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Abstract
Many physiological and cellular processes contribute to the ageing of individuals. One hypothesis argues that the genomes of somatic cells accumulate mutations, which, in turn, alter the metabolism of the cells and contribute to the ageing process. The frequency of somatic mutation approaches 10(-4) and the majority of mutagenic events at heterozygous loci is due to loss of heterozygosity as a consequence of mitotic recombination. A corollary to the argument that somatic cells accumulate mutations is that cells of the germ line and ES cells have a greater requirement for maintaining the integrity of their genomes. In the former case, a high somatic mutation frequency predicts an increase in somatic disease, which limits our lifespan. The corollary is that cells of the germline and ES cells must minimize the mutational burden to limit the frequency of congenital disease and to ensure the proper transmission of undamaged DNA to the gene pool. This report describes two mechanisms utilized by murine ES cells to minimize DNA damage within the proliferative pool. In the first case, murine ES cells display a frequency of mutation and mitotic recombination that is about 100-fold lower than that observed in somatic cells. Second, ES cells lack a G1 checkpoint following DNA damage. When subjected to ionizing radiation, the fraction of apoptotic cells increases to about 40%. Ectopic expression of Chk2 is sufficient to establish a G1 arrest and the concomitant protection from cell death.
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Affiliation(s)
- Peter J Stambrook
- Department of Cell and Cancer Biology, 3125 Eden Avenue, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0521, USA.
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2
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Shimizu M, Yoshimoto T, Sato M, Matsuzawa A, Takeda Y. Frequency and resistance of CD95 (Fas/Apo-1) gene-transfected tumor cells to CD95-mediated apoptosis by the elimination and methylation of integrated DNA. Int J Cancer 2006; 119:585-92. [PMID: 16506211 DOI: 10.1002/ijc.21873] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
It is important for more effective gene therapies to clarify the mechanisms by which cDNA integrated into cells can maintain or lose its function in vivo. We evaluated genetic and epigenetic events leading to alternation of the introduced CD95 (Fas/Apo-1) gene as a model of gene therapy. Solid tumors formed by CD95 cDNA-transfected hepatoma cells (F6b) were almost completely cured by a single treatment of anti-CD95 monoclonal antibody (mAb) but recurred in gld/gld lpr/lpr mice after initial complete response. Recurred tumors were resistant to repeated mAb treatment. The ratio of resistant cells in tumors was estimated as 4.2 cells per 10(6) cells. The CD95-resistant tumor contained CD95-vanished and CD95-decreased cells. CD95-vanished cells were due to the deletion of CD95cDNA. However, CD95-decreased cells retained CD95cDNA, which was highly methylated when determined with methylation-dependent enzymes and a demethylation reagent, indicating that DNA methylation was responsible for the reduced CD95 expression and resistance to mAb. CD95-decreased cells reduced the CD95 expression further but did not delete cDNA after a second in vivo treatment with anti-CD95 mAb, suggesting that the elimination of cDNA is not induced after its methylation and that cells containing methylated genes became more resistant by further methylation. Thus, the elimination and methylation of integrated cDNA appear to occur through different mechanisms. Our study of resistant tumor cells, which arose by both mutational and epigenetic modifications of the introduced CD95 plasmid, provides important and fundamental information about the fate of introduced cDNA, augmenting the efficiency of gene therapy.
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MESH Headings
- Animals
- Antibodies, Monoclonal/pharmacology
- Apoptosis/drug effects
- Apoptosis/genetics
- Cell Line, Tumor
- Cell Survival/drug effects
- Cell Survival/genetics
- DNA Methylation
- DNA, Complementary/genetics
- DNA, Complementary/metabolism
- Deoxyribonuclease HpaII/metabolism
- Dose-Response Relationship, Drug
- Drug Resistance, Neoplasm/genetics
- Gene Expression Regulation, Neoplastic
- Gene Frequency
- Liver Neoplasms, Experimental/drug therapy
- Liver Neoplasms, Experimental/genetics
- Liver Neoplasms, Experimental/pathology
- Mice
- Mice, Inbred C3H
- Nuclear Proteins/genetics
- Nuclear Receptor Co-Repressor 1
- Repressor Proteins/genetics
- Transfection
- fas Receptor/genetics
- fas Receptor/immunology
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Affiliation(s)
- Motomu Shimizu
- Medical R&D Center, Tokyo Metropolitan Institute of Medical Science, Tokyo Metropolitan Organization for Medical Research, Tokyo, 113-8613 Japan.
