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Park JI, Jung SY, Song KH, Lee DH, Ahn J, Hwang SG, Jung IS, Lim DS, Song JY. Predictive DNA damage signaling for low‑dose ionizing radiation. Int J Mol Med 2024; 53:56. [PMID: 38695243 DOI: 10.3892/ijmm.2024.5380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 04/17/2024] [Indexed: 05/16/2024] Open
Abstract
Numerous studies have attempted to develop biological markers for the response to radiation for broad and straightforward application in the field of radiation. Based on a public database, the present study selected several molecules involved in the DNA damage repair response, cell cycle regulation and cytokine signaling as promising candidates for low‑dose radiation‑sensitive markers. The HuT 78 and IM‑9 cell lines were irradiated in a concentration‑dependent manner, and the expression of these molecules was analyzed using western blot analysis. Notably, the activation of ataxia telangiectasia mutated (ATM), checkpoint kinase 2 (CHK2), p53 and H2A histone family member X (H2AX) significantly increased in a concentration‑dependent manner, which was also observed in human peripheral blood mononuclear cells. To determine the radioprotective effects of cinobufagin, as an ATM and CHK2 activator, an in vivo model was employed using sub‑lethal and lethal doses in irradiated mice. Treatment with cinobufagin increased the number of bone marrow cells in sub‑lethal irradiated mice, and slightly elongated the survival of lethally irradiated mice, although the difference was not statistically significant. Therefore, KU60019, BML‑277, pifithrin‑α, and nutlin‑3a were evaluated for their ability to modulate radiation‑induced cell death. The use of BML‑277 led to a decrease in radiation‑induced p‑CHK2 and γH2AX levels and mitigated radiation‑induced apoptosis. On the whole, the present study provides a novel approach for developing drug candidates based on the profiling of biological radiation‑sensitive markers. These markers hold promise for predicting radiation exposure and assessing the associated human risk.
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Affiliation(s)
- Jeong-In Park
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - Seung-Youn Jung
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - Kyung-Hee Song
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - Dong-Hyeon Lee
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - Jiyeon Ahn
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - Sang-Gu Hwang
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - In-Su Jung
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
| | - Dae-Seog Lim
- Department of Biotechnology, CHA University, Seongnam, Gyeonggi‑do 13488, Republic of Korea
| | - Jie-Young Song
- Division of Radiation Biomedical Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Republic of Korea
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2
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Coyle JP, Johnson C, Jensen J, Farcas M, Derk R, Stueckle TA, Kornberg TG, Rojanasakul Y, Rojanasakul LW. Variation in pentose phosphate pathway-associated metabolism dictates cytotoxicity outcomes determined by tetrazolium reduction assays. Sci Rep 2023; 13:8220. [PMID: 37217524 DOI: 10.1038/s41598-023-35310-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 05/16/2023] [Indexed: 05/24/2023] Open
Abstract
Tetrazolium reduction and resazurin assays are the mainstay of routine in vitro toxicity batteries. However, potentially erroneous characterization of cytotoxicity and cell proliferation can arise if verification of baseline interaction of test article with method employed is neglected. The current investigation aimed to demonstrate how interpretation of results from several standard cytotoxicity and proliferation assays vary in dependence on contributions from the pentose phosphate pathway (PPP). Non-tumorigenic Beas-2B cells were treated with graded concentrations of benzo[a]pyrene (B[a]P) for 24 and 48 h prior to cytotoxicity and proliferation assessment with commonly used MTT, MTS, WST1, and Alamar Blue assays. B[a]P caused enhanced metabolism of each dye assessed despite reductions in mitochondrial membrane potential and was reversed by 6-aminonicotinamide (6AN)-a glucose-6-phosphate dehydrogenase inhibitor. These results demonstrate differential sensitivity of standard cytotoxicity assessments on the PPP, thus (1) decoupling "mitochondrial activity" as an interpretation of cellular formazan and Alamar Blue metabolism, and (2) demonstrating the implicit requirement for investigators to sufficiently verify interaction of these methods in routine cytotoxicity and proliferation characterization. The nuances of method-specific extramitochondrial metabolism must be scrutinized to properly qualify specific endpoints employed, particularly under the circumstances of metabolic reprogramming.
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Affiliation(s)
- Jayme P Coyle
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA.
- Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 1095 Willowdale Rd., Morgantown, WV, 26505, USA.
| | - Caroline Johnson
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA
| | - Jake Jensen
- Department of Environmental Health, Harvard University, Boston, MA, USA
| | - Mariana Farcas
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA
- Department of Pharmaceutical Sciences, West Virginia University, Morgantown, WV, USA
| | - Raymond Derk
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA
| | - Todd A Stueckle
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA
| | - Tiffany G Kornberg
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA
| | - Yon Rojanasakul
- Department of Pharmaceutical Sciences, West Virginia University, Morgantown, WV, USA
| | - Liying W Rojanasakul
- HELD/ACIB, National Institute for Occupational Safety and Health, Morgantown, WV, USA.
- Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 1095 Willowdale Rd., Morgantown, WV, 26505, USA.
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3
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Luo D, Mladenov E, Soni A, Stuschke M, Iliakis G. The p38/MK2 Pathway Functions as Chk1-Backup Downstream of ATM/ATR in G 2-Checkpoint Activation in Cells Exposed to Ionizing Radiation. Cells 2023; 12:1387. [PMID: 37408221 DOI: 10.3390/cells12101387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Revised: 05/06/2023] [Accepted: 05/11/2023] [Indexed: 07/07/2023] Open
Abstract
We have recently reported that in G2-phase cells (but not S-phase cells) sustaining low loads of DNA double-strand break (DSBs), ATM and ATR regulate the G2-checkpoint epistatically, with ATR at the output-node, interfacing with the cell cycle through Chk1. However, although inhibition of ATR nearly completely abrogated the checkpoint, inhibition of Chk1 using UCN-01 generated only partial responses. This suggested that additional kinases downstream of ATR were involved in the transmission of the signal to the cell cycle engine. Additionally, the broad spectrum of kinases inhibited by UCN-01 pointed to uncertainties in the interpretation that warranted further investigations. Here, we show that more specific Chk1 inhibitors exert an even weaker effect on G2-checkpoint, as compared to ATR inhibitors and UCN-01, and identify the MAPK p38α and its downstream target MK2 as checkpoint effectors operating as backup to Chk1. These observations further expand the spectrum of p38/MK2 signaling to G2-checkpoint activation, extend similar studies in cells exposed to other DNA damaging agents and consolidate a role of p38/MK2 as a backup kinase module, adding to similar backup functions exerted in p53 deficient cells. The results extend the spectrum of actionable strategies and targets in current efforts to enhance the radiosensitivity in tumor cells.
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Affiliation(s)
- Daxian Luo
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Emil Mladenov
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Aashish Soni
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
| | - Martin Stuschke
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- German Cancer Consortium (DKTK), Partner Site University Hospital Essen, 45147 Essen, Germany
- German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
- Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
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Khan MGM, Wang Y. Advances in the Current Understanding of How Low-Dose Radiation Affects the Cell Cycle. Cells 2022; 11:cells11030356. [PMID: 35159169 PMCID: PMC8834401 DOI: 10.3390/cells11030356] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/15/2022] [Accepted: 01/20/2022] [Indexed: 12/12/2022] Open
Abstract
Cells exposed to ionizing radiation undergo a series of complex responses, including DNA damage, reproductive cell death, and altered proliferation states, which are all linked to cell cycle dynamics. For many years, a great deal of research has been conducted on cell cycle checkpoints and their regulators in mammalian cells in response to high-dose exposures to ionizing radiation. However, it is unclear how low-dose ionizing radiation (LDIR) regulates the cell cycle progression. A growing body of evidence demonstrates that LDIR may have profound effects on cellular functions. In this review, we summarize the current understanding of how LDIR (of up to 200 mGy) regulates the cell cycle and cell-cycle-associated proteins in various cellular settings. In light of current findings, we also illustrate the conceptual function and possible dichotomous role of p21Waf1, a transcriptional target of p53, in response to LDIR.
