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Minko I, Luzadder M, Vartanian V, Rice SM, Nguyen M, Sanchez-Contreras M, Van P, Kennedy S, McCullough A, Lloyd R. Frequencies and spectra of aflatoxin B 1-induced mutations in liver genomes of NEIL1-deficient mice as revealed by duplex sequencing. NAR MOLECULAR MEDICINE 2024; 1:ugae006. [PMID: 38779538 PMCID: PMC11105970 DOI: 10.1093/narmme/ugae006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 04/18/2024] [Accepted: 05/16/2024] [Indexed: 05/25/2024]
Abstract
Increased risk for the development of hepatocellular carcinoma (HCC) is driven by a number of etiological factors including hepatitis viral infection and dietary exposures to foods contaminated with aflatoxin-producing molds. Intracellular metabolic activation of aflatoxin B1 (AFB1) to a reactive epoxide generates highly mutagenic AFB1-Fapy-dG adducts. Previously, we demonstrated that repair of AFB1-Fapy-dG adducts can be initiated by the DNA glycosylase NEIL1 and that male Neil1-/- mice were significantly more susceptible to AFB1-induced HCC relative to wild-type mice. To investigate the mechanisms underlying this enhanced carcinogenesis, WT and Neil1-/- mice were challenged with a single, 4 mg/kg dose of AFB1 and frequencies and spectra of mutations were analyzed in liver DNAs 2.5 months post-injection using duplex sequencing. The analyses of DNAs from AFB1-challenged mice revealed highly elevated mutation frequencies in the nuclear genomes of both males and females, but not the mitochondrial genomes. In both WT and Neil1-/- mice, mutation spectra were highly similar to the AFB1-specific COSMIC signature SBS24. Relative to wild-type, the NEIL1 deficiency increased AFB1-induced mutagenesis with concomitant elevated HCCs in male Neil1-/- mice. Our data establish a critical role of NEIL1 in limiting AFB1-induced mutagenesis and ultimately carcinogenesis.
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Affiliation(s)
- Irina G Minko
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Michael M Luzadder
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Vladimir L Vartanian
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Sean P M Rice
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
- School of Public Health, Oregon Health & Science University - Portland State University, Portland, OR, USA
| | - Megan M Nguyen
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | | | - Phu Van
- TwinStrand Biosciences, Inc., Seattle, WA, USA
| | - Scott R Kennedy
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Amanda K McCullough
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
- Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR, USA
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
- Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR, USA
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Zhao Y, Zeng R, Chen P, Huang C, Xu K, Huang X, Wang X. Transcriptomic and Proteomic Insights into the Effect of Sterigmatocystin on Aspergillus flavus. J Fungi (Basel) 2023; 9:1193. [PMID: 38132793 PMCID: PMC10745003 DOI: 10.3390/jof9121193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Revised: 12/02/2023] [Accepted: 12/04/2023] [Indexed: 12/23/2023] Open
Abstract
Aspergillus flavus is an important fungus that produces aflatoxins, among which aflatoxin B1 (AFB1) is the most toxic and contaminates food and poses a high risk to human health. AFB1 interacts with another mycotoxin sterigmatocystin (STC), which is also a precursor of AFB1. Herein, we determined the effect of STC on AFB1 by evaluating A. flavus transcriptomic and proteomic profiles in the presence or absence of STC by RNA-seq and isobaric tagging, respectively. Overall, 3377 differentially expressed genes were identified by RNA-seq. These genes were mainly associated with the cellular component organisation and biosynthesis, the synthesis of valine, leucine, and isoleucine, and the synthesis of aflatoxin. Clustered genes responsible for AFB1 biosynthesis exhibited varying degrees of downregulation, and norB expression was completely suppressed in the experimental group. During proteomic analysis, 331 genes were differentially expressed in response to STC. These differentially expressed proteins were associated with cell parts and catalytic and antioxidant activities. Differentially expressed proteins predominantly participated in metabolic pathways associated with aflatoxin biosynthesis, glycolysis/gluconeogenesis, glutathione metabolism, and carbon metabolism. Notably, the upregulated and downregulated enzymes in carbohydrate and glutathione metabolisms may serve as potential gateways for inhibiting aflatoxin biosynthesis. Moreover, twelve proteins including seven downregulated ones involved in aflatoxin biosynthesis were identified; among them, AflG was the most downregulated, suggesting that it may be the key enzyme responsible for inhibiting aflatoxin synthesis. These findings provide novel insights into A. flavus control and the mechanisms regulating mycotoxin production.
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Affiliation(s)
- Yarong Zhao
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
| | - Rui Zeng
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
| | - Peirong Chen
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
| | - Chulan Huang
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
| | - Kaihang Xu
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
| | - Xiaomei Huang
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
| | - Xu Wang
- Institute of Quality Standard and Monitoring Technology for Agro-Product of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; (Y.Z.); (R.Z.); (P.C.); (C.H.); (K.X.); (X.H.)
- Laboratory of Quality and Safety Risk Assessment for Agro-Product (Guangzhou), Ministry of Agriculture, Guangzhou 510640, China
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3
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The Molecular Basis of Toxins' Interactions with Intracellular Signaling via Discrete Portals. Toxins (Basel) 2017; 9:toxins9030107. [PMID: 28300784 PMCID: PMC5371862 DOI: 10.3390/toxins9030107] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Revised: 03/02/2017] [Accepted: 03/04/2017] [Indexed: 12/20/2022] Open
Abstract
An understanding of the molecular mechanisms by which microbial, plant or animal-secreted toxins exert their action provides the most important element for assessment of human health risks and opens new insights into therapies addressing a plethora of pathologies, ranging from neurological disorders to cancer, using toxinomimetic agents. Recently, molecular and cellular biology dissecting tools have provided a wealth of information on the action of these diverse toxins, yet, an integrated framework to explain their selective toxicity is still lacking. In this review, specific examples of different toxins are emphasized to illustrate the fundamental mechanisms of toxicity at different biochemical, molecular and cellular- levels with particular consideration for the nervous system. The target of primary action has been highlighted and operationally classified into 13 sub-categories. Selected examples of toxins were assigned to each target category, denominated as portal, and the modulation of the different portal’s signaling was featured. The first portal encompasses the plasma membrane lipid domains, which give rise to pores when challenged for example with pardaxin, a fish toxin, or is subject to degradation when enzymes of lipid metabolism such as phospholipases A2 (PLA2) or phospholipase C (PLC) act upon it. Several major portals consist of ion channels, pumps, transporters and ligand gated ionotropic receptors which many toxins act on, disturbing the intracellular ion homeostasis. Another group of portals consists of G-protein-coupled and tyrosine kinase receptors that, upon interaction with discrete toxins, alter second messengers towards pathological levels. Lastly, subcellular organelles such as mitochondria, nucleus, protein- and RNA-synthesis machineries, cytoskeletal networks and exocytic vesicles are also portals targeted and deregulated by other diverse group of toxins. A fundamental concept can be drawn from these seemingly different toxins with respect to the site of action and the secondary messengers and signaling cascades they trigger in the host. While the interaction with the initial portal is largely determined by the chemical nature of the toxin, once inside the cell, several ubiquitous second messengers and protein kinases/ phosphatases pathways are impaired, to attain toxicity. Therefore, toxins represent one of the most promising natural molecules for developing novel therapeutics that selectively target the major cellular portals involved in human physiology and diseases.
