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Release of paused RNA-Polymerase II at specific introns and chromatin domains favors spontaneous DNA double strand break formation and predicts cancer translocations [RNA-seq]

ABSTRACT: Transcriptional activation leads to transient accumulation of DNA Double Strand Breaks (DSBs), which might promote formation of chromosomal translocations. We report here the genomic distribution of DSBs in non-transformed mammary cells grown under unperturbed conditions, using genome-wide Breaks Labeling In Situ and Sequencing (BLISS). We found thousands of high-confidence DSBs, which were enriched at the promoters of a subset of moderately- to highly-transcribed genes (fragile promoters) and co-localized with Topoisomerase II beta. Analyses of DSB-predictive features identified gene length and paused RNA Polymerase II, but not transcription, as critical factors (84% prediction accuracy). Analyses of DSB signaling and repair factors showed high levels of XRCC4, but not of gammaH2AX and NBS1, and no RAD51. Finally, the observed DSBs were predictive of a significant fraction of the recurrent translocations found in human breast cancers. These data suggest that, in normal cells, basal transcription from a specific class of promoters entails accumulation of TOP2B, leading to unresolved DSBs and increased probability of chromosomal translocations.

ORGANISM(S): Homo sapiens

PROVIDER: GSE93039 | GEO | 2019/03/12

REPOSITORIES: GEO

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Release of paused RNA-Polymerase II at specific introns and chromatin domains favors spontaneous DNA double strand break formation and predicts cancer translocations [ChIP-seq & BLISS]

Project description:Transcriptional activation leads to transient accumulation of DNA Double Strand Breaks (DSBs), which might promote formation of chromosomal translocations. We report here the genomic distribution of DSBs in non-transformed mammary cells grown under unperturbed conditions, using genome-wide Breaks Labeling In Situ and Sequencing (BLISS). We found thousands of high-confidence DSBs, which were enriched at the promoters of a subset of moderately- to highly-transcribed genes (fragile promoters) and co-localized with Topoisomerase II beta. Analyses of DSB-predictive features identified gene length and paused RNA Polymerase II, but not transcription, as critical factors (84% prediction accuracy). Analyses of DSB signaling and repair factors showed high levels of XRCC4, but not of gammaH2AX and NBS1, and no RAD51. Finally, the observed DSBs were predictive of a significant fraction of the recurrent translocations found in human breast cancers. These data suggest that, in normal cells, basal transcription from a specific class of promoters entails accumulation of TOP2B, leading to unresolved DSBs and increased probability of chromosomal translocations.

2019-03-12 | GSE93038 | GEO

Total protein abundances upon Mcm6 knockdown in the murine CH12 cells

Project description:Chromosomal translocations result from joining of DNA double-strand breaks (DSBs) and frequently cause cancer. Yet, the steps linking DSB formation to DSB ligation remain undeciphered. We report that DNA replication timing (RT) directly regulates lymphomagenic Myc translocations during antibody maturation in B-cells downstream of DSBs and independently of DSB frequency. Depletion of minichromosome-maintenance (MCM) complexes alters replication origin activity, decreases translocations and abrogates global RT. Ablating a single origin at Myc causes an early-to-late RT switch, loss of translocations and reduced nuclear proximity with a translocation partner locus, phenotypes that were reversed by restoring early RT. Disruption of shared early RT also reduced tumorigenic translocations in human leukemic cells. Thus, RT constitutes a new, unprecedented mechanism in translocation biogenesis linking DSB formation to DSB ligation

2022-09-13 | PXD034446 | Pride

DNA replication timing directly regulates the frequency of oncogenic chromosomal translocations

Project description:Chromosomal translocations result from the joining of DNA double-strand breaks (DSBs) and frequentlycause cancer. However, the steps linking DSB formation to DSB ligation remain undeciphered. Wereport that DNA replication timing (RT) directly regulates lymphomagenicMyctranslocations duringantibody maturation in B cells downstream of DSBs and independently of DSB frequency. Depletion ofminichromosome maintenance complexes alters replication origin activity, decreases translocations,and deregulates global RT. Ablating a single origin atMyccauses an early-to-late RT switch, loss oftranslocations, and reduced proximity with the immunoglobulin heavy chain (Igh) gene, its majortranslocation partner. These phenotypes were reversed by restoring early RT. Disruption of early RT alsoreduced tumorigenic translocations in human leukemic cells. Thus, RT constitutes a general mechanismin translocation biogenesis linking DSB formation to DSB ligation.

