1
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Tan IL, Perez AR, Lew RJ, Sun X, Baldwin A, Zhu YK, Shah MM, Berger MS, Doudna JA, Fellmann C. Targeting the non-coding genome and temozolomide signature enables CRISPR-mediated glioma oncolysis. Cell Rep 2023; 42:113339. [PMID: 37917583 PMCID: PMC10725516 DOI: 10.1016/j.celrep.2023.113339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 07/25/2023] [Accepted: 10/10/2023] [Indexed: 11/04/2023] Open
Abstract
Glioblastoma (GBM) is the most common lethal primary brain cancer in adults. Despite treatment regimens including surgical resection, radiotherapy, and temozolomide (TMZ) chemotherapy, growth of residual tumor leads to therapy resistance and death. At recurrence, a quarter to a third of all gliomas have hypermutated genomes, with mutational burdens orders of magnitude greater than in normal tissue. Here, we quantified the mutational landscape progression in a patient's primary and recurrent GBM, and we uncovered Cas9-targetable repeat elements. We show that CRISPR-mediated targeting of highly repetitive loci enables rapid elimination of GBM cells, an approach we term "genome shredding." Importantly, in the patient's recurrent GBM, we identified unique repeat sequences with TMZ mutational signature and demonstrated that their CRISPR targeting enables cancer-specific cell ablation. "Cancer shredding" leverages the non-coding genome and therapy-induced mutational signatures for targeted GBM cell depletion and provides an innovative paradigm to develop treatments for hypermutated glioma.
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Affiliation(s)
- I-Li Tan
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA; Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Alexendar R Perez
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, San Francisco, CA 94131, USA; Silico Therapeutics, San Francisco, CA 94131, USA
| | - Rachel J Lew
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Xiaoyu Sun
- Silico Therapeutics, San Francisco, CA 94131, USA
| | - Alisha Baldwin
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA; Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Yong K Zhu
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA; Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Mihir M Shah
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Mitchel S Berger
- Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA 94131, USA
| | - Jennifer A Doudna
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA; Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Christof Fellmann
- Gladstone Institute of Data Science and Biotechnology, Gladstone Institutes, San Francisco, CA 94158, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158, USA.
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2
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Amar-Schwartz A, Ben Hur V, Jbara A, Cohen Y, Barnabas GD, Arbib E, Siegfried Z, Mashahreh B, Hassouna F, Shilo A, Abu-Odeh M, Berger M, Wiener R, Aqeilan R, Geiger T, Karni R. S6K1 phosphorylates Cdk1 and MSH6 to regulate DNA repair. eLife 2022; 11:79128. [PMID: 36189922 PMCID: PMC9529248 DOI: 10.7554/elife.79128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Accepted: 08/26/2022] [Indexed: 11/22/2022] Open
Abstract
The mTORC1 substrate, S6 Kinase 1 (S6K1), is involved in the regulation of cell growth, ribosome biogenesis, glucose homeostasis, and adipogenesis. Accumulating evidence has suggested a role for mTORC1 signaling in the DNA damage response. This is mostly based on the findings that mTORC1 inhibitors sensitized cells to DNA damage. However, a direct role of the mTORC1-S6K1 signaling pathway in DNA repair and the mechanism by which this signaling pathway regulates DNA repair is unknown. In this study, we discovered a novel role for S6K1 in regulating DNA repair through the coordinated regulation of the cell cycle, homologous recombination (HR) DNA repair (HRR) and mismatch DNA repair (MMR) mechanisms. Here, we show that S6K1 orchestrates DNA repair by phosphorylation of Cdk1 at serine 39, causing G2/M cell cycle arrest enabling homologous recombination and by phosphorylation of MSH6 at serine 309, enhancing MMR. Moreover, breast cancer cells harboring RPS6KB1 gene amplification show increased resistance to several DNA damaging agents and S6K1 expression is associated with poor survival of breast cancer patients treated with chemotherapy. Our findings reveal an unexpected function of S6K1 in the DNA repair pathway, serving as a tumorigenic barrier by safeguarding genomic stability. Damage to the DNA in our cells can cause harmful changes that, if unchecked, can lead to the development of cancer. To help prevent this, cellular mechanisms are in place to repair defects in the DNA. A particular process, known as the mTORC1-S6K1 pathway is suspected to be important for repair because when this pathway is blocked, cells become more sensitive to DNA damage. It is still unknown how the various proteins involved in the mTORC1-S6K1 pathway contribute to repairing DNA. One of these proteins, S6K1, is an enzyme involved in coordinating cell growth and survival. The tumor cells in some forms of breast cancer produce more of this protein than normal, suggesting that S6K1 benefits these cells’ survival. However, it is unclear exactly how the enzyme does this. Amar-Schwartz, Ben-Hur, Jbara et al. studied the role of S6K1 using genetically manipulated mouse cells and human cancer cells. These experiments showed that the protein interacts with two other proteins involved in DNA repair and activates them, regulating two different repair mechanisms and protecting cells against damage. These results might explain why some breast cancer tumors are resistant to radiotherapy and chemotherapy treatments, which aim to kill tumor cells by damaging their DNA. If this is the case, these findings could help clinicians choose more effective treatment options for people with cancers that produce additional S6K1. In the future, drugs that block the activity of the enzyme could make cancer cells more susceptible to chemotherapy.
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Affiliation(s)
- Adi Amar-Schwartz
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Vered Ben Hur
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Amina Jbara
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Yuval Cohen
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Georgina D Barnabas
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Eliran Arbib
- Lautenberg Center for Immunology and Cancer Research, Department of Immunology and Cancer Research, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Zahava Siegfried
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Bayan Mashahreh
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Fouad Hassouna
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Asaf Shilo
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Mohammad Abu-Odeh
- Lautenberg Center for Immunology and Cancer Research, Department of Immunology and Cancer Research, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Michael Berger
- Lautenberg Center for Immunology and Cancer Research, Department of Immunology and Cancer Research, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Reuven Wiener
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Rami Aqeilan
- Lautenberg Center for Immunology and Cancer Research, Department of Immunology and Cancer Research, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Tamar Geiger
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Rotem Karni
- Department of Biochemistry and Molecular Biology, the Institute for Medical Research Israel-Canada, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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3
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Gupta D, Heinen CD. The mismatch repair-dependent DNA damage response: Mechanisms and implications. DNA Repair (Amst) 2019; 78:60-69. [PMID: 30959407 DOI: 10.1016/j.dnarep.2019.03.009] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 02/25/2019] [Accepted: 03/16/2019] [Indexed: 12/22/2022]
Abstract
An important role for the DNA mismatch repair (MMR) pathway in maintaining genomic stability is embodied in its conservation through evolution and the link between loss of MMR function and tumorigenesis. The latter is evident as inheritance of mutations within the major MMR genes give rise to the cancer predisposition condition, Lynch syndrome. Nonetheless, how MMR loss contributes to tumorigenesis is not completely understood. In addition to preventing the accumulation of mutations, MMR also directs cellular responses, such as cell cycle checkpoint or apoptosis activation, to different forms of DNA damage. Understanding this MMR-dependent DNA damage response may provide insight into the full tumor suppressing capabilities of the MMR pathway. Here, we delve into the proposed mechanisms for the MMR-dependent response to DNA damaging agents. We discuss how these pre-clinical findings extend to the clinical treatment of cancers, emphasizing MMR status as a crucial variable in selection of chemotherapeutic regimens. Also, we discuss how loss of the MMR-dependent damage response could promote tumorigenesis via the establishment of a survival advantage to endogenous levels of stress in MMR-deficient cells.
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Affiliation(s)
- Dipika Gupta
- Center for Molecular Oncology, UConn Health, Farmington, CT 06030, USA
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4
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Azenha D, Lopes MC, Martins TC. Claspin: From replication stress and DNA damage responses to cancer therapy. DNA Repair (Amst) 2019; 115:203-246. [DOI: 10.1016/bs.apcsb.2018.10.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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5
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Cui J, Wang J, Huang S, Jiang X, Li Y, Wu W, Zhang X. The G2 phase arrest induced by sterigmatocystin is dependent on hMLH1- ERK/p38-p53 pathway in human esophageal epithelium cells in vitro. Food Chem Toxicol 2018; 115:205-211. [DOI: 10.1016/j.fct.2018.03.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 03/06/2018] [Accepted: 03/09/2018] [Indexed: 01/12/2023]
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6
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DNA mismatch repair protein Mlh1 is required for tetravalent chromium intermediate-induced DNA damage. Oncotarget 2017; 8:83975-83985. [PMID: 29137397 PMCID: PMC5663569 DOI: 10.18632/oncotarget.20150] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Accepted: 05/22/2017] [Indexed: 12/02/2022] Open
Abstract
Hexavalent chromium (Cr[VI]) is associated with occupational lung cancer and poses a significant public health concern. When exposed to Cr[VI], cells rapidly internalize this compound and metabolize it to Cr[III]. Byproducts of Cr[VI] metabolism include unstable Cr[V] and Cr[IV] intermediates that are believed to be directly responsible for the genotoxicity and carcinogenicity caused by Cr[VI] exposure; however, the carcinogenic potential of the Cr intermediates and the mechanisms of Cr-induced carcinogenesis remain to be further defined. Utilizing synthetic Cr[IV] and Cr[V] compounds, we demonstrate here that Cr[IV] or Cr[V] exposure induces DNA double-strand breaks; however, of the two compounds, mammalian cells only respond to Cr[V]-induced DNA damage. Exposure to Cr[V], but not Cr[IV], results in initiation of cell cycle checkpoints and activates the ATM kinase, a critical regulator of the DNA damage response. Furthermore, cells exposed to Cr[IV] have significantly increased mutation frequencies in the HPRT gene compared to cells exposed to Cr[V], indicating that Cr[IV] possesses a higher mutagenic potential than Cr[V]. We also find that MLH1, a critical mismatch repair (MMR) protein, is required for activation of the G2/M cell cycle checkpoint in response to Cr[VI] exposure and to limit Cr-induced mutagenesis. Our results provide evidence for Cr[IV] as the ultimate mutagenic intermediate produced during Cr[VI] metabolism and indicate that functional MMR is crucial in the cellular response to chromium exposure.
