适应游离氨基酸(AA)短缺是由两条途径介导的,整合应激反应(ISR)和雷帕霉素的机制靶标(mTOR)。为了应对降低的水平,主要是亮氨酸或精氨酸,在其复合物1构型中的mTOR(mTORC1)被抑制,导致翻译起始和延伸的减少。eIF2α激酶一般对照不可抑制的2(GCN2)被不带电荷的tRNA激活,导致ISR的诱导,以应对更广泛的AA短缺。ISR赋予了减少的翻译启动,同时促进应激蛋白的选择性合成,比如ATF4。为了有效地适应AA饥饿,这两种途径在多个水平上交叉调节。在这里,我们确定了ISR/mTORC1串扰的新机制,该机制优化了AA饥饿下的生存,当mTORC1被迫保持活动状态时。急性AA短缺期间的mTORC1激活,以GCN2依赖性方式增强ATF4表达。在这些条件下,增强的GCN2活性不依赖于tRNA传感,推断不同的激活机制。我们确定了GCN2和mTOR之间的不稳定的物理相互作用,导致mTOR在丝氨酸230上磷酸化GCN2,这促进了GCN2活性。当在长时间的AA饥饿下检查时,通过mTOR的GCN2磷酸化促进存活。我们的数据揭示了一种适应AA饥饿的机制,当mTORC1逃避抑制。
Adaptation to the shortage in free amino acids (AA) is mediated by 2 pathways, the integrated stress response (ISR) and the mechanistic target of rapamycin (mTOR). In response to reduced levels, primarily of leucine or arginine, mTOR in its complex 1 configuration (mTORC1) is suppressed leading to a decrease in translation initiation and elongation. The eIF2α kinase general control nonderepressible 2 (GCN2) is activated by uncharged tRNAs, leading to induction of the ISR in response to a broader range of AA shortage. ISR confers a reduced translation initiation, while promoting the selective synthesis of stress proteins, such as ATF4. To efficiently adapt to AA starvation, the 2 pathways are cross-regulated at multiple levels. Here we identified a new mechanism of ISR/mTORC1 crosstalk that optimizes survival under AA starvation, when mTORC1 is forced to remain active. mTORC1 activation during acute AA shortage, augmented ATF4 expression in a GCN2-dependent manner. Under these conditions, enhanced GCN2 activity was not dependent on tRNA sensing, inferring a different activation mechanism. We identified a labile physical interaction between GCN2 and mTOR that results in a phosphorylation of GCN2 on serine 230 by mTOR, which promotes GCN2 activity. When examined under prolonged AA starvation, GCN2 phosphorylation by mTOR promoted survival. Our data unveils an adaptive mechanism to AA starvation, when mTORC1 evades inhibition.