1
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Hartmann P, Schnabl B. Fungal infections and the fungal microbiome in hepatobiliary disorders. J Hepatol 2023; 78:836-851. [PMID: 36565724 PMCID: PMC10033447 DOI: 10.1016/j.jhep.2022.12.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 12/05/2022] [Accepted: 12/07/2022] [Indexed: 12/24/2022]
Abstract
Liver and biliary diseases affect more than a billion people worldwide, with high associated morbidity and mortality. The impact of the intestinal bacterial microbiome on liver diseases has been well established. However, the fungal microbiome, or mycobiome, has been overlooked for a long time. Recently, several studies have shed light on the role of the mycobiome in the development and progression of hepatobiliary diseases. In particular, the fungal genus Candida has been found to be involved in the pathogenesis of multiple hepatobiliary conditions. Herein, we compare colonisation and infection, describe mycobiome findings in the healthy state and across the various hepatobiliary conditions, and point toward communalities. We detail how quantitation of immune responses to fungal antigens can be employed to predict disease severity, e.g. using antibodies to Saccharomyces cerevisiae or specific anti-Candida albicans antibodies. We also show how fungal products (e.g. beta-glucans, candidalysin) activate the host's immune system to exacerbate liver and biliary diseases. Finally, we describe how the gut mycobiome can be modulated to ameliorate hepatobiliary conditions.
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Affiliation(s)
- Phillipp Hartmann
- Department of Medicine, University of California San Diego, La Jolla, CA, USA; Department of Pediatrics, University of California San Diego, La Jolla, CA, USA; Division of Gastroenterology, Hepatology & Nutrition, Rady Children's Hospital San Diego, San Diego, CA, USA
| | - Bernd Schnabl
- Department of Medicine, University of California San Diego, La Jolla, CA, USA; Department of Medicine, VA San Diego Healthcare System, San Diego, CA, USA.
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Pujari SS, Jokipii Krueger CC, Chao C, Hutchins S, Hurben AK, Boysen G, Tretyakova N. DEB-FAPy-dG Adducts of 1,3-Butadiene: Synthesis, Structural Characterization, and Formation in 1,2,3,4-Diepoxybutane Treated DNA. Chemistry 2022; 28:e202103245. [PMID: 34767297 PMCID: PMC10603587 DOI: 10.1002/chem.202103245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Indexed: 11/10/2022]
Abstract
Metabolic activation of the human carcinogen 1,3-butadiene (BD) by cytochrome 450 monooxygenases gives rise to a genotoxic diepoxide, 1,2,3,4-diepoxybutane (DEB). This reactive electrophile alkylates guanine bases in DNA to produce N7-(2-hydroxy-3,4-epoxy-1-yl)-dG (N7-DE-dG) adducts. Because of the positive charge at the N7 position of the purine heterocycle, N7-DEB-dG adducts are inherently unstable and can undergo spontaneous depurination or base-catalyzed imidazole ring opening to give N6 -[2-deoxy-D-erythro-pentofuranosyl]-2,6-diamino-3,4-dihydro-4-oxo-5-N-1-(oxiran-2-yl)propan-1-ol-formamidopyrimidine (DEB-FAPy-dG) adducts. Here we report the first synthesis and structural characterization of DEB-FAPy-dG adducts. Authentic standards of DEB-FAPy-dG and its 15 N3 -labeled analogue were used for the development of a quantitative nanoLC-ESI+ -HRMS/MS method, allowing for adduct detection in DEB-treated calf thymus DNA. DEB-FAPy-dG formation in DNA was dependent on DEB concentration and pH, with higher numbers observed under alkaline conditions.
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Affiliation(s)
- Suresh S Pujari
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Caitlin C Jokipii Krueger
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Christopher Chao
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Spencer Hutchins
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Alexander K Hurben
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Gunnar Boysen
- Department of Environmental and Occupational Health and the Winthrop P Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, 4301 West Markham St., Slot 820, Little Rock, AR, 72205, USA
| | - Natalia Tretyakova
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
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Groehler AS, Najjar D, Pujari SS, Sangaraju D, Tretyakova NY. N 6-(2-Deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine Adducts of 1,3-Butadiene: Synthesis, Structural Identification, and Detection in Human Cells. Chem Res Toxicol 2018; 31:885-897. [PMID: 30016111 DOI: 10.1021/acs.chemrestox.8b00123] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
1,3-Butadiene (BD) is an environmental and occupational toxicant classified as a human carcinogen. BD is metabolically activated by cytochrome P450 monooxygenases to 3,4-epoxy-1-butene (EB), which alkylates DNA to form a range of nucleobase adducts. Among these, the most abundant are the hydrolytically labile N7-guanine adducts such as N7-(2-hydroxy-3-buten-1-yl)-guanine (N7-EB-dG). We now report that N7-EB-dG can be converted to the corresponding ring open N6-(2-deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine (EB-Fapy-dG) adducts. EB-Fapy-dG lesions were detected in EB-treated calf thymus DNA and in EB-treated mammalian cells using quantitative isotope dilution nanoLC-ESI+-MS/MS. EB-Fapy-dG adduct formation in EB-treated calf thymus DNA was concentration dependent and was greatly accelerated at an increased pH. EB-FAPy-dG adduct amounts were 2-fold higher in base excision repair-deficient NEIL1-/- mouse embryonic fibroblasts (MEF) as compared to isogenic controls (NEIL1+/+), suggesting that this lesion may be a substrate for NEIL1. Furthermore, NEIL1-/- cells were sensitized to EB treatment as compared to NEIL1+/+ fibroblasts. Overall, our results indicate that ring-opened EB-FAPy-dG adducts form under physiological conditions, prompting future studies to determine their contributions to genotoxicity and mutagenicity of BD.
