Phosphorylation of the α-subunit of the eukaryotic initiation factor-2 (eIF2α) reduces protein synthesis and enhances apoptosis in response to proteasome inhibition
Phosphorylation of the α-subunit of the eukaryotic initiation factor-2 (eIF2α) reduces protein synthesis and enhances apoptosis in response to proteasome inhibition
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DOI：
10.1074/jbc.m413660200
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发表时间：
2005-04-08
影响因子：
4.8
通讯作者：
Wek, RC
中科院分区：
文献类型：
--
作者：
Jiang, HY;Wek, RC
蛋白质泛素化和随后的蛋白酶体降解是调节细胞周期、生长和分化以及凋亡的重要机制。最近的癌症治疗研究表明，破坏泛素/蛋白酶体途径的药物可诱导细胞凋亡，并使恶性细胞和肿瘤对常规化疗敏感。在这项研究中，我们解决了α-亚基真核起始因子-2（eIF 2）的磷酸化的作用，及其伴随的基因表达调控，在细胞应激反应蛋白酶体抑制。在蛋白酶体抑制的小鼠胚胎成纤维细胞（MEF）中eIF 2 α的磷酸化导致蛋白质合成的显著减少，伴随着bZIP转录调节因子ATF 4及其靶基因CHOP/GADD 153的诱导表达。通过将这些成纤维细胞暴露于蛋白酶体抑制而激活的主要eIF 2 α激酶是GCN 2（EIF 2AK 4），其在细胞质应激信号的识别中具有核心作用。内质网（ER）应激在经受蛋白酶体抑制的MEF细胞中未被有效诱导，在蛋白酶体抑制剂处理长达6小时后，ER应激感觉蛋白、eIF 2 α激酶PEK（PERK/EIF 2AK 3）、IRE 1蛋白激酶和转录调节因子ATF 6的活化最小。eIF 2 α磷酸化的丧失阻碍半胱天冬酶活化并延迟细胞凋亡。在蛋白酶体抑制期间，eIF 2 α激酶的这种促凋亡功能的中心是转录调节因子CHOP，因为MEF细胞中CHOP的缺失阻碍了凋亡。我们的结论是eIF 2 α激酶是蛋白酶体抑制剂诱导的细胞应激途径的组成部分，可能是靶向泛素/蛋白酶体途径的抗癌药物疗效的核心。
Protein ubiquitination and subsequent degradation by the proteasome are important mechanisms regulating cell cycle, growth and differentiation, and apoptosis. Recent studies in cancer therapy suggest that drugs that disrupt the ubiquitin/ proteasome pathway induce apoptosis and sensitize malignant cells and tumors to conventional chemotherapy. In this study we addressed the role of phosphorylation of the alpha- subunit eukaryotic initiation factor- 2 ( eIF2), and its attendant regulation of gene expression, in the cellular stress response to proteasome inhibition. Phosphorylation of eIF2 alpha in mouse embryo fibroblast ( MEF) cells subjected to proteasome inhibition leads to a significant reduction in protein synthesis, concomitant with induced expression of the bZIP transcription regulator, ATF4, and its target gene CHOP/ GADD153. The primary eIF2 alpha kinase activated by exposure of these fibroblast cells to proteasome inhibition is GCN2 ( EIF2AK4), which has a central role in the recognition of cytoplasmic stress signals. Endoplasmic reticulum ( ER) stress is not effectively induced in MEF cells subjected to proteasome inhibition, with minimal activation of the ER stress sensory proteins, eIF2 alpha kinase PEK ( PERK/ EIF2AK3), IRE1 protein kinase and the transcription regulator ATF6 following up to 6 h of proteasome inhibitor treatment. Loss of eIF2 alpha phosphorylation thwarts caspase activation and delays apoptosis. Central to this pro- apoptotic function of eIF2 alpha kinases during proteasome inhibition is the transcriptional regulator CHOP, as deletion of CHOP in MEF cells impedes apoptosis. We conclude that eIF2 alpha kinases are integral to cellular stress pathways induced by proteasome inhibitors, and may be central to the efficacy of anticancer drugs that target the ubiquitin/ proteasome pathway.