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3
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Lohman PHM. International Commission for the Protection of the Environment against Mutagens and Carcinogens: a historical perspective. Mutat Res 2002; 511:63-71. [PMID: 11906842 DOI: 10.1016/s1383-5742(02)00002-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- P H M Lohman
- Department of Radiation Genetics and Chemical Mutagenesis, Leiden University Medical Center, Leiden, The Netherlands.
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4
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Ono T, Ikehata H, Nakamura S, Saito Y, Hosoi Y, Takai Y, Yamada S, Onodera J, Yamamoto K. Age-associated increase of spontaneous mutant frequency and molecular nature of mutation in newborn and old lacZ-transgenic mouse. Mutat Res 2000; 447:165-77. [PMID: 10751600 DOI: 10.1016/s0027-5107(99)00200-6] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Accumulation of mutation has long been hypothesized to be a cause of aging and contribute to many of the degenerative diseases, which appear in the senescent phase of life. To test this hypothesis, age-associated changes in spontaneous mutation in different tissues of the body as well as the molecular nature of such changes should be examined. This kind of approach has become feasible only lately with a development of new transgenic mice suitable for mutation assay. Here, using one of these transgenic mice harboring lacZ gene, we have shown that the age-associated increase in spontaneous mutant frequency is common to all tissues examined; spleen, liver, heart, brain, skin and testis, while the rates of increase in mutant frequency differed among the tissues. DNA sequencing of the 496 lacZ mutants recovered from the tissues of newborn and old mice has revealed that spectra of mutations are similar at the two age points with G:C to A:T transition at CpG site being a predominant type of mutation. Furthermore, some mutations in old tissues are complex type and not found in tissues of newborn mice. These results suggest that similar mechanisms may be operating for mutation induction in fetal and postnatal aging process. In addition, the appearance of complex types of mutations in the old tissues suggests a unique cause for these mutations in aging tissues.
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Affiliation(s)
- T Ono
- Department of Cell Biology, Graduate School of Medicine, Tohoku University, Aoba-ku, Japan.
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5
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Hyland PL, Keegan AL, Curran MD, Middleton D, McKenna PG, Barnett YA. Effect of a dCTP:dTTP pool imbalance on DNA replication fidelity in Friend murine erythroleukemia cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2000; 36:87-96. [PMID: 11013406 DOI: 10.1002/1098-2280(2000)36:2<87::aid-em2>3.0.co;2-a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Nucleotide pool imbalances have been reported to affect the fidelity of DNA replication and repair in prokaryotic and eukaryotic cells. We have reported previously that the mutagen-hypersensitive thymidine kinase (TK)-deficient Friend erythroleukemia (FEL) cells (subclones 707BUF and 707BUE), have a more than sixfold increase in the dCTP:dTTP pool ratio when compared to that of wild-type, TK-positive (TK(+)) clone 707 cells. In this study we present the results of an investigation of the effect of the dCTP:dTTP pool imbalance on the accuracy of DNA replication within 707BUF cells. We examined the spontaneous mutation spectra occurring at the adenine phosphoribosyltransferase (aprt) locus within clone 707 (TK(+)) and 707BUF (TK(-)) FEL cells. Mutations recovered at the aprt locus in FEL cells comprised: base substitutions (43:73), frameshifts (14:13.5), and deletions (43:13.5) [clone 707 (TK(+)):707BUF (TK(-)), respectively, expressed as percentages]. A comparison of the mutation spectra obtained for the two cell lines did not reveal any significant increase in misincorporation of dCTP, the nucleotide in excess, in 707BUF (TK(-)) cells, during DNA replication synthesis. These data suggest that the dCTP:dTTP pool imbalance does not alter the fidelity of DNA replication synthesis in 707BUF (TK(-)) FEL cells. Rather, the predominance of GC --> AT transitions (53%) in the 707BUF (TK(-)) spectrum may reflect a reduced efficiency of repair by uracil DNA glycosylase of uracil residues within these cells.