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Affiliation(s)
- Md Gulam Musawwir Khan
- Radiobiology and Health, Canadian Nuclear Laboratories (CNL), Chalk River, ON K0J 1J0, Canada;
| | - Yi Wang
- Radiobiology and Health, Canadian Nuclear Laboratories (CNL), Chalk River, ON K0J 1J0, Canada;
- Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Correspondence:
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Petsalaki E, Zachos G. An ATM-Chk2-INCENP pathway activates the abscission checkpoint. J Cell Biol 2021; 220:211635. [PMID: 33355621 PMCID: PMC7769160 DOI: 10.1083/jcb.202008029] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 10/29/2020] [Accepted: 11/23/2020] [Indexed: 02/07/2023] Open
Abstract
During cell division, in response to chromatin bridges, the chromosomal passenger complex (CPC) delays abscission to prevent chromosome breakage or tetraploidization. Here, we show that inhibition of ATM or Chk2 kinases impairs CPC localization to the midbody center, accelerates midbody resolution in normally segregating cells, and correlates with premature abscission and chromatin breakage in cytokinesis with trapped chromatin. In cultured human cells, ATM activates Chk2 at late midbodies. In turn, Chk2 phosphorylates human INCENP-Ser91 to promote INCENP binding to Mklp2 kinesin and CPC localization to the midbody center through Mklp2 association with Cep55. Expression of truncated Mklp2 that does not bind to Cep55 or nonphosphorylatable INCENP-Ser91A impairs CPC midbody localization and accelerates abscission. In contrast, expression of phosphomimetic INCENP-Ser91D or a chimeric INCENP protein that is targeted to the midbody center rescues the abscission delay in Chk2-deficient or ATM-deficient cells. Furthermore, the Mre11–Rad50–Nbs1 complex is required for ATM activation at the midbody in cytokinesis with chromatin bridges. These results identify an ATM–Chk2–INCENP pathway that imposes the abscission checkpoint by regulating CPC midbody localization.
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Affiliation(s)
- Eleni Petsalaki
- Department of Biology, University of Crete, Heraklion, Greece
| | - George Zachos
- Department of Biology, University of Crete, Heraklion, Greece
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Petsalaki E, Zachos G. DNA damage response proteins regulating mitotic cell division: double agents preserving genome stability. FEBS J 2020; 287:1700-1721. [PMID: 32027459 DOI: 10.1111/febs.15240] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 01/10/2020] [Accepted: 02/04/2020] [Indexed: 12/11/2022]
Abstract
The DNA damage response recognizes DNA lesions and coordinates a cell cycle arrest with the repair of the damaged DNA, or removal of the affected cells to prevent the passage of genetic alterations to the next generation. The mitotic cell division, on the other hand, is a series of processes that aims to accurately segregate the genomic material from the maternal to the two daughter cells. Despite their great importance in safeguarding genomic integrity, the DNA damage response and the mitotic cell division were long viewed as unrelated processes, mainly because animal cells that are irradiated during mitosis continue cell division without repairing the broken chromosomes. However, recent studies have demonstrated that DNA damage proteins play an important role in mitotic cell division. This is performed through regulation of the onset of mitosis, mitotic spindle formation, correction of misattached kinetochore-microtubules, spindle checkpoint signaling, or completion of cytokinesis (abscission), in the absence of DNA damage. In this review, we summarize the roles of DNA damage proteins in unperturbed mitosis, analyze the molecular mechanisms involved, and discuss the potential implications of these findings in cancer therapy.
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Affiliation(s)
- Eleni Petsalaki
- Department of Biology, University of Crete, Heraklion, Greece
| | - George Zachos
- Department of Biology, University of Crete, Heraklion, Greece
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Póti Á, Gyergyák H, Németh E, Rusz O, Tóth S, Kovácsházi C, Chen D, Szikriszt B, Spisák S, Takeda S, Szakács G, Szallasi Z, Richardson AL, Szüts D. Correlation of homologous recombination deficiency induced mutational signatures with sensitivity to PARP inhibitors and cytotoxic agents. Genome Biol 2019; 20:240. [PMID: 31727117 PMCID: PMC6857305 DOI: 10.1186/s13059-019-1867-0] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 10/28/2019] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND Homologous recombination (HR) repair deficiency arising from defects in BRCA1 or BRCA2 is associated with characteristic patterns of somatic mutations. In this genetic study, we ask whether inactivating mutations in further genes of the HR pathway or the DNA damage checkpoint also give rise to somatic mutation patterns that can be used for treatment prediction. RESULTS Using whole genome sequencing of an isogenic knockout cell line panel, we find a universal HR deficiency-specific base substitution signature that is similar to COSMIC signature 3. In contrast, we detect different deletion phenotypes corresponding to specific HR mutants. The inactivation of BRCA2 or PALB2 leads to larger deletions, typically with microhomology, when compared to the disruption of BRCA1, RAD51 paralogs, or RAD54. Comparison with the deletion spectrum of Cas9 cut sites suggests that most spontaneously arising genomic deletions are not the consequence of double-strand breaks. Surprisingly, the inactivation of checkpoint kinases ATM and CHK2 has no mutagenic consequences. Analysis of tumor exomes with biallelic inactivating mutations in the investigated genes confirms the validity of the cell line models. We present a comprehensive analysis of sensitivity of the investigated mutants to 13 therapeutic agents for the purpose of correlating genomic mutagenic phenotypes with drug sensitivity. CONCLUSION Our results suggest that no single genomic mutational class shows perfect correlation with sensitivity to common treatments, but the contribution of COSMIC signature 3 to base substitutions, or a combined measure of different features, may be reasonably good at predicting platinum and PARP inhibitor sensitivity.
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Affiliation(s)
- Ádám Póti
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Hella Gyergyák
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Eszter Németh
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Orsolya Rusz
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
- Department of Oncotherapy, University of Szeged, Szeged, Hungary
| | - Szilárd Tóth
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Csenger Kovácsházi
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Dan Chen
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Bernadett Szikriszt
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
| | - Sándor Spisák
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, 02215, USA
- Center for Functional Cancer Epigenetics, Dana-Farber Cancer Institute, Boston, MA, 02215, USA
| | - Shunichi Takeda
- Department of Radiation Genetics, Kyoto University Medical School, Kyoto, 606-8501, Japan
| | - Gergely Szakács
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary
- Institute of Cancer Research, Medical University Vienna, Vienna, Austria
| | - Zoltan Szallasi
- Computational Health Informatics Program (CHIP), Boston Children's Hospital, Boston, MA, USA
- Harvard Medical School, Boston, MA, USA
- Danish Cancer Society Research Center, Copenhagen, Denmark
- SE-NAP, Brain Metastasis Research Group, 2nd Department of Pathology, Semmelweis University, Budapest, Hungary
| | | | - Dávid Szüts
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudosok krt 2, Budapest, H-1117, Hungary.