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7
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Fujii N. Potential Strategies to Target Protein-Protein Interactions in the DNA Damage Response and Repair Pathways. J Med Chem 2017; 60:9932-9959. [PMID: 28654754 DOI: 10.1021/acs.jmedchem.7b00358] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This review article discusses some insights about generating novel mechanistic inhibitors of the DNA damage response and repair (DDR) pathways by focusing on protein-protein interactions (PPIs) of the key DDR components. General requirements for PPI strategies, such as selecting the target PPI site on the basis of its functionality, are discussed first. Next, on the basis of functional rationale and biochemical feasibility to identify a PPI inhibitor, 26 PPIs in DDR pathways (BER, MMR, NER, NHEJ, HR, TLS, and ICL repair) are specifically discussed for inhibitor discovery to benefit cancer therapies using a DNA-damaging agent.
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Affiliation(s)
- Naoaki Fujii
- Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital , 262 Danny Thomas Place, MS1000, Memphis, Tennessee 38105, United States
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8
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Xu J, Li Z, Su Q, Zhao J, Ma J. Embryonic develop-associated gene 1 is overexpressed and acts as a tumor promoter in thyroid carcinoma. Biomed Pharmacother 2016; 81:86-92. [DOI: 10.1016/j.biopha.2016.03.052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Revised: 03/30/2016] [Accepted: 03/31/2016] [Indexed: 11/15/2022] Open
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9
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Li Z, Pearlman AH, Hsieh P. DNA mismatch repair and the DNA damage response. DNA Repair (Amst) 2016; 38:94-101. [PMID: 26704428 PMCID: PMC4740233 DOI: 10.1016/j.dnarep.2015.11.019] [Citation(s) in RCA: 199] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Revised: 09/17/2015] [Accepted: 11/30/2015] [Indexed: 12/12/2022]
Abstract
This review discusses the role of DNA mismatch repair (MMR) in the DNA damage response (DDR) that triggers cell cycle arrest and, in some cases, apoptosis. Although the focus is on findings from mammalian cells, much has been learned from studies in other organisms including bacteria and yeast [1,2]. MMR promotes a DDR mediated by a key signaling kinase, ATM and Rad3-related (ATR), in response to various types of DNA damage including some encountered in widely used chemotherapy regimes. An introduction to the DDR mediated by ATR reveals its immense complexity and highlights the many biological and mechanistic questions that remain. Recent findings and future directions are highlighted.
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Affiliation(s)
- Zhongdao Li
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 5 Rm. 324, 5 Memorial Dr. MSC 0538, Bethesda, MD 20892-0538, USA
| | - Alexander H Pearlman
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 5 Rm. 324, 5 Memorial Dr. MSC 0538, Bethesda, MD 20892-0538, USA
| | - Peggy Hsieh
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 5 Rm. 324, 5 Memorial Dr. MSC 0538, Bethesda, MD 20892-0538, USA.
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10
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Heinen CD. Mismatch repair defects and Lynch syndrome: The role of the basic scientist in the battle against cancer. DNA Repair (Amst) 2015; 38:127-134. [PMID: 26710976 DOI: 10.1016/j.dnarep.2015.11.025] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Revised: 08/21/2015] [Accepted: 11/30/2015] [Indexed: 12/24/2022]
Abstract
We have currently entered a genomic era of cancer research which may soon lead to a genomic era of cancer treatment. Patient DNA sequencing information may lead to a personalized approach to managing an individual's cancer as well as future cancer risk. The success of this approach, however, begins not necessarily in the clinician's office, but rather at the laboratory bench of the basic scientist. The basic scientist plays a critical role since the DNA sequencing information is of limited use unless one knows the function of the gene that is altered and the manner by which a sequence alteration affects that function. The role of basic science research in aiding the clinical management of a disease is perhaps best exemplified by considering the case of Lynch syndrome, a hereditary disease that predisposes patients to colorectal and other cancers. This review will examine how the diagnosis, treatment and even prevention of Lynch syndrome-associated cancers has benefitted from extensive basic science research on the DNA mismatch repair genes whose alteration underlies this condition.
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Affiliation(s)
- Christopher D Heinen
- Center for Molecular Medicine and Neag Comprehensive Cancer Center, University of Connecticut Health, Farmington, CT 06030, USA.
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11
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Klapacz J, Pottenger LH, Engelward BP, Heinen CD, Johnson GE, Clewell RA, Carmichael PL, Adeleye Y, Andersen ME. Contributions of DNA repair and damage response pathways to the non-linear genotoxic responses of alkylating agents. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2015; 767:77-91. [PMID: 27036068 DOI: 10.1016/j.mrrev.2015.11.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 11/26/2015] [Accepted: 11/27/2015] [Indexed: 11/27/2022]
Abstract
From a risk assessment perspective, DNA-reactive agents are conventionally assumed to have genotoxic risks at all exposure levels, thus applying a linear extrapolation for low-dose responses. New approaches discussed here, including more diverse and sensitive methods for assessing DNA damage and DNA repair, strongly support the existence of measurable regions where genotoxic responses with increasing doses are insignificant relative to control. Model monofunctional alkylating agents have in vitro and in vivo datasets amenable to determination of points of departure (PoDs) for genotoxic effects. A session at the 2013 Society of Toxicology meeting provided an opportunity to survey the progress in understanding the biological basis of empirically-observed PoDs for DNA alkylating agents. Together with the literature published since, this review discusses cellular pathways activated by endogenous and exogenous alkylation DNA damage. Cells have evolved conserved processes that monitor and counteract a spontaneous steady-state level of DNA damage. The ubiquitous network of DNA repair pathways serves as the first line of defense for clearing of the DNA damage and preventing mutation. Other biological pathways discussed here that are activated by genotoxic stress include post-translational activation of cell cycle networks and transcriptional networks for apoptosis/cell death. The interactions of various DNA repair and DNA damage response pathways provide biological bases for the observed PoD behaviors seen with genotoxic compounds. Thus, after formation of DNA adducts, the activation of cellular pathways can lead to the avoidance of a mutagenic outcome. The understanding of the cellular mechanisms acting within the low-dose region will serve to better characterize risks from exposures to DNA-reactive agents at environmentally-relevant concentrations.
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Affiliation(s)
- Joanna Klapacz
- Toxicology & Environmental Research and Consulting, The Dow Chemical Company, Midland, MI 48674, USA.
| | - Lynn H Pottenger
- Toxicology & Environmental Research and Consulting, The Dow Chemical Company, Midland, MI 48674, USA; Current Address: Olin Corporation, Midland, MI 48674, USA
| | - Bevin P Engelward
- Department of Biological Engineering, MA Institute of Technology, Cambridge, MA 02139, USA
| | - Christopher D Heinen
- Center for Molecular Medicine, Neag Comprehensive Cancer Center, University of CT Health Center, Farmington, CT 06030, USA
| | - George E Johnson
- Institute of Life Science, College of Medicine, Swansea University, SA2 8PP, UK
| | - Rebecca A Clewell
- Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA
| | - Paul L Carmichael
- Unilever, Safety & Environmental Assurance Centre, Colworth Science Park, Sharnbrook, Bedfordshire MK44 1LQ, UK
| | - Yeyejide Adeleye
- Unilever, Safety & Environmental Assurance Centre, Colworth Science Park, Sharnbrook, Bedfordshire MK44 1LQ, UK
| | - Melvin E Andersen
- Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA
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NPM-ALK mediates phosphorylation of MSH2 at tyrosine 238, creating a functional deficiency in MSH2 and the loss of mismatch repair. Blood Cancer J 2015; 5:e311. [PMID: 25978431 PMCID: PMC4476014 DOI: 10.1038/bcj.2015.35] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Revised: 03/16/2015] [Accepted: 04/07/2015] [Indexed: 12/22/2022] Open
Abstract
The vast majority of anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ALCL) tumors express the characteristic oncogenic fusion protein NPM-ALK, which mediates tumorigenesis by exerting its constitutive tyrosine kinase activity on various substrates. We recently identified MSH2, a protein central to DNA mismatch repair (MMR), as a novel binding partner and phosphorylation substrate of NPM-ALK. Here, using liquid chromatography–mass spectrometry, we report for the first time that MSH2 is phosphorylated by NPM-ALK at a specific residue, tyrosine 238. Using GP293 cells transfected with NPM-ALK, we confirmed that the MSH2Y238F mutant is not tyrosine phosphorylated. Furthermore, transfection of MSH2Y238F into these cells substantially decreased the tyrosine phosphorylation of endogenous MSH2. Importantly, gene transfection of MSH2Y238F abrogated the binding of NPM-ALK with endogenous MSH2, re-established the dimerization of MSH2:MSH6 and restored the sensitivity to DNA mismatch-inducing drugs, indicative of MMR return. Parallel findings were observed in two ALK+ALCL cell lines, Karpas 299 and SUP-M2. In addition, we found that enforced expression of MSH2Y238F into ALK+ALCL cells alone was sufficient to induce spontaneous apoptosis. In conclusion, our findings have identified NPM-ALK-induced phosphorylation of MSH2 at Y238 as a crucial event in suppressing MMR. Our studies have provided novel insights into the mechanism by which oncogenic tyrosine kinases disrupt MMR.
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13
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Zannini L, Delia D, Buscemi G. CHK2 kinase in the DNA damage response and beyond. J Mol Cell Biol 2014; 6:442-57. [PMID: 25404613 PMCID: PMC4296918 DOI: 10.1093/jmcb/mju045] [Citation(s) in RCA: 284] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Revised: 09/17/2014] [Accepted: 09/24/2014] [Indexed: 12/21/2022] Open
Abstract
The serine/threonine kinase CHK2 is a key component of the DNA damage response. In human cells, following genotoxic stress, CHK2 is activated and phosphorylates >20 proteins to induce the appropriate cellular response, which, depending on the extent of damage, the cell type, and other factors, could be cell cycle checkpoint activation, induction of apoptosis or senescence, DNA repair, or tolerance of the damage. Recently, CHK2 has also been found to have cellular functions independent of the presence of nuclear DNA lesions. In particular, CHK2 participates in several molecular processes involved in DNA structure modification and cell cycle progression. In this review, we discuss the activity of CHK2 in response to DNA damage and in the maintenance of the biological functions in unstressed cells. These activities are also considered in relation to a possible role of CHK2 in tumorigenesis and, as a consequence, as a target of cancer therapy.
