Estrogen induces dynamic ERa and RING1B recruitment to control gene and enhancer activities in luminal breast cancer

We have previously shown that RING1B, a core Polycomb Repressive Complex 1 subunit, is amplified in 22% of breast cancer patients. In ER+ breast cancer, RING1B functionally interacts and co-localizes with ERa at enhancers and actively transcibed genes to modulate oncogenic transcriptional programs. However, the molecular mechanisms underlying this interaction is unclear. Here we demonstrate that in ER+ breast cancer cells, prolonged estrogen (E2) administration induces fluctuations in transcriptional output and chromatin landscape. RING1B loss impairs full E2-mediated gene expression and chromatin accessibility at genomic loci where key breast cancer transcription factors bind. RING1B mediates E2-induced gene expression and chromatin architectural changes both dependently and independently of its enzymatic activity and nucleosomal binding ability. We found that RING1B is recruited to ER, FOXA1, and GRHL2 co-bound sites in a cyclic manner during E2 administration and regulates E2-induced enhancers and ER recruitment. Finally, we characterized the spacial organization pattern between ER, FOXA1, GRHL2, and RING1B on the chromatin at single-nucleotide resolution genome-wide. ChIP-seq of H3K27Ac, RING1B, ERa, and FOXA1 in T47D shCtrl and shRING1B cells in HD and after 45', 8h, and 24h of E2 treatment. Pair-end ATAC-seq of T47D shCtrl and shRING1B cells in HD and after 4h, 8h, 12h, and 24h of E2 in duplicates. RNA-seq of T47D shCtrl and shRING1B cells (same cells as the ATAC-seq) in HD and after 4h, 8h, 12h, and 24h of E2 in duplicates. RNA-seq of T47D cells expressing RING1B wild type, RING1B R98A, and RING1B I53A in HD and after 24h of E2 in duplicates. ChIP-exo of RING1B, ERa, FOXA1, and GRHL2 in T47D parental cells in HD and after 45' of E2 treatment. RNA-seq of T47D shRING1B cells rescued with exogenous RING1B wild type in HD and after 24h of E2 in duplicates.