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Darbeheshti F, Makrigiorgos GM. Enzymatic Methods for Mutation Detection in Cancer Samples and Liquid Biopsies. Int J Mol Sci 2023; 24:923. [PMID: 36674433 PMCID: PMC9865676 DOI: 10.3390/ijms24020923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Revised: 12/28/2022] [Accepted: 12/29/2022] [Indexed: 01/06/2023] Open
Abstract
Low-level tumor somatic DNA mutations in tissue and liquid biopsies obtained from cancer patients can have profound implications for development of metastasis, prognosis, choice of treatment, follow-up, or early cancer detection. Unless detected, such low-frequency DNA alterations can misinform patient management decisions or become missed opportunities for personalized medicine. Next-generation sequencing technologies and digital-PCR can resolve low-level mutations but require access to specialized instrumentation, time, and resources. Enzymatic-based approaches to detection of low-level mutations provide a simple, straightforward, and affordable alternative to enrich and detect such alterations and is broadly available to low-resource laboratory settings. This review summarizes the traditional uses of enzymatic mutation detection and describes the latest exciting developments, potential, and applications with specific reference to the field of liquid biopsy in cancer.
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Affiliation(s)
| | - G. Mike Makrigiorgos
- Department of Radiation Oncology, Dana Farber Cancer Institute, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02215, USA
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Pre-PCR Mutation-Enrichment Methods for Liquid Biopsy Applications. Cancers (Basel) 2022; 14:cancers14133143. [PMID: 35804916 PMCID: PMC9264780 DOI: 10.3390/cancers14133143] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 06/20/2022] [Accepted: 06/23/2022] [Indexed: 01/25/2023] Open
Abstract
Liquid biopsy is having a remarkable impact on healthcare- and disease-management in the context of personalized medicine. Circulating free DNA (cfDNA) is one of the most instructive liquid-biopsy-based biomarkers and harbors valuable information for diagnostic, predictive, and prognostic purposes. When it comes to cancer, circulating DNA from the tumor (ctDNA) has a wide range of applications, from early cancer detection to the early detection of relapse or drug resistance, and the tracking of the dynamic genomic make-up of tumor cells. However, the detection of ctDNA remains technically challenging, due, in part, to the low frequency of ctDNA among excessive circulating cfDNA originating from normal tissues. During the past three decades, mutation-enrichment methods have emerged to boost sensitivity and enable facile detection of low-level mutations. Although most developed techniques apply mutation enrichment during or following initial PCR, there are a few techniques that allow mutation selection prior to PCR, which provides advantages. Pre-PCR enrichment techniques can be directly applied to genomic DNA and diminish the influence of PCR errors that can take place during amplification. Moreover, they have the capability for high multiplexity and can be followed by established mutation detection and enrichment technologies without changes to their established procedures. The first approaches for pre-PCR enrichment were developed by employing restriction endonucleases directly on genomic DNA in the early 1990s. However, newly developed pre-PCR enrichment methods provide higher sensitivity and versatility. This review describes the available pre-PCR enrichment methods and focuses on the most recently developed techniques (NaME-PrO, UVME, and DEASH/MAESTRO), emphasizing their applications in liquid biopsies.
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Watanabe M, Toudou M, Uchida T, Yoshikawa M, Aso H, Suemaru K. Change in mutation frequency at a TP53 hotspot during culture of ENU-mutagenised human lymphoblastoid cells. Mutagenesis 2019; 34:331-340. [PMID: 31291449 DOI: 10.1093/mutage/gez014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Accepted: 05/14/2019] [Indexed: 11/14/2022] Open
Abstract
Mutations in oncogenes or tumour suppressor genes cause increases in cell growth capacity. In some cases, fully malignant cancer cells develop after additional mutations occur in initially mutated cells. In such instances, the risk of cancer would increase in response to growth of these initially mutated cells. To ascertain whether such a situation might occur in cultured cells, three independent cultures of human lymphoblastoid GM00130 cells were treated with N-ethyl-N-nitrosourea to induce mutations, and the cells were maintained for 12 weeks. Mutant frequencies and spectra of the cells at the MspI and HaeIII restriction sites located at codons 247-250 of the TP53 gene were examined. Mutant frequencies at both sites in the gene exhibited a declining trend during cell culture and reached background levels after 12 weeks; this was also supported by mutation spectra findings. These results indicate that the mutations detected under our assay conditions are disadvantageous to cell growth.
