ABSTRACT: Phosphorylation of the histone variant H2AX forms γ-H2AX that marks DNA double-strand break (DSB). Here we generated the sequencing-based maps of H2AX and γ-H2AX positioning in resting and proliferating cells before and after ionizing irradiation. Genome-wide locations of possible endogenous and exogenous DSBs were identified based on γ-H2AX distribution in dividing cancer cells without irradiation and that in resting cells upon irradiation, respectively. γ-H2AX-enriched regions of endogenous origin in replicating cells included telomeres and active transcription start sites, apparently reflecting replication- and transcription-mediated stress during rapid cell division. Surprisingly, H2AX itself, prior to phosphorylation, was specifically located at these endogenous hotspots. This phenomenon was only observed in dividing cancer cells but not in resting cells. Endogenous H2AX was concentrated on the transcription start site of actively transcribed genes but was irrelevant to pausing of RNA polymerase II (pol II), which precisely coincided with γ-H2AX of endogenous origin. γ-H2AX enrichment upon irradiation also coincided with actively transcribed regions, but unlike endogenous γ-H2AX, it extended into the gene body and was not specifically concentrated on the pausing site of pol II. Subtelomeres were not responsive to external DNA damage. Our findings provide insight into DNA repair programs of cancer and may have implications for cancer therapy. Overall design: Profiles of H2AX and gamma-H2AX in normal resting and cancer T cells with and without ionizing irradiation.
Project description:Phosphorylation of the histone variant H2AX forms γ-H2AX that marks DNA double-strand break (DSB). Here we generated the sequencing-based maps of H2AX and γ-H2AX positioning in resting and proliferating cells before and after ionizing irradiation. Genome-wide locations of possible endogenous and exogenous DSBs were identified based on γ-H2AX distribution in dividing cancer cells without irradiation and that in resting cells upon irradiation, respectively. γ-H2AX-enriched regions of endogenous origin in replicating cells included telomeres and active transcription start sites, apparently reflecting replication- and transcription-mediated stress during rapid cell division. Surprisingly, H2AX itself, prior to phosphorylation, was specifically located at these endogenous hotspots. This phenomenon was only observed in dividing cancer cells but not in resting cells. Endogenous H2AX was concentrated on the transcription start site of actively transcribed genes but was irrelevant to pausing of RNA polymerase II (pol II), which precisely coincided with γ-H2AX of endogenous origin. γ-H2AX enrichment upon irradiation also coincided with actively transcribed regions, but unlike endogenous γ-H2AX, it extended into the gene body and was not specifically concentrated on the pausing site of pol II. Subtelomeres were not responsive to external DNA damage. Our findings provide insight into DNA repair programs of cancer and may have implications for cancer therapy. Profiles of H2AX and gamma-H2AX in normal resting and cancer T cells with and without ionizing irradiation.
Project description:Phosphorylation of the histone variant H2AX forms γ-H2AX, which serves as a marker of DNA repair response. Here we provide ChIP-seq-based maps of histone H2AX, γ-H2AX, H2AZ, INO80, SRCAP, and RNA polymerase II in activated T cells. Matched data for H2AX and γ-H2AX in resting T cells and Jurkat cancer T cells are available in GSE25577. CD4+ T cells were stimulated in two different ways (IL-2 alone or IL-2 plus anti-CD3 and anti-CD28), and H2AX, γ-H2AX, H2AZ, INO80, and SRCAP profiles were examined by ChIP-seq
Project description:In Saccharomyces cerevisiae, a single double-strand break (DSB) triggers extensive phosphorylation of histone H2A (known as gammaH2AX) over 50 kb on either side of the DSB. This modification is carried out by either of yeasts checkpoint kinases, the ATM homolog, Tel1, or the ATR homolog, Mec1. In G1-arrested cells, where there is very little 5 to 3 processing of DSB ends, only Tel1 promotes this modification. We have recently described a second modification gammaH2B - the phosphorylation of the C terminal T129 locus of histone H2B which is also carried out by both Mec1 and Tel1 kinases. To understand in detail how gamma-H2AX and gamma-H2B spread along the chromosome from a DSB we have undertaken a high-density analysis of their occupancy where there is a DSB on three different chromosomes. gamma-H2AX and gamma-H2B modifications