Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P16104 (H2AX)
 3,930 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cellular response to DNA damage includes the orderly recruitment of many protein complexes to DNA lesions. The MRE11-RAD50-NBS1 (MRN) complex is well known to localize early to sites of DNA damage, but the post-translational modifications required to mobilize it to DNA damage sites are poorly understood. Recently, we have shown that MRE11 is arginine methylated in a C-terminal glycine-arginine rich (GAR) domain by protein arginine methyltransferase 1 (PRMT1). Arginine methylation is required for the exonuclease activity of MRE11 and the intra-S phase DNA damage response. Herein, we report that cells treated with methylase inhibitors failed to relocalize MRE11 from PML nuclear bodies to sites of DNA damage and formed few gamma-H2AX foci. We also demonstrate that PRMT1 is a component of PML nuclear bodies where it colocalizes with MRE11.Using cellular fractionation, we demonstrate that methylated MRE11 is predominantly associated with nuclear structures and that MRE11 methylated arginines were required for this association. These results suggest that MRE11 methylation regulates its association with nuclear structures such as PML nuclear bodies and sites of DNA damage.
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PMID:Methylation of MRE11 regulates its nuclear compartmentalization. 1597 Jun 67

Hypomorphic mutations which lead to decreased function of the NBS1 gene are responsible for Nijmegen breakage syndrome, a rare autosomal recessive hereditary disorder that imparts an increased predisposition to development of malignancy. The NBS1 protein is a component of the MRE11/RAD50/NBS1 complex that plays a critical role in cellular responses to DNA damage and the maintenance of chromosomal integrity. Using small interfering RNA transfection, we have knocked down NBS1 protein levels and analyzed relevant phenotypes in two closely related human lymphoblastoid cell lines with different p53 status, namely wild-type TK6 and mutated WTK1. Both TK6 and WTK1 cells showed an increased level of ionizing radiation-induced mutation at the TK and HPRT loci, impaired phosphorylation of H2AX (gamma-H2AX), and impaired activation of the cell cycle checkpoint regulating kinase, Chk2. In TK6 cells, ionizing radiation-induced accumulation of p53/p21 and apoptosis were reduced. There was a differential response to ionizing radiation-induced cell killing between TK6 and WTK1 cells after NBS1 knockdown; TK6 cells were more resistant to killing, whereas WTK1 cells were more sensitive. NBS1 deficiency also resulted in a significant increase in telomere association that was independent of radiation exposure and p53 status. Our results provide the first experimental evidence that NBS1 deficiency in human cells leads to hypermutability and telomere associations, phenotypes that may contribute to the cancer predisposition seen among patients with this disease.
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PMID:NBS1 knockdown by small interfering RNA increases ionizing radiation mutagenesis and telomere association in human cells. 1599 26

The Mre11/Rad50/NBS1 (MRN) complex is mutated in inherited genomic instability syndromes featuring cancer predisposition, mental retardation and immunodeficiency. It functions both in DNA double-strand break repair and in controlling the ataxia telangiectasia mutated (ATM) kinase during the response to these lesions. Patients inheriting homozygosity for an NBS1 hypomorphic allele display reduced phosphorylation of signaling factors such as Chk1, but not of chromatin-associated factor H2AX, after stresses that activate the ATM-related kinase, ATR. Therefore, we tested whether MRN has a global controlling role over the ATR kinase through the study of MRN deficiencies generated via RNA interference. We show for the first time that MRN is required for ATR-dependent phosphorylation of structural maintenance of chromosomes 1 (Smc1), which acts within chromatin to ensure sister chromatid cohesion and to effect several DNA damage responses. We have uncovered novel phenotypes caused by MRN deficiency that support a functional link between this complex, ATR and Smc1, including hypersensitivity to UV exposure, a defective UV responsive intra-S phase checkpoint and a specific pattern of genomic instability. In addition, certain ATR-dependent responses do not require MRN. These studies demonstrate that there is indeed a controlling role for MRN over the ATR kinase and have established that the downstream events under this control are broad, including both chromatin-associated and diffuse signaling factors, but may not be universal. These studies contribute to our understanding of the central role that MRN plays in damage detection and signaling, which serve to maintain genomic stability and resist neoplastic transformation.
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PMID:Rad50 depletion impacts upon ATR-dependent DNA damage responses. 1608 84