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Affiliation(s)
- Laura Zannini
- Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Via Amadeo 42, 20133 Milan, Italy
| | - Domenico Delia
- Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Via Amadeo 42, 20133 Milan, Italy
| | - Giacomo Buscemi
- Department of Biosciences, University of Milan, via Celoria 26, 20133 Milan, Italy
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14
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Lin B, Gupta D, Heinen CD. Human pluripotent stem cells have a novel mismatch repair-dependent damage response. J Biol Chem 2014; 289:24314-24. [PMID: 25012654 DOI: 10.1074/jbc.m114.570937] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human pluripotent stem cells (PSCs) are presumed to have robust DNA repair pathways to ensure genome stability. PSCs likely need to protect against mutations that would otherwise be propagated throughout all tissues of the developing embryo. How these cells respond to genotoxic stress has only recently begun to be investigated. Although PSCs appear to respond to certain forms of damage more efficiently than somatic cells, some DNA damage response pathways such as the replication stress response may be lacking. Not all DNA repair pathways, including the DNA mismatch repair (MMR) pathway, have been well characterized in PSCs to date. MMR maintains genomic stability by repairing DNA polymerase errors. MMR is also involved in the induction of cell cycle arrest and apoptosis in response to certain exogenous DNA-damaging agents. Here, we examined MMR function in PSCs. We have demonstrated that PSCs contain a robust MMR pathway and are highly sensitive to DNA alkylation damage in an MMR-dependent manner. Interestingly, the nature of this alkylation response differs from that previously reported in somatic cell types. In somatic cells, a permanent G2/M cell cycle arrest is induced in the second cell cycle after DNA damage. The PSCs, however, directly undergo apoptosis in the first cell cycle. This response reveals that PSCs rely on apoptotic cell death as an important defense to avoid mutation accumulation. Our results also suggest an alternative molecular mechanism by which the MMR pathway can induce a response to DNA damage that may have implications for tumorigenesis.
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Affiliation(s)
- Bo Lin
- From the Center for Molecular Medicine and Neag Comprehensive Cancer Center, University of Connecticut Health Center, Farmington, Connecticut 06030-3101
| | - Dipika Gupta
- From the Center for Molecular Medicine and Neag Comprehensive Cancer Center, University of Connecticut Health Center, Farmington, Connecticut 06030-3101
| | - Christopher D Heinen
- From the Center for Molecular Medicine and Neag Comprehensive Cancer Center, University of Connecticut Health Center, Farmington, Connecticut 06030-3101
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15
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Impairment of cell cycle progression by sterigmatocystin in human pulmonary cells in vitro. Food Chem Toxicol 2014; 66:89-95. [DOI: 10.1016/j.fct.2014.01.024] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 01/11/2014] [Accepted: 01/14/2014] [Indexed: 01/11/2023]
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16
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Eich M, Roos WP, Nikolova T, Kaina B. Contribution of ATM and ATR to the resistance of glioblastoma and malignant melanoma cells to the methylating anticancer drug temozolomide. Mol Cancer Ther 2013; 12:2529-40. [PMID: 23960094 DOI: 10.1158/1535-7163.mct-13-0136] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The major cytotoxic DNA adduct induced by temozolomide and other methylating agents used in malignant glioma and metastasized melanoma therapy is O(6)-methylguanine (O(6)-MeG). This primary DNA damage is converted by mismatch repair into secondary lesions, which block replication and in turn induce DNA double-strand breaks that trigger the DNA damage response (DDR). Key upstream players in the DDR are the phosphoinositide 3-kinases ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3 related (ATR). Here, we addressed the question of the importance of ATM and ATR in the cell death response following temozolomide. We show that (i) ATM- and ATR-mutated cells are hypersensitive to temozolomide, (ii) O(6)-MeG triggers ATM and ATR activation, (iii) knockdown of ATM and ATR enhances cell kill in gliobalstoma and malignant melanoma cells with a stronger and significant effect in ATR knockdown cells, (iv) ATR, but not ATM, knockdown abolished phosphorylation of H2AX, CHK1, and CHK2 in glioma cells, and (v) temozolomide-induced cell death was more prominently enhanced by pharmacologic inhibition of CHK1 compared with CHK2. The data suggest that ATM and, even better, ATR inhibition is a useful strategy in sensitizing cancer cells to temozolomide and presumably also other anticancer drugs.
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Affiliation(s)
- Marcus Eich
- Corresponding Author: Bernd Kaina, Institute of Toxicology, Medical Center of the University Mainz, Obere Zahlbacher Str. 67, D-55131 Mainz, Germany.
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Tentori L, Leonetti C, Muzi A, Dorio AS, Porru M, Dolci S, Campolo F, Vernole P, Lacal PM, Praz F, Graziani G. Influence of MLH1 on colon cancer sensitivity to poly(ADP-ribose) polymerase inhibitor combined with irinotecan. Int J Oncol 2013; 43:210-8. [PMID: 23653048 DOI: 10.3892/ijo.2013.1932] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 03/01/2013] [Indexed: 11/06/2022] Open
Abstract
Poly(ADP-ribose) polymerase inhibitors (PARPi) are currently evaluated in clinical trials in combination with topoisomerase I (Top1) inhibitors against a variety of cancers, including colon carcinoma. Since the mismatch repair component MLH1 is defective in 10-15% of colorectal cancers we have investigated whether MLH1 affects response to the Top1 inhibitor irinotecan, alone or in combination with PARPi. To this end, the colon cancer cell lines HCT116, carrying MLH1 mutations on chromosome 3 and HCT116 in which the wild-type MLH1 gene was replaced via chromosomal transfer (HCT116+3) or by transfection of the corresponding MLH1 cDNA (HCT116 1-2) were used. HCT116 cells or HCT116+3 cells stably silenced for PARP-1 expression were also analysed. The results of in vitro and in vivo experiments indicated that MLH1, together with low levels of Top1, contributed to colon cancer resistance to irinotecan. In the MLH1-proficient cells SN-38, the active metabolite of irinotecan, induced lower levels of DNA damage than in MLH1-deficient cells, as shown by the weaker induction of γ-H2AX and p53 phosphorylation. The presence of MLH1 contributed to induce of prompt Chk1 phosphorylation, restoring G2/M cell cycle checkpoint and repair of DNA damage. On the contrary, in the absence of MLH1, HCT116 cells showed minor Chk1 phosphorylation and underwent apoptosis. Remarkably, inhibition of PARP function by PARPi or by PARP-1 gene silencing always increased the antitumor activity of irinotecan, even in the presence of low PARP-1 expression.
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Affiliation(s)
- Lucio Tentori
- Department of System Medicine, University of Rome 'Tor Vergata', I-00133 Rome, Italy
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Ito M, Ohba S, Gaensler K, Ronen SM, Mukherjee J, Pieper RO. Early Chk1 phosphorylation is driven by temozolomide-induced, DNA double strand break- and mismatch repair-independent DNA damage. PLoS One 2013; 8:e62351. [PMID: 23667469 PMCID: PMC3646831 DOI: 10.1371/journal.pone.0062351] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 03/21/2013] [Indexed: 01/06/2023] Open
Abstract
Temozolomide (TMZ) is a DNA methylating agent used to treat brain cancer. TMZ-induced O6-methylguanine adducts, in the absence of repair by O6-methylguanine DNA methyltransferase (MGMT), mispair during DNA replication and trigger cycles of futile mismatch repair (MMR). Futile MMR in turn leads to the formation of DNA single and double strand breaks, Chk1 and Chk2 phosphorylation/activation, cell cycle arrest, and ultimately cell death. Although both pChk1 and pChk2 are considered to be biomarkers of TMZ-induced DNA damage, cell-cycle arrest, and TMZ induced cytotoxicity, we found that levels of pChk1 (ser345), its downstream target pCdc25C (ser216), and the activity of its upstream activator ATR, were elevated within 3 hours of TMZ exposure, long before the onset of TMZ-induced DNA double strand breaks, Chk2 phosphorylation/activation, and cell cycle arrest. Furthermore, TMZ-induced early phosphorylation of Chk1 was noted in glioma cells regardless of whether they were MGMT-proficient or MGMT-deficient, and regardless of their MMR status. Early Chk1 phosphorylation was not associated with TMZ-induced reactive oxygen species, but was temporally associated with TMZ-induced alkalai-labile DNA damage produced by the non-O6-methylguanine DNA adducts and which, like Chk1 phosphorylation, was transient in MGMT-proficient cells but persistent in MGMT-deficient cells. These results re-define the TMZ-induced DNA damage response, and show that Chk1 phosphorylation is driven by TMZ-induced mismatch repair-independent DNA damage independently of DNA double strand breaks, Chk2 activation, and cell cycle arrest, and as such is a suboptimal biomarker of TMZ-induced drug action.
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Affiliation(s)
- Motokazu Ito
- Department of Neurological Surgery, University of California-San Francisco, San Francisco, California, United States of America
- The Brain Tumor Research Center, University of California-San Francisco, San Francisco, California, United States of America
| | - Shigeo Ohba
- Department of Neurological Surgery, University of California-San Francisco, San Francisco, California, United States of America
- The Brain Tumor Research Center, University of California-San Francisco, San Francisco, California, United States of America
| | - Karin Gaensler
- Department of Hematology/Oncology, University of California-San Francisco, San Francisco, California, United States of America
| | - Sabrina M. Ronen
- Department of Radiology and Biomedical Imaging, University of California-San Francisco, San Francisco, California, United States of America
- The Brain Tumor Research Center, University of California-San Francisco, San Francisco, California, United States of America
| | - Joydeep Mukherjee
- Department of Neurological Surgery, University of California-San Francisco, San Francisco, California, United States of America
- The Brain Tumor Research Center, University of California-San Francisco, San Francisco, California, United States of America
| | - Russell O. Pieper
- Department of Neurological Surgery, University of California-San Francisco, San Francisco, California, United States of America
- The Brain Tumor Research Center, University of California-San Francisco, San Francisco, California, United States of America
- * E-mail: .
