BRD4 promotes DNA repair and mediates the formation of TMPRSS2-ERG gene rearrangements in prostate cancer
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE106258 | GEO | 2018/01/04
SECONDARY ACCESSION(S): PRJNA416055
REPOSITORIES: GEO
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Project description:BRD4 belongs to the bromodomain and extraterminal (BET) family of chromatin reader proteins that bind acetylated histones and regulate gene expression. Pharmacological inhibition of BRD4 by BET inhibitors (BETi) has indicated antitumor activity against multiple cancer types. We show that BRD4 is essential for the repair of DNA double-strand breaks (DSBs) and mediates the formation of oncogenic gene rearrangements by engaging the non-homologous end joining (NHEJ) pathway. Mechanistically, genome-wide DNA breaks are associated with enhanced acetylation of histone H4, leading to BRD4 recruitment, and stable establishment of the DNA repair complex. In support of this, we also show that, in clinical tumor samples, BRD4 protein levels are negatively associated with outcome after prostate cancer (PCa) radiation therapy. Thus, in addition to regulating gene expression, BRD4 is also a central player in the repair of DNA DSBs, with significant implications for cancer therapy.
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Project description:There is increasing interest in the use of cell-free circulating tumor DNA (ctDNA) as a serum marker for therapy assessment in prostate cancer patients. Prostate cancer is characterized by relatively low numbers of mutations, and, in contrast to many other common epithelial cancers, commercially available single nucleotide mutation assays for quantification of ctDNA are insufficient for therapy assessment in this disease. However, prostate cancer shares some similarity with translocation-affected mesenchymal tumors (e.g., leukemia and Ewing sarcoma), which are common in pediatric oncology, where chromosomal translocations are used as biomarkers for quantification of the tumor burden. Approximately 50% of prostate cancers carry a chromosomal translocation resulting in generation of the TMPRSS2-ERG fusion gene, which is unique to the tumor cells of each individual patient because of variability in the fusion breakpoint sites. In the present study, we examined the structural preconditions for TMPRSS2-ERG fusion sites in comparison with mesenchymal tumors in pediatric patients to determine whether the sequence composition is suitable for the establishment of tumor-specific quantification assays in prostate cancer patients. Genomic repeat elements represent potential obstacles to establishment of quantification assays, and we found similar proportions of repeat elements at fusion sites in prostate cancer to those reported for mesenchymal tumors, where genomic fusion sequences are established as biomarkers. Our data support the development of the TMPRSS2-ERG fusion gene as a noninvasive tumor marker for therapy assessment, risk stratification, and relapse detection to improve personalized therapy strategies for patients with prostate cancer.
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Project description:TMPRSS2-ERG rearrangements occur in approximately 50% of prostate cancers and therefore represent one of the most frequently observed structural rearrangements in all cancers. However, little is known about the genomic architecture of such rearrangements. We therefore designed and optimized a pipeline involving target capture of TMPRSS2 and ERG genomic sequences coupled with paired-end next-generation sequencing to resolve genomic rearrangement breakpoints in TMPRSS2 and ERG at nucleotide resolution in a large series of primary prostate cancer specimens (n = 83). This strategy showed > 90% sensitivity and specificity in identifying TMPRSS2-ERG rearrangements, and allowed identification of intra- and inter-chromosomal rearrangements involving TMPRSS2 and ERG with known and novel fusion partners. Our results indicate that rearrangement breakpoints show strong clustering in specific intronic regions of TMPRSS2 and ERG. The observed TMPRSS2-ERG rearrangements often exhibited complex chromosomal architecture associated with several intra- and inter-chromosomal rearrangements. Nucleotide resolution analysis of breakpoint junctions revealed that the majority of TMPRSS2 and ERG rearrangements (~88%) occurred at or near regions of microhomology or involved insertions of one or more base pairs. This architecture implicates non-homologous end joining (NHEJ) and microhomology-mediated end joining (MMEJ) pathways in the generation of such rearrangements. These analyses have provided important insights into the molecular mechanisms involved in generating prostate cancer-specific recurrent rearrangements.
