Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
Toxicol In Vitro. 2010 Sep;24(6):1554-61. doi: 10.1016/j.tiv.2010.06.017. Epub 2010 Jul 3.
Recent studies demonstrated the carcinogenicity and the mutagenicity of vanadium compounds. In addition, vanadium (V(5+)) was found to enhance the effects of other genotoxic agents. However, the mechanism by which V(5+) induce toxicity remain unknown. In the current study we examined the effect of V(5+) (as ammonium metavanadate, NH(4)VO(3)) on the expression of NAD(P)H: quinone oxidoreductase 1 (NQO1) in human hepatoma HepG2 cells. Therefore, HepG2 cells were treated with increasing concentrations of V(5+) in the presence of two NQO1 inducers, the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and isothiocyanate sulforaphane (SUL). Our results showed that V(5+) inhibited the TCDD- and SUL-mediated induction of NQO1 at mRNA, protein and activity levels. Investigating the effect of V(5+) at transcriptional levels revealed that V(5+) significantly inhibited the TCDD- and SUL-mediated induction of antioxidant responsive element (ARE)-dependent luciferase reporter gene expression. In addition, V(5+) was able to decrease the TCDD- and SUL-induced nuclear accumulation of nuclear factor erythroid 2-related factor-2 (Nrf2) without affecting Nrf2 mRNA or protein levels. Looking at the post-transcriptional level, V(5+) did not affect NQO1 mRNA stability, thus eliminating the possible role of V(5+) in decreasing NQO1 mRNA levels through this mechanism. In contrast, at post-translational level, V(5+) was able to significantly decrease NQO1 protein half-life. The present study demonstrates for the first time that V(5+) down-regulates NQO1 at the transcriptional and post-translational levels in the human hepatoma HepG2 cells via AhR- and Nrf2-dependent mechanisms.
最近的研究表明，钒化合物具有致癌性和致突变性。此外，钒（V(5+)）被发现能增强其他遗传毒性物质的作用。然而，V(5+)引起毒性的机制尚不清楚。在本研究中，我们研究了 V(5+)（作为偏钒酸铵，NH(4)VO(3)）对人肝癌 HepG2 细胞中 NAD(P)H：醌氧化还原酶 1（NQO1）表达的影响。因此，用不同浓度的 V(5+)处理 HepG2 细胞，同时用两种 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）处理细胞。结果表明，V(5+)抑制 TCDD 和 SUL 介导的 NQO1 在 mRNA、蛋白和活性水平的诱导。在转录水平上研究 V(5+)的作用，结果表明，V(5+)显著抑制 TCDD 和 SUL 介导的抗氧化反应元件（ARE）依赖性荧光素酶报告基因表达。此外，V(5+)能够减少 TCDD 和 SUL 诱导的核因子红细胞 2 相关因子-2（Nrf2）的核积累，而不影响 Nrf2 的 mRNA 或蛋白水平。在转录后水平上，V(5+)不影响 NQO1 mRNA 的稳定性，因此排除了 V(5+)通过这种机制降低 NQO1 mRNA 水平的可能性。相反，在翻译后水平上，V(5+)能显著降低 NQO1 蛋白的半衰期。本研究首次表明，V(5+)通过 AhR 和 Nrf2 依赖性机制，在人肝癌 HepG2 细胞中下调 NQO1 的转录和翻译后水平。
