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Tichy ED. Specialized Circuitry of Embryonic Stem Cells Promotes Genomic Integrity. Crit Rev Oncog 2023; 27:1-15. [PMID: 36734869 DOI: 10.1615/critrevoncog.2022042332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Embryonic stem cells (ESCs) give rise to all cell types of the organism. Given the importance of these cells in this process, ESCs must employ robust mechanisms to protect genomic integrity or risk catastrophic propagation of mutations throughout the organism. Should such an event occur in daughter cells that will eventually contribute to the germline, the overall species health could dramatically decline. This review describes several key mechanisms employed by ESCs that are unique to these cells, in order to maintain their genomic integrity. Additionally, the contributions of cell cycle regulators in modulating ESC differentiation, after DNA damage exposure, are also examined. Where data are available, findings reported in ESCs are extended to include observations described in induced pluripotent stem cells (IPSCs).
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Affiliation(s)
- Elisia D Tichy
- Department of Orthopaedic Surgery, Perelman School of Medicine, The University of Pennsylvania, 371 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104-6081
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2
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Chen IC, Hernandez C, Xu X, Cooney A, Wang Y, McCarrey JR. Dynamic Variations in Genetic Integrity Accompany Changes in Cell Fate. Stem Cells Dev 2016; 25:1698-1708. [PMID: 27627671 DOI: 10.1089/scd.2016.0221] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Pluripotent stem cells hold the potential to form the basis of novel approaches to treatment of disease in vivo as well as to facilitate the generation of models for human disease, providing powerful avenues to discovery of novel diagnostic biomarkers and/or innovative drug regimens in vitro. However, this will require extensive maintenance, expansion, and manipulation of these cells in culture, which raises a concern regarding the extent to which genetic integrity will be preserved throughout these manipulations. We used a mutation reporter (lacI) transgene approach to conduct direct comparisons of mutation frequencies in cell populations that shared a common origin and genetic identity, but were induced to undergo transitions in cell fate between pluripotent and differentiated states, or vice versa. We confirm that pluripotent cells normally maintain enhanced genetic integrity relative to that in differentiated cells, and we extend this finding to show that dynamic transformations in the relative stringency at which genetic integrity is maintained are associated with transitions between pluripotent and differentiated cellular states. These results provide insight into basic biological distinctions between pluripotent and differentiated cell types that impact genetic integrity in a manner that is directly relevant to the potential clinical use of these cell types.
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Affiliation(s)
- I-Chung Chen
- 1 Department of Biology, University of Texas at San Antonio , San Antonio, Texas
| | - Christine Hernandez
- 1 Department of Biology, University of Texas at San Antonio , San Antonio, Texas
| | - Xueping Xu
- 2 Institute for Applied Cancer Science, The University of Texas MD Anderson Cancer Center , Houston, Texas
| | - Austin Cooney
- 2 Institute for Applied Cancer Science, The University of Texas MD Anderson Cancer Center , Houston, Texas.,3 Department of Pediatrics, Dell Pediatric Research Institute, University of Texas at Austin Dell , Medical School, Austin, Texas
| | - Yufeng Wang
- 1 Department of Biology, University of Texas at San Antonio , San Antonio, Texas
| | - John R McCarrey
- 1 Department of Biology, University of Texas at San Antonio , San Antonio, Texas
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3
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Li Z, Pearlman AH, Hsieh P. DNA mismatch repair and the DNA damage response. DNA Repair (Amst) 2016; 38:94-101. [PMID: 26704428 PMCID: PMC4740233 DOI: 10.1016/j.dnarep.2015.11.019] [Citation(s) in RCA: 199] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Revised: 09/17/2015] [Accepted: 11/30/2015] [Indexed: 12/12/2022]
Abstract
This review discusses the role of DNA mismatch repair (MMR) in the DNA damage response (DDR) that triggers cell cycle arrest and, in some cases, apoptosis. Although the focus is on findings from mammalian cells, much has been learned from studies in other organisms including bacteria and yeast [1,2]. MMR promotes a DDR mediated by a key signaling kinase, ATM and Rad3-related (ATR), in response to various types of DNA damage including some encountered in widely used chemotherapy regimes. An introduction to the DDR mediated by ATR reveals its immense complexity and highlights the many biological and mechanistic questions that remain. Recent findings and future directions are highlighted.