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Mladenov E, Fan X, Paul-Konietzko K, Soni A, Iliakis G. DNA-PKcs and ATM epistatically suppress DNA end resection and hyperactivation of ATR-dependent G 2-checkpoint in S-phase irradiated cells. Sci Rep 2019; 9:14597. [PMID: 31601897 PMCID: PMC6787047 DOI: 10.1038/s41598-019-51071-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 09/20/2019] [Indexed: 11/29/2022] Open
Abstract
We previously reported that cells exposed to low doses of ionizing radiation (IR) in the G2-phase of the cell cycle activate a checkpoint that is epistatically regulated by ATM and ATR operating as an integrated module. In this module, ATR interphases exclusively with the cell cycle to implement the checkpoint, mainly using CHK1. The ATM/ATR module similarly regulates DNA end-resection at low IR-doses. Strikingly, at high IR-doses, the ATM/ATR coupling relaxes and each kinase exerts independent contributions to resection and the G2-checkpoint. DNA-PKcs links to the ATM/ATR module and defects cause hyper-resection and hyperactivation of G2-checkpoint at all doses examined. Surprisingly, our present report reveals that cells irradiated in S-phase utilize a different form of wiring between DNA-PKcs/ATM/ATR: The checkpoint activated in G2-phase is regulated exclusively by ATR/CHK1; similarly at high and low IR-doses. DNA end-resection supports ATR-activation, but inhibition of ATR leaves resection unchanged. DNA-PKcs and ATM link now epistatically to resection and their inhibition causes hyper-resection and ATR-dependent G2-checkpoint hyperactivation at all IR-doses. We propose that DNA-PKcs, ATM and ATR form a modular unit to regulate DSB processing with their crosstalk distinctly organized in S- and G2- phase, with strong dependence on DSB load only in G2-phase.
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Affiliation(s)
- Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
| | - Xiaoxiang Fan
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Katja Paul-Konietzko
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Aashish Soni
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
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9
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Mladenov E, Fan X, Dueva R, Soni A, Iliakis G. Radiation-dose-dependent functional synergisms between ATM, ATR and DNA-PKcs in checkpoint control and resection in G 2-phase. Sci Rep 2019; 9:8255. [PMID: 31164689 PMCID: PMC6547644 DOI: 10.1038/s41598-019-44771-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 04/23/2019] [Indexed: 12/31/2022] Open
Abstract
Using data generated with cells exposed to ionizing-radiation (IR) in G2-phase of the cell cycle, we describe dose-dependent interactions between ATM, ATR and DNA-PKcs revealing unknown mechanistic underpinnings for two key facets of the DNA damage response: DSB end-resection and G2-checkpoint activation. At low IR-doses that induce low DSB-numbers in the genome, ATM and ATR regulate epistatically the G2-checkpoint, with ATR at the output-node, interfacing with the cell-cycle predominantly through Chk1. Strikingly, at low IR-doses, ATM and ATR epistatically regulate also resection, and inhibition of either activity fully suppresses resection. At high IR-doses that induce high DSB-numbers in the genome, the tight ATM/ATR coupling relaxes and independent outputs to G2-checkpoint and resection occur. Consequently, both kinases must be inhibited to fully suppress checkpoint activation and resection. DNA-PKcs integrates to the ATM/ATR module by regulating resection at all IR-doses, with defects in DNA-PKcs causing hyper-resection and G2-checkpoint hyper-activation. Notably, hyper-resection is absent from other c-NHEJ mutants. Thus, DNA-PKcs specifically regulates resection and adjusts the activation of the ATM/ATR module. We propose that selected DSBs are shepherd by DNA-PKcs from c-NHEJ to resection-dependent pathways for processing under the regulatory supervision of the ATM/ATR module.
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Affiliation(s)
- Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Xiaoxiang Fan
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Rositsa Dueva
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Aashish Soni
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
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10
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Chromatin control in double strand break repair. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2019. [PMID: 30798938 DOI: 10.1016/bs.apcsb.2018.11.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/15/2023]
Abstract
DNA double strand breaks (DSB) are the most deleterious type of damage inflicted on DNA by various environmental factors and as consequences of normal cellular metabolism. The multistep nature of DSB repair and the need to assemble large protein complexes at repair sites necessitate multiple chromatin changes there. This review focuses on the key findings of how chromatin regulators exert temporal and spatial control on DSB repair. These mechanisms coordinate repair with cell cycle progression, lead to DSB repair pathway choice, provide accessibility of repair machinery to damaged sites and move the lesions to nuclear environments permissive for repair.
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11
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Shuryak I. Modeling species richness and abundance of phytoplankton and zooplankton in radioactively contaminated water bodies. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2018; 192:14-25. [PMID: 29883873 DOI: 10.1016/j.jenvrad.2018.05.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 04/04/2018] [Accepted: 05/22/2018] [Indexed: 06/08/2023]
Abstract
Water bodies polluted by the Mayak nuclear plant in Russia provide valuable information on multi-generation effects of radioactive contamination on freshwater organisms. For example, lake Karachay was probably the most radioactive lake in the world: its water contained ∼2 × 107 Bq/L of radionuclides and estimated dose rates to plankton exceeded 5 Gy/h. We performed quantitative modeling of radiation effects on phytoplankton and zooplankton species richness and abundance in Mayak-contaminated water bodies. Due to collinearity between radioactive contamination, water body size and salinity, we combined these variables into one (called HabitatFactors). We employed a customized machine learning approach, where synthetic noise variables acted as benchmarks of predictor performance. HabitatFactors was the only predictor that outperformed noise variables and, therefore, we used it for parametric modeling of plankton responses. Best-fit model predictions suggested 50% species richness reduction at HabitatFactors values corresponding to dose rates of 104-105 μGy/h for phytoplankton, and 103-104 μGy/h for zooplankton. Under conditions similar to those in lake Karachay, best-fit models predicted 81-98% species richness reductions for various taxa (Cyanobacteria, Bacillariophyta, Chlorophyta, Rotifera, Cladocera and Copepoda), ∼20-300-fold abundance reduction for total zooplankton, but no abundance reduction for phytoplankton. Rotifera was the only taxon whose fractional abundance increased with contamination level, reaching 100% in lake Karachay, but Rotifera species richness declined with contamination level, as in other taxa. Under severe radioactive and chemical contamination, one species of Cyanobacteria (Geitlerinema amphibium) dominated phytoplankton, and rotifers from the genus Brachionus dominated zooplankton. The modeling approaches proposed here are applicable to other radioecological data sets. The results provide quantitative information and easily interpretable model parameter estimates for the shapes and magnitudes of freshwater plankton responses to a wide range of radioactive contamination levels.
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Affiliation(s)
- Igor Shuryak
- Center for Radiological Research, Columbia University, New York, NY, United States.