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Abstract
DNA nucleobases are the prime targets for chemical modifications by endogenous and exogenous electrophiles. Alkylation of the N7 position of guanine and adenine in DNA triggers base-catalyzed imidazole ring opening and the formation of N5-substituted formamidopyrimidine (N5-R-FAPy) lesions. Me-FAPy-dG adducts induced by exposure to methylating agents and AFB-FAPy-dG lesions formed by aflatoxin B1 have been shown to persist in cells and to contribute to toxicity and mutagenicity. In contrast, the biological outcomes of other N5-substituted FAPy lesions have not been fully elucidated. To enable their structural and biological evaluation, N5-R-FAPy adducts must be site-specifically incorporated into synthetic DNA strands using phosphoramidite building blocks, which can be complicated by their unusual structural complexity. N5-R-FAPy exist as a mixture of rotamers and can undergo isomerization between α, β anomers and furanose-pyranose forms. In this Perspective, we will discuss the main types of N5-R-FAPy adducts and summarize the strategies for their synthesis and structural elucidation. We will also summarize the chemical biology studies conducted with N5-R-FAPy-containing DNA to elucidate their effects on DNA replication and to identify the mechanisms of N5-R-FAPy repair.
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Affiliation(s)
- Suresh S. Pujari
- Department of Medicinal Chemistry and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Natalia Tretyakova
- Department of Medicinal Chemistry and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Carvajal M. Transformación de la aflatoxina B1 de alimentos, en el cancerígeno humano, aducto AFB1-ADN. TIP REVISTA ESPECIALIZADA EN CIENCIAS QUÍMICO-BIOLÓGICAS 2013. [DOI: 10.1016/s1405-888x(13)72082-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Cavalcanti BC, Barros FWA, Cabral IO, Ferreira JRO, Magalhães HIF, Júnior HVN, da Silva Júnior EN, de Abreu FC, Costa CO, Goulart MOF, Moraes MO, Pessoa C. Preclinical genotoxicology of nor-β-lapachone in human cultured lymphocytes and Chinese hamster lung fibroblasts. Chem Res Toxicol 2011; 24:1560-74. [PMID: 21830773 DOI: 10.1021/tx200180y] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Nor-β-lapachone has shown several biological properties. Regarding cytotoxic activity against cancer cell lines, it has been recognized as an important prototype. However, quinonoid drugs present a major challenge because of their toxicity. In this study, we evaluated the cytotoxicity and genetic toxicity of nor-β-lapachone in human lymphocytes and HL-60 leukemia cells and murine V79 fibroblasts, to shed some light on its selectivity toward cancer cells. As measured by MTT test, exposure of V79 cells to nor-β-lapachone resulted in a weak cytotoxicity (IC(50) = 13.41 μM), and at a concentration up to 21.9 μM, no cytotoxic effect was observed in lymphocytes, while in HL-60 cells, nor-β-lapachone elicited significantly greater cytotoxicity (IC(50) = 1.89 μM). Cultures coexposed to GSH-OEt showed an increased viability, which may indicate a neutralization of ROS generated by quinonoid treatment. In fact, only the highest concentrations of nor-β-lapachone (10 or 20 μM) caused an increase in oxidative stress in nontumor levels cells as measured by TBARS and nitrite/nitrate detection. This was accompanied by an alteration in intracellular thiol content. However, NAC pre-exposure restored the redox equilibrium of the cells and the concentration of thiol levels to control values. Nor-β-lapachone at 2.5 and 5 μM failed to induce DNA damage in nontumor cells, but at the highest concentrations tested, it induced single and double DNA strand breaks and increased the frequency of chromosomal aberrations. Interestingly, these damages were prevented by NAC pretreatment or exacerbated by prior exposure to the GSH-depleting agent 1-bromoheptane. In electrochemical experiments, nor-β-lapachone at the same concentrations as those used in genotoxic tests did not damage DNA directly, but at the highest concentration tested (200 μM), it caused a very weak DNA interaction. Corroborating electrochemical data, oxidative modifications of DNA bases were observed, as checked by DNA repair enzymes EndoIII and FPG, which reinforced the indirect actions caused by nor-β-lapachone through ROS generation and not via DNA intercalation. The DNA repair capacities were higher for nontumor cells than for leukemia cells, which may be related to the selective cytoxicity of nor-β-lapachone toward cancer cells. Our data suggest that ROS play an important role in nor-β-lapachone toxicity and that its DNA-damaging effect occurs only at concentrations several times higher than that needed for its antiproliferative effect on cancer cells.
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Affiliation(s)
- Bruno C Cavalcanti
- National Laboratory of Experimental Oncology, Department of Physiology and Pharmacology, Federal University of Ceará, Fortaleza, Brazil.
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7
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DNA damage in fetal liver cells of turkey and chicken eggs dosed with aflatoxin B1. Arch Toxicol 2011; 85:1167-72. [DOI: 10.1007/s00204-011-0653-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Accepted: 01/13/2011] [Indexed: 10/18/2022]
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Bentle MS, Reinicke KE, Dong Y, Bey EA, Boothman DA. Nonhomologous end joining is essential for cellular resistance to the novel antitumor agent, beta-lapachone. Cancer Res 2007; 67:6936-45. [PMID: 17638905 DOI: 10.1158/0008-5472.can-07-0935] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Commonly used antitumor agents, such as DNA topoisomerase I/II poisons, kill cancer cells by creating nonrepairable DNA double-strand breaks (DSBs). To repair DSBs, error-free homologous recombination (HR), and/or error-prone nonhomologous end joining (NHEJ) are activated. These processes involve the phosphatidylinositol 3'-kinase-related kinase family of serine/threonine enzymes: ataxia telangiectasia mutated (ATM), ATM- and Rad3-related for HR, and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) for NHEJ. Alterations in these repair processes can cause drug/radiation resistance and increased genomic instability. beta-Lapachone (beta-lap; also known as ARQ 501), currently in phase II clinical trials for the treatment of pancreatic cancer, causes a novel caspase- and p53-independent cell death in cancer cells overexpressing NAD(P)H:quinone oxidoreductase-1 (NQO1). NQO1 catalyzes a futile oxidoreduction of beta-lap leading to reactive oxygen species generation, DNA breaks, gamma-H2AX foci formation, and hyperactivation of poly(ADP-ribose) polymerase-1, which is required for cell death. Here, we report that beta-lap exposure results in NQO1-dependent activation of the MRE11-Rad50-Nbs-1 complex. In addition, ATM serine 1981, DNA-PKcs threonine 2609, and Chk1 serine 345 phosphorylation were noted; indicative of simultaneous HR and NHEJ activation. However, inhibition of NHEJ, but not HR, by genetic or chemical means potentiated beta-lap lethality. These studies give insight into the mechanism by which beta-lap radiosensitizes cancer cells and suggest that NHEJ is a potent target for enhancing the therapeutic efficacy of beta-lap alone or in combination with other agents in cancer cells that express elevated NQO1 levels.
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Affiliation(s)
- Melissa S Bentle
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA
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9
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Jayaguru P, Raghunathan M. Group I intron renders differential susceptibility of Candida albicans to Bleomycin. Mol Biol Rep 2006; 34:11-7. [PMID: 17115251 DOI: 10.1007/s11033-006-9002-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2006] [Accepted: 08/21/2006] [Indexed: 10/24/2022]
Abstract
The alarming increase in drug resistance gained by fungal pathogens has raised an urgent need to develop drugs against novel targets. Candida albicans, an opportunistic fungal pathogen, harbors in its 25S rRNA gene, a self-splicing Group I intron, which can act as a selective drug target. We report that Bleomycin selectively inhibits the self-splicing of Group I intron of C. albicans at IC(50) = 1.2 microM, leading to accumulation of precursor RNA as evinced by Reverse Transcriptase PCR. Drug susceptibility assays including MIC determination, growth curve analysis and disc diffusion assays indicate a strong susceptibility of the intron-containing strain (4-1) than the intronless strain (62-1). These results on the preferential targeting of Group I intron of C. albicans by Bleomycin might form a basis for design of small molecules that inhibit self-splicing of RNA as a antimicrobial tool against life-threatening microorganisms.