Werner syndrome is an autosomal recessive accelerated-aging disorder caused by a defect in the WRN gene, which encodes a member of the RecQ family of DNA helicases with an exonuclease activity. In vitro experiments have suggested that WRN functions in several DNA repair processes, but the actual functions of WRN in living cells remain unknown. Here, we analyzed the kinetics of the intranuclear mobilization of WRN protein in response to a variety of types of DNA damage produced locally in the nucleus of human cells. A striking accumulation of WRN was observed at laser-induced double-strand breaks, but not at single-strand breaks or oxidative base damage. The accumulation of WRN at double-strand breaks was rapid, persisted for many hours, and occurred in the absence of several known interacting proteins including polymerase beta, poly(ADP-ribose) polymerase 1 (PARP1), Ku80, DNA-dependent protein kinase (DNA-PKcs), NBS1 and histone H2AX. Abolition of helicase activity or deletion of the exonuclease domain had no effect on accumulation, whereas the presence of the HRDC (helicase and RNaseD C-terminal) domain was necessary and sufficient for the accumulation. Our data suggest that WRN functions mainly at DNA double-strand breaks and structures resembling double-strand breaks in living cells, and that an autonomous accumulation through the HRDC domain is the initial response of WRN to the double-strand breaks.
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PMID:Accumulation of Werner protein at DNA double-strand breaks in human cells. 1614 Dec 34

Double strand DNA breaks in the genome lead to the activation of the ataxia-telangiectasia mutated (ATM) kinase in a process that requires ATM autophosphorylation at serine-1981. ATM autophosphorylation only occurs if ATM is previously acetylated by Tip60. The activated ATM kinase phosphorylates proteins involved in arresting the cell cycle, including p53, and in repairing the DNA breaks. Chloroquine treatment and other manipulations that produce chromatin defects in the absence of detectable double strand breaks also trigger ATM phosphorylation and the phosphorylation of p53 in primary human fibroblasts, while other downstream substrates of ATM that are involved in the repair of DNA double strand breaks remain unphosphorylated. This raises the issue of whether ATM is constitutively activated in patients with genetic diseases that display chromatin defects. We examined lymphoblastoid cell lines (LCLs) generated from patients with different types of chromatin disorders: Immunodeficiency, Centromeric instability, Facial anomalies (ICF) syndrome, Coffin Lowry syndrome, Rubinstein Taybi syndrome and Fascioscapulohumeral Muscular Dystrophy. We show that ATM is phosphorylated on serine-1981 in LCLs derived from ICF patients but not from the other syndromes. The phosphorylated ATM in ICF cells did not phosphorylate the downstream targets NBS1, SMC1 and H2AX, all of which require the presence of double strand breaks. We demonstrate that ICF cells respond normally to ionizing radiation, ruling out the possibility that genetic deficiency in ICF cells renders activated ATM incapable of phosphorylating its downstream substrates. Surprisingly, p53 was also not phosphorylated in ICF cells or in chloroquine-treated wild type LCLs. In this regard the response to chromatin-altering agents differs between primary fibroblasts and LCLs. Our findings indicate that although phosphorylation at serine-1981 is essential in the activation of the ATM kinase, serine-1981 phosphorylation is insufficient to render ATM an active kinase towards downstream substrates, including p53.
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PMID:Constitutive phosphorylation of ATM in lymphoblastoid cell lines from patients with ICF syndrome without downstream kinase activity. 1642 3

Topoisomerase II is essential for cell proliferation and survival and has been a target of various anticancer drugs. ICRF-193 has long been used as a catalytic inhibitor to study the function of topoisomerase II. Here, we show that ICRF-193 treatment induces DNA damage signaling. Treatment with ICRF-193 induced G2 arrest and DNA damage signaling involving gamma-H2AX foci formation and CHK2 phosphorylation. DNA damage by ICRF-193 was further demonstrated by formation of the nuclear foci of 53BP1, NBS1, BRCA1, MDC1, and FANCD2 and increased comet tail moment. The DNA damage signaling induced by ICRF-193 was mediated by ATM and ATR and was restricted to cells in specific cell cycle stages such as S, G2, and mitosis including late and early G1 phases. Downstream signaling of ATM and ATR involved the phosphorylation of CHK2 and BRCA1. Altogether, our results demonstrate that ICRF-193 induces DNA damage signaling in a cell cycle-dependent manner and suggest that topoisomerase II might be essential for the progression of the cell cycle at several stages including DNA decondensation.
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PMID:Cell cycle-dependent DNA damage signaling induced by ICRF-193 involves ATM, ATR, CHK2, and BRCA1. 1663 Jun 10

