Translational Control by Nutrients

描述（由申请人提供）：本提案的研究将确定在氨基酸限制的细胞应激过程中诱导哺乳动物氨基酸转运基因的分子机制及其生理意义。氨基酸是细胞生长和维持的必需营养素。氨基酸在质膜上的转移是由蛋白质介导的，这些蛋白质识别、结合并将这些氨基酸从细胞外介质转运到细胞内，反之亦然。必需的阳离子氨基酸，精氨酸和赖氨酸，主要通过Y+系统的cat-1（阳离子氨基酸转运蛋白1）蛋白进行转运。哺乳动物细胞已经对氨基酸可用性的变化产生了适应性反应。当氨基酸供应受限时，蛋白质合成减少，细胞蛋白质分解代谢、氨基酸生物合成和氨基酸跨质膜转运增加。这些反应共同提供了细胞生存所必需的氨基酸。这种适应性反应的一个重要部分是猫-1基因表达的增加。我们发现了一种新的机制，用于在氨基酸供应有限的情况下合成cat-1蛋白，当整体蛋白质合成被抑制时。这涉及通过内部核糖体进入序列（IRES）启动翻译，具有病毒（IRES介导）和细菌（先导肽内翻译）蛋白质合成的共同特征，指出氨基酸代谢的进化保守机制。我们的假设是，IRES是由翻译起始因子和IRES特异性蛋白（ITAFs）结合而激活的，ITAFs招募核糖体并将其定位在正确的翻译起始密码子上。拟议的研究旨在鉴定这些蛋白质并描述它们如何激活IRES。这是关于营养物质调节IRES活性的第一份报告。

DESCRIPTION (provided by applicant): The studies in this proposal will determine the molecular mechanisms that induce a mammalian amino acid transporter gene during the cellular stress of amino acid limitation and the physiological significance of this process. Amino acids are essential nutrients for cell growth and maintenance. Transfer of amino acids across the plasma membrane is mediated by proteins that recognize, bind and transport these amino acids from the extracellular medium into the cell and vice versa. The essential cationic amino acids, arginine and lysine, are mainly transported via the cat-1 (cationic amino acid transporter 1) protein of the Y+ system. Mammalian cells have developed an adaptive response to changes in amino acid availability. When the amino acid supply is limited, protein synthesis decreases and there are increases in catabolism of cellular proteins, amino acid biosynthesis, and amino acid transport across the plasma membrane. Together these responses provide the amino acids that are essential for cell survival. A significant part of this adaptive response is the increased expression of the cat-1 gene. We discovered a novel mechanism used for the synthesis of the cat-1 protein during limited amino acid supply, when global protein synthesis is inhibited. This involves translation initiation via an internal ribosomal entry sequence (IRES), with common features with both viral (IRES-mediated) and bacterial (translation within a leader peptide) protein synthesis pointing to the evolutionary conserved mechanisms in amino acid metabolism. Our hypothesis is that the IRES is activated by the binding of translation initiation factors and IRES-specific proteins (ITAFs) which recruit the ribosome and position it at the correct translation initiation codon. The proposed studies aim to identify these proteins and characterize how they activate the IRES. This is the first report on the regulation of the activity of the IRES by nutrients.