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Ng YB, Akincilar SC. Shaping DNA damage responses: Therapeutic potential of targeting telomeric proteins and DNA repair factors in cancer. Curr Opin Pharmacol 2024; 76:102460. [PMID: 38776747 DOI: 10.1016/j.coph.2024.102460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Revised: 10/06/2023] [Accepted: 10/11/2023] [Indexed: 05/25/2024]
Abstract
Shelterin proteins regulate genomic stability by preventing inappropriate DNA damage responses (DDRs) at telomeres. Unprotected telomeres lead to persistent DDR causing cell cycle inhibition, growth arrest, and apoptosis. Cancer cells rely on DDR to protect themselves from DNA lesions and exogenous DNA-damaging agents such as chemotherapy and radiotherapy. Therefore, targeting DDR machinery is a promising strategy to increase the sensitivity of cancer cells to existing cancer therapies. However, the success of these DDR inhibitors depends on other mutations, and over time, patients develop resistance to these therapies. This suggests the need for alternative approaches. One promising strategy is co-inhibiting shelterin proteins with DDR molecules, which would offset cellular fitness in DNA repair in a mutation-independent manner. This review highlights the associations and dependencies of the shelterin complex with the DDR proteins and discusses potential co-inhibition strategies that might improve the therapeutic potential of current inhibitors.
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Affiliation(s)
- Yu Bin Ng
- Laboratory of NFκB Signalling, Institute of Molecular and Cell Biology (IMCB), Agency for Science, Technology and Research (A∗STAR), 61 Biopolis Drive, Proteos, Singapore 138673, Republic of Singapore
| | - Semih Can Akincilar
- Laboratory of NFκB Signalling, Institute of Molecular and Cell Biology (IMCB), Agency for Science, Technology and Research (A∗STAR), 61 Biopolis Drive, Proteos, Singapore 138673, Republic of Singapore.
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2
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Xing M, Xiong Y, Zhang Y. Ku80 is indispensable for repairing DNA double-strand breaks at highly methylated sites in human HCT116 cells. DNA Repair (Amst) 2024; 134:103627. [PMID: 38219597 DOI: 10.1016/j.dnarep.2024.103627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2023] [Revised: 01/01/2024] [Accepted: 01/03/2024] [Indexed: 01/16/2024]
Abstract
DNA double-strand breaks (DSBs) are harmful to mammalian cells and a few of them can cause cell death. Accumulating DSBs in these cells to analyze their genomic distribution and their potential impact on chromatin structure is difficult. In this study, we used CRISPR to generate Ku80-/- human cells and arrested the cells in G1 phase to accumulate DSBs before conducting END-seq and Nanopore analysis. Our analysis revealed that DNA with high methylation level accumulates DSB hotspots in Ku80-/- human cells. Furthermore, we identified chromosome structural variants (SVs) using Nanopore sequencing and observed a higher number of SVs in Ku80-/- human cells. Based on our findings, we suggest that the high efficiency of Ku80 knockout in human HCT116 cells makes it a promising model for characterizing SVs in the context of 3D chromatin structure and studying the alternative-end joining (Alt-EJ) DSB repair pathway.
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Affiliation(s)
- Mengtan Xing
- Institute for Regenerative Medicine, Department of Neurosurgery, Shanghai East Hospital, Shanghai Key Laboratory of Signaling and Disease Research, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Yanhong Xiong
- Institute for Regenerative Medicine, Department of Neurosurgery, Shanghai East Hospital, Shanghai Key Laboratory of Signaling and Disease Research, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Yong Zhang
- Institute for Regenerative Medicine, Department of Neurosurgery, Shanghai East Hospital, Shanghai Key Laboratory of Signaling and Disease Research, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai 200092, China.
