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Unmack JL, Bud Jenkins VC, Shammas MA. Redefining Board Certified Toxicologist by Consumer Products Safety Commission May Increase Potential Risk of Exposure to Carcinogens among Consumers in United States of America. Front Public Health 2017; 5:29. [PMID: 28293552 PMCID: PMC5328997 DOI: 10.3389/fpubh.2017.00029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2016] [Accepted: 02/13/2017] [Indexed: 11/13/2022] Open
Affiliation(s)
| | | | - Masood A. Shammas
- Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute, Boston, MA, USA
- *Correspondence: Masood A. Shammas, ,
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2
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Shammas MA, Rajput SA, Ahmad D, Ahmed M, Mustafa Z, Ahmad G. Inclusion of “Toxicological Review Expiry Dates” in Art Material Labels May Further Reduce the Risk of Chronic Toxicity, Including That of Cancer. Front Oncol 2016; 6:4. [PMID: 26835419 PMCID: PMC4720026 DOI: 10.3389/fonc.2016.00004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Accepted: 01/03/2016] [Indexed: 11/28/2022] Open
Affiliation(s)
- Masood A. Shammas
- Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute, Boston, MA, USA
- *Correspondence: Masood A. Shammas, ,
| | | | | | - Masood Ahmed
- Department of Anatomy and Histology, College of Medicine, Qassim University, Buraydah, Saudi Arabia
| | - Zahid Mustafa
- University of California Riverside, Riverside, CA, USA
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3
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Levin B, Lech D, Friedenson B. Evidence that BRCA1- or BRCA2-associated cancers are not inevitable. Mol Med 2012; 18:1327-37. [PMID: 22972572 PMCID: PMC3521784 DOI: 10.2119/molmed.2012.00280] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 09/05/2012] [Indexed: 11/06/2022] Open
Abstract
Inheriting a BRCA1 or BRCA2 gene mutation can cause a deficiency in repairing complex DNA damage. This step leads to genomic instability and probably contributes to an inherited predisposition to breast and ovarian cancer. Complex DNA damage has been viewed as an integral part of DNA replication before cell division. It causes temporary replication blocks, replication fork collapse, chromosome breaks and sister chromatid exchanges (SCEs). Chemical modification of DNA may also occur spontaneously as a byproduct of normal processes. Pathways containing BRCA1 and BRCA2 gene products are essential to repair spontaneous complex DNA damage or to carry out SCEs if repair is not possible. This scenario creates a theoretical limit that effectively means there are spontaneous BRCA1/2-associated cancers that cannot be prevented or delayed. However, much evidence for high rates of spontaneous DNA mutation is based on measuring SCEs by using bromodeoxyuridine (BrdU). Here we find that the routine use of BrdU has probably led to overestimating spontaneous DNA damage and SCEs because BrdU is itself a mutagen. Evidence based on spontaneous chromosome abnormalities and epidemiologic data indicates strong effects from exogenous mutagens and does not support the inevitability of cancer in all BRCA1/2 mutation carriers. We therefore remove a theoretical argument that has limited efforts to develop chemoprevention strategies to delay or prevent cancers in BRCA1/2 mutation carriers.
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Affiliation(s)
- Bess Levin
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois Chicago, Chicago, Illinois, United States of America
| | - Denise Lech
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois Chicago, Chicago, Illinois, United States of America
| | - Bernard Friedenson
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois Chicago, Chicago, Illinois, United States of America
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Shammas MA. Repetitive sequences, genomic instability and Barrett's esophageal adenocarcinoma. Mob Genet Elements 2011; 1:208-212. [PMID: 22479688 DOI: 10.4161/mge.1.3.17456] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 07/22/2011] [Indexed: 11/19/2022] Open
Abstract
Barrett's esophageal adenocarcinoma (BAC) is a cancer associated with heartburn. If gastroesophageal reflux is not treated, the exposure to acid over the years, leads to a premalignant condition known as Barrett's esophagus (BE) which then progresses through low grade and high grade dysplasias to Barrett's adenocarcinoma. Genomic instability, which seems to arise early at BE stage, leads to accrual of mutational changes which underlie the the succession of histological and physiological changes associated with this disease. Genomic instability is therefore an important target for prevention and treatment of cancer and it is important to elucidate the mechanisms associated with this problem. We have shown that elevated/deregulated homologous recombination mediates genomic instability in cancer. Recently we also demonstrated that the mutational rates of individual chromosomes in BAC cells correlate with their ALU frequency. The aims of this article are to briefly discuss different types of repetitive sequences and highlight their importance in physiology of normal and cancer cells, especially BAC.
