Bax and Bak are required for apoptosis induction by sulforaphane, a cruciferous vegetable-derived cancer chemopreventive agent
Bax and Bak are required for apoptosis induction by sulforaphane, a cruciferous vegetable-derived cancer chemopreventive agent
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DOI：
10.1158/0008-5472.can-04-3616
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发表时间：
2005-03-01
期刊：
影响因子：
11.2
通讯作者：
Singh, SV
中科院分区：
文献类型：
--
作者：
Choi, S;Singh, SV
萝卜硫素是包括西兰花在内的许多可食用十字花科蔬菜中的一种成分，通过诱导细胞凋亡有效地抑制了培养和体内癌细胞的增殖，但导致细胞死亡的事件顺序尚不清楚。在这里，我们证明了多结构域促凋亡的Bcl2家族成员Bax和Bak在萝卜硫素诱导细胞凋亡中起着关键作用。这一结论基于以下观察：(A)萝卜硫素处理引起SV40转化的野生型小鼠胚胎成纤维细胞(MEF)Bax和Bak蛋白水平的浓度和时间依赖性增加以及Bax的构象变化和线粒体移位，从而触发细胞内凋亡分子(细胞色素c和Smac/Diablo)的释放，激活caspase-9和caspase-3，最终导致细胞死亡；(B)Bax或Bak基因敲除小鼠来源的MEF抵抗萝卜硫素诱导的细胞死亡，以及(C)与野生型或单一基因敲除细胞相比，Bax和Bak双基因敲除小鼠来源的MEF对萝卜硫素诱导的细胞色素c释放、caspase激活和细胞凋亡具有更强的保护作用。有趣的是，萝卜硫素处理还引起野生型、Baz(-/-)和Bak(-/-)MEF的APAF-1蛋白水平呈剂量和时间依赖性的增加，但在双基因敲除中没有。这表明Bax和Bak可能调节萝卜硫素介导的APAF-1蛋白的诱导。萝卜硫素处理后，X连锁的细胞凋亡抑制因子的蛋白水平也明显下降。因此，可以合理地假设萝卜硫素诱导的细胞凋亡是通过降低X连锁的凋亡抑制因子水平而被放大的，后者通过抑制caspase的活性来阻止细胞死亡。综上所述，本研究结果表明Bax和Bak蛋白在萝卜硫素诱导的细胞死亡中起着关键作用。
Sulforaphane, a constituent of many edible cruciferous vegetables, including broccoli, effectively suppresses proliferation of cancer cells in culture and in vivo by causing apoptosis induction, but the sequence of events leading to cell death is poorly defined. Here, we show that multidomain proapoptotic Bcl-2 family members Bax and Bak play a critical role in apoptosis induction by sulforaphane. This conclusion is based on the following observations: (a) sulforaphane treatment caused a dose- and time-dependent increase in the protein levels of both Bax and Bak and conformational change and mitochondrial translocation of Bax in SV40-transformed mouse embryonic fibroblasts (MEF) derived from wild-type mice to trigger cytosolic release of apoptogenic molecules (cytochrome c and Smac/DIABLO), activation of caspase-9 and caspase-3, and ultimately cell death; (b) MEFs derived from Bax or Bak knockout mice resisted cell death by sulforaphane, and (c) MEFs derived from Bax and Bak double knockout mice exhibited even greater protection against sulforaphane-induced cytochrome c release, caspase activation, and apoptosis compared with wild-type or single knockout cells. Interestingly, sulforaphane treatment also caused a dose- and time-dependent increase in the protein level of Apaf-1 in wild-type, Baz(-/-), and Bak(-/-)MEFs but not in double knockout, suggesting that Bax and Bak might regulate sulforaphane-mediated induction of Apaf-1 protein. A marked decline in the protein level of X-linked inhibitor of apoptosis on treatment with sulforaphane was also observed. Thus, it is reasonable to postulate that sulforaphane-induced apoptosis is amplified by a decrease in X-linked inhibitor of apoptosis level, which functions to block cell death by inhibiting activities of caspases. In conclusion, the results of the present study indicate that Bax and Bak proteins play a critical role in initiation of cell death by sulforaphane.