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Iwaizumi M, Tseng-Rogenski S, Carethers JM. Acidic tumor microenvironment downregulates hMLH1 but does not diminish 5-fluorouracil chemosensitivity. Mutat Res 2013; 747-748:19-27. [PMID: 23643670 DOI: 10.1016/j.mrfmmm.2013.04.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Revised: 03/31/2013] [Accepted: 04/17/2013] [Indexed: 12/12/2022]
Abstract
Human DNA mismatch repair (MMR) recognizes and binds 5-fluorouracil (5FU) incorporated into DNA and triggers a MMR-dependent cell death. Absence of MMR in a patient's colorectal tumor abrogates 5FU's beneficial effects on survival. Changes in the tumor microenvironment like low extracellular pH (pHe) may diminish DNA repair, increasing genomic instability. Here, we explored if low pHe modifies MMR recognition of 5FU, as 5FU can exist in ionized and non-ionized forms depending on pH. We demonstrate that MMR-proficient cells at low pHe show downregulation of hMLH1, whereas expression of TDG and MBD4, known DNA glycosylases for base excision repair (BER) that can remove 5FU from DNA, were unchanged. We show in vitro that 5FU within DNA pairs with adenine (A) at high and low pH (in absence of MMR and BER). Surprisingly, 5FdU:G was repaired to C:G in hMLH1-deficient cells cultured at both low and normal pHe, similar to MMR-proficient cells. Moreover, both hMSH6 and hMSH3, components of hMutSα and hMutSβ, respectively, bound 5FU within DNA (hMSH6>hMSH3) but is influenced by hMLH1. We conclude that an acidic tumor microenvironment triggers downregulation of hMLH1, potentially removing the execution component of MMR for 5FU cytotoxicity, whereas other mechanisms remain stable to implement overall 5FU sensitivity.
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Affiliation(s)
- Moriya Iwaizumi
- Division of Gastroenterology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, United States
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Cui J, Liu J, Wu S, Wang Y, Shen H, Xing L, Wang J, Yan X, Zhang X. Oxidative DNA damage is involved in ochratoxin A-induced G2 arrest through ataxia telangiectasia-mutated (ATM) pathways in human gastric epithelium GES-1 cells in vitro. Arch Toxicol 2013; 87:1829-40. [PMID: 23515941 DOI: 10.1007/s00204-013-1043-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Accepted: 03/08/2013] [Indexed: 01/17/2023]
Abstract
Ochratoxin A (OTA), one of the most abundant mycotoxin food contaminants, is classified as "possibly carcinogenic to humans." Our previous study showed that OTA could induce a G2 arrest in immortalized human gastric epithelium cells (GES-1). To explore the putative roles of oxidative DNA damage and the ataxia telangiectasia-mutated (ATM) pathways on the OTA-induced G2 arrest, the current study systematically evaluated the roles of reactive oxygen species (ROS) production, DNA damage, and ATM-dependent pathway activation on the OTA-induced G2 phase arrest in GES-1 cells. The results showed that OTA exposure elevated intracellular ROS production, which directly induced DNA damage and increased the levels of 8-OHdG and DNA double-strand breaks (DSBs). In addition, it was found that OTA treatment induced the phosphorylation of the ATM protein, as well as its downstream molecules Chk2 and p53, in response to DNA DSBs. Inhibition of ATM by the pharmacological inhibitor caffeine or siRNA effectively prevented the activation of ATM-dependent pathways and rescued the G2 arrest elicited by OTA. Finally, pretreatment with the antioxidant N-acetyl-L-cysteine (NAC) reduced the OTA-induced DNA DSBs, ATM phosphorylation, and G2 arrest. In conclusion, the results of this study suggested that OTA-induced oxidative DNA damage triggered the ATM-dependent pathways, which ultimately elicited a G2 arrest in GES-1 cells.
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Affiliation(s)
- Jinfeng Cui
- Department of Pathology, The Second Hospital, Hebei Medical University, No. 215, Heping Western Road, Shijiazhuang, Hebei, People's Republic of China
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21
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Wang J, Huang S, Xing L, Shen H, Yan X, Wang J, Zhang X. Role of hMLH1 in sterigmatocystin-induced G2 phase arrest in human esophageal epithelial Het-1A cells in vitro. Toxicol Lett 2013; 217:226-34. [DOI: 10.1016/j.toxlet.2012.12.020] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2012] [Revised: 12/19/2012] [Accepted: 12/27/2012] [Indexed: 12/12/2022]
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22
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Noonan EM, Shah D, Yaffe MB, Lauffenburger DA, Samson LD. O6-Methylguanine DNA lesions induce an intra-S-phase arrest from which cells exit into apoptosis governed by early and late multi-pathway signaling network activation. Integr Biol (Camb) 2013; 4:1237-55. [PMID: 22892544 DOI: 10.1039/c2ib20091k] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The O(6)-methylguanine (O(6)MeG) DNA lesion is well known for its mutagenic, carcinogenic, and cytotoxic properties, and understanding how a cell processes such damage is of critical importance for improving current cancer therapy. Here we use human cells differing only in their O(6)MeG DNA methyltransferase (MGMT) or mismatch repair (MMR) status to explore the O(6)MeG/MMR-dependent molecular and cellular responses to treatment with the methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). We find that O(6)MeG triggers MMR-dependent cell cycle perturbations in both the first and second cell cycle post treatment. At lower levels of damage, we show that a transient arrest in the second S-phase precedes survival and progression into subsequent cell cycles. However, at higher levels of damage, arrest in the second S-phase coincides with a cessation of DNA replication followed by initiation of apoptotic cell death. Further, we show that entry into apoptotic cell death is specifically from S-phase of the second cell cycle. Finally, we demonstrate the key role of an O(6)MeG/MMR-dependent multi-pathway, multi-time-scale signaling network activation, led by early ATM, H2AX, CHK1, and p53 phosphorylation and followed by greatly amplified late phosphorylation of the early pathway nodes along with activation of the CHK2 kinase and the stress-activated JNK kinase.
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Affiliation(s)
- Ericka M Noonan
- Biological Engineering Department, Biology Department, Center for Environmental Health Sciences, Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Exonuclease 1 (Exo1) is required for activating response to S(N)1 DNA methylating agents. DNA Repair (Amst) 2012; 11:951-64. [PMID: 23062884 DOI: 10.1016/j.dnarep.2012.09.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 09/08/2012] [Accepted: 09/11/2012] [Indexed: 11/23/2022]
Abstract
S(N)1 DNA methylating agents are genotoxic agents that methylate numerous nucleophilic centers within DNA including the O(6) position of guanine (O(6)meG). Methylation of this extracyclic oxygen forces mispairing with thymine during DNA replication. The mismatch repair (MMR) system recognizes these O(6)meG:T mispairs and is required to activate DNA damage response (DDR). Exonuclease I (EXO1) is a key component of MMR by resecting the damaged strand; however, whether EXO1 is required to activate MMR-dependent DDR remains unknown. Here we show that knockdown of the mouse ortholog (mExo1) in mouse embryonic fibroblasts (MEFs) results in decreased G2/M checkpoint response, limited effects on cell proliferation, and increased cell viability following exposure to the S(N)1 methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), establishing a phenotype paralleling MMR deficiency. MNNG treatment induced formation of γ-H2AX foci with which EXO1 co-localized in MEFs, but mExo1-depleted MEFs displayed a significant diminishment of γ-H2AX foci formation. mExo1 depletion also reduced MSH2 association with DNA duplexes containing G:T mismatches in vitro, decreased MSH2 association with alkylated chromatin in vivo, and abrogated MNNG-induced MSH2/CHK1 interaction. To determine if nuclease activity is required to activate DDR we stably overexpressed a nuclease defective form of human EXO1 (hEXO1) in mExo1-depleted MEFs. These experiments indicated that expression of wildtype and catalytically null hEXO1 was able to restore normal response to MNNG. This study indicates that EXO1 is required to activate MMR-dependent DDR in response to S(N)1 methylating agents; however, this function of EXO1 is independent of its nucleolytic activity.
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MSH2 is required for cell proliferation, cell cycle control and cell invasiveness in colorectal cancer cells. CHINESE SCIENCE BULLETIN-CHINESE 2012. [DOI: 10.1007/s11434-012-5258-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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25
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Papaioannou I, Simons JP, Owen JS. Oligonucleotide-directed gene-editing technology: mechanisms and future prospects. Expert Opin Biol Ther 2012; 12:329-42. [PMID: 22321001 DOI: 10.1517/14712598.2012.660522] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
INTRODUCTION Gene editing, as defined here, uses short synthetic oligonucleotides to introduce small, site-specific changes into mammalian genomes, including repair of genetic point mutations. Early RNA-DNA oligonucleotides (chimeraplasts) were problematic, but application of single-stranded all-DNA molecules (ssODNs) has matured the technology into a reproducible tool with therapeutic potential. AREAS COVERED The review illustrates how gene-editing mechanisms are linked to DNA repair systems and DNA replication, and explains that while homologous recombination (HR) and nucleotide excision repair (NER) are implicated, the mismatch repair (MMR) system is inhibitory. Although edited cells often arrest in late S-phase or G2-phase, alternative ssODN chemistries can improve editing efficiency and cell viability. The final section focuses on the exciting tandem use of ssODNs with zinc finger nucleases to achieve high frequency genome editing. EXPERT OPINION For a decade, changing the genetic code of cells via ssODNs was largely done in reporter gene systems to optimize methods and as proof-of-principle. Today, editing endogenous genes is advancing, driven by a clearer understanding of mechanisms, by effective ssODN designs and by combination with engineered endonuclease technologies. Success is becoming routine in vitro and ex vivo, which includes editing embryonic stem (ES) and induced pluripotent stem (iPS) cells, suggesting that in vivo organ gene editing is a future option.
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Affiliation(s)
- Ioannis Papaioannou
- UCL Medical School, Division of Medicine (Upper 3rd Floor), Royal Free Campus, Rowland Hill Street, London NW3 2PF, UK
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26
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Drug-sensitive DNA polymerase δ reveals a role for mismatch repair in checkpoint activation in yeast. Genetics 2011; 189:1211-24. [PMID: 21926300 DOI: 10.1534/genetics.111.131938] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have used a novel method to activate the DNA damage S-phase checkpoint response in Saccharomyces cerevisiae to slow lagging-strand DNA replication by exposing cells expressing a drug-sensitive DNA polymerase δ (L612M-DNA pol δ) to the inhibitory drug phosphonoacetic acid (PAA). PAA-treated pol3-L612M cells arrest as large-budded cells with a single nucleus in the bud neck. This arrest requires all of the components of the S-phase DNA damage checkpoint: Mec1, Rad9, the DNA damage clamp Ddc1-Rad17-Mec3, and the Rad24-dependent clamp loader, but does not depend on Mrc1, which acts as the signaling adapter for the replication checkpoint. In addition to the above components, a fully functional mismatch repair system, including Exo1, is required to activate the S-phase damage checkpoint and for cells to survive drug exposure. We propose that mismatch repair activity produces persisting single-stranded DNA gaps in PAA-treated pol3-L612M cells that are required to increase DNA damage above the threshold needed for checkpoint activation. Our studies have important implications for understanding how cells avoid inappropriate checkpoint activation because of normal discontinuities in lagging-strand replication and identify a role for mismatch repair in checkpoint activation that is needed to maintain genome integrity.