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Affiliation(s)
- Prathiba Jayaguru
- Department of Genetics, Dr ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai, 600 113, India
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Smela ME, Currier SS, Bailey EA, Essigmann JM. The chemistry and biology of aflatoxin B(1): from mutational spectrometry to carcinogenesis. Carcinogenesis 2001; 22:535-45. [PMID: 11285186 DOI: 10.1093/carcin/22.4.535] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Dietary exposure to aflatoxin B(1) (AFB(1)) is associated with an increased incidence of hepatocellular carcinoma (HCC), especially in populations in which exposure to hepatitis B virus (HBV) is a common occurrence. Most HCC samples from people living where HBV is prevalent have one striking mutational hotspot: a GC-->TA transversion at the third position of codon 249 of the p53 gene. In this review, the chemical reaction of an electrophilic derivative of aflatoxin with specific DNA sequences is examined, along with the types of mutations caused by AFB(1) and the sequence context dependence of those mutations. An attempt is made to assign the source of these mutations to specific chemical forms of AFB(1)-DNA damage. In addition, epidemiological and experimental data are examined regarding the synergistic effects of AFB(1) and HBV on HCC formation and the predominance of one hotspot GC-->TA transversion in the p53 gene of affected individuals.
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Affiliation(s)
- M E Smela
- Department of Chemistry and Division of Bioengineering and Environmental Health Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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11
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Bigger CA, Pontén I, Page JE, Dipple A. Mutational spectra for polycyclic aromatic hydrocarbons in the supF target gene. Mutat Res 2000; 450:75-93. [PMID: 10838135 DOI: 10.1016/s0027-5107(00)00017-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
An SV40-based shuttle vector system was used to identify the types of mutational changes and the sites of mutation within the supF DNA sequence generated by the four stereoisomers of benzo[c]phenanthrene 3,4-dihydrodiol 1,2-epoxide (B[c]PhDE), by racemic mixtures of bay or fjord region dihydrodiol epoxides (DE) of 5-methylchrysene, of 5, 6-dimethylchrysene, of benzo[g]chrysene and of 7-methylbenz[a]anthracene and by two direct acting polycyclic aromatic hydrocarbon carcinogens, 7-bromomethylbenz[a]anthracene (7-BrMeBA) and 7-bromomethyl-12-methylbenz[a]anthracene (7-BrMe-12-MeBA). The results of these studies demonstrated that the predominant type of mutation induced by these compounds is the base substitution. The chemical preference for reaction at deoxyadenosine (dAdo) or deoxyguanosine (dGuo) residues in DNA, which is in general correlated with the spatial structure (planar or non-planar) of the reactive polycyclic aromatic hydrocarbon, is reflected in the preference for mutation at A&z.ccirf;T or G&z.ccirf;C pairs. In addition, if the ability to react with DNA in vivo is taken into account, the relative mutagenic potencies of the B[c]PhDE stereoisomers are consistent with the higher tumorigenic activity associated with non-planar polycyclic aromatic hydrocarbons and their extensive reaction with dAdo residues in DNA. Comparison of the types of mutations generated by polycyclic aromatic hydrocarbons and other bulky carcinogens in this shuttle vector system suggests that all bulky lesions may be processed by a similar mechanism related to that involved in replication past apurinic sites. However, inspection of the distribution of mutations over the target gene induced by the different compounds demonstrated that individual polycyclic aromatic hydrocarbons induce unique patterns of mutational hotspots within the target gene. A polymerase arrest assay was used to determine the sequence specificity of the interaction of reactive polycyclic aromatic hydrocarbons with the shuttle vector DNA. The results of these assays revealed a divergence between mutational hotspots and polymerase arrest sites for all compounds investigated, i.e., sites of mutational hotspots do not correspond to sites where high levels of adduct formation occur, and suggested that some association between specific adducts and sequence context may be required to constitute a premutagenic lesion. A site-specific mutagenesis system employing a single-stranded vector (M13mp7L2) was used to investigate the mutational events a single benzo[a]pyrene or benzo[c]phenanthrene dihydrodiol epoxide-DNA adduct elicits within specific sequence contexts. These studies showed that sequence context can cause striking differences in mutagenic frequencies for given adducts. In addition, these sequence context effects do not originate only from nucleotides immediately adjacent to the adduct, but are also modulated by more distal nucleotides. The implications of these results for mechanisms of polycyclic aromatic hydrocarbon-induced mutagenesis and carcinogenesis are discussed.
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Affiliation(s)
- C A Bigger
- Chemistry of Carcinogenesis Laboratory, Basic Research Program, Advanced BioScience Laboratories, Frederick Cancer Research and Development Center, National Cancer Institute, Frederick, MD 21702, USA.
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12
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O'Brien T, Babcock G, Cornelius J, Dingeldein M, Talaska G, Warshawsky D, Mitchell K. A comparison of apoptosis and necrosis induced by hepatotoxins in HepG2 cells. Toxicol Appl Pharmacol 2000; 164:280-90. [PMID: 10799338 DOI: 10.1006/taap.2000.8917] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
7H-Dibenzo[c,g]carbazole (DBC), an N-heterocyclic aromatic hydrocarbon, is cytotoxic and carcinogenic in rodent liver. While DBC leads to necrotic lesions in the liver, the induction of apoptosis by DBC has not been investigated. The focus of this study was to determine the degree to which apoptosis and necrosis contributed to DBC cytotoxicity in a human hepatoma cell line (HepG2). To determine if these effects were unique to DBC, the results were compared to another hepatotoxin, aflatoxin B(1) (AFB(1)). DBC produced a distinct biphasic LDH release curve within 24 h of exposure. During the same time period lower concentrations of DBC (<10 microM) induced the formation of DBC-DNA adducts and increased p53 protein levels followed by apoptotic cell death. However, increasing the concentration of DBC to 80 microM led to lower DNA adduct and p53 protein levels. At this concentration, intracellular ATP levels were rapidly depleted followed by cell swelling and loss of membrane integrity consistent with necrotic cell death. In contrast to DBC, a biphasic LDH release curve was not observed for AFB(1). Instead, AFB(1) induced a concentration-dependent increase in apoptosis that reached two- to threefold higher levels than DBC. These results suggest that differences exist in the extent and type of cell death induced by DBC and AFB(1) at equimolar concentrations. Apoptosis and necrosis result from low and high concentrations of DBC, respectively, and may be dependent upon intracellular ATP levels.
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Affiliation(s)
- T O'Brien
- Department of Environmental Health, University of Cincinnati Medical Center, Cincinnati, Ohio, 45267-0056, USA
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13
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Murray V. A survey of the sequence-specific interaction of damaging agents with DNA: emphasis on antitumor agents. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1999; 63:367-415. [PMID: 10506836 DOI: 10.1016/s0079-6603(08)60727-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
This article reviews the literature concerning the sequence specificity of DNA-damaging agents. DNA-damaging agents are widely used in cancer chemotherapy. It is important to understand fully the determinants of DNA sequence specificity so that more effective DNA-damaging agents can be developed as antitumor drugs. There are five main methods of DNA sequence specificity analysis: cleavage of end-labeled fragments, linear amplification with Taq DNA polymerase, ligation-mediated polymerase chain reaction (PCR), single-strand ligation PCR, and footprinting. The DNA sequence specificity in purified DNA and in intact mammalian cells is reviewed for several classes of DNA-damaging agent. These include agents that form covalent adducts with DNA, free radical generators, topoisomerase inhibitors, intercalators and minor groove binders, enzymes, and electromagnetic radiation. The main sites of adduct formation are at the N-7 of guanine in the major groove of DNA and the N-3 of adenine in the minor groove, whereas free radical generators abstract hydrogen from the deoxyribose sugar and topoisomerase inhibitors cause enzyme-DNA cross-links to form. Several issues involved in the determination of the DNA sequence specificity are discussed. The future directions of the field, with respect to cancer chemotherapy, are also examined.
