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Ding Q, Hou Z, Zhao Z, Chen Y, Zhao L, Xiang Y. Identification of the prognostic signature based on genomic instability-related alternative splicing in colorectal cancer and its regulatory network. Front Bioeng Biotechnol 2022; 10:841034. [PMID: 35923577 PMCID: PMC9340224 DOI: 10.3389/fbioe.2022.841034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 06/27/2022] [Indexed: 11/15/2022] Open
Abstract
Background: Colorectal cancer (CRC) is a heterogeneous disease with many somatic mutations defining its genomic instability. Alternative Splicing (AS) events, are essential for maintaining genomic instability. However, the role of genomic instability-related AS events in CRC has not been investigated. Methods: From The Cancer Genome Atlas (TCGA) program, we obtained the splicing profiles, the single nucleotide polymorphism, transcriptomics, and clinical information of CRC. Combining somatic mutation and AS events data, a genomic instability-related AS signature was constructed for CRC. Mutations analyses, clinical stratification analyses, and multivariate Cox regression analyses evaluated this signature in training set. Subsequently, we validated the sensitivity and specificity of this prognostic signature using a test set and the entire TCGA dataset. We constructed a nomogram for the prognosis prediction of CRC patients. Differentially infiltrating immune cells were screened by using CIBERSORT. Inmmunophenoscore (IPS) analysis was used to evaluate the response of immunotherapy. The AS events-related splicing factors (SF) were analyzed by Pearson’s correlation. The effects of SF regulating the prognostic AS events in proliferation and migration were validated in Caco2 cells. Results: A prognostic signature consisting of seven AS events (PDHA1-88633-ES, KIAA1522-1632-AP, TATDN1-85088-ES, PRMT1-51042-ES, VEZT-23786-ES, AIG1-77972-AT, and PHF11-25891-AP) was constructed. Patients in the high-risk score group showed a higher somatic mutation. The genomic instability risk score was an independent variable associated with overall survival (OS), with a hazard ratio of a risk score of 1.537. The area under the curve of receiver operator characteristic curve of the genomic instability risk score in predicting the OS of CRC patients was 0.733. Furthermore, a nomogram was established and could be used clinically to stratify patients to predict prognosis. Patients defined as high-risk by this signature showed a lower proportion of eosinophils than the low-risk group. Patients with low risk were more sensitive to anti-CTLA4 immunotherapy. Additionally, HSPA1A and FAM50B were two SF regulating the OS-related AS. Downregulation of HSPA1A and FAM50B inhibited the proliferation and migration of Caco2 cells. Conclusion: We constructed an ideal prognostic signature reflecting the genomic instability and OS of CRC patients. HSPA1A and FAM50B were verified as two important SF regulating the OS-related AS.
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Affiliation(s)
- Qiuying Ding
- Centre for Lipid Research, Key Laboratory of Molecular Biology for Infectious Diseases, Ministry of Education, Department of Infectious Diseases, Institute for Viral Hepatitis, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Zhengping Hou
- Centre for Lipid Research, Key Laboratory of Molecular Biology for Infectious Diseases, Ministry of Education, Department of Infectious Diseases, Institute for Viral Hepatitis, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Zhibo Zhao
- The Department of Hepatobiliary Surgery of the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Yao Chen
- Centre for Lipid Research, Key Laboratory of Molecular Biology for Infectious Diseases, Ministry of Education, Department of Infectious Diseases, Institute for Viral Hepatitis, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
- *Correspondence: Yao Chen, ; Lei Zhao, ; Yue Xiang,
| | - Lei Zhao
- Centre for Lipid Research, Key Laboratory of Molecular Biology for Infectious Diseases, Ministry of Education, Department of Infectious Diseases, Institute for Viral Hepatitis, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
- *Correspondence: Yao Chen, ; Lei Zhao, ; Yue Xiang,
| | - Yue Xiang
- Centre for Lipid Research, Key Laboratory of Molecular Biology for Infectious Diseases, Ministry of Education, Department of Infectious Diseases, Institute for Viral Hepatitis, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
- *Correspondence: Yao Chen, ; Lei Zhao, ; Yue Xiang,
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Qing Y, Gerson SL. Mismatch repair deficient hematopoietic stem cells are preleukemic stem cells. PLoS One 2017; 12:e0182175. [PMID: 28767666 PMCID: PMC5540588 DOI: 10.1371/journal.pone.0182175] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 07/13/2017] [Indexed: 12/27/2022] Open
Abstract
Whereas transformation events in hematopoietic malignancies may occur at different developmental stages, the initial mutation originates in hematopoietic stem cells (HSCs), creating a preleukemic stem cell (PLSC). Subsequent mutations at either stem cell or progenitor cell levels transform the PLSC into lymphoma/leukemia initiating cells (LIC). Thymic lymphomas have been thought to develop from developing thymocytes. T cell progenitors are generated from HSCs in the bone marrow (BM), but maturation and proliferation of T cells as well as T-lymphomagenesis depends on both regulatory mechanisms and microenvironment within the thymus. We studied PLSC linked to thymic lymphomas. In this study, we use MSH2-/- mice as a model to investigate the existence of PLSC and the evolution of PLSC to LIC. Following BM transplantation, we found that MSH2-/- BM cells from young mice are able to fully reconstitute multiple hematopoietic lineages of lethally irradiated wild-type recipients. However, all recipients developed thymic lymphomas within three and four months post transplantation. Transplantation of different fractions of BM cells or thymocytes from young health MSH2-/- mice showed that an HSC enriched fraction always reconstituted hematopoiesis followed by lymphoma development. In addition, lymphomas did not occur in thymectomized recipients of MSH2-/- BM. These results suggest that HSCs with DNA repair defects such as MSH2-/- are PLSCs because they retain hematopoietic function, but also carry an obligate lymphomagenic potential within their T-cell progeny that is dependent on the thymic microenvironment.