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Affiliation(s)
| | - Masae Toudou
- School of Pharmacy, Shujitsu University, Naka-ku, Okayama, Japan
| | - Taeko Uchida
- School of Pharmacy, Shujitsu University, Naka-ku, Okayama, Japan
| | - Misato Yoshikawa
- School of Pharmacy, Shujitsu University, Naka-ku, Okayama, Japan
| | - Hiroaki Aso
- School of Pharmacy, Shujitsu University, Naka-ku, Okayama, Japan
| | - Katsuya Suemaru
- School of Pharmacy, Shujitsu University, Naka-ku, Okayama, Japan
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Soltys DT, Pereira CP, Rowies FT, Farfel JM, Grinberg LT, Suemoto CK, Leite RE, Rodriguez RD, Ericson NG, Bielas JH, Souza-Pinto NC. Lower mitochondrial DNA content but not increased mutagenesis associates with decreased base excision repair activity in brains of AD subjects. Neurobiol Aging 2019; 73:161-170. [DOI: 10.1016/j.neurobiolaging.2018.09.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Revised: 08/13/2018] [Accepted: 09/13/2018] [Indexed: 12/15/2022]
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Kimoto T, Kay JE, Li N, Engelward BP. Recombinant cells in the lung increase with age via de novo recombination events and clonal expansion. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2017; 58:135-145. [PMID: 28370323 PMCID: PMC5827959 DOI: 10.1002/em.22082] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Revised: 01/29/2017] [Accepted: 02/21/2017] [Indexed: 06/07/2023]
Abstract
Homologous recombination (HR) is a critical DNA repair pathway, which is usually error-free, but can sometimes lead to cancer-promoting mutations. Despite the importance of HR as a driver of mutations, the spontaneous frequency of such mutations has proven difficult to study. To gain insight to location, cell type, and subsequent proliferation of mutated cells, we used the Rosa26 Direct Repeat (RaDR) mice for in situ detection and quantification of recombinant cells in the lung. We developed a method for automated enumeration of recombinant cells in lung tissue using the Metafer 4 slide-scanning platform. The mean spontaneous HR frequencies of the lung tissue in young and aged mice were 2 × 10-6 and 30 × 10-6 , respectively, which is consistent with our previous reports that mutated cells accumulate with age. In addition, by using the capability of Metafer 4 to mark the position of fluorescent cells, we found that recombinant cells from the aged mice formed clusters in the lung tissue, likely due to clonal expansion of a single mutant cell. The recombinant cells primarily consisted of alveolar epithelial type II or club (previously known as Clara) cells, both of which have the potential to give rise to cancer. This approach to tissue image analysis reveals the location and cell types that have undergone HR. Being able to quantify mutant cells in situ within lung tissue opens doors to studies of exposure-induced mutations and clonal expansion, giving rise to new opportunities for understanding how genetic and environmental factors cause tumorigenic mutations. Environ. Mol. Mutagen. 58:135-145, 2017. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Takafumi Kimoto
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Jennifer E. Kay
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Na Li
- Department of Microbiology, National University of Singapore, 5 Science Drive 2, Block MD4 Level 3, 117597, Singapore
- Singapore-MIT Alliance for Research and Technology, Infectious Diseases Interdisciplinary Group, 1 CREATE Way, #03-10/11 Innovation Wing, #03-12/13/14 Enterprise Wing, Singapore, 138602, Singapore
| | - Bevin P. Engelward
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
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Schulz D, Wirth M, Piontek G, Buchberger AMS, Schlegel J, Reiter R, Multhoff G, Pickhard A. HNSCC cells resistant to EGFR pathway inhibitors are hypermutated and sensitive to DNA damaging substances. Am J Cancer Res 2016; 6:1963-1975. [PMID: 27725902 PMCID: PMC5043106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 02/29/2016] [Indexed: 06/06/2023] Open
Abstract
