1
|
Swift LP, Lagerholm BC, Henderson LR, Ratnaweera M, Baddock HT, Sengerova B, Lee S, Cruz-Migoni A, Waithe D, Renz C, Ulrich HD, Newman JA, Schofield CJ, McHugh PJ. SNM1A is crucial for efficient repair of complex DNA breaks in human cells. Nat Commun 2024; 15:5392. [PMID: 38918391 PMCID: PMC11199599 DOI: 10.1038/s41467-024-49583-5] [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: 07/18/2023] [Accepted: 06/11/2024] [Indexed: 06/27/2024] Open
Abstract
DNA double-strand breaks (DSBs), such as those produced by radiation and radiomimetics, are amongst the most toxic forms of cellular damage, in part because they involve extensive oxidative modifications at the break termini. Prior to completion of DSB repair, the chemically modified termini must be removed. Various DNA processing enzymes have been implicated in the processing of these dirty ends, but molecular knowledge of this process is limited. Here, we demonstrate a role for the metallo-β-lactamase fold 5'-3' exonuclease SNM1A in this vital process. Cells disrupted for SNM1A manifest increased sensitivity to radiation and radiomimetic agents and show defects in DSB damage repair. SNM1A is recruited and is retained at the sites of DSB damage via the concerted action of its three highly conserved PBZ, PIP box and UBZ interaction domains, which mediate interactions with poly-ADP-ribose chains, PCNA and the ubiquitinated form of PCNA, respectively. SNM1A can resect DNA containing oxidative lesions induced by radiation damage at break termini. The combined results reveal a crucial role for SNM1A to digest chemically modified DNA during the repair of DSBs and imply that the catalytic domain of SNM1A is an attractive target for potentiation of radiotherapy.
Collapse
Affiliation(s)
- Lonnie P Swift
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - B Christoffer Lagerholm
- Wolfson Imaging Centre, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
- Cell Imaging and Cytometry Core, Turku Bioscience Centre, University of Turku and Åbo Akademi, ku, Finland
| | - Lucy R Henderson
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Malitha Ratnaweera
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Hannah T Baddock
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
- Calico Life Sciences, South San Francisco, CA, USA
| | - Blanka Sengerova
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Sook Lee
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Abimael Cruz-Migoni
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Dominic Waithe
- Wolfson Imaging Centre, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Christian Renz
- Institute of Molecular Biology gGmbH (IMB), Mainz, Germany
| | - Helle D Ulrich
- Institute of Molecular Biology gGmbH (IMB), Mainz, Germany
| | - Joseph A Newman
- Centre for Medicines Discovery, University of Oxford, Oxford, United Kingdom
| | - Christopher J Schofield
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford, United Kingdom
| | - Peter J McHugh
- Department of Oncology, MRC-Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
| |
Collapse
|
2
|
Zhang T, Rawal Y, Jiang H, Kwon Y, Sung P, Greenberg RA. Break-induced replication orchestrates resection-dependent template switching. Nature 2023; 619:201-208. [PMID: 37316655 PMCID: PMC10937050 DOI: 10.1038/s41586-023-06177-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2022] [Accepted: 05/05/2023] [Indexed: 06/16/2023]
Abstract
Break-induced telomere synthesis (BITS) is a RAD51-independent form of break-induced replication that contributes to alternative lengthening of telomeres1,2. This homology-directed repair mechanism utilizes a minimal replisome comprising proliferating cell nuclear antigen (PCNA) and DNA polymerase-δ to execute conservative DNA repair synthesis over many kilobases. How this long-tract homologous recombination repair synthesis responds to complex secondary DNA structures that elicit replication stress remains unclear3-5. Moreover, whether the break-induced replisome orchestrates additional DNA repair events to ensure processivity is also unclear. Here we combine synchronous double-strand break induction with proteomics of isolated chromatin segments (PICh) to capture the telomeric DNA damage response proteome during BITS1,6. This approach revealed a replication stress-dominated response, highlighted by repair synthesis-driven DNA damage tolerance signalling through RAD18-dependent PCNA ubiquitination. Furthermore, the SNM1A nuclease was identified as the major effector of ubiquitinated PCNA-dependent DNA damage tolerance. SNM1A recognizes the ubiquitin-modified break-induced replisome at damaged telomeres, and this directs its nuclease activity to promote resection. These findings show that break-induced replication orchestrates resection-dependent lesion bypass, with SNM1A nuclease activity serving as a critical effector of ubiquitinated PCNA-directed recombination in mammalian cells.
Collapse
Affiliation(s)
- Tianpeng Zhang
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Yashpal Rawal
- Department of Biochemistry and Structural Biology and Greehey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Haoyang Jiang
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Youngho Kwon
- Department of Biochemistry and Structural Biology and Greehey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Patrick Sung
- Department of Biochemistry and Structural Biology and Greehey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Roger A Greenberg
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
| |
Collapse
|
3
|
Tatin X, Muggiolu G, Sauvaigo S, Breton J. Evaluation of DNA double-strand break repair capacity in human cells: Critical overview of current functional methods. MUTATION RESEARCH. REVIEWS IN MUTATION RESEARCH 2021; 788:108388. [PMID: 34893153 DOI: 10.1016/j.mrrev.2021.108388] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 06/17/2021] [Accepted: 06/23/2021] [Indexed: 02/05/2023]
Abstract
DNA double-strand breaks (DSBs) are highly deleterious lesions, responsible for mutagenesis, chromosomal translocation or cell death. DSB repair (DSBR) is therefore a critical part of the DNA damage response (DDR) to restore molecular and genomic integrity. In humans, this process is achieved through different pathways with various outcomes. The balance between DSB repair activities varies depending on cell types, tissues or individuals. Over the years, several methods have been developed to study variations in DSBR capacity. Here, we mainly focus on functional techniques, which provide dynamic information regarding global DSB repair proficiency or the activity of specific pathways. These methods rely on two kinds of approaches. Indirect techniques, such as pulse field gel electrophoresis (PFGE), the comet assay and immunofluorescence (IF), measure DSB repair capacity by quantifying the time-dependent decrease in DSB levels after exposure to a DNA-damaging agent. On the other hand, cell-free assays and reporter-based methods directly track the repair of an artificial DNA substrate. Each approach has intrinsic advantages and limitations and despite considerable efforts, there is currently no ideal method to quantify DSBR capacity. All techniques provide different information and can be regarded as complementary, but some studies report conflicting results. Parameters such as the type of biological material, the required equipment or the cost of analysis may also limit available options. Improving currently available methods measuring DSBR capacity would be a major step forward and we present direct applications in mechanistic studies, drug development, human biomonitoring and personalized medicine, where DSBR analysis may improve the identification of patients eligible for chemo- and radiotherapy.