are similar, but there is a marked absence of gamma-H2B near telomeres. We find that there is reduced gamma-H2AX and gamma-H2B modification over strongly transcribed regions, even taking into account the reduced histone occupancy of these genes. When transcription of the galactose-regulated genes GAL1, GAL10, GAL7 are turned off by the addition of glucose, gamma-H2AX is restored within 5 min; when these genes are again induced, gamma-H2AX is rapidly lost. Regions more distal to the GAL genes have markedly reduced gamma-H2AX levels that rise rapidly when transcription is repressed, suggesting that transcription acts as a barrier to the propagation of gamma-H2AX away from the DSB. The restoration of gamma-H2AX in transcribed regions can be carried out by either Mec1 or Tel1, even 7 h after break induction, suggesting that Tel1 remains associated with damaged chromosomes for an extended time. In addition, we show that gamma-H2AX can be transferred in trans, to regions unlinked to the DSB that lie in close proximity the DSB. Specifically, if a DSB is generated 14 kb from CEN2, gamma-H2AX is transferred to regions around all the other centromeres, in keeping with observed close proximity of all centromere-adjacent chromosome arms. This transfer can be observed even in the absence of formaldehyde crosslinking of the samples.
Project description:DNA damage activates a complex signaling network in cells that blocks cell cycle progression, recruits factors involved in DNA repair, and/or triggers programs that control senescence or programmed cell death. Alterations in chromatin structure are known to be important for the initiation and propagation of the DNA damage response, although the molecular details are unclear. We investigated the role of chromatin structure in the DNA damage response by monitoring multiple timedependent checkpoint signaling and response events with a high-content multiplex image-based RNAi screen of chromatin modifying and interacting genes. We discovered that Brd4, a double bromodomain-containing protein, functions as an endogenous inhibitor of DNA damage signaling by binding to acetylated histones at sites of open chromatin and altering chromatin accessibility. Loss of Brd4 or disruption of acetyl-lysine binding results in an increase in both the number and size of radiation-induced !H2AX nuclear foci while overexpression of a Brd4 splice isoform completely suppresses !H2AX formation, despite equivalent double strand break formation. Brd4 knock-down cells displayed altered chromatin structure, prolonged cell cycle checkpoint arrest and enhanced survival after irradiation, while overexpression of Brd4 isoform B results in enhanced radiationinduced lethality. Brd4 is the target of the t(15;19) chromosomal translocation in a rare form of cancer, NUT Midline Carcinoma. Acetyl lysine-bromodomain interactions of the Brd4-NUT fusion protein suppresses !H2AX foci in discrete nuclear compartments, rendering cells more radiosensitive, mimicking overexpression of Brd4 isoform B. NUT Midline Carcinoma is sensitive to radiotherapy, however tumor material from this rare cancer is scarce. We therefore investigated Brd4 expression in another human cancer commonly treated with radiotherapy, glioblastoma multiforme, and found that expression of Brd4 isoform B correlated specifically with treatment response to radiotherapy. These data implicate Brd4 as an endogenous insulator of DNA damage signaling through recognition of epigenetic modifications in chromatin and suggest that expression of the Brd4 in human cancer can modulate the clinical response to DNA-damaging cancer therapy. Two replicates each of U2OS cells expressing either Brd4 shRNA or a control shRNA
Project description:Purpose: Severe late normal tissue damage limits radiotherapy treatment regimens. This study aims to validate γ-H2AX foci decay ratios and induced expression levels of DNA double strand break (DSB) repair genes, found in a retrospective study, as possible predictors for late radiation toxicity. Methods and Materials: Prospectively, decay ratios (initial/residual γ-H2AX foci numbers) and genome-wide expression profiles were examined in ex vivo irradiated lymphocytes of 198 prostate cancer patients. All patients were followed ≥2 years after radiotherapy, clinical characteristics were assembled and toxicity was recorded using the Common Terminology Criteria (CTCAE) v4.0. Results: No clinical factors were correlated with late radiation toxicity. Analysis of γ-H2AX foci uncovered a negative correlation between the foci decay ratio