Role of Epigenetic Mechanisms in Differential Regulation of the Dioxin-Inducible Human CYP1A1 and CYP1B1 Genes
Role of Epigenetic Mechanisms in Differential Regulation of the Dioxin-Inducible Human CYP1A1 and CYP1B1 Genes
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DOI：
10.1124/mol.110.064899
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发表时间：
2010-10-01
影响因子：
3.6
通讯作者：
Hankinson, Oliver
中科院分区：
文献类型：
--
作者：
Beedanagari, Sudheer R.;Taylor, Robert T.;Hankinson, Oliver
芳烃受体（AhR）通过与其增强子区域中的异生素响应元件（XRE）结合介导2，3，7，8-四氯二苯并-rho-二恶英（二恶英）对CYP 1A 1和CYP 1B 1的诱导。CYP 1A 1和CYP 1B 1在人MCF-7细胞中均可被二恶英诱导。然而，只有CYP 1A 1在人HepG 2细胞中是可诱导的。进一步的实验集中在为最后一个观察结果提供解释。二恶英诱导AHR和转录辅激活因子p300和p300/cAMP反应元件结合蛋白结合蛋白相关因子（PCAF）在HepG 2细胞中向CYP 1B 1增强子的募集，但未能诱导RNA聚合酶II（poIII）或TATA结合蛋白（TBP）的募集以及组蛋白3和4的乙酰化或组蛋白3在启动子处的甲基化。由于p300是二恶英诱导CYP 1B 1启动子处的上述组蛋白修饰和诱导CYP 1B 1转录（在MCF-7细胞中）所必需的，因此p300和AhR的募集虽然是必需的，但不足以引发对二恶英的上述反应。在增强子处的CpG二核苷酸内的胞嘧啶残基，包括XRE内的那些，被部分甲基化，而在启动子处的那些被完全甲基化。用5-氮杂-2 '-脱氧胞苷处理HepG 2细胞导致启动子部分去甲基化，恢复poIII和TBP结合，并诱导CYP 1B 1。因此，HepG 2细胞中CYP 1B 1诱导的缺陷可归因于启动子处的胞嘧啶甲基化，这阻止了TBP和poIII的募集。值得注意的是，我们的数据表明，稳定募集的p300和PCAF的CYP 1B 1基因不需要他们的拴系到启动子和增强子。
The aryl hydrocarbon receptor (AhR) mediates induction of CYP1A1 and CYP1B1 by 2,3,7,8-tetrachlorodibenzo-rho-dioxin (dioxin) via binding to xenobiotic-responsive elements (XREs) in their enhancer regions. CYP1A1 and CYP1B1 were both inducible by dioxin in human MCF-7 cells. However, only CYP1A1 was inducible in human HepG2 cells. Further experiments focused on providing an explanation for this last observation. Dioxin induced the recruitment of AHR and the transcriptional coactivators p300 and p300/cAMP response element-binding protein binding protein-associated factor (PCAF) to the CYP1B1 enhancer in HepG2 cells but failed to induce recruitment of RNA polymerase II (poIII) or the TATA binding protein (TBP) and acetylations of histones 3 and 4 or methylation of histone 3 at the promoter. Because p300 was required for dioxin induction of the aforementioned histone modifications at the CYP1B1 promoter and for induction of CYP1B1 transcription (in MCF-7 cells), the recruitments of p300 and AhR, although necessary, are not sufficient for eliciting the above responses to dioxin. Cytosine residues within CpG dinucleotides at the enhancer, including those within the XREs, were partially methylated, whereas those at the promoter were fully methylated. Treatment of HepG2 cells with 5-aza-2'-deoxycytidine led to partial demethylation of the promoter, restored poIII and TBP binding, and CYP1B1 inducibility. Thus, the deficiency of CYP1B1 induction in HepG2 cells is ascribable to cytosine methylation at the promoter, which prevents recruitment of TBP and poIII. It is noteworthy that our data indicate that stable recruitment of p300 and PCAF to the CYP1B1 gene does not require their tethering to the promoter and to the enhancer.