Department of Microbiology and Immunology, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan.
Cancer Chemother Pharmacol. 2010 Aug;66(3):475-84. doi: 10.1007/s00280-009-1183-6. Epub 2009 Nov 26.
Selenium (Se) compounds are well known to inhibit cell proliferation and induce cell death in human cancer cells. Respective chemical forms of Se are intracellularly metabolized via complicated pathways, which target distinct molecules and exhibit varying degrees of anti-carcinogenicity in different cancer types; however, the precise mechanisms by which Se activates apoptosis remain poorly understood.
The effects of Se compounds, Se-methylselenocysteine (MSC), selenomethionine (SeMet), and selenite on cell proliferation, apoptosis and its pathway in established human carcinoma cell lines (HSC-3, -4, A549, and MCF-7) were investigated. Cancer cells were treated with each Se compound during different periods. Cell apoptosis, caspase activity and ER stress markers were analyzed by flow cytometric or immunoblotting analysis, respectively.
We examined four cell lines for their sensitivity to MSC and SeMet in comparison with selenite. SeMet increased apoptotic cells in p53-positive A549 cells, whereas MSC increased apoptotic cells in p53-mutated HSC-3 cells. High activities of caspase-3, -8 and -9 were observed during apoptosis, and a pan-caspase inhibitor, z-VAD-fmk, rescued the cell viability of HSC-3 cells exposed to MSC. In addition, the occurrence of endoplasmic reticulum (ER) stress was suggested by the observation that levels of phosphorylated eIF2alpha and caspase-12 activity are increased in Se-treated cells. Selenite and MSC were accompanied with the concurrent reduction of phosphorylated Akt levels, and the inhibitory effects of these Se compounds on vascular endothelial growth factor expression were observed with identical patterns.
The present findings demonstrate that Se-induced apoptosis in carcinoma cells is basically a caspase-dependent process involving complicated mechanisms. Activation of both the intrinsic apoptotic pathway and ER stress pathway plays a major and concurrent role, while p53 activation seems to have only a functional role in SeMet.
硒（Se）化合物已被证实能够抑制人类癌细胞的增殖并诱导细胞死亡。Se 的不同化学形式通过复杂的途径在细胞内代谢，针对不同的分子，并在不同类型的癌症中表现出不同程度的抗癌作用；然而，Se 激活细胞凋亡的确切机制仍知之甚少。
研究了 Se 化合物、硒代蛋氨酸（SeMet）、硒代半胱氨酸（MSC）和亚硒酸钠对已建立的人癌细胞系（HSC-3、-4、A549 和 MCF-7）增殖、凋亡及其途径的影响。在不同时期用各 Se 化合物处理癌细胞。通过流式细胞术或免疫印迹分析分别分析细胞凋亡、半胱天冬酶活性和内质网应激标志物。
我们比较了 SeMet 和 MSC 对 p53 阳性 A549 细胞和 p53 突变的 HSC-3 细胞的敏感性，发现 SeMet 增加了 p53 阳性 A549 细胞中的凋亡细胞，而 MSC 增加了 p53 突变的 HSC-3 细胞中的凋亡细胞。凋亡过程中观察到 caspase-3、-8 和 -9 的高活性，pan-caspase 抑制剂 z-VAD-fmk 挽救了暴露于 MSC 的 HSC-3 细胞的细胞活力。此外，通过观察到 Se 处理细胞中磷酸化 eIF2alpha 水平和 caspase-12 活性增加，表明内质网（ER）应激的发生。亚硒酸钠和 MSC 伴随着磷酸化 Akt 水平的同时降低，并且观察到这些 Se 化合物对血管内皮生长因子表达的抑制作用具有相同的模式。
本研究结果表明，Se 诱导的癌细胞凋亡基本上是一个 caspase 依赖性过程，涉及复杂的机制。内源性凋亡途径和 ER 应激途径的激活起着主要和并发的作用，而 p53 激活似乎在 SeMet 中仅具有功能作用。
