title: Acute treatment with TNF-alpha attenuates insulin-stimulated protein synthesis in cultures of C2C12 myotubes through a MEK1-sensitive mechanism.
abstract: Insulin and TNF-alpha exert opposing effects on skeletal muscle protein synthesis that are mediated in part by the rapamycin-sensitive mammalian target of rapamycin (mTOR) pathway and the PD-98059-sensitive, extracellular signal-regulated kinase (ERK)1/2 pathway. The present study examined the separate and combined effects of insulin (INS), TNF, PD-98059, or dnMEK1 adenovirus on the translational control of protein synthesis in C(2)C(12) myotubes. Cultures were treated with INS, TNF, PD-98059, dnMEK1, or a combination of INS + TNF with PD-98059 or dnMEK1. INS stimulated protein synthesis, enhanced eIF4E.eIF4G association, and eIF4G phosphorylation and repressed eIF4E.4E-BP1 association vs. control. INS also promoted phosphorylation of ERK1/2, S6K1, and 4E-BP1 and dephosphorylation of eIF4E. TNF alone did not have an effect on protein synthesis (vs. control), eIF4E.eIF4G association, or the phosphorylation of eIF4G, S6K1, or 4E-BP1, although it transiently increased ERK1/2 and eIF4E phosphorylation. When myotubes were treated with TNF + INS, the cytokine blocked the insulin-induced stimulation of protein synthesis. This appeared to be due to an attenuation of insulin-stimulated eIF4E.eIF4G association, because other stimulatory effects of INS, e.g., phosphorylation of ERK1/2, 4E-BP1, S6K1, eIF4G, and eIF4E and eIF4E.4E-BP1 association, were unaffected. Finally, treatment of myotubes with PD-98059 or dnMEK1 adenovirus before TNF + INS addition resulted in a derepression of protein synthesis and the association of eIF4G with eIF4E. These findings suggest that TNF abrogates insulin-induced stimulation of protein synthesis in myotubes through a decrease in eIF4F complex assembly independently of S6K1 and 4E-BP1 signaling and dependently on a MEK1-sensitive signaling pathway.
authors.affiliation: Department of Cellular and Molecular Physiology, H166, The Pennsylvania State University College of Medicine, 500 Univ. Dr., Hershey, PA 17033, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Williamson
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Jefferson
mesh_terms: D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D007328:Insulin / Q000494:pharmacology*; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D004338:Drug Combinations; D007328:Insulin; D014409:Tumor Necrosis Factor-alpha; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse