ESR1 and breast cancer: Methylation-specific PCR analysis further revealed that ZEB1 overexpression in two luminal (MCF-7 and ZR-75-1) breast cancer cell types enhanced DNA methylation of the ER-α promoter (Figures 1d and e; Supplementary Figure S1c), whereas ZEB1 knockdown in two basal (MDA-MB-231 and SUM-159) breast cancer cell types (Figures 1f and g; Supplementary Figure S1d) reduced this methylation.