DNMT1 and breast cancer: Collectively, these results demonstrate that although ZC3H18 depletion reduces BRCA1 expression in both ovarian and breast cancer cells, the mechanisms underlying ZC3H18 regulation of BRCA1 differs in the two cells types, with ZC3H18 regulating the recruitment of E2F1 and DNMT1 to the BRCA1 promoter to repress transcription in ovarian cancer cells.