Department of Surgery, University of Iowa, Iowa City, IA 52242-1086, USA.
Oncogene. 2013 Aug 22;32(34):4043-51. doi: 10.1038/onc.2012.400. Epub 2012 Sep 10.
The complexity of gene regulation has created obstacles to defining mechanisms that establish the patterns of gene expression characteristic of the different clinical phenotypes of breast cancer. TFAP2C is a transcription factor that has a critical role in the regulation of both estrogen receptor-alpha (ERα) and c-ErbB2/HER2 (Her2). Herein, we performed chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in four breast cancer cell lines. Comparing the genomic binding sites for TFAP2C, we identified that glutathione peroxidase (GPX1) is regulated by TFAP2C through an AP-2 regulatory region in the promoter of the GPX1 gene. Knockdown of TFAP2C, but not the related factor TFAP2A, resulted in an abrogation of GPX1 expression. Selenium-dependent GPX activity correlated with endogenous GPX1 expression and overexpression of exogenous GPX1 induced GPX activity and significantly increased resistance to tert-butyl hydroperoxide. Methylation of the CpG island encompassing the AP-2 regulatory region was identified in cell lines where TFAP2C failed to bind the GPX1 promoter and GPX1 expression was unresponsive to TFAP2C. Furthermore, in cell lines where GPX1 promoter methylation was associated with gene silencing, treatment with 5'-aza-2-deoxycytidine (5'-aza-dC) (an inhibitor of DNA methylation) allowed TFAP2C to bind to the GPX1 promoter resulting in the activation of GPX1 RNA and protein expression. Methylation of the GPX1 promoter was identified in ∼20% of primary breast cancers and a highly significant correlation between the TFAP2C and GPX1 expression was confirmed when considering only those tumors with an unmethylated promoter, whereas the related factor, TFAP2A, failed to demonstrate a correlation. The results demonstrate that TFAP2C regulates the expression of GPX1, which influences the redox state and sensitivity to oxidative stress induced by peroxides. Given the established role of GPX1 in breast cancer, the results provide an important mechanism for TFAP2C to further influence oncogenesis and progression of breast carcinoma cells.
基因调控的复杂性给确定建立乳腺癌不同临床表型特征的基因表达模式的机制造成了障碍。TFAP2C 是一种转录因子，在雌激素受体-α（ERα）和 c-ErbB2/HER2（Her2）的调控中具有关键作用。在此，我们在四种乳腺癌细胞系中对 TFAP2C 进行了染色质免疫沉淀和直接测序（ChIP-seq）。比较 TFAP2C 的基因组结合位点，我们发现谷胱甘肽过氧化物酶（GPX1）受 TFAP2C 调控，其通过 GPX1 基因启动子中的 AP-2 调控区进行调控。TFAP2C 的敲低，但不是相关因子 TFAP2A，导致 GPX1 表达的中断。硒依赖性 GPX 活性与内源性 GPX1 表达相关，外源性 GPX1 的过表达诱导 GPX 活性并显著增加对叔丁基过氧化物的抗性。在 TFAP2C 未能结合 GPX1 启动子且 GPX1 表达对 TFAP2C 无反应的细胞系中，鉴定出包含 AP-2 调控区的 CpG 岛的甲基化。此外，在与基因沉默相关的 GPX1 启动子甲基化的细胞系中，用 5'-氮杂-2'-脱氧胞苷（5'-aza-2'-脱氧胞苷）（一种 DNA 甲基化抑制剂）处理可使 TFAP2C 结合到 GPX1 启动子上，从而激活 GPX1 RNA 和蛋白表达。在约 20%的原发性乳腺癌中发现了 GPX1 启动子的甲基化，当仅考虑那些启动子未甲基化的肿瘤时，TFAP2C 和 GPX1 表达之间存在高度显著的相关性，而相关因子 TFAP2A 则未能表现出相关性。结果表明，TFAP2C 调节 GPX1 的表达，这影响了由过氧化物诱导的氧化还原状态和对氧化应激的敏感性。鉴于 GPX1 在乳腺癌中的既定作用，该结果为 TFAP2C 进一步影响乳腺癌细胞的癌变和进展提供了一个重要的机制。
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