Chronic morphine acts via a protein kinase Cgamma-G(beta)-adenylyl cyclase complex to augment phosphorylation of G(beta) and G(betagamma) stimulatory adenylyl cyclase signaling.
Chronic morphine augments protein kinase C (PKC) phosphorylation of G(beta), which enhances the potency of G(betagamma) to stimulate adenylyl cyclase II (ACII) activity. The present study demonstrates an in vivo association between phosphorylated G(beta) and a specific PKC isoform, PKCgamma. We investigated the association of G(beta) and PKCgamma by assessing the ability of anti-PKCgamma antibodies to co-immunoprecipitate G(beta) from (32)P-radiolabeled Chinese Hamster Ovary cells stably transfected with a mu-opioid receptor (MOR-CHO). PKCgamma immunoprecipitate (IP) obtained from MOR-CHO membranes contained radiolabeled signals of approximately equals 33 and 36--38 kDa that were subsequently identified as G(beta)(s). Chronic morphine significantly increased ( approximately equals 75%) the magnitude of (32)P incorporated into G(beta) present in PKCgamma IP. This suggests that G(beta) is an in vivo substrate for PKCgamma, which mediates the chronic morphine-induced increment in G(beta) phosphorylation. In order to evaluate AC as a putative effector for phosphorylated G(betagamma), its presence in IP obtained using anti-AC antibodies was evaluated. Autoradiographic analyses of AC IP also revealed the presence of phosphorylated G(beta)(s), the magnitude of which was significantly enhanced ( approximately equals 60%) following chronic morphine treatment. This indicates that phosphorylated G(betagamma) associates and presumably interacts in vivo with AC, indicating that it is a target for the enhanced phosphorylated G(betagamma) that is generated following chronic morphine treatment. This would contribute to the previously observed shift from predominantly G(ialpha) inhibitory to G(betagamma) stimulatory AC signaling following chronic morphine. The PKCgamma-G(beta)-AC complex identified in this study provides an organizational framework for understanding the well-documented participation of PKCgamma in opioid tolerance-producing mechanisms.
Chakrabarti
Sumita
S
Department of Biochemistry, State University of New York, Downstate Medical Center, Box 8, 450 Clarkson Avenue, Brooklyn, NY 11203, USA.
Regec
Annette
A
Gintzler
Alan R
AR
D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism*; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D000818:Animals; D001345:Autoradiography / Q000379:methods; D015153:Blotting, Western / Q000379:methods; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004334:Drug Administration Schedule; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000187:drug effects / Q000378:metabolism*; D047468:Immunoprecipitation / Q000379:methods; D046911:Macromolecular Substances; D008970:Molecular Weight; D009020:Morphine / Q000008:administration & dosage*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010759:Phosphorus Isotopes / Q000493:pharmacokinetics; D010766:Phosphorylation / Q000187:drug effects; D020033:Protein Isoforms / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D014162:Transfection / Q000379:methods
D000701:Analgesics, Opioid; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D046911:Macromolecular Substances; D016376:Oligonucleotides, Antisense; D010759:Phosphorus Isotopes; D020033:Protein Isoforms; D012333:RNA, Messenger; D009020:Morphine; C087857:protein kinase C gamma; D011493:Protein Kinase C; D000262:Adenylyl Cyclases