Collapse
Affiliation(s)
- Xavier Tatin
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, 38000 Grenoble, France; LXRepair, 5 Avenue du Grand Sablon, 38700 La Tronche, France
| | | | - Sylvie Sauvaigo
- LXRepair, 5 Avenue du Grand Sablon, 38700 La Tronche, France
| | - Jean Breton
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, 38000 Grenoble, France.
| |
Collapse
|
4
|
Schneider U, Vasi F, Schmidli K, Besserer J. A model of radiation action based on nanodosimetry and the application to ultra-soft X-rays. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2020; 59:439-450. [PMID: 32277259 DOI: 10.1007/s00411-020-00842-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 03/30/2020] [Indexed: 06/11/2023]
Abstract
A radiation action model based on nanodosimetry is presented. It is motivated by the finding that the biological effects of various types of ionizing radiation lack a consistent relation with absorbed dose. It is postulated that the common fundamental cause of these effects is the production of elementary sublesions (DSB), which are created at a rate that is proportional to the probability to produce more than two ionisations within a volume of 10 base pairs of the DNA. The concepts of nanodosimetry allow for a quantitative characterization of this process in terms of the cumulative probability F2. The induced sublesions can interact in two ways to produce lethal damage. First, if two or more sublesions accumulate in a locally limited spherical volume of 3-10 nm in diameter, clustered DNA damage is produced. Second, consequent interactions or rearrangements of some of the initial damage over larger distances (~ µm) can produce additional lethal damage. From the comparison of theoretical predictions deduced from this concept with experimental data on relative biological effectiveness, a cluster volume with a diameter of 7.5 nm could be determined. It is shown that, for electrons, the predictions agree well with experimental data over a wide energy range. The only free parameter needed to model cell survival is the intersection cross-section which includes all relevant cell-specific factors. Using ultra-soft X-rays it could be shown that the energy dependence of cell survival is directly governed by the nanodosimetric characteristics of the radiation track structure. The cell survival model derived in this work exhibits exponential cell survival at a high dose and a finite gradient of cell survival at vanishing dose, as well as the dependence on dose-rate.
Collapse
Affiliation(s)
- Uwe Schneider
- Department of Physics, Science Faculty, University of Zürich, Zurich, Switzerland.
- Radiotherapy Hirslanden, Witellikerstrasse 40, 8032, Zurich, Switzerland.
| | - Fabiano Vasi
- Department of Physics, Science Faculty, University of Zürich, Zurich, Switzerland
- Radiotherapy Hirslanden, Witellikerstrasse 40, 8032, Zurich, Switzerland
| | - Kevin Schmidli
- Department of Physics, Science Faculty, University of Zürich, Zurich, Switzerland
- Radiotherapy Hirslanden, Witellikerstrasse 40, 8032, Zurich, Switzerland
| | - Jürgen Besserer
- Department of Physics, Science Faculty, University of Zürich, Zurich, Switzerland
- Radiotherapy Hirslanden, Witellikerstrasse 40, 8032, Zurich, Switzerland
| |
Collapse
|
5
|
Gopalakrishnan V, Dahal S, Radha G, Sharma S, Raghavan SC, Choudhary B. Characterization of DNA double-strand break repair pathways in diffuse large B cell lymphoma. Mol Carcinog 2018; 58:219-233. [DOI: 10.1002/mc.22921] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 09/18/2018] [Accepted: 10/07/2018] [Indexed: 11/09/2022]
Affiliation(s)
- Vidya Gopalakrishnan
- Institute of Bioinformatics and Applied Biotechnology; Electronics City; Bangalore India
- Manipal Academy of Higher Education; Manipal Karnataka India
| | - Sumedha Dahal
- Department of Biochemistry; Indian Institute of Science; Bangalore India
| | - Gudapureddy Radha
- Department of Biochemistry; Indian Institute of Science; Bangalore India
| | - Shivangi Sharma
- Department of Biochemistry; Indian Institute of Science; Bangalore India
| | | | - Bibha Choudhary
- Institute of Bioinformatics and Applied Biotechnology; Electronics City; Bangalore India
| |
Collapse
|
6
|
Abstract
Double-strand breaks (DSB) in genomic DNA are induced by ionizing radiation or radiomimetic drugs but also occur spontaneously during the cell cycle at quite significant frequencies. In vertebrate cells, nonhomologous DNA end joining (NHEJ) is considered the major pathway of DSB repair which is able to rejoin two broken DNA termini directly end-to-end irrespective of sequence and structure. Genetic studies in various radiosensitive and DSB repair-deficient cell lines yielded insight into the factors involved in NHEJ. Studies in cell-free systems derived from Xenopus eggs and mammalian cells allowed the dissection of the underlying mechanisms. In the present chapter, we describe a protocol for the preparation of whole cell extracts from mammalian cells and a plasmid-based in vitro assay which permits the easy analysis of the efficiency and fidelity of DSB repair via NHEJ in different cell types.
