Lu Yongke, Cederbaum Arthur
Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Free Radic Biol Med. 2007 Oct 1;43(7):1061-75. doi: 10.1016/j.freeradbiomed.2007.06.021. Epub 2007 Jul 6.
In a previous study, E47 HepG2 cells that overexpress human CYP2E1 were shown to be more sensitive to cisplatin than C34 cells that do not express CYP2E1. In this study, we found that this sensitivity was due to an earlier activation of ERK in the E47 cells compared to the C34 cells. Glutathione depletion by L-buthionine sulfoximine (BSO) enhanced cisplatin cytotoxicity via increasing production of reactive oxygen species (ROS) and activation of ERK. In contrast, elevation of glutathione by glutathione ethyl ester (GSHE) decreased cisplatin/BSO cytotoxicity by decreasing ROS production and ERK activation. Inhibition of ERK activation by U0126 protected against cisplatin/BSO cytotoxicity via inhibiting ROS production but not restoring intracellular glutathione content. Examination of the mode of cell death showed that U0126 inhibited cisplatin-induced necrosis but not apoptosis. Cisplatin-induced apoptosis was caspases-dependent; BSO switched cisplatin-induced apoptosis to necrosis via decreasing activity of caspases, and GSHE switched cisplatin/BSO-induced necrosis back to apoptosis through maintaining activity of caspases. Similar to GSHE, U0126 partially switched cisplatin/BSO induced necrosis to apoptosis via restoring activity of caspases. Cisplatin lowered levels of thioredoxin, especially in the presence of BSO. Although U0126 failed in restoring intracellular glutathione levels, it restored thioredoxin levels, which maintain the activity of the caspases. These results suggest that thioredoxin can replace glutathione to promote the active thiol redox state necessary for caspase activity, and thus glutathione and thioredoxin regulate the mode of cisplatin toxicity in E47 cells via redox regulation of caspase activity.
在先前的一项研究中，过表达人CYP2E1的E47 HepG2细胞比不表达CYP2E1的C34细胞对顺铂更敏感。在本研究中，我们发现这种敏感性是由于与C34细胞相比，E47细胞中ERK的激活更早。L-丁硫氨酸亚砜胺（BSO）消耗谷胱甘肽通过增加活性氧（ROS）的产生和ERK的激活增强了顺铂的细胞毒性。相反，谷胱甘肽乙酯（GSHE）提高谷胱甘肽水平通过减少ROS产生和ERK激活降低了顺铂/BSO的细胞毒性。U0126抑制ERK激活通过抑制ROS产生保护细胞免受顺铂/BSO的细胞毒性，但不能恢复细胞内谷胱甘肽含量。对细胞死亡模式的研究表明，U0126抑制顺铂诱导的坏死但不抑制凋亡。顺铂诱导的凋亡是半胱天冬酶依赖性的；BSO通过降低半胱天冬酶的活性将顺铂诱导的凋亡转变为坏死，而GSHE通过维持半胱天冬酶的活性将顺铂/BSO诱导的坏死转变回凋亡。与GSHE类似，U0126通过恢复半胱天冬酶的活性部分地将顺铂/BSO诱导的坏死转变为凋亡。顺铂降低了硫氧还蛋白的水平，尤其是在存在BSO的情况下。虽然U0126未能恢复细胞内谷胱甘肽水平，但它恢复了硫氧还蛋白水平，而硫氧还蛋白维持了半胱天冬酶的活性。这些结果表明，硫氧还蛋白可以替代谷胱甘肽来促进半胱天冬酶活性所需的活性硫醇氧化还原状态，因此谷胱甘肽和硫氧还蛋白通过对半胱天冬酶活性的氧化还原调节来调控E47细胞中顺铂毒性的模式。