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Affiliation(s)
- Arnold S Groehler
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Dominic Najjar
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Suresh S Pujari
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Dewakar Sangaraju
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Natalia Y Tretyakova
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
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4
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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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Li L, Brown KL, Ma R, Stone MP. DNA Sequence Modulates Geometrical Isomerism of the trans-8,9- Dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)- 9-hydroxy Aflatoxin B1 Adduct. Chem Res Toxicol 2016; 28:225-37. [PMID: 25587868 PMCID: PMC4332041 DOI: 10.1021/tx5003832] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
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Aflatoxin
B1 (AFB1), a mycotoxin produced
by Aspergillus flavus, is oxidized
by cytochrome P450 enzymes to aflatoxin B1-8,9-epoxide,
which alkylates DNA at N7-dG. Under basic conditions,
this N7-dG adduct rearranges to yield the trans-8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxy
aflatoxin B1 (AFB1–FAPY) adduct. The
AFB1–FAPY adduct exhibits geometrical isomerism
involving the formamide moiety. NMR analyses of duplex oligodeoxynucleotides
containing the 5′-XA-3′, 5′-XC-3′, 5′-XT-3′,
and 5′-XY-3′ sequences (X = AFB1–FAPY;
Y = 7-deaza-dG) demonstrate that the equilibrium between E and Z isomers is controlled by major groove hydrogen
bonding interactions. Structural analysis of the adduct in the 5′-XA-3′
sequence indicates the preference of the E isomer
of the formamide group, attributed to formation of a hydrogen bond
between the formyl oxygen and the N6 exocyclic amino group
of the 3′-neighbor adenine. While the 5′-XA-3′
sequence exhibits the E isomer, the 5′-XC-3′
sequence exhibits a 7:3 E:Z ratio
at equilibrium at 283 K. The E isomer is favored
by a hydrogen bond between the formyl oxygen and the N4-dC exocyclic amino group of the 3′-neighbor cytosine. The
5′-XT-3′ and 5′-XY-3′ sequences cannot
form such a hydrogen bond between the formyl oxygen and the 3′-neighbor
T or Y, respectively, and in these sequence contexts the Z isomer is favored. Additional equilibria between α and β
anomers and the potential to exhibit atropisomers about the C5–N5 bond do not depend upon sequence. In each
of the four DNA sequences, the AFB1–FAPY adduct
maintains the β deoxyribose configuration. Each of these four
sequences feature the atropisomer of the AFB1 moiety that
is intercalated above the 5′-face of the damaged guanine. This
enforces the Ra axial conformation for
the C5–N5 bond.
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Pollock BH, Elmore S, Romoser A, Tang L, Kang MS, Xue K, Rodriguez M, Dierschke NA, Hayes HG, Hansen HA, Guerra F, Wang JS, Phillips T. Intervention trial with calcium montmorillonite clay in a south Texas population exposed to aflatoxin. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2016; 33:1346-54. [PMID: 27321368 DOI: 10.1080/19440049.2016.1198498] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
South Texas currently has the highest incidence of hepatocellular carcinoma (HCC) in the United States, a disease that disproportionately affects Latino populations in the region. Aflatoxin B1 (AFB1) is a potent liver carcinogen that has been shown to be present in a variety of foods in the United States, including corn and corn products. Importantly, it is a dietary risk factor contributing to a higher incidence of HCC in populations frequently consuming AFB1-contaminated diets. In a randomised double-blind placebo controlled trial, we evaluated the effects of a 3-month administration of ACCS100 (refined calcium montmorillonite clay) on serum AFB1-lysine adduct (AFB-Lys) level and serum biochemistry in 234 healthy men and women residing in Bexar and Medina counties, Texas. Participants recruited from 2012 to 2014 received either a placebo, 1.5 g or 3 g ACCS100 each day for 3 months, and no treatment during the fourth month. Adverse event rates were similar across treatment groups and no significant differences were observed for serum biochemistry and haematology parameters. Differences in levels of AFB-Lys at 1, 3 and 4 months were compared between placebo and active treatment groups. Although serum AFB-Lys levels were decreased by month 3 for both treatment groups, the low dose was the only treatment that was significant (p = 0.0005). In conclusion, the observed effect in the low-dose treatment group suggests that the use of ACCS100 may be a viable strategy to reduce dietary AFB1 bioavailability during aflatoxin outbreaks and potentially in populations chronically exposed to this carcinogen.
