Department of Pharmacology and Chemical Biology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pennsylvania, USA.
Cancer Prev Res (Phila). 2010 Jun;3(6):718-26. doi: 10.1158/1940-6207.CAPR-10-0048. Epub 2010 May 18.
We have shown previously that cruciferous vegetable constituent benzyl isothiocyanate (BITC) suppresses viability of cultured MCF-7 and MDA-MB-231 human breast cancer cells and retards mammary cancer development in MMTV-neu mice by causing apoptosis, but the mechanism of cell death is not fully understood. We now show that whereas p53 is dispensable for BITC-induced cell death, proapoptotic response to this promising chemopreventive agent is mediated by suppression of X-linked inhibitor of apoptosis (XIAP) protein expression. The BITC treatment increased levels of total and Ser(15)-phosphorylated p53 protein in MCF-7 cells, but the proapoptotic response to this agent was maintained even after knockdown of the p53 protein level. Exposure of MCF-7 and MDA-MB-231 cells to BITC resulted in a marked decrease in protein level of XIAP as early as 8 hours after treatment. Ectopic expression of XIAP conferred statistically significant protection against BITC-mediated cytoplasmic histone-associated apoptotic DNA fragmentation in both cell lines. Moreover, inhibition of MDA-MB-231 cell growth in vivo in female athymic mice by BITC administration correlated with a modest but statistically significant decrease in XIAP protein level in the tumor xenograft. The BITC treatment also resulted in induction as well as nuclear translocation of survivin only in the MCF-7 cells. The BITC-induced apoptosis was modestly but statistically significantly augmented by RNA interference of survivin in MCF-7 cells. In conclusion, the present study provides novel insight into the molecular circuitry of BITC-induced apoptosis to indicate suppression of XIAP expression as a critical mediator of this process.
我们之前已经证明，十字花科蔬菜成分苯乙基异硫氰酸酯（BITC）通过诱导细胞凋亡来抑制 MCF-7 和 MDA-MB-231 人乳腺癌细胞的活力并延缓 MMTV-neu 小鼠的乳腺癌发展，但细胞死亡的机制尚不完全清楚。我们现在表明，尽管 p53 对于 BITC 诱导的细胞死亡不是必需的，但这种有前途的化学预防剂的促凋亡反应是通过抑制 X 连锁凋亡抑制剂（XIAP）蛋白表达来介导的。BITC 处理增加了 MCF-7 细胞中总 p53 和丝氨酸（15）磷酸化 p53 蛋白的水平，但即使在降低 p53 蛋白水平后，该药物对细胞的促凋亡反应仍能维持。 MCF-7 和 MDA-MB-231 细胞暴露于 BITC 后，XIAP 蛋白水平早在处理后 8 小时就明显下降。在两种细胞系中，XIAP 的异位表达赋予了对 BITC 介导的细胞质组蛋白相关凋亡 DNA 片段化的统计学上显著保护作用。此外，BITC 给药在雌性无胸腺小鼠体内对 MDA-MB-231 细胞生长的抑制与肿瘤异种移植物中 XIAP 蛋白水平的适度但统计学显著降低相关。BITC 处理还导致 survivin 的诱导以及仅在 MCF-7 细胞中的核易位。在 MCF-7 细胞中，用 survivin 的 RNA 干扰适度但统计学显著增强了 BITC 诱导的细胞凋亡。总之，本研究为 BITC 诱导的细胞凋亡的分子机制提供了新的见解，表明抑制 XIAP 表达是该过程的关键介质。
