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DNA Damage


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  • The DNA damage checkpoint regulates a transition between yeast and hyphal growth in schizosaccharomyces japonicus. 20368354

    Dimorphic yeasts change between unicellular growth and filamentous growth. Many dimorphic yeasts species are pathogenic for humans and plants, being infectious as invasive hypha. We have studied the determinants of the dimorphic switch in the nonpathogenic fission yeast Schizosaccharomyces japonicus, which is evolutionarily close to the well-characterized fission yeast S. pombe. We report that camptothecin, an inhibitor of topoisomerase I, reversibly induced the unicellular to hyphal transition in S. japonicus at low concentrations of camptothecin that did not induce checkpoint arrest and the transition required the DNA checkpoint kinase Chk1. Furthermore, a mutation of chk1 induced hyphal transition without camptothecin. Thus, we identify a second function for Chk1 distinct from its role in checkpoint arrest. Activation of the switch from single cell bipolar growth to monopolar filamentous growth may assist cells to evade the source of DNA damage.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    Multiple

  • The DNA damage checkpoint protein RAD9A is essential for male meiosis in the mouse. 23788429

    In mitotic cells, RAD9A functions in repairing DNA double-strand breaks (DSBs) by homologous recombination and facilitates the process by cell cycle checkpoint control in response to DNA damage. DSBs occur naturally in the germline during meiosis but whether RAD9A participates in repairing such breaks is not known. In this study, we determined that RAD9A is indeed expressed in the male germ line with a peak of expression in late pachytene and diplotene stages, and the protein was found associated with the XY body. As complete loss of RAD9A is embryonic lethal, we constructed and characterized a mouse strain with Stra8-Cre driven germ cell-specific ablation of Rad9a beginning in undifferentiated spermatogonia in order to assess its role in spermatogenesis. Adult mutant male mice were infertile or sub-fertile due to massive loss of spermatogenic cells. The onset of this loss occurs during meiotic prophase, and there was an increase in the numbers of apoptotic spermatocytes as determined by TUNEL. Spermatocytes lacking RAD9A usually arrested in meiotic prophase, specifically in pachytene. The incidence of unrepaired DNA breaks increased, as detected by accumulation of γH2AX and DMC1 foci on the axes of autosomal chromosomes in pachytene spermatocytes. The DNA topoisomerase IIβ-binding protein 1 (TOPBP1) was still localized to the sex body, albeit with lower intensity, suggesting that RAD9A may be dispensable for sex body formation. We therefore show for the first time that RAD9A is essential for male fertility and for repair of DNA DSBs during meiotic prophase I.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    05-636
    Katalógusszám:
    Anti-phospho-Histone H2A.X (Ser139) Antibody, clone JBW301

  • The DNA damage/repair cascade in glioblastoma cell lines after chemotherapeutic agent treatment. 25892134

    Therapeutic resistance in glioblastoma multiforme (GBM) has been linked to a subpopulation of cells with stem cell-like properties, the glioma stem cells (GSCs), responsible for cancer progression and recurrence. This study investigated the in vitro cytotoxicity of three chemotherapeutics, temozolomide (TMZ), doxorubicin (Dox) and paclitaxel (PTX) on glioma cell lines, by analyzing the molecular mechanisms leading to DNA repair and cell resistance, or to cell death. The drugs were tested on 16 GBM cell lines, grown as neurospheres (NS) or adherent cells (AC), by studying DNA damage occurrence by Comet assay, the expression by immunofluorescence and western blotting of checkpoint/repair molecules and apoptosis. The three drugs were able to provoke a genotoxic injury and to inhibit dose- and time-dependently cell proliferation, more evidently in AC than in NS. The first cell response to DNA damage was the activation of the damage sensors (p-ATM, p-53BP1, γ-H2AX), followed by repair effectors; the expression of checkpoint/repair molecules appeared higher in NS than in AC. The non-homologous repair pathway (NHEJ) seemed more involved than the homologous one (HR). Apoptosis occurred after long treatment times, but only a small percentage of cells in NS underwent death, even at high drug concentration, whereas most cells survived in a quiescent state and resumed proliferation after drug removal. In tumor specimens, checkpoint/repair proteins were constitutively expressed in GBMs, but not in low-grade gliomas.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    Multiple
    Katalógusszám:
    Multiple

  • Tethering DNA damage checkpoint mediator proteins topoisomerase IIbeta-binding protein 1 (TopBP1) and Claspin to DNA activates ataxia-telangiectasia mutated and RAD3-rela ... 21502314

