Department of Biochemistry, Western University, London, ON, Canada.
Department of Oncology, Western University, London, ON, Canada.
Epigenetics Chromatin. 2018 Jan 29;11(1):5. doi: 10.1186/s13072-018-0176-2.
The estrogen receptor (ER) is a ligand-dependant transcription factor expressed in many breast cancers and is the target of many endocrine-based cancer therapies. Genome-wide studies have shown that the ER binds to gene-specific enhancer regions in response to β-estradiol (E2) which undergo transcription producing noncoding enhancer RNA (eRNA). While eRNAs are important for transcriptional activation of neighboring genes, the mechanism remains poorly understood.
Using ChIP-Seq we generate a global profile of thymine DNA glycosylase (TDG), an ER coactivator that plays an essential role in DNA demethylation, in response to E2 in the MCF7 breast cancer cell line. Remarkably, we found that in response to E2 TDG localized to enhancers which also recruit ERα, RNA Pol II and other coregulators and which are marked by histone modifications indicative of active enhancers. Importantly, depletion of TDG inhibits E2-mediated transcription of eRNAs and transcription of ER-target genes. Functionally, we find that TDG both sensitizes MCF7 cells to tamoxifen-mediated cytostasis and increases migration and invasion of MCF7 cells.
Taken together we find that TDG plays a central role in mediating transcription at a subset of enhancers and governs how MCF7 cells respond to both estrogenic and anti-estrogenic compounds and may be an effective therapeutic target.
雌激素受体（ER）是许多乳腺癌中表达的配体依赖性转录因子，也是许多基于内分泌的癌症治疗的靶点。全基因组研究表明，ER 结合到基因特异性增强子区域，以响应β-雌二醇（E2），从而进行转录产生非编码增强子 RNA（eRNA）。虽然 eRNAs 对于邻近基因的转录激活很重要，但机制仍不清楚。
我们使用 ChIP-Seq 生成了胸腺嘧啶 DNA 糖基化酶（TDG）的全局图谱，TDG 是一种 ER 共激活因子，在 DNA 去甲基化中发挥着重要作用，它对 MCF7 乳腺癌细胞系中的 E2 有反应。值得注意的是，我们发现，E2 响应时，TDG 定位于增强子，增强子也招募 ERα、RNA Pol II 和其他核心调节剂，并且被标记为活跃增强子的组蛋白修饰。重要的是，TDG 的耗竭抑制了 E2 介导的 eRNA 和 ER 靶基因的转录。功能上，我们发现 TDG 既使 MCF7 细胞对他莫昔芬介导的细胞停滞敏感，又增加 MCF7 细胞的迁移和侵袭。
总之，我们发现 TDG 在介导一组增强子的转录中起着核心作用，并控制 MCF7 细胞对雌激素和抗雌激素化合物的反应方式，可能是一个有效的治疗靶点。