Collapse
|
7
|
Apigenin ameliorates gamma radiation-induced cytogenetic alterations in cultured human blood lymphocytes. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2012; 747:71-76. [DOI: 10.1016/j.mrgentox.2012.04.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 03/13/2012] [Accepted: 04/02/2012] [Indexed: 11/23/2022]
|
8
|
Renouf B, Soret C, Saandi T, Delalande F, Martin E, Vanier M, Duluc I, Gross I, Freund JN, Domon-Dell C. Cdx2 homeoprotein inhibits non-homologous end joining in colon cancer but not in leukemia cells. Nucleic Acids Res 2011; 40:3456-69. [PMID: 22189105 PMCID: PMC3333856 DOI: 10.1093/nar/gkr1242] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Cdx2, a gene of the paraHox cluster, encodes a homeodomain transcription factor that plays numerous roles in embryonic development and in homeostasis of the adult intestine. Whereas Cdx2 exerts a tumor suppressor function in the gut, its abnormal ectopic expression in acute leukemia is associated to a pro-oncogenic function. To try to understand this duality, we have hypothesized that Cdx2 may interact with different protein partners in the two tissues and set up experiments to identify them by tandem affinity purification. We show here that Cdx2 interacts with the Ku heterodimer specifically in intestinal cells, but not in leukemia cells, via its homeodomain. Ku proteins do not affect Cdx2 transcriptional activity. However, Cdx2 inhibits in vivo and in vitro the DNA repair activity mediated by Ku proteins in intestinal cells. Whereas Cdx2 does not affect the recruitment of Ku proteins and DNA-PKcs into the DNA repair complex, it inhibits DNA-PKcs activity. Thus, we report here a new function of Cdx2, acting as an inhibitor of the DNA repair machinery, that may contribute to its tumor suppressor function specifically in the gut.
Collapse
|
9
|
Datta K, Purkayastha S, Neumann RD, Pastwa E, Winters TA. Base damage immediately upstream from double-strand break ends is a more severe impediment to nonhomologous end joining than blocked 3'-termini. Radiat Res 2011; 175:97-112. [PMID: 21175352 PMCID: PMC3518376 DOI: 10.1667/rr2332.1] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Radiation-induced DNA double-strand breaks (DSBs) are critical cytotoxic lesions that are typically repaired by nonhomologous end joining (NHEJ) in human cells. Our previous work indicated that the highly cytotoxic DSBs formed by (125)I decay possess base damage clustered within 8 to 10 bases of the break and 3'-phosphate (P) and 3'-OH ends. This study examined the effect of such structures on NHEJ in in vitro assays employing either (125)I decay-induced DSB linearized plasmid DNA or structurally defined duplex oligonucleotides. Duplex oligonucleotides that possess either a 3'-P or 3'-phosphoglycolate (PG) or a ligatable 3'-OH end with either an AP site or an 8-oxo-dG 1 nucleotide upstream (-1n) from the 3'-terminus have been examined for reparability. Moderate to severe end-joining inhibition was observed for modified DSB ends or 8-oxo-dG upstream from a 3'-OH end. In contrast, abolition of end joining was observed with duplexes possessing an AP site upstream from a ligatable 3'-OH end or for a lesion combination involving 3'-P plus an upstream 8-oxo-dG. In addition, base mismatches at the -1n position were also strong inhibitors of NHEJ in this system, suggesting that destabilization of the DSB terminus as a result of base loss or improper base pairing may play a role in the inhibitory effects of these structures. Furthermore, we provide data indicating that DSB end joining is likely to occur prior to removal or repair of base lesions proximal to the DSB terminus. Our results show that base damage or base loss near a DSB end may be a severe block to NHEJ and that complex combinations of lesions presented in the context of a DSB may be more inhibitory than the individual lesions alone. In contrast, blocked DSB 3'-ends alone are only modestly inhibitory to NHEJ. Finally, DNA ligase activity is implicated as being responsible for these effects.
Collapse
Affiliation(s)
- Kamal Datta
- Nuclear Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
| | - Shubhadeep Purkayastha
- Nuclear Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
| | - Ronald D. Neumann
- Nuclear Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
| | - Elzbieta Pastwa
- Department of Medicinal Chemistry, Medical University of Lodz, Lodz, Poland 92-215
| | - Thomas A. Winters
- Nuclear Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
| |
Collapse
|
10
|
Fung H, Demple B. Distinct roles of Ape1 protein in the repair of DNA damage induced by ionizing radiation or bleomycin. J Biol Chem 2010; 286:4968-77. [PMID: 21081487 DOI: 10.1074/jbc.m110.146498] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Ionizing radiation (IR) and bleomycin (BLM) are used to treat various types of cancers. Both agents generate cytotoxic double strand breaks (DSB) and abasic (apurinic/apyrimidinic (AP)) sites in DNA. The human AP endonuclease Ape1 acts on abasic or 3'-blocking DNA lesions such as those generated by IR or BLM. We examined the effect of siRNA-mediated Ape1 suppression on DNA repair and cellular resistance to IR or BLM in human B-lymphoblastoid TK6 cells and HCT116 colon tumor cells. Partial Ape1 deficiency (∼30% of normal levels) sensitized cells more dramatically to BLM than to IR cytotoxicity. In both cases, expression of the unrelated yeast AP endonuclease, Apn1, largely restored resistance. Ape1 deficiency increased DNA AP site accumulation due to IR treatment but reduced the number of DSB. In contrast, for BLM, there were more DSB under Ape1 deficiency, with little change in the accumulation of AP sites. Although the role of Ape1 in generating DSB was greater for IR, the enzyme facilitated removal of AP sites, which may mitigate the cytotoxic effects of IR. In contrast, BLM generates scattered AP sites, and the DSB have 3'-phosphoglycolate termini that require Ape1 processing. These DSB persist under Ape1 deficiency. Apoptosis induced by BLM (but not by IR) under Ape1 deficiency was partially p53-dependent, more dramatically in TK6 than HCT116 cells. Thus, Ape1 suppression or inhibition may be a more efficacious adjuvant for BLM than for IR cancer therapy, particularly for tumors with a functional p53 pathway.
