Ludwig Institute for Cancer Research, University College London, W1W7BS London, United Kingdom.
J Biol Chem. 2009 Dec 18;284(51):35287-96. doi: 10.1074/jbc.M109.050120.
The Rho GTPase family member RhoE inhibits RhoA/ROCK signaling to promote actin stress fiber and focal adhesion disassembly. We have previously reported that RhoE also inhibits cell cycle progression and Ras-induced transformation, specifically preventing cyclin D1 translation. Here we investigate the molecular mechanisms underlying those observations. RhoE inhibits the phosphorylation of the translational repressor 4E-BP1 in response to extracellular stimuli. However, RhoE does not affect the activation of mTOR, the major kinase regulating 4E-BP1 phosphorylation, as indicated by the phosphorylation levels of the mTOR substrate S6K, the dynamics of mTOR/Raptor association, and the observation that RhoE, as opposed to rapamycin, does not impair cellular growth. Interestingly, RhoE prevents the release of the eukaryotic initiation factor eIF4E from 4E-BP1, inhibiting cap-dependent translation. Accordingly, RhoE also inhibits the expression and the transcriptional activity of the eIF4E target c-Myc. Consistent with its crucial role in cell proliferation, we show that eIF4E can rescue both cell cycle progression and Ras-induced transformation in RhoE-expressing cells, indicating that the inhibition of eIF4E function is critical to mediate the anti-proliferative effects of RhoE.
Rho GTPase 家族成员 RhoE 通过抑制 RhoA/ROCK 信号通路来促进肌动蛋白应力纤维和黏着斑的解聚。我们之前曾报道 RhoE 还可以抑制细胞周期进程和 Ras 诱导的转化,特别是可以阻止细胞周期蛋白 D1 的翻译。在此,我们研究了这些观察结果背后的分子机制。RhoE 可抑制细胞外刺激下翻译抑制因子 4E-BP1 的磷酸化。然而,RhoE 并不影响调节 4E-BP1 磷酸化的主要激酶 mTOR 的激活,这可从 mTOR 底物 S6K 的磷酸化水平、mTOR/Raptor 复合物的动态变化以及 RhoE (而非雷帕霉素)不损害细胞生长这一观察结果中得到证实。有趣的是,RhoE 可阻止真核起始因子 eIF4E 从 4E-BP1 上释放,从而抑制帽依赖型翻译。因此,RhoE 还可以抑制 eIF4E 靶标 c-Myc 的表达和转录活性。与它在细胞增殖中的关键作用一致,我们表明 eIF4E 可以挽救 RhoE 表达细胞中的细胞周期进程和 Ras 诱导的转化,表明抑制 eIF4E 功能对于介导 RhoE 的抗增殖作用至关重要。