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Affiliation(s)
- P L Hyland
- School of Clinical Dentistry, The Queen's University of Belfast, Belfast, Northern Ireland
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Tan X, Grollman AP, Shibutani S. Comparison of the mutagenic properties of 8-oxo-7,8-dihydro-2'-deoxyadenosine and 8-oxo-7,8-dihydro-2'-deoxyguanosine DNA lesions in mammalian cells. Carcinogenesis 1999; 20:2287-92. [PMID: 10590221 DOI: 10.1093/carcin/20.12.2287] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The comparative mutagenicity of 8-oxo-7,8-dihydro-2'-deoxyadenosine (8-oxodA) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) was explored using simian kidney (COS-7) cells. Oligodeoxynucleotides ¿5'-TCCTCCT- G(1)X(2)CCTCTC or 5'-TCCTCCTX(1)G(2)CCTCTC (X = dA, dG, 8-oxodA or 8-oxodG) containing 8-oxodA or 8-oxodG positioned within codon 60 or 61 of the non-coding strand of human c-Ha-ras1 gene were inserted into a single-stranded phagemid shuttle vector. The vector was replicated in COS-7 cells and the progeny plasmids were used to transform Escherichia coli DH10B. The transformants were analyzed by oligodeoxynucleotide hybridization and DNA sequence analysis to establish the mutation frequency and specificity. When 8-oxodA was positioned at X(1), targeted A(oxo)-->C transversions were detected; the mutation frequency was 1.2%. When 8-oxodA was positioned at X(2), one targeted mutant among 416 colonies screened (an A(oxo)-->G transition) was detected. Thus, the mutation frequency and spectrum of 8-oxodA depend on the sequence context of the lesion. The mutation frequency of 8-oxodG at X(1) and X(2) was 5.2 and 6.8%, respectively. G(oxo)-->T transversions dominated the spectrum, accompanied by small numbers of G(oxo)-->A transitions and G(oxo)-->C transversions. We conclude that 8-oxodA has mutagenic potential in mammalian cells, generating A-->C transversions. However, when tested under similar conditions, the mutation frequency of 8-oxodA is at least four times lower than that of 8-oxodG.
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Affiliation(s)
- X Tan
- Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA
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7
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Julias JG, Pathak VK. Deoxyribonucleoside triphosphate pool imbalances in vivo are associated with an increased retroviral mutation rate. J Virol 1998; 72:7941-9. [PMID: 9733832 PMCID: PMC110126 DOI: 10.1128/jvi.72.10.7941-7949.1998] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Deoxyribonucleoside triphosphate (dNTP) pool imbalances are associated with an increase in the rate of misincorporation and hypermutation during in vitro reverse transcription reactions. However, the effects of in vivo dNTP pool imbalances on the accuracy of reverse transcription are unknown. We sought to determine the effects of in vivo dNTP pool imbalances on retroviral mutation rates and to test our hypothesis that 3'-azido-3'-deoxythymidine (AZT) increases the retroviral mutation rates through induction of dNTP pool imbalances. D17 cells were treated with thymidine, hydroxyurea (HU), or AZT, and the effects on in vivo dNTP pools were measured. Thymidine and HU treatments induced significant dNTP pool imbalances. In contrast, AZT treatment had very little effect on the dNTP pools. The effects of in vivo dNTP pool imbalances induced by thymidine and HU treatments on the retroviral mutation rates were also determined. Spleen necrosis virus (SNV)-based and murine leukemia virus (MLV)-based retroviral vectors that expressed the lacZ mutant reporter gene were used. The frequencies of inactivating mutations introduced in the lacZ gene in a single replication cycle provided a measure of the retroviral mutation rates. Treatment of D17 target cells with 500 microM thymidine increased the SNV and MLV mutant frequencies 4.7- and 4-fold, respectively. Treatment of D17 target cells with 2 mM HU increased the SNV and MLV mutant frequencies 2.1- and 2.7-fold, respectively. These results demonstrate that dNTP pool imbalances are associated with an increase in the in vivo retroviral mutation rates, but AZT treatment results in an increase in the retroviral mutation rates by a mechanism not involving alterations in dNTP pools.