    The ataxia-telangiectasia mutated and RAD3-related (ATR) kinase initiates DNA damage signaling pathways in human cells after DNA damage such as that induced upon exposure to ultraviolet light by phosphorylating many effector proteins including the checkpoint kinase Chk1. The conventional view of ATR activation involves a universal signal consisting of genomic regions of replication protein A-covered single-stranded DNA. However, there are some indications that the ATR-mediated checkpoint can be activated by other mechanisms. Here, using the well defined Escherichia coli lac repressor/operator system, we have found that directly tethering the ATR activator topoisomerase IIβ-binding protein 1 (TopBP1) to DNA is sufficient to induce ATR phosphorylation of Chk1 in an in vitro system as well as in vivo in mammalian cells. In addition, we find synergistic activation of ATR phosphorylation of Chk1 when the mediator protein Claspin is also tethered to the DNA with TopBP1. Together, these findings indicate that crowding of checkpoint mediator proteins on DNA is sufficient to activate the ATR kinase.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    AB3245

  • DNA damage signaling, impairment of cell cycle progression, and apoptosis triggered by 5-ethynyl-2'-deoxyuridine incorporated into DNA. 24115313

    The "click chemistry" approach utilizing 5-ethynyl-2'-deoxyuridine (EdU) as a DNA precursor was recently introduced to assess DNA replication and adapted to flow- and imaging-cytometry. In the present study, we observed that EdU, once incorporated into DNA, induces DNA damage signaling (DDS) such as phosphorylation of ATM on Ser1981, of histone H2AX on Ser139, of p53 on Ser15, and of Chk2 on Thr68. It also perturbs progression of cells through the cell cycle and subsequently induces apoptosis. These effects were observed in non-small cell lung adenocarcinoma A549 as well as in B-cell human lymphoblastoid TK6 and WTK1 cells, differing in the status of p53 (wt versus mutated). After 1 h EdU pulse-labeling, the most affected was cells progression through the S phase subsequent to that at which they had incorporated EdU. This indicates that DNA replication using the template containing incorporated EdU is protracted and triggers DDS. Furthermore, progression of cells having DNA pulse-labeled with EdU led to accumulation of cells in G2 , likely by activating G2 checkpoint. Consistent with the latter was activation of p53 and Chk2. Although a correlation was observed in A549 cells between the degree of EdU incorporation and the extent of γH2AX induction, such correlation was weak in TK6 and WTK1 cells. The degree of perturbation of the cell cycle kinetics by the incorporated EdU was different in the wt p53 TK6 cells as compared to their sister WTK1 cell line having mutated p53. The data are thus consistent with the role of p53 in modulating activation of cell cycle checkpoints in response to impaired DNA replication. The confocal microscopy analysis of the 3D images of cells exposed to EdU for 1 h pulse and then grown for 24 or 48 h revealed an increased number of colocalized γH2AX and p53BP1 foci considered to be markers of DNA double-strand breaks and enlarged nuclei.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    05-636
    Katalógusszám:
    Anti-phospho-Histone H2A.X (Ser139) Antibody, clone JBW301

  • Unrepaired DNA damage facilitates elimination of uniparental chromosomes in interspecific hybrid cells. 24608870

    Elimination of uniparental chromosomes occurs frequently in interspecific hybrid cells. For example, human chromosomes are always eliminated during clone formation when human cells are fused with mouse cells. However, the underlying mechanisms are still elusive. Here, we show that the elimination of human chromosomes in human-mouse hybrid cells is accompanied by continued cell division at the presence of DNA damage on human chromosomes. Deficiency in DNA damage repair on human chromosomes occurs after cell fusion. Furthermore, increasing the level of DNA damage on human chromosomes by irradiation accelerates human chromosome loss in hybrid cells. Our results indicate that the elimination of human chromosomes in human-mouse hybrid cells results from unrepaired DNA damage on human chromosomes. We therefore provide a novel mechanism underlying chromosome instability which may facilitate the understanding of carcinogenesis.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    05-636
    Katalógusszám:
    Anti-phospho-Histone H2A.X (Ser139) Antibody, clone JBW301

  • Multiple DNA damage signaling and repair pathways deregulated by simian virus 40 large T antigen. 20519379

    We demonstrated previously that expression of simian virus 40 (SV40) large T antigen (LT), without a viral origin, is sufficient to induce the hallmarks of a cellular DNA damage response (DDR), such as focal accumulation of gamma-H2AX and 53BP1, via Bub1 binding. Here we expand our characterization of LT effects on the DDR. Using comet assays, we demonstrate that LT induces overt DNA damage. The Fanconi anemia pathway, associated with replication stress, becomes activated, since FancD2 accumulates in foci, and monoubiquitinated FancD2 is detected on chromatin. LT also induces a distinct set of foci of the homologous recombination repair protein Rad51 that are colocalized with Nbs1 and PML. The FancD2 and Rad51 foci require neither Bub1 nor retinoblastoma protein binding. Strikingly, wild-type LT is localized on chromatin at, or near, the Rad51/PML foci, but the LT mutant in Bub1 binding is not localized there. SV40 infection was previously shown to trigger ATM activation, which facilitates viral replication. We demonstrate that productive infection also triggers ATR-dependent Chk1 activation and that Rad51 and FancD2 colocalize with LT in viral replication centers. Using small interfering RNA (siRNA)-mediated knockdown, we demonstrate that Rad51 and, to a lesser extent, FancD2 are required for efficient viral replication in vivo, suggesting that homologous recombination is important for high-level extrachromosomal replication. Taken together, the interplay of LT with the DDR is more complex than anticipated, with individual domains of LT being connected to different subcomponents of the DDR and repair machinery.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    05-530