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Project description:During the post-meiotic phase of spermatogenesis, transcription is progressively repressed as the nuclei of haploid spermatids are compacted through a dramatic chromatin reorganization involving hyper-acetylation and replacement of most histones with sperm-specific protamines. Although BRDT has been shown to function in transcription as well as histone removal in post-meiotic spermatids, it is unknown whether other BET family proteins play a role. Immunofluorescence of mouse testes revealed BRD4 in a complete ring around the nuclei of spermatids containing hyper-acetylated histones. The BRD4 ring lies directly adjacent to the acroplaxome, or the cytoskeletal base of the acrosome, and does not form in acrosomal mutant mice. ChIP sequencing in round spermatids revealed enrichment of BRD4 and acetylated histone H3 and H4 at the promoters of active genes. GO Term analysis showed that BRD4 and BRDT bind to distinct subsets of spermatogenesis-specific genes. Association of BRD4 with Cyclin T1 decreases as spermatogenesis progresses despite a persistence of association with acetylated H4. Moreover, acetylated histones are removed from the condensing spermatid nucleus in a wave following the progressing acrosome. These data provide evidence for an interesting mechanism in which BRD4 and perhaps acetylated histones are removed from the spermatid genome via the progressing acrosome as transcription is repressed. Single replicates each of Brd4, H3K9me3, H3K9ac, H4K5ac, H4K8ac, H4K12ac, H4K16ac, H4Kac (pan-acetyl antibody), and input in mouse round spermatid cells; input is used to control for local sonication efficiency bias.
2015-03-06 | E-GEOD-56526 | biostudies-arrayexpress
Project description:BRD4 promotes DNA repair and mediates the formation of TMPRSS2-ERG gene rearrangements in prostate cancer
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Project description:During the post-meiotic phase of spermatogenesis, transcription is progressively repressed as the nuclei of haploid spermatids are compacted through a dramatic chromatin reorganization involving hyper-acetylation and replacement of most histones with sperm-specific protamines. Although BRDT has been shown to function in transcription as well as histone removal in post-meiotic spermatids, it is unknown whether other BET family proteins play a role. Immunofluorescence of mouse testes revealed BRD4 in a complete ring around the nuclei of spermatids containing hyper-acetylated histones. The BRD4 ring lies directly adjacent to the acroplaxome, or the cytoskeletal base of the acrosome, and does not form in acrosomal mutant mice. ChIP sequencing in round spermatids revealed enrichment of BRD4 and acetylated histone H3 and H4 at the promoters of active genes. GO Term analysis showed that BRD4 and BRDT bind to distinct subsets of spermatogenesis-specific genes. Association of BRD4 with Cyclin T1 decreases as spermatogenesis progresses despite a persistence of association with acetylated H4. Moreover, acetylated histones are removed from the condensing spermatid nucleus in a wave following the progressing acrosome. These data provide evidence for an interesting mechanism in which BRD4 and perhaps acetylated histones are removed from the spermatid genome via the progressing acrosome as transcription is repressed.
2015-03-06 | GSE56526 | GEO
Project description:TMPRSS2 gene rearrangements occur at DNA breaks formed during androgen receptor-mediated transcription and activate expression of ETS transcription factors at the early stages of more than half of prostate cancers. NKX3.1, a prostate tumor suppressor that accelerates the DNA repair response, binds to androgen receptor at the ERG gene breakpoint and inhibits both the juxtaposition of the TMPRSS2 and ERG gene loci and also their recombination. NKX3.1 acts by accelerating DNA repair after androgen-induced transcriptional activation. NKX3.1 influences the recruitment of proteins that promote homology-directed DNA repair. Loss of NKX3.1 favors recruitment to the ERG gene breakpoint of proteins that promote error-prone nonhomologous end-joining. Analysis of prostate cancer tissues showed that the presence of a TMPRSS2-ERG rearrangement was highly correlated with lower levels of NKX3.1 expression consistent with the role of NKX3.1 as a suppressor of the pathogenic gene rearrangement.
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2011-05-27 | E-GEOD-29520 | biostudies-arrayexpress
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