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Affiliation(s)
- Brad H Pollock
- a Department of Public Health Sciences , University of California , Davis , CA , USA.,b Department of Epidemiology and Biostatistics , University of Texas Health Science Center at San Antonio , San Antonio , TX , USA
| | - Sarah Elmore
- c Interdisciplinary Faculty of Toxicology , Texas A&M University , College Station , TX , USA
| | - Amelia Romoser
- c Interdisciplinary Faculty of Toxicology , Texas A&M University , College Station , TX , USA
| | - Lili Tang
- d Department of Environmental Health Science, College of Public Health , University of Georgia , Athens , GA , USA
| | - Min-Su Kang
- d Department of Environmental Health Science, College of Public Health , University of Georgia , Athens , GA , USA
| | - Kathy Xue
- d Department of Environmental Health Science, College of Public Health , University of Georgia , Athens , GA , USA
| | - Marisa Rodriguez
- b Department of Epidemiology and Biostatistics , University of Texas Health Science Center at San Antonio , San Antonio , TX , USA
| | - Nicole A Dierschke
- b Department of Epidemiology and Biostatistics , University of Texas Health Science Center at San Antonio , San Antonio , TX , USA
| | - Holly G Hayes
- e Arnold School of Public Health , University of South Carolina , Columbia , SC , USA
| | - H Andrew Hansen
- f Department of Clinical Surgery , Texas A&M Health Sciences Center , College Station , TX , USA
| | - Fernando Guerra
- b Department of Epidemiology and Biostatistics , University of Texas Health Science Center at San Antonio , San Antonio , TX , USA
| | - Jia-Sheng Wang
- d Department of Environmental Health Science, College of Public Health , University of Georgia , Athens , GA , USA
| | - Timothy Phillips
- c Interdisciplinary Faculty of Toxicology , Texas A&M University , College Station , TX , USA
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7
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Delire B, Stärkel P. The Ras/MAPK pathway and hepatocarcinoma: pathogenesis and therapeutic implications. Eur J Clin Invest 2015; 45:609-23. [PMID: 25832714 DOI: 10.1111/eci.12441] [Citation(s) in RCA: 162] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 03/27/2015] [Indexed: 12/11/2022]
Abstract
BACKGROUND Hepatocellular carcinoma (HCC) is still a major health problem, often diagnosed at an advanced stage. The multikinase inhibitor sorafenib is to date the sole approved systemic therapy. Several signalling pathways are implicated in tumour development and progression. Among these pathways, the Ras/MAPK pathway is activated in 50-100% of human HCCs and is correlated with a poor prognosis. The aim of this work was to review the main intracellular mechanisms leading to aberrant Ras pathway activation in HCC and the potential therapeutic implications. MATERIALS AND METHODS This review is based on the material found on PubMed up to December 2014. 'Ras signaling, Ras dysregulation, Ras inhibition, MAPK pathway, cancer, hepatocarcinoma and liver cancer' alone or in combination were the main terms used for online research. RESULTS Multiple mechanisms lead to the deregulation of the Ras pathway in liver cancer. Ras and Raf gene mutations are rare events in human hepatocarcinogenesis in contrast to experimental models in rodents. Downregulation of several Ras/MAPK pathway inhibitors such as GAPs, RASSF proteins, DUSP1, Sprouty and Spred proteins is largely implicated in the aberrant activation of this pathway in the context of wild-type Ras and Raf genes. Epigenetic or post-transcriptional mechanisms lead to the downregulation of these tumour suppressor genes. CONCLUSION Ras/MAPK pathway effectors may be considered as potential therapeutic targets in the field of HCC. In particular after the arrival of sorafenib, more Ras/MAPK inhibitors have emerged and are still in preclinical or clinical investigation for HCC therapy.
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Affiliation(s)
- Bénédicte Delire
- Laboratory of Hepato-Gastroenterology, Institut de Recherche Expérimentale et Clinique (IREC), Catholic University of Louvain, Brussels, Belgium
| | - Peter Stärkel
- Laboratory of Hepato-Gastroenterology, Institut de Recherche Expérimentale et Clinique (IREC), Catholic University of Louvain, Brussels, Belgium.,Department of Gastroenterology, Saint-Luc Academic Hospital and Institute of Clinical Research, Catholic University of Louvain, Brussels, Belgium
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Kar P. Risk factors for hepatocellular carcinoma in India. J Clin Exp Hepatol 2014; 4:S34-42. [PMID: 25755609 PMCID: PMC4284237 DOI: 10.1016/j.jceh.2014.02.155] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 02/19/2014] [Indexed: 12/12/2022] Open
Abstract
Hepatocellular carcinoma (HCC) is an important cause of death all over the world, more so in Asia and Africa. The representative data on epidemiology of HCC in India is very scanty and cancer is not a reportable disease in India and the cancer registries in India are mostly urban. 45 million people who are suffering from chronic Hepatitis B virus (HBV) infection and approximately 15 million people who are afflicted with chronic Hepatitis C virus (HCV) infection in India. HBV and HCV infection is considered an important etiologic factor in HCC. Positive association between HCC and consumption of alcohol where alcohol contribute as a cofactor for hepatotoxins and hepatitis viruses. Aflatoxin contamination in the diets, Hepatitis B virus infection and liver cirrhosis in Andhra Pradesh, India and direct chronic exposure to aflatoxins was shown to cause liver cirrhosis. Cirrhosis of liver of any cause lead to develop about 70%-90% of HCC. Aflatoxin interact synergistically with Hepatitis B virus (HBV)/Hepatitis C virus (HCV) infection which increase the risk of HCC. HBV infection, HBV infection with Aflatoxin exposure, viral infection and alcohol consumption leading to overt cirrhosis of the liver, alcohol consumption leading to cirrhosis of the liver with viral infection are the predominant risk factor for the development of HCC. HCV and alcohol are also associated with HCC in India. Indians develop diabetes at younger age, Asians have strong genetic susceptibility for type II diabetes. Diabetes mellitus is identified as a risk factor for HCC. Prevention of viral infection by universal vaccination against hepatitis virus, HCC surveillance program, preventing alcoholic liver diseases, fungal contamination of grains and ground crops to prevent basically Aflatoxin exposure are important measures to prevent liver diseases and HCC among those at risk.
