title: Orphanin FQ/nociceptin potentiates [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin-Induced mu-opioid receptor phosphorylation.
abstract: In this study, we investigate the molecular mechanisms by which acute orphanin FQ/nociceptin (OFQ/N), acting through the nociceptin opioid peptide (NOP) receptor, desensitizes the mu-opioid receptor. We described previously the involvement of protein kinase C and G-protein-coupled receptor kinases (GRK) 2 and 3 in OFQ/N-induced mu receptor desensitization. Because phosphorylation of the mu receptor triggers the successive regulatory mechanisms responsible for desensitization, such as receptor uncoupling, internalization, and down-regulation, we investigated the ability of OFQ/N to modulate [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO)-induced mu receptor phosphorylation in BE(2)-C human neuroblastoma cells transfected with epitope-tagged mu receptors. OFQ/N treatment (100 nM, 60 min) potentiated DAMGO-induced mu receptor phosphorylation; inhibition of GRK2 or protein kinase C concomitant with OFQ/N treatment blocked the OFQ/N-mediated increase in DAMGO-induced phosphorylation. Inclusion of the NOP antagonist peptide III-BTD during OFQ/N pretreatment blocked the potentiation of DAMGO-induced phosphorylation by OFQ/N, which is consistent with the potentiation being mediated via actions of the NOP receptor. In addition, in cells expressing mu receptors in which the GRK-mediated phosphorylation site Ser(375) was mutated to alanine, OFQ/N treatment failed to potentiate DAMGO-induced mu receptor phosphorylation and failed to desensitize the mu receptor. However, DAMGO-induced mu receptor phosphorylation and OFQ/N-induced mu receptor desensitization occurred in cells expressing mu receptors lacking non-GRK phosphorylation sites. These data suggest that OFQ/N binds to NOP receptors and activates protein kinase C, which then increases the ability of GRK2 to phosphorylate the agonist-occupied mu receptor, heterologously regulating homologous mu receptor desensitization.
authors.affiliation: Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 4800 Calhoun Road, 521 Science and Research Building 2, Houston, TX 77204-5037, USA.
authors.forename: Hatice Z
authors.initials: HZ
authors.lastname: Ozsoy
authors.forename: Deepak R
authors.initials: DR
authors.lastname: Thakker
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Standifer
mesh_terms: D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D018847:Opioid Peptides / Q000378:metabolism / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D000097629:Nociceptin
chemical_list: D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D018847:Opioid Peptides; D017450:Receptors, Opioid, mu; D000097629:Nociceptin