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Affiliation(s)
- V Murray
- School of Biochemistry and Molecular Genetics, University of New South Wales, Sydney, Australia
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14
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Denissenko MF, Cahill J, Koudriakova TB, Gerber N, Pfeifer GP. Quantitation and mapping of aflatoxin B1-induced DNA damage in genomic DNA using aflatoxin B1-8,9-epoxide and microsomal activation systems. Mutat Res 1999; 425:205-11. [PMID: 10216213 DOI: 10.1016/s0027-5107(99)00038-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Aflatoxin B1 (AFB1) is a mutagenic and carcinogenic mycotoxin which may play a role in the etiology of human liver cancer. In vitro studies have shown that AFB1 adducts form primarily at the N7 position of guanine. Using quantitative PCR (QPCR) and ligation-mediated PCR (LMPCR), we have mapped total AFB1 adducts in genomic DNA treated with AFB1-8,9-epoxide and in hepatocytes exposed to AFB1 activated by rat liver microsomes or human liver and enterocyte microsomal preparations. The p53 gene-specific adduct frequencies in DNA, modified in cells with 40-400 microM AFB1, were 0.07-0.74 adducts per kilobase (kb). In vitro modification with 0. 1-4 ng AFB1-8,9-epoxide per microgram DNA produced 0.03-0.58 lesions per kb. The adduct patterns obtained with the epoxide and the different microsomal systems were virtually identical indicating that adducts form with a similar sequence-specificity in vitro and in vivo. The lesions were detected exclusively at guanines with a preference towards GpG and methylated CpG sequences. The methods utilizing QPCR and LMPCR thus provide means to assess gene-specific and sequence-specific AFB1 damage. The results also prove that microsomally-mediated damage is a suitable method for avoiding manipulations with very unstable DNA-reactive metabolites and that this damage can be detected by QPCR and LMPCR.
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Affiliation(s)
- M F Denissenko
- Department of Biology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
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15
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Abstract
Mycotoxins are toxic fungal metabolites which are structurally diverse, common contaminants of the ingredients of animal feed and human food. To date, mycotoxins with carcinogenic potency in experimental animal models include aflatoxins, sterigmatocystin, ochratoxin, fumonisins, zearalenone, and some Penicillium toxins. Most of these carcinogenic mycotoxins are genotoxic agents with the exception of fumonisins, which is currently believed to act by disrupting the signal transduction pathways of the target cells. Aflatoxin B1 (AFB1), a category I known human carcinogen and the most potent genotoxic agent, is mutagenic in many model systems and produces chromosomal aberrations, micronuclei, sister chromatid exchange, unscheduled DNA synthesis, and chromosomal strand breaks, as well as forms adducts in rodent and human cells. The predominant AFB1-DNA adduct was identified as 8, 9-dihydro-8-(N7-guanyl)-9-hydroxy-AFB1 (AFB1-N7-Gua), which derives from covalent bond formation between C8 of AFB1-8,9-epoxides and N7 of guanine bases in DNA. Initial AFB1-N7-guanine adduct can convert to a ring-opened formamidopyrimidine derivative, AFB1-FAPY. The formation of AFB1-N7-guanine adduct was linear over the low-dose range in all species examined, and liver, the primary target organ, had the highest level of the adduct. Formation of initial AFB1-N7-guanine adduct was correlated with the incidence of hepatic tumor in trout and rats. The AFB1-N7-guanine adduct was removed from DNA rapidly and was excreted exclusively in urine of exposed rats. Several human studies have validated the similar correlation between dietary exposure to AFB1 and excretion of AFB1-N7-guanine in urine. Replication of DNA containing AFB1-N7-guanine adduct-induced G-->T mutations in an experimental model. Activation of ras protooncogene has been found in AFB1-induced tumors in mouse, rat, and fish. More strikingly, the relationship between aflatoxin exposure and development of human hepatocellular carcinoma (HHC) was demonstrated by the studies on the p53 tumor suppressor gene. High frequency of p53 mutations (G-->T transversion at codon 249) was found to occur in HHC collected from populations exposed to high levels of dietary aflatoxin in China and Southern Africa. Furthermore, AFB1-induced DNA damage and hepatocarcinogenesis in experimental models can be modulated by a variety of factors including nutrients, chemopreventive agents, and other factors such as food restriction and viral infection, as well as genetic polymorphisms.
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Affiliation(s)
- J S Wang
- Department of Environmental Health Sciences, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, MD 21205, USA
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16
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Jones WR, Stone MP. Site-specific targeting of aflatoxin adduction directed by triple helix formation in the major groove of oligodeoxyribonucleotides. Nucleic Acids Res 1998; 26:1070-5. [PMID: 9461470 PMCID: PMC147363 DOI: 10.1093/nar/26.4.1070] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The targeted adduction of aflatoxin B1- exo -8,9-epoxide (AFB1- exo -8,9-epoxide) to a specific guanine within an oligodeoxyribonucleotide containing multiple guanines was achieved using a DNA triplex to control sequence selectivity. The oligodeoxyribonucleotide d(AGAGAAGATTTTCTTCTCTTTTTTTTCTCTT), designated '3G', spontaneously formed a triplex in which nucleotides C27*G2*C18 and C29*G4*C16 formed base triplets, and nucleotides G7*C13formed a Watson-Crick base pair. The oligodeoxyribonucleotide d(AAGAAATTTTTTCTTTTTTTTTTCTT), designated '1G', also formed a triplex in which nucleotides C24*G3*C24 formed a triplet. Reaction of the two oligodeoxyribonucleotides with AFB1-exo-8,9-epoxide revealed that only the 3G sequence formed an adduct, as determined by UV absorbance and piperidine cleavage of the 5'-labeled adduct, followed by denaturing polyacrylamide gel electrophoresis. This site was identified as G7by comparison to the guanine-specific cleavage pattern. The chemistry was extended to a series of nicked bimolecular triple helices, constructed from d(AAAGGGGGAA) and d(CnTTCTTTTTCCCCCTTTATTTTTTC5-n) (n = 1-5). Each oligomer in the series differed only in the placement of the nick. Reaction of the nicked triplexes with AFB1- exo -8,9-epoxide, piperidine cleavage of the 5'-labeled adduct, followed by denaturing polyacrylamide gel electrophoresis, revealed cleavage corresponding to the guanine closest to the pyrimidine strand nick. By using the appropriate pyrimidine sequence the lesion was positioned within the purine strand.
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Affiliation(s)
- W R Jones
- Department of Chemistry and Center in Molecular Toxicology, Vanderbilt University, Nashville, TN 37235, USA
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17
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Kobertz WR, Wang D, Wogan GN, Essigmann JM. An intercalation inhibitor altering the target selectivity of DNA damaging agents: synthesis of site-specific aflatoxin B1 adducts in a p53 mutational hotspot. Proc Natl Acad Sci U S A 1997; 94:9579-84. [PMID: 9275165 PMCID: PMC23223 DOI: 10.1073/pnas.94.18.9579] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Aflatoxin B1 (AFB1) is a potent human carcinogen implicated in the etiology of hepatocellular carcinoma. Upon metabolic activation to the reactive epoxide, AFB1 forms DNA adducts primarily at the N7 position of guanines. To elucidate more fully the molecular mechanism of AFB1-induced mutagenesis, an intercalation inhibitor was designed to probe the effects of intercalation by AFB1 epoxide on its reaction with DNA. DNA duplexes were prepared consisting of a target strand containing multiple potentially reactive guanines and a nontarget strand containing a cis-syn thymidine-benzofuran photoproduct. Because the covalently linked benzofuran moiety physically occupies an intercalation site, we reasoned that such a site would be rendered inaccessible to AFB1 epoxide. By strategic positioning of this intercalation inhibitor in the intercalation site 5' to a specific guanine, the adduct yield at that site was greatly diminished, indicating that intercalation by AFB1 epoxide contributes favorably to adduct formation. Using this approach it has been possible to simplify the production of site-specifically modified oligonucleotides containing AFB1 adducts in the sequence context of a p53 mutational hotspot. Moreover, we report herein isolation of site-specifically AFB1-modified oligonucleotides in sequences containing multiple guanines. Use of intercalation inhibitors will facilitate both investigation of the ability of other carcinogens to intercalate into DNA and the synthesis of specific carcinogen-DNA adducts.
