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Query: UMLS:C0004135 (ATM)
 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Effective medical treatment and preventive measures for chemical warfare agent sulfur mustard (HD)-caused incapacitating skin toxicity are lacking, because of limited knowledge of its mechanism of action. The proliferating basal epidermal cells are primary major sites of attack during HD-caused skin injury. Therefore, employing mouse JB6 and human HaCaT epidermal cells, here, we investigated the molecular mechanism of HD analogue 2-chloroethyl ethyl sulfide (CEES)-induced skin cytotoxicity. As compared to the control, up to 1 mM CEES treatment of these cells for 2, 4, and 24 h caused dose-dependent decreases in cell viability and proliferation as measured by DNA synthesis, together with S and G2-M phase arrest in cell cycle progression. Mechanistic studies showed phosphorylation of DNA damage sensors and checkpoint kinases, ataxia telangiectasia-mutated (ATM) at ser1981 and ataxia telangiectasia-Rad3-related (ATR) at ser428 within 30 min of CEES exposure, and modulation of S and G2-M phase-associated cell cycle regulatory proteins, which are downstream targets of ATM and ATR kinases. Hoechst-propidium iodide staining demonstrated that CEES-induced cell death was both necrotic and apoptotic in nature, and the latter was induced at 4 and 24 h of CEES treatment in HaCaT and JB6 cells, respectively. An increase in caspase-3 activity and both caspase-3 and poly(ADP-ribose)polymerase (PARP) cleavage coinciding with CEES-caused apoptosis in both cell lines suggested the involvement of the caspase pathway. Together, our findings suggest a DNA-damaging effect of CEES that activates ATM/ATR cell cycle checkpoint signaling as well as caspase-PARP pathways, leading to cell cycle arrest and apoptosis/necrosis in both JB6 and HaCaT cells. The identified molecular targets, quantitative biomarkers, and epidermal cell models in this study have the potential and usefulness in rapid development of effective prophylactic and therapeutic interventions against HD-induced skin toxicity.
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PMID:Biological and molecular mechanisms of sulfur mustard analogue-induced toxicity in JB6 and HaCaT cells: possible role of ataxia telangiectasia-mutated/ataxia telangiectasia-Rad3-related cell cycle checkpoint pathway. 2046 12

As single agents, chemical inhibitors of poly(ADP-ribose) polymerase (PARP) are nontoxic and have clinical efficacy against BRCA1- and BRCA2-deficient tumors. PARP inhibitors also enhance the cytotoxicity of ionizing radiation and alkylating agents but will only improve clinical outcomes if tumor sensitization exceeds effects on normal tissues. It is unclear how tumor DNA repair proficiency affects the degree of sensitization. We have previously shown that the radiosensitizing effect of PARP inhibition requires DNA replication and will therefore affect rapidly proliferating tumors more than normal tissues. Because many tumors exhibit defective DNA repair, we investigated the impact of double-strand break (DSB) repair integrity on the sensitizing effects of the PARP inhibitor olaparib. Sensitization to ionizing radiation and the alkylating agent methylmethane sulfonate was enhanced in DSB repair-deficient cells. In Artemis(-/-) and ATM(-/-) mouse embryo fibroblasts, sensitization was replication dependent and associated with defective repair of replication-associated damage. Radiosensitization of Ligase IV(-/-) mouse embryo fibroblasts was independent of DNA replication and is explained by inhibition of "alternative" end joining. After methylmethane sulfonate treatment, PARP inhibition promoted replication-independent accumulation of DSB, repair of which required Ligase IV. Our findings predict that the sensitizing effects of PARP inhibitors will be more pronounced in rapidly dividing and/or DNA repair defective tumors than normal tissues and show their potential to enhance the therapeutic ratio achieved by conventional DNA-damaging agents.
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PMID:Sensitization to radiation and alkylating agents by inhibitors of poly(ADP-ribose) polymerase is enhanced in cells deficient in DNA double-strand break repair. 2053 Jul 11