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Yamamoto A, Sakamoto Y, Masumura K, Honma M, Nohmi T. Involvement of mismatch repair proteins in adaptive responses induced by N-methyl-N'-nitro-N-nitrosoguanidine against γ-induced genotoxicity in human cells. Mutat Res 2011; 713:56-63. [PMID: 21704047 DOI: 10.1016/j.mrfmmm.2011.05.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2011] [Revised: 05/20/2011] [Accepted: 05/23/2011] [Indexed: 10/18/2022]
Abstract
As humans are exposed to a variety of chemical agents as well as radiation, health effects of radiation should be evaluated in combination with chemicals. To explore combined genotoxic effects of radiation and chemicals, we examined modulating effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a direct-acting methylating agent, against genotoxicity of γ-radiation. Human lymphoblastoid TK6 cells and its mismatch-deficient derivative, i.e., MT1 cells, were treated with MNNG for 24h before they were exposed to γ-irradiation at a dose of 1.0 Gy, and the resulting genotoxicity was examined. In TK6 cells, the pretreatments with MNNG at low doses suppressed frequencies of the thymidine kinase (TK) gene mutation and micronucleus (MN) formation induced by γ-irradiation and thus the dose responses of TK and MN assays were U-shaped along with the pretreatment doses of MNNG. In contrast, the genotoxic effects of MNNG and γ-irradiation were additive in MT1 cells and the frequencies of TK mutations and MN induction increased along with the doses of MNNG. Apoptosis induced by γ-radiation was suppressed by the pretreatments in TK6 cells, but not in MT1 cells. The expression of p53 was induced and cell cycle was delayed at G2/M phase in TK6, but not in MT1 cells, by the treatments with MNNG. These results suggest that pretreatments of MNNG at low doses suppress genotoxicity of γ-radiation in human cells and also that mismatch repair proteins are involved in the apparent adaptive responses.
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Affiliation(s)
- Ayumi Yamamoto
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
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28
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Qi Y, Schoene NW, Lartey FM, Cheng WH. Selenium compounds activate ATM-dependent DNA damage response via the mismatch repair protein hMLH1 in colorectal cancer cells. J Biol Chem 2010; 285:33010-33017. [PMID: 20709753 DOI: 10.1074/jbc.m110.137406] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Epidemiological and animal studies indicate that selenium supplementation suppresses risk of colorectal and other cancers. The majority of colorectal cancers are characterized by a defective DNA mismatch repair (MMR). Here, we have employed the MMR-deficient HCT 116 colorectal cancer cells and the MMR-proficient HCT 116 cells with hMLH1 complementation to investigate the role of hMLH1 in selenium-induced DNA damage response, a tumorigenesis barrier. The ATM (ataxia telangiectasia mutated) protein responds to clastogens and initiates DNA damage response. We show that hMLH1 complementation sensitizes HCT 116 cells to methylseleninic acid, methylselenocysteine, and sodium selenite via reactive oxygen species and facilitates the selenium-induced oxidative 8-oxoguanine damage, DNA breaks, G(2)/M checkpoint response, and ATM pathway activation. Pretreatment of the hMLH1-complemented HCT 116 cells with the antioxidant N-acetylcysteine or 2,2,6,6-tetramethylpiperidine-1-oxyl or the ATM kinase inhibitor KU55933 suppresses hMLH1-dependent DNA damage response to selenium exposure. Selenium treatment stimulates the association between hMLH1 and hPMS2 proteins, a heterodimer critical for functional MMR, in a manner dependent on ATM and reactive oxygen species. Taken together, the results suggest a new role of selenium in mitigating tumorigenesis by targeting the MMR pathway, whereby the lack of hMLH1 renders the HCT 116 colorectal cancer cells resistant to selenium-induced DNA damage response.
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Affiliation(s)
- Yongmei Qi
- From the Department of Nutrition and Food Science, University of Maryland, College Park, Maryland 20742; School of Life Science, Lanzhou University, Lanzhou, Gansu 730000, China
| | - Norberta W Schoene
- Diet, Genomics, and Immunology Laboratory, Beltsville Human Nutrition Research Center, United States Department of Agriculture, Beltsville, Maryland 20705
| | - Frederick M Lartey
- From the Department of Nutrition and Food Science, University of Maryland, College Park, Maryland 20742
| | - Wen-Hsing Cheng
- From the Department of Nutrition and Food Science, University of Maryland, College Park, Maryland 20742.
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Vasquez KM. Targeting and processing of site-specific DNA interstrand crosslinks. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2010; 51:527-39. [PMID: 20196133 PMCID: PMC2895014 DOI: 10.1002/em.20557] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
DNA interstrand crosslinks (ICLs) are among the most cytotoxic types of DNA damage, and thus ICL-inducing agents such as cyclophosphamide, melphalan, cisplatin, psoralen, and mitomycin C have been used clinically as anticancer drugs for decades. ICLs can also be formed endogenously as a consequence of cellular metabolic processes. ICL-inducing agents continue to be among the most effective chemotherapeutic treatments for many cancers; however, treatment with these agents can lead to secondary malignancies, in part due to mutagenic processing of the DNA lesions. The mechanisms of ICL repair have been characterized more thoroughly in bacteria and yeast than in mammalian cells. Thus, a better understanding of the molecular mechanisms of ICL processing offers the potential to improve the efficacy of these drugs in cancer therapy. In mammalian cells, it is thought that ICLs are repaired by the coordination of proteins from several pathways, including nucleotide excision repair (NER), base excision repair (BER), mismatch repair (MMR), homologous recombination (HR), translesion synthesis (TLS), and proteins involved in Fanconi anemia (FA). In this review, we focus on the potential functions of NER, MMR, and HR proteins in the repair of and response to ICLs in human cells and in mice. We will also discuss a unique approach, using psoralen covalently linked to triplex-forming oligonucleotides to direct ICLs to specific sites in the mammalian genome.
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Affiliation(s)
- Karen M Vasquez
- Department of Carcinogenesis, The University of Texas M.D. Anderson Cancer Center, Science Park-Research Division, Smithville, Texas 78957, USA.
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Deckbar D, Stiff T, Koch B, Reis C, Löbrich M, Jeggo PA. The Limitations of the G1-S Checkpoint. Cancer Res 2010; 70:4412-21. [DOI: 10.1158/0008-5472.can-09-3198] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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31
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Jiang Z, Jin S, Yalowich JC, Brown KD, Rajasekaran B. The mismatch repair system modulates curcumin sensitivity through induction of DNA strand breaks and activation of G2-M checkpoint. Mol Cancer Ther 2010; 9:558-68. [PMID: 20145018 PMCID: PMC2837109 DOI: 10.1158/1535-7163.mct-09-0627] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The highly conserved mismatch (MMR) repair system corrects postreplicative errors and modulates cellular responses to genotoxic agents. Here, we show that the MMR system strongly influences cellular sensitivity to curcumin. Compared with MMR-proficient cells, isogenically matched MMR-deficient cells displayed enhanced sensitivity to curcumin. Similarly, cells suppressed for MLH1 or MSH2 expression by RNA interference displayed increased curcumin sensitivity. Curcumin treatment generated comparable levels of reactive oxygen species and the mutagenic adduct 8-oxo-guanine in MMR-proficient and MMR-deficient cells; however, accumulation of gammaH2AX foci, a marker for DNA double-strand breaks (DSB), occurred only in MMR-positive cells in response to curcumin treatment. Additionally, MMR-positive cells showed activation of Chk1 and induction of G(2)-M cell cycle checkpoint following curcumin treatment and inhibition of Chk1 by UCN-01 abrogated Chk1 activation and heightened apoptosis in MMR-proficient cells. These results indicate that curcumin triggers the accumulation of DNA DSB and induction of a checkpoint response through a MMR-dependent mechanism. Conversely, in MMR-compromised cells, curcumin-induced DSB is significantly blunted, and as a result, cells fail to undergo cell cycle arrest, enter mitosis, and die through mitotic catastrophe. The results have potential therapeutic value, especially in the treatment of tumors with compromised MMR function.
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Affiliation(s)
- Zhihua Jiang
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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Mastrocola AS, Heinen CD. Nuclear reorganization of DNA mismatch repair proteins in response to DNA damage. DNA Repair (Amst) 2010; 9:120-33. [PMID: 20004149 PMCID: PMC2819642 DOI: 10.1016/j.dnarep.2009.11.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2009] [Revised: 10/16/2009] [Accepted: 11/04/2009] [Indexed: 12/16/2022]
Abstract
The DNA mismatch repair (MMR) system is highly conserved and vital for preserving genomic integrity. Current mechanistic models for MMR are mainly derived from in vitro assays including reconstitution of strand-specific MMR and DNA binding assays using short oligonucleotides. However, fundamental questions regarding the mechanism and regulation in the context of cellular DNA replication remain. Using synchronized populations of HeLa cells we demonstrated that hMSH2, hMLH1 and PCNA localize to the chromatin during S-phase, and accumulate to a greater extent in cells treated with a DNA alkylating agent. In addition, using small interfering RNA to deplete hMSH2, we demonstrated that hMLH1 localization to the chromatin is hMSH2-dependent. hMSH2/hMLH1/PCNA proteins, when associated with the chromatin, form a complex that is greatly enhanced by DNA damage. The DNA damage caused by high doses of alkylating agents leads to a G(2) arrest after only one round of replication. In these G(2)-arrested cells, an hMSH2/hMLH1 complex persists on chromatin, however, PCNA is no longer in the complex. Cells treated with a lower dose of alkylating agent require two rounds of replication before cells arrest in G(2). In the first S-phase, the MMR proteins form a complex with PCNA, however, during the second S-phase PCNA is missing from that complex. The distinction between these complexes may suggest separate functions for the MMR proteins in damage repair and signaling. Additionally, using confocal immunofluorescence, we observed a population of hMSH6 that localized to the nucleolus. This population is significantly reduced after DNA damage suggesting that the protein is shuttled out of the nucleolus in response to damage. In contrast, hMLH1 is excluded from the nucleolus at all times. Thus, the nucleolus may act to segregate a population of hMSH2-hMSH6 from hMLH1-hPMS2 such that, in the absence of DNA damage, an inappropriate response is not invoked.