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Affiliation(s)
- Zhongdao Li
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 5 Rm. 324, 5 Memorial Dr. MSC 0538, Bethesda, MD 20892-0538, USA
| | - Alexander H Pearlman
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 5 Rm. 324, 5 Memorial Dr. MSC 0538, Bethesda, MD 20892-0538, USA
| | - Peggy Hsieh
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 5 Rm. 324, 5 Memorial Dr. MSC 0538, Bethesda, MD 20892-0538, USA.
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4
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Tsaalbi-Shtylik A, Ferrás C, Pauw B, Hendriks G, Temviriyanukul P, Carlée L, Calléja F, van Hees S, Akagi JI, Iwai S, Hanaoka F, Jansen JG, de Wind N. Excision of translesion synthesis errors orchestrates responses to helix-distorting DNA lesions. J Cell Biol 2015; 209:33-46. [PMID: 25869665 PMCID: PMC4395481 DOI: 10.1083/jcb.201408017] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Accepted: 02/13/2015] [Indexed: 01/13/2023] Open
Abstract
In addition to correcting mispaired nucleotides, DNA mismatch repair (MMR) proteins have been implicated in mutagenic, cell cycle, and apoptotic responses to agents that induce structurally aberrant nucleotide lesions. Here, we investigated the mechanistic basis for these responses by exposing cell lines with single or combined genetic defects in nucleotide excision repair (NER), postreplicative translesion synthesis (TLS), and MMR to low-dose ultraviolet light during S phase. Our data reveal that the MMR heterodimer Msh2/Msh6 mediates the excision of incorrect nucleotides that are incorporated by TLS opposite helix-distorting, noninstructive DNA photolesions. The resulting single-stranded DNA patches induce canonical Rpa-Atr-Chk1-mediated checkpoints and, in the next cell cycle, collapse to double-stranded DNA breaks that trigger apoptosis. In conclusion, a novel MMR-related DNA excision repair pathway controls TLS a posteriori, while initiating cellular responses to environmentally relevant densities of genotoxic lesions. These results may provide a rationale for the colorectal cancer tropism in Lynch syndrome, which is caused by inherited MMR gene defects.
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Affiliation(s)
| | - Cristina Ferrás
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Bea Pauw
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Giel Hendriks
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Piya Temviriyanukul
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Leone Carlée
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Fabienne Calléja
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Sandrine van Hees
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Jun-Ichi Akagi
- Faculty of Science, Gakushuin University, Tokyo 171-0031, Japan
| | - Shigenori Iwai
- School of Engineering Science, Osaka University, Osaka 565-0871, Japan
| | - Fumio Hanaoka
- Faculty of Science, Gakushuin University, Tokyo 171-0031, Japan
| | - Jacob G Jansen
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
| | - Niels de Wind
- Department of Human Genetics, Leiden University Medical Center, 2300 RC Leiden, Netherlands
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5
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Brash DE. UV signature mutations. Photochem Photobiol 2014; 91:15-26. [PMID: 25354245 DOI: 10.1111/php.12377] [Citation(s) in RCA: 257] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 10/22/2014] [Indexed: 12/17/2022]
Abstract
Sequencing complete tumor genomes and exomes has sparked the cancer field's interest in mutation signatures for identifying the tumor's carcinogen. This review and meta-analysis discusses signatures and their proper use. We first distinguish between a mutagen's canonical mutations—deviations from a random distribution of base changes to create a pattern typical of that mutagen—and the subset of signature mutations, which are unique to that mutagen and permit inference backward from mutations to mutagen. To verify UV signature mutations, we assembled literature datasets on cells exposed to UVC, UVB, UVA, or solar simulator light (SSL) and tested canonical UV mutation features as criteria for clustering datasets. A confirmed UV signature was: ≥60% of mutations are C→T at a dipyrimidine site, with ≥5% CC→TT. Other canonical features such as a bias for mutations on the nontranscribed strand or at the 3' pyrimidine had limited application. The most robust classifier combined these features with criteria for the rarity of non-UV canonical mutations. In addition, several signatures proposed for specific UV wavelengths were limited to specific genes or species; UV's nonsignature mutations may cause melanoma BRAF mutations; and the mutagen for sunlight-related skin neoplasms may vary between continents.