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Affiliation(s)
- Yulan Qing
- Case Comprehensive Cancer Center, National Center for Regenerative Medicine, Case Western Reserve University, Cleveland, Ohio, United States of America
| | - Stanton L. Gerson
- Case Comprehensive Cancer Center, National Center for Regenerative Medicine, Case Western Reserve University, Cleveland, Ohio, United States of America
- * E-mail:
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Pereira CS, Oliveira MVMD, Barros LO, Bandeira GA, Santos SHS, Basile JR, Guimarães ALS, De Paula AMB. Low expression of MSH2 DNA repair protein is associated with poor prognosis in head and neck squamous cell carcinoma. J Appl Oral Sci 2014; 21:416-21. [PMID: 24212987 PMCID: PMC3881843 DOI: 10.1590/1679-775720130206] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Accepted: 05/23/2013] [Indexed: 11/22/2022] Open
Abstract
Objective This study aimed to investigate the expression of the MSH2 DNA repair protein in
head and neck squamous cell carcinoma (HNSCC) in order to analyze its association
with clinicopathologic factors and overall survival of patients. Material and Methods Clinical data and primary lesions of HNSSC were collected from 55 patients who
underwent surgical resection with postoperative radiotherapy in Montes Claros,
state of Minas Gerais, Brazil, between 2000 and 2008. Immunohistochemical
reactions were performed to analyze MSH2 protein expression. Results Bivariate analysis showed no significant correlation or association between MSH2
expression and clinicopathologic parameters by Mann-Whitney and Kruskal-Wallis
tests. Patients with locoregional metastatic disease (OR=4.949, p<0.001) and
lower MSH2 immunohistochemical expressions (OR=2.943, p=0.032) presented poorer
survival for HNSCC by Cox regression models. Conclusions Our data demonstrated that lower MSH2 expression might contribute to a higher
clinic aggressiveness of HNSCC by promoting an unfavorable outcome.
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Affiliation(s)
- Camila Santos Pereira
- Nucleus of Epidemiological and Molecular Research Catrumano, Health Research Laboratory, Health Science Post-Graduate Programme, Universidade Estadual de Montes Claros, Montes ClarosMG, Brazil
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4
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Souza LR, Fonseca-Silva T, Pereira CS, Santos EP, Lima LC, Carvalho HA, Gomez RS, Guimarães ALS, De Paula AMB. Immunohistochemical analysis of p53, APE1, hMSH2 and ERCC1 proteins in actinic cheilitis and lip squamous cell carcinoma. Histopathology 2011; 58:352-60. [PMID: 21323960 DOI: 10.1111/j.1365-2559.2011.03756.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
AIMS This study has compared the tissue expression of the p53 tumour suppressor protein and DNA repair proteins APE1, hMSH2 and ERCC1 in normal, dysplastic and malignant lip epithelium. METHODS AND RESULTS Morphological analysis and immunohistochemistry were performed on archived specimens of normal lip mucosa (n=15), actinic cheilitis (AC) (n=30), and lip squamous cell carcinoma (LSCC) (n=27). AC samples were classified morphologically according to the severity of epithelial dysplasia and risk of malignant transformation. LSCC samples were morphologically staged according to WHO and invasive front grading (IFG) criteria. Differences between groups and morphological stages were determined by bivariate statistical analysis. Progressive increases in the percentage of epithelial cells expressing p53 and APE1 were associated with increases in morphological malignancy from normal lip mucosa to LSCC. There was also a significant reduction in epithelial cells expressing hMSH2 and ERCC1 proteins in the AC and LSCC groups. A higher percentage of malignant cells expressing APE1 was found in samples with an aggressive morphological IFG grade. CONCLUSIONS Our data showed that epithelial cells from premalignant to malignant lip disease exhibited changes in the expression of p53, APE1, hMSH2 and ERCC1 proteins; these molecular change might contribute to lip carcinogenesis.
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Affiliation(s)
- Ludmilla R Souza
- Health Science Programme, State University of Montes Claros, Montes Claros, MG, Brazil
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5
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McDonald DA, Shenkar R, Shi C, Stockton RA, Akers AL, Kucherlapati MH, Kucherlapati R, Brainer J, Ginsberg MH, Awad IA, Marchuk DA. A novel mouse model of cerebral cavernous malformations based on the two-hit mutation hypothesis recapitulates the human disease. Hum Mol Genet 2011; 20:211-22. [PMID: 20940147 PMCID: PMC3005897 DOI: 10.1093/hmg/ddq433] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Revised: 09/13/2010] [Accepted: 10/01/2010] [Indexed: 11/14/2022] Open
Abstract
Cerebral cavernous malformations (CCMs) are vascular lesions of the central nervous system appearing as multicavernous, blood-filled capillaries, leading to headache, seizure and hemorrhagic stroke. CCM occurs either sporadically or as an autosomal dominant disorder caused by germline mutation of one of the three genes: CCM1/KRIT1, CCM2/MGC4607 and CCM3/PDCD10. Surgically resected human CCM lesions have provided molecular and immunohistochemical evidence for a two-hit (germline plus somatic) mutation mechanism. In contrast to the equivalent human genotype, mice heterozygous for a Ccm1- or Ccm2-null allele do not develop CCM lesions. Based on the two-hit hypothesis, we attempted to improve the penetrance of the model by crossing Ccm1 and Ccm2 heterozygotes into a mismatch repair-deficient Msh2(-/-) background. Ccm1(+/-)Msh2(-/-) mice exhibit CCM lesions with high penetrance as shown by magnetic resonance imaging and histology. Significantly, the CCM lesions range in size from early-stage, isolated caverns to large, multicavernous lesions. A subset of endothelial cells within the CCM lesions revealed somatic loss of CCM protein staining, supporting the two-hit mutation mechanism. The late-stage CCM lesions displayed many of the characteristics of human CCM lesions, including hemosiderin deposits, immune cell infiltration, increased endothelial cell proliferation and increased Rho-kinase activity. Some of these characteristics were also seen, but to a lesser extent, in early-stage lesions. Tight junctions were maintained between CCM lesion endothelial cells, but gaps were evident between endothelial cells and basement membrane was defective. In contrast, the Ccm2(+/-)Msh2(-/-) mice lacked cerebrovascular lesions. The CCM1 mouse model provides an in vivo tool to investigate CCM pathogenesis and new therapies.