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Affiliation(s)
- J G Julias
- Department of Biochemistry and Mary Babb Randolph Cancer Center, West Virginia University, Morgantown, West Virginia 26506, USA
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8
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Rossman TG, Goncharova EI. Spontaneous mutagenesis in mammalian cells is caused mainly by oxidative events and can be blocked by antioxidants and metallothionein. Mutat Res 1998; 402:103-10. [PMID: 9675254 DOI: 10.1016/s0027-5107(97)00287-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Little is known about endogenous processes causing spontaneous mutagenesis in mammalian cells. To study this problem, a mathematical model and method developed previously in our laboratory was used to measure the spontaneous mutation rate in mammalian cells at the transgenic gpt locus in Chinese hamster G12 cells. We found that spontaneous mutagenesis increased when cells were cultured in low (<0.25%) serum. These cells also contained higher oxidant levels, measured by dichloroflourescein (DCF) fluorescence, suggesting that the elevated spontaneous mutagenesis resulted from endogenous oxidants which are normally quenched by serum antioxidants. This was found to be the case. Spontaneous mutagenesis was significantly reduced in serum-depleted as well as control cells when catalase (100 ng/ml) or the antioxidants ascorbate (50 microg/ml) or mannitol (100-500 microg/ml) were added to the medium. Overexpression of metallothionein in these cells also suppressed spontaneous mutagenesis and mutagenesis induced by oxygen radical-generating compounds. Cells expressing metallothionein antisense RNA become mutators. Taken together, these results suggest that the major cause of spontaneous mutagenesis in mammalian cells is endogenously-generated oxidative DNA damage which can be blocked by metallothionein or by dietary antioxidants carried by the blood supply.
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Affiliation(s)
- T G Rossman
- New York University Medical Center, Nelson Institute of Environmental Medicine, and Kaplan Cancer Center, 550 First Avenue, New York, NY 10016, USA.
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9
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DeMarini DM, Shelton ML, Abu-Shakra A, Szakmary A, Levine JG. Spectra of spontaneous frameshift mutations at the hisD3052 allele of Salmonella typhimurium in four DNA repair backgrounds. Genetics 1998; 149:17-36. [PMID: 9584083 PMCID: PMC1460133 DOI: 10.1093/genetics/149.1.17] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
To characterize the hisD3052 -1 frameshift allele of Salmonella typhimurium, we analyzed approximately 6000 spontaneous revertants (rev) for a 2-base deletion hotspot within the sequence (CG)4, and we sequenced approximately 500 nonhotspot rev. The reversion target is a minimum of 76 bases (nucleotides 843-918) that code for amino acids within a nonconserved region of the histidinol dehydrogenase protein. Only 0.4-3.9% were true rev. Of the following classes, 182 unique second-site mutations were identified: hotspot, complex frameshifts requiring DeltauvrB + pKM101 (TA98-specific) or not (concerted), 1-base insertions, duplications, and nonhotspot deletions. The percentages of hotspot mutations were 13.8% in TA1978 (wild type), 24.5% in UTH8413 (pKM101), 31.6% in TA1538 (DeltauvrB), and 41.0% in TA98 (DeltauvrB, pKM101). The DeltauvrB allele decreased by three times the mutant frequency (MF, rev/10(8) survivors) of duplications and increased by about two times the MF of deletions. Separately, the DeltauvrB allele or pKM101 plasmid increased by two to three times the MF of hotspot mutations; combined, they increased this MF by five times. The percentage of 1-base insertions was not influenced by either DeltauvrB or pKM101. Hotspot deletions and TA98-specific complex frameshifts are inducible by some mutagens; concerted complex frameshifts and 1-base insertions are not; and there is little evidence for mutagen-induced duplications and nonhotspot deletions. Except for the base substitutions in TA98-specific complex frameshifts, all spontaneous mutations of the hisD3052 allele are likely templated. The mechanisms may involve (1) the potential of direct and inverted repeats to undergo slippage and misalignment and to form quasi-palindromes and (2) the interaction of these sequences with DNA replication and repair proteins.
