Decoding Bromodomain and Extra-Terminal Domain Protein-Mediated Epigenetic Mechanisms in Human Uterine Fibroids

Uterine Fibroids (UFs) are the most common benign tumors in women of reproductive age, affecting ~77% of women overall and are clinically manifest in ~25% by age 50. Bromodomain and extra-terminal domain (BET) proteins play key roles in epigenetic transcriptional regulation, influencing many biological processes, such as proliferation, differentiation, and DNA damage response. Although BET dysregulation contributes to various diseases, their specific role in the pathogenesis of UFs remains largely unexplored. The present study aimed to determine the expression pattern of BET proteins in UFs and matched myometrium and further assess the impact of BET inhibitors on UF phenotype and epigenetic changes. Our studies demonstrated that the levels of Bromodomain-containing protein (BRD)2 and detection rate of BRD4 were significantly altered in UFs compared to matched myometrium, suggesting that aberrant BET protein expression may contribute to the pathogenesis of UFs. To investigate the biological effects of BET proteins, two small-molecule inhibitors, JQ1 and I-BET762, were used to assess their impact on UF cell behavior and transcriptomic profiles. Targeted inhibition of BET proteins markedly reduced UF cell viability compared with myometrial cells and induced cell cycle arrest. Unbiased transcriptomic profiling coupled with bioinformatic analysis revealed that BET inhibition altered multiple biological pathways, including G2M checkpoint, E2F targets, mitotic spindle, mTORC1 signaling, TNF-α signaling via NF-κB, and inflammatory response, as well as reprogrammed the UF cell epigenome. Notably, BET inhibition decreased the expression of several genes encoding extracellular matrix (ECM) proteins, a hallmark of UFs. Collectively, these results support that BET proteins play a pivotal role in regulating key signaling pathways and cellular processes in UFs. Targeting BET proteins may therefore represent a promising non-hormonal therapeutic strategy for UF treatment.