Breast cancer cell resistance to hormonal and targeted therapeutics is correlated with the inactivation of the NR6A1 axis

<b>Aim:</b> Resistance to hormonal and targeted therapies in breast cancer limits treatment efficacy. Epigenetic alterations, including changes mediated by DNA methyltransferases, play a key role in this process. Previously, we identified that resistance to tamoxifen and rapamycin is associated with the suppression of DNMT3A. This study aims to further explore the mechanisms underlying this suppression, with a focus on identifying NR6A1 as a novel regulatory factor. <b>Methods:</b> Acquisition of resistant breast cancer cell sublines, MTT-test, immunoblotting, transient transfection and reporter analysis, lentiviral infection, qRT-PCR, and analysis of methylation using bisulfite pyrosequencing. <b>Results:</b> Our findings indicate that the development of cross-resistance in breast cancer cells to hormonal and targeted therapies involves a shift in cell signaling to alternative AKT pathways, marked by a localized suppression of the NR6A1/DNMT3A axis and associated DNA methylation changes. We demonstrated the critical role of NR6A1 downregulation in resistance development. Additionally, we observed activation of Snail - a key regulator in the epithelial-mesenchymal transition - as a mediator of the effects of NR6A1 depletion, establishing a direct link between Snail expression and resistance formation. <b>Conclusion:</b> The coordinated suppression of NR6A1 and DNMT3A may contribute to sustaining the resistant phenotype in breast cancer cells. This pathway could serve as a predictive marker, helping guide the selection of optimal therapeutic strategies for breast cancer treatment in the future.