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Affiliation(s)
- D M DeMarini
- Environmental Carcinogenesis Division, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA.
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10
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Julias JG, Kim T, Arnold G, Pathak VK. The antiretrovirus drug 3'-azido-3'-deoxythymidine increases the retrovirus mutation rate. J Virol 1997; 71:4254-63. [PMID: 9151812 PMCID: PMC191640 DOI: 10.1128/jvi.71.6.4254-4263.1997] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
It was previously observed that the nucleoside analog 5-azacytidine increased the spleen necrosis virus (SNV) mutation rate 13-fold in one cycle of retrovirus replication (V. K. Pathak and H. M. Temin, J. Virol. 66:3093-3100, 1992). Based on this observation, we hypothesized that nucleoside analogs used as antiviral drugs may also increase retrovirus mutation rates. We sought to determine if 3'-azido-3'-deoxythymidine (AZT), the primary treatment for human immunodeficiency virus type 1 (HIV-1) infection, increases the retrovirus mutation rate. Two assays were used to determine the effects of AZT on retrovirus mutation rates. The strategy of the first assay involved measuring the in vivo rate of inactivation of the lacZ gene in one replication cycle of SNV- and murine leukemia virus-based retroviral vectors. We observed 7- and 10-fold increases in the SNV mutant frequency following treatment of target cells with 0.1 and 0.5 microM AZT, respectively. The murine leukemia virus mutant frequency increased two- and threefold following treatment of target cells with 0.5 and 1.0 microM AZT, respectively. The second assay used an SNV-based shuttle vector containing the lacZ alpha gene. Proviruses were recovered as plasmids in Escherichia coli, and the rate of inactivation of lacZ alpha was measured. The results indicated that treatment of target cells increased the overall mutation rate two- to threefold. DNA sequence analysis of mutant proviruses indicated that AZT increased both the deletion and substitution rates. These results suggest that AZT treatment of HIV-1 infection may increase the degree of viral variation and alter virus evolution or pathogenesis.
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Affiliation(s)
- J G Julias
- Department of Biochemistry, Mary Babb Randolph Cancer Center, West Virginia University, Morgantown 26506, USA
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11
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“Might as Well Jump!” Template Switching by Retroviral Reverse Transcriptase, Defective Genome Formation, and Recombination. ACTA ACUST UNITED AC 1997. [DOI: 10.1006/smvy.1997.0114] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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12
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Kim T, Mudry RA, Rexrode CA, Pathak VK. Retroviral mutation rates and A-to-G hypermutations during different stages of retroviral replication. J Virol 1996; 70:7594-602. [PMID: 8892879 PMCID: PMC190828 DOI: 10.1128/jvi.70.11.7594-7602.1996] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Retroviruses mutate at a high rate in vivo during viral replication. Mutations may occur during proviral transcription by RNA polymerase II, during minus-strand DNA synthesis (RNA template) by viral reverse transcriptase, or during plus-strand DNA synthesis (DNA template) by reverse transcriptase. To determine the contributions of different stages of replication to the retroviral mutation rates, we developed a spleen necrosis virus-based in vivo system to selectively identify mutations occurring during the early stage (RNA transcription plus minus-strand synthesis) and the late stage (plus-strand synthesis plus DNA repair). A lacZalpha reporter gene was inserted into the long terminal repeat (LTR) of a spleen necrosis virus shuttle vector, and proviruses were recovered from infected cells as plasmids containing either one or both LTRs. Plasmids containing both LTRs generated a mutant phenotype only if the lacZalpha genes in both LTRs were mutated, which is most likely to occur during the early stage. Mutant phenotypes were identified from plasmids containing one LTR regardless of the stage at which the mutations occurred. Thus, mutant frequencies obtained after recovery of plasmids containing both LTRs or one LTR provided early-stage and total mutation rates, respectively. Analysis of 56,409 proviruses suggested that the retroviral mutation rates during the early and late stages of replication were equal or within twofold of each other. In addition, two mutants with A-to-G hypermutations were discovered, suggesting a role for mammalian double-stranded RNA adenosine deaminase enzyme in retroviral mutations. These experiments provide a system to selectively identify mutations in the early stage of retroviral replication and to provide upper and lower limits to the in vivo mutation rates during minus-strand and plus-strand synthesis, respectively.