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12
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Shuryak I, Matrosova VY, Gaidamakova EK, Tkavc R, Grichenko O, Klimenkova P, Volpe RP, Daly MJ. Microbial cells can cooperate to resist high-level chronic ionizing radiation. PLoS One 2017; 12:e0189261. [PMID: 29261697 PMCID: PMC5738026 DOI: 10.1371/journal.pone.0189261] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 11/22/2017] [Indexed: 11/18/2022] Open
Abstract
Understanding chronic ionizing radiation (CIR) effects is of utmost importance to protecting human health and the environment. Diverse bacteria and fungi inhabiting extremely radioactive waste and disaster sites (e.g. Hanford, Chernobyl, Fukushima) represent new targets of CIR research. We show that many microorganisms can grow under intense gamma-CIR dose rates of 13–126 Gy/h, with fungi identified as a particularly CIR-resistant group of eukaryotes: among 145 phylogenetically diverse strains tested, 78 grew under 36 Gy/h. Importantly, we demonstrate that CIR resistance can depend on cell concentration and that certain resistant microbial cells protect their neighbors (not only conspecifics, but even radiosensitive species from a different phylum), from high-level CIR. We apply a mechanistically-motivated mathematical model of CIR effects, based on accumulation/removal kinetics of reactive oxygen species (ROS) and antioxidants, in bacteria (3 Escherichia coli strains and Deinococcus radiodurans) and in fungi (Candida parapsilosis, Kazachstania exigua, Pichia kudriavzevii, Rhodotorula lysinophila, Saccharomyces cerevisiae, and Trichosporon mucoides). We also show that correlations between responses to CIR and acute ionizing radiation (AIR) among studied microorganisms are weak. For example, in D. radiodurans, the best molecular correlate for CIR resistance is the antioxidant enzyme catalase, which is dispensable for AIR resistance; and numerous CIR-resistant fungi are not AIR-resistant. Our experimental findings and quantitative modeling thus demonstrate the importance of investigating CIR responses directly, rather than extrapolating from AIR. Protection of radiosensitive cell-types by radioresistant ones under high-level CIR is a potentially important new tool for bioremediation of radioactive sites and development of CIR-resistant microbiota as radioprotectors.
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Affiliation(s)
- Igor Shuryak
- Center for Radiological Research, Columbia University, New York, NY, United States of America
- * E-mail:
| | - Vera Y. Matrosova
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States of America
| | - Elena K. Gaidamakova
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States of America
| | - Rok Tkavc
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States of America
| | - Olga Grichenko
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States of America
| | - Polina Klimenkova
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States of America
| | - Robert P. Volpe
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, United States of America
| | - Michael J. Daly
- Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, MD, United States of America
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Geraldo JM, Scalzo S, Reis DS, Leão TL, Guatimosim S, Ladeira LO, Andrade LM. HDR brachytherapy decreases proliferation rate and cellular progression of a radioresistant human squamous cell carcinoma in vitro. Int J Radiat Biol 2017; 93:958-966. [DOI: 10.1080/09553002.2017.1341661] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Jony M. Geraldo
- Departamento de Anatomia por Imagens, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
- Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Brazil
| | - Sérgio Scalzo
- Departamento de Fisiologia e Biofisica, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Daniela S. Reis
- Departamento de Bioquimica e imunologia, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Thiago L. Leão
- Departamento de Microbiologia, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Silvia Guatimosim
- Departamento de Fisiologia e Biofisica, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Luiz O. Ladeira
- Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Brazil
- Departamento de Fisica, Nanobiomedical Research Group, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Lídia M. Andrade
- Departamento de Fisica, Nanobiomedical Research Group, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
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14
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Zheng W, Luo Z, Zhang J, Min P, Li W, Xu D, Zhang Z, Xiong P, Liang H, Liu J. Neural precursor cell expressed, developmentally downregulated 8-activating enzyme inhibitor MLN4924 sensitizes colorectal cancer cells to oxaliplatin by inducing DNA damage, G2 cell cycle arrest and apoptosis. Mol Med Rep 2017; 15:2795-2801. [DOI: 10.3892/mmr.2017.6305] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Accepted: 01/19/2017] [Indexed: 11/05/2022] Open
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15
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Qin CJ, Song XM, Chen ZH, Ren XQ, Xu KW, Jing H, He YL. XRCC2 as a predictive biomarker for radioresistance in locally advanced rectal cancer patients undergoing preoperative radiotherapy. Oncotarget 2016; 6:32193-204. [PMID: 26320178 PMCID: PMC4741669 DOI: 10.18632/oncotarget.4975] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 07/16/2015] [Indexed: 12/15/2022] Open
Abstract
XRCC2 has been shown to increase the radioresistance of some cancers. Here, XRCC2 expression was investigated as a predictor of preoperative radiotherapy (PRT) treatment response in locally advanced rectal cancer (LARC). XRCC2 was found to be overexpressed in rectal cancer tissues resected from patients who underwent surgery without PRT. In addition, overall survival for LARC patients was improved in XRCC2-negative patients compared with XRCC2-positive patients after treatment with PRT (P < 0.001). XRCC2 expression was also associated with an increase in LARC radioresistance. Conversely, XRCC2-deficient cancer cells were more sensitive to irradiation in vitro, and a higher proportion of these cells underwent cell death induced by G2/M phase arrest and apoptosis. When XRCC2 was knocked down, the repair of DNA double-strand breaks caused by irradiation was impaired. Therefore, XRCC2 may increases LARC radioresistance by repairing DNA double-strand breaks and preventing cancer cell apoptosis. Moreover, the present data suggest that XRCC2 is a useful predictive biomarker of PRT treatment response in LARC patients. Thus, inhibition of XRCC2 expression or activity represents a potential therapeutic strategy for improving PRT response in LARC patients.
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Affiliation(s)
- Chang-Jiang Qin
- Department of Gastrointestinal and Pancreatic Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.,Department of Gastrointestinal Surgery, Huaihe Hospital of Hennan University, Kaifeng, China
| | - Xin-Ming Song
- Department of Gastrointestinal and Pancreatic Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Zhi-Hui Chen
- Department of Gastrointestinal and Pancreatic Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Xue-Qun Ren
- Department of Gastrointestinal Surgery, Huaihe Hospital of Hennan University, Kaifeng, China
| | - Kai-Wu Xu
- Department of Gastrointestinal and Pancreatic Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Hong Jing
- Department of Pathology, Huaihe Hospital of Hennan University, Kaifeng, China
| | - Yu-Long He
- Department of Gastrointestinal and Pancreatic Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
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16
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Lin HY, Hung SK, Lee MS, Chiou WY, Huang TT, Tseng CE, Shih LY, Lin RI, Lin JMJ, Lai YH, Chang CB, Hsu FC, Chen LC, Tsai SJ, Su YC, Li SC, Lai HC, Hsu WL, Liu DW, Tai CK, Wu SF, Chan MWY. DNA methylome analysis identifies epigenetic silencing of FHIT as a determining factor for radiosensitivity in oral cancer: an outcome-predicting and treatment-implicating study. Oncotarget 2015; 6:915-34. [PMID: 25460508 PMCID: PMC4359265 DOI: 10.18632/oncotarget.2821] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 11/24/2014] [Indexed: 12/17/2022] Open
Abstract
Radioresistance is still an emerging problem for radiotherapy of oral cancer. Aberrant epigenetic alterations play an important role in cancer development, yet the role of such alterations in radioresistance of oral cancer is not fully explored. Using a methylation microarray, we identified promoter hypermethylation of FHIT (fragile histidine triad) in radioresistant OML1-R cells, established from hypo-fractionated irradiation of parental OML1 radiosensitive oral cancer cells. Further analysis confirmed that transcriptional repression of FHIT was due to promoter hypermethylation, H3K27me3 and overexpression of methyltransferase EZH2 in OML1-R cells. Epigenetic interventions or depletion of EZH2 restored FHIT expression. Ectopic expression of FHIT inhibited tumor growth in both in vitro and in vivo models, while also resensitizing radioresistant cancer cells to irradiation, by restoring Chk2 phosphorylation and G2/M arrest. Clinically, promoter hypermethylation of FHIT inversely correlated with its expression and independently predicted both locoregional control and overall survival in 40 match-paired oral cancer patient samples. Further in vivo therapeutic experiments confirmed that inhibition of DNA methylation significantly resensitized radioresistant oral cancer cell xenograft tumors. These results show that epigenetic silencing of FHIT contributes partially to radioresistance and predicts clinical outcomes in irradiated oral cancer. The radiosensitizing effect of epigenetic interventions warrants further clinical investigation.
