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Hoogervorst EM, van Oostrom CTM, Beems RB, van Benthem J, Gielis S, Vermeulen JP, Wester PW, Vos JG, de Vries A, van Steeg H. p53 Heterozygosity Results in an Increased 2-Acetylaminofluorene-Induced Urinary Bladder but not Liver Tumor Response in DNA Repair-Deficient Xpa Mice. Cancer Res 2004; 64:5118-26. [PMID: 15289314 DOI: 10.1158/0008-5472.can-04-0350] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Both nucleotide excision repair (NER) and the p53 tumor suppressor protein play crucial roles in the prevention of cells becoming cancerous. This is clearly demonstrated by the fact that NER-deficient xeroderma pigmentosum patients and Li-Fraumeni patients who carry a germ-line p53 mutation are highly tumor prone. The NER-deficient Xpa and the p53(+/-) mouse models clearly mimic their human counterparts, because they are both tumor prone as well. The aim of the study presented here was to analyze the relative contribution of these two pathways in tumor suppression and to analyze a possible link between NER and p53 activation in vivo. For this, we exposed Xpa, p53(+/-), and Xpa/p53(+/-) mice to 2-acetylaminofluorene (2-AAF). We show that 2-AAF-induced urinary bladder tumor suppression is dependent on p53 status, because p53(+/-) mice were highly tumor prone. Xpa/p53(+/-) mice were even more tumor prone, whereas no increased tumor response was found in Xpa mice. Short-term assays revealed a decreased apoptotic response in Xpa/p53(+/-) mice, pointing in vivo toward a link between NER and p53-mediated apoptosis. In contrast, liver tumor response was primarily dependent on appropriate DNA repair, because Xpa-deficient mice were liver tumor prone. p53 heterozygosity had no influence on liver tumor incidences, in line with the results obtained from the short-term 2-AAF studies revealing no altered cellular response in p53(+/-) or Xpa/p53(+/-) mice. Interestingly, however, mice completely deficient in both NER and p53 (Xpa/p53(-/-) mice) showed a dramatic increase of hepatocellular proliferation accompanied by lacZ reporter gene mutations.
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Affiliation(s)
- Esther M Hoogervorst
- National Institute of Public Health and the Environment, Laboratory of Toxicology, Pathology and Genetics, 3720 BA Bilthoven, the Netherlands
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2
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Abstract
Genetically modified mouse models with defects in DNA repair pathways, especially in nucleotide excision repair (NER) and mismatch repair (MMR), are powerful tools to study processes like carcinogenesis and mutagenesis. The use of mutant mice in these studies has many advantages over using normal wild type mice with respect to costs, number of animals, predictive value towards carcinogenic compounds and the duration of study. Short-term carcinogenicity assays still require considerable number of animals and extensive pathological analyses. Therefore, alternatives demanding less animals and shorter exposure times would be desirable. In this respect, one approach could be the use of transgenic mice harbouring marker genes, that can easily detect mutagenic features of carcinogenic compounds, especially when such models are in a DNA repair deficient background. Here, we review the progress made in the development and use of DNA repair deficient mouse models as replacements for long-term cancer assays and discuss the applicability of enhanced gene mutant frequencies as early indicators of tumourigenesis. Although promising models exist, there is still a need for more universally responding and highly sensitive mouse models, since it is likely that non-genotoxic carcinogens will go undetected in a DNA repair deficient mouse. One attractive candidate mouse model, having a presumptive broad detective range, is the Xpa/p53 mutant mouse model, which will be discussed in more detail.
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Affiliation(s)
- Susan W P Wijnhoven
- National Institute of Public Health and Environment, RIVM/TOX pb12, P.O. Box 1, 3720 BA Bilthoven, The Netherlands.
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Gulezian D, Jacobson-Kram D, McCullough CB, Olson H, Recio L, Robinson D, Storer R, Tennant R, Ward JM, Neumann DA. Use of transgenic animals for carcinogenicity testing: considerations and implications for risk assessment. Toxicol Pathol 2000; 28:482-99. [PMID: 10862569 DOI: 10.1177/019262330002800320] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Advances in genetic engineering have created opportunities for improved understanding of the molecular basis of carcinogenesis. Through selective introduction, activation, and inactivation of specific genes, investigators can produce mice of unique genotypes and phenotypes that afford insights into the events and mechanisms responsible for tumor formation. It has been suggested that such animals might be used for routine testing of chemicals to determine their carcinogenic potential because the animals may be mechanistically relevant for understanding and predicting the human response to exposure to the chemical being tested. Before transgenic and knockout mice can be used as an adjunct or alternative to the conventional 2-year rodent bioassay, information related to the animal line to be used, study design, and data analysis and interpretation must be carefully considered. Here, we identify and review such information relative to Tg.AC and rasH2 transgenic mice and p53+/- and XPA-/- knockout mice, all of which have been proposed for use in chemical carcinogenicity testing. In addition, the implications of findings of tumors in transgenic and knockout animals when exposed to chemicals is discussed in the context of human health risk assessment.
