Role of Selenium-containing Proteins in Cancer and Development

硒领域的许多研究者已经提出，低分子量的硒是硒的主要来源。 硒化合物对硒的许多健康益处负责， 其他人认为硒蛋白可能是原因。这些健康益处 包括预防癌症、心脏病和其他心血管和肌肉疾病， 抑制病毒表达，延缓HIV阳性患者中AIDS的进展， 减缓衰老过程，在哺乳动物发育、雄性生殖和 免疫功能几年前，我们提出，这些健康益处主要是由于 硒蛋白中的硒以氨基酸硒代半胱氨酸（Sec）的形式存在。因此，我们建议， 为了阐明硒蛋白在癌症预防和发展中的作用， 表征了几种硒蛋白的功能。在过去的一年里，我们专注于 我们的注意力放在更详细地研究三种硒蛋白，硫氧还蛋白， 过氧化物酶1（TR 1）、谷胱甘肽过氧化物酶4（GPx 4）和硒蛋白15（Sep 15）。我们有 以前的研究表明，在肺癌中使用RNA干扰技术敲低TR 1， 细胞系（JBC 281：13005，2006）和由致癌k-ras驱动的癌细胞系（PLoS One 2：e1112; 1-7，2007）导致几种恶性表型被逆转更多 表明TR 1缺陷是抗肿瘤的。过去的这个 2009年，我们继续关注TR 1在癌症发展中作用的分子基础， 已经详细研究了TR 1在乳腺癌细胞系中凋亡中的作用。乳房 选择癌细胞系是因为我们发现乳腺癌细胞中TR 1敲低显示， 对TNF-α诱导的细胞凋亡的敏感性高得多。我们目前正在确认这些 小鼠体内的发现，如项目1（Z 01 BC 005317）中进一步讨论的。我们也 我们继续研究GPx 4在细胞内的作用，发现GPx 4是至关重要的， 修复膜脂质过氧化。此外，我们有证据表明， 硒蛋白可能参与神经退行性疾病如阿尔茨海默病的病因 帕金森病GPx 4在阿尔茨海默氏症患者的脑组织中的水平降低， 帕金森病小鼠模型。GPx 4是一种含硒的抗氧化酶， 细胞内功能尚未完全解决。为了阐明其在细胞内的功能， 我们在小鼠成纤维细胞系（NIH 3 T3细胞）中靶向去除GPx 4， 当这种酶的水平降低到其活性的80%以下时， 正常水平。其表达的部分减少导致严重的生长迟缓。 出乎意料的是，GPx 4敲低细胞的活性氧水平几乎没有变化， 但这些细胞表现出氧化脂质副产物的高度增加， 膜脂过氧化损伤迄今为止的数据已经确定了一个重要的作用， GPx 4在膜脂质氢过氧化物代谢中的作用，令人惊讶的是， 作为一般的抗氧化酶。在过去的一年里，我们发现9月15日似乎有一个 在结直肠癌中的作用。我们的研究结果表明，敲低Sep 15的表达， 在小鼠结肠癌细胞系CT-26中，使用RNAi导致表型变化更多， 对正常细胞的影响，包括细胞生长率下降和细胞生长速率降低 锚定独立的生长能力。此外，CT-26、Sep 15敲低细胞，当 注射到相同背景的小鼠中并与质粒转染的对照相比， 显示出形成局部皮下肿瘤和肺的能力显著降低， 体内转移。小鼠刘易斯肺癌细胞（LLC 1），用相同的siSep 15转染 构建体，似乎保持其原始生长特征，表明 Sep 15的敲低降低了结肠（CT 26）细胞的致瘤性，但不降低肺（LLC 1）细胞的致瘤性。我们 继续研究这种明显的组织特异性，以及可能的功能， Sep 15在结肠和其他组织中。

Numerous investigators in the selenium field have proposed that low molecular weight selenocompounds are responsible for the numerous health benefits attributed to selenium, while others have suggested that selenoproteins are likely responsible. These health benefits include preventing cancer, heart disease and other cardiovascular and muscle disorders, inhibiting viral expression, delaying the progression of AIDS in HIV positive patients, slowing the aging process and having roles in mammalian development, male reproduction and immune function. We proposed several years ago that these health benefits are due largely to the presence of selenium in selenoproteins as the amino acid, selenocysteine (Sec). Therefore, to elucidate the role of selenoproteins in cancer prevention and development, we are characterizing the function of several selenoproteins. During the past year, we have focused our attention on studying in greater detail the role of three selenoproteins, thioredoxin peroxidase 1 (TR1), glutathione peroxidase 4 (GPx4) and selenoprotein 15 (Sep15). We had previously shown that the knockdown of TR1 using RNA interference technology in a lung cancer cell line (JBC 281: 13005, 2006) and in a cancer cell line driven by oncogenic k-ras (PLoS One 2: e1112; 1-7, 2007) resulted in several of the malignant phenotypes being reversed more towards those of normal cells suggesting that TR1 deficiency is antitumorigenic. This past year, we have continued to focus on the molecular basis of TR1s role in cancer development and have examined the role of TR1 in apoptosis in a breast cancer cell line in detail. The breast cancer cell line was selected since we found that TR1 knockdown in breast cancer cells showed a much higher sensitivity to TNF-alpha induced apoptosis. We are currently confirming these findings in mice in vivo as further discussed in Project 1 (Z01 BC 005317). We are also continuing our study on the intracellular role of GPx4 and have found GPx4 is essential for repairing membrane lipid hydroperoxidation. Furthermore, we have evidence that this selenoprotein may be involved in the etiology of neurodegenerative diseases such as Alzheimers and Parkinsons diseases. GPx4 has decreased levels in brain tissue of Alzheimers and Parkinsons disease mouse models. GPx4 is a selenium-containing, antioxidant enzyme whose intracellular function has not been fully resolved. To elucidate its function intracellularly, we targeted the removal of GPx4 in a mouse fibroblast cell line (NIH3T3 cells) that resulted in severe damage to the cells when the level of this enzyme was reduced below 80% of its normal level. Partial reduction in its expression led to severe growth retardation. Unexpectedly, GPx4 knockdown cells showed little change in levels of reactive oxygen species, but these cells manifested highly increased levels of oxidized lipid byproducts suggesting membrane lipid hydroperoxidation damage. The data thus far have established an essential role of GPx4 in the metabolism of membrane lipid hydroperoxides, and surprisingly, a limited role as a general antioxidant enzyme. In the past year, we have found that Sep15 appears to have a role in colorectal cancer. Our findings demonstrate that knocking down the expression of Sep15 in the murine colon carcinoma cell line, CT-26, using RNAi resulted in phenotypic changes more towards normal cells that included decreased cell growth rates and reduced anchorage-independent growth abilities. Furthermore, CT-26, Sep15 knockdown cells, when injected into mice of the same background and compared to plasmid-transfected controls, also demonstrated a significantly reduced ability to form localized subcutaneous tumors and lung metastases in vivo. Mouse Lewis lung carcinoma cells (LLC1), transfected with the same siSep15 construct, appeared to maintain their original growth characteristics, indicating that knockdown of Sep15 reduced tumorigenicity of colon (CT26), but not lung (LLC1) cells. We are continuing to investigate this apparent tissue specificity, as well as possible functions of Sep15 in colon and other tissues.