Role of Selenium in Cancer and Health

硒是人类和其他哺乳动物饮食中必需的微量营养素。它有许多已知的健康益处，如预防各种形式的癌症（如结肠癌、前列腺癌、肺癌和肝癌），预防心脏病和其他心血管和肌肉疾病，作为抗病毒药物，并在延缓衰老过程、延缓艾滋病毒阳性患者艾滋病的进展、免疫功能、哺乳动物发育和男性生殖方面发挥作用。尽管已经进行了许多人体临床试验，以阐明这种元素在癌症预防、延缓艾滋病进展等方面的作用，花费了数亿美元，但对硒在分子水平上发挥这些健康益处的机制知之甚少。我们提出，这种健康益处主要是由于硒蛋白中存在这种元素作为含硒氨基酸，硒半胱氨酸（Sec）。因此，我们的项目重点是：1)开发小鼠模型，以评估硒和特定硒蛋白在人类健康和癌症预防中的作用；2)硒是如何被生物合成并整合到蛋白质中的。本文讨论的项目考察了我们对硒在健康和癌症预防中的作用的研究。在过去的一年里，我们完成并发表了我们关于敲低和敲硒蛋白表达的项目，为研究蛋白质功能提供了一种新的替代方法。我们在开发这项技术时使用的一个硒蛋白是硫氧还蛋白还原酶1 （TR1）。由于TR1在许多癌细胞中过表达，并且由于这种含硒的氧化还原酶已被提出作为癌症治疗的靶点，我们在小鼠肺癌细胞系（LLC1）中敲低了它的表达，并报道了大多数恶性表型向正常细胞的表型逆转。这些研究已经扩展到表明许多人类和小鼠细胞系的恶性表型也可以通过TR1敲低而改变，从而产生类似的癌症抑制作用。我们从NIH3T3细胞中获得了一株Ras过表达的致癌细胞系，并敲低TR1来分析其生长抑制特性的潜在机制，发现细胞在S期存在缺陷。我们目前正在研究这种抑制作用的确切机制。此外，在过去的几年里，我们已经开发了几种转基因、敲除、条件敲除和敲除的细胞和小鼠系，这些细胞和小鼠系干扰Sec tRNA的合成，从而调节硒蛋白的表达，作为更好地了解硒和硒蛋白代谢及其在健康中的作用的模型。利用loxP-Cre技术，我们已经靶向去除几种组织和器官中的硒蛋白表达。最近，我们在这一领域的主要焦点之一是硒蛋白在免疫功能和皮肤细胞功能中的作用。我们针对t细胞和巨噬细胞中硒蛋白表达的去除来研究免疫功能，并在小鼠表皮中研究皮肤细胞功能。我们之前发现，硒蛋白缺乏的T细胞表现出T细胞增殖缺陷、ERK1/2磷酸化、IL2R&#945；表达和凋亡率增加。在过去的一年里，我们完成了体内免疫研究，测量ROS的产生和挽救有缺陷的增殖。体内挑战研究表明，T细胞硒蛋白缺陷小鼠的免疫功能受损，因为敲除小鼠在挑战时表现出明显低于兄弟姐妹，野生型对照的各种igg水平。缺陷T细胞也被发现在刺激下产生和积累更多的活性氧；在使用外部抗氧化剂后，有缺陷的T细胞增殖完全恢复了。与野生型对照相比，巨噬细胞中硒蛋白的去除显示未刺激的硒蛋白KO巨噬细胞中ROS的积累。体外脂多糖（LPS）刺激后骨髓源性巨噬细胞的细胞因子分析显示IL-6和TNF-的产生减少，而体内血清细胞因子分析似乎显示注射LPS后TNF-的产生显著增加。然而，在体内LPS刺激下，KO小鼠与对照组小鼠在LPS诱导的致死性休克中没有显著差异。目前正在研究lps诱导的促炎信号级联反应。在皮肤中缺乏硒蛋白的小鼠中，这些动物表现出生长迟缓，随着年龄的增长，这种情况变得更加突出，与正常的幼崽相比，它们的寿命要短得多。基因敲除小鼠皮肤出现片状和多皱纹，病理分析显示表皮中度增生，伴有表皮和口腔黏膜急性凝固性坏死。我们最近启动了一项肝癌研究，以检查硒蛋白在肝癌预防中的作用。本研究进行的扩展我们之前发现老鼠生存与硒蛋白的完整切除的肝脏和响应请求美国国会参众两院的通过,美国国家癌症研究所应该付出更多努力肝癌研究肝癌发病率的增加和少量的有效的治疗方法截然不同的是,许多其他形式的癌症发病率在哪里和下降治疗方案正在迅速增加。这些研究还处于早期阶段，我们正在研究无自体蛋白小鼠对致癌物质的反应

Selenium is an essential micronutrient in the diet of humans and other mammals. It has many known health benefits such as preventing various forms of cancer (e.g., colon, prostate, lung and liver), preventing heart disease and other cardiovascular and muscle disorders, serving as an antiviral agent, and playing roles in delaying the aging process, delaying the progression of AIDS in HIV positive patients, in immune function, mammalian development and male reproduction. Even though many human clinical trails have been undertaken to elucidate the role of this element in cancer prevention, delaying the progression of AIDS, etc., at the cost of hundreds of millions of dollars, little is known about the mechanism of how selenium acts at the molecular level in exerting these many health benefits. We proposed that the health benefits are due largely to the presence of this element in selenoproteins as the selenium-containing amino acid, selenocysteine (Sec). Our program therefore focuses on 1) developing mouse models to assess the role of selenium and specific selenoproteins in human health and cancer prevention and 2) the means by which Sec is biosynthesized and incorporated into protein. The project discussed herein examines our research on the role of selenium in health and cancer prevention. During the past year, we finished and published our project on knocking down and knocking in selenoprotein expression providing an alternative and novel means of studying protein function. One of the selenoproteins we used as a model in developing this technique was thioredoxin reductase 1 (TR1). Since TR1 is overexpressed in many cancer cells, and since this selenium-containing oxidoreductase has been proposed to be a target for cancer therapy, we knocked down its expression in a mouse lung cancer cell line (LLC1) and reported that most of the malignant phenotypes were reversed more towards those of normal cells. These studies have been expanded to show that the malignant phenotypes of numerous human and mouse cell lines