and toxicity grade. Significantly smaller decay ratios were found in grade≥3 compared to grade 0 patients (p=0.02), indicating less efficient DNA-DSB repair in radio-sensitive patients. Moreover, utilizing a foci decay ratio threshold determined in our previous retrospective study correctly classified 23 of the 28 grade≥3 patients (sensitivity, 82%) and 9 of the 14 grade 0 patients (specificity, 64%). Grade of toxicity also correlated with a reduced induction of the homologous recombination (HR) repair gene-set. The difference in average fold induction of the HR gene-set was most pronounced between grade 0 and grade≥3 patients (p=0.008). Conclusions: Reduced responsiveness of HR repair genes to irradiation and inefficient DSB repair correlate with an increased risk of late radiation toxicity. Using a decay ratio classifier, we could correctly classify 82% of the patients with grade≥3 toxicity. Additional studies are required to further optimize and validate the foci decay assay and to assess its predictive value for late radiation toxicity in patients prostate cancer Overall design: Between 2009 and 2013, we prospectively accrued 200 patients diagnosed with prostate cancer receiving curative external beam radiotherapy in combination with hormonal therapy at the Academic Medical Center (AMC) of the University of Amsterdam, with a follow-up of ≥2 years. After written informed consent, 40 ml whole blood was collected of all patients before start of treatment. Peripheral lymphocytes were isolated using Ficoll (Ficoll-Paque PLUS, GE Healthcare) gradient separation, and stored in liquid nitrogen. Development of late toxicities was monitored over more than 2 years after treatment using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Toxicity grade was determined mainly focusing on late gastrointestinal (GI) and genitourinary (GU) toxicities. Lymphocytes were cultured stimulated by phytohemagglutinin (concentration of 1μg/ml). After two weeks, half of the cells were irradiated at room temperature with 2Gy gamma rays from a 137Cs source, dose rate of approximately 0.5Gy/min and the other half of the cells was left untreated. Total cellular RNA was isolated and gene expression levels were measured using the Affymetrix HT HG-U133+ PM Array platform for 400 samples (2 per patient) and 12 technical replicates (all labelled as 'prospective' below). Samples were also included for 7 patients [4 with (overresponding, R) and 3 without (non-responding, NR) severe late radiation toxicity] from a previous retrospective study (International Journal of Radiation Oncology, Biology, Physics, 88(3):664-70; 2014) using total RNA isolated following an identical experimental protocol from whole-blood samples collected at least 2 years after radiation treatment. This was done either using previously isolated RNA stored at –80°C (14 samples, labelled as 'retrospective (old)' below) and freshly isolated RNA from newly collected whole-blood samples (14 samples, labelled as 'retrospective (new)' below). Samples were hybridized in two batches, the first batch consisting of 104 arrays on five array plates (2x16, 3x24) and the second batch of 336 arrays on five plates (2x24, 3x96). For all patients the irradiated (2Gy) and the control sample (0Gy) had by design been hybridrized in the same batch and, for the second and largest batch, on the same plate. Genes and genesets were determined that respond differently to irradiation between the four toxicity CTCAE 4.0 score-based patient groups. For 198 of the 200 patients from the prospective study the induction and decay of radiation-induced DNA–DSB breaks was monitored in ex vivo irradiated lymphocytes by detecting γ-H2AX foci 30min and 24h post radiation.
Project description:H2AX phosphorylation at Ser139 (gH2AX) is an early key event of the DNA damage response (DDR) following DNA double strand breaks (DSB) induction. Although gH2AX distribution has been extensively used as a damage marker, genome-wide investigation of the subsequent DNA repair has been poorly addressed. Here we present ChIP-Seq-based distributions of Histone H3, H2AX and gH2AX under physiological conditions in HeLa cells. Additionally the same histones were studied after a single exposure to 10 Gy X-ray at 0.5, 3 and 24 hours post irradiation Overall design: In HeLa cells ChIP-seq data for histone H3, H2AX and gammaH2AX were analysed in unirradiated cells as well as after 0.5, 3 and 24 h. Input samples were included and one technical (Sequencing) and one biological (irradiation, library prep and sequencing) replicate was done.