Collapse
Affiliation(s)
- Hua Fung
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA
| | | |
Collapse
|
11
|
Sharma S, Raghavan SC. Nonhomologous DNA end joining in cell-free extracts. J Nucleic Acids 2010; 2010. [PMID: 20936167 PMCID: PMC2945661 DOI: 10.4061/2010/389129] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 07/14/2010] [Accepted: 08/05/2010] [Indexed: 12/19/2022] Open
Abstract
Among various DNA damages, double-strand breaks (DSBs) are considered as most deleterious, as they may lead to chromosomal rearrangements and cancer when unrepaired. Nonhomologous DNA end joining (NHEJ) is one of the major DSB repair pathways in higher organisms. A large number of studies on NHEJ are based on in vitro systems using cell-free extracts. In this paper, we summarize the studies on NHEJ performed by various groups in different cell-free repair systems.
Collapse
Affiliation(s)
- Sheetal Sharma
- Department of Biochemistry, Indian Institute of Science, Bangalore 560 012, India
| | | |
Collapse
|
12
|
Hendrickson CL, Purkayastha S, Pastwa E, Neumann RD, Winters TA. Coincident In Vitro Analysis of DNA-PK-Dependent and -Independent Nonhomologous End Joining. J Nucleic Acids 2010; 2010:823917. [PMID: 20706599 PMCID: PMC2919755 DOI: 10.4061/2010/823917] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2010] [Accepted: 06/06/2010] [Indexed: 01/22/2023] Open
Abstract
In mammalian cells, DNA double-strand breaks (DSBs) are primarily repaired by nonhomologous end joining (NHEJ). The current model suggests that the Ku 70/80 heterodimer binds to DSB ends and recruits DNA-PKcs to form the active DNA-dependent protein kinase, DNA-PK. Subsequently, XRCC4, DNA ligase IV, XLF and most likely, other unidentified components participate in the final DSB ligation step. Therefore, DNA-PK plays a key role in NHEJ due to its structural and regulatory functions that mediate DSB end joining. However, recent studies show that additional DNA-PK-independent NHEJ pathways also exist. Unfortunately, the presence of DNA-PKcs appears to inhibit DNA-PK-independent NHEJ, and in vitro analysis of DNA-PK-independent NHEJ in the presence of the DNA-PKcs protein remains problematic. We have developed an in vitro assay that is preferentially active for DNA-PK-independent DSB repair based solely on its reaction conditions, facilitating coincident differential biochemical analysis of the two pathways. The results indicate the biochemically distinct nature of the end-joining mechanisms represented by the DNA-PK-dependent and -independent NHEJ assays as well as functional differences between the two pathways.
Collapse
Affiliation(s)
- Cynthia L Hendrickson
- Radiology & Imaging Sciences Department, Nuclear Medicine Section, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | | | | | |
Collapse
|
13
|
Poplawski T, Pastwa E, Blasiak J. Non-homologous DNA end joining in normal and cancer cells and its dependence on break structures. Genet Mol Biol 2010; 33:368-73. [PMID: 21637496 PMCID: PMC3036873 DOI: 10.1590/s1415-47572010005000018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2009] [Accepted: 10/06/2009] [Indexed: 11/21/2022] Open
Abstract
DNA double-strand breaks (DSBs) are a serious threat to the cell, for if not or miss-repaired, they can lead to chromosomal aberration, mutation and cancer. DSBs in human cells are repaired via non-homologous DNA end joining (NHEJ) and homologous recombination repair pathways. In the former process, the structure of DNA termini plays an important role, as does the genetic constitution of the cells, through being different in normal and pathological cells. In order to investigate the dependence of NHEJ on DSB structure in normal and cancer cells, we used linearized plasmids with various, complementary or non-complementary, single-stranded or blunt DNA termini, as well as whole-cell extract isolated from normal human lymphocytes, chronic myeloid leukemia K562 cells and lung cancer A549 cells. We observed a pronounced variability in the efficacy of NHEJ reaction depending on the type of ends. Plasmids with complementary and blunt termini were more efficiently repaired than the substrate with 3' protruding single-strand ends. The hierarchy of the effectiveness of NHEJ was on average, from the most effective to the least, A549/ normal lymphocytes/ K562. Our results suggest that the genetic constitution of the cells together with the substrate terminal structure may contribute to the efficacy of the NHEJ reaction. This should be taken into account on considering its applicability in cancer chemo- or radiotherapy by pharmacologically modulating NHEJ cellular responses.