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3
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Kelly RD, Parmar G, Bayat L, Maitland MER, Lajoie GA, Edgell DR, Schild-Poulter C. Noncanonical functions of Ku may underlie essentiality in human cells. Sci Rep 2023; 13:12162. [PMID: 37500706 PMCID: PMC10374653 DOI: 10.1038/s41598-023-39166-7] [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: 02/17/2023] [Accepted: 07/20/2023] [Indexed: 07/29/2023] Open
Abstract
The Ku70/80 heterodimer is a key player in non-homologous end-joining DNA repair but is involved in other cellular functions like telomere regulation and maintenance, in which Ku's role is not fully characterized. It was previously reported that knockout of Ku80 in a human cell line results in lethality, but the underlying cause of Ku essentiality in human cells has yet to be fully explored. Here, we established conditional Ku70 knockout cells using CRISPR/Cas9 editing to study the essentiality of Ku70 function. While we observed loss of cell viability upon Ku depletion, we did not detect significant changes in telomere length, nor did we record lethal levels of DNA damage upon loss of Ku. Analysis of global proteome changes following Ku70 depletion revealed dysregulations of several cellular pathways including cell cycle/mitosis, RNA related processes, and translation/ribosome biogenesis. Our study suggests that the driving cause of loss of cell viability in Ku70 knockouts is not linked to the functions of Ku in DNA repair or at telomeres. Moreover, our data shows that loss of Ku affects multiple cellular processes and pathways and suggests that Ku plays critical roles in cellular processes beyond DNA repair and telomere maintenance to maintain cell viability.
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Affiliation(s)
- Rachel D Kelly
- Department of Biochemistry, Western University, London, ON, Canada
- Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Gursimran Parmar
- Department of Biochemistry, Western University, London, ON, Canada
- Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Laila Bayat
- Department of Biochemistry, Western University, London, ON, Canada
- Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Matthew E R Maitland
- Department of Biochemistry, Western University, London, ON, Canada
- Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Gilles A Lajoie
- Department of Biochemistry, Western University, London, ON, Canada
| | - David R Edgell
- Department of Biochemistry, Western University, London, ON, Canada
| | - Caroline Schild-Poulter
- Department of Biochemistry, Western University, London, ON, Canada.
- Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.
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4
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Seo JH, Jeon YJ. Global Proteomic Analysis of Mesenchymal Stem Cells Derived from Human Embryonic Stem Cells via Connective Tissue Growth Factor Treatment under Chemically Defined Feeder-Free Culture Conditions. J Microbiol Biotechnol 2022; 32:126-140. [PMID: 34750284 PMCID: PMC9628825 DOI: 10.4014/jmb.2110.10032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 10/28/2021] [Accepted: 11/04/2021] [Indexed: 12/15/2022]
Abstract
Stem cells can be applied usefully in basic research and clinical field due to their differentiation and self-renewal capacity. The aim of this study was to establish an effective novel therapeutic cellular source and create its molecular expression profile map to elucidate the possible therapeutic mechanism and signaling pathway. We successfully obtained a mesenchymal stem cell population from human embryonic stem cells (hESCs) cultured on chemically defined feeder-free conditions and treated with connective tissue growth factor (CTGF) and performed the expressive proteomic approach to elucidate the molecular basis. We further selected 12 differentially expressed proteins in CTGF-induced hESC-derived mesenchymal stem cells (C-hESC-MSCs), which were found to be involved in the metabolic process, immune response, cell signaling, and cell proliferation, as compared to bone marrow derived-MSCs(BM-MSCs). Moreover, these up-regulated proteins were potentially related to the Wnt/β-catenin pathway. These results suggest that C-hESC-MSCs are a highly proliferative cell population, which can interact with the Wnt/β-catenin signaling pathway; thus, due to the upregulated cell survival ability or downregulated apoptosis effects of C-hESC-MSCs, these can be used as an unlimited cellular source in the cell therapy field for a higher therapeutic potential. Overall, the study provided valuable insights into the molecular functioning of hESC derivatives as a valuable cellular source.