Project description:Telogen (resting phase) hair follicles are more radioresistant than anagen (growth phase) ones. Irradiation of BALB/c mice in the anagen phase with γ-rays at 6 Gy induced hair follicle dystrophy, whereas irradiation in the telogen phase induced the arrest of hair follicle elongation without any dystrophy after post-irradiation depilation. In contrast, FGF18 was highly expressed in the telogen hair follicles to maintain the telogen phase and also the quiescence of hair follicle stem cells. Therefore, the inhibition of FGF receptor signaling at telogen induced the dystrophy after post-irradiation depilation. In addition, the administration of recombinant FGF18 suppressed cell proliferation in the hair follicles and enhanced the repair of radiation-induced DNA damage, so FGF18 protected the anagen hair follicles against radiation damage to enhance hair regeneration. Moreover, FGF18 reduced the expression of cyclin B1 and cdc2 in the skin and FGF18 signaling induced G2/M arrest in the keratinocyte cell line HaCaT, although no obvious change of the expression of DNA repair genes was detected by DNA microarray analysis. These findings suggest that FGF18 signaling for the hair cycle resting phase causes radioresistance in telogen hair follicles by arresting the proliferation of hair follicle cells. Overall design: Portions of dorsal skin of 7-week-old male BALB/c mice were depilated to induce anagen phase of hair follicles. One hundred micrograms of FGF18 diluted in saline containing 5 μg/μl heparin was administered intraperitoneally to mice 6 days after depilation, and then mice were subjected to total body irradiation with γ-rays at 6 Gy 24 h after FGF administration. The skin was removed from treated mice 4 h after irradiation and total RNAs were isolated from the skin. The mRNA expression profiles were obtained using Affymetrix GeneChip Mouse Gene 2.0 ST Array (Affymetrix, Santa Clara, CA, USA).
Project description:Phosphorylation of histone H2AX is an early response to DNA damage in eukaryotes. In Saccharomyces cerevisiae, DNA damage or replication fork stalling results in histone H2A phosphorylation to yield gamma-H2A (yeast gamma-H2AX) in a Mec1 (ATR)- and Tel1 (ATM)- dependent manner. Here, we describe the genome-wide location analysis of gamma-H2A as a strategy to identify loci prone to engage the Mec1 and Tel1 pathways. Remarkably, gamma-H2A enrichment overlaps with loci prone to replication fork stalling and is caused by the action of Mec1 and Tel1, indicating that these loci are prone to breakage. Moreover, about half the sites enriched for gamma-H2A map to repressed protein-coding genes, and histone deacetylases are necessary for formation of gamma-H2A at these loci. Finally, our work indicates that high resolution mapping of gamma-H2AX is a fruitful route to map fragile sites in eukaryotic genomes. Overall design: To identify loci enriched in gamma-H2A, we carried out chromatin immunoprecipitations with a phospho-specific antibody that recognizes gamam-H2A in yeast and hybridized to high-density tiling arrays surveying the genome at an average density of one probe per 275 bp. In a typical experiment, we performed competitive hybridization of DNA precipitated from HTA1 HTA2 cells with DNA precipitated from the gamma-H2A-deficient hta1-S129A hta2-S129A cells (referred to hereafter as S129A). All experiments were done at least in duplicate and combined using a weighted average method.
Project description:Analysis of HeLa cell with overexpression of an EGFP-tagged dominant-negative truncation (73- 563 a.a.) of human REST/NRSF. RNA polymerase II and DNA damage repair factor γ-H2AX binding data provide insight into the molecular bases of how REST/NRSF perturbation impairs genome stability. Overall design: Identification of RNA polymerase II and γ-H2AX binding sites in normal and REST-disrupted HeLa cells. An antibody targeting the YSPTSPS repeats in the C-terminal domain (CTD) of the largest subunit of RNAP II was utilized to immunoprecipitate RNAP II, regardless of its phosphorylation status.