Desensitization of endogenously expressed delta-opioid receptors: no evidence for involvement of G protein-coupled receptor kinase 2.
The involvement of G protein-coupled receptor kinase 2 (GRK2) in the agonist-induced desensitization of delta-opioid receptor-mediated inhibition of cAMP formation in NG108-15 mouse neuroblastomaxrat glioma hybrid cells was investigated. Pretreatment of wild-type cells with the delta-opioid receptor agonist [D-Pen(2,5)]-enkephalin (DPDPE; 100 nM) for as little as 5 min produced marked desensitization of subsequent DPDPE-mediated inhibition of iloprost (300 nM)-stimulated cAMP formation. In NG108-15 cells stably overexpressing wild-type GRK2 or dominant negative mutant GRK2 (DNM GRK2), the DPDPE-induced desensitization of cAMP inhibition was the same as in plasmid-transfected control cells. Pretreatment of wild-type cells with the inhibitors of receptor internalization, concanavalin A (0.25 mg ml(-1)) or hypertonic sucrose (0.4 M), also failed to inhibit DPDPE-mediated desensitization. Finally, in NG108-15 cells stably overexpressing G protein-coupled receptor kinase 6 (GRK6), DPDPE-induced desensitization was significantly increased as compared to plasmid-transfected control cells. These results indicate that GRK2 is unlikely to mediate the desensitization of endogenous delta-opioid receptors in NG108-15 cells, but that other GRKs, such as GRK6, may be more important.
Willets
J
J
Department of Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
Kelly
E
E
D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism* / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology*; D054769:G-Protein-Coupled Receptor Kinase 2; D054770:G-Protein-Coupled Receptor Kinase 3; D054768:G-Protein-Coupled Receptor Kinases; D006822:Hybrid Cells; D016285:Iloprost; D051379:Mice; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis; D051381:Rats; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D051552:beta-Adrenergic Receptor Kinases
D017465:Receptors, Opioid, delta; D009271:Naltrexone; D020881:Enkephalin, D-Penicillamine (2,5)-; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C517850:GRK3 protein, mouse; C496569:Grk2 protein, rat; C517851:Grk3 protein, rat; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D054768:G-Protein-Coupled Receptor Kinases; C089176:G-protein-coupled receptor kinase 6; C055382:naltrindole; D016285:Iloprost