Selenoprotein Synthesis: Redefinition of Selenocysteine-encoding UGA Codons

描述(由研究人员提供)：硒是一种基本的微量营养素，对人类健康至关重要。随着新的研究表明，可以归因于硒的一系列意想不到的健康益处，这一点变得越来越清楚。报道的益处从预防癌症、心脏病和肌肉疾病，到维持适当的免疫功能，甚至延缓衰老过程。这种单一的微量营养素在人类健康中的许多不同作用是由于硒作为第21种氨基酸硒半胱氨酸加入到蛋白质中。硒半胱氨酸(Sec)在硒蛋白mRNAs中由UGA密码子编码，UGA密码子在其他mRNAs中启动翻译终止。在真核生物中重新定义UGA SEC密码子需要3‘UTR(SECIS)中的顺式作用序列和几种已被很好描述的反式作用因子(SBP2、eEFSec和SEC-tRNASec)。这位首席研究员最近的一份报告发现了一个迄今未知的调控元件，位于硒蛋白mRNAs的一个子集内。在硒蛋白mRNAs的编码部分含有额外的解码信息，这一发现对硒半胱氨酸插入的机制和硒蛋白表达的调控具有潜在的深远意义。这项应用的总体目标是通过阐明这些真核生物硒半胱氨酸密码子退缩元件(SRES)的作用来加深我们对硒蛋白生物合成的理解。本研究提出的具体目标是：(1)在体外和培养细胞中利用系统发育和突变分析相结合的方法鉴定和表征硒蛋白重新定义元件；(2)研究一般或组织特异性反式作用因子与SRE元件之间的相互作用；(3)研究SRE元件对硒蛋白mRNA稳定性的影响，以及释放因子介导的UGA密码子终止和解码之间的竞争；以及(4)研究SRE元件在缺少3‘UTRSECIS元件的mRNAs中对UGA和UAG密码子重新定义的作用。更全面地了解硒半胱氨酸插入机制及其在硒蛋白表达中的作用，将有助于洞察硒蛋白功能障碍引起的疾病，并最终有助于确定哪些人可以从补硒中受益。

DESCRIPTION (provided by investigator): Selenium is an essential micronutrient fundamentally important for human health. This has become increasingly clear as new research has shown a remarkably broad range of unsuspected health benefits which can be attributed to selenium. Reported benefits range from prevention of cancer, heart disease, and muscle disorders, to the maintenance of proper immune function, and even slowing of the aging process. Many of the diverse roles for this single micronutrient in human health are due to the incorporation of selenium into proteins as selenocysteine, the 21st amino acid. Selenocysteine (Sec) is encoded in selenoprotein mRNAs by a UGA codon which in other mRNAs initiates translational termination. Redefinition of the UGA Sec codon in eukaryotes is known to require a cis-acting sequence in the 3' UTR (SECIS) and several well characterized trans-acting factors (SBP2, eEFSec, and Sec-tRNASec). A recent report by this Principal Investigator has uncovered a hitherto unknown regulatory element located within a subset of selenoprotein mRNAs. The discovery that additional decoding information is contained in the coding portion of selenoprotein mRNAs has potentially far reaching implications for the mechanism of selenocysteine insertion and the regulation of selenoprotein expression. The overall objective of this application is to further our understanding of selenoprotein biosynthesis by elucidating the role of these eukaryotic Selenocysteine codon Receding Element (SREs). Specific Aims proposed here are: (1) to identify and characterize selenoprotein redefinition elements using a combination of phylogenetic and mutagenic analysis in vitro and in cultured cells; (2) to investigate interactions between general or tissue specific trans-acting factors and the SRE elements; (3) to investigate the effects of SREs on selenoprotein mRNA stability, and competition between release factor mediated termination and decoding at UGA codons; and, (4) to examine the role of SRE elements in redefinition of UGA and UAG codons in mRNAs which lack 3' UTR SECIS elements. A more complete understanding of selenocysteine insertion mechanisms and its role in selenoprotein expression will provide insight into diseases arising from selenoprotein dysfunction, and may ultimately facilitate the identification of individuals who could benefit from selenium supplementation.