Anwar-Mohamed Anwar, El-Kadi Ayman O S
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
Toxicol Appl Pharmacol. 2009 May 1;236(3):261-9. doi: 10.1016/j.taap.2009.02.002.
Recent data suggest that vanadium (V5+) compounds exert protective effects against chemical-induced carcinogenesis, mainly through modifying various xenobiotic metabolizing enzymes. In fact, we have shown that V5+ down-regulates the expression of Cyp1a1 at the transcriptional level through an ATP-dependent mechanism. However, incongruously, there is increasing evidence that V5+ is found in higher amounts in cancer cells and tissues than in normal cells or tissues. Therefore, the current study aims to address the possible effect of this metal on the regulation of expression of an enzyme that helps maintain endogenous antioxidants used to protect tissues/cells from mutagens, carcinogens, and oxidative stress damage, NAD(P) H:quinone oxidoreductase 1 (Nqo1). In an attempt to examine these effects, Hepa 1c1c7 cells and its AhRdeficient version, c12, were treated with increasing concentrations of V5+ in the presence of two distinct Nqo1 inducers, the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and isothiocyanate sulforaphane (SUL). Our results showed that V5+ inhibits the TCDD- and SUL-mediated induction of Nqo1 at mRNA, protein, and catalytic activity levels. At transcriptional level, V5+ was able to decrease the TCDD- and SUL-induced nuclear accumulation of Nrf2 and the subsequent binding to antioxidant responsive element (ARE) without affecting Nrf2 protein levels. Looking at post-transcriptional level; we found that V5+ did not affect Nqo1 mRNA transcripts turn-over rates. However, at the post-translational level V5+ increased Nqo1 protein half-life. In conclusion, the present study demonstrates that V5+ down-regulates Nqo1 at the transcriptional level, possibly through inhibiting the ATP-dependent activation of Nrf2.
近期数据表明，钒（V5+）化合物对化学诱导的致癌作用具有保护效应，主要是通过调节各种外源性物质代谢酶来实现。事实上，我们已经表明V5+通过一种ATP依赖机制在转录水平下调Cyp1a1的表达。然而，矛盾的是，越来越多的证据表明，癌细胞和组织中的V5+含量高于正常细胞或组织。因此，本研究旨在探讨这种金属对一种有助于维持内源性抗氧化剂的酶的表达调控可能产生的影响，这种抗氧化剂用于保护组织/细胞免受诱变剂、致癌物和氧化应激损伤，即NAD(P)H:醌氧化还原酶1（Nqo1）。为了研究这些影响，在两种不同的Nqo1诱导剂2,3,7,8-四氯二苯并对二恶英（TCDD）和异硫氰酸酯萝卜硫素（SUL）存在的情况下，用浓度递增的V5+处理Hepa 1c1c7细胞及其AhR缺陷型细胞c12。我们的结果表明，V5+在mRNA、蛋白质和催化活性水平上抑制TCDD和SUL介导的Nqo1诱导。在转录水平上，V5+能够降低TCDD和SUL诱导的Nrf2核内积累以及随后与抗氧化反应元件（ARE）的结合，而不影响Nrf2蛋白水平。在转录后水平上，我们发现V5+不影响Nqo1 mRNA转录本的周转速率。然而，在翻译后水平上，V5+增加了Nqo1蛋白的半衰期。总之，本研究表明V5+可能通过抑制Nrf2的ATP依赖激活在转录水平下调Nqo1。
