SAT426 Long-term Nanomolar Bisphenol A (BPA) Exposure of MCF7 Cells Induces DNA Methylation Changes

Disclosure: S.L. Dela Cruz: None. M.C. Velarde: None. P.D. Bagamasbad: None. Breast cancer (BCa) has the highest worldwide prevalence and mortality rate among cancers. For ER-positive luminal BCa, hormone deprivation therapy using drugs that inhibit the estrogen signaling axis is commonly employed. However, activation of ER may persist due to the presence of endocrine disrupting chemicals (EDCs) that are structurally similar to endogenous estrogens. Bisphenol A (BPA) is a known EDC found in consumer products and has been associated with increased BCa risk in various animal models. Mechanistically, BPA weakly binds and activates ER resulting in transcriptional changes. In addition, studies show that BPA potentially reprograms the epigenome through changes in DNA methylation. While methylome studies on BPA-exposed cancer models have been conducted, to the best of our knowledge, this has not been done on luminal BCa cells chronically exposed to environmentally relevant doses of BPA. The use of a chronic, nanomolar-dose treatment paradigm is significant as it more accurately reflects non-occupational environmental exposure. In this study, we investigated the epigenetic effects of chronic (8 weeks) nanomolar doses (10 nM) of BPA on the ER-positive BCa cell line MCF7. We probed single gene-level DNA methylation through Bisulfite Sequencing PCR (BSP) and genome-wide methylation through Reduced Representation Bisulfite PCR (RRBS). In silico analysis of publicly available data identified potential differentially methylated regions (DMRs) upon chronic BPA treatment. BSP showed minimal changes in methylation levels of CpGs within the target DMRs, while gene expression analysis via RT-qPCR did not find significant changes in mRNA levels of genes encompassing the target regions. Methylome-wide profiling of chronically treated cells identified DMRs that fall under gene promoters (DMPs) and gene coding regions (DMGs). Pathway analysis of DMPs indicated an association with death receptor signaling, with an overall predicted effect in inhibiting apoptosis. Network analysis revealed genes encompassing DMPs that interact with the BCa markers ESR1/2, BRCA1, and PGR. Based on the pathway and network analyses, we selected 8 genes for gene expression analysis and found that the expression of all 8 genes are unchanged following chronic BPA treatment. Taken together, our results show that chronic BPA exposure of MCF7 can induce subtle changes in DNA methylation. Although initial validation did not reveal changes in gene expression associated with differential methylation, we speculate that the incremental DNA methylation changes could accumulate over time resulting in further ER signaling dysregulation, exacerbating the BCa phenotype. Presentation: Saturday, June 17, 2023