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Affiliation(s)
- Douglas E Brash
- Departments of Therapeutic Radiology and Dermatology, Yale School of Medicine, New Haven, CT
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6
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Brosh RM, Cantor SB. Molecular and cellular functions of the FANCJ DNA helicase defective in cancer and in Fanconi anemia. Front Genet 2014; 5:372. [PMID: 25374583 PMCID: PMC4204437 DOI: 10.3389/fgene.2014.00372] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 10/05/2014] [Indexed: 01/11/2023] Open
Abstract
The FANCJ DNA helicase is mutated in hereditary breast and ovarian cancer as well as the progressive bone marrow failure disorder Fanconi anemia (FA). FANCJ is linked to cancer suppression and DNA double strand break repair through its direct interaction with the hereditary breast cancer associated gene product, BRCA1. FANCJ also operates in the FA pathway of interstrand cross-link repair and contributes to homologous recombination. FANCJ collaborates with a number of DNA metabolizing proteins implicated in DNA damage detection and repair, and plays an important role in cell cycle checkpoint control. In addition to its role in the classical FA pathway, FANCJ is believed to have other functions that are centered on alleviating replication stress. FANCJ resolves G-quadruplex (G4) DNA structures that are known to affect cellular replication and transcription, and potentially play a role in the preservation and functionality of chromosomal structures such as telomeres. Recent studies suggest that FANCJ helps to maintain chromatin structure and preserve epigenetic stability by facilitating smooth progression of the replication fork when it encounters DNA damage or an alternate DNA structure such as a G4. Ongoing studies suggest a prominent but still not well-understood role of FANCJ in transcriptional regulation, chromosomal structure and function, and DNA damage repair to maintain genomic stability. This review will synthesize our current understanding of the molecular and cellular functions of FANCJ that are critical for chromosomal integrity.
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Affiliation(s)
- Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health Baltimore, MD, USA
| | - Sharon B Cantor
- Department of Cancer Biology, University of Massachusetts Medical School - UMASS Memorial Cancer Center Worcester, MA, USA
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7
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Cooper DJ, Walter CA, McCarrey JR. Co-regulation of pluripotency and genetic integrity at the genomic level. Stem Cell Res 2014; 13:508-19. [PMID: 25451711 DOI: 10.1016/j.scr.2014.09.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Revised: 09/12/2014] [Accepted: 09/20/2014] [Indexed: 12/20/2022] Open
Abstract
The Disposable Soma Theory holds that genetic integrity will be maintained at more pristine levels in germ cells than in somatic cells because of the unique role germ cells play in perpetuating the species. We tested the hypothesis that the same concept applies to pluripotent cells compared to differentiated cells. Analyses of transcriptome and cistrome databases, along with canonical pathway analysis and chromatin immunoprecipitation confirmed differential expression of DNA repair and cell death genes in embryonic stem cells and induced pluripotent stem cells relative to fibroblasts, and predicted extensive direct and indirect interactions between the pluripotency and genetic integrity gene networks in pluripotent cells. These data suggest that enhanced maintenance of genetic integrity is fundamentally linked to the epigenetic state of pluripotency at the genomic level. In addition, these findings demonstrate how a small number of key pluripotency factors can regulate large numbers of downstream genes in a pathway-specific manner.
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Affiliation(s)
- Daniel J Cooper
- Department of Biology, University of Texas at San Antonio, USA
| | - Christi A Walter
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, USA
| | - John R McCarrey
- Department of Biology, University of Texas at San Antonio, USA.
