Bromodomain Gene Research Articles

BRD4 Bromodomain Gene Rearrangement in Aggressive Carcinoma with Translocation t(15;19)

Translocation t(15;19)(q13;p13.1) defines a lethal midline carcinoma arising adjacent to respiratory tract in young people. To characterize molecular alterations responsible for the distinctly aggressive biological behavior of this cancer, we mapped the chromosome 15 and 19 translocation breakpoints by fluorescence in situ hybridization (FISH) and Southern blotting. To evaluate preliminarily the frequency, anatomical distribution, and histological features of t(15;19) cancer, we developed a FISH assay for paraffin sections. Our findings reveal a novel oncogenic mechanism in which the chromosome 19 translocation breakpoint interrupts the coding sequence of a bromodomain gene, BRD4. These studies implicate BRD4 as a potential partner in a t(15;19)-associated fusion oncogene. In addition, we localized the chromosome 15 breakpoint to a 9-kb region in each of two cases, thereby identifying several candidate oncogenes which might represent the BRD4 fusion partner. FISH evaluation of 13 pediatric carcinomas revealed t(15;19) in one of four sinonasal carcinomas, whereas this translocation was not detected in thymic (n = 3), mucoepidermoid (n = 3), laryngeal (n = 2), or nasopharyngeal (n = 1) carcinomas. Our studies shed light on the oncogenic mechanism underlying t(15;19) and provide further evidence that this highly lethal cancer arises from respiratory mucosa.

Identification and Characterization of BPTF, a Novel Bromodomain Transcription Factor

The bromodomain is a 110-amino-acid conserved structural region associated with proteins that regulate signal-dependent, nonbasal transcription. The bromodomain can regulate histone acetyl transferase activity and interacts specifically with acetylated lysine residues. A key role for bromodomain proteins in maintaining normal proliferation is indicated by the implication of several bromodomain proteins in cancer, with four of these identified at translocation breakpoints. We searched EST databases for novel bromodomain genes. The sequence from one EST was used to initiate generation of a full-length clone from a testis cDNA library. The completed sequence encodes a predicted protein of 2781 amino acids, which, in addition to the bromodomain, harbors further motifs characteristic of a transcriptional coactivator: two PHD fingers and an extensive glutamine-rich acidic domain. There are several other regions that are conserved with the Caenorhabditis elegans putative protein F26H11, which may be functionally homologous. The novel gene, called BPTF, is expressed in all tissues examined as a 10.5-kb transcript. The protein has extensive identity with the smaller FAC1 protein, suggesting that the two either are derived from the same locus or are synonymous. BPTF has been mapped to 17q23. Functional domains found within BPTF are consistent with a role for this protein in hormonally regulated, chromatin-mediated regulation of transcription.

A Novel Family of Bromodomain Genes

The bromodomain is a structural motif characteristic of proteins involved in chromatin-dependent regulation of transcription. Bromodomain proteins have been identified as integral components of chromatin remodeling complexes and frequently possess histone acetyltransferase activity. Their encoding genes have been identified at translocation breakpoints, and at least one, CBP, is a tumor suppressor gene. We have identified a series of novel bromodomain genes by EST database and cDNA library screening. Comparison of sequences for four clones indicated that they represent genes belonging to a novel bromodomain family. Full-length sequences for these genes, which are widely expressed, predict encoded proteins of between 1527 and 1972 amino acids. In addition to a carboxy-terminal bromodomain, an adjacent PHD finger, and a WACZ motif, at least four other conserved novel motifs are present in each protein. The genes contain regions conserved with Drosophila Acf1 and Caenorhabditis elegans ZK783.4. The novel genes, termed BAZ1A, BAZ1B, BAZ2A, and BAZ2B, localize to chromosomes 14q12–q13, 7q11–q21, 12q24.3–qter, and 2q23–q24, respectively. Conservation of multiple domains throughout these genes with Acf1 indicates that they are likely to be components of chromatin remodeling complexes.

Identification and Characterization of BRDT: A Testis-Specific Gene Related to the Bromodomain Genes RING3 andDrosophila fsh

The RING3 gene encodes a 90-kDa mitogen-activated nuclear protein. In proliferating cells, including in leukemia, RING3 has serine–threonine kinase and autophosphorylation activities. The cloning of D26362, a gene closely related to RING3, suggests a gene family. RING3 and D26362 are also related to theDrosophiladevelopmental genefsh.A database search for further members of the RING3 family identified an EST derived from a testis-specific library. cDNA clones representing the full coding sequence of the gene were isolated. The gene encodes a protein of 947 amino acids with extensive homology to RING3, D26362, andfsh.Similar to these proteins, it possesses two bromodomain motifs and a PEST sequence. Northern analysis of 16 normal tissues and eight cancer cell lines shows transcripts of 3.5 and 4.0 kb expressed specifically in testis. The gene has been named BRDT (for bromodomain, testis specific). PCR analysis of a panel of monochromosomal human/rodent hybrid cell lines and the GeneBridge 4 panel of radiation hybrids localizes the gene to chromosome 1p between markers WI-7719 and WI-3099 (D1S2154).