The BRD4 Antibody Sampler Kit provides an economical means of detecting various BRD4 isoforms. The kit includes enough antibodies to perform two western blot experiments with each primary antibody.

Bromodomain-containing protein 4 (BRD4) is a member of the bromodomains and extra terminal (BET) family of proteins, which also includes BRD2, BRD3, and BRDT (1-3). BET family proteins contain two tandem bromodomains and an extra terminal (ET) domain, and bind acetyl lysine residues (3). BRD4 is a chromatin-binding protein with a preference for Lys14 on histone H3 as well as Lys5 and Lys12 on histone H4 (4). BRD4 chromatin binding occurs throughout the cell cycle, including condensed mitotic chromosomes, when the majority of genes are silenced (5). BRD4 association with chromatin during mitosis is thought to be an important part of the bookmarking mechanism to accelerate reactivation of the silenced genes upon exit from mitosis (2,6). BRD4 has been shown to facilitate transcription by recruiting the positive transcription elongation factor b (pTEFb) complex that phosphorylates Ser2 of the heptapeptide repeat of the carboxy-terminal domain of RNA polymerase II, promoting transcription elongation (3,7,8). In addition, BRD4 has been found to be part of the super elongation complex and the polymerase associated factor complex (PAFc) in MLL-fusion derived leukemia cell lines, demonstrating a role for BRD4 in the regulation of transcription elongation (9). Research studies have shown that BRD4 (and BET family proteins) may be promising therapeutic targets for various Myc-driven cancers, such as Burkitt’s lymphoma and certain acute myeloid leukemias (1,10,11). Investigators have found molecular inhibition of BET proteins to be effective in inducing apoptosis in various MLL-fusion driven leukemic cell lines by competing BRD3 and BRD4 from chromatin, leading to reduced expression of Bcl-2, Myc, and CDK6 (9). BET inhibition has also been shown to have antitumor activities against nuclear protein in testis (NUT) midline carcinoma cell lines and xenografts in mice where BRD4 is found to be a frequent translocation partner of the NUT protein (12). In addition, BRD4 regulates the expression of some inflammatory genes, and inhibition of BRD4 (and BET family proteins) chromatin binding causes reduced expression of a subset of inflammatory genes in macrophages, leading to protection against endotoxic shock and sepsis (13).

The expression of BRD4 isoform C, also known as the short isoform (BRD4-S), is similar to the long isoform (BRD4-L). The balance of expression between the two isoforms has been shown to contribute to disease states, where BRD4-S has shown to be oncogenic in a few contexts (14-16). BRD4-S is the predominant isoform that binds to modified histones and has a stronger affinity than BRD4-L (17,18). BRD4-S also plays a role in DNA damage, where it recruits the condensin II complex to enhance DNA damage induced cell death (18).