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8
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Guillemette S, Branagan A, Peng M, Dhruva A, Schärer OD, Cantor SB. FANCJ localization by mismatch repair is vital to maintain genomic integrity after UV irradiation. Cancer Res 2013; 74:932-44. [PMID: 24351291 DOI: 10.1158/0008-5472.can-13-2474] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Nucleotide excision repair (NER) is critical for the repair of DNA lesions induced by UV radiation, but its contribution in replicating cells is less clear. Here, we show that dual incision by NER endonucleases, including XPF and XPG, promotes the S-phase accumulation of the BRCA1 and Fanconi anemia-associated DNA helicase FANCJ to sites of UV-induced damage. FANCJ promotes replication protein A phosphorylation and the arrest of DNA synthesis following UV irradiation. Interaction defective mutants of FANCJ reveal that BRCA1 binding is not required for FANCJ localization, whereas interaction with the mismatch repair (MMR) protein MLH1 is essential. Correspondingly, we find that FANCJ, its direct interaction with MLH1, and the MMR protein MSH2 function in a common pathway in response to UV irradiation. FANCJ-deficient cells are not sensitive to killing by UV irradiation, yet we find that DNA mutations are significantly enhanced. Thus, we considered that FANCJ deficiency could be associated with skin cancer. Along these lines, in melanoma we found several somatic mutations in FANCJ, some of which were previously identified in hereditary breast cancer and Fanconi anemia. Given that, mutations in XPF can also lead to Fanconi anemia, we propose collaborations between Fanconi anemia, NER, and MMR are necessary to initiate checkpoint activation in replicating human cells to limit genomic instability.
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Affiliation(s)
- Shawna Guillemette
- Authors' Affiliations: Department of Cancer Biology, University of Massachusetts Medical School, Women's Cancers Program, UMASS Memorial Cancer Center, Worcester, Massachusetts; and Department of Pharmacological Sciences & Department of Chemistry, Stony Brook University, Stony Brook, New York
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9
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Maintenance of genomic stability in mouse embryonic stem cells: relevance in aging and disease. Int J Mol Sci 2013; 14:2617-36. [PMID: 23358251 PMCID: PMC3588006 DOI: 10.3390/ijms14022617] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Revised: 01/11/2013] [Accepted: 01/12/2013] [Indexed: 01/15/2023] Open
Abstract
Recent studies have shown that mouse embryonic stem cells (mESCs) rely on a distinctive genome caretaking network. In this review, we will discuss how mESCs functionally respond to DNA damage and describe several modifications in mESC DNA damage response, which accommodate dynamic cycling and preservation of genetic information. Subsequently, we will discuss how the transition from mESCs to adult stem/progenitor cells can be involved in the decline of tissue integrity and function in the elderly.
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10
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Cheung MC, Evans JG, McKenna B, Ehrlich DJ. Deep ultraviolet mapping of intracellular protein and nucleic acid in femtograms per pixel. Cytometry A 2011; 79:920-32. [PMID: 21796773 PMCID: PMC3199293 DOI: 10.1002/cyto.a.21111] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 06/28/2011] [Accepted: 06/30/2011] [Indexed: 11/09/2022]
Abstract
By using imaging spectrophotometry with paired images in the 200- to 280-nm wavelength range, we have directly mapped intracellular nucleic acid and protein distributions across a population of Chinese hamster ovary (CHO-K1) cells. A broadband 100× objective with a numerical aperture of 1.2 NA (glycerin immersion) and a novel laser-induced-plasma point source generated high-contrast images with short (∼100 ms) exposures and a lateral resolution nearing 200 nm that easily resolves internal organelles. In a population of 420 CHO-K1 cells and 477 nuclei, we found a G1 whole-cell nucleic acid peak at 26.6 pg, a nuclear-isolated total nucleic acid peak at 11.4 pg, and, as inferred by RNase treatment, a G1 total DNA mass of 7.4 pg. At the G1 peak, we found a whole-cell protein mass of 95.6 pg, and a nuclear-isolated protein mass of 39.3 pg. An algorithm for protein quantification that senses peptide-bond (220-nm) absorbance was found to have a higher signal-to-noise ratio and to provide more reliable nucleic acid and protein determinations when compared to more classical 280/260-nm algorithms when used for intracellular mass mapping. Using simultaneous imaging with common nuclear stains (Hoechst 33342, Syto-14, and Sytox Orange), we have compared staining patterns to deep-UV images of condensed chromatin and have confirmed bias of these common nuclear stains related to nuclear packaging. The approach allows absolute mass measurements with no special sample preparation or staining. It can be used in conjunction with normal fluorescence microscopy and with relatively modest modification of the microscope.
