Regulation of DNA Methylation at Enhancers by TET2 Finetunes Gene Transcription in ERa-Positive Breast Cancer Cells

Background: Aberrant DNA methylation is an epigenetic hallmark of most malignant tumors including breast cancer. However, the exact role of TET2-mediated DNA demethylation in ERa-positive luminal breast cancer is not well understood. Results: Here we showed by TCGA analyses that lower TET2 mRNA expression level is associated with worse clinical outcomes (i.e., overall survival) in ERa-positive but not ERa-negative breast cancer. Moreover, depletion of TET2 by CRISPR/Cas9 results in increased tumorigenesis capability of MCF7 cells in vitro. Whole genome bisulfite sequencing (WGBS) analysis revealed that DNA hypermethylation (gain-of-5mC) occurs within a subgroup of enhancers including estrogen responsive element (EREs) in MCF7 cells upon TET2 depletion. ChIP-seq and RNA-seq analysis showed that TET2 depletion impairs E2-induced ERa binding to these 'gain-of-5mC' EREs and gene transcription. Conclusions: Our data suggest that TET2-mediated enhancer DNA demethylation fine-tunes ERa-dependent and independent gene transcription in ERa-positive breast cancer cells. Overall design: We used WGBS-seq, ChIP-seq and RNA-seq to study the regulation role of TET2 on the relationship among DNA methylation, histone modification and gene transcription in ERa positive MCF7 cell line.