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

RING1B, a core Polycomb repressive complex 1 subunit, is a histone H2A ubiquitin ligase essential for development. RING1B is overexpressed in patients with luminal breast cancer (BC) and recruited to actively transcribed genes and enhancers co-occupied by the estrogen receptor alpha (ER alpha). Whether ER alpha-induced transcriptional programs are mediated by RING1B is not understood. We show that prolonged estrogen administration induces transcriptional output and chromatin landscape fluctuations. RING1B loss impairs full estrogen-mediated gene expression and chromatin accessibility for key BC transcription factors. These effects were mediated, in part, by RING1B enzymatic activity and nucleosome binding functions. RING1B is recruited in a cyclic manner to ER alpha, FOXA1, and GRHL2 cobound sites and regulates estrogen-induced enhancers and ER alpha recruitment. Last, ChIP exo revealed multiple binding events of these factors at single-nucleotide resolution, including RING1B occupancy approximately 10 base pairs around ER alpha bound sites. We propose RING1B as a key regulator of the dynamic, liganded-ER alpha transcriptional regulatory circuit in luminal BC.