BRD4 promotes p63 and GRHL3 expression downstream of FOXO in mammary epithelial cells

Abstract

Bromodomain-containing protein 4 (BRD4) is a member of the bromo- and extraterminal (BET) domain-containing family of epigenetic readers which is under intensive investigation as a target for anti-tumor therapy. BRD4 plays a central role in promoting the expression of select subsets of genes including many driven by oncogenic transcription factors and signaling pathways. However, the role of BRD4 and the effects of BET inhibitors in non-transformed cells remain mostly unclear. We demonstrate that BRD4 is required for the maintenance of a basal epithelial phenotype by regulating the expression of epithelial-specific genes including TP63 and Grainy Head-like transcription factor-3 (GRHL3) in non-transformed basal-like mammary epithelial cells. Moreover, BRD4 occupancy correlates with enhancer activity and enhancer RNA (eRNA) transcription. Motif analyses of cell context-specific BRD4-enriched regions predicted the involvement of FOXO transcription factors. Consistently, activation of FOXO1 function via inhibition of EGFR-AKT signaling promoted the expression of TP63 and GRHL3. Moreover, activation of Src kinase signaling and FOXO1 inhibition decreased the expression of FOXO/BRD4 target genes. Together, our findings support a function for BRD4 in promoting basal mammary cell epithelial differentiation, at least in part, by regulating FOXO factor function on enhancers to activate TP63 and GRHL3 expression.

RUNX2 expression in thyroid and breast cancer requires the cooperation of three non-redundant enhancers under the control of BRD4 and c-JUN

“…Finally, we observed that JQ1 treatment profoundly inhibits RAINs expression with a stronger effect than the one observed on RUNX2 expression (Figure 8F ). This is coherent with the observation that BRD4 controls the transcription of non-coding RNAs from regulatory ENHs ( 49 , 50 ). These data describe a new family of RUNX2 associated intergenic lncRNAs and envisage a functional relationship between RUNX2 and its cognate lncRNAs in cancer.…”

p53-R273H promotes cancer cell migration via upregulation of neuraminidase-1

“…The question remains how p53-R273H promotes NEU1 expression. It has been demonstrated that activated AKT signaling regulates a series of gene transcription pathways, including c-Myc and p63 36 . Interestingly, it has been shown that mutant p53 can activate AKT signaling by enhancing EGFR trafficking 18 .…”

Super enhancers – new analyses and perspectives on the low hanging fruit

“…While the frequent association of SE with master regulators may justify the recent interest in their characterization, SEs may simply be the "low hanging fruit" of enhancers that can prejudice our investigations and prevent us from identifying other important regulatory elements that can have significant impacts and effects. Instead, a differential occupancy approach as we recently described, 7,8 may provide a more effective approach to identify functionally important enhancers and their underlying transcription factor networks.…”

“…7 Similarly, we showed that the majority of BRD4enriched regions in mammary epithelial cells were associated with putative enhancers. 8 Remarkably, more than one-third of epithelial-to-mesenchymal transition-related genes showed an enrichment of BRD4 at an adjacent distal region. Overall, enhancers emerge as a common and decisive mechanism in BRD4-mediated regulation of gene transcription.…”

“…However, the exact characteristics that render an enhancer "super" and not "typical" are still poorly defined and fairly arbitrary. In our previous work, 7,8 we identified potential enhancers important for mediating tissuespecific BRD4 activity using a differential occupancy approach, independent of "super" classification. This work resulted in important insights into BRD4 function at putative distal enhancer regions, which could be functionally verified in both systems.…”