The Polycomb protein RING1B enables estrogen-mediated gene expression by promoting enhancer-promoter interaction and R-loop formation

Polycomb complexes have traditionally been prescribed roles as transcriptional repressors, though increasing evidence demonstrate they can also activate gene expression. However, the mechanisms underlying positive gene regulation mediated by Polycomb proteins are poorly understood. Here, we show that RING1B, a core component of Polycomb Repressive Complex 1, regulates enhancer-promoter interaction of the bona fide estrogen-activated GREB1 gene. Systematic characterization of RNA:DNA hybrid formation (R-loops), nascent transcription, and RNA Pol II activity upon estrogen administration revealed a key role of RING1B in gene activation by regulating R-loop formation and RNA Pol II elongation. We also found that the estrogen receptor (ER) and RNA are both necessary for full RING1B recruitment to estrogen-activated genes. Notably, RING1B recruitment was mostly unaffected upon RNA Pol II depletion by triptolide. Our findings delineate the functional interplay between RING1B, RNA, and ER to safeguard chromatin architecture perturbations required for estrogen-mediated gene regulation, and highlight the crosstalk between steroid hormones and Polycomb proteins to regulate oncogenic programs. ChIP-seq of RING1B, ERa, and RNA Pol II in T47D cells treated with DMSO or Triptolide (10 uM) for 9 hours in HD and after 45' of E2 treatment. RING1B and ERa ChIP-seq are provided in duplicates. Pair-end ATAC-seq of T47D shCtrl and shRING1B cells in HD and after45' of E2 in duplicates. RNA-seq of T47D shCtrl and shRING1B cells in HD and after 45' of E2 in duplicates. RING1B and ERa rChIP of T47D cells treated with DMSO for 9 hours followed by E2 for 45' provided in duplicates. DRIP-seq of T47D cells in HD and after 45' of E2 along with negative controls. DRIP-seq of T47D shCtrl and shRING1B cells in HD and after 45' of E2 along with negative controls. 4C-seq of T47D shCtrl and shRING1B cells in HD and after 45' of E2.