Regulation and Function of Integrated Stress Response

细胞通过快速调整蛋白质合成的速度来适应外部和内在的压力。一个 这种翻译控制的重要机制涉及翻译启动因子eIF2的磷酸化 它与GTP偶联，将Met-tRNAi(Met)运送到核糖体。例如，在营养限制期间，GCN2 (EIF2AK4)eIF2(eIF2-P)的磷酸化阻止eIF2-GDP到eIF2-GTP的交换，从而减少 全局翻译启动，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，蛋白质降解中断，以及某些细胞分化期间 类型。EIF2-P与抑制全球蛋白质合成一致，增强了选择的mRNAs的翻译， 如ATF4，编码受综合应激反应(ISR)影响的基因的转录激活因子。 ISR中的翻译控制包括上游开放阅读框(UORF)，它充当 扫描核糖体以描绘优先从或抑制的mRNA翻译而来的mRNA 对eIF2-P无动于衷。需要强调的是，大多数哺乳动物的mRNAs都含有uORF，因此 他们的存在本身并不足以指导优先翻译。相反，我们确定了这个序列 和uORF的语境是ISR中优先翻译的关键决定因素。此外，虽然 不同的压力导致了ISR，我们的研究表明ISR实施了翻译控制 提供最适合细胞适应特定压力的不同基因表达程序 条件。我们的假设是，GCN2被不同的细胞扰动激活，促进了基因的模式 为适应特定压力条件而量身定做的表情。在这项提案中，我们解决了重要的差距 在我们对ISR的了解中。使用创新的概念和技术，以生物化学、分子 和细胞生物学，以及基因组和结构的观点，我们将讨论三个基本的ISR 问题。1)GCN2识别不同的应激条件和调用的机制是什么 翻译控制？2)eIF2-P如何诱导不同的mRNA翻译模式，从而一些 MRNA优先被翻译，而其他的是耐受或被eIF2-P抑制的？最后，3)如何 EIF2-P激活的翻译调控结合应激诱导的蛋白分解是否改变了蛋白质组 以及指导细胞生存的信号通路？拟议研究的完成将获得新的见解 不同应激激活GCN2的机制和核糖体的过程 差异翻译mRNA。这些研究还将提供对ISR如何有助于 应激相关疾病的进展，包括糖尿病和相关的代谢紊乱， 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.