Collapse
Affiliation(s)
- Tomasz Poplawski
- Department of Molecular Genetics, University of Lodz, Banacha, Lodz Poland
| | | | | |
Collapse
|
14
|
Mladenov E, Kalev P, Anachkova B. The complexity of double-strand break ends is a factor in the repair pathway choice. Radiat Res 2009; 171:397-404. [PMID: 19397440 DOI: 10.1667/rr1487.1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The repair of double-strand breaks in mammalian cells is carried out by two pathways: homologous recombination and nonhomologous end joining. The factors that regulate the mechanism through which a specific repair pathway is activated are still not clearly defined. To study whether the complexity of the double-strand break ends is a factor that determines the choice of the repair pathway, we examined the involvement of homologous recombination by the formation of Rad51 foci in human HeLa cells treated with bleomycin and ionizing radiation. The quantity of double-strand breaks was determined by gel electrophoresis and the formation of gamma-H2AX foci. Two hours after treatment with low doses of the agents that induced similar quantities of double-strand breaks that could be repaired effectively by the cells, Rad51 foci were observed only in the irradiated cells. Rad51 foci appeared in bleomycin-treated cells after prolonged exposure to the drug when the cells were arrested in the G2 phase of the cell cycle. Since bleomycin produces double-strand breaks that are less complex than the breaks induced by ionizing radiation, these results indicate that the complexity of the break ends is a factor in the choice of repair pathway and that homologous recombination is recruited in the repair of breaks with more complex multiply damaged ends during the late S and G2 phases of the cell cycle.
Collapse
Affiliation(s)
- Emil Mladenov
- Institute of Molecular Biology, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
| | | | | |
Collapse
|
15
|
Pastwa E, Somiari RI, Malinowski M, Somiari SB, Winters TA. In vitro non-homologous DNA end joining assays--the 20th anniversary. Int J Biochem Cell Biol 2008; 41:1254-60. [PMID: 19110069 DOI: 10.1016/j.biocel.2008.11.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2008] [Revised: 11/20/2008] [Accepted: 11/28/2008] [Indexed: 11/16/2022]
Abstract
DNA double-strand breaks (DSBs) are the most serious forms of DNA damage in cells. Unrepaired or misrepaired DSBs account for some of the genetic instabilities that lead to mutations or cell death, and consequently, to cancer predisposition. In human cells non-homologous DNA end joining (NHEJ) is the main repair mechanism of these breaks. Systems for DNA end joining study have been developing during the last 20 years. New assays have some advantages over earlier in vitro DSBs repair assays because they are less time-consuming, allow the use of clinical material and examination of the joining DNA ends produced physiologically in mammalian cells. Proteins involved in NHEJ repair pathway can serve as biomarkers or molecular targets for anticancer drugs. Results of studies on NHEJ in cancer could help to select potent repair inhibitors that may selectively sensitize tumor cells to ionizing radiation (IR) and chemotherapy. Here, we review the principles and practice of in vitro NHEJ assays and provide some insights into the future prospects of this assay in cancer diagnosis and treatment.
Collapse
Affiliation(s)
- Elzbieta Pastwa
- Department of Molecular Genetics, Medical University of Lodz, Mazowiecka 6/8, 92-215 Lodz, Poland.
| | | | | | | | | |
Collapse
|
16
|
Machella N, Terry MB, Zipprich J, Gurvich I, Liao Y, Senie RT, Kennedy DO, Santella RM. Double-strand breaks repair in lymphoblastoid cell lines from sisters discordant for breast cancer from the New York site of the BCFR. Carcinogenesis 2008; 29:1367-72. [PMID: 18566018 DOI: 10.1093/carcin/bgn140] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Unrepaired DNA double-strand breaks (DSBs) may have serious consequences for cells by inducing chromosomal aberrations, thereby increasing genetic instability and cancer risk. One's capacity to repair DSB is therefore an important factor to consider when estimating cancer risk. We assessed DNA end-joining (EJ) capacity in cell lines derived from sisters discordant for breast cancer to determine if individual differences in DSB repair are a significant risk factor. We used an in vitro phenotypic assay on nuclear extracts from lymphoblasts of 179 subjects including 86 cases and 93 controls. EJ activity was functionally estimated as the ability of extracts to join together monomers of the plasmid pUC18 linearized either with sticky (EcoRI) or blunt ends (HincII). Mean percentage of EJ capacity was slightly lower in cases than controls, both for EcoRI (cases 27.9 +/- 11.1; controls 29.6 +/- 10.7, P = 0.28) and HincII substrates (cases 28.8 +/- 12.2; controls 30.6 +/- 13.0, P = 0.36); however, no significant differences were observed. Categorizing EJ capacity into tertiles and using the highest activity as the referent, we observed elevated associations for each tertile of decreased repair [Odds ratio (OR) = 2.20, 95% confidence interval (CI) = 0.77-6.22 and OR = 4.22, 95% CI thinsp;= 1.22-14.0, P = 0.02], respectively, for EcoRI. Results were not statistically significant for HincII (OR = 1.37, 95% CI = 0.51-3.70 and OR = 2.32, 95% CI = 0.57-9.38, P = 0.24). These data suggest that individual differences in EJ capacity may represent a risk factor predisposing women to breast cancer.