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Affiliation(s)
- Ji-Hye Seo
- Department of Dental Pharmacology, School of Dentistry, Jeonbuk National University, Jeonju 54896, Republic of Korea
| | - Young-Joo Jeon
- Stem Cell Convergence Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 34141, Republic of Korea,Corresponding author Phone: +82-42-860-4386 Fax: +82-42-860-4608 E-mail:
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5
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Abbasi S, Parmar G, Kelly RD, Balasuriya N, Schild-Poulter C. The Ku complex: recent advances and emerging roles outside of non-homologous end-joining. Cell Mol Life Sci 2021; 78:4589-4613. [PMID: 33855626 PMCID: PMC11071882 DOI: 10.1007/s00018-021-03801-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 01/29/2021] [Accepted: 02/24/2021] [Indexed: 12/15/2022]
Abstract
Since its discovery in 1981, the Ku complex has been extensively studied under multiple cellular contexts, with most work focusing on Ku in terms of its essential role in non-homologous end-joining (NHEJ). In this process, Ku is well-known as the DNA-binding subunit for DNA-PK, which is central to the NHEJ repair process. However, in addition to the extensive study of Ku's role in DNA repair, Ku has also been implicated in various other cellular processes including transcription, the DNA damage response, DNA replication, telomere maintenance, and has since been studied in multiple contexts, growing into a multidisciplinary point of research across various fields. Some advances have been driven by clarification of Ku's structure, including the original Ku crystal structure and the more recent Ku-DNA-PKcs crystallography, cryogenic electron microscopy (cryoEM) studies, and the identification of various post-translational modifications. Here, we focus on the advances made in understanding the Ku heterodimer outside of non-homologous end-joining, and across a variety of model organisms. We explore unique structural and functional aspects, detail Ku expression, conservation, and essentiality in different species, discuss the evidence for its involvement in a diverse range of cellular functions, highlight Ku protein interactions and recent work concerning Ku-binding motifs, and finally, we summarize the clinical Ku-related research to date.
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Affiliation(s)
- Sanna Abbasi
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Gursimran Parmar
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Rachel D Kelly
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Nileeka Balasuriya
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Caroline Schild-Poulter
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada.
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6
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Adler BL, Boin F, Wolters PJ, Bingham CO, Shah AA, Greider C, Casciola-Rosen L, Rosen A. Autoantibodies targeting telomere-associated proteins in systemic sclerosis. Ann Rheum Dis 2021; 80:912-919. [PMID: 33495152 DOI: 10.1136/annrheumdis-2020-218918] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 01/04/2021] [Accepted: 01/12/2021] [Indexed: 02/07/2023]
Abstract
OBJECTIVES Systemic sclerosis (SSc) is an autoimmune fibrotic disease affecting multiple tissues including the lung. A subset of patients with SSc with lung disease exhibit short telomeres in circulating lymphocytes, but the mechanisms underlying this observation are unclear. METHODS Sera from the Johns Hopkins and University of California, San Francisco (UCSF) Scleroderma Centers were screened for autoantibodies targeting telomerase and the shelterin proteins using immunoprecipitation and ELISA. We determined the relationship between autoantibodies targeting the shelterin protein TERF1 and telomere length in peripheral leucocytes measured by qPCR and flow cytometry and fluorescent in situ hybridisation (Flow-FISH). We also explored clinical associations of these autoantibodies. RESULTS In a subset of patients with SSc, we identified autoantibodies targeting telomerase and the shelterin proteins that were rarely present in rheumatoid arthritis, myositis and healthy controls. TERF1 autoantibodies were present in 40/442 (9.0%) patients with SSc and were associated with severe lung disease (OR 2.4, p=0.04, Fisher's exact test) and short lymphocyte telomere length. 6/6 (100%) patients with TERF1 autoantibodies in the Hopkins cohort and 14/18 (78%) patients in the UCSF cohort had a shorter telomere length in lymphocytes or leukocytes, respectively, relative to the expected age-adjusted telomere length. TERF1 autoantibodies were present in 11/152 (7.2%) patients with idiopathic pulmonary fibrosis (IPF), a fibrotic lung disease believed to be mediated by telomere dysfunction. CONCLUSIONS Autoantibodies targeting telomere-associated proteins in a subset of patients with SSc are associated with short lymphocyte telomere length and lung disease. The specificity of these autoantibodies for SSc and IPF suggests that telomere dysfunction may have a distinct role in the pathogenesis of SSc and pulmonary fibrosis.