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Affiliation(s)
- D Gulezian
- Taconic Farms, Inc, Madison, Connecticut 06443, USA
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Abstract
Short- and medium-term rodent bioassays have been proposed under ICH guidelines for use in testing for the carcinogenic potential of pharmaceuticals. Further evaluation of these models is needed urgently and coordinated efforts are in progress worldwide to expand the available database. Models currently being investigated include transgenic mice (Tg-rasH2, Tg.AC, p53(+/-), XPA(-/-)) and neonatal mice. As more data become available on the performance of these assays, regulatory and industry scientists will be faced with the difficult challenge of determining how the performance (accuracy) of each assay will be measured and deciding which assays have value in the risk assessment process.
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Affiliation(s)
- R D Storer
- Department of Genetic and Cellular Toxicology, Merck Research Laboratories, WP45-311, West Point, PA, USA.
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Shannon M, Lamerdin JE, Richardson L, McCutchen-Maloney SL, Hwang MH, Handel MA, Stubbs L, Thelen MP. Characterization of the mouse Xpf DNA repair gene and differential expression during spermatogenesis. Genomics 1999; 62:427-35. [PMID: 10644440 DOI: 10.1006/geno.1999.6016] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human XPF protein, an endonuclease subunit essential for DNA excision repair, may also function in homologous recombination. To investigate a possible link between mammalian XPF and recombination that occurs during meiosis, we isolated, characterized, and determined an expression profile for the mouse Xpf gene. The predicted mouse XPF protein, encoded by a 3.4-kb cDNA, contains 917 amino acids and is 86% identical to human XPF. Appreciable similarity also exists between mouse XPF and homologous proteins in budding yeast (Rad1), fission yeast (Rad16), and fruit fly (Mei-9), all of which have dual functions in excision repair and recombination. Sequence analysis of the 38.3-kb Xpf gene, localized to a region in proximal mouse chromosome 16, revealed greater than 72% identity to human XPF in 16 regions. Of these conserved elements, 11 were exons and 5 were noncoding sequence within introns. Xpf transcript and protein levels were specifically elevated in adult mouse testis. Moreover, increased levels of Xpf and Ercc1 mRNAs correlated with meiotic and early postmeiotic spermatogenic cells. These results support a distinct role for the XPF/ERCC1 junction-specific endonuclease during meiosis, most likely in the resolution of heteroduplex intermediates that arise during recombination.
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Affiliation(s)
- M Shannon
- Molecular and Structural Biology Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
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Maeda T, Eller MS, Hedayati M, Grossman L, Gilchrest BA. Enhanced repair of benzo(a)pyrene-induced DNA damage in human cells treated with thymidine dinucleotides. Mutat Res 1999; 433:137-45. [PMID: 10102040 DOI: 10.1016/s0921-8777(98)00071-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The small DNA fragment thymidine dinucleotide (pTpT) stimulates photoprotective responses in mammalian cells and intact skin. These responses include increased melanogenesis (tanning) and enhanced repair of DNA damage induced by ultraviolet (UV) light. Here we show that pTpT treatment of human keratinocytes enhances their repair of DNA damaged by the chemical carcinogen benzo(a)pyrene (BP), as determined by increased expression of a transfected BP-damaged reporter plasmid containing the chloramphenicol acetyltransferase (CAT) gene. The pTpT-enhanced repair of this BP-damaged plasmid is accomplished at least in part through activation of the p53 tumor suppressor protein and transcription factor, because p53-null H1299 cells showed enhanced repair only if previously transfected with a p53-expression vector. To elucidate the mechanism of this enhanced DNA repair, we examined the expression of p21 and proliferating cell nuclear antigen (PCNA), proteins known to be regulated by p53, as well as the XPA protein, which is mutated in the inherited repair-deficient disorder xeroderma pigmentosum (XP) group A and is necessary for the recognition of UV-induced DNA photoproducts. The p53, PCNA and XPA proteins were all up-regulated within 48 h after the addition of pTpT. Taken together, these data demonstrate that pTpT-enhanced repair of DNA damaged by either UV irradiation or chemical mutagens can be achieved in human cells by exposure to small DNA fragments at least in part through the activation of p53 and increased expression of p53-regulated genes.