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Affiliation(s)
- Hon-Yi Lin
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC.,Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Shih-Kai Hung
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Moon-Sing Lee
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Wen-Yen Chiou
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Tze-Ta Huang
- Department of Oral and Maxillofacial Surgery, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC.,Institute of Oral Medicine, National Cheng Kung University, Tainan, Taiwan, ROC
| | - Chih-En Tseng
- Department of Anatomic Pathology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Liang-Yu Shih
- Department of Anatomic Pathology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Ru-Inn Lin
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC.,Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Jora M J Lin
- Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.,Department of Life Science, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Yi-Hui Lai
- Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.,Department of Life Science, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Chia-Bin Chang
- Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.,Department of Life Science, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Feng-Chun Hsu
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC
| | - Liang-Cheng Chen
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC
| | - Shiang-Jiun Tsai
- Department of Radiation Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC
| | - Yu-Chieh Su
- Department of Hematology-Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Szu-Chi Li
- Department of Hematology-Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Hung-Chih Lai
- Department of Hematology-Oncology, Buddhist Dalin Tzu Chi General Hospital, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Wen-Lin Hsu
- Department of Radiation Oncology, Buddhist Tzu Chi General Hospital, Hualien, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Dai-Wei Liu
- Department of Radiation Oncology, Buddhist Tzu Chi General Hospital, Hualien, Taiwan, ROC.,School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Chien-Kuo Tai
- Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.,Department of Life Science, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Shu-Fen Wu
- Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.,Department of Life Science, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
| | - Michael W Y Chan
- Institute of Molecular Biology, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.Department of Life Science, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC.Human Epigenomics Center, National Chung Cheng University, Min-Hsiung, Chia-Yi, Taiwan, ROC
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17
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Davari K, Frankenberger S, Schmidt A, Tomi NS, Jungnickel B. Checkpoint kinase 2 is required for efficient immunoglobulin diversification. Cell Cycle 2015; 13:3659-69. [PMID: 25483076 DOI: 10.4161/15384101.2014.964112] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Maintenance of genome integrity relies on multiple DNA repair pathways as well as on checkpoint regulation. Activation of the checkpoint kinases Chk1 and Chk2 by DNA damage triggers cell cycle arrest and improved DNA repair, or apoptosis in case of excessive damage. Chk1 and Chk2 have been reported to act in a complementary or redundant fashion, depending on the physiological context. During secondary immunoglobulin (Ig) diversification in B lymphocytes, DNA damage is abundantly introduced by activation-induced cytidine deaminase (AID) and processed to mutations in a locus-specific manner by several error-prone DNA repair pathways. We have previously shown that Chk1 negatively regulates Ig somatic hypermutation by promoting error-free homologous recombination and Ig gene conversion. We now report that Chk2 shows opposite effects to Chk1 in the regulation of these processes. Chk2 inactivation in B cells leads to decreased Ig hypermutation and Ig class switching, and increased Ig gene conversion activity. This is linked to defects in non-homologous end joining and increased Chk1 activation upon interference with Chk2 function. Intriguingly, in the context of physiological introduction of substantial DNA damage into the genome during Ig diversification, the 2 checkpoint kinases thus function in an opposing manner, rather than redundantly or cooperatively.
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Key Words
- AID, activation-induced cytidine deaminase
- APE1, apurinic endonuclease 1
- ATM, ataxia telangiectasia mutated
- ATR, ataxia telangiectasia and rad3 related
- Chk, checkpoint kinase
- DNA repair
- HR, homologous recombination
- Ig, immunoglobulin
- MMR mismatch repair
- MMS, methyl methansulfonate
- NHEJ, non-homologous end joining
- UNG, uracil N-glycosilase
- checkpoint signaling
- germinal center
- immunoglobulin diversification
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Affiliation(s)
- Kathrin Davari
- a Department of Cell Biology; Institute of Biochemistry and Biophysics; Center for Molecular Biomedicine ; Friedrich-Schiller University Jena ; Jena , Germany
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18
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Kabacik S, Manning G, Raffy C, Bouffler S, Badie C. Time, Dose and Ataxia Telangiectasia Mutated (ATM) Status Dependency of Coding and Noncoding RNA Expression after Ionizing Radiation Exposure. Radiat Res 2015; 183:325-37. [DOI: 10.1667/rr13876.1] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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19
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Petsalaki E, Zachos G. Chk2 prevents mitotic exit when the majority of kinetochores are unattached. J Cell Biol 2014; 205:339-56. [PMID: 24798733 PMCID: PMC4018780 DOI: 10.1083/jcb.201310071] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Accepted: 04/04/2014] [Indexed: 11/29/2022] Open
Abstract
The spindle checkpoint delays exit from mitosis in cells with spindle defects. In this paper, we show that Chk2 is required to delay anaphase onset when microtubules are completely depolymerized but not in the presence of relatively few unattached kinetochores. Mitotic exit in Chk2-deficient cells correlates with reduced levels of Mps1 protein and increased Cdk1-tyrosine 15 inhibitory phosphorylation. Chk2 localizes to kinetochores and is also required for Aurora B-serine 331 phosphorylation in nocodazole or unperturbed early prometaphase. Serine 331 phosphorylation contributed to prometaphase accumulation in nocodazole after partial Mps1 inhibition and was required for spindle checkpoint establishment at the beginning of mitosis. In addition, expression of a phosphomimetic S331E mutant Aurora B rescued chromosome alignment or segregation in Chk2-deficient cells. We propose that Chk2 stabilizes Mps1 and phosphorylates Aurora B-serine 331 to prevent mitotic exit when most kinetochores are unattached. These results highlight mechanisms of an essential function of Chk2 in mitosis.
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Affiliation(s)
- Eleni Petsalaki
- Department of Biology, University of Crete, Heraklion 70013, Greece
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20
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Rich T, Henderson LB, Becker DL, Cornell H, Patterson-Kane JC. Indicators of replicative damage in equine tendon fibroblast monolayers. BMC Vet Res 2013; 9:180. [PMID: 24025445 PMCID: PMC3847935 DOI: 10.1186/1746-6148-9-180] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Accepted: 09/10/2013] [Indexed: 11/18/2022] Open
Abstract
Background Superficial digital flexor tendon (SDFT) injuries of horses usually follow cumulative matrix microdamage; it is not known why the reparative abilities of tendon fibroblasts are overwhelmed or subverted. Relevant in vitro studies of this process require fibroblasts not already responding to stresses caused by the cell culture protocols. We investigated indicators of replicative damage in SDFT fibroblast monolayers, effects of this on their reparative ability, and measures that can be taken to reduce it. Results We found significant evidence of replicative stress, initially observing consistently large numbers of binucleate (BN) cells. A more variable but prominent feature was the presence of numerous gammaH2AX (γH2AX) puncta in nuclei, this being a histone protein that is phosphorylated in response to DNA double-stranded breaks (DSBs). Enrichment for injury detection and cell cycle arrest factors (p53 (ser15) and p21) occurred most frequently in BN cells; however, their numbers did not correlate with DNA damage levels and it is likely that the two processes have different causative mechanisms. Such remarkable levels of injury and binucleation are usually associated with irradiation, or treatment with cytoskeletal-disrupting agents. Both DSBs and BN cells were greatest in subconfluent (replicating) monolayers. The DNA-damaged cells co-expressed the replication markers TPX2/repp86 and centromere protein F. Once damaged in the early stages of culture establishment, fibroblasts continued to express DNA breaks with each replicative cycle. However, significant levels of cell death were not measured, suggesting that DNA repair was occurring. Comet assays showed that DNA repair was delayed in proportion to levels of genotoxic stress. Conclusions Researchers using tendon fibroblast monolayers should assess their “health” using γH2AX labelling. Continued use of early passage cultures expressing initially high levels of γH2AX puncta should be avoided for mechanistic studies and ex-vivo therapeutic applications, as this will not be resolved with further replicative cycling. Low density cell culture should be avoided as it enriches for both DNA damage and mitotic defects (polyploidy). As monolayers differing only slightly in baseline DNA damage levels showed markedly variable responses to a further injury, studies of effects of various stressors on tendon cells must be very carefully controlled.