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Affiliation(s)
- Brittany L Adler
- Rheumatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Francesco Boin
- Rheumatology, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | - Paul J Wolters
- Pulmonary, University of California, San Francisco, San Francisco, California, USA
| | - Clifton O Bingham
- Rheumatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Ami A Shah
- Rheumatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Carol Greider
- Molecular Biology and Genetics, Johns Hopkins University, Baltimore, Maryland, USA
| | - Livia Casciola-Rosen
- Rheumatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Antony Rosen
- Rheumatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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7
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Manic G, Maurin-Marlin A, Laurent F, Vitale I, Thierry S, Delelis O, Dessen P, Vincendeau M, Leib-Mösch C, Hazan U, Mouscadet JF, Bury-Moné S. Impact of the Ku complex on HIV-1 expression and latency. PLoS One 2013; 8:e69691. [PMID: 23922776 PMCID: PMC3726783 DOI: 10.1371/journal.pone.0069691] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Accepted: 06/17/2013] [Indexed: 01/20/2023] Open
Abstract
Ku, a cellular complex required for human cell survival and involved in double strand break DNA repair and multiple other cellular processes, may modulate retroviral multiplication, although the precise mechanism through which it acts is still controversial. Recently, Ku was identified as a possible anti-human immunodeficiency virus type 1 (HIV-1) target in human cells, in two global approaches. Here we investigated the role of Ku on the HIV-1 replication cycle by analyzing the expression level of a panel of non-replicative lentiviral vectors expressing the green fluorescent protein in human colorectal carcinoma HCT 116 cells, stably or transiently depleted of Ku. We found that in this cellular model the depletion of Ku did not affect the efficiency of (pre-)integrative steps but decreased the early HIV-1 expression by acting at the transcriptional level. This negative effect was specific of the HIV-1 promoter, required the obligatory step of viral DNA integration and was reversed by transient depletion of p53. We also provided evidence on a direct binding of Ku to HIV-1 LTR in transduced cells. Ku not only promotes the early transcription from the HIV-1 promoter, but also limits the constitution of viral latency. Moreover, in the presence of a normal level of Ku, HIV-1 expression was gradually lost over time, likely due to the counter-selection of HIV-1-expressing cells. On the contrary, the reactivation of transgene expression from HIV-1 by means of trichostatin A- or tumor necrosis factor α-administration was enhanced under condition of Ku haplodepletion, suggesting a phenomenon of provirus latency. These observations plead in favor of the hypothesis that Ku has an impact on HIV-1 expression and latency at early- and mid-time after integration.
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Affiliation(s)
- Gwenola Manic
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Aurélie Maurin-Marlin
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Fanny Laurent
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Ilio Vitale
- Regina Elena National Cancer Institute, Rome, Italy
- National Institute of Health, Rome, Italy
| | - Sylvain Thierry
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Olivier Delelis
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Philippe Dessen
- Institut Gustave Roussy, Villejuif, France
- Institut National de la Santé et de la Recherche Médicale-U985, Villejuif, France
| | - Michelle Vincendeau
- Institute of Virology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Research Unit Cellular Signal Integration, Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Christine Leib-Mösch
- Institute of Virology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Department of Hematology and Oncology, Mannheim Medical Center, University of Heidelberg, Mannheim, Germany
| | - Uriel Hazan
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Jean-François Mouscadet
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
| | - Stéphanie Bury-Moné
- Laboratoire de Biologie et Pharmacologie Appliquée, Centre national de la recherche scientifique-UMR8113, Ecole Normale Supérieure de Cachan, Cachan, France
- * E-mail:
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Woodbine L, Neal JA, Sasi NK, Shimada M, Deem K, Coleman H, Dobyns WB, Ogi T, Meek K, Davies EG, Jeggo PA. PRKDC mutations in a SCID patient with profound neurological abnormalities. J Clin Invest 2013; 123:2969-80. [PMID: 23722905 DOI: 10.1172/jci67349] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 03/28/2013] [Indexed: 12/30/2022] Open
Abstract
The DNA-dependent protein kinase catalytic subunit (DNA-PKcs; encoded by PRKDC) functions in DNA non-homologous end-joining (NHEJ), the major DNA double strand break (DSB) rejoining pathway. NHEJ also functions during lymphocyte development, joining V(D)J recombination intermediates during antigen receptor gene assembly. Here, we describe a patient with compound heterozygous mutations in PRKDC, low DNA-PKcs expression, barely detectable DNA-PK kinase activity, and impaired DSB repair. In a heterologous expression system, we found that one of the PRKDC mutations inactivated DNA-PKcs, while the other resulted in dramatically diminished but detectable residual function. The patient suffered SCID with reduced or absent T and B cells, as predicted from PRKDC-deficient animal models. Unexpectedly, the patient was also dysmorphic; showed severe growth failure, microcephaly, and seizures; and had profound, globally impaired neurological function. MRI scans revealed microcephaly-associated cortical and hippocampal dysplasia and progressive atrophy over 2 years of life. These neurological features were markedly more severe than those observed in patients with deficiencies in other NHEJ proteins. Although loss of DNA-PKcs in mice, dogs, and horses was previously shown not to impair neuronal development, our findings demonstrate a stringent requirement for DNA-PKcs during human neuronal development and suggest that high DNA-PK protein expression is required to sustain efficient pre- and postnatal neurogenesis.
