Role of BRD4 and histone acetylation in estrogen receptor-positive breast cancers
von Sankari Nagarajan
Datum der mündl. Prüfung:2015-05-18
Betreuer:Prof. Dr. Steven Johnsen
Gutachter:Prof. Dr. Dieter Kube
Gutachter:Dr. Shcherbata Halyna
EnglischThe estrogen receptor-α (ERα) acts as a nuclear transcription factor to promote estrogen-induced transcription and plays a central role in the progression of ER-positive tumors. ERα binds to the consensus DNA elements referred to as Estrogen Response Elements (EREs) which act as enhancers mostly occupying distal regions. In our study, we show that Bromodomain-containing protein, BRD4 depletion/inhibition regulates estrogen-induced transcription by affecting RNA polymerase II (RNAPII) and histone monoubiquitination in ER-positive MCF7 cells. Furthermore, BRD4 controls the proliferation of breast and endometrial cancer cell lines in vitro and estrogen-dependent uterine growth in vivo. Genome-wide studies demonstrate the increased occupancy of BRD4 near transcriptional start sites (TSS) upon estrogen stimulation and BRD4 inhibition decreases estrogen-stimulated H2B monoubiquitination across gene bodies substantially on the genes which display estrogen-induced de novo polymerase recruitment. Consistently, BRD4 binding correlates with active transcriptional marks on the promoters. Moreover, BRD4 also occupies ERα and FOXA1-bound distal elements after the appearance of ERα, H3K27ac and Cohesin. Interestingly, BRD4 inhibition regulates the RNAPII recruitment as well as phosphorylation on distal regions and inhibits the production of enhancer RNAs (eRNAs). Altogether these findings establish a specific coactivator function of BRD4 in estrogen-dependent transcription (Nagarajan et al., 2014). BRD4 binds to the acetylated chromatin preferentially on histone H4 at Lys 5, 8, 12 and 16 residues. In our study, we also show that the presence of H4K12ac correlates with BRD4 occupancy during estrogen-driven transcription. Consistent with BRD4 binding, H4K12ac occupancy increases adjacent to estrogen-induced gene promoters and distal ERα-bound regions. H4K12ac is correlated with eRNA transcription and RNAPII occupancy on enhancers. Surprisingly, H4K12ac occupancy is increased in ER-positive cell lines compared to ER-negative cell lines and estrogen promotes global acetylation of H4K12ac in ER-positive cells. Notably, estrogen-induced H4K12ac occupancy is highly dependent on ERα expression and activity. Altogether these findings confirm the importance of H4K12ac and BRD4 in ERα-induced transcription and provide a strong rationale for the development of Summary XII potential therapeutic approaches for targeting histone acetylation and BRD4 in ERα-positive breast tumors (Nagarajan et al., 2015).
Keywords: Bromodomain; Histone acetylation; Estrogen receptor; epigenetics; Enhancer RNA; Histone modifications