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Affiliation(s)
- T Kim
- Department of Biochemistry and Mary Babb Randolph Cancer Center, West Virginia University, Morgantown 26506, USA
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13
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Darè E, Zhang LH, Jenssen D. Characterization of mutants involving partial exon duplications in the hprt gene of Chinese hamster V79 cells. SOMATIC CELL AND MOLECULAR GENETICS 1996; 22:201-10. [PMID: 8914605 DOI: 10.1007/bf02369910] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Sequencing of hprt cDNA revealed that three spontaneous mutants in V79 Chinese hamster cells exhibit tandem duplications of exon(s), i.e., either exons 2 and 3 or exon 7. Sequences of different sizes (4.5-8 Kb) were found to be duplicated and inserted in tandem into the hprt gene. These mutants demonstrated spontaneous reversion frequencies which were about 40-fold higher than those observed with other types of spontaneous mutants, but on the same order of magnitude as spontaneous reversions in Sp5, a mutant with a duplication insertion involving exon 2 in this gene. These data suggest that all of the duplications found have the same genetic instability, regardless of the type, size or position of the duplicated fragment. The coding sequence of the hprt cDNA and the restriction pattern of the revertants were virtually identical to the wild-type, indicating restoration of a functional hprt gene by precise deletion of the duplicated fragment.
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Affiliation(s)
- E Darè
- Department of Molecular Medicine, Karolinska Hospital, Stockholm, Sweden.
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14
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Curry J, Khaidakov M, da Cruz A, Karnaoukhova L, Kusser WC, de Boer J, Moffat J, Glickman BW. Mutational specificity and cancer chemoprevention. J Cell Biochem 1996. [DOI: 10.1002/(sici)1097-4644(1996)25+<99::aid-jcb14>3.0.co;2-i] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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15
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Curry J, Rowley GT, Saddi V, Beare D, Cole J, Glickman BW. Determination of hprt mutant and mutation frequencies and the molecular characterization of human derived in vivo T-lymphocyte mutants. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 1995; 25:167-179. [PMID: 7737134 DOI: 10.1002/em.2850250302] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Using a T-lymphocyte clonal assay, 73 6-thioguanine resistant T-lymphocytes were isolated from two blood samples obtained 4 months apart from a 50-year-old male subject. Sixty-six of these mutants were characterized at the DNA sequence level using cDNA. One particular single base substitution was recovered a total of 23 times. The majority of T-cell receptors (TCR) of these mutants all share a common gamma-TCR rearrangement, and thus likely represent a single mutational event that underwent clonal expansion in vivo. Siblings of this clone were recovered in both collections. Three other single base substitutions were also recovered more than once. In two of the three cases, the mutants were also found to be clonally related, while in one case they were not. A number of identical exon loss events were also recovered, yet none of these were clonally related. This probably reflects the multiple pathways by which these mutations can arise. The TCR data was used to correct the observed mutant frequency to produce an estimate of the actual mutation frequency. The two mutant frequencies, 18 x 10(-6) and 19 x 10(-6), obtained from the first and second sampling periods, respectively, can thus be corrected to yield true mutation frequency's of 12 x 10(-6) each.