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Affiliation(s)
- Lisa Woodbine
- Genome Damage and Stability Centre, University of Sussex, Brighton, United Kingdom
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9
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Thompson LH. Recognition, signaling, and repair of DNA double-strand breaks produced by ionizing radiation in mammalian cells: the molecular choreography. Mutat Res 2012; 751:158-246. [PMID: 22743550 DOI: 10.1016/j.mrrev.2012.06.002] [Citation(s) in RCA: 261] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 06/09/2012] [Accepted: 06/16/2012] [Indexed: 12/15/2022]
Abstract
The faithful maintenance of chromosome continuity in human cells during DNA replication and repair is critical for preventing the conversion of normal diploid cells to an oncogenic state. The evolution of higher eukaryotic cells endowed them with a large genetic investment in the molecular machinery that ensures chromosome stability. In mammalian and other vertebrate cells, the elimination of double-strand breaks with minimal nucleotide sequence change involves the spatiotemporal orchestration of a seemingly endless number of proteins ranging in their action from the nucleotide level to nucleosome organization and chromosome architecture. DNA DSBs trigger a myriad of post-translational modifications that alter catalytic activities and the specificity of protein interactions: phosphorylation, acetylation, methylation, ubiquitylation, and SUMOylation, followed by the reversal of these changes as repair is completed. "Superfluous" protein recruitment to damage sites, functional redundancy, and alternative pathways ensure that DSB repair is extremely efficient, both quantitatively and qualitatively. This review strives to integrate the information about the molecular mechanisms of DSB repair that has emerged over the last two decades with a focus on DSBs produced by the prototype agent ionizing radiation (IR). The exponential growth of molecular studies, heavily driven by RNA knockdown technology, now reveals an outline of how many key protein players in genome stability and cancer biology perform their interwoven tasks, e.g. ATM, ATR, DNA-PK, Chk1, Chk2, PARP1/2/3, 53BP1, BRCA1, BRCA2, BLM, RAD51, and the MRE11-RAD50-NBS1 complex. Thus, the nature of the intricate coordination of repair processes with cell cycle progression is becoming apparent. This review also links molecular abnormalities to cellular pathology as much a possible and provides a framework of temporal relationships.
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Affiliation(s)
- Larry H Thompson
- Biology & Biotechnology Division, L452, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, United States.
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10
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Fink LS, Lerner CA, Torres PF, Sell C. Ku80 facilitates chromatin binding of the telomere binding protein, TRF2. Cell Cycle 2010; 9:3798-806. [PMID: 20890109 DOI: 10.4161/cc.9.18.13129] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The Ku70/80 heterodimer is central to non-homologous end joining repair of DNA double-strand breaks and the Ku80 gene appears to be essential for human but not rodent cell survival. The Ku70/80 heterodimer is located at telomeres but its precise function in telomere maintenance is not known. In order to examine the role of Ku80 beyond DNA repair in more detail, we have taken a knockdown approach using a human fibroblast strain. Following targeted Ku80 knockdown, telomere defects are observed and the steady state levels of the TRF2 protein are reduced. Inhibitor studies indicate that this loss of TRF2 is mediated by the proteasome and degradation of TRF2 following Ku depletion appears to involve a decrease in chromatin binding of TRF2, suggesting that the Ku heterodimer enhances TRF2 chromatin association and that non-chromatin bound TRF2 is targeted to the proteasome.
