title: Differential effects of tumor necrosis factor-alpha on protein kinase C isoforms alpha and delta mediate inhibition of insulin receptor signaling.
abstract: Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional cytokine that interferes with insulin signaling, but the molecular mechanisms of this effect are unclear. Because certain protein kinase C (PKC) isoforms are activated by insulin, we examined the role of PKC in TNF-alpha inhibition of insulin signaling in primary cultures of mouse skeletal muscle. TNF-alpha, given 5 min before insulin, inhibited insulin-induced tyrosine phosphorylation of insulin receptor (IR), IR substrate (IRS)-1, insulin-induced association of IRS-1 with the p85 subunit of phosphatidylinositol 3-kinase (PI3-K), and insulin-induced glucose uptake. Insulin and TNF-alpha each caused tyrosine phosphorylation and activation of PKCs delta and alpha, but when TNF-alpha preceded insulin, the effects were less than that produced by each substance alone. Insulin induced PKCdelta specifically to coprecipitate with IR, an effect blocked by TNF-alpha. Both PKCalpha and -delta are constitutively associated with IRS-1. Whereas insulin decreased coprecipitation of IRS-1 with PKCalpha, it increased coprecipitation of IRS-1 with PKCdelta. TNF-alpha blocked the effects of insulin on association of both PKCs with IRS-1. To further investigate the involvement of PKCs in inhibitory actions of TNF-alpha on insulin signaling, we overexpressed specific PKC isoforms in mature myotubes. PKCalpha overexpression inhibited basal and insulin-induced IR autophosphorylation, whereas PKCdelta overexpression increased IR autophosphorylation and abrogated the inhibitory effect of TNF-alpha on IR autophosphorylation and signaling to PI3-K. Blockade of PKCalpha antagonized the inhibitory effects of TNF-alpha on both insulin-induced IR tyrosine phosphorylation and IR signaling to PI3-K. We suggest that the effects of TNF-alpha on IR tyrosine phosphorylation are mediated via alteration of insulin-induced activation and association of PKCdelta and -alpha with upstream signaling molecules.
authors.affiliation: Faculty of Life Sciences, Gonda-Goldschmied Center, Bar-Ilan University, Ramat-Gan, Israel.
authors.forename: Tovit
authors.initials: T
authors.lastname: Rosenzweig
authors.forename: Liora
authors.initials: L
authors.lastname: Braiman
authors.forename: Asia
authors.initials: A
authors.lastname: Bak
authors.forename: Addy
authors.initials: A
authors.lastname: Alt
authors.forename: Toshio
authors.initials: T
authors.lastname: Kuroki
authors.forename: Sanford R
authors.initials: SR
authors.lastname: Sampson
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D007163:Immunosorbent Techniques; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018482:Muscle, Skeletal / Q000378:metabolism; D016296:Mutagenesis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D011972:Receptor, Insulin / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D007527:Isoenzymes; D010750:Phosphoproteins; D014409:Tumor Necrosis Factor-alpha; D019000:Phosphotyrosine; D019869:Phosphatidylinositol 3-Kinases; C497259:Prkcd protein, mouse; D011972:Receptor, Insulin; C496630:Prkca protein, mouse; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta