Mi Lixin, Chung Fung-Lung
Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA.
Nutr Cancer. 2008;60 Suppl 1:12-20. doi: 10.1080/01635580802381287.
The upstream events by which isothiocyanates (ITCs) induce apoptosis have not been fully investigated. Numerous studies have reported that the apoptosis was induced by ITCs through generation of reactive oxygen species (ROS) as a result of conjugating with and, consequently, depleting cellular glutathione. As electrophiles, ITCs could potentially trigger apoptosis by binding to macromolecules including DNA and proteins. The results showed that DNA damage may not be an important early event for the apoptosis induction by ITCs. Phenethyl isothiocyanate (PEITC) is a more potent inducer of apoptosis than sulforaphane (SFN) in A549 cells, but SFN induces more ROS generation and oxidative damages than PEITC, suggesting that oxidative stress again is probably not a trigger for apoptosis in these cells. In contrast, we found that PEITC binds more to intracellular proteins than SFN. We identified tubulin as 1 of the protein targets of ITCs through proteomics approach. We showed that the relative tubulin binding affinity of ITCs correlates well with their potency of cell growth inhibition and apoptosis induction. These results collectively suggest that the covalent binding to protein targets, such as tubulin, by ITCs is an important chemical event in apoptosis induction by ITCs in human lung A549 cells.
异硫氰酸酯（ITCs）诱导细胞凋亡的上游事件尚未得到充分研究。大量研究报告称，ITCs通过与细胞内谷胱甘肽结合并使其消耗，从而产生活性氧（ROS）来诱导细胞凋亡。作为亲电试剂，ITCs可能通过与包括DNA和蛋白质在内的大分子结合来触发细胞凋亡。结果表明，DNA损伤可能不是ITCs诱导细胞凋亡的重要早期事件。在A549细胞中，异硫氰酸苯乙酯（PEITC）比萝卜硫素（SFN）更能有效诱导细胞凋亡，但SFN比PEITC产生活更多的ROS并造成更多氧化损伤，这表明氧化应激可能不是这些细胞凋亡的触发因素。相反，我们发现PEITC比SFN更易与细胞内蛋白质结合。我们通过蛋白质组学方法确定微管蛋白是ITCs的蛋白质靶点之一。我们发现，ITCs与微管蛋白的相对结合亲和力与其抑制细胞生长和诱导细胞凋亡的能力密切相关。这些结果共同表明，ITCs与蛋白质靶点（如微管蛋白）的共价结合是其诱导人肺A549细胞凋亡过程中的一个重要化学事件。
