Bromodomain-containing Protein 4 (BRD4) is Required for the Maintenance of a Mammary Epithelial Phenotype [ChIP-Seq]

Bromodomain-containing protein 4 (BRD4) is an important epigenetic reader which promotes gene transcription to modulate cell-specific functions and is under intensive investigation for its potential as an anti-tumor therapeutic target. However, the role of BRD4 in non-transformed cells remains unclear. Here we demonstrate that BRD4 is required for the expression of epithelial-specific genes and suppression of stem cell-like properties by binding to the distal regions of epithelial-related genes. Moreover, BRD4 occupancy correlates with enhancer activity and enhancer RNA (eRNA) transcription of epithelial differentiation-specific genes. Interestingly, we show that BRD4 perturbation regulates the expression of Grainy Head-like transcription factor, GRHL3, whose depletion partially mimics BRD4 inhibition and blocks differentiated phenotype. By binding to the distal regions of GRHL3, BRD4 promotes RNA polymerase-II occupancy and thus affects eRNA transcription. Altogether, these findings provide evidence that BRD4 promotes a differentiated epithelial phenotype in non-transformed mammary cells at least in part through the activation of GRHL3 expression.