title: Nociceptor sensitization by extracellular signal-regulated kinases.
abstract: Inflammatory pain, characterized by a decrease in mechanical nociceptive threshold (hyperalgesia), arises through actions of inflammatory mediators, many of which sensitize primary afferent nociceptors via G-protein-coupled receptors. Two signaling pathways, one involving protein kinase A (PKA) and one involving the epsilon isozyme of protein kinase C (PKCepsilon), have been implicated in primary afferent nociceptor sensitization. Here we describe a third, independent pathway that involves activation of extracellular signal-regulated kinases (ERKs) 1 and 2. Epinephrine, which induces hyperalgesia by direct action at beta(2)-adrenergic receptors on primary afferent nociceptors, stimulated phosphorylation of ERK1/2 in cultured rat dorsal root ganglion cells. This was inhibited by a beta(2)-adrenergic receptor blocker and by an inhibitor of mitogen and extracellular signal-regulated kinase kinase (MEK), which phosphorylates and activates ERK1/2. Inhibitors of G(i/o)-proteins, Ras farnesyltransferases, and MEK decreased epinephrine-induced hyper-algesia. In a similar manner, phosphorylation of ERK1/2 was also decreased by these inhibitors. Local injection of dominant active MEK produced hyperalgesia that was unaffected by PKA or PKCepsilon inhibitors. Conversely, hyperalgesia produced by agents that activate PKA or PKCepsilon was unaffected by MEK inhibitors. We conclude that a Ras-MEK-ERK1/2 cascade acts independent of PKA or PKCepsilon as a novel signaling pathway for the production of inflammatory pain. This pathway may present a target for a new class of analgesic agents.
authors.affiliation: Departments of Medicine and Oral Surgery, National Institutes of Health Pain Center at the University of California, San Francisco, San Francisco, California 94143, USA.
authors.forename: K O
authors.initials: KO
authors.lastname: Aley
authors.forename: A
authors.initials: A
authors.lastname: Martin
authors.forename: T
authors.initials: T
authors.lastname: McMahon
authors.forename: J
authors.initials: J
authors.lastname: Mok
authors.forename: J D
authors.initials: JD
authors.lastname: Levine
authors.forename: R O
authors.initials: RO
authors.lastname: Messing
mesh_terms: D058672:Adrenergic beta-2 Receptor Antagonists; D000818:Animals; D002478:Cells, Cultured; D003433:Crosses, Genetic; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000503:physiopathology; D020962:Heterotrimeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009619:Nociceptors / Q000187:drug effects / Q000503:physiopathology*; D010147:Pain Measurement; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051744:Protein Kinase C-epsilon; D051381:Rats; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D018631:ras Proteins / Q000378:metabolism
chemical_list: D058672:Adrenergic beta-2 Receptor Antagonists; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D018343:Receptors, Adrenergic, beta-2; C497256:Prkce protein, mouse; C497257:Prkce protein, rat; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020962:Heterotrimeric GTP-Binding Proteins; D018631:ras Proteins