Role of TET Dioxygenases and DNA Hydroxymethylation in Bisphenols-Stimulated Proliferation of Breast Cancer Cells.

BACKGROUND: Bisphenol A (BPA), a ubiquitous environmental endocrine disruptor targeting estrogen receptors (ERs), has been implicated in the promotion of breast cancer. Perinatal exposure of BPA could induce longitudinal alteration of DNA hydroxymethylation in imprinted loci of mouse blood cells. To date, no data has been reported on the effects of BPA on DNA hydroxymethylation in breast cells. Therefore, we asked whether BPA can induce DNA hydroxymethylation change in human breast cells. Given that dysregulated epigenetic DNA hydroxymethylation is observed in various cancers, we wondered how DNA hydroxymethylation modulates cancer development, and specifically, whether and how BPA and its analogs promote breast cancer development via DNA hydroxymethylation. OBJECTIVES: We aimed to explore the interplay of the estrogenic activity of bisphenols at environmental exposure dose levels with TET dioxygenase-catalyzed DNA hydroxymethylation and to elucidate their roles in the proliferation of ER+ breast cancer cells as stimulated by environmentally relevant bisphenols. METHODS: Human MCF-7 and T47D cell lines were used as ER-dependent breast cell proliferation models, and the human MDA-MB-231 cell line was used as an ER-independent breast cell model. These cells were treated with BPA or bisphenol S (BPS) to examine BPA/BPS-related proliferation. Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and enzyme-linked immunosorbent assays (ELISAs) were used to detect DNA hydroxymethylation. Crispr/Cas9 and RNA interference technologies, quantitative polymerase chain reaction (qPCR), and Western blot analyses were used to evaluate the expression and function of genes. Co-immunoprecipitation (Co-IP), bisulfite sequencing-PCR (BSP), and chromatin immunoprecipitation-qPCR (ChIP-qPCR) were used to identify the interactions of target proteins. RESULTS: We measured higher proliferation in ER' breast cancer cells treated with BPA or its replacement, BPS, accompanied by an ER alpha-dependent decrease in genomic DNA hydroxymethylation. The results of our overexpression, knockout, knockdown, and inhibition experiments suggested that TET2-catalyzed DNA hydroxymethylation played a suppressive role in BPA/BPS-stimulated cell proliferation. On the other hand, we observed that TET2 was negatively regulated by the activation of ER alpha (dimerized and phosphorylated), which was also induced by BPA/BPS binding. Instead of a direct interaction between TET2 and ER alpha, data of our Co-IP, BSP, and ChIP-qPCR experiments indicated that the activated ER alpha increased the DNA methyltransferase (DNMT)-mediated promoter methylation of TET2, leading to an inhibition of the TET2 expression and DNA hydroxymethylation. CONCLUSIONS: We identified a new feedback circuit of ERa activation-DNMT-TET2-DNA hydroxymethylation in ER+ breast cancer cells and uncovered a pivotal role of TET2-mediated DNA hydroxymethylation in modulating BPA/BPS-stimulated proliferation. Moreover, to our knowledge, we for the first time established a linkage among chemical exposure, DNA hydroxymethylation, and tumor-associated proliferation. These findings further clarify the estrogenic activity of BPA/BPS and its profound implications for the regulation of epigenetic DNA hydroxymethylation and cell proliferation.