The combination of poly(ADP-ribose)polymerase (PARP) inhibitors and alkylating agents is currently being investigated in cancer therapy clinical trials. However, the DNA lesions producing the synergistic cell killing effect in tumors are not fully understood. Treatment of human and mouse fibroblasts with the monofunctional DNA methylating agent methyl methanesulfonate (MMS) in the presence of a PARP inhibitor has been shown to trigger a cell cycle checkpoint response. Among other changes, this DNA damage response to combination treatment includes activation of ATM/Chk2 and phosphorylation of histone H2A.X. These changes are consistent with DNA double-strand break (DSB) formation during the response, but the measurement of DSBs has not been addressed. Such DSB evaluation is important in understanding this DNA damage response because events other than DSB formation are known to lead to ATM/Chk2 activation and H2A.X phosphorylation. Here, we examined the structural integrity of genomic DNA after the combined treatment of cells with MMS and a PARP inhibitor, i.e., exposure to a sub-lethal dose of MMS in the presence of the PARP inhibitor 4-amino-1,8-napthalimide (4-AN). We used pulsed field gel electrophoresis (PFGE) for measurement of DSBs in both human and mouse embryonic fibroblasts, and flow cytometry to follow the phosphorylated form of H2A.X (gamma-H2A.X). The results indicate that DSBs are formed with the combination treatment, but not following treatment with either agent alone. Our data also show that formation of gamma-H2A.X correlates with PARP-1-expressing cells in S-phase of the cell cycle. The observations support the model that persistence of PARP-1 at base excision repair intermediates, as cells move into S-phase, leads to DSBs and the attendant checkpoint responses.
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PMID:Alkylation DNA damage in combination with PARP inhibition results in formation of S-phase-dependent double-strand breaks. 2057 51

Prostate cancer is the most common male cancer and up to one fifth of diagnosed patients will die of their disease. Current prognostic variables including T-category (of the TNM staging), the absolute or kinetics of prostatic specific antigen (PSA) and the pathologic Gleason score (GS) are utilized to place men in low, intermediate and high-risk prostate cancer risk groupings. There is great heterogeneity within the non-indolent intermediate risk group with respect to clinical response. It is therefore imperative that further genetic and other prognostic factors be identified to better individualize treatment. Somatic alterations in prostate cancer. Herein, we review the potential for somatic alterations in tumor-associated genes (based on comparative genomic hybridization (CGH) in prostate cancers to be novel prognostic, and possibly predictive, factors for prostate cancer radiotherapy response. Intermediate risk prostate cancers show alterations in a number of genes thought to be involved in radiosensitivity, DNA repair, cell death and stem cell renewal. These include deletions at 21q (TMPRSS2: ERG), 13q (RB1), 10q (PTEN), 8p (NKX3.1), additions at 8q21 (containing c-Myc)) and haplo-insufficiency for p53, PARP1, ATM and DNA-PKcs. Conclusions. The use of high-resolution CGH for fine-mapping of deletions and amplifications in pre-radiotherapy prostate cancer biopsies is feasible. Genetic alterations may delineate localized prostate cancer from systemic disease and be used as a predictive factor in that patients would be individually triaged to local (surgery versus radiotherapy) and/or adjuvant (adjuvant androgen ablation or post-operative radiotherapy) therapies in a prospective fashion to improve outcome. The knowledge of abnormal DNA repair pathways within in a given patient could allow for the judicious use of targeted agents (PARP/ATM inhibitors) as personalized medicine.
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PMID:Array CGH as a potential predictor of radiocurability in intermediate risk prostate cancer. 2059 Mar 66

The Ataxia Telangiectasia Mutated (ATM) gene is frequently inactivated in lymphoid malignancies such as chronic lymphocytic leukemia (CLL), T-prolymphocytic leukemia (T-PLL), and mantle cell lymphoma (MCL) and is associated with defective apoptosis in response to alkylating agents and purine analogues. ATM mutant cells exhibit impaired DNA double strand break repair. Poly (ADP-ribose) polymerase (PARP) inhibition that imposes the requirement for DNA double strand break repair should selectively sensitize ATM-deficient tumor cells to killing. We investigated in vitro sensitivity to the poly (ADP-ribose) polymerase inhibitor olaparib (AZD2281) of 5 ATM mutant lymphoblastoid cell lines (LCL), an ATM mutant MCL cell line, an ATM knockdown PGA CLL cell line, and 9 ATM-deficient primary CLLs induced to cycle and observed differential killing compared with ATM wildtype counterparts. Pharmacologic inhibition of ATM and ATM knockdown confirmed the effect was ATM-dependent and mediated through mitotic catastrophe independently of apoptosis. A nonobese diabetic/severe combined immunodeficient (NOD/SCID) murine xenograft model of an ATM mutant MCL cell line demonstrated significantly reduced tumor load and an increased survival of animals after olaparib treatment in vivo. Addition of olaparib sensitized ATM null tumor cells to DNA-damaging agents. We suggest that olaparib would be an appropriate agent for treating refractory ATM mutant lymphoid tumors.
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PMID:The PARP inhibitor olaparib induces significant killing of ATM-deficient lymphoid tumor cells in vitro and in vivo. 2073 57

