Rapamycin-induced translational derepression of GCN4 mRNA involves a novel mechanism for activation of the eIF2α kinase GCN2
Rapamycin-induced translational derepression of GCN4 mRNA involves a novel mechanism for activation of the eIF2α kinase GCN2
复制标题
DOI：
10.1074/jbc.c300133200
复制
发表时间：
2003-06-06
影响因子：
4.8
通讯作者：
Ito, T
中科院分区：
文献类型：
--
作者：
Kubota, H;Obata, T;Ito, T
当缺乏氨基酸时，酿酒酵母会积累未带电的trna来激活其唯一的真核起始因子（eIF） 2 α激酶GCN2。随后的eIF2alpha磷酸化会阻碍一般的翻译，但会在翻译上抑制转录因子GCN4，从而诱导各种生物合成基因的表达，从而引发一般的氨基酸控制反应。相反，当提供足够的营养物质时，酵母激活雷帕霉素信号通路的靶点，通过促进eIF4F的组装来刺激翻译启动。通过雷帕霉素诱导GCN4 mRNA的翻译，两种途径之间可能存在交叉对话。在这里，我们发现雷帕霉素导致磷酸化的eIF2alpha增加，从而翻译抑制GCN4。在表达哺乳动物非GCN2 eif2 α激酶代替GCN2的细胞中没有观察到这种增加。这表明雷帕霉素不抑制eIF2alpha的去磷酸化，而是激活GCN2激酶。这种激活似乎需要激酶和未带电的tRNA之间的相互作用，因为雷帕霉素，类似于氨基酸饥饿，不能在tRNA结合缺陷的GCN2细胞中诱导eIF2alpha磷酸化。然而，与氨基酸饥饿相比，雷帕霉素激活GCN2并不增加未带电tRNA的数量，而可能是通过修改GCN2的tRNA结合亲和力来激活的。
When starved for amino acids, Saccharomyces cerevisiae accumulates uncharged tRNAs to activate its sole eukaryotic initiation factor (eIF) 2alpha kinase GCN2. Subsequent phosphorylation of eIF2alpha impedes general translation, but translationally derepresses the transcription factor GCN4, which induces expression of various biosynthetic genes to elicit general amino acid control response. By contrast, when supplied with enough nutrients, the yeast activates the target of rapamycin signaling pathway to stimulate translation initiation by facilitating the assembly of eIF4F. A cross-talk was suggested between the two pathways by rapamycin-induced translation of GCN4 mRNA. Here we show that rapamycin causes an increase in phosphorylated eIF2alpha to translationally derepress GCN4. This increment is not observed in the cells expressing mammalian non-GCN2 eIF2alpha kinases in place of GCN2. It is thus suggested that rapamycin does not inhibit dephosphorylation of eIF2alpha but rather activates the kinase GCN2. This activation seems to require an interaction between the kinase and uncharged tRNAs, because rapamycin, similar to amino acid starvation, fails to induce eIF2alpha phosphorylation in the cells with GCN2 defective in tRNA binding. However, in contrast with amino acid starvation, rapamycin activates GCN2 without increasing the amount of uncharged tRNAs, but presumably by modifying the tRNA binding affinity of GCN2.