title: Modulating micro-opioid receptor phosphorylation switches agonist-dependent signaling as reflected in PKCepsilon activation and dendritic spine stability.
abstract: A new role of G protein-coupled receptor (GPCR) phosphorylation was demonstrated in the current studies by using the μ-opioid receptor (OPRM1) as a model. Morphine induces a low level of receptor phosphorylation and uses the PKCε pathway to induce ERK phosphorylation and receptor desensitization, whereas etorphine, fentanyl, and [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) induce extensive receptor phosphorylation and use the β-arrestin2 pathway. Blocking OPRM1 phosphorylation (by mutating Ser363, Thr370 and Ser375 to Ala) enabled etorphine, fentanyl, and DAMGO to use the PKCε pathway. This was not due to the decreased recruitment of β-arrestin2 to the receptor signaling complex, because these agonists were unable to use the PKCε pathway when β-arrestin2 was absent. In addition, overexpressing G protein-coupled receptor kinase 2 (GRK2) decreased the ability of morphine to activate PKCε, whereas overexpressing dominant-negative GRK2 enabled etorphine, fentanyl, and DAMGO to activate PKCε. Furthermore, by overexpressing wild-type OPRM1 and a phosphorylation-deficient mutant in primary cultures of hippocampal neurons, we demonstrated that receptor phosphorylation contributes to the differential effects of agonists on dendritic spine stability. Phosphorylation blockage made etorphine, fentanyl, and DAMGO function as morphine in the primary cultures. Therefore, agonist-dependent phosphorylation of GPCR regulates the activation of the PKC pathway and the subsequent responses.
authors.affiliation: Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota 55455-0217, USA. zhenhui2055@hotmail.com
authors.forename: Hui
authors.initials: H
authors.lastname: Zheng
authors.forename: Ji
authors.initials: J
authors.lastname: Chu
authors.forename: Yuhan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Horace H
authors.initials: HH
authors.lastname: Loh
authors.forename: Ping-Yee
authors.initials: PY
authors.lastname: Law
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D002460:Cell Line; D049229:Dendritic Spines / Q000187:drug effects / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D005048:Etorphine / Q000494:pharmacology; D005283:Fentanyl / Q000494:pharmacology; D006801:Humans; D051379:Mice; D009020:Morphine / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D051744:Protein Kinase C-epsilon / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000071557:beta-Arrestins
chemical_list: D000701:Analgesics, Opioid; D019390:Arrestins; D017450:Receptors, Opioid, mu; D000071557:beta-Arrestins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005048:Etorphine; D009020:Morphine; D051744:Protein Kinase C-epsilon; D005283:Fentanyl