Despite remarkable successes with targeted therapies in the treatment of cancer, resistance can occur which limits the clinical outcome. In this study, we generated and characterized resistant cell clones derived from two different head and neck squamous cell carcinoma (HNSCC) cell lines (Cal27, UD-SCC-5) by long-term exposure to five targeted- and chemotherapeutics (afatinib, MK2206, BEZ235, olaparib and cisplatin). The resistant tumor cell clones showed an increased ERK1/2 expression and an altered expression of the stem-cell markers CD44, ALDH1, Oct4, Sox2, Nanog and Bmi1. None of the single markers alone was predictive for resistance to all five targeted- and chemotherapeutics. Furthermore, long-term exposure of tumor cells to these five drugs resulted in an eightfold increase in the mutational rate compared to untreated cells. Interestingly, targeted- and chemotherapy resistant cell clones remained sensitive to irradiation. Lastly, clones that were resistant to afatinib, MK2206 or BEZ235 showed cross-resistance to further treatment with therapeutics that affect the same signaling pathway, but remained sensitive to those affecting different pathways such as cisplatin and olaparib. In contrast, cell clones which were once resistant to cisplatin or olaparib were found to be multidrug-resistant. These data might indicate that patients with HNSCC benefit more by a first line targeted therapy followed by cisplatin as a second line therapy.
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Affiliation(s)
- Dominik Schulz
- Department of Otolaryngology Head and Neck Surgery, Technical University of MunichIsmaninger Straße 22, Munich, Germany
| | - Markus Wirth
- Department of Otolaryngology Head and Neck Surgery, Technical University of MunichIsmaninger Straße 22, Munich, Germany
| | - Guido Piontek
- Department of Otolaryngology Head and Neck Surgery, Technical University of MunichIsmaninger Straße 22, Munich, Germany
| | | | - Jürgen Schlegel
- Division of Neuropathology, Institute of Pathology, Technical University of MunichIsmaninger Straße 22, Munich, Germany
| | - Rudolf Reiter
- Department of Otolaryngology Head and Neck Surgery, Section of Phoniatrics and Pedaudiology, University of UlmPrittwitzstraße 43, Ulm, Germany
| | - Gabriele Multhoff
- Department of Radiotherapy, Technical University of MunichIsmaninger Straße 22, Munich, Germany
| | - Anja Pickhard
- Department of Otolaryngology Head and Neck Surgery, Technical University of MunichIsmaninger Straße 22, Munich, Germany
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Valente WJ, Ericson NG, Long AS, White PA, Marchetti F, Bielas JH. Mitochondrial DNA exhibits resistance to induced point and deletion mutations. Nucleic Acids Res 2016; 44:8513-8524. [PMID: 27550180 PMCID: PMC5062989 DOI: 10.1093/nar/gkw716] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 08/04/2016] [Indexed: 12/17/2022] Open
Abstract
The accumulation of somatic mitochondrial DNA (mtDNA) mutations contributes to the pathogenesis of human disease. Currently, mitochondrial mutations are largely considered results of inaccurate processing of its heavily damaged genome. However, mainly from a lack of methods to monitor mtDNA mutations with sufficient sensitivity and accuracy, a link between mtDNA damage and mutation has not been established. To test the hypothesis that mtDNA-damaging agents induce mtDNA mutations, we exposed MutaTMMouse mice to benzo[a]pyrene (B[a]P) or N-ethyl-N-nitrosourea (ENU), daily for 28 consecutive days, and quantified mtDNA point and deletion mutations in bone marrow and liver using our newly developed Digital Random Mutation Capture (dRMC) and Digital Deletion Detection (3D) assays. Surprisingly, our results demonstrate mutagen treatment did not increase mitochondrial point or deletion mutation frequencies, despite evidence both compounds increase nuclear DNA mutations and demonstrated B[a]P adduct formation in mtDNA. These findings contradict models of mtDNA mutagenesis that assert the elevated rate of mtDNA mutation stems from damage sensitivity and abridged repair capacity. Rather, our results demonstrate induced mtDNA damage does not readily convert into mutation. These findings suggest robust mitochondrial damage responses repress induced mutations after mutagen exposure.