DNA double-strand breaks (DSBs) induced during clinical radiotherapy are potent inducers of cell death. Poly(ADP-ribose) polymerase (PARP)-1 is a 113-kD nuclear protein that binds to both single- and double-strand DNA breaks and is actively involved in DNA single-strand break repair and base excision repair. Recently, potent and specific chemical inhibitors of PARP activity have been developed that are effective tumor cell radiosensitizers in vitro and in vivo. Because of synthetic lethality, PARP inhibitors may be highly effective as a single agent in patients whose tumors have germline or somatic defects in DNA damage and repair genes (eg, ATM, BRCA1, BRCA2, and NBS1) or defects in genes involved in phosphatase and tensin homolog gene (PTEN) signaling. Defects in specific DNA repair pathways also appear to enhance the radiosensitizing effects of PARP inhibition. In addition to inherent genetics, tumor cells may also be preferentially sensitized to radiotherapy by diverse mechanisms, including proliferation-dependent radiosensitization, targeting of the endothelium and tumor vasculature, and increased sensitivity to PARP inhibitors within repair-deficient hypoxic cells. Because biologically active doses of PARP inhibitors caused minimal toxicity in phase I to II clinical trials, careful scheduling of these agents in combination with radiotherapy may maintain the therapeutic ratio and increase tumor radiocurability.
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PMID:Poly(ADP-ribose) polymerase inhibition as a model for synthetic lethality in developing radiation oncology targets. 2083 20

We recently demonstrated that human embryonic stem cells (hESCs) utilize homologous recombination repair (HRR) as primary means of double-strand break (DSB) repair. We now show that hESCs also use nonhomologous end joining (NHEJ). NHEJ kinetics were several-fold slower in hESCs and neural progenitors (NPs) than in astrocytes derived from hESCs. ATM and DNA-PKcs inhibitors were ineffective or partially effective, respectively, at inhibiting NHEJ in hESCs, whereas progressively more inhibition was seen in NPs and astrocytes. The lack of any major involvement of DNA-PKcs in NHEJ in hESCs was supported by siRNA-mediated DNA-PKcs knockdown. Expression of a truncated XRCC4 decoy or XRCC4 knock-down reduced NHEJ by more than half suggesting that repair is primarily canonical NHEJ. Poly(ADP-ribose) polymerase (PARP) was dispensable for NHEJ suggesting that repair is largely independent of backup NHEJ. Furthermore, as hESCs differentiated a progressive decrease in the accuracy of NHEJ was observed. Altogether, we conclude that NHEJ in hESCs is largely independent of ATM, DNA-PKcs, and PARP but dependent on XRCC4 with repair fidelity several-fold greater than in astrocytes.
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PMID:ATM-independent, high-fidelity nonhomologous end joining predominates in human embryonic stem cells. 2084 17

Exposure to hypoxia-induced replication arrest initiates a DNA damage response that includes both ATR- and ATM-mediated signaling. DNA fiber analysis was used to show that these conditions lead to a replication arrest during both the initiation and elongation phases, and that this correlated with decreased levels of nucleotides. The DNA damage response induced by hypoxia is distinct from the classical pathways induced by damaging agents, primarily due to the lack of detectable DNA damage, but also due to the coincident repression of DNA repair in hypoxic conditions. The principle aims of the hypoxia-induced DNA damage response seem to be the induction of p53-dependent apoptosis or the preservation of replication fork integrity. The latter is of particular importance should reoxygenation occur. Tumor reoxygenation occurs as a result of spontaneous changes in blood flow and also therapy. Cells experiencing hypoxia and/or reoxygenation are, therefore, sensitive to loss or inhibition of components of the DNA damage response, including Chk1, ATM, ATR, and poly(ADP-ribose) polymerase (PARP). In addition, restoration of hypoxia-induced p53-mediated signaling may well be effective in the targeting of hypoxic cells. The DNA damage response is also induced in endothelial cells at moderate levels of hypoxia, which do not induce replication arrest. In this situation, phosphorylation of H2AX has been shown to be required for proliferation and angiogenesis and is, therefore, an attractive potential therapeutic target.
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PMID:Targeting hypoxic cells through the DNA damage response. 2087 54