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Affiliation(s)
- Tina Rich
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, 120 University Place, Glasgow G12 8TA, UK.
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21
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Chung EJ, Urick ME, Kurshan N, Shield W, Asano H, Smith PD, Scroggins BS, Burkeen J, Citrin DE. MEK1/2 inhibition enhances the radiosensitivity of cancer cells by downregulating survival and growth signals mediated by EGFR ligands. Int J Oncol 2013; 42:2028-36. [PMID: 23588995 PMCID: PMC3699614 DOI: 10.3892/ijo.2013.1890] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 11/12/2012] [Indexed: 12/31/2022] Open
Abstract
The inhibition of the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway through the suppression of mutated Ras or MAPK/extracellular signal-regulated kinase 1/2 (MEK1/2) has been shown to sensitize tumor cells to ionizing radiation (IR). The molecular mechanisms of this sensitization however, are not yet fully understood. In this study, we investigated the role of transforming growth factor-α (TGF-α) in the radiosensitizing effects of selumetinib, a selective inhibitor of MEK1/2. The expression of epidermal growth factor receptor (EGFR) ligands was assessed by ELISA in both Ras wild-type and Ras mutant cells that were exposed to radiation with or without selumetinib. The effects of selumetinib on the TGF-α/EGFR signaling cascade in response to radiation were examined by western blot analysis, clonogenic assay and by determing the yield of mitotic catastrophe. The treatment of cells with selumetinib reduced the basal and IR-induced secretion of TGF-α in both Ras wild-type and Ras mutant cell lines in vitro and in vivo. The reduction of TGF-α secretion was accompanied with a reduction in phosphorylated tumor necrosis factor-α converting enzyme (TACE) in the cells treated with selumetinib with or without IR. The treatment of cells with selumetinib with or without IR inhibited the phosphorylation of EGFR and check-point kinase 2 (Chk2), and reduced the expression of survivin. Supplementation with exogenous TGF-α partially rescued the selumetinib-treated cells from IR-induced cell death, restored EGFR and Chk2 phosphorylation and increased survivin expression. These data suggest that the inhibition of MEK1/2 with selumetinib may provide a mechanism to sensitize tumor cells to IR in a fashion that prevents the activation of the TGF-α autocrine loop following IR.
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Affiliation(s)
- Eun Joo Chung
- Section of Translational Radiation Oncology, Radiation Oncology Branch, National Institutes of Health, Bethesda 20892, MD, USA
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22
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Wu H, Chen Q, Zhang Y, Wu G, Meng R, Cheng J. The role of DNA damage repair and Chk2 protein in hyper-radiosensitivity of lung adenocarcinoma A549 cells. ACTA ACUST UNITED AC 2012; 32:750-754. [DOI: 10.1007/s11596-012-1029-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Indexed: 11/30/2022]
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23
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Thompson LH. Recognition, signaling, and repair of DNA double-strand breaks produced by ionizing radiation in mammalian cells: the molecular choreography. Mutat Res 2012; 751:158-246. [PMID: 22743550 DOI: 10.1016/j.mrrev.2012.06.002] [Citation(s) in RCA: 261] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 06/09/2012] [Accepted: 06/16/2012] [Indexed: 12/15/2022]
Abstract
The faithful maintenance of chromosome continuity in human cells during DNA replication and repair is critical for preventing the conversion of normal diploid cells to an oncogenic state. The evolution of higher eukaryotic cells endowed them with a large genetic investment in the molecular machinery that ensures chromosome stability. In mammalian and other vertebrate cells, the elimination of double-strand breaks with minimal nucleotide sequence change involves the spatiotemporal orchestration of a seemingly endless number of proteins ranging in their action from the nucleotide level to nucleosome organization and chromosome architecture. DNA DSBs trigger a myriad of post-translational modifications that alter catalytic activities and the specificity of protein interactions: phosphorylation, acetylation, methylation, ubiquitylation, and SUMOylation, followed by the reversal of these changes as repair is completed. "Superfluous" protein recruitment to damage sites, functional redundancy, and alternative pathways ensure that DSB repair is extremely efficient, both quantitatively and qualitatively. This review strives to integrate the information about the molecular mechanisms of DSB repair that has emerged over the last two decades with a focus on DSBs produced by the prototype agent ionizing radiation (IR). The exponential growth of molecular studies, heavily driven by RNA knockdown technology, now reveals an outline of how many key protein players in genome stability and cancer biology perform their interwoven tasks, e.g. ATM, ATR, DNA-PK, Chk1, Chk2, PARP1/2/3, 53BP1, BRCA1, BRCA2, BLM, RAD51, and the MRE11-RAD50-NBS1 complex. Thus, the nature of the intricate coordination of repair processes with cell cycle progression is becoming apparent. This review also links molecular abnormalities to cellular pathology as much a possible and provides a framework of temporal relationships.
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Affiliation(s)
- Larry H Thompson
- Biology & Biotechnology Division, L452, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, United States.
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24
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Wang S, Hunter LA, Arslan Z, Wilkerson MG, Wickliffe JK. Chronic exposure to nanosized, anatase titanium dioxide is not cyto- or genotoxic to Chinese hamster ovary cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2011; 52:614-22. [PMID: 21786335 DOI: 10.1002/em.20660] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 05/23/2011] [Accepted: 05/24/2011] [Indexed: 05/14/2023]
Abstract
Titanium dioxide nanoparticles (nano-TiO(2) ) are widely used in cosmetics, skin care products, paints, and water treatment processes. Disagreement remains regarding the safety of nano-TiO(2) , and little epidemiological data is available to provide needed resolution. Most studies have examined effects using acute exposure experiments with relatively few studies using a chronic exposure design. We examined cyto- and genotoxicity in CHO-K1 cells following 60 days of continuous exposure to defined levels of nano-TiO(2) (0, 10, 20, or 40 μg/ml). Oxidative stress increased in a concentration-dependent manner in short- (2 days) and long-term cultures, but long-term cultures had lower levels of oxidative stress. The primary reactive oxygen species appeared to be superoxide, and ROS indicators were lowered with the addition of superoxide dismutase (SOD). No cyto- or genotoxic effects were apparent using the XTT, trypan-blue exclusion, and colony-forming assays for viability and the Comet and Hprt gene mutation assays for genotoxicity. Nano-TiO(2) increased the percentage of cells in the G2/M phase of the cell cycle, but this effect did not appear to influence cell viability or cell division. Cellular Ti content was dose-dependent, but chronically exposed cells had lower amounts than acutely exposed cells. CHO cells appear to adapt to chronic exposure to nano-TiO(2) and detoxify excess ROS possibly through upregulation of SOD in addition to reducing particle uptake.
