Regulation and Function of Integrated Stress Response

细胞通过快速调节蛋白质合成速率来适应外在和内在压力。一个 这种翻译控制的重要机制涉及eIF2的磷酸化，eIF2是一种翻译起始因子 与GTP偶联并将Met-tRNAi（Met）递送至核糖体。例如，在营养限制期间，GCN 2 eIF2（eIF2-P）的磷酸化（EIF2AK4）阻断eIF2-GDP交换为eIF2-GTP，从而降低了eIF2-GTP的表达。 全局翻译起始，允许细胞保存资源并重新编程基因表达。GCN2是 也被UV-B辐射激活，破坏蛋白质降解，以及在某些细胞的分化过程中 类型与抑制整体蛋白质合成相一致，eIF2-P增强了选择mRNA的翻译， 如ATF 4，编码受综合应激反应（ISR）影响的基因的转录激活因子。 ISR中的翻译控制涉及上游开放阅读框（uORF），其用作"条形码"， 扫描核糖体以描绘优先从那些被抑制或 重要的是要强调，大多数哺乳动物的mRNA含有uORF，所以 它们的存在本身不足以指导优先翻译。相反，我们确定， uORFs的结构和上下文是ISR中优先翻译的关键决定因素。此外，虽然 不同的应激诱导ISR，我们的研究表明，ISR的翻译控制的实施， 提供了最适合细胞适应给定压力的不同基因表达程序 条件我们的假设是，GCN 2是由不同的细胞扰动激活，促进基因的模式， 表达，以适应特定的压力条件。在本提案中，我们解决了重要的差距， 我们对情报监视系统的了解利用创新的概念和技术， 和细胞生物学，以及基因组和结构的观点，我们将解决三个基本的ISR 问题. 1)GCN 2通过什么机制识别不同的压力条件并调用 翻译控制？2)eIF2-P如何诱导不同的mRNA翻译模式， mRNA的优先翻译，而其他人是容忍或抑制eIF2-P？（3）如何 由eIF2-P引起的翻译控制，结合应激诱导的蛋白水解，是否改变了蛋白质组 以及指导细胞存活的信号通路完成拟议的研究将获得新的见解 不同压力激活GCN 2的机制以及核糖体 差异翻译mRNA。这些研究还将帮助我们了解ISR如何有助于 压力相关疾病的进展，包括糖尿病和相关代谢紊乱， 神经病理学和癌症，并有望开发新的诊断和治疗策略。

Cells adapt to extrinsic and intrinsic stresses by rapidly adjusting the rates of protein synthesis. An important mechanism for this translational control involves phosphorylation of eIF2, a translation initiator factor that couples with GTP and delivers Met-tRNAi(Met) to ribosomes. For example during nutrient limitation, GCN2 (EIF2AK4) phosphorylation of eIF2 (eIF2-P) blocks the exchange of eIF2-GDP to eIF2-GTP, thus reducing global translation initiation which allows cells to conserve resources and reprogram gene expression. GCN2 is also activated by UV-B irradiation, disruption in protein degradation, and during differentiation of certain cell types. Coincident with repression of global protein synthesis, eIF2-P enhances translation of select mRNAs, such as ATF4, encoding a transcriptional activator of genes subject to the Integrated Stress Response (ISR). Translational control in the ISR involves upstream open reading frames (uORFs) that serve as “bar codes” for scanning ribosomes to delineate mRNAs that are preferentially translated from those that are repressed by or indifferent to eIF2-P. It is important to emphasize that a majority of mammalian mRNAs contain uORFs, so their presence alone is not sufficient to direct preferential translation. Rather we determined that the sequence and context of uORFs are critical determinants for preferential translation in the ISR. Furthermore, while diverse stresses induce the ISR, our research suggests that the ISR implementation of translational control provides for different programs of gene expression that are best suited for cell adaptation to a given stress condition. Our hypothesis is that GCN2 is activated by diverse cell perturbations, facilitating patterns of gene expression that are tailored to adapt to a specific stress condition. In this proposal we address important gaps in our knowledge of the ISR. Using innovative concepts and technologies that feature biochemistry, molecular and cellular biology, and genomic and structural perspectives, we will address three fundamental ISR questions. 1) What are the mechanisms by which GCN2 recognizes diverse stress conditions and invokes translational control? 2) How does eIF2-P induce different patterns of mRNA translation, whereby some mRNAs are preferentially translated, whereas others are tolerant of or repressed by eIF2-P? Finally, 3) How does translational control invoked by eIF2-P, combined with stress-induced proteolysis, change the proteome and signaling pathways that direct cell survival? Completion of the proposed studies will garner new insights into the mechanisms by which diverse stresses activate GCN2 and the processes by which ribosomes differentially translate mRNAs. These studies will also provide an understanding for how the ISR contributes to the progression of stress-related diseases, including diabetes and related metabolic disorders, neuropathologies, and cancer, with the promise of developing new strategies for diagnosis and treatment.