title: Oxytocin-induced activation of eukaryotic elongation factor 2 in myometrial cells is mediated by protein kinase C.
abstract: The nonapeptide oxytocin (OT) mediates a wide spectrum of biological action, many of them related to reproduction. Recently, we have shown that OT exerts a trophic effect on uterine smooth muscle cells and induces dephosphorylation, and thus activation, of the translation elongation factor eukaryotic elongation factor 2 (eEF2). The present study was designed to elucidate the mechanisms underlying this novel action of OT in the well-characterized human myometrial cell line hTERT-C3. Pathways known to induce eEF2 dephosphorylation are mammalian target of rapamycin (mTOR), and the MAPKs ERK1/2 and p38. Using a panel of chemical inhibitors of specific signaling pathways, we determined that none of these pathways played a role in OT-mediated eEF2 dephosphorylation. Because the OT receptor is a G protein-coupled receptor linked to Galphaq, we tested the possibility that this OT action was mediated via protein kinase C (PKC). PKC activity was blocked by application of the general PKC chemical inhibitor Go6983 or by incubation with the cell-permeable PKC inhibitor peptide myr-psi PKC. With either approach, the effect of OT on eEF2 dephosphorylation was suppressed, indicating that the PKC pathway is essential for this OT action. Consistent with this idea, we also found that direct stimulation of PKC with the phorbol ester phorbol 12-myristate 13-acetate induced eEF2 dephosphorylation. Moreover, we observed that the stimulatory effect of OT on [(35)S]methionine incorporation into nascent proteins was blocked by PKC inhibition. Overall, these results define a novel hormonal signaling pathway that leads to eEF2 dephosphorylation and activation of protein synthesis.
authors.affiliation: Department of Pharmacology & Therapeutics, McGill University, 3655 Promenade Sir-William-Osler, Montreal, Quebec, Canada H3G 1Y6.
authors.forename: Dominic
authors.initials: D
authors.lastname: Devost
authors.forename: Marie-Eve
authors.initials: ME
authors.lastname: Carrier
authors.forename: Hans H
authors.initials: HH
authors.lastname: Zingg
mesh_terms: D002478:Cells, Cultured; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D005260:Female; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D009215:Myometrium / Q000187:drug effects* / Q000378:metabolism; D010121:Oxytocin / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; D047428:Protein Kinase Inhibitors; D010121:Oxytocin; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases