Regulation of selenoprotein synthesis by SECIS-binding proteins

描述（由申请人提供）：硒是一种必需的微量营养素，具有许多重要的健康益处。该元素以硒代半胱氨酸（Sec）的形式掺入硒蛋白中。哺乳动物硒蛋白在抗氧化防御、甲状腺激素代谢、雄性生殖和发育中发挥重要作用。Sec由UGA编码，UGA通常被解读为终止密码子。将UGA重新编码为Sec需要硒蛋白mRNA中的Sec插入序列（SECIS）元件。虽然在理解Sec掺入机制方面取得了很大进展，但对该途径的调控知之甚少。在硒缺乏时，某些对健康和发育至关重要的硒蛋白表达，而其他非必需的硒蛋白丢失。我们的建议的中心假设是，这种复杂的层次结构的硒蛋白表达的多个反式作用因子之间的相互作用，选择性地结合到不同的SECIS元素。我们发现了两个新的SECIS结合蛋白，核仁素和真核生物起始因子4a3（eIF4a3），发挥相反的作用，选择性地调节硒蛋白的合成。我们发现eIF4a3连接硒状态与差异硒蛋白表达。EIF4a3在缺硒细胞中上调，在缺硒细胞中它选择性地抑制Sec掺入到执行非必需功能的两种硒蛋白中。在初步研究中，我们确定了eIF4a3的新靶点，并建立了eIF4a3与SECIS相互作用的模型。我们还提出的证据表明，hnRNP K选择性地结合到SECIS从一个非必需的硒蛋白，但不是从一个必需的硒蛋白。在这个项目中，我们将阐明eIF4a3和hnRNP K在调节硒蛋白质组的表达，使用体外试验，细胞培养系统和小鼠模型的组合的作用。该项目的成功完成将为哺乳动物细胞如何在硒不足期间优先利用硒提供重要的见解，硒不足是世界许多地区的一个重要健康问题。通过确定这些调控途径，我们的研究将为开发更特异和更有针对性的方法来调节体内硒蛋白表达提供坚实的基础。

DESCRIPTION (provided by applicant): Selenium is an essential micronutrient that exerts many important health benefits. The element is incorporated into selenoproteins as selenocysteine (Sec). The mammalian selenoproteins perform critical functions in anti-oxidant defense, thyroid hormone metabolism, male reproduction, and development. Sec is encoded by UGA, which is normally read as a stop codon. The recoding of UGA as Sec requires the Sec Insertion Sequence (SECIS) element in the selenoprotein mRNA. Although much progress has been made in understanding the mechanism of Sec incorporation, much less is known about the regulation of this pathway. In selenium deficiency, certain selenoproteins that are critical for health and development are expressed while other nonessential selenoproteins are lost. The central hypothesis of our proposal is that this complex hierarchy of selenoprotein expression is maintained by the interplay between multiple trans-acting factors that bind selectively to different SECIS elements. We discovered two new SECIS-binding proteins, nucleolin and eukaryotic initiation factor 4a3 (eIF4a3) that play opposing roles in selectively modulating selenoprotein synthesis. We showed that eIF4a3 links selenium status with differential selenoprotein expression. EIF4a3 is upregulated in selenium-deficient cells where it selectively inhibits the incorporation of Sec into two selenoproteins that perform nonessential functions. In preliminary studies, we identified new targets of eIF4a3 and developed a model of the eIF4a3: SECIS interaction. We also present evidence that hnRNP K binds selectively to a SECIS from a nonessential selenoprotein but not from an essential selenoprotein. In this project, we will elucidate the roles of eIF4a3 and hnRNP K in regulating the expression of the selenoproteome using a combination of in vitro assays, cell culture systems, and mouse models. The successful completion of this project will provide critical insight into how mammalian cells prioritize the utilization of selenium during selenium insufficiency, an important health problem in many parts of the world. By identifying these regulatory pathways, our studies will provide a strong foundation for developing more specific and targeted approaches for modulating selenoprotein expression in vivo.