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Key Words
- AFB1, aflatoxin B1
- DM, diabetes mellitus
- GT, glucose tolerance
- HBV, Hepatitis B virus
- HBsAg, hepatitis-B surface antigen
- HCC
- HCC, hepatocellular carcinoma
- HCV, Hepatitis C virus
- IARC, International Agency for Research on Cancer
- NAFLD, non-alcoholic fatty liver disease
- RR, relative risk
- aflatoxin
- risk factor
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Affiliation(s)
- Premashis Kar
- Department of Medicine, Maulana Azad Medical College, University of Delhi, New Delhi 110002, India
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9
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Stone MP, Huang H, Brown KL, Shanmugam G. Chemistry and structural biology of DNA damage and biological consequences. Chem Biodivers 2011; 8:1571-615. [PMID: 21922653 PMCID: PMC3714022 DOI: 10.1002/cbdv.201100033] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The formation of adducts by the reaction of chemicals with DNA is a critical step for the initiation of carcinogenesis. The structural analysis of various DNA adducts reveals that conformational and chemical rearrangements and interconversions are a common theme. Conformational changes are modulated both by the nature of adduct and the base sequences neighboring the lesion sites. Equilibria between conformational states may modulate both DNA repair and error-prone replication past these adducts. Likewise, chemical rearrangements of initially formed DNA adducts are also modulated both by the nature of adducts and the base sequences neighboring the lesion sites. In this review, we focus on DNA damage caused by a number of environmental and endogenous agents, and biological consequences.
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Affiliation(s)
- Michael P Stone
- Department of Chemistry, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN 37235, USA.
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Banerjee S, Brown KL, Egli M, Stone MP. Bypass of aflatoxin B1 adducts by the Sulfolobus solfataricus DNA polymerase IV. J Am Chem Soc 2011; 133:12556-68. [PMID: 21790157 PMCID: PMC3154525 DOI: 10.1021/ja2015668] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Aflatoxin B(1) (AFB(1)) is oxidized to an epoxide in vivo, which forms an N7-dG DNA adduct (AFB(1)-N7-dG). The AFB(1)-N7-dG can rearrange to a formamidopyrimidine (AFB(1)-FAPY) derivative. Both AFB(1)-N7-dG and the β-anomer of the AFB(1)-FAPY adduct yield G→T transversions in Escherichia coli, but the latter is more mutagenic. We show that the Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4) bypasses AFB(1)-N7-dG in an error-free manner but conducts error-prone replication past the AFB(1)-FAPY adduct, including misinsertion of dATP, consistent with the G→T mutations observed in E. coli. Three ternary (Dpo4-DNA-dNTP) structures with AFB(1)-N7-dG adducted template:primers have been solved. These demonstrate insertion of dCTP opposite the AFB(1)-N7-dG adduct, and correct vs incorrect insertion of dATP vs dTTP opposite the 5'-template neighbor dT from a primed AFB(1)-N7-dG:dC pair. The insertion of dTTP reveals hydrogen bonding between the template N3 imino proton and the O(2) oxygen of dTTP, and between the template T O(4) oxygen and the N3 imino proton of dTTP, perhaps explaining why this polymerase does not efficiently catalyze phosphodiester bond formation from this mispair. The AFB(1)-N7-dG maintains the 5'-intercalation of the AFB(1) moiety observed in DNA. The bond between N7-dG and C8 of the AFB(1) moiety remains in plane with the alkylated guanine, creating a 16° inclination of the AFB(1) moiety with respect to the guanine. A binary (Dpo4-DNA) structure with an AFB(1)-FAPY adducted template:primer also maintains 5'-intercalation of the AFB(1) moiety. The β-deoxyribose anomer is observed. Rotation about the FAPY C5-N(5) bond orients the bond between N(5) and C8 of the AFB(1) moiety out of plane in the 5'-direction, with respect to the FAPY base. The formamide group extends in the 3'-direction. This improves stacking of the AFB(1) moiety above the 5'-face of the FAPY base, as compared to the AFB(1)-N7-dG adduct. Ternary structures with AFB(1)-β-FAPY adducted template:primers show correct vs incorrect insertion of dATP vs dTTP opposite the 5'-template neighbor dT from a primed AFB(1)-β-FAPY:dC pair. For dATP, the oxygen atom of the FAPY formamide group participates in a water-mediated hydrogen bond with Arg332. The insertion of dTTP yields a structure similar to that observed for the AFB(1)-N7-dG adduct. The differential accommodation of these AFB(1) adducts within the active site may, in part, modulate lesion bypass.
