Partnership between epigenetic reader BRD4 and transcription factor CEBPD

Vascular smooth muscle cell (SMC) state/phenotype transitions underlie neointimal hyperplasia (IH) predisposing to cardiovascular diseases. Bromodomain protein BRD4 is a histone acetylation reader and enhancer mark that co-activates transcription elongation. CCAAT enhancer binding protein delta (CEBPD) is a transcription factor typically studied in adipogenesis and immune cell differentiation. Here we investigated the association between BRD4 and CEBPD in SMC state transition. Chromatin immunoprecipitation sequencing (ChIPseq) showed enrichment of BRD4 and histone acetylation (H3K27ac) at Cebpd and enhancer in rat carotid arteries undergoing IH. In vitro, BRD4 silencing with siRNA reduced SMC expression of CEBPD. Bromodomain-1 but not bromodoamin-2 accounted for this BRD4 function. Endogenous BRD4 co-IPed with CEBPD; Cebpd promoter and enhancer DNA fragments co-IPed with CEBPD or endogenous BRD4 (ChIP-qPCR). These co-IPs were abolished by the BRD4 bromodomain blocker JQ1. TNF upregulated both BRD4 and CEBPD. Silencing CEBPD averted TNF-induced inflammatory SMC state transition (heightened IL-1{beta}, IL6, and MCP-1 mRNA levels), so did JQ1. CEBPD overexpression increased PDGFR preferentially over PDGFR{beta}; so did TNF, and JQ1 abolished TNFs effect. Our data reveal a BRD4/CEBPD partnership that promotes CEBPDs own transcription and inflammatory SMC state transition, thus shedding new light on epigenetic reader and transcription factor cooperative actions in SMC pathobiology.