2022-09-15 | GSE161818 | GEO

DNA double-strand breaks induced by AID in activated splenic B cells

Project description:Activation-induced cytidine deaminase (AID) is required for initiation of Ig class switch recombination (CSR) and somatic hypermutation (SHM) of antibody genes during immune responses. AID has also been shown to induce chromosomal translocations, mutations, and DNA double-strand breaks (DSBs) involving non-Ig genes in activated B cells. To determine what makes a DNA site a target for AID-induced DSBs, we identify off-target DSBs induced by AID by performing chromatin immunoprecipitation (ChIP) for Nbs1, a protein that binds DSBs, followed by deep sequencing (ChIP-Seq). We detect and characterize hundreds of off-target AID-dependent DSBs. Two types of tandem repeats are highly enriched within the Nbs1-binding sites: long CA repeats, which can form Z-DNA, and tandem pentamers containing the AID target hotspot WGCW. These tandem repeats are not nearly as enriched at AID-independent DSBs, which we also identified. Msh2, a component of the mismatch repair pathway and important for genome stability, increases off-target DSBs, similar to its effect on Ig switch region DSBs, which are required intermediates during CSR. Most of the off-target DSBs are two-ended, consistent with generation during G1 phase, similar to DSBs in Ig switch regions. However, a minority are one-ended, presumably due to conversion of single-strand breaks to DSBs during replication. One-ended DSBs are repaired by processes involving homologous recombination, including break-induced replication repair, which can lead to genome instability. Off-target DSBs, especially those present during S phase, can lead to chromosomal translocations, deletions and gene amplifications, resulting in the high frequency of B cell lymphomas derived from cells that express or have expressed AID.

2015-07-16 | GSE66424 | GEO

Seeding the meiotic DNA break machinery and initiating recombination on chromosome axes

Project description:Recombination-mediated linking of homologous chromosomes is a unique meiotic feature that enables the halving of chromosomal ploidy in sexual life cycles. Meiotic recombination is initiated by programmed DNA double-strand breaks (DSBs) that are generated by focal multi-protein clusters that condense onto chromosomal axes by poorly understood mechanisms. We discovered in mice that a DBF4-dependent kinase (DDK)–modulated interaction between IHO1 and the chromosomal axis component HORMAD1 effects the formation of axis-bound IHO1 platforms that enhance nucleation of cytologically distinguishable DSB-machinery clusters. This IHO1-HORMAD1-mediated seeding of the DSB-machinery ensures that sufficient DSBs form for efficient pairing of homologous chromosomes. In the absence of IHO1-HORMAD1 interaction, residual DSB activity depends on ANKRD31, which enhances both the seeding and the growth of DSB-machinery clusters. Thus, meiotic DSBs are ensured by complementing pathways that differentially effect seeding and growth of DSB-machinery clusters, and that synergistically enable assembly of the DSB machinery on chromosomal axes.