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Affiliation(s)
- W R Kobertz
- Department of Chemistry and Division of Toxicology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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18
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Oleykowski C, Mayernik J, Lim S, Groopman J, Grossman L, Wogan G, Yeung A. Repair of aflatoxin B1 DNA adducts by the UvrABC endonuclease of Escherichia coli. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53055-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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19
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Pendergrast PS, Chen Y, Ebright YW, Ebright RH. Determination of the orientation of a DNA binding motif in a protein-DNA complex by photocrosslinking. Proc Natl Acad Sci U S A 1992; 89:10287-91. [PMID: 1332042 PMCID: PMC50323 DOI: 10.1073/pnas.89.21.10287] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We have developed a straightforward biochemical method to determine the orientation of the DNA binding motif of a sequence-specific DNA binding protein relative to the DNA site in the protein-DNA complex. The method involves incorporation of a photoactivatable crosslinking agent at a single site within the DNA binding motif of the sequence-specific DNA binding protein, formation of the derivatized protein-DNA complex, UV-irradiation of the derivatized protein-DNA complex, and determination of the nucleotide(s) at which crosslinking occurs. We have applied the method to catabolite gene activator protein (CAP). We have constructed and analyzed two derivatives of CAP: one having a phenyl azide photoactivatable crosslinking agent at amino acid 2 of the helix-turn-helix motif of CAP, and one having a phenyl azide photoactivatable crosslinking agent at amino acid 10 of the helix-turn-helix motif of CAP. The results indicate that amino acid 2 of the helix-turn-helix motif is close to the top-strand nucleotides of base pairs 3 and 4 of the DNA half site in the CAP-DNA complex, and that amino acid 10 of the helix-turn-helix motif is close to the bottom-strand nucleotide of base pair 10 of the DNA half site in the CAP-DNA complex. The results define unambiguously the orientation of the helix-turn-helix motif relative to the DNA half site in the CAP-DNA complex. Comparison of the results to the crystallographic structure of the CAP-DNA complex [Schultz, S., Shields, S. & Steitz, T. (1991) Science 253, 1001-1007] indicates that the method provides accurate, high-resolution proximity and orientation information.
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Affiliation(s)
- P S Pendergrast
- Department of Chemistry, Rutgers University, New Brunswick, NJ 08855
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20
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Abstract
For many years, epidemiological studies have demonstrated a strong link between chronic hepatitis B virus (HBV) infection and the development of primary hepatocellular carcinoma (PHC). Other hepatocarcinogens such as hepatitis C virus and aflatoxin also contribute to hepatocarcinogenesis either in conjunction with HBV infection or alone. Cellular and molecular biological studies are providing explanations for the HBV-PHC relationship, and models are now being formulated to further test the relative importance of various factors such as viral DNA integration, activation of oncogenes, genetic instability, loss of tumor suppressor genes, and trans-activating properties of HBV to the pathogenesis of PHC. Further research will probably define more than a single mechanism whereby chronic HBV infection results in PHC.
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Affiliation(s)
- M Feitelson
- Department of Pathology and Cell Biology, Jefferson Medical School, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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21
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Cmarik J, Humphreys W, Bruner K, Lloyd R, Tibbetts C, Guengerich F. Mutation spectrum and sequence alkylation selectivity resulting from modification of bacteriophage M13mp18 DNA with S-(2-chloroethyl)glutathione. Evidence for a role of S-(2-N7-guanyl)ethyl)glutathione as a mutagenic lesion formed from ethylene dibromide. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)50479-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Trottier Y, Waithe WI, Anderson A. Kinds of mutations induced by aflatoxin B1 in a shuttle vector replicating in human cells transiently expressing cytochrome P4501A2 cDNA. Mol Carcinog 1992; 6:140-7. [PMID: 1326989 DOI: 10.1002/mc.2940060209] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Transient expression of rat liver cytochrome P450lA2 cDNA was combined with the use of a shuttle vector as a mutational target to determine the frequency and types of mutation caused by the conversion of aflatoxin B1 into genotoxic metabolites within human cells. Ad293 cells were first transfected with p91-lA2, a rat liver P450lA2 cDNA expression vector, or with p91-lA2(i) (a control vector that has the P450 cDNA in the inverted orientation) and incubated for 24 h to permit P450lA2 accumulation. Cells were then transfected with the pS189 shuttle-vector plasmid, which carries the Escherichia coli supF gene as a mutational target, and incubated for a further 24 h in the presence of aflatoxin B1 to permit promutagen activation and pS189 replication. In shuttle vectors replicated in p91-lA2-transfected cells, the supF point-mutation frequency increased with increasing concentration of aflatoxin B1. This frequency was nine to 23 times greater than the background point-mutation frequency obtained with aflatoxin B1-treated control (p91-lA2(i)-transfected) cells. The large majority of the aflatoxin B1-induced supF point mutations were base substitutions, mostly G:C----T:A transversions. This mutagenesis system permits the molecular analysis of mutations induced by specific P450/promutagen pairs in a shuttle vector replicating in human cells and will permit the investigation of host cell mechanisms involved in the generation of these mutations.
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Affiliation(s)
- Y Trottier
- Centre de recherche en cancérologie, Université Laval, L'Hôtel-Dieu de Québec, Canada
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23
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Fushimi S, Mineura K, Terada K, Kowada M. Distribution of DNA cleavages induced by bleomycin and neocarzinostatin in a defined sequence of rat glioma cells. Acta Oncol 1992; 31:353-7. [PMID: 1377921 DOI: 10.3109/02841869209108185] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
We have demonstrated the usefulness of a highly reiterated sequence of rat DNA as a probe sequence for evaluating the effect of bleomycin (BLM) and neocarzinostatin (NCS) at the level of individual nucleotides. The 370 base pairs (bp) DNA fragment, purified from rat glioma C6 cells after Hind III digestion, was labeled with 32P at either the 3'- or the 5'-ends and then divided into 167 bp and 203 bp by Hae III. These end-labeled DNA fragments were reacted in vitro with BLM or NCS, and electrophoresed on the denaturating 8% polyacrylamide gels according to Maxam and Gilbert's sequencing protocol. BLM created DNA strand breaks at the guanine-cytosine and guanine-thymine (5'----3') sequences, and NCS cleaved DNA at the position of thymines and adenines. The highly reiterated sequence of rat brain tumor DNA therefore provides adequate knowledge of DNA damages induced by BLM and NCS.
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Affiliation(s)
- S Fushimi
- Dept. of Neurosurgery, Akita University School of Medicine, Japan
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24
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Said B, Shank RC. Nearest neighbor effects on carcinogen binding to guanine runs in DNA. Nucleic Acids Res 1991; 19:1311-6. [PMID: 1903201 PMCID: PMC333859 DOI: 10.1093/nar/19.6.1311] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
A synthetic DNA fragment was constructed to determine the effect of 5' and 3' neighbors of guanine runs on the binding of chemical carcinogens. Determinations were made on the relative intensity of reactivity between aflatoxin B1 or benzo(a)pyrene and methylnitrosourea or 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea with various guanine positions in an endlabeled DNA fragment of known sequence. After reaction, the fragments were depurinated to produce strand breaks to allow Maxam and Gilbert sequencing for guanine positions. Relative reaction intensities were compared densitometrically. 3' neighbors exerted greater influence on carcinogen binding than did 5' neighbors, the influence extended only to the adjacent guanine and depended upon the chemical nature of the carcinogen. In addition, the presence of one carcinogen adduct in the guanine run influenced the formation of a subsequent adduct when the DNA was exposed to a second carcinogen, and this effect also depended on the nature of the second carcinogen. The results suggest that DNA adduct formation in the presence of multiple carcinogens is more complicated than an additive mechanism would suggest.
