BRD4 Regulates Transcription Factor ΔNp63α to Drive a Cancer Stem Cell Phenotype in Squamous Cell Carcinomas

Bromodomain containing protein 4 (BRD4) plays a critical role in controlling the expression of genes involved in development and cancer. Inactivation of BRD4 inhibits cancer growth, making it a promising anticancer drug target. The cancer stem cell (CSC) population is a key driver of recurrence and metastasis in patients with cancer. Here we show that cancer stem-like cells can be enriched from squamous cell carcinomas (SCC), and that these cells display an aggressive phenotype with enhanced stem cell marker expression, migration, invasion, and tumor growth. BRD4 is highly elevated in this aggressive subpopulation of cells, and its function is critical for these CSC-like properties. Moreover, BRD4 regulates Delta Np63 alpha, a key transcription factor that is essential for epithelial stem cell function that is often overexpressed in cancers. BRD4 regulates an EZH2/STAT3 complex that leads to increased Delta Np63 alpha-amediated transcription. Targeting BRD4 in human SCC reduces Delta Np63 alpha, leading to inhibition of spheroid formation, migration, invasion, and tumor growth. These studies identify a novel BRD4-regulated signaling network in a subpopulation of cancer stem-like cells, elucidating a possible avenue for effective therapeutic intervention. Significance: This study identifies a signaling cascade driven by BRD4 that upregulates Delta Np63 alpha to promote cancer stem-like properties, which has potential therapeutic implications for the treatment of squamous cell carcinomas.