ESR1 and breast cancer: In accordance with these and previous studies demonstrating that ADP-ribosylation may have an impact on the activity of ERα and its cofactor FoxA1 in BC cells [20], we observed that PARP-1 is implicated in the regulation of the gene expression machinery mediated by ERα and FoxA1 in ERα Y537S mutated BC cells (Fig. 7A-B).