BRD4

BRD4 (Bromodomain Containing Protein 4) is a member of the BET (bromodomain and extra-terminal) protein family that recognizes acetylated histones and functions as a central regulator of chromatin-associated transcriptional programs^[1][2]. Mechanistically, BRD4 promotes RNA polymerase II transcriptional elongation through functional interaction with positive transcription elongation factor b (P-TEFb), thereby facilitating productive gene expression and transcriptional pause release^[3][4][5]. Beyond transcriptional control, BRD4 contributes to chromatin organization, DNA replication, and DNA damage response pathways, linking epigenetic regulation to genome stability^[1][6]. BRD4 also supports efficient transcription elongation that limits R-loop accumulation and transcription-replication conflicts, processes that are important for maintaining cellular viability^[6]. In disease contexts, aberrant BRD4 activity has been associated with cancer, inflammatory disorders, viral infection, and neurological disease, reflecting its broad influence on gene regulatory networks^[1][2]. In multiple tumor models, BRD4 regulates transcriptional programs linked to oncogenic drivers and tumor cell survival, supporting its relevance as a therapeutic target^[7][8]. Compared with related BET family members BRD2, BRD3, and the testis-restricted BRDT, BRD4 possesses a characteristic C-terminal domain that mediates interaction with P-TEFb and plays a distinct role in transcriptional elongation control^[3][9]. For experimental applications, small-molecule BET inhibitors such as JQ1 and I-BET disrupt bromodomain-dependent chromatin interactions and have become widely used tools for investigating BRD4-dependent transcriptional mechanisms and target validation in disease models^[1][7][8].