2024-02-23 | PXD042179 | Pride

Seeding the meiotic DNA break machinery and initiating recombination on chromosome axes

2024-02-23 | PXD042221 | Pride

Activation-induced cytidine deaminase induces reproducible DNA breaks at many non-Ig loci in activated B cells

Project description:After immunization or infection, activation-induced cytidine deaminase (AID) initiates diversification of immunoglobulin (Ig) genes in B cells, introducing mutations within the antigen binding V regions (somatic hypermutation, SHM) and double-strand DNA breaks (DSBs) into switch (S) regions, leading to antibody class switch recombination (CSR). Using a candidate approach, AID has been shown to initiate mutations at numerous non-Ig genes in B cells in Peyer’s patches. However, it is not known if during B cell activation, AID also induces DNA breaks at genes other than IgH genes, which would lead to genomic instability and malignancy. Using a non-biased genome-wide approach, we have identified hundreds of reproducible AID-dependent DSBs in mouse splenic B cells shortly after induction of CSR in culture. Most interestingly, AID induces DSBs at sites syntenic with sites of translocations, deletions, and amplifications found in human B cell lymphomas, including within the oncogene B cell lymphoma11a (bcl11a)/evi9. The AID-dependent DSBs are not restricted to transcribed regions, and they frequently occur within repeated sequence elements, including CA and non-CA repeats, and SINEs. Comparison of Nbs1 binding sites in wild-type vs. aid-/- splenic B cells induced to undergo CSR; aid-dependent Nbs1 sites correlated with gene transcription (RNA Pol2).

2011-01-21 | E-GEOD-24827 | biostudies-arrayexpress

Chromosomal Instability and Molecular Defects in Induced Pluripotent Stem Cells with Nijmegen Breakage Syndrome

Project description:Nijmegen breakage syndrome (NBS) results from the absence of the NBS1 protein, responsible for detection of DNA double-strand breaks (DSBs). NBS is characterized by microcephaly, growth retardation, immunodeficiency, and cancer predisposition. Here we show successful reprogramming of NBS fibroblasts into induced pluripotent stem cells (NBS-iPSCs). Our data suggest a strong selection for karyotypically normal fibroblasts to go through the reprogramming process. NBS-iPSCs then acquire numerous chromosomal aberrations and show a delayed response to DSB induction. Furthermore, NBS-iPSCs display slower growth, mitotic inhibition, a reduced apoptotic response to stress and abnormal cell cycle-related gene expression. Importantly, NBS neural progenitor cells (NBS-NPCs) show down-regulation of neural developmental genes, which seems to be mediated by P53. Our results demonstrate the importance of NBS1 in early human development, shed new light on the molecular mechanisms underlying this severe syndrome and further expand our knowledge of the genomic stress cells experience during the reprogramming process. Gene expression analysis was performed on a total of 6 human cell lines, including WT and NBS Neural progenitor cells (NPCs) and NBS-iPSCs

2016-07-19 | E-GEOD-83686 | biostudies-arrayexpress

DNA replication timing directly regulates the frequency of oncogenic chromosomal translocations [PRO-cap]

Project description:Many cancers originate from misregulation of gene expression caused by chromosomal translocations which result from ligation of DNA double-strand breaks (DSBs). Indeed, translocations may be causal in ~20% of human cancer morbidity 1. Although the sources of DSBs are numerous2-5, we have virtually no knowledge of the steps linking DSB formation to DSB ligation. Here, we show that early replication timing of translocation partner loci, mediated by the activity of replication origins, is a critical regulator of lymphomagenic Myc translocations generated by activation-induced deaminase (AID) during antibody maturation in B-cells. Reduced levels of the replicative helicase, the minichromosome maintenance (MCM) complex6, impairs translocation genesis, decreases firing of replication origins at AID target genes and globally abrogates the replication timing program without altering cell proliferation, gene expression or genome architecture. Strikingly, deleting a single origin of replication at Myc induces a switch from early-to-late replication at Myc with concomitantly impaired translocation frequency. This phenotype is reversed by restoring early replication at Myc thereby demonstrating a direct, causal role of replication origin activity and replication timing in translocation genesis. Finally, this replication timing-mediated step acts downstream of DSBs and is independent of DSB frequency, constituting a novel regulatory step in translocation biogenesis.

2022-09-15 | GSE171623 | GEO

DNA replication timing directly regulates the frequency of oncogenic chromosomal translocations [SNS-seq]

2022-09-15 | GSE161821 | GEO

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