Role of mPKCI, a novel mu-opioid receptor interactive protein, in receptor desensitization, phosphorylation, and morphine-induced analgesia.
The human mu-opioid receptor (HmuOR) is a G-protein coupled receptor that mediates analgesia, euphoria and other important central and peripheral neurological functions. In this study, we found in a yeast two-hybrid screen that a protein kinase C-interacting protein (PKCI) specifically interacts with the C terminus of HmuOR. The interaction of PKCI with HmuOR was recapitulated in Chinese hamster ovary cells that express the full-length HmuOR and PKCI proteins. The affinity of HmuOR for an opioid ligand and its ability to mediate the activation of a G-protein were not altered by their interaction. However, the association of PKCI with HmuOR reduced agonist-induced inhibition of adenylyl cyclase and suppressed HmuOR desensitization partially at the G protein level and completely at the adenylyl cyclase level. Furthermore, PMA-induced, but not DAMGO-induced, HmuOR phosphorylation was partially inhibited by the coexpression of PKCI, suggesting that PKCI exerts a selective regulatory effect on HmuOR signaling. This effect was specific to the mu-opioid receptor because delta-opioid receptor desensitization was unaffected by PKCI. In addition, behavioral studies revealed that both basal and morphine-induced analgesia were significantly enhanced in the mutant mice that lacked expression of PKCI gene, and these mice developed a greater extent of tolerance to morphine analgesia. Taken together, these results suggest that PKCI functions as a negative regulator in HmuOR desensitization, phosphorylation, and in mediating morphine analgesia.
Guang
Wei
W
Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland Baltimore, 20 N Pine Street, Baltimore, MD 21201, USA.
Wang
Hongyan
H
Su
Tao
T
Weinstein
I Bernard
IB
Wang
Jia Bei
JB
D000595:Amino Acid Sequence; D000698:Analgesia; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D018076:DNA, Complementary / Q000032:analysis; D004361:Drug Tolerance; D005260:Female; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009020:Morphine / Q000009:adverse effects; D010766:Phosphorylation; D017450:Receptors, Opioid, mu / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*
D018076:DNA, Complementary; C493596:PKCI protein, mouse; D017450:Receptors, Opioid, mu; D009020:Morphine