Insulin-like growth factor I-induced degradation of insulin receptor substrate 1 is mediated by the 26S proteasome and blocked by phosphatidylinositol 3′-kinase inhibition
Insulin-like growth factor I-induced degradation of insulin receptor substrate 1 is mediated by the 26S proteasome and blocked by phosphatidylinositol 3′-kinase inhibition
复制标题
DOI：
10.1128/mcb.20.5.1489-1496.2000
复制
发表时间：
2000-03-01
影响因子：
5.3
通讯作者：
Yee, D
中科院分区：
文献类型：
--
作者：
Lee, AV;Gooch, JL;Yee, D
胰岛素受体底物1(IRS-1)是参与胰岛素和胰岛素样生长因子(IGF)信号转导的关键适配蛋白。由于IRS-1水平的改变可以影响对胰岛素和IGF-I的敏感性和反应，我们研究了这两种配体影响IRS-1表达的能力。IGF-I(10 NM)刺激MCF-7乳腺癌细胞可引起IRS-1的瞬时酪氨酸磷酸化，IRS-1在15min时最高，此后逐渐下降，IRS-1酪氨酸磷酸化水平的下降与IRS-1水平的明显下降相平行。IGF介导的IRS-1表达的降低是转录后的，并且是由于IRS-1蛋白半衰期的减少。胰岛素(10 NM)引起IRS-1酪氨酸磷酸化但不降解，高浓度胰岛素(10 MM)引起IRS-1降解，IGF-I(10 NM)刺激导致瞬时IRS-1磷酸化和细胞外信号相关激酶(ERK)激活。相反，胰岛素(10 NM)引起持续的IRS-1磷酸化和ERK激活。268蛋白酶体活性的抑制完全阻断了IGF介导的IRS-1的降解，免疫共沉淀实验表明，IGF-I促进了泛素与IRS-1的结合，最终IGF介导的IRS-1的降解被抑制磷脂酰肌醇3‘-激酶的活性所阻断，但不受ERK的抑制，提示这可能是IRS-1下游信号转导的直接负反馈机制。我们认为，转化生长因子-I可通过泛素介导的268蛋白酶体和磷脂酰肌醇3‘-激酶依赖的机制引起配体介导的IRS-1的降解，并且对降解的控制可能对下游信号通路的激活产生深远的影响。
Insulin receptor substrate 1 (IRS-1) is a critical adapter protein involved in both insulin and insulin-like growth factor (IGF) signaling. Due to the fact that alteration of IRS-1 levels can affect the sensitivity and response to both insulin and IGF-I, we examined the ability of each of these ligands to affect IRS-1 expression. IGF-I (10 nM) stimulation of MCF-7 breast cancer cells caused a transient tyrosine phosphorylation of IRS-1 that was maximal at 15 min and decreased thereafter, The decrease in tyrosine phosphorylation of IRS 1 was paralleled by an apparent decrease in IRS 1 levels. The IGF mediated decrease in IRS-1 expression was posttranscriptional and due to a decrease in the half-life of the IRS-1 protein. Insulin (10 nM) caused tyrosine phosphorylation of IRS-1 but not degradation, whereas high concentrations of insulin (10 mu M) resulted in degradation of IRS-1, IGF-I (10 nM) stimulation resulted in transient IRS-1 phosphorylation and extracellular signal-related kinase (ERK) activation. In contrast, insulin (10 nM) caused sustained IRS-1 phosphorylation and ERK activation. Inhibition of 268 proteasome activity by the use of lactacystin or MG132 completely blocked IGF-mediated degradation of IRS-1, Furthermore, coimmunoprecipitation experiments showed an association between ubiquitin and IRS-1 that was increased by treatment of cells with IGF-I, Finally, IGF-mediated degradation of IRS-1 was blocked by inhibition of phosphatidylinositol 3'-kinase activity but was not affected by inhibition of ERK, suggesting that this may represent a direct negative-feedback mechanism resulting from downstream IRS-1 signaling. We conclude that TGF-I can cause ligand-mediated degradation of IRS-1 via the ubiquitin-mediated 268 proteasome and a phosphatidylinositol 3'-kinase-dependent mechanism and that control of degradation may have profound effects on downstream activation of signaling pathways.