Selenoprotein Synthesis: Redefinition of Selenocysteine-encoding UGA Codons

描述（由研究者提供）：硒是一种对人体健康至关重要的必需微量营养素。这一点越来越清楚，因为新的研究表明，硒对健康有着非常广泛的意想不到的好处。报道的益处包括预防癌症，心脏病和肌肉疾病，维持适当的免疫功能，甚至减缓衰老过程。这种单一微量营养素在人类健康中的许多不同作用是由于硒作为硒代半胱氨酸（第21位氨基酸）掺入蛋白质中。硒代半胱氨酸（Sec）在硒蛋白mRNA中由UGA密码子编码，在其他mRNA中该密码子启动翻译终止。已知真核生物中UGA Sec密码子的重新定义需要在3'UTR中的顺式作用序列（SECIS）和几种充分表征的反式作用因子（SBP2、eEFSec和Sec-tRNASec）。这位主要研究者最近的一份报告发现了一个迄今为止未知的调控元件，位于硒蛋白mRNA的一个子集内。硒蛋白mRNA编码区含有额外的解码信息，这一发现对硒代半胱氨酸插入机制和硒蛋白表达调控具有潜在的深远意义。本申请的总体目标是通过阐明这些真核生物硒代半胱氨酸密码子后退元件（SREs）的作用来进一步理解硒蛋白的生物合成。本研究的具体目的是：（1）在体外和培养的细胞中，利用系统发育和诱变分析相结合的方法鉴定和表征硒蛋白重定义元件：（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SREs对硒蛋白mRNA稳定性的影响，以及释放因子介导的终止和UGA密码子处的解码之间的竞争;以及（4）检查SRE元件在缺少3'UTR SECIS元件的mRNA中UGA和UAG密码子的重定义中的作用。更全面地了解硒代半胱氨酸插入机制及其在硒蛋白表达中的作用，将有助于深入了解硒蛋白功能障碍引起的疾病，并可能最终促进对可能从硒补充中受益的个体的识别。

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.