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Affiliation(s)
- J Curry
- Center for Environmental Health, University of Victoria, British Columbia, Canada
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16
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Xu Z, Yu Y, Schwartz JL, Meltz ML, Hsie AW. Molecular nature of spontaneous mutations at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in Chinese hamster ovary cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 1995; 26:127-138. [PMID: 7556109 DOI: 10.1002/em.2850260206] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The hypoxanthine-guanine phosphoribosyltransferase (hprt) locus has been widely used as a selectable genetic marker for studies of mammalian cell mutagenesis. We report here the spontaneous mutation spectrum at the hprt locus in 64 independently isolated mutants of Chinese hamster ovary (CHO) cells. All nine hprt exons were simultaneously analyzed via multiplex polymerase chain reaction (PCR) for rapid detection of gene deletions or insertions. Structural point mutations were identified by direct sequence analysis of the PCR amplified cDNA. The molecular nature of RNA splicing errors and insertions was analyzed by solid-phase direct exon sequencing. Single base substitutions were found in 24 mutants (38%), of which 21 were missense and 3 were nonsense mutations. Transversions were about twice as frequent as transitions. Fifteen mutants (23%) had deletions involving either intragenic small fragments (2), single exons (9), or multiple exons (4). The majority of deletion breakpoints (71%) were located in regions surrounding exons 4, 5, and 6. RNA splicing mutations were observed in 15 mutants (23%) and affected exons 3-8; most (6/15) resulted in the loss of exon 7. Two insertion mutants, one with a 209 bp insert in exon 4 and the other with a 88 bp insert accompanied by a 24 bp deletion in exon 6, represent novel mutations reported for the first time in spontaneous mutants of the mammalian hprt gene.
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Affiliation(s)
- Z Xu
- Department of Preventive Medicine and Community Health, University of Texas Medical Branch, Galveston, USA
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17
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Bridges BA, Cole J, Favor J, Glickman BW, Mohrenweiser H, Sankaranarayanan K, Skopek TR. International Commission for Protection Against Environmental Mutagens and Carcinogens. Spontaneous mutation and its place in risk assessment for chemical mutagens. Report of an ICPEMC Committee. Mutat Res 1994; 304:3-11. [PMID: 7506356 DOI: 10.1016/0027-5107(94)90317-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- B A Bridges
- MRC Cell Mutation Unit, University of Sussex, Falmer, Brighton, UK
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Sankaranarayanan K. International Commission for Protection Against Environmental Mutagens and Carcinogens. Working paper no. 6. Estimation of genetic risks of exposure to chemical mutagens: relevance of data on spontaneous mutations and of experience with ionizing radiation. Mutat Res 1994; 304:139-58. [PMID: 7506354 DOI: 10.1016/0027-5107(94)90323-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
This paper examines the impact of advances in knowledge on the molecular biology of human Mendelian diseases on the estimation of genetic risks of exposure to ionizing radiation and to chemical mutagens. More specifically, it addresses the question of whether and to what extent naturally occurring Mendelian diseases can be used as a baseline for efforts in this area. Data on the molecular nature and mechanisms of origin of spontaneous mutations underlying naturally occurring Mendelian diseases and on radiation-induced mutations in experimental systems suggest that for ionizing radiation, naturally occurring Mendelian diseases may not constitute an entirely adequate frame of reference and that current risk estimates for this class of diseases are conservative; these estimates however provide a margin of safety in formulating radiation protection guidelines. Currently available data on mechanisms and specificities of action of chemical mutagens, molecular dosimetry, repair of chemically induced adducts in the DNA, adduct-mutation relationships etc., permit the tentative conclusion that naturally occurring Mendelian diseases may provide a better baseline for genetic risk estimation for chemical mutagens than for ionizing radiation. With both ionizing radiation and chemical mutagens, the question of which Mendelian diseases are potentially inducible will become answerable in the near future when more molecular data on human genetic diseases become available. It is therefore essential that risk estimators keep abreast of advances in human genetics and integrate these into their conceptual framework. However, induced Mendelian diseases (especially the dominant ones which are of more immediate concern) are likely to represent a very small fraction of the adverse genetic effects of induced mutations. More attention therefore needs to be devoted to studies on the heterozygous effects of induced mutations.
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Affiliation(s)
- K Sankaranarayanan
- MGC Department of Radiation Genetics and Chemical Mutagenesis, Sylvius Laboratories, State University of Leiden, The Netherlands
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