Chronic morphine induces the concomitant phosphorylation and altered association of multiple signaling proteins: a novel mechanism for modulating cell signaling.
Traditional mechanisms thought to underlie opioid tolerance include receptor phosphorylation/down-regulation, G-protein uncoupling, and adenylyl cyclase superactivation. A parallel line of investigation also indicates that opioid tolerance development results from a switch from predominantly opioid receptor G(i alpha) inhibitory to G(beta gamma) stimulatory signaling. As described previously, this results, in part, from the increased relative abundance of G(beta gamma)-stimulated adenylyl cyclase isoforms as well as from a profound increase in their phosphorylation [Chakrabarti, S., Rivera, M., Yan, S.-Z., Tang, W.-J. & Gintzler, A. R. (1998) Mol. Pharmacol. 54, 655-662; Chakrabarti, S., Wang, L., Tang, W.-J. & Gintzler, A. R. (1998) Mol. Pharmacol. 54, 949--953]. The present study demonstrates that chronic morphine administration results in the concomitant phosphorylation of three key signaling proteins, G protein receptor kinase (GRK) 2/3, beta-arrestin, and G(beta), in the guinea pig longitudinal muscle myenteric plexus tissue. Augmented phosphorylation of all three proteins is evident in immunoprecipitate obtained by using either anti-GRK2/3 or G(beta) antibodies, but the phosphorylation increment is greater in immunoprecipitate obtained with G(beta) antibodies. Analyses of coimmunoprecipitated proteins indicate that phosphorylation of GRK2/3, beta-arrestin, and G(beta) has varying consequences on their ability to associate. As a result, increased availability of and signaling via G(beta gamma) could occur without compromising the membrane content (and presumably activity) of GRK2/3. Induction of the concomitant phosphorylation of multiple proteins in a multimolecular complex with attendant modulation of their association represents a novel mechanism for increasing G(beta gamma) signaling and opioid tolerance formation.
Department of Biochemistry, State University of New York, Downstate Medical Center, Brooklyn, NY 11203, USA.
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Chakrabarti
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Oppermann
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Gintzler
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004347:Drug Interactions; D054770:G-Protein-Coupled Receptor Kinase 3; D019204:GTP-Binding Proteins / Q000378:metabolism; D006168:Guinea Pigs; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009197:Myenteric Plexus / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051552:beta-Adrenergic Receptor Kinases; D000071557:beta-Arrestins
D000701:Analgesics, Opioid; D019390:Arrestins; D010761:Phosphorus Radioisotopes; D000071557:beta-Arrestins; D009020:Morphine; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D054770:G-Protein-Coupled Receptor Kinase 3; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins