Translational Control by Nutrients

精氨酸/赖氨酸转运蛋白mRNA的翻译控制的氨基酸可用性的机制进行了研究。 必需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）蛋白转运。 cat-1基因在所有细胞类型中表达，并且在增殖细胞中以高水平表达，强调了cat-1蛋白对哺乳动物生长和发育的重要性。 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。 当氨基酸供应有限时，蛋白质合成减少，细胞蛋白质的催化、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cat-1基因表达的增加。 这涉及转录、mRNA稳定性和翻译的协调增加，从而使细胞能够在必需氨基酸赖氨酸和精氨酸可用时转运它们。 该提案将研究一种新的机制，用于在有限的氨基酸供应期间，当全局蛋白质合成被抑制时，cat-1蛋白的合成。 这种机制涉及通过内部核糖体进入序列（IRES）的翻译起始，这是一种已知调节感染细胞中病毒mRNA翻译的机制。 该IRES存在于cat-1 mRNA的5 '-非翻译区。 拟议的研究将确定在氨基酸饥饿期间导致IRES介导的转运蛋白mRNA翻译增加的分子事件。我们的假设是，在氨基酸饥饿期间，合成了一种蛋白质，该蛋白质通过结合在cat-1 mRNA的5 '非翻译区内，介导活性IRES构象。 我们将确定以下内容：（1）导致IRES激活的细胞信号传导途径（2）IRES活性的顺式mRNA序列/结构（3）介导IRES构象变化和翻译活性的反式作用因子。 通过底物可用性来描述调节必需氨基酸转运到哺乳动物细胞中的分子机制，将是如何在分解代谢应激条件下改善人类健康的有价值的指导。

The mechanism of translational control of the arginine/lysine transporter mRNA by amino acid availability will be studied. The essential amino acids arginine and lysine, are mainly transported via the cat-1 (cationic amino acid transporter 1) protein of the Y+ system. The cat-1 gene is expressed in all cell types and in high levels in proliferating cells, emphasizing the importance of the cat-1 protein for growth and development of mammals. 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, which are essential for cell survival. A significant part of this adaptive response is the increased expression of the cat-1 gene. This involves the coordinate increases in transcription, mRNA stability and translation, thus enabling the cells to transport the essential amino acids lysine and arginine once they become available. This proposal will study a novel mechanism, used for the synthesis of the cat-1 protein during limited amino acid supply, when global protein synthesis is inhibited. This mechanism involves translation initiation via an internal ribosomal entry sequence (IRES), a mechanism known to regulate translation of viral mRNAs in infected cells. This IRES is found within the 5'-untranslated region of the cat-1 mRNA. The studies proposed will determine the molecular events that lead to increased IRES-mediated translation of the transporter mRNA during amino acid starvation. Our hypothesis is that during amino acid starvation a protein is synthesized which by binding within the 5'-untranslated region of the cat-1 mRNA, mediates an active IRES conformation. We will determine the following: (1) the cell signaling pathway leading to IRES-activation (2) the cis-mRNA sequence/structure for IRES- activity (3) the trans-acting factors that mediate IRES- conformational change and translational activity. Delineation of the molecular mechanisms of regulation of essential amino acid transport into mammalian cells by substrate availability, will be a valuable guide of how to improve human health during catabolic stress conditions.