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Affiliation(s)
- Surajit Banerjee
- Department of Chemistry, Center in Molecular Toxicology, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
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11
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Zhang YJ. Interactions of chemical carcinogens and genetic variation in hepatocellular carcinoma. World J Hepatol 2010; 2:94-102. [PMID: 21160980 PMCID: PMC2999273 DOI: 10.4254/wjh.v2.i3.94] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 01/16/2010] [Accepted: 01/23/2010] [Indexed: 02/06/2023] Open
Abstract
In the etiology of hepatocellular carcinoma (HCC), in addition to hepatitis B virus and hepatitis C virus infections, chemical carcinogens also play important roles. For example, aflatoxin B(1) (AFB(1)) epoxide reacts with guanine in DNA and can lead to genetic changes. In HCC, the tumor suppressor gene p53 codon 249 mutation is associated with AFB(1) exposure and mutations in the K-ras oncogene are related to vinyl chloride exposure. Numerous genetic alterations accumulate during the process of hepatocarcinogenesis. Chemical carcinogen DNA-adduct formation is the basis for these genetic changes and also a molecular marker which reflects exposure level and biological effects. Metabolism of chemical carcinogens, including their activation and detoxification, also plays a key role in chemical hepatocarcinogenesis. Cytochrome p450 enzymes, N-acetyltransferases and glutathione S-transferases are involved in activating and detoxifying chemical carcinogens. These enzymes are polymorphic and genetic variation influences biological response to chemical carcinogens. This genetic variation has been postulated to influence the variability in risk for HCC observed both within and across populations. Ongoing studies seek to fully understand the mechanisms by which genetic variation in response to chemical carcinogens impacts on HCC risk.
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Affiliation(s)
- Yu-Jing Zhang
- Yu-Jing Zhang, Department of Environmental Health Sciences, Mailman School of Public Health and Cancer Center of Columbia University, New York, NY 10032, United States
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12
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Brown KL, Voehler MW, Magee SM, Harris CM, Harris TM, Stone MP. Structural perturbations induced by the alpha-anomer of the aflatoxin B(1) formamidopyrimidine adduct in duplex and single-strand DNA. J Am Chem Soc 2010; 131:16096-107. [PMID: 19831353 PMCID: PMC2773149 DOI: 10.1021/ja902052v] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
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The guanine N7 adduct of aflatoxin B1exo-8,9-epoxide hydrolyzes to form the formamidopyrimidine (AFB-FAPY) adduct, which interconverts between α and β anomers. The β anomer is highly mutagenic in Escherichia coli, producing G → T transversions; it thermally stabilizes the DNA duplex. The AFB-α-FAPY adduct blocks replication; it destabilizes the DNA duplex. Herein, the structure of the AFB-α-FAPY adduct has been elucidated in 5′-d(C1T2A3T4X5A6T7T8C9A10)-3′·5′-d(T11G12A13A14T15C16A17T18A19G20)-3′ (X = AFB-α-FAPY) using molecular dynamics calculations restrained by NMR-derived distances and torsion angles. The AFB moiety intercalates on the 5′ face of the pyrimidine moiety at the damaged nucleotide between base pairs T4·A17 and X5·C16, placing the FAPY C5−N5 bond in the Ra axial conformation. Large perturbations of the ε and ζ backbone torsion angles are observed, and the base stacking register of the duplex is perturbed. The deoxyribose orientation shifts to become parallel to the FAPY base and displaced toward the minor groove. Intrastrand stacking between the AFB moiety and the 5′ neighbor thymine remains, but strong interstrand stacking is not observed. A hydrogen bond between the formyl group and the exocyclic amine of the 3′-neighbor adenine stabilizes the E conformation of the formamide moiety. NMR studies reveal a similar 5′-intercalation of the AFB moiety for the AFB-α-FAPY adduct in the tetramer 5′-d(C1T2X3A4)-3′, involving the Ra axial conformation of the FAPY C5−N5 bond and the E conformation of the formamide moiety. Since in duplex DNA the AFB moiety of the AFB-β-FAPY adduct also intercalates on the 5′ side of the pyrimidine moiety at the damaged nucleotide, we conclude that favorable 5′-stacking leads to the Ra conformational preference about the C5−N5 bond; the same conformational preference about this bond is also observed at the nucleoside and base levels. The structural distortions and the less favorable stacking interactions induced by the AFB-α-FAPY adduct explain its lower stability as compared to the AFB-β-FAPY adduct in duplex DNA. In this DNA sequence, hydrogen bonding between the formyl oxygen and the exocyclic amine of the 3′-neighboring adenine stabilizing the E configuration of the formamide moiety is also observed for the AFB-β-FAPY adduct, and suggests that the identity of the 3′-neighbor nucleotide modulates the stability and biological processing of AFB adducts.