Exposure to ionizing radiation (IR) results in the formation of DNA double strand breaks, resulting in the activation of phosphatidylinositol 3'-kinase-like kinases ATM, ATR and DNK-PKcs. A physiologically important downstream target is the minor histone H2A variant, H2AX, which is rapidly phosphorylated on Ser 139 of the carboxyl tail after IR. Recent work suggests that phosphorylated H2AX (gamma-H2AX) plays an important role in the recruitment and/or retention of DNA repair and checkpoint proteins such as BRCA1, MRE11/RAD50/NBS1 complex, MDC1 and 53BP1. H2AX-/- mouse embryonic fibroblasts are radiation sensitive and demonstrate deficits in repairing DNA damage compared to their wildtype counterparts. Cells treated with peptide inhibitors of gamma-H2AX demonstrate increased radiosensitivity following radiation compared with untreated irradiated cells. Analysis of the kinetics of gamma-H2AX clearance after IR or other DNA damaging agents reveals a correlation between increased gamma-H2AX persistence and unrepaired DNA damage and cell death. These data highlight the potential of post-translational modifications of chromatin as a therapeutic target for enhancing the efficacy of radiotherapy. Therapies that either block gamma-H2AX foci formation by inhibiting upstream kinase activity or that directly inhibit H2AX function may interfere with DNA damage repair processes and warrant further investigation as potential radiosensitizing agents. Agents that increase persistence of gamma-H2AX after IR are likely to increase unrepaired DNA damage.
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PMID:gamma-H2AX as a therapeutic target for improving the efficacy of radiation therapy. 1671 57

The repair of DNA double-strand breaks is critical for genome integrity and tumor suppression. Here we show that following treatment with the DNA-intercalating agent actinomycin D (ActD), normal quiescent T cells accumulate double-strand breaks and die, whereas T cells from ataxia telangiectasia (AT) and Nijmegen breakage syndrome (NBS) patients are resistant to this death pathway despite a comparable amount of DNA damage. We demonstrate that the ActD-induced death pathway in quiescent T lymphocytes follows DNA damage and H2AX phosphorylation, is ATM- and NBS1-dependent and due to p53-mediated cellular apoptosis. In response to genotoxic 2-Gy gamma-irradiation, on the other hand, quiescent T cells from normal donors survive following complete resolution of the damage thus induced. T cells from AT and NBS patients also survive, but retain foci of phosphorylated H2AX due to a subtle double-strand break (DSB) repair defect. A common consequence of these two genetic defects in the DSB response is the apparent tolerance of cells containing DNA breaks. We suggest that this tolerance makes a major contribution to the oncogenic risk of patients with chromosome instability syndromes.
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PMID:Impaired elimination of DNA double-strand break-containing lymphocytes in ataxia telangiectasia and Nijmegen breakage syndrome. 1676 53

ATM (ataxia-telangiectasia mutated) is activated by a variety of noxious agent, including oxidative stress, and ATM deficiency results in an anomalous cellular response to oxidative stress. However, the mechanisms for ATM activation by oxidative stress remain to be established. Furthermore, it is not clear whether ATM responds to oxidative DNA damage or to a change in the intracellular redox state, independent of DNA damage. We found that ATM is activated by N-methyl-N'-nitro-nitrosoguanidine (MNNG) and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), in NBS1- or MSH6-deficient cells. We further found that ATM is activated by treating chromatin-free immunoprecipitated ATM with MNNG or 15d-PGJ(2), which modifies free sulfhydryl (SH) groups, and that 15d-PGJ(2) binds covalently to ATM. Interestingly, 15d-PGJ(2)-induced ATM activation leads to p53 activation and apoptosis, but not to Chk2 or H2AX phosphorylation. These results indicate that ATM is activated through the direct modification of its SH groups, independent of DNA damage, and this activation leads, downstream, to apoptosis.
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PMID:ATM activation by a sulfhydryl-reactive inflammatory cyclopentenone prostaglandin. 1682 97

The nuclear pore complex (NPC) is embedded in the nuclear envelope where it mediates transport between the cytoplasm and nucleus and helps to organize nuclear architecture. We previously isolated sonB1, a mutation encoding a single amino acid substitution within the Aspergillus nidulans SONBnNup98 NPC protein (nucleoporin). Here we demonstrate that this mutation causes marked DNA damage sensitivity at 42 degrees . Although SONBnNup98 has roles in the G2 transition, we demonstrate that the G2 DNA damage checkpoint is functional in the sonB1 mutant at 42 degrees . The MRN complex is composed of MRE11, RAD50, and NBS1 and functions in checkpoint signaling, DNA repair, and telomere maintenance. At 42 degrees we find that the DNA damage response defect of sonB1 mutants causes synthetic lethality when combined with mutations in scaANBS1, the A. nidulans homolog of NBS1. We provide evidence that this synthetic lethality is independent of MRN cell cycle checkpoint functions or MREAMRE11-mediated DNA repair functions. We also demonstrate that the single A. nidulans histone H2A gene contains the C-terminal SQE motif of histone H2AX isoforms and that this motif is required for the DNA damage response. We propose that the sonB1 nucleoporin mutation causes a defect in a novel part of the DNA damage response.
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PMID:A point mutation in the Aspergillus nidulans sonBNup98 nuclear pore complex gene causes conditional DNA damage sensitivity. 1702 24


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