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Nociceptin (ORL‐1) and μ‐Opioid Receptors Mediate Mitogen‐Activated Protein Kinase Activation in CHO Cells Through a G i ‐Coupled Signaling Pathway: Evidence for Distinct Mechanisms of Agonist‐Mediated Desensitization
Author(s) -
Hawes Brian E.,
Fried Steven,
Yao Xiaorui,
Weig Blair,
Graziano Michael P.
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.71031024.x
Subject(s) - nociceptin receptor , wortmannin , protein kinase c , chemistry , signal transduction , microbiology and biotechnology , protein kinase a , opioid receptor , g protein coupled receptor , receptor , opioid peptide , kinase , phosphatidylinositol , biology , agonist , biochemistry , opioid
The recently identified 17‐amino acid peptide nociceptin (orphanin FQ) is the endogenous ligand for the opioid receptor‐like‐1 (ORL‐1) receptor. A physiologic role for nociceptin (OFQ) activation of the ORL‐1 receptor (OFQR) may be to modulate opioid‐induced analgesia. The molecular mechanism by which nociceptin (OFQ) and ORL‐1 (OFQR) modify opioid‐stimulated effects, however, is unclear. Both ORL‐1 (OFQR) and opioid receptors mediate pertussis toxin (PTX)‐sensitive signal transduction, indicating these receptors are capable of coupling to G i /G o proteins. This study determines that nociceptin stimulates an intracellular signaling pathway, leading to activation of mitogen‐activated protein (MAP) kinase in CHO cells expressing ORL‐1 receptor (OFQR). Nociceptin (OFQ)‐stimulated MAP kinase activation was inhibited by PTX or by expression of the carboxyl terminus of β‐adrenergic receptor kinase (βARKct), which specifically blocks Gβγ‐mediated signaling. Expression of the proline‐rich domain of SOS (SOS‐PRO), which inhibits SOS interaction with p21 ras , also attenuated nociceptin (OFQ)‐stimulated MAP kinase activation. The phosphatidylinositol 3‐kinase (PI‐3K) inhibitors wortmannin and LY294002 reduced nociceptin (OFQ)‐stimulated MAP kinase activation, whereas inhibition of protein kinase C (PKC) activity by bisindolylmaleimide I or cellular depletion of PKC had no effect. In a similar manner, in cells expressing μ‐opioid receptor, [ d ‐Ala 2 , N ‐Me‐Phe 4 ,Gly‐ol]‐enkephalin (DAMGO; a μ‐opioid receptor‐selective agonist) stimulated PTX‐sensitive MAP kinase activation that was inhibited by wortmannin, LY294002, βARKct expression, or SOS‐PRO expression but not affected by inhibition of PKC activity. These results indicate that both ORL‐1 (OFQR) and μ‐opioid receptors mediate MAP kinase activation via a signaling pathway using the βγ‐subunit of G i , a PI‐3K, and SOS, independent of PKC activity. In cells expressing both ORL‐1 (OFQR) and μ‐opioid receptors, pretreatment with nociceptin decreased subsequent nociceptin (OFQ)‐ or DAMGO‐stimulated MAP kinase activation. In contrast, pretreatment of cells with DAMGO decreased subsequent DAMGO‐stimulated MAP kinase but had no effect on subsequent nociceptin (OFQ)‐stimulated MAP kinase activation. These results demonstrate that nociceptin (OFQ) activation of ORL‐1 (OFQR) can modulate μ‐opioid receptor signaling in a cellular system.