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Affiliation(s)
- David A. McDonald
- Molecular Genetics and Microbiology Department, Duke University Medical Center, Durham, NC 27710, USA
| | - Robert Shenkar
- Section of Neurosurgery, Biological Sciences Division, University of Chicago, Chicago, IL 60637, USA
| | - Changbin Shi
- Section of Neurosurgery, Biological Sciences Division, University of Chicago, Chicago, IL 60637, USA
| | - Rebecca A. Stockton
- Department of Medicine, University of California, San Diego, La Jolla, CA 92903, USA
| | - Amy L. Akers
- Molecular Genetics and Microbiology Department, Duke University Medical Center, Durham, NC 27710, USA
| | | | - Raju Kucherlapati
- Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA and
| | - James Brainer
- Department of Pathology, University of Chicago Medical Center, Chicago, IL 60637, USA
| | - Mark H. Ginsberg
- Department of Medicine, University of California, San Diego, La Jolla, CA 92903, USA
| | - Issam A. Awad
- Section of Neurosurgery, Biological Sciences Division, University of Chicago, Chicago, IL 60637, USA
| | - Douglas A. Marchuk
- Molecular Genetics and Microbiology Department, Duke University Medical Center, Durham, NC 27710, USA
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Ciavattini A, Piccioni M, Tranquilli AL, Filosa A, Pieramici T, Goteri G. Immunohistochemical expression of DNA mismatch repair (MMR) system proteins (hMLH1, hMSH2) in cervical preinvasive and invasive lesions. Pathol Res Pract 2005; 201:21-5. [PMID: 15807307 DOI: 10.1016/j.prp.2004.09.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The purpose of our study was to analyze the immunohistochemical expression of two MMR system proteins at different steps of neoplastic progression within the squamous cervical epithelium. We compared cases showing normal histologic appearance with those affected by low and high-grade squamous intraepithelial lesions and invasive cervical carcinoma. We investigated formalin-fixed and paraffin-embedded tissue specimens obtained from 83 selected patients (55 with preinvasive neoplastic lesions and 28 with invasive squamous cervical carcinoma) for the expression of hMSH2 and hMLH1 at the immunohistochemical level. We also included 30 patients with histologically normal cervix as a control group. Epithelial cells of CIN lesions showed a significant increase in the expression of both hMLH1 and hMSH2 proteins compared to non-neoplastic squamous epithelium (p < 0.0001). The cases of invasive carcinoma showed a positivity for hMLH1 protein that was statistically lower than that for non-neoplastic cells (p = 0.0009) and that for cases with CIN (p < 0.0001). Positivity for hMSH2 protein was higher than that for normal epithelium (p = 0.0007), but lower than that for preinvasive lesions (p = 0.0001). Preinvasive lesions showed increased expression of both proteins if compared with normal esocervical epithelium. Neoplastic stromal invasiveness is associated with a significant loss of hMLH1 function.
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Affiliation(s)
- Andrea Ciavattini
- Institute of Obstetrics and Gynecology, Politechnical University of Marche, Italy.
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7
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Nomdedéu JF, Perea G, Estivill C, Lasa A, Carnicer MJ, Brunet S, Aventín A, Sierra J. Microsatellite instability is not an uncommon finding in adult de novo acute myeloid leukemia. Ann Hematol 2005; 84:368-75. [PMID: 15789228 DOI: 10.1007/s00277-005-1035-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Accepted: 02/24/2005] [Indexed: 01/03/2023]
Abstract
To investigate the biologic relevance of microsatellite instability (MSI) in de novo acute myeloid leukemia (AML), 102 consecutive adult patients were analyzed by using a panel of seven microsatellites (BAT25, BAT26, D13S1267, D13S174, D2S123, D5S346 and Mdf15). Frame-shift mutations in the repetitive sequences in the coding region of MSH3, MSH6, BAX, TGFBRII and IGFRII were also investigated by using a fluorescent PCR-based assay. Methylation-specific PCR was used to determine the methylation status of hMLH1 in MSI+ cases. MSH3, MSH6 and MLH1 expression was also analyzed in 68 cases by means of real-time quantitative PCR. MSI was detected in 20 cases: 14 cases had MSI-high (instability of at least two microsatellite markers) and 6 cases corresponded to MSI-low (a single polymorphic marker with instability). Six MSI+ cases showed an associated MLL rearrangement (p=0.002). No single case showed a mutation in the repetitive sequences of the MSH3, MSH6, BAX, TGFBRII and IGFRII genes. Most samples displayed low mRNA levels of the repair genes. hMLH1 promoter was hypermethylated in five MSI+ cases. Overall survival analysis revealed no adverse effect of MSI positivity. These results suggest that MSI may be a common biologic finding in de novo AML.
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Affiliation(s)
- Josep F Nomdedéu
- Department of Hematology, Hospital de la Santa Creu i Sant Pau, Universitat Autònoma de Barcelona, Barcelona, Spain.
