Role of Selenium in Cancer and Health

硒是人类和其他哺乳动物饮食中的必需微量营养素，并且已知其在预防各种形式的癌症（例如，结肠、前列腺、肺和肝）、心脏病和其他心血管和肌肉疾病。此外，它还可作为抗病毒剂，在延缓衰老过程、延缓HIV阳性患者的艾滋病进展、免疫功能、哺乳动物发育和男性生殖方面发挥作用。硒发挥这些健康益处的方式知之甚少，但我们提出，它们主要是由于硒蛋白中存在这种元素作为氨基酸硒代半胱氨酸（Sec）。因此，我们的计划侧重于SEC被纳入蛋白质的方式以及特定硒蛋白在人类健康和发育中的作用。由于Sec tRNA是唯一已知的tRNA，支配整个类的蛋白质，硒蛋白的表达，我们已经开发了几个转基因，敲除，条件性敲除和敲低细胞和小鼠系，干扰Sec tRNA的合成，这反过来又干扰硒蛋白的表达作为模型，以更好地了解硒和硒蛋白的代谢及其在健康中的作用。在过去的一年里，我们的项目集中在使用RNAi技术来敲低几种硒蛋白和其他参与Sec生物合成的蛋白质（例如，SLA，SECp 43，PSTK，SPS 1和2），以阐明其在硒代谢中的作用，并确定该元素是如何被纳入蛋白质。本课题组进一步研究了SECp 43和SLA在Sec生物合成及其与蛋白质结合中的作用。此外，我们开发了一种新的检测方法，用于研究硒蛋白的功能，涉及敲低/敲入，并使用这种技术来研究许多新的参数硒蛋白的功能，不能很容易地接近以前。使用loxP-Cre技术，我们有针对性地去除小鼠肝脏中的硒蛋白表达，然后分别用野生型或两种不同的突变体Sec tRNA转基因完全或部分地替换硒蛋白群体。突变型Sec tRNA转基因涉及tRNA中的突变，其阻止在反密码子的摆动位置37处添加甲基，2 '-O-甲基核糖（命名为Um 34）。Um 34的缺失导致与胁迫相关的硒蛋白的表达丧失，而管家硒蛋白几乎完全表达。我们先前已经通过使用野生型和突变转基因在标准敲除小鼠中拯救硒蛋白群体表明，Um 34参与应激相关硒蛋白的合成。然而，我们现在靶向特定器官或组织的能力将使我们能够专注于硒和硒蛋白在给定细胞类型中的作用。应该进一步指出的是，这种新的蛋白质表达调控发生在翻译水平，并表现出组织特异性模式。我们还扩大了我们在各种组织和器官中硒蛋白表达的靶向敲除，并明确显示了硒蛋白在发育和疾病预防中的作用。在过去的一年里，我们在这一领域的主要焦点之一是硒蛋白在免疫功能中的作用。我们靶向去除T细胞中的硒蛋白表达，并观察到CD 8群体减少约50%，并且mIL-13在敲除小鼠的雄性中富集超过55倍，在雌性中富集超过80倍。IgG 2a在靶向小鼠中增加约两倍。这些研究表明，T细胞中的硒蛋白与炎症性变态反应有关，在T细胞的发育、分化、成熟和功能中起重要作用，是决定Th 1和Th 2应答的不可缺少的因素。

Selenium is an essential micronutrient in the diet of humans and other mammals and is known to have roles in preventing various forms of cancer (e.g., colon, prostate, lung and liver), heart disease and other cardiovascular and muscle disorders. In addition, it serves as an antiviral agent and plays a role in delaying the aging process, in delaying the progression of AIDS in HIV positive patients, in immune function, in mammalian development and in male reproduction. The means by which selenium exerts these many health benefits are poorly understood, but we have proposed that they are due largely to the presence of this element in selenoproteins as the amino acid, selenocysteine (Sec). Our program therefore focuses on the means by which Sec is incorporated into protein and the role of specific selenoproteins in human health and development. Since Sec tRNA is the only known tRNA that governs the expression of an entire class of proteins, the selenoproteins, we have developed several transgenic, knockout, conditional knockout and knockdown cell and mouse lines that perturb Sec tRNA synthesis which in turn perturbs selenoprotein expression as models to better understand selenium and selenoprotein metabolism and their roles in health. This past year, our program has focused on using RNAi technology to knockdown several selenoproteins and other proteins involved in Sec biosynthesis (e.g., SLA, SECp43, PSTK, SPS1 and 2) to elucidate their roles in selenium metabolism and to determine how this element is incorporated into protein. Our group further characterized the roles of SECp43 and SLA in the biosyntheisis of Sec and its incorporation into protein. In addition, we developed a novel assay for studying selenoprotein function that involved knockdown/knock-in and are using this technique to study many new parameters of selenoprotein function that could not readily be approached previously. Using loxP-Cre technology, we targeted the removal of selenoprotein expression in mouse liver and then replaced the selenoprotein population either fully or partially with a wild type or two different mutant Sec tRNA transgenes, respectively. The mutant Sec tRNA transgenes involve mutations in the tRNA that prevent the addition of a methyl group, 2'-O-methylribose (designated Um34), at position 37 which is the wobble position of the anticodon. The absence of Um34 results in the loss of expression of stress-related selenoproteins, while the housekeeping selenoproteins are virtually completely expressed. We had shown earlier through rescue of the selenoprotein population in a standard knockout mouse using wild type and mutant transgenes that Um34 was involved in synthesis of stress-related selenoproteins. However, our ability now to target a specific organ or tissue will permit us to focus on the role of selenium and selenoproteins in a given cell type. It should be further noted that this novel regulation of protein expression occurred at the level of translation and manifested a tissue-specific pattern. We are also expanding our targeted knockout of selenoprotein expression in various tissues and organs and have shown unequivocally a role of selenoproteins in development and disease prevention. One of our major focuses in this area over the last year has been on the role of selenoproteins in immune function. We targeted the removal of selenoprotein expression in T-cells and observed about a 50% reduction in the CD8 population and that mIL-13 was enriched more than 55 fold in males and 80 fold in females of knockout mice. IgG2a was increased about two-fold in targeted mice. These studies show thus far that selenoproteins in T-cells are associated with inflammatory allergic immune responses, have an essential role in the development/differentiation/maturation and function of T-cells and are indespensible factors in determining Th1 vs Th2 responses.