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Affiliation(s)
- B Said
- Department of Community and Environmental Medicine, University of California, Irvine 92717
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25
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An alternative and convenient strategy for generation of substantial quantities of singly 5′-32p-end-labeled double-stranded DNA for binding studies: Development of a protocol for examination of functional features of (+)-CC-1065 and the duocarmycins that contribute to their sequence-selective DNA alkylation properties. Tetrahedron 1991. [DOI: 10.1016/s0040-4020(01)81798-1] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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26
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Ellis WO, Smith JP, Simpson BK, Oldham JH. Aflatoxins in food: occurrence, biosynthesis, effects on organisms, detection, and methods of control. Crit Rev Food Sci Nutr 1991; 30:403-39. [PMID: 1910523 DOI: 10.1080/10408399109527551] [Citation(s) in RCA: 172] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Aflatoxins are secondary metabolites produced by species of Aspergilli, specifically Aspergillus flavus and Aspergillus parasiticus. These molds are ubiquitous in nature and grow on a variety of substrates, thereby producing aflatoxins. Aflatoxins are of great concern due to their biochemical and biological effects on living organisms. In this article, the occurrence of aflatoxins, their biosynthesis, factors influencing their production, their effects on living organisms, and methods of detection and control in food are reviewed. Future areas of research involving mathematical modeling of factors influencing aflatoxin production and alternative methods of control, such as modified atmosphere packaging, are also discussed.
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Affiliation(s)
- W O Ellis
- Dept. of Food Science and Agricultural Chemistry, McGill University, Montreal, Canada
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27
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Church KM, Wurdeman RL, Zhang Y, Chen FX, Gold B. N-(2-chloroethyl)-N-nitrosoureas covalently bound to nonionic and monocationic lexitropsin dipeptides. Synthesis, DNA affinity binding characteristics, and reactions with 32P-end-labeled DNA. Biochemistry 1990; 29:6827-38. [PMID: 2168742 DOI: 10.1021/bi00481a011] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The synthesis and characterization of a series of compounds that contain an N-alkyl-N-nitrosourea functionality linked to DNA minor groove binding bi- and tripeptides (lexitropsins or information-reading peptides) based on methylpyrrole-2-carboxamide subunits are described. The lexitropsins (lex) synthesized have either a 3-(dimethylamino)propyl or propyl substituent on the carboxyl terminus. The preferred DNA affinity binding sequences of these compounds were footprinted in 32P-end-labeled restriction fragments with methidiumpropyl-EDTA.Fe(II), and in common with other structural analogues, e.g., distamycin and netropsin, these nitrosoureas recognize A-T-rich runs. The affinity binding of the compound with the dimethylamino terminus, which is ionized at near-neutral pH, appeared stronger than that observed for the neutral dipeptide. The sequence specificity for DNA alkylation by (2-chloroethyl)nitrosourea-lex dipeptides (Cl-ENU-lex), with neutral and charged carboxyl termini, using 32P-end-labeled restriction fragments, was determined by the conversion of the adducted sites into single-strand breaks by sequential heating at neutral pH and exposure to base. The DNA cleavage sites were visualized by polyacrylamide gel electrophoresis and autoradiography. The alkylation of DNA by Cl-ENU-lex was compared to that by N-(2-chloroethyl)-N'-cyclohexyl-N-nitrosourea (CCNU), which has no DNA affinity binding properties. While all the Cl-ENU compounds generate DNA breaks as a consequence of the formation of N7-alkyl-guanine, the Cl-ENU-lex compounds induced, in a time- and dose-dependent fashion, intense DNA cleavage bands at adenine, cytosine, and thymine residues associated with affinity binding sites. These non-G cleavages induced by Cl-ENU-lex were inhibited by the coaddition of distamycin at concentrations that did not affect G alkylation break sites. CCNU, even at much higher concentrations, does not generate any similar detectable lesions at non-G sites. Therefore, linking the Cl-ENU moiety to minor groove binders is a viable strategy to qualitatively and quantitatively control the delivery and release of the ultimate DNA alkylating agent in a sequence-dependent fashion.
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Affiliation(s)
- K M Church
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha 68198-6805
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28
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Gupta PK, Johnson DL, Reid TM, Lee MS, Romano LJ, King CM. Mutagenesis by single site-specific arylamine-DNA adducts. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)47227-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Bonnett M, Taylor ER. The structure of the aflatoxin B1-DNA adduct at N7 of guanine. Theoretical intercalation and covalent adduct models. J Biomol Struct Dyn 1989; 7:127-49. [PMID: 2510767 DOI: 10.1080/07391102.1989.10507756] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Two theoretical models are proposed for the conformational structure of both intercalated and covalent adduct complexes of aflatoxin B1, designated AFB1, with N7 of guanine of DNA. The covalent adduct model requires the DNA to kink a minimum of 39 degrees about the covalent site of the C8 and N7 atoms comprising the bond of the covalent complex. The preference of AFB1 for specific G bases within a sequence of GC content followed that of experimental studies with the added feature that for binding to the third G base of a tetramer sequence from the 3'-end, the AFB1 displayed enhanced binding at the 3' site of the targeted guanosine. Binding of AFB1 to the second G base of a tetramer sequence from the 3'-end leads to preference for a 5' site of the targeted guanosine. Inhibition of AFB1's interaction with the targeted DNA in the presence of intercalated ethidium bromide is explained by these proposed models.
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Affiliation(s)
- M Bonnett
- Department of Chemistry, University of Southwestern Louisiana, Lafayette 70504-4370
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30
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Loechler EL, Teeter MM, Whitlow MD. Mapping the binding site of aflatoxin B1 in DNA: molecular modeling of the binding sites for the N(7)-guanine adduct of aflatoxin B1 in different DNA sequences. J Biomol Struct Dyn 1988; 5:1237-57. [PMID: 3152159 DOI: 10.1080/07391102.1988.10506467] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Aflatoxin B1 (AFB1), a potent mutagen and carcinogen, forms an adduct exclusively at the N(7) position of guanine, but the structure of this adduct in double stranded DNA is not known. Molecular modeling (using the program, PSFRODO) in conjunction with molecular mechanical calculation (using the program, AMBER) are used to assess the binding modes available to this AFB1 adduct. Two modes appear reasonable; in one the AFB1 moiety is intercalated between the base pair containing the adducted guanine and the adjacent base pair on the 5'-side in reference to the adducted guanine, while in the second it is bound externally in the major groove of DNA. Rotational flexibility appears feasible in the latter providing four, potential binding sites. Molecular modeling reveals that the binding sites around the reactive guanine in different sequences are not uniformly compatible for interaction with AFB1. As the sequence is changed, one particular external binding site would be expected to give a pattern of reactivities that is reasonably consistent with the observed sequence specificity of binding that AFB1 shows in its reaction with DNA (Benasutti, M., Ejadi, S., Whitlow, M. D. and Loechler, E. L. (1988) Biochemistry 27, 472-481). The AFB1 moiety is face-stacked in the major groove with its long axis approximately perpendicular to the helix axis. Favorable interactions are formed between exocyclic amino groups that project into the major groove on cytosines and adenines surrounding the reactive guanine, and oxygens in AFB1; unfavorable interactions involve van der Waals contacts between the methyl group on thymine and the AFB1 moiety. "Some of the sequence specificity of binding data can be rationalized more readily if it is assumed that 5'-GG-3' sequences adopt an A-DNA structure." Based upon molecular modeling/potential energy minimization calculation, it is difficult to predict how reactivity would change in different DNA sequences in the case of the intercalative binding mode; however, several arguments suggest that intercalation might not be favored. From these considerations a model of the structure for the transition state in reaction of AFB1 with DNA is proposed involving one particular external binding site.
