Rosenzweig Tovit, Braiman Liora, Bak Asia, Alt Addy, Kuroki Toshio, Sampson Sanford R
Faculty of Life Sciences, Gonda-Goldschmied Center, Bar-Ilan University, Ramat-Gan, Israel.
Diabetes. 2002 Jun;51(6):1921-30. doi: 10.2337/diabetes.51.6.1921.
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.
肿瘤坏死因子-α（TNF-α）是一种多功能细胞因子，它会干扰胰岛素信号传导，但其作用的分子机制尚不清楚。由于某些蛋白激酶C（PKC）亚型可被胰岛素激活，我们研究了PKC在小鼠骨骼肌原代培养物中TNF-α对胰岛素信号传导抑制作用中的作用。在胰岛素作用前5分钟给予TNF-α，可抑制胰岛素诱导的胰岛素受体（IR）、胰岛素受体底物（IRS）-1的酪氨酸磷酸化，胰岛素诱导的IRS-1与磷脂酰肌醇3激酶（PI3-K）的p85亚基的结合，以及胰岛素诱导的葡萄糖摄取。胰岛素和TNF-α各自均可引起PKCδ和α的酪氨酸磷酸化和激活，但当TNF-α先于胰岛素作用时，其作用小于单独使用每种物质时产生的作用。胰岛素诱导PKCδ特异性地与IR共沉淀，这一作用被TNF-α阻断。PKCα和PKCδ均与IRS-1组成性结合。胰岛素可降低IRS-1与PKCα的共沉淀，却增加IRS-1与PKCδ的共沉淀。TNF-α阻断了胰岛素对两种PKC与IRS-1结合的作用。为进一步研究PKC在TNF-α对胰岛素信号传导抑制作用中的参与情况，我们在成熟肌管中过表达特定的PKC亚型。PKCα过表达抑制基础和胰岛素诱导的IR自身磷酸化，而PKCδ过表达增加IR自身磷酸化，并消除TNF-α对IR自身磷酸化和向PI3-K信号传导的抑制作用。阻断PKCα可拮抗TNF-α对胰岛素诱导的IR酪氨酸磷酸化和IR向PI3-K信号传导的抑制作用。我们认为，TNF-α对IR酪氨酸磷酸化的作用是通过改变胰岛素诱导的PKCδ和PKCα与上游信号分子的激活及结合来介导的。
