Regulation of selenoprotein synthesis by SECIS-binding proteins

说明(申请人提供)：硒是一种基本的微量营养素，对健康有许多重要的益处。这种元素以硒半胱氨酸(SEC)的形式被结合到硒蛋白中。哺乳动物的硒蛋白在抗氧化防御、甲状腺激素代谢、雄性生殖和发育等方面发挥着重要作用。SEC由UGA编码，通常读作停止密码子。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掺入的机制方面已经取得了很大进展，但对这一途径的调控知之甚少。在缺硒的情况下，某些对健康和发育至关重要的硒蛋白会表达，而其他非必需的硒蛋白则会丢失。我们建议的中心假设是，这种复杂的硒蛋白表达层次是由多种反式作用因子之间的相互作用维持的，这些反式作用因子选择性地与不同的SECIS元件结合。我们发现了两种新的SECIS结合蛋白，核仁素和真核细胞起始因子4a3(EIF4a3)，它们在选择性调节硒蛋白合成方面发挥着相反的作用。我们发现eIF4a3将硒状态与硒蛋白的差异表达联系起来。EIF4a3在缺硒细胞中表达上调，它选择性地抑制SEC掺入两个执行非必要功能的硒蛋白中。在初步研究中，我们发现了eIF4a3的新靶点，并开发了eIF4a3：SECIS相互作用的模型。我们还提供了证据表明hnRNP K选择性地与来自非必需硒蛋白的SECIS结合，而不是来自必需硒蛋白。在这个项目中，我们将结合体外分析、细胞培养系统和小鼠模型来阐明eIF4a3和hnRNP K在调节硒蛋白质组表达中的作用。该项目的成功完成将为哺乳动物细胞如何在硒缺乏期间优先利用硒提供关键的洞察力，硒缺乏是世界许多地区的一个重要健康问题。通过识别这些调控途径，我们的研究将为开发更具特异性和针对性的方法来调节体内硒蛋白的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.