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Affiliation(s)
- Masood A Shammas
- Department of Medical Oncology; Harvard (Dana Farber) Cancer Institute; Boston, MA USA; VA Boston Healthcare System; West Roxbury, MA USA
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5
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Pal J, Bertheau R, Buon L, Qazi A, Batchu RB, Bandyopadhyay S, Ali-Fehmi R, Beer DG, Weaver DW, Shmookler Reis RJ, Goyal RK, Huang Q, Munshi NC, Shammas MA. Genomic evolution in Barrett's adenocarcinoma cells: critical roles of elevated hsRAD51, homologous recombination and Alu sequences in the genome. Oncogene 2011; 30:3585-98. [PMID: 21423218 PMCID: PMC3406293 DOI: 10.1038/onc.2011.83] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A prominent feature of most cancers including Barrett's adenocarcinoma (BAC) is genetic instability, which is associated with development and progression of disease. In this study, we investigated the role of recombinase (hsRAD51), a key component of homologous recombination (HR)/repair, in evolving genomic changes and growth of BAC cells. We show that the expression of RAD51 is elevated in BAC cell lines and tissue specimens, relative to normal cells. HR activity is also elevated and significantly correlates with RAD51 expression in BAC cells. The suppression of RAD51 expression, by short hairpin RNA (shRNA) specifically targeting this gene, significantly prevented BAC cells from acquiring genomic changes to either copy number or heterozygosity (P<0.02) in several independent experiments employing single-nucleotide polymorphism arrays. The reduction in copy-number changes, following shRNA treatment, was confirmed by Comparative Genome Hybridization analyses of the same DNA samples. Moreover, the chromosomal distributions of mutations correlated strongly with frequencies and locations of Alu interspersed repetitive elements on individual chromosomes. We conclude that the hsRAD51 protein level is systematically elevated in BAC, contributes significantly to genomic evolution during serial propagation of these cells and correlates with disease progression. Alu sequences may serve as substrates for elevated HR during cell proliferation in vitro, as they have been reported to do during the evolution of species, and thus may provide additional targets for prevention or treatment of this disease.
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Affiliation(s)
- J Pal
- Department of Adult Oncology, Dana Farber Cancer Institute, Boston, MA 02132, USA
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6
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Shammas MA, Shmookler Reis RJ, Koley H, Batchu RB, Li C, Munshi NC. Dysfunctional homologous recombination mediates genomic instability and progression in myeloma. Blood 2009; 113:2290-7. [PMID: 19050310 PMCID: PMC2652372 DOI: 10.1182/blood-2007-05-089193] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Accepted: 04/20/2008] [Indexed: 11/20/2022] Open
Abstract
A prominent feature of most if not all cancers is a striking genetic instability, leading to ongoing accrual of mutational changes, some of which underlie tumor progression, including acquisition of invasiveness, drug resistance, and metastasis. Thus, the molecular basis for the generation of this genetic diversity in cancer cells has important implications in understanding cancer progression. Here we report that homologous recombination (HR) activity is elevated in multiple myeloma (MM) cells and leads to an increased rate of mutation and progressive accumulation of genetic variation over time. We demonstrate that the inhibition of HR activity in MM cells by small inhibitory RNA (siRNAs) targeting recombinase leads to significant reduction in the acquisition of new genetic changes in the genome and, conversely, the induction of HR activity leads to significant elevation in the number of new mutations over time and development of drug resistance in MM cells. These data identify dysregulated HR activity as a key mediator of DNA instability and progression of MM, with potential as a therapeutic target.