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Affiliation(s)
- Kyle L Brown
- Department of Chemistry, Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, USA
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Nigam SK, Ghosh SK, Malaviya R. Aflatoxin, Its Metabolism and Carcinogenesis - A Historical Review. ACTA ACUST UNITED AC 2008. [DOI: 10.3109/15569549409089959] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Murugavel KG, Naranatt PP, Shankar EM, Mathews S, Raghuram K, Rajasambandam P, Jayanthi V, Surendran R, Murali A, Srinivas U, Palaniswamy KR, Srikumari D, Thyagarajan SP. Prevalence of aflatoxin B1 in liver biopsies of proven hepatocellular carcinoma in India determined by an in-house immunoperoxidase test. J Med Microbiol 2008; 56:1455-1459. [PMID: 17965344 DOI: 10.1099/jmm.0.47151-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related death in the world. The incidence of HCC in India is reportedly low and varies from 0.2 to 1.9 %. Aflatoxins, secondary metabolites produced by Aspergillus flavus and Aspergillus parasiticus, are potent human carcinogens implicated in HCC. The prevalence of aflatoxin B1 (AFB1) as co-carcinogen was analysed using an in-house immunoperoxidase test in 31 liver biopsies and 7 liver-resection specimens from histopathologically proven HCC, and in 15 liver biopsies from cirrhosis patients (control group). Serum was tested for hepatitis B and C serological markers using commercial assays, and for AFB1 using an in-house ELISA with a sensitivity of approximately 1 ng ml(-1) for AFB1. In spite of positive AFB1 immunostaining in HCC cases, all serum specimens, from both HCC and the control groups, were AFB1-negative. There were 18 (58.1 %) HCC cases that revealed AFB1 in liver biopsies; 68.8 % (n=11) of non-B non-C hepatitis cases with HCC and 46.1 % (n=6) of the hepatitis B surface-antigen-positive subjects were positive for AFB1. Out of the two hepatitis B/hepatitis C virus co-infected cases, one was positive for AFB1. Of seven tumour-resection samples, six were positive for AFB1. Only one case revealed AFB1 in the non-tumour area of the resected material. Thus AFB1 staining was significantly associated with tumour tissue (P=0.03). Aflatoxins proved to have a significant association with HCC in this peninsular part of the subcontinent. The impact seems to be a cumulative process, as revealed by the AFB1 deposits in HCC liver tissue, even though the serum levels were undetectable.
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Affiliation(s)
- K G Murugavel
- Department of Microbiology, Faculty of Medicine, Dr ALM PG Institute of Basic Medical Sciences, University of Madras, Taramani Campus, Chennai 600 113, India
| | - P P Naranatt
- Department of Microbiology, Faculty of Medicine, Dr ALM PG Institute of Basic Medical Sciences, University of Madras, Taramani Campus, Chennai 600 113, India
| | - E M Shankar
- Department of Microbiology, Faculty of Medicine, Dr ALM PG Institute of Basic Medical Sciences, University of Madras, Taramani Campus, Chennai 600 113, India
| | - S Mathews
- Medical Gastroenterology Unit of the Government General Hospital, Chennai 600 001, India
| | - K Raghuram
- Medical Gastroenterology Unit of the Government General Hospital, Chennai 600 001, India
| | - P Rajasambandam
- Medical Gastroenterology Unit of the Government General Hospital, Chennai 600 001, India
| | - V Jayanthi
- Medical and Surgical Gastroenterology Unit of the Government Stanley Medical College and Hospital, Chennai 600 001, India
| | - R Surendran
- Medical and Surgical Gastroenterology Unit of the Government Stanley Medical College and Hospital, Chennai 600 001, India
| | - A Murali
- Medical and Surgical Gastroenterology Unit of the Government Stanley Medical College and Hospital, Chennai 600 001, India
| | - U Srinivas
- Medical and Surgical Gastroenterology Unit of the Government Stanley Medical College and Hospital, Chennai 600 001, India
| | - K R Palaniswamy
- Medical and Surgical Gastroenterology Unit of the Government Stanley Medical College and Hospital, Chennai 600 001, India
| | - D Srikumari
- Government Kilpauk Medical College and Hospital, Chennai 600 029, India
| | - S P Thyagarajan
- Department of Microbiology, Faculty of Medicine, Dr ALM PG Institute of Basic Medical Sciences, University of Madras, Taramani Campus, Chennai 600 113, India
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Abstract
Hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) remains the most common form of HCC in large areas of Asia and Africa. It remains common even in some countries where hepatitis C virus (HCV)-associated HCC has become the predominant form, such as Japan. Integration of HBV in HCC DNA is found at random sites in the host genome in nearly all patients with HBV-associated HCC. It is not clear how often this integration results in insertional mutagenesis, but previously unknown growth regulating genes and cancer-associated genes have been found frequently near HBV integration sites in HCC in recent studies. In addition, HBV encodes a transactivating protein, the X protein, which could enable the randomly integrated HBV to alter the function of host genes that are not near the integration site. Mutations at two adjacent codons in HBV (1762(T)/1764(A) mutations) within the X gene are frequently found in HCC patients, and may play a role in the mutagenic or transactivational role of HBV in HCC. The presence of cirrhosis in most patients with HBV-associated HCC, and the presence of mutations in tumor suppressor genes in many, suggests that these are also factors in hepatocarcinogenesis. Few studies have examined the mutations of more than one gene in the same HCC patients. Fewstudies have evaluated the interactions between HBV mutations, host gene mutations, cirrhosis, and other potentially mutagenic stresses at the cellular level, with progression to HCC, and few studies have been conducted to determine whether these changes must accumulate in succession to lead to HCC. The recent availability of rapid sequencing methods and DNA microarray technologies has permitted expression profiling and permutation analysis of an array of genes to explore the pattern and succession of molecular changes leading to HBV-associated HCC. To date, these methods have been used to show patterns of molecular changes that differ in HBV-associated HCC (compared to HCV-associated HCC or to HCC in patients lacking either virus) and patterns that can predict survival (and hence may directly indicate different mechanisms of disease), and may soon make possible a universally accepted clinical classification scheme for HCC.
