Brd

BRD4 (Bromodomain-containing protein 4) is a member of the BET (bromodomain and extra-terminal) family of epigenetic reader proteins that recognize acetylated lysine residues on histones and transcription-associated proteins through tandem bromodomains, thereby linking chromatin acetylation to transcriptional regulation and gene expression programs^[1][2]. BRD4 functions as a chromatin-associated transcriptional regulator and remains associated with chromatin during mitosis, supporting the maintenance of transcriptional states across cell divisions^[3][4]. Mechanistically, BRD4 promotes transcriptional elongation through interactions with transcriptional machinery and contributes to the activation of genes involved in cell-cycle progression, proliferation, and oncogenic signaling pathways^[2][5]. Dysregulated BRD4 activity has been implicated in multiple cancers, including hematologic malignancies and NUT carcinoma, where BRD4-dependent transcriptional programs support tumor growth and survival^[2][6]. Compared with related BET family members, BRD4 contains a distinctive C-terminal region that is absent or less developed in BRD2 and BRD3, providing functional specialization beyond the shared bromodomain-mediated recognition of acetylated chromatin^[7][8]. Although BET proteins exhibit conserved bromodomains, genetic and pharmacological studies indicate non-redundant biological functions among BRD2, BRD3, and BRD4, supporting isoform-specific investigation in disease models^[3][9]. For experimental applications, small-molecule BET inhibitors such as JQ1 competitively block BET bromodomains, displace BRD4 from chromatin-associated targets, and have become widely used chemical probes for dissecting epigenetic transcriptional regulation and evaluating therapeutic vulnerabilities in cancer models^[2][10].