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Affiliation(s)
- Man C Cheung
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA
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11
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Tichy ED. Mechanisms maintaining genomic integrity in embryonic stem cells and induced pluripotent stem cells. Exp Biol Med (Maywood) 2011; 236:987-96. [PMID: 21768163 DOI: 10.1258/ebm.2011.011107] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Embryonic stem cells (ESCs) are pluripotent, self-renewing cells that are isolated during the blastocyst stage of embryonic development. Whether these cells are derived from humans, mice or other organisms, all ESCs must employ mechanisms that prevent the propagation of mutations, generated as a consequence of DNA damage, to somatic cells produced by normal programmed differentiation. Thus, the prevention of mutations in ESCs is important not only for the health of the individual organism derived from these cells but also, in addition, for the continued survival and genetic viability of the species by preventing the accumulation of mutations in the germline. Induced pluripotent stem cells (IPSCs) are reprogrammed somatic cells that share several characteristics with ESCs, including a similar morphology in culture, the re-expression of pluripotency markers and the ability to differentiate into defined cell lineages. This review focuses on the mechanisms employed by murine ESCs, human ESCs and, where data are available, IPSCs to preserve genetic integrity.
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Affiliation(s)
- Elisia D Tichy
- Department of Molecular Genetics, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0524, USA.
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12
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Lu L, Hu B, Yu F, Wang Y. Low dose radiation-induced adaptive response preventing HPRT mutation is Fhit independent. Int J Radiat Biol 2009; 85:532-7. [PMID: 19401904 DOI: 10.1080/09553000902883828] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
PURPOSE To study whether fragile histidine triad (Fhit) prevents IR-induced hypoxanthineguanine phosphoribosyltransferase (HPRT) mutation and whether Fhit plays any role in preventing HPRT mutation through low dose-induced adaptive response. MATERIALS AND METHODS Establishing human cell lines with or without Fhit expression by making constructs expressing hemagglutinin (HA) alone or HA-Fhit fusion protein and transfecting the vector to HeLa cells. The effects of Fhit on ionising radiation (IR)-induced mutation were examined by observing HPRT mutation rates in the established cell lines following different doses of IR. The role of Fhit on low dose IR-induced adaptive response were examined by observing HPRT mutation rates in the established cell lines that were exposed to 0.1 Gy and followed with high dose IR or ultraviolet (UV) exposure. RESULTS Low dose (0.1 Gy) does not affect HPRT mutation rates in these cell lines. Fhit prevents high dose IR (> or = 2 Gy)-induced mutation as it prevents UV-induced mutation. However, low dose of IR (0.1 Gy)-induced adaptive response prevents both high doses of IR and UV-induced mutation in both the cells with and without Fhit expression. CONCLUSIONS Fhit prevents IR-induced HPRT mutation and preventing mutation through low dose of IR-induced adaptive response is Fhit independent.
