Cho Sung-Dae, Li Guangxun, Hu Hongbo, Jiang Cheng, Kang Kyung-Sun, Lee Yong-Soon, Kim Sung-Hoon, Lu Junxuan
Hormel Institute, University of Minnesota, Austin, MN 55912, USA.
Nutr Cancer. 2005;52(2):213-24. doi: 10.1207/s15327914nc5202_11.
Sulforaphane (SFN) is a major isothiocyanate compound in cruciferous vegetables such as broccoli, cauliflower, and Brussels sprouts. Preclinical animal models have recently shown that SFN and other isothiocyanates may be useful for prostrate cancer (PCa) chemoprevention. In this study we used a DU145 human PCa cell culture model to investigate the role of protein kinase signaling pathway(s) in SFN-induced cell cycle arrest and apoptosis and whether another chemopreventive agent selenium enhances the apoptosis potency of SFN. The results showed that SFN exposure for 24 h or longer significantly decreased the number of viable DU145 cells in a dose-dependent manner with an IC50 of asymptotically equal to 10 microM. The decreased cell number was associated with G2/M phase arrest and apoptotic cell death, with the latter being evidenced by caspase-mediated cleavage of poly(ADP-ribose) polymerase and increased release of histone-associated DNA fragments. A peptide inhibitor of caspase-8 completely blocked SFN-induced apoptosis and that for caspase-9 exerted a major protection; however, neither inhibitor attenuated SFN-induced G2/M arrest. Regarding potential mediators, SFN treatment induced a transient rise of reactive oxygen species (ROS) peaking within (1/2) h and the activation of JNK within 1 h but did not have any detectable effect on the phosphorylation of p38MAPK or ERK1/2 from 6 h to 24 h. Pretreatment of cells with N-acetylcysteine to enrich intracellular glutathione blocked SFN-induced ROS and apoptotic cell death. Inhibiting the JNK activity with a pharmacologic inhibitor SP600125 abolished the induction of G2/M arrest and apoptosis by SFN, whereas chemical inhibitors for p38MAPK and MEK1/2 did not have any modulating effect on SFN-induced apoptosis. Taken together, the data indicate that SFN decreased viable DU145 cell number in large part through the generation of ROS and JNK-mediated signaling to G2/M arrest and caspase-dependent apoptosis. Selenium in the form of inorganic sodium selenite salt or methylseleninic acid did not enhance SFN-induced apoptosis in this cell culture model.
萝卜硫素（SFN）是西兰花、花椰菜和抱子甘蓝等十字花科蔬菜中的一种主要异硫氰酸酯化合物。临床前动物模型最近显示，SFN和其他异硫氰酸酯可能对前列腺癌（PCa）的化学预防有用。在本研究中，我们使用DU145人PCa细胞培养模型来研究蛋白激酶信号通路在SFN诱导的细胞周期阻滞和凋亡中的作用，以及另一种化学预防剂硒是否能增强SFN的凋亡效力。结果表明，暴露于SFN 24小时或更长时间会以剂量依赖的方式显著降低DU145活细胞数量，IC50渐近等于10微摩尔。细胞数量的减少与G2/M期阻滞和凋亡性细胞死亡有关，后者通过半胱天冬酶介导的聚（ADP-核糖）聚合酶裂解和组蛋白相关DNA片段释放增加得以证明。半胱天冬酶-8的肽抑制剂完全阻断了SFN诱导的凋亡，而半胱天冬酶-9的肽抑制剂则起到了主要的保护作用；然而，两种抑制剂均未减弱SFN诱导的G2/M阻滞。关于潜在的介质，SFN处理诱导活性氧（ROS）短暂升高，在（1/2）小时内达到峰值，并在1小时内激活JNK，但从6小时到24小时对p38MAPK或ERK1/2的磷酸化没有任何可检测到的影响。用N-乙酰半胱氨酸预处理细胞以富集细胞内谷胱甘肽可阻断SFN诱导的ROS和凋亡性细胞死亡。用药物抑制剂SP600125抑制JNK活性消除了SFN诱导的G2/M阻滞和凋亡，而p38MAPK和MEK1/2的化学抑制剂对SFN诱导的凋亡没有任何调节作用。综上所述，数据表明SFN在很大程度上通过产生ROS和JNK介导的信号传导导致G2/M阻滞和半胱天冬酶依赖性凋亡，从而降低DU145活细胞数量。在该细胞培养模型中，无机亚硒酸钠盐或甲基亚硒酸形式的硒并未增强SFN诱导的凋亡。
