Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton AB, Canada T6G 2N8.
Toxicol Appl Pharmacol. 2010 Nov 15;249(1):55-64. doi: 10.1016/j.taap.2010.08.014. Epub 2010 Aug 20.
Harman is a common compound in several foods, plants and beverages. Numerous studies have demonstrated its mutagenic, co-mutagenic and carcinogenic effects; however, the exact mechanism has not been fully identified. Aryl hydrocarbon receptor (AhR) is a transcription factor regulating the expression of the carcinogen-activating enzyme; cytochrome P450 1A1 (CYP1A1). In the present study, we examined the ability of harman to induce AhR-mediated signal transduction in human and rat hepatoma cells; HepG2 and H4IIE cells. Our results showed that harman significantly induced CYP1A1 mRNA in a time- and concentration-dependent manner. Similarly, harman significantly induced CYP1A1 at protein and activity levels in a concentration-dependent manner. Moreover, the AhR antagonist, resveratrol, inhibited the increase in CYP1A1 activity by harman. The RNA polymerase inhibitor, actinomycin D, completely abolished the CYP1A1 mRNA induction by harman, indicating a transcriptional activation. The role of AhR in CYP1A1 induction by harman was confirmed by using siRNA specific for human AhR. The ability of harman to induce CYP1A1 was strongly correlated with its ability to stimulate AhR-dependent luciferase activity and electrophoretic mobility shift assay. At post-transcriptional and post-translational levels, harman did not affect the stability of CYP1A1 at the mRNA and the protein levels, excluding other mechanisms participating in the obtained effects. We concluded that harman can directly induce CYP1A1 gene expression in an AhR-dependent manner and may represent a novel mechanism by which harman promotes mutagenicity, co-mutagenicity and carcinogenicity.
哈尔曼是几种食物、植物和饮料中的常见化合物。大量研究表明其具有致突变性、协同致突变性和致癌性；然而，确切的机制尚未完全确定。芳烃受体（AhR）是一种调节致癌剂激活酶细胞色素 P450 1A1（CYP1A1）表达的转录因子。在本研究中，我们研究了哈尔曼在人肝癌细胞 HepG2 和 H4IIE 细胞以及大鼠肝癌细胞中诱导 AhR 介导的信号转导的能力。结果表明，哈尔曼以时间和浓度依赖的方式显著诱导 CYP1A1mRNA 的表达。同样，哈尔曼以浓度依赖的方式显著诱导 CYP1A1 的蛋白和活性水平。此外，AhR 拮抗剂白藜芦醇抑制了哈尔曼对 CYP1A1 活性的增加。RNA 聚合酶抑制剂放线菌素 D 完全消除了哈尔曼对 CYP1A1mRNA 的诱导，表明其为转录激活。使用针对人 AhR 的 siRNA 证实了 AhR 在哈尔曼诱导 CYP1A1 中的作用。哈尔曼诱导 CYP1A1 的能力与它刺激 AhR 依赖性荧光素酶活性和电泳迁移率变动分析的能力密切相关。在转录后和翻译后水平上，哈尔曼对 CYP1A1mRNA 和蛋白水平的稳定性没有影响，排除了其他参与获得的效应的机制。我们得出结论，哈尔曼可以以 AhR 依赖性的方式直接诱导 CYP1A1 基因表达，可能代表了哈尔曼促进致突变性、协同致突变性和致癌性的一种新机制。
