Fretland Adrian J, Safe Stephen, Hankinson Oliver
Department of Pathology and Laboratory Medicine, Jonsson Comprehensive Cancer Center, Center for Health Sciences, University of California, Los Angeles, CA 90095-1732, USA.
Chem Biol Interact. 2004 Nov 20;150(2):161-70. doi: 10.1016/j.cbi.2004.09.007.
Regulation of gene expression by the aryl hydrocarbon (AHR) receptor is a much-studied pathway of molecular toxicology. Activation of AHR by the xenobiotic ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is hypothesized as the mechanism by which TCDD exerts its toxic and carcinogenic effects. Paradoxically, some studies have shown that TCDD acts as an antiestrogen. This has led to the hypothesis that so-called selective aryl hydrocarbon receptor modulators (SAhRMs), AHR ligands that retain the antiestrogenic effects but lack the transcriptional effects of TCDD associated with toxicity, may be utilized as cancer chemotherapeutics in conjunction with other antiestrogenic compounds such as tamoxifen. The present study attempts to further define the molecular mechanism of action of the putative SAhRMs, 6-alkyl-1,3,8-trichlorodibenzofuran (6-MCDF), and diindolylmethane (DIM), focusing particularly on the former. We tested 6-MCDF and DIM for the recruitment of AHR and RNA polymerase II (pol II) to the regulatory region of the AHR responsive gene, cytochrome P4501A1 (CYP1A1), using the chromatin immunoprecipitation (ChIP) assay in the mouse hepatoma cell line Hepa-1c1c7 (Hepa-1). We also tested the level of CYP1A1 induction in Hepa-1 cells using quantitative real-time PCR. We show no difference in the recruitment of AHR or pol II to the regulatory region of CYP1A1 in response to TCDD, 6-MCDF, or co-treatment with both TCDD and 6-MCDF. Our results also show no antagonism of CYP1A1 induction with co-treatment of Hepa-1 cells with TCDD and 6-MCDF. These data suggest that 6-MCDF exhibits agonist activity with respect to induction of CYP1A1 in the Hepa-1 cell line.
芳烃（AHR）受体对基因表达的调控是分子毒理学中一个被广泛研究的途径。异源生物配体2,3,7,8 - 四氯二苯并 - p - 二恶英（TCDD）激活AHR被认为是TCDD发挥其毒性和致癌作用的机制。矛盾的是，一些研究表明TCDD具有抗雌激素作用。这导致了一种假说，即所谓的选择性芳烃受体调节剂（SAhRMs），即保留抗雌激素作用但缺乏与毒性相关的TCDD转录作用的AHR配体，可能与他莫昔芬等其他抗雌激素化合物联合用作癌症化疗药物。本研究试图进一步确定推定的SAhRMs，6 - 烷基 - 1,3,8 - 三氯二苯并呋喃（6 - MCDF）和二吲哚甲烷（DIM）的分子作用机制，尤其关注前者。我们在小鼠肝癌细胞系Hepa - 1c1c7（Hepa - 1）中使用染色质免疫沉淀（ChIP）试验，测试了6 - MCDF和DIM将AHR和RNA聚合酶II（pol II）募集到AHR反应基因细胞色素P4501A1（CYP1A1）调控区域的情况。我们还使用定量实时PCR测试了Hepa - 1细胞中CYP1A1的诱导水平。我们发现，在TCDD、6 - MCDF或TCDD与6 - MCDF联合处理后，AHR或pol II募集到CYP1A1调控区域没有差异。我们的结果还表明，TCDD和6 - MCDF联合处理Hepa - 1细胞时，对CYP1A1诱导没有拮抗作用。这些数据表明，6 - MCDF在Hepa - 1细胞系中对CYP1A1的诱导表现出激动剂活性。
