Abstract：
Selenium is an essential trace element co-translationally incorporated into selenoproteins with important biological functions. Health benefits have long been associated with selenium supplementation. However, cytotoxicity is observed upon excessive selenium intake. The aim of this study is to investigate the metabolic pathways underlying the response to the selenium-containing amino acids selenomethionine and selenocysteine in a normal human breast epithelial cell model. We show that both selenomethionine and selenocystine inhibit the proliferation of non-cancerous MCF-10A cells in the same concentration range as cancerous MCF-7 and Hela cells, which results in apoptotic cell death. Selenocystine exposure in MCF-10A cells caused a severe depletion of free low molecular weight thiols, which might explain the observed upregulation of the expression of the oxidative stress pathway transcription factor NRF2. Both selenomethionine and selenocystine induced the expression of target genes of the unfolded protein response (GRP78, ATF4, CHOP). Using a redox-sensitive fluorescent probe targeted to the endoplasmic reticulum (ER), we show that both selenoamino acids shifted the ER redox balance towards an even more oxidizing environment. These results suggest that alteration of the redox state of the ER may disrupt protein folding and cause ER stress-induced apoptosis in MCF-10A cells exposed to selenoamino acids.
摘要：
硒是一种必需的微量元素，可共同转化为硒蛋白，具有重要的生物学功能。长期以来，补充硒对健康有益。然而,过量摄入硒时观察到细胞毒性。这项研究的目的是研究正常人乳腺上皮细胞模型中对含硒氨基酸硒代蛋氨酸和硒代半胱氨酸的反应的代谢途径。我们显示硒代蛋氨酸和硒代半胱氨酸在与癌性MCF-7和Hela细胞相同的浓度范围内抑制非癌性MCF-10A细胞的增殖，导致细胞凋亡。MCF-10A细胞中的硒酸暴露导致游离低分子量硫醇的严重消耗，这可能解释了观察到的氧化应激途径转录因子NRF2表达的上调。硒代蛋氨酸和硒代半胱氨酸均诱导未折叠蛋白反应靶基因(GRP78,ATF4,CHOP)的表达。使用针对内质网（ER）的氧化还原敏感荧光探针，我们表明，两种硒代氨基酸都将ER氧化还原平衡转向更加氧化的环境。这些结果表明，ER氧化还原状态的改变可能会破坏蛋白质折叠并引起暴露于硒氨基酸的MCF-10A细胞中ER应激诱导的凋亡。
