Analysis of the impact of FOXA1 expression on MDA::ER E2-sensitive transcriptomes and ER cistromes [ChIP-Seq data]

The primordial actions of the estrogen receptor alpha (ER) in controlling breast cancer cells proliferation rate are particularly documented. However, reintroducing ER into ER-negative cells does not reprogram their transcriptome towards an estrogen-sensitive growth phenotype. Member of the Forkhead (FKH) family of transcription factors, FOXA1 has been characterized to be essential for the appropriate binding of ER onto chromatin in MCF-7 cells. FOXA1 pioneering actions involve modulations of histone post-translational modifications (HPTMs) and local depletion in methylated CpGs. Using MDA-MB231 cells which are ER and FOXA1 negative, we aimed at determining whether the introduction of ER and FOXA1 would be sufficient to restore an estrogen-sensitive growth and to coincidently reprogram chromatin. We used ChIP-seq experiments to map ER and FOXA1 binding sites (BSs) and to profile H3K4me2 and H3K27ac marks, and surprisingly observed that FOXA1 had rather a global negative impact on ER actions, associated with an inhibition of growth and a reorientation of the transcriptome of the cells towards cell death. We demonstrate that the re-introduction of FOXA1 in these cells actually competes for the binding and pioneering actions of FOXA2, another FKH protein, on a number of ER BSs. As demonstrated for its alter ego FOXA1 in MCF-7 cells, abrogating FOXA2 expression drastically diminished ER binding onto its cognate sites, associated with a local loss of HPTMs for active chromatin. Whole-genome analysis of estrogen receptor (ER) and its FOXA1 and/or FOXA2 pioneering factors binding events associated with the cartography of two histone marks (H3K4me2 and H3K27ac) in four ER/FOXA1 positive or negative breast cancer cells.