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Affiliation(s)
- Masood A Shammas
- Department of Medicine, VA Health Care System and Harvard Medical School Boston, MA, USA
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Abrahams PJ, Houweling A, Schouten R, van der Eb AJ, Terleth C. Abnormal kinetics of induction of UV-stimulated recombination in human DNA repair disorders. DNA Repair (Amst) 2003; 2:1211-25. [PMID: 14599743 DOI: 10.1016/s1568-7864(03)00141-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Recombination can result in genetic instability, and thus constitutes an important factor in the carcinogenic conversion of mammalian cells. Here we describe the occurrence of UV-stimulated recombination called enhanced recombination (EREC), measured with the use of Herpes Simplex Viruses type 1 mutants. In normal diploid human cells, EREC is induced by UV-C, mitomycin C and ENU, but not by X-ray or MMS. The kinetics of induction of EREC is similar to that of other SOS-like responses such as enhanced reactivation (ER) and enhanced mutagenesis (EM). In contrast to the latter responses, EREC is induced to higher levels and persists for longer periods in DNA repair deficient fibroblasts derived from xeroderma pigmentosum (XP), Cockayne syndrome (CS) and Trichothiodystrophy (TTD) patients. This observation indicates that EREC is a distinct SOS-like response. Apparently, the presence of unrepaired DNA lesions in the host genome is a strongly inducing signal for EREC. On the other hand, in cells derived from patients suffering from Bloom, Werner or Rothmund-Thomson syndrome (RTS) the EREC response is absent. These data indicate that determining EREC is a useful assay to investigate diploid human fibroblasts for abnormalities in UV-stimulated recombination.
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Affiliation(s)
- Peter J Abrahams
- Department of Toxicogenetics, Leiden University Medical Center, Wassenaarseweg 72, 2333 Al Leiden, The Netherlands.
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Sengupta S, Linke SP, Pedeux R, Yang Q, Farnsworth J, Garfield SH, Valerie K, Shay JW, Ellis NA, Wasylyk B, Harris CC. BLM helicase-dependent transport of p53 to sites of stalled DNA replication forks modulates homologous recombination. EMBO J 2003; 22:1210-22. [PMID: 12606585 PMCID: PMC150347 DOI: 10.1093/emboj/cdg114] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Diverse functions, including DNA replication, recombination and repair, occur during S phase of the eukaryotic cell cycle. It has been proposed that p53 and BLM help regulate these functions. We show that p53 and BLM accumulated after hydroxyurea (HU) treatment, and physically associated and co-localized with each other and with RAD51 at sites of stalled DNA replication forks. HU-induced relocalization of BLM to RAD51 foci was p53 independent. However, BLM was required for efficient localization of either wild-type or mutated (Ser15Ala) p53 to these foci and for physical association of p53 with RAD51. Loss of BLM and p53 function synergistically enhanced homologous recombination frequency, indicating that they mediated the process by complementary pathways. Loss of p53 further enhanced the rate of spontaneous sister chromatid exchange (SCE) in Bloom syndrome (BS) cells, but not in their BLM-corrected counterpart, indicating that involvement of p53 in regulating spontaneous SCE is BLM dependent. These results indicate that p53 and BLM functionally interact during resolution of stalled DNA replication forks and provide insight into the mechanism of genomic fidelity maintenance by these nuclear proteins.
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Affiliation(s)
| | | | | | | | - Julie Farnsworth
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
| | - Susan H. Garfield
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
| | - Kristoffer Valerie
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
| | - Jerry W. Shay
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
| | - Nathan A. Ellis
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
| | - Bohdan Wasylyk
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
| | - Curtis C. Harris
- Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892,
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, Laboratory for Cancer Susceptibility, Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA and Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM, ULP, BP 10142, 67404 Illkirch Cedex, France Corresponding author e-mail:
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9
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Helleday T, Nilsson R, Jenssen D. Arsenic[III] and heavy metal ions induce intrachromosomal homologous recombination in the hprt gene of V79 Chinese hamster cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2000; 35:114-122. [PMID: 10712745 DOI: 10.1002/(sici)1098-2280(2000)35:2<114::aid-em6>3.0.co;2-q] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
In the present study the carcinogenic metal ions Cd[II], Co[II], Cr[VI], Ni[II], and Pb[II], as well as As[III], were examined for their ability to induce intrachromosomal homologous and nonhomologous recombination in the hprt gene of two V79 Chinese hamster cell lines, SPD8 and Sp5, respectively. With the exception of Pb[II], all of these ions enhanced homologous recombination, the order of potency being Cr>Cd>As>Co>Ni. In contrast, Cr[VI] was the only ion to enhance recombination of the nonhomologous type. In order to obtain additional information on the mechanism of recombination in the SPD8 cell line, individual clones exhibiting metal-induced recombination were isolated, and the sequence of their hprt gene determined. These findings confirmed that all recombinogenic events in this cell line were of the homologous type, involving predominantly a chromatid exchange mechanism. The mechanisms underlying the recombination induced by these ions are discussed in relationship to their genotoxicity, as well as to DNA repair and replication. Induced recombination may constitute a novel mechanism for induction of neoplastic disease.