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Affiliation(s)
- Shuguang Wang
- Department of Environmental Health Sciences, Tulane University, New Orleans, Louisiana 70112, USA
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25
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Xu N, Libertini S, Zhang Y, Gillespie DA. Cdk phosphorylation of Chk1 regulates efficient Chk1 activation and multiple checkpoint proficiency. Biochem Biophys Res Commun 2011; 413:465-70. [PMID: 21907702 DOI: 10.1016/j.bbrc.2011.08.119] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Accepted: 08/26/2011] [Indexed: 10/17/2022]
Abstract
It has been reported previously that both Cdk1 and Cdk2 phosphorylate Chk1 in a cell-cycle dependent manner. Cdk-mediated phosphorylation is required for efficient activation of Chk1 and checkpoint proficiency in response to DNA damage. Here, we demonstrate that Cdk-mediated phosphorylation is also required for replication stress induced Chk1 activation and S/M checkpoint proficiency. Re-introduction of Chk1 mutant (S286A/S301A) into Chk1 deficient cells is capable of restraining mitosis in cells with completely unreplicated DNA, but the mitotic delay at later stage of the cell cycle is largely impaired. The mutation strongly attenuates aphidicolin induced Chk1 activation without altering the S-phase dependent Chk1 activation. These data indicate that Cdk-mediated phosphorytion is required for efficient Chk1 activation and multiple checkpoint proficiency.
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Affiliation(s)
- Naihan Xu
- Division of Life Science, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, PR China.
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26
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Xu N, Libertini S, Black EJ, Lao Y, Hegarat N, Walker M, Gillespie DA. Cdk-mediated phosphorylation of Chk1 is required for efficient activation and full checkpoint proficiency in response to DNA damage. Oncogene 2011; 31:1086-94. [PMID: 21765472 DOI: 10.1038/onc.2011.310] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Here, we show that activation of the checkpoint effector kinase Chk1 in response to irradiation-induced DNA damage is minimal in G1, maximal during S-phase and diminishes as cells enter G2. In addition, formation of irradiation-induced replication protein A (RPA)-coated single-stranded DNA (RPA-ssDNA), a structure required for ATM and Rad3-related (ATR)-Chk1 activation, occurs in a broadly similar pattern. Cyclin-dependent kinase (Cdk) activity is thought to promote RPA-ssDNA formation by stimulating DNA strand resection at double-strand breaks (DSBs), providing one possible mechanism of imposing cell cycle dependence on DNA damage signaling. However, it has recently been shown that Chk1 itself is also subject to Cdk-mediated phosphorylation at serines 286 and 301 (S286 and 301). We show that Chk1 S301 phosphorylation increases as cells progress through S and G2 and that both Cdk1 and Cdk2 are likely to contribute to this modification in vivo. We also find that substitution of S286 and S301 with non-phosphorylatable alanine residues strongly attenuates DNA damage-induced Chk1 activation and G2 checkpoint proficiency, but does not eliminate the underlying cell cycle dependence of Chk1 regulation. Taken together, these data indicate that Cdk activity regulates multiple steps in the DNA damage response pathway including full activation of Chk1 and checkpoint proficiency.
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Affiliation(s)
- N Xu
- Beatson Institute for Cancer Research, Garscube Estate, Glasgow, UK.
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27
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Smith J, Tho LM, Xu N, Gillespie DA. The ATM-Chk2 and ATR-Chk1 pathways in DNA damage signaling and cancer. Adv Cancer Res 2011; 108:73-112. [PMID: 21034966 DOI: 10.1016/b978-0-12-380888-2.00003-0] [Citation(s) in RCA: 885] [Impact Index Per Article: 68.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
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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Affiliation(s)
- Joanne Smith
- Beatson Institute for Cancer Research, Garscube Estate, Glasgow, UK
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28
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Xu N, Hegarat N, Black EJ, Scott MT, Hochegger H, Gillespie DA. Akt/PKB suppresses DNA damage processing and checkpoint activation in late G2. ACTA ACUST UNITED AC 2010; 190:297-305. [PMID: 20679434 PMCID: PMC2922641 DOI: 10.1083/jcb.201003004] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Activated Akt suppresses checkpoint activation by cells in late G2: although they are able to detect DNA damage, the repair pathway is put on hold until mitosis is complete. Using chemical genetics to reversibly inhibit Cdk1, we find that cells arrested in late G2 are unable to delay mitotic entry after irradiation. Late G2 cells detect DNA damage lesions and form γ-H2AX foci but fail to activate Chk1. This reflects a lack of DNA double-strand break processing because late G2 cells fail to recruit RPA (replication protein A), ATR (ataxia telangiectasia and Rad3 related), Rad51, or CtIP (C-terminal interacting protein) to sites of radiation-induced damage, events essential for both checkpoint activation and initiation of DNA repair by homologous recombination. Remarkably, inhibition of Akt/PKB (protein kinase B) restores DNA damage processing and Chk1 activation after irradiation in late G2. These data demonstrate a previously unrecognized role for Akt in cell cycle regulation of DNA repair and checkpoint activation. Because Akt/PKB is frequently activated in many tumor types, these findings have important implications for the evolution and therapy of such cancers.
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Affiliation(s)
- Naihan Xu
- The Beatson Institute for Cancer Research, Glasgow G61 1BD, Scotland, UK
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29
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Kandala PK, Srivastava SK. Activation of checkpoint kinase 2 by 3,3'-diindolylmethane is required for causing G2/M cell cycle arrest in human ovarian cancer cells. Mol Pharmacol 2010; 78:297-309. [PMID: 20444961 DOI: 10.1124/mol.110.063750] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
We evaluated the effect of 3,3'-diindolylmethane (DIM) in ovarian cancer cells. DIM treatment inhibited the growth of SKOV-3, TOV-21G, and OVCAR-3 ovarian cancer cells in both a dose- and time-dependent manner with effective concentrations ranging from 40 to 100 muM. Growth-inhibitory effects of DIM were mediated by cell cycle arrest in G(2)/M phase in all the three cell lines. G(2)/M arrest was associated with DNA damage as indicated by phosphorylation of H(2)A.X at Ser139 and activation of checkpoint kinase 2 (Chk2) in all the three cell lines. Other G(2)/M regulatory molecules such as Cdc25C, Cdk1, cyclin B1 were down-regulated by DIM. Cycloheximide or Chk2 inhibitor pretreatment abrogated not only activation of Chk2 but also G(2)/M arrest and apoptosis mediated by DIM. To further establish the involvement of Chk2 in DIM-mediated G(2)/M arrest, cells were transfected with dominant-negative Chk2 (DN-Chk2). Blocking Chk2 activation by DN-Chk2 completely protected cells from DIM-mediated G(2)/M arrest. These results were further confirmed in Chk2 knockout DT40 lymphoma cells, in which DIM failed to cause cell cycle arrest. These results clearly indicate the requirement of Chk2 activation to cause G(2)/M arrest by DIM in ovarian cancer cells. Moreover, blocking Chk2 activation also abrogates the apoptosis-inducing effects of DIM. Furthermore, our results show that DIM treatment cause ROS generation. Blocking ROS generation by N-acetyl cysteine protects the cells from DIM-mediated G(2)/M arrest and apoptosis. Our results establish Chk2 as a potent molecular target of DIM in ovarian cancer cells and provide the rationale for further clinical investigation of DIM.
