ESR1 and breast cancer: Small interfering RNA (siRNA) raised against DNMT1 has been shown to restore estrogen receptor-alpha (ERα) signaling in ERα-negative human breast cancer cell lines, thus enabling the use of antiestrogens as therapy [124] while overexpression of a dominant-negative histone H3 lysine 27 mutant (H3K27R) de-repressed epigenetically silenced tumor suppressor genes and reversed drug-resistance in ovarian cancer cells [65].