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Affiliation(s)
- T Helleday
- Department of Genetic and Cellular Toxicology, Wallenberg Laboratory, Stockholm University, Stockholm, Sweden.
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Arnaudeau C, Helleday T, Jenssen D. The RAD51 protein supports homologous recombination by an exchange mechanism in mammalian cells. J Mol Biol 1999; 289:1231-8. [PMID: 10373364 DOI: 10.1006/jmbi.1999.2856] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Information concerning the function of recombination proteins in mammalian cells has been obtained from biochemical studies, but little is known about their mechanisms of action in growing cells. The eukaryotic recombination protein RAD51, a homologue of the Escherichia coli RecA protein, has been shown to interact with various proteins, including the p53 protein, the guardian of genomic stability maintenance. Here, the hamster RAD51 protein, CgRAD51, has been overexpressed in the SPD8 cell line, derived from Chinese hamster V79 cells. This cell line offers unique possibilities for studying different mechanisms for homologous recombination on endogenous substrates. We report that the SPD8 cell line contains a mutated p53 gene, which provides new insights into the recombination process in these cells. The present study demonstrates that overexpression of CgRAD51 in these cells results in a two- to threefold increase in endogenous recombination. In addition, sequence analysis indicated that RAD51 promotes homologous recombination by a chromatid exchange mechanism.
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Affiliation(s)
- C Arnaudeau
- Wallenberg Laboratory, Stockholm University, Stockholm, S-106 91, Sweden.
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Rothkamm K, Löbrich M. Misrejoining of DNA double-strand breaks in primary and transformed human and rodent cells: a comparison between the HPRT region and other genomic locations. Mutat Res 1999; 433:193-205. [PMID: 10343652 DOI: 10.1016/s0921-8777(99)00008-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Many studies of radiation response and mutagenesis have been carried out with transformed human or rodent cell lines. To study whether the transfer of results between different cellular systems is justified with regard to the repair of radiation-induced DNA double-strand breaks (DSBs), two assays that measure the joining of correct DSB ends and total rejoining in specific regions of the genome were applied to primary and cancer-derived human cells and a Chinese hamster cell line. The experimental procedure involves Southern hybridization of pulsed-field gel electrophoresis blots and quantitative analysis of specific restriction fragments detected by a single-copy probe. The yield of X-ray-induced DSBs was comparable in all cell lines analyzed, amounting to about 1 x 10(-2) breaks/Mbp/Gy. For joining correct DSB ends following an 80 Gy X-ray exposure all cell lines showed similar kinetics and the same final level of correctly rejoined breaks of about 50%. Analysis of all rejoining events revealed a considerable fraction of unrejoined DSBs (15-20%) after 24 h repair incubation in the tumor cell line, 5-10% unrejoined breaks in CHO cells and complete DSB rejoining in primary human fibroblasts. To study intragenomic heterogeneity of DSB repair, we analyzed the joining of correct and incorrect break ends in regions of different gene density and activity in human cells. A comparison of the region Xq26 spanning the hypoxanthine guanine phosphoribosyl transferase locus with the region 21q21 revealed identical characteristics for the induction and repair of DSBs, suggesting that there are no large variations between Giemsa-light and Giemsa-dark chromosomal bands.
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Affiliation(s)
- K Rothkamm
- Strahlenzentrum der Justus-Liebig-Universität Giessen, Germany
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12
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Shammas MA, Shmookler Reis RJ. Recombination and its roles in DNA repair, cellular immortalization and cancer. AGE 1999; 22:71-88. [PMID: 23604399 PMCID: PMC3455241 DOI: 10.1007/s11357-999-0009-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Genetic recombination is the creation of new gene combinations in a cell or gamete, which differ from those of progenitor cells or parental gametes. In eukaryotes, recombination may occur at mitosis or meiosis. Mitotic recombination plays an indispensable role in DNA repair, which presumably directed its early evolution; the multiplicity of recombination genes and pathways may be best understood in this context, although they have acquired important additional functions in generating diversity, both somatically (increasing the immune repertoire) and in germ line (facilitating evolution). Chromosomal homologous recombination and HsRad51 recombinase expression are increased in both immortal and preimmortal transformed cells, and may favor the occurrence of multiple oncogenic mutations. Tumorigenesis in vivo is frequently associated with karyotypic instability, locus-specific gene rearrangements, and loss of heterozygosity at tumor suppressor loci - all of which can be recombinationally mediated. Genetic defects which increase the rate of somatic mutation (several of which feature elevated recombination) are associated with early incidence and high risk for a variety of cancers. Moreover, carcinogenic agents appear to quite consistently stimulate homologous recombination. If cells with high recombination arise, either spontaneously or in response to "recombinogens," and predispose to the development of cancer, what selective advantage could favor these cells prior to the occurrence of growth-promoting mutations? We propose that the augmentation of telomere-telomere recombination may provide just such an advantage, to hyper-recombinant cells within a population of telomerase-negative cells nearing their replicative (Hayflick) limit, by extending telomeres in some progeny cells and thus allowing their continued proliferation.
