Differential Effects of Tumor Necrosis Factor-α on Protein Kinase C Isoforms α and δ Mediate Inhibition of Insulin Receptor Signaling

  1. Tovit Rosenzweig1,
  2. Liora Braiman1,
  3. Asia Bak1,
  4. Addy Alt1,
  5. Toshio Kuroki2 and
  6. Sanford R. Sampson1
  1. 1Faculty of Life Sciences, Gonda-Goldschmied Center, Bar-Ilan University, Ramat-Gan, Israel
  2. 2Institute of Molecular Oncology, Showa University, Hatanodai, Shinagawa-ku, Tokyo, Japan

    Abstract

    Tumor necrosis factor-α (TNF-α) 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-α inhibition of insulin signaling in primary cultures of mouse skeletal muscle. TNF-α, 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-α each caused tyrosine phosphorylation and activation of PKCs δ and α, but when TNF-α preceded insulin, the effects were less than that produced by each substance alone. Insulin induced PKCδ specifically to coprecipitate with IR, an effect blocked by TNF-α. Both PKCα and -δ are constitutively associated with IRS-1. Whereas insulin decreased coprecipitation of IRS-1 with PKCα, it increased coprecipitation of IRS-1 with PKCδ. TNF-α 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-α on insulin signaling, we overexpressed specific PKC isoforms in mature myotubes. PKCα overexpression inhibited basal and insulin-induced IR autophosphorylation, whereas PKCδ overexpression increased IR autophosphorylation and abrogated the inhibitory effect of TNF-α on IR autophosphorylation and signaling to PI3-K. Blockade of PKCα antagonized the inhibitory effects of TNF-α on both insulin-induced IR tyrosine phosphorylation and IR signaling to PI3-K. We suggest that the effects of TNF-α on IR tyrosine phosphorylation are mediated via alteration of insulin-induced activation and association of PKCδ and -α with upstream signaling molecules.

    Footnotes

    • Address correspondence and reprint requests to S. R. Sampson, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel. E-mail: sampsos{at}mail.biu.ac.il.

      Received for publication 17 May 2001 and accepted in revised form 11 March 2002.

      2DG, 2-deoxy-d-glucose; IR, insulin receptor; IRS, IR substrate; PI3-K, phosphatidylinositol 3-kinase; PKC, protein kinase C; TNF-α, tumor necrosis factor-α.

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