Collapse
Affiliation(s)
- Nicola Machella
- Department of Environmental Health Sciences, Epidemiology, Mailman School of Public Health, Columbia University, New York, NY 10032, USA
| | | | | | | | | | | | | | | |
Collapse
|
17
|
Internal tandem duplication of FLT3 (FLT3/ITD) induces increased ROS production, DNA damage, and misrepair: implications for poor prognosis in AML. Blood 2008; 111:3173-82. [PMID: 18192505 DOI: 10.1182/blood-2007-05-092510] [Citation(s) in RCA: 224] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Activating mutations of the FMS-like tyrosine kinase-3 (FLT3) receptor occur in approximately 30% of acute myeloid leukemia (AML) patients and, at least for internal tandem duplication (ITD) mutations, are associated with poor prognosis. FLT3 mutations trigger downstream signaling pathways including RAS-MAP/AKT kinases and signal transducer and activator of transcription-5 (STAT5). We find that FLT3/ITD mutations start a cycle of genomic instability whereby increased reactive oxygen species (ROS) production leads to increased DNA double-strand breaks (DSBs) and repair errors that may explain aggressive AML in FLT3/ITD patients. Cell lines transfected with FLT3/ITD and FLT3/ITD-positive AML cell lines and primary cells demonstrate increased ROS. Increased ROS levels appear to be produced via STAT5 signaling and activation of RAC1, an essential component of ROS-producing NADPH oxidases. A direct association of RAC1-GTP binding to phosphorylated STAT5 (pSTAT5) provides a possible mechanism for ROS generation. A FLT3 inhibitor blocked increased ROS in FLT3/ITD cells resulting in decreased DSB and increased repair efficiency and fidelity. Our study suggests that the aggressiveness of the disease and poor prognosis of AML patients with FLT3/ITD mutations could be the result of increased genomic instability that is driven by higher endogenous ROS, increased DNA damage, and decreased end-joining fidelity.
Collapse
|
18
|
Polischouk AG, Holgersson A, Zong D, Stenerlöw B, Karlsson HL, Möller L, Viktorsson K, Lewensohn R. The antipsychotic drug trifluoperazine inhibits DNA repair and sensitizes non small cell lung carcinoma cells to DNA double-strand break induced cell death. Mol Cancer Ther 2007; 6:2303-9. [PMID: 17699725 DOI: 10.1158/1535-7163.mct-06-0402] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Trifluoperazine (TFP), a member of the phenothiazine class of antipsychotic drugs, has been shown to augment the cytotoxicity of the DNA-damaging agent bleomycin. In the present study, we investigated the effect of trifluoperazine on (a) survival of bleomycin-treated human non-small cell lung carcinoma U1810 cells, (b) induction and repair of bleomycin-induced DNA strand breaks, and (c) nonhomologous end-joining (NHEJ), the major DNA double-strand break (DSB) repair pathway in mammalian cells. By using a clonogenic survival assay, we show here that concomitant administration of trifluoperazine at a subtoxic concentration enhances the cytotoxicity of bleomycin. Moreover, trifluoperazine also increases the longevity of bleomycin-induced DNA strand breaks in U1810 cells, as shown by both comet assay and fraction of activity released (FAR)-assay. This action seems to be related to suppression of cellular DNA DSB repair activities because NHEJ-mediated rejoining of DSBs occurs with significantly lower efficiency in the presence of trifluoperazine. We propose that TFP might be capable of inhibiting one or more elements of the DNA DSB repair machinery, thereby increasing the cytotoxicity of bleomycin in lung cancer cells.
Collapse
Affiliation(s)
- Anya G Polischouk
- Unit of Medical Radiation Biology, Department of Oncology-Pathology, Cancer Centrum Karolinska, Stockholm, Sweden
| | | | | | | | | | | | | | | |
Collapse
|
19
|
Datta K, Weinfeld M, Neumann RD, Winters TA. Determination and analysis of site-specific 125I decay-induced DNA double-strand break end-group structures. Radiat Res 2007; 167:152-66. [PMID: 17390723 DOI: 10.1667/rr0629.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
End groups contribute to the structural complexity of radiation-induced DNA double-strand breaks (DSBs). As such, end-group structures may affect a cell's ability to repair DSBs. The 3'-end groups of strand breaks caused by gamma radiation, or oxidative processes, under oxygenated aqueous conditions have been shown to be distributed primarily between 3'-phosphoglycolate and 3'-phosphate, with 5'-phosphate ends in both cases. In this study, end groups of the high-LET-like DSBs caused by 125I decay were investigated. Site-specific DNA double-strand breaks were produced in plasmid pTC27 in the presence or absence of 2 M DMSO by 125I-labeled triplex-forming oligonucleotide targeting. End-group structure was assessed enzymatically as a function of the DSB end to serve as a substrate for ligation and various forms of end labeling. Using this approach, we have demonstrated 3'-hydroxyl (3'-OH) and 3'-phosphate (3'-P) end groups and 5'-ends (> or = 42%) terminated by phosphate. A 32P postlabeling assay failed to detect 3'-phosphoglycolate in a restriction fragment terminated by the 125I-induced DNA double-strand break, and this is likely due to restricted oxygen diffusion during irradiation as a frozen aqueous solution. Even so, end-group structure and relative distribution varied as a function of the free radical scavenging capacity of the irradiation buffer.
