ESR1 and breast cancer: Similar to ER + breast cancer cells, ER-negative and non-tumorigenic breast cell lines, which lack BRRIAR expression but retain H3K27ac binding at the 5’ and 3’ ends of the enhancer cluster (Supplementary Fig. 2a), showed strong interactions between the enhancer and BHLHE40, and a weaker interaction with EDEM1 (Supplementary Fig. 2e).