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8
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Papp-Szabó E, Josephy PD, Coomber BL. Microenvironmental influences on mutagenesis in mammary epithelial cells. Int J Cancer 2005; 116:679-85. [PMID: 15849743 DOI: 10.1002/ijc.21088] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Tumor progression may be viewed as an evolutionary process at the cellular level. Because blood supply to solid tumors is inadequate, the cancer cells face a hostile microenvironment characterized by hypoxia or anoxia, acidic extracellular pH and nutrient deficiencies. It has been proposed that these factors result in increased levels of spontaneous mutagenesis and thereby contribute to tumor progression. We have examined spontaneous mutagenesis in vitro and in vivo, using previously characterized cell lines (mammary epithelial cells [ME] and mammary fibroblast cells [MFib]) from the mammary gland of the BigBluetrade mark rat, carrying a transgene construct suitable for the detection of mutations. Cells were exposed in vitro to control conditions, low pH, or to glucose deprivation, under normoxic or hypoxic culture conditions, and were also grown as xenografted tumors in immune-deficient mice. We examined cell survival and mutant frequency/spectrum at the cII locus. Significant increases in mutant frequency were observed in ME cells exposed to hypoxia alone or in combination with no glucose; the latter condition also resulted in reduced clonogenic survival. Cells grown as xenografts and then recovered and expanded in culture also had elevated frequencies of spontaneous mutations. We observed a shift in the spontaneous mutation spectrum between the ME cells and the MET cells (cultured in vitro or isolated from mouse xenograft tumors). These results support the concept that the tumor microenvironment contributes to tumor progression by enhancing spontaneous mutagenesis, that different cell types from the same organ can respond differently to these stresses and that differences in microenvironment may influence the types of mutations that arise.
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Affiliation(s)
- Erzsébet Papp-Szabó
- Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada
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Pongsaensook P, Ritter LE, Parks KK, Grosovsky AJ. Cis-acting transmission of genomic instability. Mutat Res 2004; 568:49-68. [PMID: 15530539 DOI: 10.1016/j.mrfmmm.2004.06.046] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2004] [Revised: 06/16/2004] [Accepted: 06/17/2004] [Indexed: 05/01/2023]
Abstract
Genomic instability is a highly pleiotropic phenotype, which may reflect a variety of underlying mechanisms. Destabilization has been shown in some cases to involve mutational alteration or inactivation of trans-acting cellular factors, for example, p53 or mismatch repair functions. However, aspects of instability are not well explained by mutational inactivation of trans-acting factors, and other epigenetic and cis-acting mechanisms have recently been proposed. The trans and cis models result in divergent predictions for the distribution of instability-associated genetic alterations within the genome, and for the inheritance of genomic instability among sibling sub-clones of unstable parents. These predictions have been tested in this study primarily by tracking the karyotypic distribution of chromosomal rearrangements in clones and sub-clones exhibiting radiation-induced genomic instability; inheritance of mutator phenotypes was also analyzed. The results indicate that genomic instability is unevenly transmitted to sibling sub-clones, that chromosomal rearrangements within unstable clones are non-randomly distributed throughout the karyotype, and that the majority of chromosomal rearrangements associated with instability affect trisomic chromosomal segments. Observations of instability in trisomic regions suggests that in addition to promoting further alterations in chromosomal number, aneuploidy can affect the recovery of structural rearrangements. In summary, these findings cannot be fully explained by invoking a homogeneously distributed factor acting in trans, but do provide support for previous suggestions that genomic instability may in part be driven by a cis-acting mechanism.
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Affiliation(s)
- Punnajit Pongsaensook
- Department of Cell Biology and Neuroscience and Environmental Toxicology Graduate Program, University of California, 5445 Boyce Hall, Riverside, CA 92521, USA
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Hill KA, Wang J, Farwell KD, Scaringe WA, Sommer SS. Spontaneous multiple mutations show both proximal spacing consistent with chronocoordinate events and alterations with p53-deficiency. Mutat Res 2004; 554:223-40. [PMID: 15450421 DOI: 10.1016/j.mrfmmm.2004.05.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Revised: 05/05/2004] [Accepted: 05/07/2004] [Indexed: 11/25/2022]
Abstract
Analysis of spontaneous multiple mutations in normal and tumor cells may constrain hypotheses about the mechanisms responsible for multiple mutations and provide insight into the mutator phenotype. In a previous study, spontaneous doublets in Big Blue mice were dramatically more frequent than expected by chance and exhibited a mutation pattern similar to that observed for single mutations [Mutat. Res. 452 (2000) 219]. The spacing between mutations in doublets was generally closer than expected by chance and the distribution of mutation spacing fit an exponential, albeit with substantial scatter. We now analyze 2658 additional mutants and confirm that doublets are enhanced dramatically relative to chance expectation. The spacing, frequency and pattern of spontaneous doublets and multiplets (domuplets) are examined as a function of age, tissue type, p53-deficiency and neoplasia in the new and combined data. The new and combined data confirm that the distribution of the spacing between mutations in doublets is non-random with the mutations more closely spaced than expected by chance (P < 0.0005; combined data), consistent with temporally coordinate (chronocoordinate) events. An exponential provides an excellent fit to the distribution (R2 = 0.98) and estimates that half of doublets have mutations separated by 120 nucleotides or less (the "half-life of mutation spacing"). We make several novel observations: (i) singlets and doublets show similar overall increases in frequency with age (ii) doublet frequency may be lower in the male germline, consistent with the generally reduced mutation frequency in the male germline (iii) doublet frequencies are elevated in somatic tissues of p53-deficient mice (Li-Fraumini cancer syndrome model; P = 0.005) and (iv) doublets and singlets in tumors from p53-deficient mice have a different mutation pattern (P = 0.007). The observations are consistent with chronocoordinate occurrence of spontaneous doublets and multiplets due to a transient error-prone condition and do not suggest a major role for the recently discovered Y family of error-prone polymerases. The enhancement of doublets in p53-deficient mice may contribute to cancer risk.