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Affiliation(s)
- Adam S. Mastrocola
- Neag Comprehensive Cancer Center and Center for Molecular Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
| | - Christopher D. Heinen
- Neag Comprehensive Cancer Center and Center for Molecular Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
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Liu Y, Fang Y, Shao H, Lindsey-Boltz L, Sancar A, Modrich P. Interactions of human mismatch repair proteins MutSalpha and MutLalpha with proteins of the ATR-Chk1 pathway. J Biol Chem 2009; 285:5974-82. [PMID: 20029092 PMCID: PMC2820822 DOI: 10.1074/jbc.m109.076109] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
At clinically relevant doses, chemotherapeutic SN1 DNA methylating agents induce an ATR-mediated checkpoint response in human cells that is dependent on functional MutSα and MutLα. Deficiency of either mismatch repair activity renders cells highly resistant to this class of drug, but the mechanisms linking mismatch repair to checkpoint activation have remained elusive. In this study we have systematically examined the interactions of human MutSα and MutLα with proteins of the ATR-Chk1 pathway using both nuclear extracts and purified proteins. Using nuclear co-immunoprecipitation, we have detected interaction of MutSα with ATR, TopBP1, Claspin, and Chk1 and interaction of MutLα with TopBP1 and Claspin. We were unable to detect interaction of MutSα or MutLα with Rad17, Rad9, or replication protein A in the extract system. Use of purified proteins confirmed direct interaction of MutSα with ATR, TopBP1, and Chk1 and of MutLα with TopBP1. MutSα-Claspin and MutLα-Claspin interactions were not demonstrable with purified proteins, suggesting that extract interactions are indirect or depend on post-translational modification. Use of a modified chromatin immunoprecipitation assay showed that proliferating cell nuclear antigen, ATR, TopBP1, and Chk1 are recruited to chromatin in a MutLα- and MutSα-dependent fashion after N-methyl-N′-nitro-N-nitrosoguanidine treatment. However, chromatin enrichment of replication protein A, Claspin, Rad17-RFC, and Rad9-Rad1-Hus1 was not detected in these experiments. Although our failure to observe enrichment of the latter activities could be due to sensitivity limitations, these observations may indicate a novel mechanism for ATR activation.
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Affiliation(s)
- Yiyong Liu
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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Martin L, Marples B, Coffey M, Lawler M, Hollywood D, Marignol L. Recognition of O6MeG lesions by MGMT and mismatch repair proficiency may be a prerequisite for low-dose radiation hypersensitivity. Radiat Res 2009; 172:405-13. [PMID: 19772461 DOI: 10.1667/rr1717.1] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Low-dose hyper-radiosensitivity (HRS) is the phenomenon whereby cells exposed to radiation doses of less than approximately 0.5 Gy exhibit increased cell killing relative to that predicted from back-extrapolating high-dose survival data using a linear-quadratic model. While the exact mechanism remains to be elucidated, the involvement of several molecular repair pathways has been documented. These processes in turn are also associated with the response of cells to O6-methylguanine (O6MeG) lesions. We propose a model in which the level of low-dose cell killing is determined by the efficiency of both pre-replicative repair by the DNA repair enzyme O6-methylguanine methyltransferase (MGMT) and post-replicative repair by the DNA mismatch repair (MMR) system. We therefore hypothesized that the response of cells to low doses of radiation is dependent on the expression status of MGMT and MMR proteins. MMR (MSH2, MSH6, MLH1, PMS1, PMS2) and MGMT protein expression signatures were determined in a panel of normal (PWR1E, RWPE1) and malignant (22RV1, DU145, PC3) prostate cell lines and correlated with clonogenic survival and cell cycle analysis. PC3 and RWPE1 cells (HRS positive) were associated with MGMT and MMR proficiency, whereas HRS negative cell lines lacked expression of at least one (MGMT or MMR) protein. MGMT inactivation had no significant effect on cell survival. These results indicate a possible role for MMR-dependent processing of damage produced by low doses of radiation.
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Affiliation(s)
- Lynn Martin
- Division of Radiation Therapy, Trinity College Dublin, Dublin, Ireland.
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Koryllou A, Patrinou-Georgoula M, Troungos C, Pletsa V. Cell death induced by N-methyl-N-nitrosourea, a model S(N)1 methylating agent, in two lung cancer cell lines of human origin. Apoptosis 2009; 14:1121-33. [PMID: 19634013 DOI: 10.1007/s10495-009-0379-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
New therapeutic approaches are needed for lung cancer, the leading cause of cancer death. Methylating agents constitute a widely used class of anticancer drugs, the effect of which on human non small cell lung cancer (NSCLC) has not been adequately studied. N-methyl-N-nitrosourea (MNU), a model S(N)1 methylating agent, induced cell death through a distinct mechanism in two human NSCLC cell lines studied, A549(p53(wt)) and H157(p53(null)). In A549(p53(wt)), MNU induced G2/M arrest, accompanied by cdc25A degradation, hnRNP B1 induction, hnRNP C1/C2 downregulation. Non-apoptotic cell death was confirmed by the lack of increase in the sub-G1 DNA content, Poly (ADP-ribose) polymerase cleavage and caspase-3, -7 activation. In H157(p53(null)), MNU induced apoptotic cell death, confirmed by cytofluorometry of DNA content and immunodetection of apoptotic markers, accompanied by overexpression of hnRNP B1 and C1/C2. Thus, the mechanism of the cell death induced by S(N)1 methylating agents is cell type-dependent and must be assessed prior treatment.
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Affiliation(s)
- Angeliki Koryllou
- Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Athens, Greece
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Sun G, Jin S, Baskaran R. MMR/c-Abl-dependent activation of ING2/p73alpha signaling regulates the cell death response to N-methyl-N'-nitro-N-nitrosoguanidine. Exp Cell Res 2009; 315:3163-75. [PMID: 19766113 DOI: 10.1016/j.yexcr.2009.09.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2009] [Revised: 09/10/2009] [Accepted: 09/10/2009] [Indexed: 01/09/2023]
Abstract
Agents inducing O(6)-methylguanine (O(6)MeG) in DNA such as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) are cytotoxic and a deficiency in mismatch repair (MMR) results in lack of sensitivity to this genotoxin (termed alkylation tolerance). Here, we show that ING2, a member of the inhibitor of growth family, is required for cell death induced by MNNG. We further observe that MNNG treatment increases cellular protein levels of ING2 that is dependent on intact MMR function and that MNNG-induced ING2 localizes and associates with p73alpha in the nucleus. Suppression of ING2 by short hairpin RNA (shRNA) in MMR-proficient colorectal cancer cells decreased its sensitivity to MNNG and, in addition, abrogated MNNG-induced stabilization and acetylation of p73alpha. Interestingly, suppression of p73alpha had a greater impact on MNNG-induced cell death than ING2 leading us to conclude that ING2 regulates the cell death response, in part, through p73alpha. Inhibition of c-Abl by STI571 or suppression of c-Abl expression by shRNA blocked ING2 induction and p73alpha acetylation induced by this alkylator. Similarly, suppression of MMR (MLH1) by shRNA abrogated ING2 induction/p73alpha acetylation. Taken together, these results demonstrate that MLH1/c-Abl-dependent activation of ING2>p73alpha signaling regulates cell death triggered by MNNG and further suggests that dysregulation of this event may, in part, be responsible for alkylation tolerance observed in MMR compromised cells.
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Affiliation(s)
- Guoming Sun
- Department of Microbiology and Molecular Genetics, School of Medicine, University of Pittsburgh, E1205 Biomedical Science Tower, Pittsburgh, PA 15261, USA
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MLH1 mediates PARP-dependent cell death in response to the methylating agent N-methyl-N-nitrosourea. Br J Cancer 2009; 101:441-51. [PMID: 19623177 PMCID: PMC2720233 DOI: 10.1038/sj.bjc.6605186] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Background: Methylating agents such as N-methyl-N-nitrosourea (MNU) can cause cell cycle arrest and death either via caspase-dependent apoptosis or via a poly(ADP-ribose) polymerase (PARP)-dependent form of apoptosis. We wished to investigate the possible role of MLH1 in signalling cell death through PARP. Methods: Fibroblasts are particularly dependent on a PARP-mediated cell death response to methylating agents. We used hTERT-immortalised normal human fibroblasts (WT) to generate isogenic MLH1-depleted cells, confirmed by quantitative PCR and western blotting. Drug resistance was measured by clonogenic and cell viability assays and effects on the cell cycle by cell sorting. Damage signalling was additionally investigated using immunostaining. Results: MLH1-depleted cells were more resistant to MNU, as expected. Despite having an intact G2/M checkpoint, the WT cells did not initially undergo cell cycle arrest but instead triggered cell death directly by PARP overactivation and nuclear translocation of apoptosis-inducing factor (AIF). The MLH1-depleted cells showed defects in this pathway, with decreased staining for phosphorylated H2AX, altered PARP activity and reduced AIF translocation. Inhibitors of PARP, but not of caspases, blocked AIF translocation and greatly decreased short-term cell death in both WT and MLH1-depleted cells. This MLH1-dependent response to MNU was not blocked by inhibitors of ATM/ATR or p53. Conclusion: These novel data indicate an important role for MLH1 in signalling PARP-dependent cell death in response to the methylating agent MNU.
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Jardim MJ, Wang Q, Furumai R, Wakeman T, Goodman BK, Wang XF. Reduced ATR or Chk1 expression leads to chromosome instability and chemosensitization of mismatch repair-deficient colorectal cancer cells. Mol Biol Cell 2009; 20:3801-9. [PMID: 19570909 DOI: 10.1091/mbc.e09-04-0303] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Genomic instability in colorectal cancer is categorized into two distinct classes: chromosome instability (CIN) and microsatellite instability (MSI). MSI is the result of mutations in the mismatch repair (MMR) machinery, whereas CIN is often thought to be associated with a disruption in the APC gene. Clinical data has recently shown the presence of heterozygous mutations in ATR and Chk1 in human cancers that exhibit MSI, suggesting that those mutations may contribute to tumorigenesis. To determine whether reduced activity in the DNA damage checkpoint pathway would cooperate with MMR deficiency to induce CIN, we used siRNA strategies to partially decrease the expression of ATR or Chk1 in MMR-deficient colorectal cancer cells. The resultant cancer cells display a typical CIN phenotype, as characterized by an increase in the number of chromosomal abnormalities. Importantly, restoration of MMR proficiency completely inhibited induction of the CIN phenotype, indicating that the combination of partial checkpoint blockage and MMR deficiency is necessary to trigger CIN. Moreover, disruption of ATR and Chk1 in MMR-deficient cells enhanced the sensitivity to treatment with the commonly used colorectal chemotherapeutic compound, 5-fluorouracil. These results provide a basis for the development of a combination therapy for those cancer patients.
