regulation. As a mechanistic basis for the observed effects we suggested an interaction/heterodimerization of MOR and mGluR5, which is supported by the DAMGO-induced co-internalization of MOR and mGluR5 and by the increase of MPEP binding sites (Bmax) and a change of the binding affinity (K(D)) of mGluR5 receptors after the co-expression of MOR. In addition, co-immunoprecipitation experiments revealed evidence for an interaction between MOR and mGluR5 which is facilitated by MPEP treatment.
authors.affiliation: Dept of Pharmacology and Toxicology, Otto-von-Guericke University, Leipziger Str. 44, 39120 Magdeburg, Germany. helmut.schroeder@med.ovgu.de
authors.forename: H
authors.initials: H
authors.lastname: Schröder
authors.forename: D F
authors.initials: DF
authors.lastname: Wu
authors.forename: A
authors.initials: A
authors.lastname: Seifert
authors.forename: M
authors.initials: M
authors.lastname: Rankovic
authors.forename: S
authors.initials: S
authors.lastname: Schulz
authors.forename: V
authors.initials: V
authors.lastname: Höllt
authors.forename: T
authors.initials: T
authors.lastname: Koch
mesh_terms: D000701:Analgesics, Opioid / Q000378:metabolism / Q000494:pharmacology*; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000378:metabolism / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D008024:Ligands; D018613:Microscopy, Confocal; D009474:Neurons / Q000187:drug effects; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D011869:Radioligand Assay; D018092:Kainic Acid Receptors / Q000737:chemistry / Q000187:drug effects*; D017450:Receptors, Opioid, mu / Q000187:drug effects*; D014162:Transfection
chemical_list: D000701:Analgesics, Opioid; D000242:Cyclic AMP; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008024:Ligands; D011725:Pyridines; D018092:Kainic Acid Receptors; D017450:Receptors, Opioid, mu; C121465:6-methyl-2-(phenylethynyl)pyridine