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Affiliation(s)
- Kathleen A Hill
- Department of Molecular Genetics and Molecular Diagnosis, Beckman Research Institute, City of Hope National Medical Center, Duarte, CA, USA
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11
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Christensen LA, Conti CJ, Fischer SM, Vasquez KM. Mutation frequencies in murine keratinocytes as a function of carcinogenic status. Mol Carcinog 2004; 40:122-33. [PMID: 15170817 DOI: 10.1002/mc.20026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A link between genetic abnormalities and carcinogenesis is well established. It follows that a correlation exists between mutation frequency and malignant progression. We have determined the spontaneous and DNA damage-induced mutation frequencies for a series of cell lines derived from SENCAR mouse keratinocytes at various stages of malignant progression. Nontumorigenic mouse keratinocytes (3PC), papillomas (MT1/2), squamous-cell carcinomas (CH72), and spindle-cell carcinomas (CH72T4) were transfected with damaged or undamaged shuttle vectors containing a supF mutation reporter gene. The plasmid mutation frequencies were determined by blue/white screening. The spontaneous plasmid mutation frequency of the squamous-cell carcinoma line was slightly higher than the mutation frequencies of the other cell lines tested. The DNA damage induced by triplex-directed psoralen crosslinks increased the mutation frequencies sixfold to eighteenfold in all cell lines tested, with no significant differences among the cell lines. Sequence analyses revealed that the spindle-cell carcinoma line had a different spontaneous mutation spectrum from the other cell lines. DNA damage-induced mutations were predominantly point mutations at the triplex-duplex junction in all of the cell lines tested, as expected. These data suggested that a strong mutator phenotype was not required for progression to an advanced malignant phenotype in our model system.
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Affiliation(s)
- Laura A Christensen
- Department of Carcinogenesis, The University of Texas M.D. Anderson Cancer Center, Science Park-Research Division, Smithville, Texas, USA
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12
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Ono T, Uehara Y, Saito Y, Ikehata H. Mutation theory of aging, assessed in transgenic mice and knockout mice. Mech Ageing Dev 2002; 123:1543-52. [PMID: 12470892 DOI: 10.1016/s0047-6374(02)00090-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
A vital question in the mutation theory of aging is whether mutation accumulates with age. If it does, what are the causes and consequences of the accumulation of mutation? The recent development of transgenic mice has made it possible to study mutation in different kinds of tissues and at a molecular level. An application of these mice to the study of age-dependent alteration has revealed that mutation does accumulate in the aging process. Studies have also revealed several important characteristics of mutation associated with aging. (1) The rate of age-dependent increase of mutant frequency varies among different types of tissue. (2) The rate is not in parallel with the cell proliferation rate of the tissue. (3) Some types of mutation are unique to specific tissues, suggesting the presence of a mechanism of mutation relative to tissue type. On the other hand, several kinds of knockout mice defective in DNA repair have been shown to exhibit tissue lesions and shortened life span. These characteristics provide a new view on the relationship between aging and the genome maintenance system. Here we review the current status of research on the correlation between mutation and aging undertaken by the use of transgenic and knockout mice.
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Affiliation(s)
- Tetsuya Ono
- Department of Cell Biology, Graduate School of Medicine, Tohoku University, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
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13
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Rockwood LD, Torrey TA, Kim JS, Coleman AE, Kovalchuk AL, Xiang S, Ried T, Morse HC, Janz S. Genomic instability in mouse Burkitt lymphoma is dominated by illegitimate genetic recombinations, not point mutations. Oncogene 2002; 21:7235-40. [PMID: 12370814 DOI: 10.1038/sj.onc.1205697] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2002] [Revised: 05/15/2002] [Accepted: 05/20/2002] [Indexed: 01/19/2023]
Abstract
lambda-MYC-induced mouse Burkitt lymphoma (BL) harboring the shuttle vector pUR288, which includes a lacZ reporter gene to study mutagenesis, was employed to assess genomic instability associated with MYC deregulation. The frequency of lacZ mutations in lymphomas was elevated only 1.75-fold above that in normal tissue, indicating that mouse BL does not exhibit a phenotype of hypermutability. However, the nature of lacZ mutations was strikingly different in normal tissues and lymphomas. While point mutations comprised approximately 75% of the mutations found in normal tissues, apparent translocations, deletions and inversions constituted the majority of mutations ( approximately 65%) in lymphomas. Genomic instability in mouse BL thus seems characterized by a preponderance of illegitimate genetic rearrangements in the context of near-background mutant frequencies. SKY analyses of cell lines from primary BL tumors revealed substantial changes in chromosomal structure, confirming the lacZ studies. Bi-allelic deletions of the tumor suppressor p16(Ink4a) were detected in six out of 16 cell lines, illustrating cellular selection of advantageous mutations. Together, these approaches indicate that MYC may contribute to lymphomagenesis through the dominant mutator effect of inducing chromosomal instability. The results further suggest that a phenotype of hypermutability (elevated mutant frequency) may not always be required for oncogenesis to occur.
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Affiliation(s)
- Lynne D Rockwood
- Laboratory of Genetics, Center for Cancer Research (CCR), NCI, Bethesda, Maryland, MD 20892, USA
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14
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Mark SC, Sandercock LE, Luchman HA, Baross A, Edelmann W, Jirik FR. Elevated mutant frequencies and predominance of G:C to A:T transition mutations in Msh6(-/-) small intestinal epithelium. Oncogene 2002; 21:7126-30. [PMID: 12370835 DOI: 10.1038/sj.onc.1205861] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2002] [Revised: 07/03/2002] [Accepted: 07/09/2002] [Indexed: 01/18/2023]
Abstract
The DNA mismatch repair (MMR) system is primarily responsible for purging newly synthesized DNA of errors incurred during semi-conservative replication. Lesion recognition is initially carried out by one of two heterodimeric protein complexes, MutS(alpha) or MutS(beta). While the former, comprised of MSH2 and MSH6, recognizes mispairs as well as short (1-2 nucleotide) insertions/deletions (IDLs), the latter, made up of MSH2 and MSH3, is primarily responsible for recognizing 2-6 nucleotide IDLs. As most of the functional information on these heterodimers is derived from in vitro studies, it was of interest to study the in vivo consequences of a lack of MutS(alpha). To this end, Big Blue( trade mark ) mice, that carry a lacI(+) transgenic lambda shuttle-phage mutational reporter, were crossed with Msh6(-/-) mice to evaluate the specific contribution of MutS(alpha) to genome integrity. Consistent with the importance of MutS(alpha) in lesion surveillance, small intestine epithelial cell DNA derived from lacI(+) Msh6(-/-) mice exhibited striking increases (average of 41-fold) in spontaneous mutant frequencies. Furthermore, the lacI gene mutation spectrum was dominated by G:C to A:T transitions, highlighting the critical importance of the MutS(alpha) complex in suppressing this frequently observed type of spontaneous mutation.
