Faculty of Pharmacy & Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
Cell Biol Toxicol. 2010 Oct;26(5):421-34. doi: 10.1007/s10565-010-9153-7. Epub 2010 Mar 11.
We recently demonstrated that V(5+) downregulates 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated induction of Cyp1a1 mRNA, protein, and catalytic activity levels in Hepa 1c1c7 cells through transcriptional mechanism. Therefore, it is important to investigate whether similar changes occur in humans. For this purpose, we examined the effect of V(5+) (as ammonium metavanadate, NH(4)VO(3)) on the expression of aryl hydrocarbon receptor (AhR)-regulated gene; cytochrome P450 1A1 (CYP1A1) at each step of the AhR signal transduction pathway in human hepatoma HepG2 cells. Our results show a significant reduction in TCDD-mediated induction of CYP1A1 mRNA, protein, and activity levels after V(5+) treatment in a dose-dependent manner. Investigating the effect of co-exposure to V(5+) and TCDD at transcriptional levels revealed that V(5+) significantly inhibited TCDD-mediated induction of AhR-dependent luciferase reporter gene expression. Looking at the posttranscriptional level, V(5+) did not affect CYP1A1 mRNA stability, thus eliminating the possible role of V(5+) in modifying CYP1A1 gene expression through this mechanism. On the other hand, at the posttranslational level, V(5+) was able to significantly decrease CYP1A1 protein half-life contributing to the inconsistency between catalytic activity and transcriptional level. Importantly, we showed that V(5+) did not significantly alter the heme oxygenase-1 mRNA level, thus eliminating any possibility that V(5+) might have decreased CYP1A1 activity through affecting its heme content. This study demonstrates for the first time that V(5+) downregulates the expression of CYP1A1 at the transcriptional, posttranscriptional and posttranslational mechanisms in the human hepatoma HepG2 cells.
我们最近的研究表明，V(5+) 通过转录机制下调 Hepa 1c1c7 细胞中 2,3,7,8-四氯二苯并对二恶英（TCDD）介导的 Cyp1a1mRNA、蛋白和催化活性水平。因此，研究人类是否存在类似变化非常重要。为此，我们研究了 V(5+)（作为硫酸氧钒，NH(4)VO(3)）对人肝癌 HepG2 细胞芳烃受体（AhR）调控基因；细胞色素 P4501A1（CYP1A1）在 AhR 信号转导途径各个步骤的表达的影响。结果表明，V(5+)以剂量依赖的方式显著降低 TCDD 介导的 CYP1A1mRNA、蛋白和活性水平的诱导。在转录水平上研究 V(5+)和 TCDD 共同暴露的影响，结果表明 V(5+)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。在转录后水平上观察，V(5+)不影响 CYP1A1mRNA 稳定性，因此排除了 V(5+)通过这种机制改变 CYP1A1 基因表达的可能性。另一方面，在翻译后水平上，V(5+)能够显著降低 CYP1A1 蛋白半衰期，导致催化活性与转录水平之间的不一致。重要的是，我们表明 V(5+) 对血红素加氧酶-1mRNA 水平没有显著影响，因此排除了 V(5+) 通过影响其血红素含量而降低 CYP1A1 活性的可能性。本研究首次表明，V(5+) 下调 HepG2 细胞中 CYP1A1 的转录、转录后和翻译后表达机制。