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Brown KL, Deng JZ, Iyer RS, Iyer LG, Voehler MW, Stone MP, Harris CM, Harris TM. Unraveling the aflatoxin-FAPY conundrum: structural basis for differential replicative processing of isomeric forms of the formamidopyrimidine-type DNA adduct of aflatoxin B1. J Am Chem Soc 2007; 128:15188-99. [PMID: 17117870 PMCID: PMC2693076 DOI: 10.1021/ja063781y] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Aflatoxin B1 (AFB) epoxide forms an unstable N7 guanine adduct in DNA. The adduct undergoes base-catalyzed ring opening to give a highly persistent formamidopyrimidine (FAPY) adduct which exists as a mixture of forms. Acid hydrolysis of the FAPY adduct gives the FAPY base which exists in two separable but interconvertible forms that have been assigned by various workers as functional, positional, or conformational isomers. Recently, this structural question became important when one of the two major FAPY species in DNA was found to be potently mutagenic and the other a block to replication [Smela, M. E.; Hamm, M. L.; Henderson, P. T.; Harris, C. M.; Harris, T. M.; Essigmann, J. M. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 6655-6660]. NMR studies carried out on the AFB-FAPY bases and deoxynucleoside 3',5'-dibutyrates now establish that the separable FAPY bases and nucleosides are diastereomeric N5 formyl derivatives involving axial asymmetry around the congested pyrimidine C5-N5 bond. Anomerization of the protected beta-deoxyriboside was not observed, but in the absence of acyl protection, both anomerization and furanosyl --> pyranosyl ring expansion occurred. In oligodeoxynucleotides, two equilibrating FAPY species, separable by HPLC, are assigned as anomers. The form normally present in duplex DNA is the mutagenic species. It has previously been assigned as the beta anomer by NMR (Mao, H.; Deng, Z. W.; Wang, F.; Harris, T. M.; Stone, M. P. Biochemistry 1998, 37, 4374-4387). In single-stranded environments the dominant species is the beta anomer; it is a block to replication.
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Affiliation(s)
- Kyle L Brown
- Department of Chemistry, Center in Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235, USA
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He XY, Tang L, Wang SL, Cai QS, Wang JS, Hong JY. Efficient activation of aflatoxin B1 by cytochrome P450 2A13, an enzyme predominantly expressed in human respiratory tract. Int J Cancer 2006; 118:2665-71. [PMID: 16385575 DOI: 10.1002/ijc.21665] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The worldwide human exposure to aflatoxin B1 (AFB1), particularly in developing countries, remains to be a serious public health concern. Although AFB1 is best known as a hepatocarcinogen, epidemiological studies have shown a positive association between human lung cancer occurrence and inhalation exposure to AFB1. Cytochrome P450 (CYP)-catalyzed metabolic activation is required for AFB1 to exert its carcinogenicity. Previous studies have identified CYP1A2 and CYP3A4 as the major enzymes for AFB1 activation in human liver. However, the key CYP enzymes in human lung that can efficiently activate AFB1 in situ are unknown. In the present study, we demonstrate that CYP2A13, an enzyme predominantly expressed in human respiratory tract, has a significant activity in metabolizing AFB1 to its carcinogenic/toxic AFB1-8,9-epoxide and AFM1-8,9-epoxide at both low (15 microM) and high (150 microM) substrate concentrations. Under the same conditions, there was no detectable AFB1 epoxide formation by CYP2A6, which was also reported to be involved in the metabolic activation of AFB1. Consistent with the activity data, there was an approximately 800-fold difference in LC50 values of AFB1 (48-hr treatment) between Chinese hamster ovary (CHO) cells expressing CYP2A13 and CYP2A6 (50 nM versus 39 microM). We further demonstrate that amino acid residues Ala117 and His372 in CYP2A13 protein are important for AFB1 epoxidation and its related cytotoxicity. Our results suggest that CYP2A13-catalyzed metabolic activation in situ may play a critical role in human lung carcinogenesis related to inhalation exposure to AFB1.