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Affiliation(s)
- Sean C Mark
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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15
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Zhang S, Lloyd R, Bowden G, Glickman BW, de Boer JG. Thymic lymphomas arising in Msh2 deficient mice display a large increase in mutation frequency and an altered mutational spectrum. Mutat Res 2002; 500:67-74. [PMID: 11890935 DOI: 10.1016/s0027-5107(01)00297-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Mismatch repair (MMR) genes, such as Msh2, are classified as "mutator" genes, responsible for the microsatellite instability identified in many tumors. In the current study, the mutation frequency and mutational spectrum in thymic lymphoma arising in Msh2 deficient mice are investigated. Thymic lymphoma developed in Msh2-/- background displayed an eight to nine-fold increase in mutation frequency compared to the normal thymi in Msh2 deficient animals. Sequencing demonstrated significantly different mutational spectra between normal thymus tissue and thymic lymphomas in Msh2-/- mice (P=0.02). The tumor mutational spectrum is characterized by an increase in base substitutions occurring at A:T sites, and multiple mutations, as well as a minor increase in -1 frameshifts. We analyzed mutations in different parts of the tumors, and different regional hotspots could be identified. Several hotspot mutations that are a rare event in normal tissues were identified in the tumor tissues. We conclude that thymic lymphomas arising in Msh2 deficient genetic background are hypermutable and the altered mutational spectrum might be an indication of infidelity of DNA replication during tumorigenesis.
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Affiliation(s)
- Shulin Zhang
- Department of Biology, Centre for Environmental Health, University of Victoria, Victoria, BC, Canada V8W 3N5
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16
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Affiliation(s)
- Johan G de Boer
- Centre for Biomedical Research, Department of Biology, University of Victoria, Victoria, BC, Canada
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17
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Liu S, Liu W, Jakubczak JL, Erexson GL, Tindall KR, Chan R, Muller WJ, Adhya S, Garges S, Merlino G. Genetic instability favoring transversions associated with ErbB2-induced mammary tumorigenesis. Proc Natl Acad Sci U S A 2002; 99:3770-5. [PMID: 11867754 PMCID: PMC122599 DOI: 10.1073/pnas.052710299] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been argued that genetic instability is required to generate the myriad mutations that fuel tumor initiation and progression and, in fact, patients with heritable cancer susceptibility syndromes harbor defects in specific genes that normally maintain DNA integrity. However, the vast majority of human cancers arise sporadically, in the absence of deficiencies in known "mutator" genes. We used a cII-based mutation detection assay to show that the mean frequency of forward mutations in primary mammary adenocarcinomas arising in mouse mammary tumor virus-c-erbB2 transgenic mice harboring multiple copies of the lambda bacteriophage genome was significantly higher than in aged-matched, wild-type mammary tissue. Analysis of the cII mutational spectrum within the mammary tumor genomic DNA demonstrated a >6-fold elevation in transversion mutation frequency, resulting in a highly unusual inversion of the transition/transversion ratio characteristic of normal epithelium; frameshift mutation frequencies were unaltered. Arising oncogenic point mutations within the c-erbB2 transgene of such tumors were predominantly transversions as well. Data from this model system support the notion that elaboration of a mutator phenotype is a consequential event in breast cancer and suggest that a novel DNA replication/repair gene is a relatively early mutational target in c-erbB2-induced mammary tumorigenesis.
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MESH Headings
- Adenocarcinoma/genetics
- Adenocarcinoma/virology
- Aging
- Amino Acid Sequence
- Animals
- Bacteriophage lambda/genetics
- Cell Transformation, Neoplastic/genetics
- DNA Damage/genetics
- DNA Mutational Analysis
- Female
- Fibroblasts
- Gene Frequency/genetics
- Kinetics
- Male
- Mammary Glands, Animal/metabolism
- Mammary Glands, Animal/pathology
- Mammary Neoplasms, Animal/genetics
- Mammary Neoplasms, Animal/virology
- Mammary Tumor Virus, Mouse/physiology
- Mice
- Mice, Transgenic
- Molecular Sequence Data
- Mutagenesis/genetics
- Mutation, Missense/genetics
- Receptor, ErbB-2/genetics
- Receptor, ErbB-2/metabolism
- Transgenes/genetics
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Affiliation(s)
- Shiquan Liu
- Laboratory of Molecular Biology, National Cancer Institute, Bethesda, MD 20892-4264, USA
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18
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Shin CY, Mellon I, Turker MS. Multiple mutations are common at mouse Aprt in genotoxin-exposed mismatch repair deficient cells. Oncogene 2002; 21:1768-76. [PMID: 11896608 DOI: 10.1038/sj.onc.1205241] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2001] [Revised: 11/30/2001] [Accepted: 12/06/2001] [Indexed: 11/09/2022]
Abstract
Mismatch repair deficiency is known to contribute to elevated rates of mutations, particularly at mono- and dinucleotide repeat sequences. However, such repeats are often missing from the coding regions of endogenous genes. To determine the types of mutations that can occur within an endogenous gene lacking highly susceptible repeat sequences, we examined mutagenic events at the 2.3 kb mouse Aprt gene in kidney cell lines derived from mice deficient for the PMS2 and MLH1 mismatch repair proteins. The Aprt mutation rate was increased 33-fold and 3.6-20-fold for Mlh1 and Pms2 null cell lines, respectively, when compared with a wild-type kidney cell line. For the Pms2 null cells this increase resulted from both intragenic events, which were predominantly base-pairs substitutions, and loss of heterozygosity events. Almost all mutations in the Mlh1 null cells were due to base-pair substitutions. A:T-->G:C transitions (54% of small events) were predominant in the Pms2 null cells whereas G:C-->A:T transitions (36%) were the most common base-pair change in the Mlh1 null cells. Interestingly, 4-9% of the spontaneous mutant alleles in the mismatch repair deficient cells exhibited two well-separated base-pair substitution events. The percentage of mutant alleles with two and occasionally three base-pair substitutions increased when the Pms2 and Mlh1 null cells were treated with ultraviolet radiation (15-21%) and when the Mlh1 null cells were treated with hydrogen peroxide (35%). In most cases the distance separating the multiple base-pair substitutions on a given allele was in excess of 100 base-pairs, suggesting that the two mutational events were not linked directly to a single DNA lesion. The significance of these results is discussed with regards to the roles for the PMS2 and MLH1 proteins in preventing spontaneous and genotoxin-related mutations.