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Affiliation(s)
- Lin Lu
- Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA, USA
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13
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Hofstra RMW, Spurdle AB, Eccles D, Foulkes WD, de Wind N, Hoogerbrugge N, Hogervorst FBL. Tumor characteristics as an analytic tool for classifying genetic variants of uncertain clinical significance. Hum Mutat 2008; 29:1292-303. [PMID: 18951447 DOI: 10.1002/humu.20894] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
It is important to identify a germline mutation in a patient with an inherited cancer syndrome to allow mutation carriers to be included in cancer surveillance programs, which have been proven to save lives. Many of the mutations identified result in premature termination of translation, and thus in loss-of-function of the encoded mutated protein. However, the significance of a large proportion of the sequence changes reported is unknown. Some of these variants will be associated with a high risk of cancer and have direct clinical consequence. Many criteria can be used to classify variants with unknown significance; most criteria are based on the characteristics of the amino acid change, on segregation data and appearance of the variant, on the presence of the variant in controls, or on functional assays. In inherited cancers, tumor characteristics can also be used to classify variants. It is worthwhile to examine the clinical, morphological and molecular features of a patient, and his or her family, when assessing whether the role of a variant is likely to be neutral or pathogenic. Here we describe the advantages and disadvantages of using the tumor characteristics of patients carrying germline variants of uncertain significance (VUS) in BRCA1, BRCA2, or in one of the mismatch repair (MMR) genes, MLH1, MSH2, or MSH6, to infer pathogenicity.
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Affiliation(s)
- Robert M W Hofstra
- Department of Genetics, University Medical Center Groningen and University of Groningen, Groningen, the Netherlands.
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14
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Tichy ED, Stambrook PJ. DNA repair in murine embryonic stem cells and differentiated cells. Exp Cell Res 2008; 314:1929-36. [PMID: 18374918 PMCID: PMC2532524 DOI: 10.1016/j.yexcr.2008.02.007] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 02/15/2008] [Accepted: 02/15/2008] [Indexed: 01/06/2023]
Abstract
Embryonic stem (ES) cells are rapidly proliferating, self-renewing cells that have the capacity to differentiate into all three germ layers to form the embryo proper. Since these cells are critical for embryo formation, they must have robust prophylactic mechanisms to ensure that their genomic integrity is preserved. Indeed, several studies have suggested that ES cells are hypersensitive to DNA damaging agents and readily undergo apoptosis to eliminate damaged cells from the population. Other evidence suggests that DNA damage can cause premature differentiation in these cells. Several laboratories have also begun to investigate the role of DNA repair in the maintenance of ES cell genomic integrity. It does appear that ES cells differ in their capacity to repair damaged DNA compared to differentiated cells. This minireview focuses on repair mechanisms ES cells may use to help preserve genomic integrity and compares available data regarding these mechanisms with those utilized by differentiated cells.
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Affiliation(s)
- Elisia D Tichy
- Department of Cell and Cancer Biology, University of Cincinnati, Cincinnati, OH 45267, USA.
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15
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Barrera-Oro J, Liu TY, Gorden E, Kucherlapati R, Shao C, Tischfield JA. Role of the mismatch repair gene, Msh6, in suppressing genome instability and radiation-induced mutations. Mutat Res 2008; 642:74-9. [PMID: 18538799 DOI: 10.1016/j.mrfmmm.2008.04.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Revised: 04/18/2008] [Accepted: 04/21/2008] [Indexed: 11/26/2022]
Abstract
Mismatch repair (MMR) is critical for preserving genomic integrity. Failure of this system can accelerate somatic mutation and increase the risk of developing cancer. MSH6, in complex with MSH2, is the MMR protein that mediates DNA repair through the recognition of 1- and 2-bp mismatches. To evaluate the effects of MSH6 deficiency on genomic stability we compared the frequency of in vivo loss of heterozygosity (LOH) between MSH6-proficient and deficient, 129S2xC57BL/6 F1 hybrid mice that were heterozygous for our reporter gene Aprt. We recovered mutant cells that had functionally lost APRT protein activity and categorized the spectrum of mutations responsible for the LOH events. We also measured the mutant frequency at the X-linked gene, Hprt, as a second reporter for point mutation. In Msh6-/-Aprt+/- mice, mutation frequency at Aprt was elevated in both T cells and fibroblasts by 2.5-fold and 5.7-fold, respectively, over Msh6+/+Aprt+/- littermate controls. While a modest increase in mitotic recombination (MR) was observed in MSH6-deficient fibroblasts compared to wild type controls, point mutation was the predominant mechanism leading to APRT deficiency in both cell types. Base substitution, consisting of multiple types of transitions, accounted for all of the point mutations identified within the Aprt coding region. We also assessed the role of MSH6 in preventing mutations caused by a common environmental mutagen, ionizing radiation (IR). In Msh6-/-Aprt+/- mice, 4Gy of X-irradiation induced a significant increase in point mutations at both Aprt and Hprt in T cells, but not in fibroblasts. These findings indicate that MutS alpha reduces spontaneous and IR-induced mutation in a cell type-dependant manner.