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Affiliation(s)
- T Maeda
- Department of Dermatology, Boston University School of Medicine, MA 02118-2394, USA
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Abstract
At present (putative) human carcinogens are identified via epidemiological studies and testing using the chronic 2-yr rodent bioassay. Both methods have severe limitations in that they are slow, insensitive, expensive, and are also hampered by many uncertainties. The development of methods to modify specific genes in the mammalian genome has provided promising new tools for use in identifying carcinogens and characterizing their (qualitative) risk. Several transgenic mouse lines are currently under study to test their possible use in short-term carcinogenicity testing. One such candidate alternative transgenic model is the XPA knock-out mouse. These mice have an almost complete deficiency in DNA nucleotide excision repair (NER). Nevertheless, XPA-deficient mice are viable and have a background of a low incidence of spontaneous development of cancers. Approximately 15% of the mice develop hepatocellular adenomas (only after 1.5 yr). After treatment with ultraviolet-B radiation or 7,12-dimethylbenz(a)anthracene, the XPA-deficient mice developed squamous cell carcinomas and papillomas, respectively, on their skin. Oral treatment of XPA-deficient mice with benzo[a]pyrene (B[a]P), 2-acetylaminofluorene (2-AAF), and 2-amino-1-methyl-6-phenylimidazo [4,5-b]-pyridine (PhIP) resulted in lymphomas (B[a]P), liver and bladder tumors (2-AAF), and intestinal adenomas plus lymphomas (PhIP). These results look encouraging, but it should be noted that the compounds and agents tested thus far have all been substrate for nucleotide excision repair. Animal studies with different genotoxic or nongenotoxic compounds, as organized for instance within the framework of the International Life Sciences Institute/Health and Environmental Sciences Institute program, are needed to further evaluate the suitability of the XPA model for short-term carcinogenicity testing.
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Affiliation(s)
- H van Steeg
- Laboratory of Health Effects Research, National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
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Sugasawa K, Ng JM, Masutani C, Iwai S, van der Spek PJ, Eker AP, Hanaoka F, Bootsma D, Hoeijmakers JH. Xeroderma pigmentosum group C protein complex is the initiator of global genome nucleotide excision repair. Mol Cell 1998; 2:223-32. [PMID: 9734359 DOI: 10.1016/s1097-2765(00)80132-x] [Citation(s) in RCA: 632] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The XPC-HR23B complex is specifically involved in global genome but not transcription-coupled nucleotide excision repair (NER). Its function is unknown. Using a novel DNA damage recognition-competition assay, we identified XPC-HR23B as the earliest damage detector to initiate NER: it acts before the known damage-binding protein XPA. Coimmunoprecipitation and DNase I footprinting show that XPC-HR23B binds to a variety of NER lesions. These results resolve the function of XPC-HR23B, define the first NER stages, and suggest a two-step mechanism of damage recognition involving damage detection by XPC-HR23B followed by damage verification by XPA. This provides a plausible explanation for the extreme damage specificity exhibited by global genome repair. In analogy, in the transcription-coupled NER subpathway, RNA polymerase II may take the role of XPC. After this subpathway-specific initial lesion detection, XPA may function as a common damage verifier and adaptor to the core of the NER apparatus.
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Affiliation(s)
- K Sugasawa
- Department of Cell Biology and Genetics, Medical Genetic Centre, Erasmus University, Rotterdam, The Netherlands.
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Abstract
Transgenic mouse modelling has proved to be a powerful approach to explore the various steps involved in spontaneous and induced carcinogenesis. Some of the multitude of models currently available have the potential to become a substitute for the expensive, long-term rodent bioassay to predict carcinogenicity of environmental compounds. Here, we review the progress in the development and use of transgenic mouse models specifically for the purpose of carcinogenicity and mutagenicity testing.