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Affiliation(s)
- Melanie J Jardim
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710, USA
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Papaioannou I, Disterer P, Owen JS. Use of internally nuclease-protected single-strand DNA oligonucleotides and silencing of the mismatch repair protein, MSH2, enhances the replication of corrected cells following gene editing. J Gene Med 2009; 11:267-74. [PMID: 19153972 DOI: 10.1002/jgm.1296] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND Gene editing is potentially a powerful technology for introducing genetic changes by using short single-stranded DNA oligonucleotides (ssODNs). However, their efficiency is reduced by the mismatch repair system, especially MSH2, which may suppress gene editing, although findings vary depending on readout and type of oligonucleotide used. Additionally, successfully edited cells are reported to arrest at the S- or G2-phase. In the present study, we evaluate whether a novel ssODN design and down-regulation of MSH2 expression allows the isolation of replicating gene-edited cells. METHODS Cultured Chinese hamster ovary cells expressing mutated enhanced green fluorescent protein were targeted with ssODNs of varying design, all capable of restoring fluorescence, which allows the monitoring of correction events by flow cytometry. Converted cells were isolated by cell sorting and grown to determine colony formation efficiencies. MSH2 expression was suppressed with small interfering RNA and the cell cycle distribution of cells transfected with ssODN was quantified by flow cytometry, following propidium iodide or DRAQ5 staining. RESULTS Although efficiency was higher using ssODN end-protected with phosphorothioate, the potential of edited cells to form colonies was lower than those targeted with unmodified ssODN. We established that ssODN transfection itself perturbs the cell cycle and that MSH2 gene silencing increases correction efficiency. In both cases, however, the effect was dependent on the positioning of the protected nucleotides. Importantly, when internally protected ssODN was used in combination with MSH2 suppression, a higher proportion of G1-phase corrected cells was observed 48-64 h after transfection. CONCLUSIONS Use of internally protected ssODN and downregulating cellular MSH2 activity may facilitate isolation of viable, actively replicating gene-edited cells.
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Affiliation(s)
- Ioannis Papaioannou
- Department of Medicine, Royal Free and University College Medical School, Royal Free Campus, London, UK
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Cui B, Johnson SP, Bullock N, Ali-Osman F, Bigner DD, Friedman HS. Bifunctional DNA alkylator 1,3-bis(2-chloroethyl)-1-nitrosourea activates the ATR-Chk1 pathway independently of the mismatch repair pathway. Mol Pharmacol 2009; 75:1356-63. [PMID: 19261750 DOI: 10.1124/mol.108.053124] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The presence of DNA damage initiates signaling through the ataxia-telangiectasia mutated kinase (ATM) and the ATM- and the Rad3-related kinase (ATR), which phosphorylate, thus activating, the checkpoint kinases (Chk) 1 and 2, which leads to cell cycle arrest. The bifunctional DNA alkylator 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) is cytotoxic primarily by inducing DNA monoadducts and ultimately, interstrand cross-links, which block DNA replication. In this study, we investigated the activation of the ATR-Chk1 pathway in response to BCNU treatment and the dependence of this response on the DNA mismatch repair (MMR) capacity. Medulloblastoma cells were exposed to low and moderate doses of BCNU, and the effects on this DNA damage signaling pathway were examined. In response to BCNU, Chk1 was found to be phosphorylated at serine 345 and exhibited increased kinase activity. Caffeine and wortmannin, which are broad-spectrum inhibitors of ATM and ATR, reduced this phosphorylation. Cell cycle analysis further revealed an accumulation of cells in the S phase in response to BCNU, an effect that was attenuated by caffeine. Small interfering RNA knockdown of ATR also reduced Chk1 phosphorylation after exposure to BCNU. However, knockdown of ATM had no effect on the observed Chk1 phosphorylation, suggesting that ATR was primarily responsible for Chk1 activation. Analysis of Chk1 activation in cells deficient in MMR proteins MutLalpha or MutSalpha indicated that the DNA damage response induced by BCNU was independent of the MMR apparatus. This MMR-independent activation seems to be the result of DNA interstrand cross-link formation.
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Affiliation(s)
- B Cui
- Departments of Surgery, Duke University Medical Center, Durham, NC 27710, USA
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Abstract
Genetically engineered mice are essential tools in both mechanistic studies and drug development in colon cancer research. Mice with mutations in the Apc gene, as well as in genes that modify or interact with Apc, are important models of familial adenomatous polyposis. Mice with mutations in the beta-catenin signaling pathway have also revealed important information about colon cancer pathogenesis, along with models for hereditary nonpolyposis colon cancer and inflammatory bowel diseases associated with colon cancer. Finally, transplantation models (xenografts)have been useful in the study of metastasis and for testing potential therapeutics. This review discusses what models have been developed most recently and what they have taught us about colon cancer formation, progression, and possible treatment strategies.
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Affiliation(s)
- Makoto Mark Taketo
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York, USA
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Kinsella TJ. Coordination of DNA mismatch repair and base excision repair processing of chemotherapy and radiation damage for targeting resistant cancers. Clin Cancer Res 2009; 15:1853-9. [PMID: 19240165 DOI: 10.1158/1078-0432.ccr-08-1307] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
DNA damage processing by mismatch repair (MMR) and/or base excision repair (BER) can determine the therapeutic index following treatment of human cancers using radiation therapy and several classes of chemotherapy drugs. Over the last decade, basic and translational cancer research in DNA repair has led to an increased understanding of how these two DNA repair pathways can modify cytotoxicity to chemotherapy and/or ionizing radiation treatments in both normal and malignant tissues. This Molecular Pathways article provides an overview of the current understanding of mechanisms involved in MMR and BER damage processing, including insights into possible coordination of these two DNA repair pathways after chemotherapy and/or ionizing radiation damage. It also introduces principles of systems biology that have been applied to better understand the complexities and coordination of MMR and BER in processing these DNA damages. Finally, it highlights novel therapeutic approaches to target resistant (or DNA damage tolerant) human cancers using chemical and molecular modifiers of chemotherapy and/or ionizing radiation including poly (ADP-ribose) polymerase inhibitors, methoxyamine and iododeoxyuridine (and the prodrug, 5-iodo-2-pyrimidinone-2'-deoxyribose).
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Affiliation(s)
- Timothy J Kinsella
- Case Integrative Cancer Biology Program, Case Western Reserve University, Cleveland, OH, USA.
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Wu Q, Vasquez KM. Human MLH1 protein participates in genomic damage checkpoint signaling in response to DNA interstrand crosslinks, while MSH2 functions in DNA repair. PLoS Genet 2008; 4:e1000189. [PMID: 18787700 PMCID: PMC2526179 DOI: 10.1371/journal.pgen.1000189] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Accepted: 08/05/2008] [Indexed: 11/21/2022] Open
Abstract
DNA interstrand crosslinks (ICLs) are among the most toxic types of damage to a cell. For this reason, many ICL-inducing agents are effective therapeutic agents. For example, cisplatin and nitrogen mustards are used for treating cancer and psoralen plus UVA (PUVA) is useful for treating psoriasis. However, repair mechanisms for ICLs in the human genome are not clearly defined. Previously, we have shown that MSH2, the common subunit of the human MutSα and MutSβ mismatch recognition complexes, plays a role in the error-free repair of psoralen ICLs. We hypothesized that MLH1, the common subunit of human MutL complexes, is also involved in the cellular response to psoralen ICLs. Surprisingly, we instead found that MLH1-deficient human cells are more resistant to psoralen ICLs, in contrast to the sensitivity to these lesions displayed by MSH2-deficient cells. Apoptosis was not as efficiently induced by psoralen ICLs in MLH1-deficient cells as in MLH1-proficient cells as determined by caspase-3/7 activity and binding of annexin V. Strikingly, CHK2 phosphorylation was undetectable in MLH1-deficient cells, and phosphorylation of CHK1 was reduced after PUVA treatment, indicating that MLH1 is involved in signaling psoralen ICL-induced checkpoint activation. Psoralen ICLs can result in mutations near the crosslinked sites; however, MLH1 function was not required for the mutagenic repair of these lesions, and so its signaling function appears to have a role in maintaining genomic stability following exposure to ICL-induced DNA damage. Distinguishing the genetic status of MMR-deficient tumors as MSH2-deficient or MLH1-deficient is thus potentially important in predicting the efficacy of treatment with psoralen and perhaps with other ICL-inducing agents. Crosslinks, linking the complementary stands of the DNA double helix, can lead to cell death, because they are so effective at interfering with normal genomic transactions such as DNA replication. This property of crosslinking agents has long been utilized in cancer therapy. The purpose of our research is to understand the function of DNA repair proteins in cellular responses to DNA interstrand crosslinking agents. MSH2 is a central protein in the recognition of DNA mismatches, and we previously found that it plays an important role in protecting cells against the toxicity of crosslinks. The MLH1 protein functions in DNA mismatch repair in a later step, and we hypothesized that MLH1 may also be involved in repair of crosslinks. We were surprised to find that MLH1 function is important for DNA crosslink-induced signaling, rather than DNA repair. MLH1-deficient cells are more resistant to crosslinks and have defective signaling to processes that signal cell death. This work may have clinical consequences, as mutations in MSH2 and MLH1 are common in tumors. MSH2-deficient cells may be more vulnerable to DNA crosslink-inducing agents than normal, while MLH1-deficient cells have a greater potential to survive crosslinking treatment, which could instead potentiate further tumor initiation.
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Affiliation(s)
- Qi Wu
- Department of Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Science Park-Research Division, Smithville, Texas, United States of America
| | - Karen M. Vasquez
- Department of Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Science Park-Research Division, Smithville, Texas, United States of America
- * E-mail:
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Dicarbonyl-induced accelerated aging in vitro in human skin fibroblasts. Biogerontology 2008; 10:203-11. [DOI: 10.1007/s10522-008-9172-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Accepted: 08/14/2008] [Indexed: 10/21/2022]
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Hsieh P, Yamane K. DNA mismatch repair: molecular mechanism, cancer, and ageing. Mech Ageing Dev 2008; 129:391-407. [PMID: 18406444 PMCID: PMC2574955 DOI: 10.1016/j.mad.2008.02.012] [Citation(s) in RCA: 291] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2007] [Revised: 02/22/2008] [Accepted: 02/28/2008] [Indexed: 02/09/2023]
Abstract
DNA mismatch repair (MMR) proteins are ubiquitous players in a diverse array of important cellular functions. In its role in post-replication repair, MMR safeguards the genome correcting base mispairs arising as a result of replication errors. Loss of MMR results in greatly increased rates of spontaneous mutation in organisms ranging from bacteria to humans. Mutations in MMR genes cause hereditary nonpolyposis colorectal cancer, and loss of MMR is associated with a significant fraction of sporadic cancers. Given its prominence in mutation avoidance and its ability to target a range of DNA lesions, MMR has been under investigation in studies of ageing mechanisms. This review summarizes what is known about the molecular details of the MMR pathway and the role of MMR proteins in cancer susceptibility and ageing.
