Inhibition of mammalian target of rapamycin activates apoptosis signal-regulating kinase 1 signaling by suppressing protein phosphatase 5 activity
Inhibition of mammalian target of rapamycin activates apoptosis signal-regulating kinase 1 signaling by suppressing protein phosphatase 5 activity
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DOI：
10.1074/jbc.m401208200
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发表时间：
2004-08-27
影响因子：
4.8
通讯作者：
Houghton, PJ
中科院分区：
文献类型：
--
作者：
Huang, SL;Shu, LL;Houghton, PJ
在无血清条件下，雷帕霉素，一种哺乳动物雷帕霉素靶蛋白（mTOR）的抑制剂，诱导细胞应激反应，其特征在于凋亡信号调节激酶1（ASK 1）信号通路的快速和持续激活以及缺乏功能性p53的细胞的选择性凋亡。在这里，我们研究了mTOR如何使用p53突变型横纹肌肉瘤细胞调节ASK 1信号。在Rh 30细胞中，发现ASK 1与蛋白磷酸酶5（PP 5）发生物理相互作用，PP 5先前被鉴定为ASK 1的负调节因子。雷帕霉素不影响PP 5的蛋白水平或PP 5与ASK 1的结合。相反，雷帕霉素导致PP 2A-B”调节亚基（PR 72）从PP 5-ASK 1复合物中快速解离，这与PP 5的磷酸酶活性降低有关。这种作用依赖于真核起始因子4 E结合蛋白1（4 E-BP 1）的表达。雷帕霉素下调PP 5活性协同激活ASK 1，导致c-Jun磷酸化水平升高。与雷帕霉素抑制mTOR信号传导一样，氨基酸剥夺也抑制PP 5活性，导致PR 72快速解离，并激活ASK 1信号传导。PP 5的过表达，而不是PP 2A催化亚基，阻断了雷帕霉素诱导的c-Jun磷酸化，并保护细胞免受雷帕霉素诱导的凋亡。结果表明，PP 5是mTOR的下游，并受到mTOR通路的正调控。这些发现表明，在没有血清因子的情况下，mTOR信号通过PP 5活性的正调节和细胞应激的抑制来抑制细胞凋亡。
Under serum-free conditions, rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), induces a cellular stress response characterized by rapid and sustained activation of the apoptosis signal-regulating kinase 1 (ASK1) signaling pathway and selective apoptosis of cells lacking functional p53. Here we have investigated how mTOR regulates ASK1 signaling using p53-mutant rhabdomyosarcoma cells. In Rh30 cells, ASK1 was found to physically interact with protein phosphatase 5 (PP5), previously identified as a negative regulator of ASK1. Rapamycin did not affect either protein level of PP5 or association of PP5 with ASK1. Instead, rapamycin caused rapid dissociation of the PP2A-B" regulatory subunit (PR72) from the PP5-ASK1 complex, which was associated with reduced phosphatase activity of PP5. This effect was dependent on expression of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). Down-regulation of PP5 activity by rapamycin coordinately activated ASK1, leading to elevated phosphorylation of c-Jun. Amino acid deprivation, which like rapamycin inhibits mTOR signaling, also inhibited PP5 activity, caused rapid dissociation of PR72, and activated ASK1 signaling. Overexpression of PP5, but not the PP2A catalytic subunit, blocked rapamycin-induced phosphorylation of c-Jun, and protected cells from rapamycin-induced apoptosis. The results suggest that PP5 is downstream of mTOR, and positively regulated by the mTOR pathway. The findings suggest that in the absence of serum factors, mTOR signaling suppresses apoptosis through positive regulation of PP5 activity and suppression of cellular stress.