IL-1β induced methylation of the estrogen receptor ERα gene correlates with EMT and chemoresistance in breast cancer cells.

Inflammation has been recently acknowledged as a key participant in the physiopathology of oncogenesis and tumor progression. The inflammatory cytokine IL-1β has been reported to induce the expression of markers associated with malignancy in breast cancerous cells through Epithelial-Mesenchymal Transition (EMT). Aggressive breast cancer tumors classified as Triple Negative do not respond to hormonal treatment because they lack three crucial receptors, one of which is the estrogen receptor alpha (ERα). Expression of ERα is then considered a good prognostic marker for tamoxifen treatment of this type of cancer, as the binding of this drug to the receptor blocks the transcriptional activity of the latter. Although it has been suggested that inflammatory cytokines in the tumor microenvironment could regulate ERα expression, the mechanism(s) involved in this process have not yet been established. We show here that, in a cell model of breast cancer cells (6D cells), in which the inflammatory cytokine IL-1β induces EMT by activation of the IL-1β/IL-1RI/β-catenin pathway, the up regulation of TWIST1 leads to methylation of the ESR1 gene promoter. This epigenetic modification produced significant decrease of the ERα receptor levels and increased resistance to tamoxifen. The direct participation of IL-1β in these processes was validated by blockage of the cytokine-induced signaling pathway by wortmannin inactivation of the effectors PI3K/AKT. These results support our previous reports that have suggested direct participation of the inflammatory cytokine IL-1β in the transition to malignancy of breast cancer cells.