Inhibition of BRD4 suppresses tumor growth in prostate cancer via the enhancement of FOXO1 expression

Prostate cancer (PCa) is a malignant tumor with a high incidence in males. Localized tumors can be treated via surgery or radiation; however, it remains difficult to prevent disease progression. Bromodomain-containing protein 4 (BRD4) is an epigenetic reader protein that binds to acetylated lysine on histones and has been reported to serve critical roles in numerous types of cancers. In the present study, it was demonstrated that BRD4 expression levels were significantly increased in cancerous prostate tissue specimens and cells, which were associated with clinical stage and metastasis. In addition, the present study reported that inhibition of BRD4 via short hairpin RNA or JQ1 (a bromo-domain inhibitor) decreased PCa cell proliferation, induced G0/G1 cell cycle arrest and apoptosis, mitigated cell invasion and migration in vitro, and impaired tumor growth in vivo. Mechanistically, BRD4 inhibition-induced suppression of cell cycle progression was associated with the upregulation of p21 and cyclin D1. c-Myc and B-cell lymphoma-2 (Bcl-2), important genes responsible for cell cycle regulation and anti-apoptotic functions, were downregulated in response to BRD4 inhibition. Furthermore, the present study revealed that c-Myc expression was negatively regulated by p21, and that the induction of p21 via BRD4 inhibition was mediated by forkhead box protein O1 (FOXO1), rather than p53. In summary, the results of the present study suggested that the aberrant expression of BRD4 in PCa may induce carcinogenesis. In addition, a mechanism by which BRD4 inhibition suppresses cell proliferation via the regulation of FOXO1-p21-Myc signaling was proposed in the present study, which may contribute to the development of novel therapeutic approaches in the management of PCa.