AR interacts with GATA3 to induce a luminal epithelial phenotype in breast cancer through regulation of lineage-restricted genes [ER-negative_cell_line_ChIP-seq]

GATA3 transcription factor is considered critical for luminal development and differentiation in normal and malignant mammary epithelial cells (MECs). The androgen receptor (AR) has also been associated with luminal gene expression profiles in breast cancer, independent of the estrogen receptor (ER), and has been shown to promote a basal to luminal phenotype transition in mouse MECs. To date, the potential interaction of GATA3 and AR in transcriptional regulation of lineage driver genes in breast cancer has never been investigated. Our unbiased proteomic analysis identified GATA3 as a novel AR interacting protein in a variety of breast cancer cell types regardless of ER expression. We showed that AR and GATA3 interact in the cytoplasm and nucleus of normal and malignant breast epithelia, an interaction increased by androgen treatment. Androgen stimulation of breast cancer cells also induced nuclear translocation of AR and GATA3 and resulted in enrichment of co-localized AR and GATA3 chromatin binding events. Using ER+ and/or ER- breast cancer cell lines and ER+ patient-derived xenograft (PDX) models of breast cancer, we identified a conserved subset of AR agonist-induced AR and GATA3 co-occupied cis-regulatory elements across all models. Knockdown experiments indicated that GATA3 acts as an AR co-regulator to upregulate transcription of known luminal-lineage genes (e.g. EHF, AQP3, and KDM4B) and downregulate basal-lineage genes (e.g. SMAD3 and ELK3). Also, we showed an induction in the chromatin accessibility at those subsets of common AR-GATA3 cis-regulatory elements, which drive the luminal lineage identity in breast cancer upon androgen stimulation. Collectively, AR-GATA3 interaction and function provide a mechanism underpinning epithelial breast cancer cells that are classified as having a luminal mature transcriptome independent of ER status, through regulating the expression of lineage-restricted markers. Overall design: AR, GATA3, and H3K27ac ChIP-seq on two estrogen receptor-negative breast cancer cell lines (MDA-MB-453 and MFM-223) under serum-deplete conditions, after 4 h vehicle or DHT treatment.