Retinoic acid mediates degradation of IRS-1 by the ubiquitin-proteasome pathway, via a PKC-dependant mechanism
Retinoic acid mediates degradation of IRS-1 by the ubiquitin-proteasome pathway, via a PKC-dependant mechanism
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DOI：
10.1038/sj.onc.1208104
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发表时间：
2004-12-09
期刊：
影响因子：
8
通讯作者：
Miller, WH
中科院分区：
文献类型：
--
作者：
del Rincón, SV;Guo, Q;Miller, WH
胰岛素受体底物 1 (IRS-1) 介导来自胰岛素样生长因子 I 型受体的信号传导。我们发现，全反式视黄酸 (RA) 会降低 MCF-7、T47-D 和 ZR75.1 乳腺癌细胞中的 IRS-1 蛋白水平，这些细胞会因 RA 而生长停滞，但不会降低 RA 耐药性 MDA-MB-231 和 MDA-MB-468 细胞中的 IRS-1 蛋白水平。根据之前关于泛素介导的 IRS-1 降解的报道，我们研究了 RA 处理的乳腺癌细胞中 IRS-1 的泛素化情况。两种蛋白酶体抑制剂 MG-132 和lactacystin 可阻断 RA 介导的 IRS-1 降解，并且 RA 会增加 RA 敏感性乳腺癌细胞中 IRS-1 的泛素化。此外，我们发现 RA 增加了 IRS-1 的丝氨酸磷酸化。为了阐明导致该磷酸化事件的信号传导途径，使用了药物抑制剂。两种 PKC 抑制剂（而非 MAPK 抑制剂）可阻断 RA 诱导的 IRS-1 降解和丝氨酸磷酸化。我们证明 RA 在敏感细胞中激活 PKC-delta，但在耐药细胞中则不然，其时间过程与 RA 诱导的 IRS-1 减少一致。我们还表明：（1）RA 激活的 PKC-δ 在体外磷酸化 IRS-1，（2）PKC-δ 和 IRS-1 在 RA 处理的细胞中相互作用，以及（3）IRS-1 中的三个 PKC-δ 丝氨酸位点突变为丙氨酸导致 RA 诱导的 IRS-1 体外磷酸化不存在。总之，这些结果表明 RA 通过泛素-蛋白酶体途径调节 IRS-1 水平，涉及 PKC 敏感机制。
Insulin receptor substrate-1 (IRS-1) mediates signaling from the insulin-like growth factor type-I receptor. We found that all-trans retinoic acid ( RA) decreases IRS-1 protein levels in MCF-7, T47-D, and ZR75.1 breast cancer cells, which are growth arrested by RA, but not in the RA-resistant MDA-MB-231 and MDA-MB-468 cells. Based on prior reports of ubiquitin-mediated degradation of IRS-1, we investigated the ubiquitination of IRS-1 in RA-treated breast cancer cells. Two proteasome inhibitors, MG-132 and lactacystin, blocked the RA-mediated degradation of IRS-1, and RA increased ubiquitination of IRS-1 in the RA-sensitive breast cancer cells. In addition, we found that RA increases serine phosphorylation of IRS-1. To elucidate the signaling pathway responsible for this phosphorylation event, pharmacologic inhibitors were used. Two PKC inhibitors, but not a MAPK inhibitor, blocked the RA-induced degradation and serine phosphorylation of IRS-1. We demonstrate that RA activates PKC-delta in the sensitive, but not in the resistant cells, with a time course that is consistent with the RA-induced decrease of IRS-1. We also show that: ( 1) RA-activated PKC-delta phosphorylates IRS-1 in vitro, ( 2) PKC-delta and IRS-1 interact in RA-treated cells, and ( 3) mutation of three PKC-delta serine sites in IRS-1 to alanines results in no RA-induced in vitro phosphorylation of IRS-1. Together, these results indicate that RA regulates IRS-1 levels by the ubiquitin - proteasome pathway, involving a PKC-sensitive mechanism.