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Affiliation(s)
- J Vijg
- Harvard Medical School and Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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Abstract
The capacity of human and other eukaryotic cells to recognize a disparate variety of damaged sites in DNA, and selectively excise and repair them, resides in a deceptively small simple protein, a 38-42 kDa zinc-finger binding protein, XPA (xeroderma pigmentosum group A), that has no inherent catalytic properties. One key to its damage-recognition ability resides in a DNA-binding domain which combines a zinc finger and a single-strand binding region which may infiltrate small single-stranded regions caused by helix-destabilizing lesions. Another is the augmentation of its binding capacity by interactions with other single-stranded binding proteins and helicases which co-operate in the binding and are unloaded at the binding site to facilitate further unwinding of the DNA and subsequent catalysis. The properties of these reactions suggest there must be considerable conformational changes in XPA and associated proteins to provide a flexible fit to a wide variety of damaged structures in the DNA.
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Affiliation(s)
- J E Cleaver
- Laboratory of Radiobiology and Environmental Health, University of California, San Francisco 94143-0750, USA
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Abstract
Several pathways of DNA repair are essential for maintaining genomic integrity in mammalian cells. Mismatch repair is the final line of defense against polymerase errors during normal cellular replication. Base excision repair removes endogenous DNA damage resulting from normal cellular metabolism. Nucleotide excision repair removes bulky, transcription blocking, lesions resulting from endogenous and environmental insults to the DNA. The role of DNA repair in mammalian development is not well understood. Nevertheless, clues to the essential nature of these processes are evident in the human DNA repair syndromes, in the nature of the interactions between DNA repair and other proteins, and in the phenotypes of genetically engineered, knockout mice lacking functional repair genes. Questions remain: what is the relative importance of endogenous vs. environmental DNA damage and is repair itself critical for normal development or are transcription-repair interactions more crucial?
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Affiliation(s)
- E T Snow
- Nelson Institute of Environmental Medicine, New York University Medical Center, Tuxedo, NY 10987, USA
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Abstract
Enhanced expression of the nucleotide excision repair gene XPA is associated with resistance to cisplatin treatment in human ovarian cancer. Understanding the cause of enhanced XPA expression will provide new molecular targets for therapy directed at overcoming chemoresistance. Enhanced gene expression in cancer cells is often caused by mutations or gene amplification. Molecular analyses of the XPA genes in human ovarian cancers indicate that gene mutation and amplification are not the cause of enhanced XPA mRNA levels in ovarian cancers overexpressing XPA. Altered nucleotide excision repair (NER) gene regulation in chemoresistant tumors is discussed.
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Affiliation(s)
- J C States
- Center for Molecular Medicine and Genetics, Wayne State University, Detroit, MI,
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Abstract
We cloned the human xeroderma pigmentosum group A gene (XPA) and characterized the XPA promoter (pXPA) by transient cat expression. The pXPA is extraordinarily weak in human fibroblasts (1% of RSV-LTR) and appears to function without any of the usual promoter elements. Regions containing positive and negative control elements were localized.
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Affiliation(s)
- R S Topping
- Center for Molecular Medicine and Genetics, Wayne State University, Detroit, MI 48201, USA
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de Vries A, van Oostrom CT, Hofhuis FM, Dortant PM, Berg RJ, de Gruijl FR, Wester PW, van Kreijl CF, Capel PJ, van Steeg H, Verbeek SJ. Increased susceptibility to ultraviolet-B and carcinogens of mice lacking the DNA excision repair gene XPA. Nature 1995; 377:169-73. [PMID: 7675086 DOI: 10.1038/377169a0] [Citation(s) in RCA: 296] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Xeroderma pigmentosum patients with a defect in the nucleotide-excision repair gene XPA are characterized by, for example, a > 1,000-fold higher risk of developing sunlight-induced skin cancer. Nucleotide-excision repair (NER) is involved in the removal of a wide spectrum of DNA lesions. The XPA protein functions in a pre-incision step, the recognition of DNA damage. To permit the functional analysis of the XPA gene in vivo, we have generated XPA-deficient mice by gene targeting in embryonic stem cells. The XPA-/-mice appear normal, at least until the age of 13 months. XPA-/-mice are highly susceptible to ultraviolet (UV)-B-induced skin and eye tumours and to 7,12-dimethylbenz[a]anthracene (DMBA)-induced skin tumours. We conclude that the XPA-deficient mice strongly mimic the phenotype of humans with xeroderma pigmentosum.
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Affiliation(s)
- A de Vries
- Department of Immunology, University of Utrecht, The Netherlands
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