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Affiliation(s)
- Prabodh K Kandala
- Department of Biomedical Sciences, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
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30
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Role of ATM and the damage response mediator proteins 53BP1 and MDC1 in the maintenance of G(2)/M checkpoint arrest. Mol Cell Biol 2010; 30:3371-83. [PMID: 20421415 DOI: 10.1128/mcb.01644-09] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
ATM-dependent initiation of the radiation-induced G(2)/M checkpoint arrest is well established. Recent results have shown that the majority of DNA double-strand breaks (DSBs) in G(2) phase are repaired by DNA nonhomologous end joining (NHEJ), while approximately 15% of DSBs are slowly repaired by homologous recombination. Here, we evaluate how the G(2)/M checkpoint is maintained in irradiated G(2) cells, in light of our current understanding of G(2) phase DSB repair. We show that ATM-dependent resection at a subset of DSBs leads to ATR-dependent Chk1 activation. ATR-Seckel syndrome cells, which fail to efficiently activate Chk1, and small interfering RNA (siRNA) Chk1-treated cells show premature mitotic entry. Thus, Chk1 significantly contributes to maintaining checkpoint arrest. Second, sustained ATM signaling to Chk2 contributes, particularly when NHEJ is impaired by XLF deficiency. We also show that cells lacking the mediator proteins 53BP1 and MDC1 initially arrest following radiation doses greater than 3 Gy but are subsequently released prematurely. Thus, 53BP1(-/-) and MDC1(-/-) cells manifest a checkpoint defect at high doses. This failure to maintain arrest is due to diminished Chk1 activation and a decreased ability to sustain ATM-Chk2 signaling. The combined repair and checkpoint defects conferred by 53BP1 and MDC1 deficiency act synergistically to enhance chromosome breakage.
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31
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Watrin E, Peters JM. The cohesin complex is required for the DNA damage-induced G2/M checkpoint in mammalian cells. EMBO J 2009; 28:2625-35. [PMID: 19629043 PMCID: PMC2738698 DOI: 10.1038/emboj.2009.202] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Accepted: 06/22/2009] [Indexed: 01/05/2023] Open
Abstract
Cohesin complexes mediate sister chromatid cohesion. Cohesin also becomes enriched at DNA double-strand break sites and facilitates recombinational DNA repair. Here, we report that cohesin is essential for the DNA damage-induced G2/M checkpoint. In contrast to cohesin's role in DNA repair, the checkpoint function of cohesin is independent of its ability to mediate cohesion. After RNAi-mediated depletion of cohesin, cells fail to properly activate the checkpoint kinase Chk2 and have defects in recruiting the mediator protein 53BP1 to DNA damage sites. Earlier work has shown that phosphorylation of the cohesin subunits Smc1 and Smc3 is required for the intra-S checkpoint, but Smc1/Smc3 are also subunits of a distinct recombination complex, RC-1. It was, therefore, unknown whether Smc1/Smc3 function in the intra-S checkpoint as part of cohesin. We show that Smc1/Smc3 are phosphorylated as part of cohesin and that cohesin is required for the intra-S checkpoint. We propose that accumulation of cohesin at DNA break sites is not only needed to mediate DNA repair, but also facilitates the recruitment of checkpoint proteins, which activate the intra-S and G2/M checkpoints.
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Affiliation(s)
- Erwan Watrin
- Research Institute of Molecular Pathology (I.M.P.), Vienna, Austria
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32
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Stephan H, Concannon C, Kremmer E, Carty MP, Nasheuer HP. Ionizing radiation-dependent and independent phosphorylation of the 32-kDa subunit of replication protein A during mitosis. Nucleic Acids Res 2009; 37:6028-41. [PMID: 19671522 PMCID: PMC2764457 DOI: 10.1093/nar/gkp605] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The human single-stranded DNA-binding protein, replication protein A (RPA), is regulated by the N-terminal phosphorylation of its 32-kDa subunit, RPA2. RPA2 is hyperphosphorylated in response to various DNA-damaging agents and also phosphorylated in a cell-cycle-dependent manner during S- and M-phase, primarily at two CDK consensus sites, S23 and S29. Here we generated two monoclonal phospho-specific antibodies directed against these CDK sites. These phospho-specific RPA2-(P)-S23 and RPA2-(P)-S29 antibodies recognized mitotically phosphorylated RPA2 with high specificity. In addition, the RPA2-(P)-S23 antibody recognized the S-phase-specific phosphorylation of RPA2, suggesting that during S-phase only S23 is phosphorylated, whereas during M-phase both CDK sites, S23 and S29, are phosphorylated. Immunofluorescence microscopy revealed that the mitotic phosphorylation of RPA2 starts at the onset of mitosis, and dephosphorylation occurs during late cytokinesis. In mitotic cells treated with ionizing radiation (IR), we observed a rapid hyperphosphorylation of RPA2 in addition to its mitotic phosphorylation at S23 and S29, associated with a significant change in the subcellular localization of RPA. Our data also indicate that the RPA2 hyperphosphorylation in response to IR is facilitated by the activity of both ATM and DNA-PK, and is associated with activation of the Chk2 pathway.
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Affiliation(s)
- Holger Stephan
- Cell Cycle Control Laboratory, School of Natural Sciences, National University of Ireland, Galway, Galway, Ireland
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33
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Mitotic catastrophe is the predominant response to histone acetyltransferase depletion. Cell Death Differ 2008; 16:483-97. [PMID: 19096391 DOI: 10.1038/cdd.2008.182] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Histone acetylation induces chromatin opening by perturbing higher-order chromatin compaction and folding, suggesting that histone acetylation and deacetylation dynamics are central to chromosome condensation or decondensation. The condensation of chromosomes during mitosis is an essential prerequisite for successful chromosome segregation. In this study, we depleted three representative histone acetyltransferases (HATs; p300, CBP, and P/CAF) using shRNAs to explore their role in regulating mitotic progression and chromosome segregation. We showed that HAT depletion severely interfered with the normal timing of mitotic progression, and it reduced condensin subunit levels. The predominant response to HAT depletion, in both human primary and cancer cells, was a mitotic catastrophe following aberrant mitotic arrest. Alternatively, adaptation to HAT depletion, particularly in cancer cells, led to multinucleation and aneuploidy. Interestingly, mitotic catastrophe induced by HAT depletion appeared to be coupled to the signaling process of H2AX phosphorylation and foci formation, independently of DNA double-strand breaks and DNA damage. Taken together, our results provide novel molecular evidence that HAT proteins maintain mitotic chromatin assembly and integrity as a cellular determinant of mitotic cell death.
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34
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Rainey MD, Charlton ME, Stanton RV, Kastan MB. Transient inhibition of ATM kinase is sufficient to enhance cellular sensitivity to ionizing radiation. Cancer Res 2008; 68:7466-74. [PMID: 18794134 DOI: 10.1158/0008-5472.can-08-0763] [Citation(s) in RCA: 194] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In response to DNA damage, the ATM protein kinase activates signal transduction pathways essential for coordinating cell cycle progression with DNA repair. In the human disease ataxia-telangiectasia, mutation of the ATM gene results in multiple cellular defects, including enhanced sensitivity to ionizing radiation (IR). This phenotype highlights ATM as a potential target for novel inhibitors that could be used to enhance tumor cell sensitivity to radiotherapy. A targeted compound library was screened for potential inhibitors of the ATM kinase, and CP466722 was identified. The compound is nontoxic and does not inhibit phosphatidylinositol 3-kinase (PI3K) or PI3K-like protein kinase family members in cells. CP466722 inhibited cellular ATM-dependent phosphorylation events and disruption of ATM function resulted in characteristic cell cycle checkpoint defects. Inhibition of cellular ATM kinase activity was rapidly and completely reversed by removing CP466722. Interestingly, clonogenic survival assays showed that transient inhibition of ATM is sufficient to sensitize cells to IR and suggests that therapeutic radiosensitization may only require ATM inhibition for short periods of time. The ability of CP466722 to rapidly and reversibly regulate ATM activity provides a new tool to ask questions about ATM function that could not easily be addressed using genetic models or RNA interference technologies.
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Affiliation(s)
- Michael D Rainey
- Department of Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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