A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1.
A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1.
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DOI：
10.1210/mend.14.6.0446
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发表时间：
2000-06
影响因子：
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通讯作者：
T. Haruta;T. Uno;J. Kawahara;A. Takano;K. Egawa;Prem M. Sharma;J. Olefsky;J. Olefsky;M. Kobayashi
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文献类型：
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作者：
T. Haruta;T. Uno;J. Kawahara;A. Takano;K. Egawa;Prem M. Sharma;J. Olefsky;J. Olefsky;M. Kobayashi
胰岛素受体底物-1(IRS-1)是胰岛素受体的主要底物，是含有信号分子的Src同源2结构域的对接蛋白，这些信号分子介导了胰岛素的许多多效性作用。胰岛素刺激引起IRS-1的丝氨酸/苏氨酸磷酸化，在SDS-PAGE上产生迁移率变化，然后在长时间刺激后IRS-1的降解。我们在3T3-L1脂肪细胞中研究了这些现象的分子机制和功能后果。PI 3-激酶抑制剂或雷帕霉素，而不是MEK抑制剂，可以阻止胰岛素诱导的凝胶迁移率改变和IRS-1的降解。腺病毒介导的p110亚基磷脂酰肌醇3-激酶(P110CAAX)膜靶向表达可诱导IRS-1的迁移率漂移和降解，这两种作用均被雷帕霉素抑制。Lactacystin是一种特异的蛋白酶体抑制剂，可抑制胰岛素诱导的IRS-1降解，但对其凝胶迁移率没有任何影响。抑制迁移率改变并不显著影响IRS-1或下游胰岛素信号的酪氨酸磷酸化。相反，阻断IRS-1的降解导致持续激活Akt、p70S6和丝裂原激活蛋白(MAP)激酶。这些结果表明，胰岛素诱导的丝氨酸/苏氨酸磷酸化和IRS-1的降解是由一条雷帕霉素敏感的通路介导的，该通路位于PI3-激酶下游，不依赖于ras/MAP激酶。该途径导致蛋白酶体降解IRS-1，蛋白酶体在长时间刺激期间下调某些胰岛素活动起主要作用。
Insulin receptor substrate-1 (IRS-1) is a major substrate of the insulin receptor and acts as a docking protein for Src homology 2 domain containing signaling molecules that mediate many of the pleiotropic actions of insulin. Insulin stimulation elicits serine/threonine phosphorylation of IRS-1, which produces a mobility shift on SDS-PAGE, followed by degradation of IRS-1 after prolonged stimulation. We investigated the molecular mechanisms and the functional consequences of these phenomena in 3T3-L1 adipocytes. PI 3-kinase inhibitors or rapamycin, but not the MEK inhibitor, blocked both the insulin-induced electrophoretic mobility shift and degradation of IRS-1. Adenovirus-mediated expression of a membrane-targeted form of the p110 subunit of phosphatidylinositol (PI) 3-kinase (p110CAAX) induced a mobility shift and degradation of IRS-1, both of which were inhibited by rapamycin. Lactacystin, a specific proteasome inhibitor, inhibited insulin-induced degradation of IRS-1 without any effect on its electrophoretic mobility. Inhibition of the mobility shift did not significantly affect tyrosine phosphorylation of IRS-1 or downstream insulin signaling. In contrast, blockade of IRS-1 degradation resulted in sustained activation of Akt, p70 S6 kinase, and mitogen-activated protein (MAP) kinase during prolonged insulin treatment. These results indicate that insulin-induced serine/threonine phosphorylation and degradation of IRS-1 are mediated by a rapamycin-sensitive pathway, which is downstream of PI 3-kinase and independent of ras/MAP kinase. The pathway leads to degradation of IRS-1 by the proteasome, which plays a major role in down-regulation of certain insulin actions during prolonged stimulation.