  • DNA damage responses in Drosophila nbs mutants with reduced or altered NBS function. 19395318

    The MRN complex, composed of MRE11, RAD50 and NBS, plays important roles in responding to DNA double-strand breaks (DSBs). In metazoans, functional studies of genes encoding these proteins have been challenging because complete loss-of-function mutations are lethal at the organismal level and because NBS has multiple functions in DNA damage responses. To study functions of Drosophila NBS in DNA damage responses, we used a separation-of-function mutation that causes loss of the forkhead-associated (FHA) domain. Loss of the FHA domain resulted in hypersensitivity to ionizing radiation and defects in gap repair by homologous recombination, but had only a small effect on the DNA damage checkpoint response and did not impair DSB repair by end joining. We also found that heterozygosity for an nbs null mutation caused reduced gap repair and loss of the checkpoint response to low-dose irradiation. These findings shed light on possible sources of the cancer predisposition found in human carriers of NBN mutations.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    06-570
    Katalógusszám:
    Anti-phospho-Histone H3 (Ser10) Antibody, Mitosis Marker

  • DNA damage promotes histone deacetylase 4 nuclear localization and repression of G2/M promoters, via p53 C-terminal lysines. 16293626

    Repression of G(2)/M promoters after DNA damage is an active mechanism that requires the p53 tumor suppressor. We have recently found that histone deacetylase 4 (HDAC4) is recruited on NF-Y-dependent repressed promoters. In this report, we describe the relationship between p53 and HDAC4 recruitment following DNA damage using immunofluorescence, chromatin immunoprecipitation, and transfection experiments. HDAC4 shuttles from the cytoplasm into the nucleus, following DNA damage, independently of the activation of p53 and becomes associated with promoters through a p53-dependent mechanism. The C-terminal lysines of p53, which are acetylated and methylated, are required for HDAC4 recruitment and transcriptional repression. Trichostatin treatment, but not HDAC4 functional inactivation, relieves the adriamycin-mediated repression of G(2)/M promoters. Our results indicate that HDAC4 is a component of the DNA damage response and that post-translational modifications of p53 are important for repression of G(2)/M genes.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    Multiple
    Katalógusszám:
    Multiple

  • DNA Damage Signaling Is Induced in the Absence of Epstein-Barr Virus (EBV) Lytic DNA Replication and in Response to Expression of ZEBRA. 25950714

    Epstein Barr virus (EBV), like other oncogenic viruses, modulates the activity of cellular DNA damage responses (DDR) during its life cycle. Our aim was to characterize the role of early lytic proteins and viral lytic DNA replication in activation of DNA damage signaling during the EBV lytic cycle. Our data challenge the prevalent hypothesis that activation of DDR pathways during the EBV lytic cycle occurs solely in response to large amounts of exogenous double stranded DNA products generated during lytic viral DNA replication. In immunofluorescence or immunoblot assays, DDR activation markers, specifically phosphorylated ATM (pATM), H2AX (γH2AX), or 53BP1 (p53BP1), were induced in the presence or absence of viral DNA amplification or replication compartments during the EBV lytic cycle. In assays with an ATM inhibitor and DNA damaging reagents in Burkitt lymphoma cell lines, γH2AX induction was necessary for optimal expression of early EBV genes, but not sufficient for lytic reactivation. Studies in lytically reactivated EBV-positive cells in which early EBV proteins, BGLF4, BGLF5, or BALF2, were not expressed showed that these proteins were not necessary for DDR activation during the EBV lytic cycle. Expression of ZEBRA, a viral protein that is necessary for EBV entry into the lytic phase, induced pATM foci and γH2AX independent of other EBV gene products. ZEBRA mutants deficient in DNA binding, Z(R183E) and Z(S186E), did not induce foci of pATM. ZEBRA co-localized with HP1β, a heterochromatin associated protein involved in DNA damage signaling. We propose a model of DDR activation during the EBV lytic cycle in which ZEBRA induces ATM kinase phosphorylation, in a DNA binding dependent manner, to modulate gene expression. ATM and H2AX phosphorylation induced prior to EBV replication may be critical for creating a microenvironment of viral and cellular gene expression that enables lytic cycle progression.
    Dokumentumtípus:
    Reference
    Katalógusszám:
    Multiple
    Katalógusszám:
    Multiple