Bromodomain-containing protein 4 (BRD4) is an intracellular protein that regulates expression of various cellular functions. This study investigated whether BRD4 inhibition can alter the immunomodulatory and antitumor effects of radiation therapy (RT). A murine breast cancer cell line was implanted into BALB/c mice. The dual-tumor model was used to evaluate the abscopal effects of RT. A total of 24 Gy was delivered and BRD4 inhibitor was injected intravenously. Tumor size was measured and in vivo imaging was performed to evaluate tumor growth. Flow cytometry and immunohistochemistry were performed to examine immunologic changes upon treatment. The combination of BRD4 inhibitor and RT significantly suppressed tumor growth compared to RT alone. BRD4 inhibitor reduced the size of the unirradiated tumor indicating that it may induce systemic immune responses. Expression of HIF-1α and PD-L1 in tumor was significantly downregulated by the BRD4 inhibitor. Proportion of M1 tumor-associated macrophages (TAMs) increased, and proportion of M2 TAMs decreased upon BRD4 inhibition. BRD4 inhibitor expanded CD4+ and CD8+ T cell populations and reduced the population of monocytic myeloid-derived suppressor cells (M-MDSCs). RT-induced splenic M-MDSCs decreased upon addition of BRD4 inhibitor. Therefore, addition of BRD4 inhibition significantly enhanced the systemic antitumor responses of local RT.

Respiratory Syncytial Virus (RSV) causes severe inflammation and airway pathology in children and the elderly by infecting the epithelial cells of the upper and lower respiratory tract. RSV replication is sensed by intracellular pattern recognition receptors upstream of the IRF and NF-B transcription factors. These proteins coordinate an innate inflammatory response via Bromodomain containing protein 4 (BRD4), a protein that functions as a scaffold for unknown transcriptional regulators. To better understand the pleiotropic regulatory function of BRD4, we examine the BRD4 interactome and identify how RSV infection dynamically alters it. To accomplish these goals, we leverage native immunoprecipitation and Parallel Accumulation – Serial Fragmentation (PASEF) mass spectrometry to examine BRD4 complexes isolated from human alveolar epithelial cells in the absence or presence of RSV infection. In addition, we explore the role of BRD4’s acetyl-lysine binding bromodomains in mediating these interactions by using a highly selective competitive bromodomain inhibitor. We identify 101 proteins that are significantly enriched in the BRD4 complex and are responsive to both RSV-infection and BRD4 inhibition. These proteins are highly enriched in transcription factors and transcriptional coactivators. Among them, we identify members of the AP1 transcription factor complex, a complex important in innate signaling and cell stress responses. We independently confirm the BRD4/AP1 interaction in primary human small airway epithelial cells. We conclude that BRD4 recruits multiple transcription factors during RSV infection in a manner dependent on acetyl-lysine binding domain interactions. This data suggests that BRD4 recruits transcription factors to target its RNA processing complex to regulate gene expression in innate immunity and inflammation.

While the mortality rates of cancer are generally declining, pancreatic cancer persists to be an exception with a 5-year-survival rate of less than 7%. Late diagnosis and resistance to conventional therapies contribute to high mortality rates in spite of the remarkable recent advances in cancer management and research. Consequently, there is an urgent need to find new and unconventional therapeutic targets to improve prognosis and survival of pancreatic cancer patients. In this review, we discuss the transcriptional effects of the most widely used epigenetic inhibitors in pancreatic cancer focusing on Bromodomain and Extraterminal domain (BET) and Histone Deacetylase (HDAC) inhibitors, which are currently highly promising therapeutic options. We suggest that these inhibitors can be better utilized at lower doses which exploit their transcriptional modulatory effects on pancreatic cancer transcriptional programs directed by specific factors such as MYC and FOXA1, rather than simply based on their anti-proliferative effects. This approach can potentially help avoid the intolerable adverse events frequently elicited by the use of these treatments at higher doses. In particular, we underscore the crucial role of distal regulatory elements in mediating the specific effects of these epigenetic inhibitors and propose using them in a more selective and prudent manner.

Most oral squamous cell carcinomas (OSCCs) arise from oral epithelial dysplasia; however, there is no useful marker for early OSCC detection, likely owing to the inability to continuously observe the carcinoma sequence. We aimed to establish an experimental model to observe changes in the sequential expression pattern of mRNA and protein in the same rat using liquid-based cytology techniques. Cytology specimens were collected from a 4-nitroquinoline 1-oxide-induced rat tongue cancer model at 2, 5, 8, 11, 14, 17, and 21 weeks. We examined candidate biomarker expression using immunocytochemistry and quantitative real-time PCR. The percentage of positively stained nuclei was calculated as the labeling index (LI). All rats had OSCC of the tongue at 21 weeks. Brd4 (Brd4), Myc (c-Myc), and Tp53 (p53) mRNA levels were upregulated during progression from negative for intraepithelial lesion or malignancy to SCC. Brd4- and c-Myc-LI were increased in low- and high-grade squamous intraepithelial lesions and SCC specimens. p53-LI was significantly increased in SCC specimens. Our experimental model allowed the observation of sequential morphological changes and mRNA and protein expression patterns in the same rat during carcinogenesis. By reducing the false negative rate, BRD4 and c-Myc can be useful markers for the early detection of OSCC.