Long-term intermittent estradiol exposure induces epithelial-mesenchymal transition-like plasticity in MCF10A cells.

Epidemiological evidence links prolonged menstrual duration with breast cancer risk, yet its underlying mechanisms remain unclear. Given that the estradiol levels fluctuate during the menstrual cycle, we hypothesized that the temporal pattern of exposure, rather than the cumulative amount of estradiol, may critically influence the state of epithelial cells. Using the non-tumorigenic mammary epithelial cell line MCF10A, we compared the long-term effects between continuous and intermittent estradiol stimulations over a period of 40 weeks. Intermittent exposure induced a spindle-like morphology, reduced cellular adhesion, and sustained proliferation, defining a cell population that we termed Estradiol Long-term Intermittently Exposed (ELITE) cells. These changes were partially reversible after hormone withdrawal. Transcriptome analysis showed that the ELITE cells uniquely upregulated an epithelial-mesenchymal transition-associated program involving ZEB1 and ZEB2. ATAC-seq revealed corresponding changes in chromatin accessibility, including enrichment of the ZEB1/2 binding sites near epithelial genes. Together, these findings suggest that long-term fluctuating hormonal signals can reprogram the epithelial cells into a more plastic state, highlighting the importance of exposure patterns in shaping cell state transitions. In this ERα/ERβ-negative model, estradiol effects may be mediated through non-canonical pathways such as GPER.