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Affiliation(s)
- Julio Barrera-Oro
- Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
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16
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Kwok WM, Ma C, Phillips DL. A doorway state leads to photostability or triplet photodamage in thymine DNA. J Am Chem Soc 2008; 130:5131-9. [PMID: 18335986 DOI: 10.1021/ja077831q] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ultraviolet irradiation of DNA produces electronic excited states that predominantly eliminate the excitation energy by returning to the ground state (photostability) or following minor pathways into mutagenic photoproducts (photodamage). The cyclobutane pyrimidine dimer (CPD) formed from photodimerization of thymines in DNA is the most common form of photodamage. The underlying molecular processes governing photostability and photodamage of thymine-constituted DNA remain unclear. Here, a combined femtosecond broadband time-resolved fluorescence and transient absorption spectroscopies were employed to study a monomer thymidine and a single-stranded thymine oligonucleotide. We show that the protecting deactivation of a thymine multimer is due to an ultrafast single-base localized stepwise mechanism where the initial excited state decays via a doorway state to the ground state or proceeds via the doorway state to a triplet state identified as a major precursor for CPD photodamage. These results provide new mechanistic characterization of and a dynamic link between the photoexcitation of DNA and DNA photostability and photodamage.
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Affiliation(s)
- Wai-Ming Kwok
- Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
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17
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Abstract
The replication of damaged DNA templates by translesion synthesis (TLS) is associated with mutagenesis and carcinogenesis. This perspective discusses the different levels at which TLS may be controlled and proposes a model for TLS of severely helix-distorting DNA lesions that includes a decisive role for the Rad9-Hus1-Rad1 DNA-damage-signaling clamp. The dual involvement of this clamp in both DNA-damage signaling and TLS may have profound implications in determining cellular responses to DNA damage.
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McCulloch SD, Wood A, Garg P, Burgers PMJ, Kunkel TA. Effects of accessory proteins on the bypass of a cis-syn thymine-thymine dimer by Saccharomyces cerevisiae DNA polymerase eta. Biochemistry 2007; 46:8888-96. [PMID: 17608453 PMCID: PMC2288658 DOI: 10.1021/bi700234t] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Among several hypotheses to explain how translesion synthesis (TLS) by DNA polymerase eta (pol eta) suppresses ultraviolet light-induced mutagenesis in vivo despite the fact that pol eta copies DNA with low fidelity, here we test whether replication accessory proteins enhance the fidelity of TLS by pol eta. We first show that the single-stranded DNA binding protein RPA, the sliding clamp PCNA, and the clamp loader RFC slightly increase the processivity of yeast pol eta and its ability to recycle to new template primers. However, these increases are small, and they are similar when copying an undamaged template and a template containing a cis-syn TT dimer. Consequently, the accessory proteins do not strongly stimulate the already robust TT dimer bypass efficiency of pol eta. We then perform a comprehensive analysis of yeast pol eta fidelity. We show that it is much less accurate than other yeast DNA polymerases and that the accessory proteins have little effect on fidelity when copying undamaged templates or when bypassing a TT dimer. Thus, although accessory proteins clearly participate in pol eta functions in vivo, they do not appear to help suppress UV mutagenesis by improving pol eta bypass fidelity per se.
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Affiliation(s)
- Scott D McCulloch
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
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