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Affiliation(s)
- William J Valente
- Translational Research Program, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA Medical Scientist Training Program, University of Washington School of Medicine, Seattle, WA 98195, USA Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, WA 98195, USA
| | - Nolan G Ericson
- Translational Research Program, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Alexandra S Long
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON K1A 0K9, Canada
| | - Paul A White
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON K1A 0K9, Canada
| | - Francesco Marchetti
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON K1A 0K9, Canada
| | - Jason H Bielas
- Translational Research Program, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, WA 98195, USA Department of Pathology, University of Washington, Seattle, WA 98195, USA Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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Masumura K, Toyoda-Hokaiwado N, Ukai A, Gondo Y, Honma M, Nohmi T. Estimation of the frequency of inherited germline mutations by whole exome sequencing in ethyl nitrosourea-treated and untreated gpt delta mice. Genes Environ 2016; 38:10. [PMID: 27350829 PMCID: PMC4918133 DOI: 10.1186/s41021-016-0035-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 02/11/2016] [Indexed: 11/29/2022] Open
Abstract
Background Germline mutations are heritable and may cause health disadvantages in the next generation. To investigate trans-generational mutations, we treated male gpt delta mice with N-ethyl-N-nitrosourea (ENU) (85 mg/kg intraperitoneally, weekly on two occasions). The mice were mated with untreated female mice and offspring were obtained. Whole exome sequencing analyses were performed to identify de novo mutations in the offspring. Results At 20 weeks after the treatment, the gpt mutant frequencies in the sperm of ENU-treated mice were 21-fold higher than those in the untreated control. Liver DNA was extracted from six mice, including the father, mother, and four offspring from each family of the ENU-treated or untreated mice. In total, 12 DNA samples were subjected to whole exome sequencing analyses. We identified de novo mutations in the offspring by comparing single nucleotide variations in the parents and offspring. In the ENU-treated group, we detected 148 mutation candidates in four offspring and 123 (82 %) were confirmed as true mutations by Sanger sequencing. In the control group, we detected 12 candidate mutations, of which, three (25 %) were confirmed. The frequency of inherited mutations in the offspring from the ENU-treated family was 184 × 10−8 per base, which was 17-fold higher than that in the control family (11 × 10−8 per base). The de novo mutation spectrum in the next generation exhibited characteristic ENU-induced somatic mutations, such as base substitutions at A:T bp. Conclusions These results suggest that direct sequencing analyses can be a useful tool for investigating inherited germline mutations and that the germ cells could be a good endpoint for evaluating germline mutations, which are transmitted to offspring as inherited mutations. Electronic supplementary material The online version of this article (doi:10.1186/s41021-016-0035-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Kenichi Masumura
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
| | - Naomi Toyoda-Hokaiwado
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
| | - Akiko Ukai
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
| | - Yoichi Gondo
- RIKEN BioResource Center, 3-1-1 Koyadai, Tsukuba, Ibaraki, 305-0074 Japan
| | - Masamitsu Honma
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
| | - Takehiko Nohmi
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan ; Biological Safety Research Center, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
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Abstract
This chapter describes the use of real-time qPCR to analyze the integrity of mitochondrial nucleic acids quantitatively. The method has low material requirement, is low cost, and can detect modifications with high resolution. The method is specifically designed for mitochondrial RNA and DNA, but can be easily transferred to other high-copy number cases. This procedure describes analyses of brain nucleic acids, but other tissues or cells can be analyzed similarly.