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Affiliation(s)
- Chi Y Shin
- Center for Research on Occupational and Environmental Toxicology, Oregon Health Sciences University, Portland, Oregon, OR 97201, USA
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19
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Kotoula V, Hytiroglou P, Kaloutsi V, Barbanis S, Kouidou S, Papadimitriou CS. Mismatch repair gene expression in malignant lymphoproliferative disorders of B-cell origin. Leuk Lymphoma 2002; 43:393-9. [PMID: 11999575 DOI: 10.1080/10428190290006215] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
We investigated mismatch repair (MMR) gene expression in 31 lymphoid tissue specimens and bone marrow aspirates with malignant lymphoproliferative disorders of B-cell origin (25 cases of lymphoma and six cases of plasma cell myeloma). A multiplex RT-PCR assay was employed to assess the relative expression of the hMSH2, hMLH1 and hPMS1 genes, as compared to beta-actin, which was used as an internal control of gene expression. MSH2 was further evaluated at the protein level by immunohistochemistry. The findings were compared to those of a control group of lymphoid tissue specimens without evidence of malignancy (n = 6). Changes in MMR gene expression were observed in 10 out of 31 cases of the study group (32%). All three MMR gene transcripts were low in two out of six plasma cell myelomas, which had extensive bone marrow infiltration by neoplastic cells. The hMSH2 transcript was present in all cases of lymphoma, while the expression of hMLH1 and hPMS1 was significantly low in some large B-cell lymphomas (four and five out of 14 cases, respectively) and in mantle cell lymphomas of the blastoid type (two out of two cases). No MMR gene aberrations were found in seven cases of B-cell lymphocytic leukemia and two cases of mantle cell lymphoma of centrocyte-like type. These findings demonstrate that the expression rates of the hMSH2, hMLH1 and hPMS1 genes differ among various types of B-cell lymphoproliferative disorders, and suggest that MMR gene expression may be related to the natural history of these neoplasms. This study identified a higher incidence of MMR gene aberrations in lymphoma types characterized by aggressive biologic behavior, as compared to neoplasms with a more indolent course.
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Affiliation(s)
- Vassiliki Kotoula
- Department of Pathology, Medical School, Aristotle University, Thessaloniki, Greece
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20
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Aquilina G, Bignami M. Mismatch repair in correction of replication errors and processing of DNA damage. J Cell Physiol 2001; 187:145-54. [PMID: 11267994 DOI: 10.1002/jcp.1067] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The primary role of mismatch repair (MMR) is to maintain genomic stability by removing replication errors from DNA. This repair pathway was originally implicated in human cancer through an association between microsatellite instability in colorectal tumors in hereditary nonpolyposis colon cancer (HNPCC) kindreds. Microsatellites are short repetitive sequences which are often copied incorrectly by DNA polymerases because the template and daughter strands in these regions are particularly prone to misalignment. These replication-dependent events create loops of extrahelical bases which would produce frameshift mutations unless reversed by MMR. One consequence of MMR loss is a widespread expansion and contraction of these repeated sequences that affects the whole genome. Defective MMR is therefore associated with a mutator phenotype. Since the same pathway is also responsible for repairing base:base mismatches, defective cells also experience large increases in the frequency of spontaneous transition and transversion mutations. Three different approaches have been used to investigate the function of individual components of the MMR pathway. The first is based on the biochemical characterization of the purified protein complexes using synthetic DNA substrates containing loops or single mismatches. In the second, the biological consequences of MMR loss are inferred from the phenotype of cell lines established from repair-deficient human tumors, from tolerant cells or from mice defective in single MMR genes. In particular, molecular analysis of the mutations in endogenous or reporter genes helped to identify the DNA substrates for MMR. Finally, mice bearing single inactive MMR genes have helped to define the involvement of MMR in cancer prevention.
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Affiliation(s)
- G Aquilina
- Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanita', Rome, Italy
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21
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Abstract
Mismatch repair (MMR) systems play a central role in promoting genetic stability by repairing DNA replication errors, inhibiting recombination between non-identical DNA sequences and participating in responses to DNA damage. The discovery of a link between human cancer and MMR defects has led to an explosion of research on eukaryotic MMR. The key proteins in MMR are highly conserved from bacteria to mammals, and this conservation has been critical for defining the components of eukaryotic MMR systems. In eukaryotes, there are multiple homologs of the key bacterial MutS and MutL MMR proteins, and these homologs form heterodimers that have discrete roles in MMR-related processes. This review describes the genetic and biochemical approaches used to study MMR, and summarizes the diverse roles that MMR proteins play in maintaining genetic stability.