DNA damage is a key factor both in the evolution and treatment of cancer. Genomic instability is a common feature of cancer cells, fuelling accumulation of oncogenic mutations, while radiation and diverse genotoxic agents remain important, if imperfect, therapeutic modalities. Cellular responses to DNA damage are coordinated primarily by two distinct kinase signaling cascades, the ATM-Chk2 and ATR-Chk1 pathways, which are activated by DNA double-strand breaks (DSBs) and single-stranded DNA respectively. Historically, these pathways were thought to act in parallel with overlapping functions; however, more recently it has become apparent that their relationship is more complex. In response to DSBs, ATM is required both for ATR-Chk1 activation and to initiate DNA repair via homologous recombination (HRR) by promoting formation of single-stranded DNA at sites of damage through nucleolytic resection. Interestingly, cells and organisms survive with mutations in ATM or other components required for HRR, such as BRCA1 and BRCA2, but at the cost of genomic instability and cancer predisposition. By contrast, the ATR-Chk1 pathway is the principal direct effector of the DNA damage and replication checkpoints and, as such, is essential for the survival of many, although not all, cell types. Remarkably, deficiency for HRR in BRCA1- and BRCA2-deficient tumors confers sensitivity to cisplatin and inhibitors of poly(ADP-ribose) polymerase (PARP), an enzyme required for repair of endogenous DNA damage. In addition, suppressing DNA damage and replication checkpoint responses by inhibiting Chk1 can enhance tumor cell killing by diverse genotoxic agents. Here, we review current understanding of the organization and functions of the ATM-Chk2 and ATR-Chk1 pathways and the prospects for targeting DNA damage signaling processes for therapeutic purposes.
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PMID:The ATM-Chk2 and ATR-Chk1 pathways in DNA damage signaling and cancer. 2103 66

Treatment of PARP-1-expressing cells with the combination of a DNA methylating agent (MMS) and the PARP inhibitor 4-amino-1,8-naphthalimide (4-AN) leads to an ATR/Chk1-dependent S phase checkpoint and cell death by apoptosis. Activation of ATM/Chk2 is involved in sustaining the S phase checkpoint, and double strand break (DSB) accumulation was demonstrated. NBS1, part of the MRN complex that responds to DSBs, is known to modulate ATR- and ATM-dependent checkpoint responses to UV and IR, but a role in the response to PARP inhibition has not been addressed. Here we show that the S phase checkpoint observed 4-8h after MMS+4-AN treatment was absent in cells deficient in NBS1, but was present in NBS1-complemented (i.e., functionally wild-type) cells, indicating a critical role for NBS1 in this checkpoint response. NBS1 was phosphorylated in response to MMS+4-AN treatment, and this was partially ATR- and ATM-dependent, suggesting involvement of both upstream kinases. NBS1 expression had little effect on ATR-mediated phosphorylation of Chk1 and ATM-mediated phosphorylation of Chk2 in response to MMS+4-AN. Phosphorylation of SMC1 was also observed in response to MMS+4-AN treatment. In the absence of ATM and NBS1, phosphorylation of SMC1 was weak, especially at early times after MMS+4-AN treatment. In the absence of ATR activation, reduced SMC1 phosphorylation was seen over a 24h time course. These results suggested that both ATR and ATM phosphorylate SMC1 in response to MMS+4-AN and that this phosphorylation is enhanced by phospho-NBS1. The loss of the MMS+4-AN-induced S phase checkpoint in NBS1-deficient cells may be due to a reduced cellular level of the critical downstream effector, phospho-SMC1.
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PMID:Requirement for NBS1 in the S phase checkpoint response to DNA methylation combined with PARP inhibition. 2113 Jul 14


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