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Affiliation(s)
- E L Loechler
- Department of Biology, Boston University, MA 02215
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31
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Stone MP, Gopalakrishnan S, Harris TM, Graves DE. Carcinogen-nucleic acid interactions: equilibrium binding studies of aflatoxins B1 and B2 with DNA and the oligodeoxynucleotide d(ATGCAT)2. J Biomol Struct Dyn 1988; 5:1025-41. [PMID: 3152158 DOI: 10.1080/07391102.1988.10506447] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Equilibrium binding is believed to play an important role in directing the subsequent covalent attachment of many carcinogens to DNA. We have utilized UV spectroscopy to examine the non-covalent interactions of aflatoxin B1 and B2 with calf thymus DNA, poly(dAdT):poly(dAdT), and poly(dGdC):poly(dGdC), and have utilized NMR spectroscopy to examine non-covalent interactions of aflatoxin B2 with the oligodeoxynucleotide d(ATGCAT)2. UV-VIS binding isotherms suggest a greater binding affinity for calf thymus DNA and poly(dAdT):poly(dAdT) than for poly(dGdC):poly(dGdC). Scatchard analysis of aflatoxin B1 binding to calf thymus DNA in 0.1 M NaCl buffer indicates that binding of the carcinogen at levels of bound aflatoxin less than 1 carcinogen per 200 base pairs occurs with positive cooperativity. The cooperative binding effect is dependent on the ionic strength of the medium; when the NaCl concentration is reduced to 0.01 M, positive cooperativity is observed at carcinogen levels less than 1 carcinogen per 500 base pairs. The Scatchard data may be fit using a "two-site" binding model [L.S. Rosenberg, M.J. Carvlin, and T.R. Krugh, Biochemistry 25, 1002-1008 (1986)]. This model assumes two independent sets of binding sites on the DNA lattice, one a high affinity site which binds the carcinogen with positive cooperativity, the second consisting of lower affinity binding sites to which non-specific binding occurs. NMR analysis of aflatoxin B2 binding to d(ATGCAT)2 indicates that the aflatoxin B2/oligodeoxynucleotide complex is in fast exchange on the NMR time scale. Upfield chemical shifts of 0.1-0.5 ppm are observed for the aflatoxin B2 4-OCH3, H5, and H6a protons. Much smaller chemical shift changes (less than or equal to 0.06 ppm) are observed for the oligodeoxynucleotide protons. The greatest effect for the oligodeoxynucleotide protons is observed for the adenine H2 protons, located in the minor groove. Nonselective T1 experiments demonstrate a 15-25% decrease in the relaxation time for the adenine H2 protons when aflatoxin B2 is added to the solution. This result suggests that aflatoxin B2 protons in the bound state may be in close proximity to these protons, providing a source of dipolar relaxation. Further experiments are in progress to probe the nature of the aflatoxin B1 and B2 complexes with polymeric DNA and oligodeoxynucleotides, and to establish the relationship between the non-covalent DNA-carcinogen complexes observed in these experiments, and covalent aflatoxin B1-guanine N7 DNA adducts.
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Affiliation(s)
- M P Stone
- Department of Chemistry, Vanderbilt University Nashville, Tennessee 37235
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Mattes WB, Hartley JA, Kohn KW. DNA sequence selectivity of guanine-N7 alkylation by nitrogen mustards. Nucleic Acids Res 1986; 14:2971-87. [PMID: 3960738 PMCID: PMC339715 DOI: 10.1093/nar/14.7.2971] [Citation(s) in RCA: 182] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Nitrogen mustards alkylate DNA primarily at the N7 position of guanine. Using an approach analogous to that of the Maxam-Gilbert procedure for DNA sequence analysis, we have examined the relative frequencies of alkylation for a number of nitrogen mustards at different guanine-N7 sites on a DNA fragment of known sequence. Most nitrogen mustards were found to have similar patterns of alkylation, with the sites of greatest alkylation being runs of contiguous guanines, and relatively weak alkylation at isolated guanines. Uracil mustard and quinacrine mustard, however, were found to have uniquely enhanced reaction with at least some 5'-PyGCC-3' and 5'-GT-3' sequences, respectively. In addition, quinacrine mustard showed a greater reaction at runs of contiguous guanines than did other nitrogen mustards, whereas uracil mustard showed little preference for these sequences. A comparison of the sequence-dependent variations of molecular electrostatic potential at the N7-position of guanine with the sequence dependent variations of alkylation intensity for mechlorethamine and L-phenylalanine mustard showed a good correlation in some regions of the DNA, but not others. It is concluded that electrostatic interactions may contribute strongly to the reaction rates of cationic compounds such as the reactive aziridinium species of nitrogen mustards, but that other sequence selectivities can be introduced in different nitrogen mustard derivatives.
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Hsieh DP. Biological reactive intermediates of mycotoxins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1986; 197:597-610. [PMID: 3094340 DOI: 10.1007/978-1-4684-5134-4_56] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The various reactions involved in the formation and actions of biological reactive intermediates of AFB1 are undoubtedly common to the wide variety of mycotoxins. The structural diversity of mycotoxins and their widespread occurrence in nature has made them a significant class of model environmental toxicants for mode of action studies. Identification of the reactive intermediates of prototype mycotoxins and elucidation of their reactions with molecular receptors will provide information useful for the design of antidotes of other remedial measures and for a better understanding of the mechanisms of action of comparable environmental toxicants. This type of studies will also permit the more precise biochemical analyses to be applied to the assessment of health risk due to exposure to mycotoxins.
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Wogan GN, McMahon G. Intragenomic localization of carcinogen-DNA damage. BASIC LIFE SCIENCES 1986; 38:127-34. [PMID: 3741326 DOI: 10.1007/978-1-4615-9462-8_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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Doetsch PW, Chan GL, Haseltine WA. T4 DNA polymerase (3'-5') exonuclease, an enzyme for the detection and quantitation of stable DNA lesions: the ultraviolet light example. Nucleic Acids Res 1985; 13:3285-304. [PMID: 2987881 PMCID: PMC341235 DOI: 10.1093/nar/13.9.3285] [Citation(s) in RCA: 86] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Ultraviolet light irradiation of DNA results in the formation of two major types of photoproducts, cyclobutane dimers and 6-4' [pyrimidin-2'-one] -pyrimidine photoproducts. The enzyme T4 DNA polymerase possesses a 3' to 5' exonuclease activity and hydrolyzes both single and double stranded DNA in the absence of deoxynucleotide triphosphate substrates. Here we describe the use of T4 DNA polymerase associated exonuclease for the detection and quantitation of UV light-induced damage on both single and double stranded DNA. Hydrolysis of UV-irradiated single or double stranded DNA by the DNA polymerase associated exonuclease is quantitatively blocked by both cyclobutane dimers and (6-4) photoproducts. The enzyme terminates digestion of UV-irradiated DNA at the 3' pyrimidine of both cyclobutane dimers and (6-4) photoproducts. For a given photoproduct site, the induction of cyclobutane dimers was the same for both single and double stranded DNA. A similar relationship was also found for the induction of (6-4) photoproducts. These results suggest that the T4 DNA polymerase proofreading activity alone cannot remove these UV photoproducts present on DNA templates, but instead must function together with enzymes such as the T4 pyrimidine dimer-specific endonuclease in the repair of DNA photoproducts. The T4 DNA polymerase associated exonuclease should be useful for the analysis of a wide variety of bulky, stable DNA adducts.