can also be altered by TR1 knockdown yielding a similar cancer inhibitory effect. We obtained an oncogenic, Ras overexpressing cell line from NIH3T3 cells and knocked down TR1 to analyze the underlying mechanism of the resulting growth inhibitory properties and found that the cells had a defect in the S phase. We are currently examining the precise mechanism for this inhibition. In addition, during the last few years, we have developed several transgenic, knockout, conditional knockout and knockdown cell and mouse lines that perturb Sec tRNA synthesis which in turn modulate selenoprotein expression as models to better understand selenium and selenoprotein metabolism and their roles in health. Using loxP-Cre technology, we have targeted the removal of selenoprotein expression in several tissues and organs. One of our major focuses in this area has recently been on the role of selenoproteins in immune function and skin cell function. We targeted the removal of selenoprotein expression in T-cells and in macrophages to investigate immune function and in mouse epidermis to investigate skin cell function. We previously found that T cells deficient in selenoproteins exhibit defective T cell proliferation, phosphorylation of ERK1/2, IL2Rα expression and an increased rate of apoptosis. This past year we completed in vivo immunization studies, measurement of ROS production and rescuing the defective proliferation. In vivo challenging studies showed that T cell selenoprotein deficient mice are immuno-compromised as the knockout mice exhibit significantly lower levels of various Igs upon challenging compared to sibling, wild type controls. The defective T cells were also found to generate and accumulate higher amounts of ROS upon stimulation; and upon using an external source of antioxidant, defective T cell proliferation was completely rescued. Removal of selenoproteins in macrophages showed an accumulation of ROS in unstimulated selenoprotein KO macrophages compared to wild type controls. Cytokine analysis of bone marrow-derived macrophages following in vitro stimulation with lipopolysaccharide (LPS) showed a decrease in IL-6 and TNF-α production while in vivo serum cytokine analysis appeared to show a significant increase in TNF-α production following injection with LPS. However, an in vivo challenge with LPS showed no significant difference in LPS-induced lethal shock between KO and control mice. An examination of the LPS-induced pro-inflammatory signaling cascade is currently being investigated. In our skin selenoproteinless mice, the animals exhibited stunted growth, which became more prominent with age, and they have a much shorter life span as compared to normal littermates. The knockout mice have flakiness and multiple wrinkles in skin, and pathological analysis revealed moderate epidermal hyperplasia along with acute coagulative necrosis of the epidermis and oral mucosa. We recently initiated a liver cancer study to examine the role of selenoproteins in liver cancer prevention. This study was undertaken as an extension of our previous finding that mice survive with the complete removal of selenoproteins in their liver and in response to the request by both houses of the US Congress that the National Cancer Institute should devote more effort to liver cancer research as the increased incidence of liver cancer and the small number of effective treatments is in sharp contrast to many other forms of cancer where the incidence is declining and the treatment options are rapidly increasing. These studies are in the early stages and we are examining the response of the selnoproteinless mice to carcinogens