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Abstract
The mutator phenotype hypothesis proposes that the mutation rate of normal cells is insufficient to account for the large number of mutations found in human cancers. Consequently, human tumors exhibit an elevated mutation rate that increases the likelihood of a tumor acquiring advantageous mutations. The hypothesis predicts that tumors are composed of cells harboring hundreds of thousands of mutations, as opposed to a small number of specific driver mutations, and that malignant cells within a tumor therefore constitute a highly heterogeneous population. As a result, drugs targeting specific mutated driver genes or even pathways of mutated driver genes will have only limited anticancer potential. In addition, because the tumor is composed of such a diverse cell population, tumor cells harboring drug-resistant mutations will exist prior to the administration of any chemotherapeutic agent. We present recent evidence in support of the mutator phenotype hypothesis, major arguments against this concept, and discuss the clinical consequences of tumor evolution fueled by an elevated mutation rate. We also consider the therapeutic possibility of altering the rate of mutation accumulation. Most significantly, we contend that there is a need to fundamentally reconsider current approaches to personalized cancer therapy. We propose that targeting cellular pathways that alter the rate of mutation accumulation in tumors will ultimately prove more effective than attempting to identify and target mutant driver genes or driver pathways.
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Affiliation(s)
- Edward J Fox
- Department of Pathology, University of Washington, Seattle, WA, 98195, USA
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Wright JH, Johnson MM, Shimizu-Albergine M, Bauer RL, Hayes BJ, Surapisitchat J, Hudkins KL, Riehle KJ, Johnson SC, Yeh MM, Bammler TK, Beyer RP, Gilbertson DG, Alpers CE, Fausto N, Campbell JS. Paracrine activation of hepatic stellate cells in platelet-derived growth factor C transgenic mice: evidence for stromal induction of hepatocellular carcinoma. Int J Cancer 2013; 134:778-88. [PMID: 23929039 DOI: 10.1002/ijc.28421] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Accepted: 07/16/2013] [Indexed: 12/13/2022]
Abstract
Cirrhosis is the primary risk factor for the development of hepatocellular carcinoma (HCC), yet the mechanisms by which cirrhosis predisposes to carcinogenesis are poorly understood. Using a mouse model that recapitulates many aspects of the pathophysiology of human liver disease, we explored the mechanisms by which changes in the liver microenvironment induce dysplasia and HCC. Hepatic expression of platelet-derived growth factor C (PDGF-C) induces progressive fibrosis, chronic inflammation, neoangiogenesis and sinusoidal congestion, as well as global changes in gene expression. Using reporter mice, immunofluorescence, immunohistochemistry and liver cell isolation, we demonstrate that receptors for PDGF-CC are localized on hepatic stellate cells (HSCs), which proliferate, and transform into myofibroblast-like cells that deposit extracellular matrix and lead to production of growth factors and cytokines. We demonstrate induction of cytokine genes at 2 months, and stromal cell-derived hepatocyte growth factors that coincide with the onset of dysplasia at 4 months. Our results support a paracrine signaling model wherein hepatocyte-derived PDGF-C stimulates widespread HSC activation throughout the liver leading to chronic inflammation, liver injury and architectural changes. These complex changes to the liver microenvironment precede the development of HCC. Further, increased PDGF-CC levels were observed in livers of patients with nonalcoholic fatty steatohepatitis and correlate with the stage of disease, suggesting a role for this growth factor in chronic liver disease in humans. PDGF-C transgenic mice provide a unique model for the in vivo study of tumor-stromal interactions in the liver.
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Degtyareva NP, Heyburn L, Sterling J, Resnick MA, Gordenin DA, Doetsch PW. Oxidative stress-induced mutagenesis in single-strand DNA occurs primarily at cytosines and is DNA polymerase zeta-dependent only for adenines and guanines. Nucleic Acids Res 2013; 41:8995-9005. [PMID: 23925127 PMCID: PMC3799438 DOI: 10.1093/nar/gkt671] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Localized hyper-mutability caused by accumulation of lesions in persistent single-stranded (ss) DNA has been recently found in several types of cancers. An increase in endogenous levels of reactive oxygen species (ROS) is considered to be one of the hallmarks of cancers. Employing a yeast model system, we addressed the role of oxidative stress as a potential source of hyper-mutability in ssDNA by modulation of the endogenous ROS levels and by exposing cells to oxidative DNA-damaging agents. We report here that under oxidative stress conditions the majority of base substitution mutations in ssDNA are caused by erroneous, DNA polymerase (Pol) zeta-independent bypass of cytosines, resulting in C to T transitions. For all other DNA bases Pol zeta is essential for ROS-induced mutagenesis. The density of ROS-induced mutations in ssDNA is lower, compared to that caused by UV and MMS, which suggests that ssDNA could be actively protected from oxidative damage. These findings have important implications for understanding mechanisms of oxidative mutagenesis, and could be applied to development of anticancer therapies and cancer prevention.