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High ratio of alkali-sensitive lesions to total DNA modification induced by benzo(a)pyrene diol epoxide. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)90627-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Leadon SA, Zolan ME, Hanawalt PC. Restricted repair of aflatoxin B1 induced damage in alpha DNA of monkey cells. Nucleic Acids Res 1983; 11:5675-89. [PMID: 6412212 PMCID: PMC326306 DOI: 10.1093/nar/11.16.5675] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
We have investigated the processing of adducts formed by covalent binding of aflatoxin B1 (AFB1) to DNA in confluent cultures of African green monkey cells. Repair synthesis elicited by AFB1 adducts was deficient in alpha DNA sequences compared to that in bulk DNA, although the initial levels of modification were the same for these DNAs. The removal of the primary initial adduct, AFB1-N7-Guanine, was deficient in alpha DNA and the kinetics of its loss resembled those previously reported for removal from total DNA in xeroderma pigmentosum cells of complementation group A. Spontaneous loss of the AFB1 moiety or the concomitant loss of the guanine to yield an apurinic site account for these results. The formation of the more chemically stable secondary product, AFB1-triamino-Pyrimidine, occurred more rapidly and to a greater extent in alpha DNA than in bulk DNA, probably because of slower removal of the primary product. The excision repair patch size for AFB1 adducts in alpha DNA was only 10 nucleotides compared to 20 nucleotides for repair of AFB1 adducts in bulk DNA. Irradiation of cells with low doses of UV prior to or immediately after treatment with AFB1 increased the rate and extent of removal of AFB1 adducts from alpha DNA to the levels found in the bulk DNA, indicating that the formation of pyrimidine dimers or their repair may alter the chromatin structure of alpha DNA sufficiently to facilitate its repair.
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Abstract
Methods for determining sequence specificities of anticancer drugs, carcinogens, and mutagens which interact with natural DNA's are presented. For drugs which nick or covalently bind to DNA and thus leave a permanent record of their residence position on the helix, the sequences important in drug action can be readily determined. For agents which interact with DNA in an equilibrium fashion, "footprinting" analysis, a technique used to investigate protein-DNA binding, has proved to be useful in studying drug-DNA interactions. The sequence specificities of a number of small ligands which interact with natural DNA's are also presented.
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Muench KF, Misra RP, Humayun MZ. Sequence specificity in aflatoxin B1--DNA interactions. Proc Natl Acad Sci U S A 1983; 80:6-10. [PMID: 6218504 PMCID: PMC393298 DOI: 10.1073/pnas.80.1.6] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The activated form of aflatoxin B1 (AFB1) causes covalent modification primarily of guanine residues, leading to alkali-labile sites in DNA. A simple extension of the Maxam-Gilbert procedure for sequence analysis permits the identification of alkali-labile sites induced by AFB1 and determination of the frequency of alkali-labile AFB1 modifications at particular sites on a DNA fragment of known sequence. Using this strategy, we have investigated the influence of flanking nucleotide sequences on AFB1 modification in a number of DNA fragments of known sequence. Our results show that certain guanine residues in double-stranded DNA are preferentially attacked by AFB1 over others in a manner predictable from a knowledge of vicinal nucleotide sequences. The observed in vitro sequence specificity is independent of a number of tested parameters and is likely to occur in vivo.
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Royer-Pokora B, Gordon LK, Haseltine WA. Use of exonuclease III to determine the site of stable lesions in defined sequences of DNA: the cyclobutane pyrimidine dimer and cis and trans dichlorodiammine platinum II examples. Nucleic Acids Res 1981; 9:4595-609. [PMID: 6272211 PMCID: PMC327461 DOI: 10.1093/nar/9.18.4595] [Citation(s) in RCA: 126] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
A method to detect chemically stable lesions in DNA has been developed using Exonuclease III, a double strand specific nuclease, to digest 5'-end labeled DNA. The products, when analyzed on high resolution DNA sequencing gels, reveal the sites of DNA modification. Cyclobutane pyrimidine dimers induced by UV irradiation can be localized by comparison of the fragments produced by Exonuclease III digestion with fragments obtained after digestion of the DNA with UV specific endonuclease. The experiments demonstrate the Exonuclease III stops one base away from the cyclobutane pyrimidine dimers. Similar experiments with cis- and trans-dichlorodiammine-platinum (II) showed that modification of DNA by these agents also impede Exonuclease III digestion. In general the same stop sites were found for cis-and trans-platinum adducts. They occur at sites of guanine bases. Additional stop sites were found for cis-platinum at sites of adjacent guanine bases. These results are in agreement with the model that cis-platinum forms intrastrand guanine-guanine dimers, whereas trans-platinum does not.
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Groopman JD, Croy RG, Wogan GN. In vitro reactions of aflatoxin B1-adducted DNA. Proc Natl Acad Sci U S A 1981; 78:5445-9. [PMID: 6795633 PMCID: PMC348762 DOI: 10.1073/pnas.78.9.5445] [Citation(s) in RCA: 80] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The chemical stability of aflatoxin B1 bound to calf thymus DNA was studied over a 48-hour exposure to phosphate buffers at pH 6.8-8.0 (37 degrees C). During this time, aliquots of the aflatoxin B1-modified DNA were acid-hydrolyzed and analyzed for the presence of 2,3-dihydro-2-(N7-guanyl)-3-hydroxyflatoxin B1, 2,3-dihydro-2,3-dihydroxy-aflatoxin B1, and the tentatively identified, 2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl-3-hydroxyflatoxin B1 and 2,3-dihydro-2-(8,9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxyaflatoxin B1. Initial experiments determined the stability of 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 in DNA at levels of modification of one residue per 60 and 1500 nucleotides. The acid-hydrolysis products obtained from these modified nucleic acids were qualitatively similar, but their proportional concentrations were different. These quantitative differences were dependent upon both pH and the initial level of modification of the DNA. During the first 6 hr of incubation, under all conditions examined, the formation of 2,3-dihydro-2,3-dihydroxyaflatoxin B1 was responsible for the initial decrease of the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 adduct in DNA. After 48 hr of incubation at pH 7.0, the major reaction of the modified DNA was depurination of the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 adduct. However, at pH 8.0, the predominant reaction product formed in 48 hr was the putative 2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl)-3-hydroxy-aflatoxin B1. The putative DNA-bound products resulting from the elimination of the positive charge in the imidazole ring of the aflatoxin-N7-guanine adduct [2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl)-3-hydroxy-aflatoxin B1 and 2,3-dihydro-2-(8,9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxyaflatoxin B1] were found to be stable in DNA for at least 24 hr at both pH 6.8 and 7.4. Taken together with observed patterns of stability of aflatoxin B1 adducts in vivo, these observations strongly suggest the involvement of enzymatic repair processes in removal of the N7-guanyl adduct and also emphasize the possible biological significance of the stable imidazole ring-opened adduct.
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Autrup H, Schwartz RD, Essigmann JM, Smith L, Trump BF, Harris CC. Metabolism of aflatoxin B1, benzo[a]pyrene, and 1,2-dimethylhydrazine by cultured rat and human colon. TERATOGENESIS, CARCINOGENESIS, AND MUTAGENESIS 1981; 1:3-13. [PMID: 6119799 DOI: 10.1002/tcm.1770010103] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
A model system for comparing carcinogen metabolism between human and rat colon has been developed. Tissue explants maintained under chemically defined conditions were treated with radioactively labeled carcinogens. After incubation for 24 hours, the binding of radioactive carcinogen to DNA was quantitated. Further, the carcinogen-DNA adducts and carcinogen metabolites released into the culture media were identified. Both human and rat colon activate benzo[a]pyrene (BP), aflatoxin B1 (AFB), and 1,2-dimethylhydrazine (DMH) into chemical species that reacted with cellular macromolecules. When human and rat colons were compared, the metabolism of AFB and DMH was qualitatively similar - the same major carcinogen-DNA adducts and metabolic profile. However, the mean binding levels of DMH and AFB to colonic DNA were higher in rats than in humans. BP-guanine adducts were the major adducts formed by both rat and human colonic DNA. However, BP-adenine adducts were observed in rat colonic DNA but not in human colonic DNA. A positive correlation for the binding of BP and DMH to human DNA of different individuals was observed, but no correlation was found between BP and AFB. The data suggest that similar enzyme systems may be involved in the metabolism of BP and DMH, whereas different enzymes might be involved in the metabolic activation of AFB.
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Grunberger D, Weinstein IB. Biochemical effects of the modification of nucleic acids by certain polycyclic aromatic carcinogens. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1980; 23:105-49. [PMID: 95052 DOI: 10.1016/s0079-6603(08)60132-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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