Collapse
Affiliation(s)
- Kamal Datta
- Nuclear Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | |
Collapse
|
20
|
Datta K, Neumann RD, Winters TA. An in vitro nonhomologous end-joining assay using linear duplex oligonucleotides. Anal Biochem 2006; 358:155-7. [PMID: 16934213 DOI: 10.1016/j.ab.2006.06.035] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2006] [Accepted: 06/27/2006] [Indexed: 02/06/2023]
Affiliation(s)
- Kamal Datta
- Department of Nuclear Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | |
Collapse
|
21
|
Jagetia GC, Venkatesha VA. Mangiferin protects human peripheral blood lymphocytes against γ-radiation–induced DNA strand breaks: a fluorescence analysis of DNA unwinding assay. Nutr Res 2006. [DOI: 10.1016/j.nutres.2006.06.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
22
|
Lee JW, Blanco L, Zhou T, Garcia-Diaz M, Bebenek K, Kunkel TA, Wang Z, Povirk LF. Implication of DNA polymerase lambda in alignment-based gap filling for nonhomologous DNA end joining in human nuclear extracts. J Biol Chem 2003; 279:805-11. [PMID: 14561766 DOI: 10.1074/jbc.m307913200] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Accurate repair of free radical-mediated DNA double-strand breaks by the nonhomologous end joining pathway requires replacement of fragmented nucleotides in the aligned ends by a gap-filling DNA polymerase. Nuclear extracts of human HeLa cells, supplemented with recombinant XRCC4-DNA ligase IV complex (XRCC4/ligase IV), were capable of accurately rejoining model double-strand break substrates with a 1- or 2-base gap, and the gap-filling step was dependent on XRCC4/ligase IV. To determine what polymerase was responsible for gap filling, end joining was examined in the presence of polyclonal antibodies against each of two prime candidate enzymes, DNA polymerases mu and lambda, both of which were present in the extracts. For a DNA substrate with partially complementary 3' overhangs and a 2-base gap, antibodies to polymerase lambda completely eliminated both gap filling and accurate end joining, whereas antibodies to polymerase mu had little effect. Immunodepletion of polymerase lambda, but not polymerase mu, likewise blocked both gap filling and end joining, and both functions could be restored by addition of recombinant polymerase lambda. Recombinant polymerase mu, and a truncated polymerase lambda lacking the Brca1 C-terminal domain, were at least 10-fold less active in restoring gap filling to the immunodepleted extracts, and polymerase beta was completely inactive. The results suggest that polymerase lambda is the primary gap-filling polymerase for accurate nonhomologous end joining, and that the Brca1 C-terminal domain is required for this activity.
Collapse
Affiliation(s)
- Jae Wan Lee
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia 23298, USA
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Abstract
The double-strand break (DSB) is believed to be one of the most severe types of DNA damage, and if left unrepaired is lethal to the cell. Several different types of repair act on the DSB. The most important in mammalian cells are nonhomologous end-joining (NHEJ) and homologous recombination repair (HRR). NHEJ is the predominant type of DSB repair in mammalian cells, as opposed to lower eucaryotes, but HRR has recently been implicated in critical cell signaling and regulatory functions that are essential for cell viability. Whereas NHEJ repair appears constitutive, HRR is regulated by the cell cycle and inducible signal transduction pathways. More is known about the molecular details of NHEJ than HRR in mammalian cells. This review focuses on the mechanisms and regulation of DSB repair in mammalian cells, the signaling pathways that regulate these processes and the potential crosstalk between NHEJ and HRR, and between repair and other stress-induced pathways with emphasis on the regulatory circuitry associated with the ataxia telangiectasia mutated (ATM) protein.
Collapse
Affiliation(s)
- Kristoffer Valerie
- Department of Radiation Oncology, Medical College of Virginia Commonwealth University, Richmond, VA 23298-0058, USA.
| | | |
Collapse
|
24
|
Diggle CP, Bentley J, Kiltie AE. Development of a rapid, small-scale DNA repair assay for use on clinical samples. Nucleic Acids Res 2003; 31:e83. [PMID: 12888535 PMCID: PMC169971 DOI: 10.1093/nar/gng083] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Double-strand breaks (DSBs) are the most lethal form of DNA damage. They can be repaired by one of two pathways, homologous recombination and non-homologous end joining (NHEJ). A NHEJ assay has previously been reported which measures joining using cell-free extracts and a linearised plasmid as DNA substrate. This assay was designed for 3 x 10(9) cells grown in vitro and utilised radioactively labelled substrate. We have scaled down the method to use smaller cell numbers in a variety of cell lines. Altering the cellular extraction procedure decreased background DNA contamination. The cleaner preparations allowed us to use SYBR Green I staining to identify joined products, which was as sensitive as 32P-end-labelled DNA. NHEJ was found in established tumour cell lines from different originating tissues, though actual levels and fidelity of repair differed. This method also allowed end joining to be assessed in clinical specimens (human blood, brain and bladder tumours) within 24 h of receiving samples. The application of this method will allow investigation of the role of DSB DNA repair pathways in human tumours.
Collapse
Affiliation(s)
- Christine P Diggle
- Cancer Research UK Clinical Centre, St James's University Hospital, Leeds LS9 7TF, UK
| | | | | |
Collapse
|
25
|
Winn LM, Kim PM, Nickoloff JA. Oxidative stress-induced homologous recombination as a novel mechanism for phenytoin-initiated toxicity. J Pharmacol Exp Ther 2003; 306:523-7. [PMID: 12730361 DOI: 10.1124/jpet.103.052639] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Although the mechanism(s) of phenytoin-initiated toxicity is unknown, phenytoin can be enzymatically bioactivated to a reactive intermediate leading to increased formation of reactive oxygen species, which can damage essential macromolecules, including DNA. The oxidation of DNA can induce DNA double-strand breaks (DSBs), which may be repaired through homologous recombination. Increased levels of DSBs may induce hyper-recombination, leading to deleterious genetic changes. We hypothesize that these genetic changes mediate phenytoin-initiated toxicity. To investigate this hypothesis we used a Chinese hamster ovary cell line containing a neo direct repeat recombination substrate to determine whether phenytoin-initiated DNA oxidation increases homologous recombination. Cells were treated with 0 to 800 microM phenytoin for 5 or 24 h, and homologous recombination frequencies and recombinant product structures were determined. Phenytoin-initiated DNA oxidation was determined by measuring the formation of 8-hydroxy-2'-deoxyguanosine. We demonstrate that phenytoin increases both DNA oxidation and homologous recombination in a concentration- and time-dependent manner. All recombination products analyzed arose via gene conversion without associated crossover. Our data demonstrate that phenytoin-initiated DNA damage can induce homologous recombination, which may be a novel mechanism mediating phenytoin-initiated toxicity.