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Affiliation(s)
- B D Harfe
- Department of Biology, Emory University, Atlanta, Georgia 30322, USA
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22
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Buettner VL, Hill KA, Scaringe WA, Sommer SS. Evidence that proximal multiple mutations in Big Blue transgenic mice are dependent events. Mutat Res 2000; 452:219-29. [PMID: 11024481 DOI: 10.1016/s0027-5107(00)00090-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
To characterize the nature of multiple mutations in the tissues of an intact animal, the Big Blue transgenic mouse mutation detection system was used to examine 1459 mutants from eight normal tissues and 507 mutants from 11 tumors. Multiple mutations occurred and predominantly doublet mutants were identified (i.e. two mutations within one mutant lacI gene), but multiplets of up to five mutations were observed. The frequency of doublets in normal tissues and spontaneous tumors from p53-deficient mice was enhanced to the same degree (660 and 667 fold, respectively) over that expected for two independent mutational events. Doublets, multiplets and singlets have similar patterns of mutation. The distance between mutations in doublets fits an exponential distribution, not that expected for randomly spaced events, suggesting that many doublets occur in rapid succession within the same cell cycle.
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Affiliation(s)
- V L Buettner
- Department of Molecular Genetics, City of Hope/Beckman Research Institute, 91010, Duarte, CA 91010, USA
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23
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Tumors arising in DNA mismatch repair-deficient mice show a wide variation in mutation frequency as assessed by a transgenic reporter gene. Carcinogenesis 2000. [DOI: 10.1093/carcin/21.6.1259] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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24
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Abstract
DNA mismatch repair (MMR) is one of multiple replication, repair, and recombination processes that are required to maintain genomic stability in prokaryotes and eukaryotes. In the wake of the discoveries that hereditary nonpolyposis colorectal cancer (HNPCC) and other human cancers are associated with mutations in MMR genes, intensive efforts are under way to elucidate the biochemical functions of mammalian MutS and MutL homologs, and the consequences of defects in these genes. Genetic studies in cultured mammalian cells and mice are proving to be instrumental in defining the relationship between the functions of MMR in mutation and tumor avoidance. Furthermore, these approaches have raised awareness that MMR homologs contribute to DNA damage surveillance, transcription-coupled repair, and recombinogenic and meiotic processes.
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Affiliation(s)
- A B Buermeyer
- Department of Molecular and Medical Genetics, Oregon Health Sciences University, Portland 97201-3098, USA
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25
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Abstract
Aging has been explained in terms of an accumulation of mutations in the genome of somatic cells, leading to tissue atrophy and neoplasms, as well as increased loss of function. Recent advances in transgenic mouse modeling and genomics technology have created, for the first time, the opportunity to begin testing this theory. In this paper the existing evidence for a possible role of somatic mutation accumulation in aging will be re-evaluated on the basis of the evolutionary logic of aging and recent insights in genome structure and function. New strategies for investigating the relationship between genome instability, mutation accumulation and aging will be discussed.
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Affiliation(s)
- J Vijg
- Cancer Therapy and Research Center and University of Texas Health Science Center, San Antonio, TX 78229, USA.
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26
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27
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28
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Manley K, Shirley TL, Flaherty L, Messer A. Msh2 deficiency prevents in vivo somatic instability of the CAG repeat in Huntington disease transgenic mice. Nat Genet 1999; 23:471-3. [PMID: 10581038 DOI: 10.1038/70598] [Citation(s) in RCA: 295] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Huntington disease (HD), an autosomal dominant, progressive neurodegenerative disorder, is caused by an expanded CAG repeat sequence leading to an increase in the number of glutamine residues in the encoded protein. The normal CAG repeat range is 5-36, whereas 38 or more repeats are found in the diseased state; the severity of disease is roughly proportional to the number of CAG repeats. HD shows anticipation, in which subsequent generations display earlier disease onsets due to intergenerational repeat expansion. For longer repeat lengths, somatic instability of the repeat size has been observed both in human cases at autopsy and in transgenic mouse models containing either a genomic fragment of human HD exon 1 (ref. 9) or an expanded repeat inserted into the endogenous mouse gene Hdh (ref. 10). With increasing repeat number, the protein changes conformation and becomes increasingly prone to aggregation, suggesting important functional correlations between repeat length and pathology. Because dinucleotide repeat instability is known to increase when the mismatch repair enzyme MSH2 is missing, we examined instability of the HD CAG repeat by crossing transgenic mice carrying exon 1 of human HD (ref. 16) with Msh2-/- mice. Our results show that Msh2 is required for somatic instability of the CAG repeat.
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Affiliation(s)
- K Manley
- Wadsworth Center, New York State Department of Health, David Axelrod Institute, Albany, New York, USA
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29
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Tran HT, Degtyareva NP, Gordenin DA, Resnick MA. Genetic factors affecting the impact of DNA polymerase delta proofreading activity on mutation avoidance in yeast. Genetics 1999; 152:47-59. [PMID: 10224242 PMCID: PMC1460598 DOI: 10.1093/genetics/152.1.47] [Citation(s) in RCA: 42] [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
Base selectivity, proofreading, and postreplication mismatch repair are important for replication fidelity. Because proofreading plays an important role in error correction, we have investigated factors that influence its impact in the yeast Saccharomyces cerevisiae. We have utilized a sensitive mutation detection system based on homonucleotide runs of 4 to 14 bases to examine the impact of DNA polymerase delta proofreading on mutation avoidance. The contribution of DNA polymerase delta proofreading on error avoidance was found to be similar to that of DNA polymerase epsilon proofreading in short homonucleotide runs (A4 and A5) but much greater than the contribution of DNA polymerase epsilon proofreading in longer runs. We have identified an intraprotein interaction affecting mutation prevention that results from mutations in the replication and the proofreading regions, resulting in an antimutator phenotype relative to a proofreading defect. Finally, a diploid strain with a defect in DNA polymerase delta proofreading exhibits a higher mutation rate than a haploid strain. We suggest that in the diploid population of proofreading defective cells there exists a transiently hypermutable fraction that would be inviable if cells were haploids.
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Affiliation(s)
- H T Tran
- Chromosome Stability Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
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