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Affiliation(s)
- Peggy Hsieh
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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Campregher C, Luciani MG, Gasche C. Activated neutrophils induce an hMSH2-dependent G2/M checkpoint arrest and replication errors at a (CA)13-repeat in colon epithelial cells. Gut 2008; 57:780-7. [PMID: 18272544 PMCID: PMC2564829 DOI: 10.1136/gut.2007.141556] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Revised: 01/08/2008] [Accepted: 02/02/2008] [Indexed: 12/19/2022]
Abstract
OBJECTIVE Chronic inflammation in ulcerative colitis is associated with increased risk for colorectal cancer. Its molecular pathway of cancer development is poorly understood. We investigated the role of neutrophil-derived cellular stress in an in vitro model of neutrophils as effectors and colon epithelial cells as targets, and tested for changes in cell cycle distribution and the appearance of replication errors. DESIGN Colon epithelial cells with different mismatch repair phenotypes were co-cultured with activated neutrophils. Target cells were analysed for cell cycle distribution and replication errors by flow cytometry. Changes in nuclear and DNA-bound levels of mismatch repair- and checkpoint-related proteins were analysed by western blotting. RESULTS Activated neutrophils cause an accumulation of target cells in G2/M, consistent with the installation of a DNA-damage checkpoint. Cells that do not express hMSH2, p53 or p21(waf1/cip1) failed to undergo the G2/M arrest. Phosphorylation of p53 at site Ser15 and Chk1 at Ser317, as well as accumulation of p21(waf1/cip1), was observed within 8-24 h. Superoxide dismutase and catalase were unable to overcome this G2/M arrest, possibly indicating that neutrophil products other than superoxide or H(2)O(2) are involved in this cellular response. Finally, exposure to activated neutrophils increased the number of replication errors. CONCLUSIONS By using an in vitro co-culture model that mimics intestinal inflammation in ulcerative colitis, we provide molecular evidence for an hMSH2-dependent G2/M checkpoint arrest and for the presence of replication errors.
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Affiliation(s)
- C Campregher
- AKH Wien, Division of Gastroenterology and Hepatology, Währinger Gürtel 18, A-1090 Vienna, Austria
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Wagner MW, Li LS, Morales JC, Galindo CL, Garner HR, Bornmann WG, Boothman DA. Role of c-Abl kinase in DNA mismatch repair-dependent G2 cell cycle checkpoint arrest responses. J Biol Chem 2008; 283:21382-93. [PMID: 18480061 DOI: 10.1074/jbc.m709953200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Current published data suggest that DNA mismatch repair (MMR) triggers prolonged G(2) cell cycle checkpoint arrest after alkylation damage from N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) by activating ATR (ataxia telangiectasia-Rad3-related kinase). However, analyses of isogenic MMR-proficient and MMR-deficient human RKO colon cancer cells revealed that although ATR/Chk1 signaling controlled G(2) arrest in MMR-deficient cells, ATR/Chk1 activation was not involved in MMR-dependent G(2) arrest. Instead, we discovered that disrupting c-Abl activity using STI571 (Gleevec, a c-Abl inhibitor) or stable c-Abl knockdown abolished MMR-dependent p73alpha stabilization, induction of GADD45alpha protein expression, and G(2) arrest. In addition, inhibition of c-Abl also increased the survival of MNNG-exposed MMR-proficient cells to a level comparable with MMR-deficient cells. Furthermore, knocking down GADD45alpha (but not p73alpha) protein levels affected MMR-dependent G(2) arrest responses. Thus, MMR-dependent G(2) arrest responses triggered by MNNG are dependent on a human MLH1/c-Abl/GADD45alpha signaling pathway and activity. Furthermore, our data suggest that caution should be taken with therapies targeting c-Abl kinase because increased survival of mutator phenotypes may be an unwanted consequence.
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Affiliation(s)
- Mark W Wagner
- Laboratory of Molecular Stress Responses, Program in Cell Stress and Cancer Nanomedicine, Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
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Ai L, Kim WJ, Demircan B, Dyer LM, Bray KJ, Skehan RR, Massoll NA, Brown KD. The transglutaminase 2 gene (TGM2), a potential molecular marker for chemotherapeutic drug sensitivity, is epigenetically silenced in breast cancer. Carcinogenesis 2008; 29:510-8. [PMID: 18174247 DOI: 10.1093/carcin/bgm280] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Tissue transglutaminase (TG2) is a ubiquitously expressed enzyme capable of catalyzing protein cross-links. TG2-dependent cross-links are important in extracellular matrix integrity and it has been proposed that this TG2 activity establishes a barrier to tumor spread. Furthermore, TG2 controls sensitivity to the chemotherapeutic drug doxorubicin. Both doxorubicin sensitivity and TG2 expression are highly variable in cultured human breast cancer cell lines and inspection of the human gene (termed TGM2) determined that a canonical CpG island exists within its 5' flank. These features, when combined with its potential tumor suppressor activity, make TG2 an attractive candidate for epigenetic silencing. Consistent with this, we observed that culturing breast tumor cells with the DNA demethylating agent 5-aza-2'-deoxycytidine (5-azadC) resulted in a robust increase in TG2 expression. Analysis of DNA harvested from cultured lines and primary breast tumor samples indicated that TGM2 often displays aberrant hypermethylation and that there is a statistically significant correlation between gene methylation and reduced expression. Finally, we observed that doxorubicin-resistant MCF-7/ADR cells do not show TGM2 silencing but that doxorubicin-sensitive MCF-7 cells do and that culturing MCF-7 cells on 5-azadC and subsequently restoring TG2 expression reduced sensitivity to doxorubicin. This work indicates that the TGM2 gene is a target for epigenetic silencing in breast cancer and suggests that this aberrant molecular event is a potential marker for chemotherapeutic drug sensitivity.
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Affiliation(s)
- Lingbao Ai
- Department of Biochemistry and Molecular Biology and University of Florida Shands Cancer Center Program in Cancer Genetics, Epigenetics and Tumor Virology, University of Florida College of Medicine, Box 100245, Gainesville, FL 32610, USA
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TLR9 engagement on CD4 T lymphocytes represses gamma-radiation-induced apoptosis through activation of checkpoint kinase response elements. Blood 2007; 111:2704-13. [PMID: 18086870 DOI: 10.1182/blood-2007-07-104141] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
T cell-based therapies have much promise in cancer treatment. This approach may be enhanced if used in combination with radiotherapy provided that tumor-specific T cells can be protected against the effects of radiotherapy. Previously, we demonstrated that administration of TLR9 ligand into mice decreased activation- and serum deprivation-induced cell death in T cells. We hypothesized that TLR9 engagement on T lymphocytes decreased apoptosis after cellular stress. We show that TLR9 engagement on murine CD4 T cells reduces gamma-radiation-induced apoptosis as judged by decreased annexin-V/PI staining, caspase-3 activation, and PARP cleavage. TLR9-stimulated cells show heightened accumulation at the G2 cell-cycle phase and increased DNA repair rates. Irradiated, TLR9-engaged cells showed higher levels of phosphorylated Chk1 and Chk2. While the levels of activated ATM in response to IR did not differ between TLR9-stimulated and unstimulated cells, inhibition of ATM/ATR and Chk1/Chk2 kinases abolished the radioprotective effects in TLR9-stimulated cells. In vivo, TLR9-stimulated cells displayed higher radio resistance than TLR9-stimulated MyD88(-/-) T cells and responded to antigenic stimulation after total body irradiation. These findings show, for the first time, that TLR9 engagement on CD4 T cells reduces IR-induced apoptosis by influencing cell-cycle checkpoint activity, potentially allowing for combinatorial immunotherapy and radiotherapy.
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Ai L, Kim WJ, Kim TY, Fields CR, Massoll NA, Robertson KD, Brown KD. Epigenetic silencing of the tumor suppressor cystatin M occurs during breast cancer progression. Cancer Res 2007; 66:7899-909. [PMID: 16912163 DOI: 10.1158/0008-5472.can-06-0576] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cystatin M is a secreted inhibitor of lysosomal cysteine proteases. Several lines of evidence indicate that cystatin M is a tumor suppressor important in breast malignancy; however, the mechanism(s) that leads to inactivation of cystatin M during cancer progression is unknown. Inspection of the human cystatin M locus uncovered a large and dense CpG island within the 5' region of this gene (termed CST6). Analysis of cultured human breast tumor lines indicated that cystatin M expression is either undetectable or in low abundance in several lines; however, enhanced gene expression was measured in cells cultured on the DNA demethylating agent 5-aza-2'-deoxycytidine (5-aza-dC). Increased cystatin M expression does not correlate with a cytotoxic response to 5-aza-dC; rather, various molecular approaches indicated that the CST6 gene was aberrantly methylated in these tumor lines as well as in primary breast tumors. Moreover, 60% (12 of 20) of primary tumors analyzed displayed CST6 hypermethylation, indicating that this aberrant characteristic is common in breast malignancies. Finally, preinvasive and invasive breast tumor cells were microdissected from nine archival breast cancer specimens. Of the five tumors displaying CST6 gene methylation, four tumors displayed methylation in both ductal carcinoma in situ and invasive breast carcinoma lesions and reduced expression of cystatin M in these tumors was confirmed by immunohistochemistry. In summary, this study establishes that the tumor suppressor cystatin M is a novel target for epigenetic silencing during mammary tumorigenesis and that this aberrant event can occur before development of invasive breast cancer.
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Affiliation(s)
- Lingbao Ai
- Department of Biochemistry and Molecular Biology and University of Florida Shands Cancer Center Program in Cancer Genetics, Epigenetics, and Tumor Virology, University of Florida College of Medicine, Gainesville, FL 32610, USA
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