Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada.
Free Radic Biol Med. 2011 Nov 1;51(9):1675-85. doi: 10.1016/j.freeradbiomed.2011.07.021. Epub 2011 Jul 31.
NAD(P)H:quinone oxidoreductase (NQO1)-mediated detoxification of quinones plays a critical role in cancer prevention. Heavy metals such as mercury (Hg(2+)) alter the carcinogenicity of aryl hydrocarbon receptor ligands, mainly by modifying various xenobiotic-metabolizing enzymes such as NQO1. Therefore, we examined the effect of Hg(2+) on the expression of NQO1 in human hepatoma HepG2 cells. For this purpose HepG2 cells were incubated with various concentrations of Hg(2+) (2.5, 5, and 10μM) in the presence and absence of two NQO1 inducers, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and isothiocyanate sulforaphane (SUL), as bifunctional and monofunctional inducers, respectively. Analysis of the time-dependent effect of Hg(2+) revealed that Hg(2+) increased the expression of NQO1 mRNA in a time-dependent manner. In addition, Hg(2+) increased NQO1 at the mRNA, protein, and activity levels in the presence and absence of both NQO1 inducers, TCDD and SUL, which coincided with increased nuclear accumulation of Nrf2 protein. Investigating the effect of Hg(2+) at the transcriptional level revealed that Hg(2+) significantly induced the antioxidant-responsive element-dependent luciferase reporter gene expression in the absence and the presence of both NQO1 inducers. NQO1 mRNA and protein decay experiments revealed a lack of posttranscriptional and posttranslational mechanisms. Transfecting HepG2 cells with siRNA for Nrf2 significantly decreased the Hg(2+)-mediated induction of NQO1 mRNA and catalytic activity by approximately 90%. In conclusion, we demonstrated that Hg(2+) regulates the expression of the NQO1 gene through a transcriptional mechanism in human hepatoma HepG2 cells. In addition, Nrf2 is involved in the modulation of NQO1 by Hg(2+).
NAD(P)H：醌氧化还原酶 (NQO1)介导的醌解毒在癌症预防中起着关键作用。重金属如汞 (Hg(2+)) 改变芳烃受体配体的致癌性，主要通过修饰各种外源性代谢酶，如 NQO1。因此，我们研究了 Hg(2+) 对人肝癌 HepG2 细胞中 NQO1 表达的影响。为此，将 HepG2 细胞用不同浓度的 Hg(2+)（2.5、5 和 10μM）孵育，同时存在和不存在两种 NQO1 诱导剂，2,3,7,8-四氯二苯并-p-二恶英（TCDD）和异硫氰酸酯萝卜硫素（SUL），分别作为双功能和单功能诱导剂。分析 Hg(2+) 的时间依赖性效应表明，Hg(2+) 以时间依赖性方式增加 NQO1 mRNA 的表达。此外，Hg(2+) 增加了 NQO1 在 NQO1 诱导剂 TCDD 和 SUL 的存在和不存在下的 mRNA、蛋白质和活性水平，同时伴随着 Nrf2 蛋白的核积累增加。研究 Hg(2+) 在转录水平的影响表明，Hg(2+) 显著诱导抗氧化反应元件依赖性荧光素酶报告基因在 NQO1 诱导剂的存在和不存在的情况下表达。NQO1 mRNA 和蛋白质衰减实验表明缺乏转录后和翻译后机制。用 Nrf2 的 siRNA 转染 HepG2 细胞可使 Hg(2+) 介导的 NQO1 mRNA 和催化活性降低约 90%。总之，我们证明 Hg(2+) 通过人肝癌 HepG2 细胞中的转录机制调节 NQO1 基因的表达。此外，Nrf2 参与 Hg(2+) 对 NQO1 的调节。
