Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada T6G 2N8.
Free Radic Biol Med. 2010 May 15;48(10):1399-409. doi: 10.1016/j.freeradbiomed.2010.02.027. Epub 2010 Feb 25.
Aryl hydrocarbon receptor (AhR) ligands, typified by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and metals, typified by arsenite (As(III)), are environmental cocontaminants, and their molecular interaction may disrupt the coordinated regulation of the carcinogen activating enzyme cytochrome P450 1A1 (CYP1A1). Therefore, in this study we examined the effects of coexposure to As(III) and TCDD on the expression of CYP1A1 in HepG2 cells. Our results showed that As(III) caused a dose-dependent decrease in TCDD-mediated induction of CYP1A1 mRNA, protein, and catalytic activity levels. As(III) significantly inhibited TCDD-mediated induction of AhR-dependent luciferase reporter gene expression without altering CYP1A1 mRNA stability. In addition, As(III) increased heme oxygenase-1 (HO-1) mRNA, which coincided with a further decrease in the CYP1A1 catalytic activity levels. When a competitive HO-1 inhibitor, tin mesoporphyrin, was applied to HepG2 cells or the cells were transfected with siRNA for HO-1 there was a partial restoration of the inhibition of TCDD-mediated induction of CYP1A1 catalytic activity. Treatment of cells with heme or hemoglobin partially restored the As(III)-mediated inhibition of CYP1A1 catalytic activity. On the other hand, cobalt protoporphyrin increased HO-1 mRNA, with a concomitant decrease in CYP1A1 activity, without affecting CYP1A1 mRNA, which was reversed by HO-1 siRNA transfection. This study demonstrates that As(III) down-regulates CYP1A1 through transcriptional and posttranslational mechanisms. In addition, HO-1 is involved in the As(III)-mediated down-regulation of CYP1A1 at the catalytic activity level.
芳香烃受体 (AhR) 配体，以 2,3,7,8-四氯二苯并对二恶英 (TCDD) 为代表，和金属，以亚砷酸盐 (As(III)) 为代表，是环境共污染物，它们的分子相互作用可能会破坏致癌剂激活酶细胞色素 P450 1A1 (CYP1A1) 的协调调节。因此，在这项研究中，我们研究了 As(III) 和 TCDD 共暴露对 HepG2 细胞中 CYP1A1 表达的影响。我们的结果表明，As(III) 导致 TCDD 介导的 CYP1A1 mRNA、蛋白和催化活性水平的诱导呈剂量依赖性降低。As(III) 显著抑制 TCDD 介导的 AhR 依赖性荧光素酶报告基因表达的诱导，而不改变 CYP1A1 mRNA 的稳定性。此外，As(III) 增加血红素加氧酶-1 (HO-1) mRNA，同时进一步降低 CYP1A1 催化活性水平。当将竞争性 HO-1 抑制剂锡 mesoporphyrin 应用于 HepG2 细胞或用 HO-1 的 siRNA 转染细胞时，TCDD 介导的 CYP1A1 催化活性诱导的抑制作用部分恢复。用血红素或血红蛋白处理细胞部分恢复了 As(III) 介导的 CYP1A1 催化活性的抑制作用。另一方面，钴原卟啉 IX 增加了 HO-1 mRNA，同时降低了 CYP1A1 活性，但不影响 CYP1A1 mRNA，这可被 HO-1 siRNA 转染逆转。本研究表明，As(III) 通过转录和翻译后机制下调 CYP1A1。此外，HO-1 参与了 As(III) 介导的 CYP1A1 催化活性水平的下调。