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Affiliation(s)
- Masood A. Shammas
- />Dept. of Geriatrics, University of Arkansas for Medical Sciences, USA
- />J.L. McClellan Veterans Medical Center — Research 151, 4300 West 7th Street, Little Rock, AR 72205
| | - Robert J. Shmookler Reis
- />Dept. of Geriatrics, University of Arkansas for Medical Sciences, USA
- />Dept. of Biochemistry & Molecular Biology, University of Arkansas for Medical Sciences, USA
- />Dept. of Medicine, University of Arkansas for Medical Sciences, USA
- />J.L. McClellan Veterans Medical Center — Research 151, 4300 West 7th Street, Little Rock, AR 72205
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Shcherbakova PV, Kunkel TA. Mutator phenotypes conferred by MLH1 overexpression and by heterozygosity for mlh1 mutations. Mol Cell Biol 1999; 19:3177-83. [PMID: 10082584 PMCID: PMC84111 DOI: 10.1128/mcb.19.4.3177] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Loss of DNA mismatch repair due to mutation or diminished expression of the MLH1 gene is associated with genome instability and cancer. In this study, we used a yeast model system to examine three circumstances relevant to modulation of MLH1 function. First, overexpression of wild-type MLH1 was found to cause a strong elevation of mutation rates at three different loci, similar to the mutator effect of MLH1 gene inactivation. Second, haploid yeast strains with any of six mlh1 missense mutations that mimic germ line mutations found in human cancer patients displayed a strong mutator phenotype consistent with loss of mismatch repair function. Five of these mutations affect amino acids that are homologous to residues suggested by recent crystal structure and biochemical analysis of Escherichia coli MutL to participate in ATP binding and hydrolysis. Finally, using a highly sensitive reporter gene, we detected a mutator phenotype of diploid yeast strains that are heterozygous for mlh1 mutations. Evidence suggesting that this mutator effect results not from reduced mismatch repair in the MLH1/mlh1 cells but rather from loss of the wild-type MLH1 allele in a fraction of cells is presented. Exposure to bleomycin or to UV irradiation strongly enhanced mutagenesis in the heterozygous strain but had little effect on the mutation rate in the wild-type strain. This damage-induced hypermutability may be relevant to cancer in humans with germ line mutations in only one MLH1 allele.
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Affiliation(s)
- P V Shcherbakova
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
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15
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Vispé S, Cazaux C, Lesca C, Defais M. Overexpression of Rad51 protein stimulates homologous recombination and increases resistance of mammalian cells to ionizing radiation. Nucleic Acids Res 1998; 26:2859-64. [PMID: 9611228 PMCID: PMC147643 DOI: 10.1093/nar/26.12.2859] [Citation(s) in RCA: 250] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Rad51 proteins share both structural and functional homologies with the bacterial recombinase RecA. The human Rad51 (HsRad51) is able to catalyse strand exchange between homologous DNA molecules in vitro . However the biological functions of Rad51 in mammals are largely unknown. In order to address this question, we have cloned hamster Rad51 cDNA and overexpressed the corresponding protein in CHO cells. We found that 2-3-fold overexpression of the protein stimulated the homologous recombination between integrated genes by 20-fold indicating that Rad51 is a functional and key enzyme of an intrachromosomal recombination pathway. Cells overexpressing Rad51 were resistant to ionizing radiation when irradiated in late S/G2phase of the cell cycle. This suggests that Rad51 participate in the repair of double-strand breaks most likely by homologous recombination involving sister chromatids formed after the S phase.
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Affiliation(s)
- S Vispé
- Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, UPR 9062, 205 route de Narbonne, 31077 Toulouse cédex, France
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