Collapse
Affiliation(s)
- Louise M Winn
- Department of Pharmacology and Toxicology and School of Environmental Studies, Queen's University, Kingston, ON, Canada.
| | | | | |
Collapse
|
26
|
Pastwa E, Neumann RD, Mezhevaya K, Winters TA. Repair of radiation-induced DNA double-strand breaks is dependent upon radiation quality and the structural complexity of double-strand breaks. Radiat Res 2003; 159:251-61. [PMID: 12537531 DOI: 10.1667/0033-7587(2003)159[0251:roridd]2.0.co;2] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Mammalian cells primarily repair DSBs by nonhomologous end joining (NHEJ). To assess the ability of human cells to mediate end joining of complex DSBs such as those produced by chemicals, oxidative events, or high- and low-LET radiation, we employed an in vitro double-strand break repair assay using plasmid DNA linearized by these various agents. We found that human HeLa cell extracts support end joining of complex DSBs and form multimeric plasmid products from substrates produced by the radiomimetic drug bleomycin, 60Co gamma rays, and the effects of 125I decay in DNA. End joining was found to be dependent on the type of DSB-damaging agent, and it decreased as the cytotoxicity of the DSB-inducing agent increased. In addition to the inhibitory effects of DSB end-group structures on repair, NHEJ was found to be strongly inhibited by lesions proximal to DSB ends. The initial repair rate for complex non-ligatable bleomycin-induced DSBs was sixfold less than that of similarly configured (blunt-ended) but less complex (ligatable) restriction enzyme-induced DSBs. Repair of DSBs produced by gamma rays was 15-fold less efficient than repair of restriction enzyme-induced DSBs. Repair of the DSBs produced by 125I was near the lower limit of detection in our assay and was at least twofold lower than that of gamma-ray-induced DSBs. In addition, DSB ends produced by 125I were shown to be blocked by 3'-nucleotide fragments: the removal of these by E. coli endonuclease IV permitted ligation.
Collapse
Affiliation(s)
- Elzbieta Pastwa
- Nuclear Medicine Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | |
Collapse
|
27
|
Lee JW, Inamdar KV, Hannah MF, Lees-Miller SP, Povirk LF. DNA end sequestration by DNA-dependent protein kinase and end joining of sterically constrained substrates in whole-cell extracts. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2003; 42:279-287. [PMID: 14673873 DOI: 10.1002/em.10197] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Extracts of Xenopus eggs and of cultured human and hamster cells have the capacity to join nonhomologous DNA ends, and all do so with similar specificity. To examine the formation of repair complexes on DNA under conditions of end joining, end-labeled fragments were incubated with the various extracts and then subjected to DNase-I footprinting. Human and Xenopus extracts produced footprints virtually identical to that of purified DNA-dependent protein kinase holoenzyme (Ku plus DNA-PKcs), with protection of the terminal 28 bp. Extracts of hamster cells were more variable, but usually produced a 16-bp footprint, similar to that of Ku alone. In all cases a 28-bp holoenzyme-like footprint was associated with wortmannin-sensitive end joining, minimal 3'-5' exonucleolytic resection, and a predominance of accurate end-joining products. To determine whether the short segments of DNA occupied by Ku and DNA-PK were sufficient to support end joining, Y-shaped substrates were constructed in which only one arm was available for end joining. A Y substrate with a 31-bp arm bearing a partially cohesive 3' overhang was accurately joined by a Xenopus egg extract, whereas a substrate with a 21-bp arm was not. Surprisingly, a human cell extract did not join the Y substrates at all. The results suggest that differences in wortmannin sensitivity and in the distribution of in vitro end-joining products may be attributable to the variations in the levels of DNA-PKcs in the extracts. In addition, end joining in human extracts appears to involve interactions with significantly longer segments of DNA than the approximately 28 bp occupied by DNA-PK.
Collapse
Affiliation(s)
- Jae Wan Lee
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia 23298-0230, USA
| | | | | | | | | |
Collapse
|
28
|
Preston CR, Engels W, Flores C. Efficient repair of DNA breaks in Drosophila: evidence for single-strand annealing and competition with other repair pathways. Genetics 2002; 161:711-20. [PMID: 12072467 PMCID: PMC1462149 DOI: 10.1093/genetics/161.2.711] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
We show evidence that DNA double-strand breaks induced in the Drosophila germ line can be repaired very efficiently by the single-strand annealing (SSA) mechanism. A double-strand break was made between two copies of a 1290-bp direct repeat by mobilizing a P transposon. In >80% of the progeny that acquired this chromosome, repair resulted in loss of the P element and loss of one copy of the repeat, as observed in SSA. The frequency of this repair was much greater than seen for gene conversion using an allelic template, which is only approximately 7%. A similar structure, but with a smaller duplication of only 158 bp, also yielded SSA-like repair events, but at a reduced frequency, and gave rise to some products by repair pathways other than SSA. The 1290-bp repeats carried two sequence polymorphisms that were examined in the products. The allele nearest to a nick in the putative heteroduplex intermediate was lost most often. This bias is predicted by the SSA model, although other models could account for it. We conclude that SSA is the preferred repair pathway in Drosophila for DNA breaks between sequence repeats, and it competes with gene conversion by the synthesis-dependent strand annealing (SDSA) pathway.
Collapse
Affiliation(s)
- Christine R Preston
- Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA
| | | | | |
Collapse
|