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Affiliation(s)
- Natalya P Degtyareva
- Department of Biochemistry, Winship Cancer Institute, Emory University School of Medicine, 4013 Rollins Research Center, Atlanta, GA 30322, USA, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences (NIH, DHHS), Research Triangle Park, NC 27709, USA and Department of Radiation Oncology, Emory University School of Medicine, 4013 Rollins Research Center, Atlanta, GA 30322, USA
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Kamath-Loeb AS, Shen JC, Schmitt MW, Loeb LA. The Werner syndrome exonuclease facilitates DNA degradation and high fidelity DNA polymerization by human DNA polymerase δ. J Biol Chem 2012; 287:12480-90. [PMID: 22351772 DOI: 10.1074/jbc.m111.332577] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA Polymerase δ (Pol δ) and the Werner syndrome protein, WRN, are involved in maintaining cellular genomic stability. Pol δ synthesizes the lagging strand during replication of genomic DNA and also functions in the synthesis steps of DNA repair and recombination. WRN is a member of the RecQ helicase family, loss of which results in the premature aging and cancer-prone disorder, Werner syndrome. Both Pol δ and WRN encode 3' → 5' DNA exonuclease activities. Pol δ exonuclease removes 3'-terminal mismatched nucleotides incorporated during replication to ensure high fidelity DNA synthesis. WRN exonuclease degrades DNA containing alternate secondary structures to prevent formation and enable resolution of stalled replication forks. We now observe that similarly to WRN, Pol δ degrades alternate DNA structures including bubbles, four-way junctions, and D-loops. Moreover, WRN and Pol δ form a complex with enhanced ability to hydrolyze these structures. We also present evidence that WRN can proofread for Pol δ; WRN excises 3'-terminal mismatches to enable primer extension by Pol δ. Consistent with our in vitro observations, we show that WRN contributes to the maintenance of DNA synthesis fidelity in vivo. Cells expressing limiting amounts (∼10% of normal) of WRN have elevated mutation frequencies compared with wild-type cells. Together, our data highlight the importance of WRN exonuclease activity and its cooperativity with Pol δ in preserving genome stability, which is compromised by the loss of WRN in Werner syndrome.
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Poovathingal SK, Gruber J, Ng LF, Halliwell B, Gunawan R. Maximizing signal-to-noise ratio in the random mutation capture assay. Nucleic Acids Res 2011; 40:e35. [PMID: 22180539 PMCID: PMC3300001 DOI: 10.1093/nar/gkr1221] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The ‘Random Mutation Capture’ assay allows for the sensitive quantitation of DNA mutations at extremely low mutation frequencies. This method is based on PCR detection of mutations that render the mutated target sequence resistant to restriction enzyme digestion. The original protocol prescribes an end-point dilution to about 0.1 mutant DNA molecules per PCR well, such that the mutation burden can be simply calculated by counting the number of amplified PCR wells. However, the statistical aspects associated with the single molecular nature of this protocol and several other molecular approaches relying on binary (on/off) output can significantly affect the quantification accuracy, and this issue has so far been ignored. The present work proposes a design of experiment (DoE) using statistical modeling and Monte Carlo simulations to obtain a statistically optimal sampling protocol, one that minimizes the coefficient of variance in the measurement estimates. Here, the DoE prescribed a dilution factor at about 1.6 mutant molecules per well. Theoretical results and experimental validation revealed an up to 10-fold improvement in the information obtained per PCR well, i.e. the optimal protocol achieves the same coefficient of variation using one-tenth the number of wells used in the original assay. Additionally, this optimization equally applies to any method that relies on binary detection of a small number of templates.
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Affiliation(s)
- Suresh Kumar Poovathingal
- Department of Biochemistry, Neurobiology and Ageing Program, Centre for Life Science (CeLS), 28 Medical Drive, 117456 Singapore, Singapore
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