Tang Li, Zhang Yuesheng
Department of Chemoprevention, Roswell Park Cancer Institute, Basic Science 711, Elm and Carlton Streets, Buffalo, NY 14263, USA.
Mol Cancer Ther. 2005 Aug;4(8):1250-9. doi: 10.1158/1535-7163.MCT-05-0041.
Many isothiocysanates (ITC) are promising cancer-preventive agents, and induction of apoptosis is one of their underlying mechanisms of action. We recently found that caspase-9 was preferentially activated over other initiator caspases in human bladder cancer UM-UC-3 cells. We report here that caspase-9 activation is the major step leading to ITC-induced apoptosis in this cell line. More importantly, our results show that caspase-9 activation by the ITCs may result primarily from mitochondrial damage. Four common naturally occurring ITCs were studied, including allyl ITC, benzyl ITC (BITC), phenethyl ITC (PEITC), and sulforaphane. BITC and PEITC showed more potent mitochondria-damaging ability than the other two ITCs, correlating well with their stronger apoptosis-inducing potentials. Furthermore, BITC and PEITC damaged both the outer and inner mitochondrial membranes. Use of isolated mitochondria allowed us to establish that ITCs, and more importantly their major intracellular derivatives (glutathione conjugates) at concentrations that are readily achievable in cells, damage mitochondria, leading to the collapse of mitochondrial trans-membrane potential and release of cytochrome c. The mitochondria-damaging potencies of the ITCs correlate well with their lipophilicities. Bcl-2 family members are known to influence the stability of mitochondrial membrane. Our results show that the ITCs caused phosphorylation of Bcl-2, induced mitochondrial translocation of Bak, and disrupted the association of Bcl-xl with both Bak and Bax in mitochondrial membrane, indicating that ITC-induced mitochondrial damage results at least in part from modulation of select Bcl-2 family members.
许多异硫氰酸盐（ITC）是很有前景的癌症预防剂，诱导细胞凋亡是其潜在作用机制之一。我们最近发现，在人膀胱癌UM-UC-3细胞中，半胱天冬酶-9（caspase-9）比其他起始半胱天冬酶更易被激活。我们在此报告，caspase-9激活是该细胞系中ITC诱导细胞凋亡的主要步骤。更重要的是，我们的结果表明，ITC激活caspase-9可能主要源于线粒体损伤。研究了四种常见的天然存在的ITC，包括烯丙基ITC、苄基ITC（BITC）、苯乙基ITC（PEITC）和萝卜硫素。BITC和PEITC比其他两种ITC表现出更强的线粒体损伤能力，这与其更强的诱导细胞凋亡潜力密切相关。此外，BITC和PEITC破坏了线粒体外膜和内膜。使用分离的线粒体使我们能够确定，ITC及其更重要的细胞内主要衍生物（谷胱甘肽共轭物）在细胞中易于达到的浓度下会损伤线粒体，导致线粒体跨膜电位崩溃和细胞色素c释放。ITC的线粒体损伤能力与其亲脂性密切相关。已知Bcl-2家族成员会影响线粒体膜的稳定性。我们的结果表明，ITC导致Bcl-2磷酸化，诱导Bak向线粒体转位，并破坏线粒体内膜中Bcl-xl与Bak和Bax的结合，表明ITC诱导的线粒体损伤至少部分是由特定Bcl-2家族成员的调节引起的。