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Affiliation(s)
- Lauren S Fink
- Drexel University College of Medicine, Department of Pathology and Laboratory Medicine, Philadelphia, Pennsylvania, USA
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11
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Meek K, Jutkowitz A, Allen L, Glover J, Convery E, Massa A, Mullaney T, Stanley B, Rosenstein D, Bailey SM, Johnson C, Georges G. SCID dogs: similar transplant potential but distinct intra-uterine growth defects and premature replicative senescence compared with SCID mice. THE JOURNAL OF IMMUNOLOGY 2009; 183:2529-36. [PMID: 19635917 DOI: 10.4049/jimmunol.0801406] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We have previously described DNA-dependent protein kinase (DNA-PKcs) mutations in horses and dogs that result in deficits in V(D)J recombination, DNA repair, and SCID. In this paper, we document substantial developmental growth defects in DNA-PKcs-deficient dogs that are not apparent in SCID mice. Fibroblast cell strains derived from either fetal or adult SCID dogs proliferate poorly in culture and undergo premature replicative senescence, somewhat reminiscent of cells derived from Ku-deficient mice. A limited number of animals have been immune reconstituted (by bone marrow transplantation) so that they can be maintained in a normal environment for long periods. Several of these animals have developed conditions associated with premature ageing at 2-3 years of age, roughly 20% of their expected lifespan. These conditions include intestinal malabsorption and primary neural cell neoplasia. These results suggest that DNA-PKcs deficiency is not tolerated equally in all species, perhaps providing insight into why DNA-PKcs deficiency has not been observed in humans. Finally, this study demonstrates the feasibility of maintaining SCID dogs for extended periods of time and documents their utility for bone marrow transplantation studies and as hosts for the propagation of xenografts. In sum, SCID dogs may present researchers with new possibilities for the development of animal models of human disease.
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Affiliation(s)
- Katheryn Meek
- Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan StateUniversity, East Lansing, MI 48824, USA.
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12
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Fattah KR, Ruis BL, Hendrickson EA. Mutations to Ku reveal differences in human somatic cell lines. DNA Repair (Amst) 2008; 7:762-74. [PMID: 18387344 DOI: 10.1016/j.dnarep.2008.02.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Revised: 02/01/2008] [Accepted: 02/04/2008] [Indexed: 11/15/2022]
Abstract
NHEJ (non-homologous end joining) is the predominant mechanism for repairing DNA double-stranded breaks in human cells. One essential NHEJ factor is the Ku heterodimer, which is composed of Ku70 and Ku86. Here we have generated heterozygous loss-of-function mutations for each of these genes in two different human somatic cell lines, HCT116 and NALM-6, using gene targeting. Previous work had suggested that phenotypic differences might exist between the genes and/or between the cell lines. By providing a side-by-each comparison of the four cell lines, we demonstrate that there are indeed subtle differences between loss-of-function mutations for Ku70 versus Ku86, which is accentuated by whether the mutations were derived in the HCT116 or NALM-6 genetic background. Overall, however, the phenotypes of the four lines are quite similar and they provide a compelling argument for the hypothesis that Ku loss-of-function mutations in human somatic cells result in demonstrable haploinsufficiencies. Collectively, these studies demonstrate the importance of proper biallelic expression of these genes for NHEJ and telomere maintenance and they provide insights into why these genes are uniquely essential for primates.
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Affiliation(s)
- Kazi R Fattah
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States
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13
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Abstract
The DNA-dependent protein kinase (DNA-PK) is central to the process of nonhomologous end joining because it recognizes and then binds double strand breaks initiating repair. It has long been appreciated that DNA-PK protects DNA ends to promote end joining. Here we review recent work from our laboratories and others demonstrating that DNA-PK can regulate end access both positively and negatively. This is accomplished via distinct autophosphorylation events that result in opposing effects on DNA end access. Additional autophosphorylations that are both physically and functionally distinct serve to regulate kinase activity and complex dissociation. Finally, DNA-PK both positively and negatively regulates DNA end access to repair via the homologous recombination pathway. This has particularly important implications in human cells because of DNA-PK's cellular abundance.
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Affiliation(s)
- Katheryn Meek
- College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA
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