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Affiliation(s)
- Xiao-Yang He
- School of Public Health/Environmental and Occupational Health Sciences Institute, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854, USA
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Jowsey IR, Jiang Q, Itoh K, Yamamoto M, Hayes JD. Expression of the aflatoxin B1-8,9-epoxide-metabolizing murine glutathione S-transferase A3 subunit is regulated by the Nrf2 transcription factor through an antioxidant response element. Mol Pharmacol 2003; 64:1018-28. [PMID: 14573750 DOI: 10.1124/mol.64.5.1018] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
High expression of the aflatoxin B1 (AFB1)-8,9-epoxide-conjugating glutathione S-transferase A3 (mGSTA3) subunit in mouse liver confers intrinsic resistance to AFB1 hepatocarcinogenesis. It is not known how the gene encoding this protein is regulated. The murine mGSTA3 gene has been identified using bioinformatics. It localizes to mouse chromosome 1 (A3-4), spans approximately 24.6 kilobases (kb) of DNA, and comprises seven exons. High levels of mGSTA3 mRNA are present in organs associated with detoxification. Expression of mGSTA3 in Hepa1c1c7 mouse hepatoma cells was found to be inducible by sulforaphane, an organic isothiocyanate that can transcriptionally activate genes through the antioxidant response element (ARE). Sulforaphane also induced transcription of a luciferase reporter containing a 1.5 kb fragment of the mGSTA3 5'-upstream region. A putative ARE, with sequence 5'-TGACATTGC-3', was identified within this fragment, approximately 150 base pairs upstream of exon 1. Mutation of this sequence abrogated both basal and sulforaphane-inducible reporter activity. Overexpression of the basic-region leucine zipper Nrf2 transcription factor augmented activity of the mGSTA3-luciferase reporter through this ARE. Electrophoretic mobility shift assays demonstrated that Nrf2 binds the mGSTA3 ARE. Measurement of mGSTA3 mRNA levels in tissues isolated from both wild-type and nrf2-null mice revealed that loss of the Nrf2 transcription factor is associated with a reduction in basal expression of mGSTA3. Collectively, these data demonstrate a role for Nrf2 and the ARE in regulating transcription of mGSTA3.
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Affiliation(s)
- Ian R Jowsey
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, UK.
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Bai F, Nakanishi Y, Takayama K, Pei XH, Inoue K, Harada T, Izumi M, Hara N. Codon 64 of K-ras gene mutation pattern in hepatocellular carcinomas induced by bleomycin and 1-nitropyrene in A/J mice. TERATOGENESIS, CARCINOGENESIS, AND MUTAGENESIS 2003; Suppl 1:161-70. [PMID: 12616606 DOI: 10.1002/tcm.10071] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Bleomycin is a radiomimetic antitumor agent with unique genotoxic properties. 1-nitropyrene is an environmental mutagen and carcinogen that undergoes both oxidative and reductive metabolism. In the present study, hepatocellular carcinomas were induced in male A/J mice by the intraperitoneal injection of bleomycin (120 mg/kg) followed by the intraperitoneal administration of 1-nitropyrene (total dose: 1,575 mg/kg). In order to understand the mechanism by which these two compounds induce hepatocellular carcinomas, the incidence and spectrum of mutations in the K-ras proto-oncogene in these hepatocellular carcinomas were analyzed. The hepatocellular carcinomas were induced by the administration of bleomycin and 1-nitropyrene were evaluated for point mutations in exon 1 and exon 2 of the K-ras gene by the polymerase chain reaction and a sequencing analysis. No mutation was found in the hotspots regions of the K-ras gene codon 12, 13, or 61. However, the codon 64 of the K-ras gene mutation was identified in 10 of 10 (100%) hepatocellular carcinomas. All mutations showed the same pattern, which was TAC-CAC transition. Codon 64 of the K-ras gene mutation may thus play an important role in the induction of hepatocellular carcinomas by bleomycin in the existence of 1-nitropyrene. As far as we know, this is the first report of a codon 64 mutation in the K-ras gene in a chemically induced tumor.
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Affiliation(s)
- Feng Bai
- Research Institute for Diseases of the Chest, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
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Hengstler JG, Bogdanffy MS, Bolt HM, Oesch F. Challenging dogma: thresholds for genotoxic carcinogens? The case of vinyl acetate. Annu Rev Pharmacol Toxicol 2003; 43:485-520. [PMID: 12415124 DOI: 10.1146/annurev.pharmtox.43.100901.140219] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although many questions remain unanswered, the general principle of the sequence of events leading to cancer after exposure to genotoxic carcinogens has become increasingly clear. This helps to understand the parameters that influence the shape of the dose-effect curve for carcinogenesis, including metabolic activation and inactivation of carcinogens, DNA repair, cell cycle control, apoptosis, and control by the immune system. A linear dose-response relationship with no observable threshold seems to be a conservative but adequate description for the carcinogenic activity of many genotoxic carcinogens, such as aflatoxin B1, the tobacco-specific nitrosoketone NNK, and probably N,N-diethylnitrosamine. However, extrapolation models connecting the high-level risk to the zero intercept have clearly resulted in overestimations of risk. Vinyl acetate is an example that is discussed extensively in this review. At extremely high and toxic doses, vinyl acetate is carcinogenic in rats and mice and causes chromosomal aberrations. In tissues of contact, vinyl acetate is converted to acetic acid and acetaldehyde. Only when threshold levels are achieved do critical steps in the mechanism ultimately leading to cancer become active, namely pH reduction in exposed cells of more than 0.15 units leading to cytotoxicity, damage to DNA, and regenerative proliferation. Consistent with the known exposure to endogenous acetic acid and acetaldehyde, tissues sustain a certain level of exposure without adverse effects. Physiological modeling shows that the conditions necessary for carcinogenesis are in place only when threshold levels of vinyl acetate are exceeded. The example of vinyl acetate underlines the importance of toxicological research that unequivocally identifies genotoxic carcinogens acting through a threshold process.
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Affiliation(s)
- J G Hengstler
- Institute of Toxicology, University of Mainz, D-55131 Mainz, Germany.
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21
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Abstract
The trans-8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B(1) cationic guanine N7 adduct of aflatoxin B(1) thermally stabilizes the DNA duplex, as reflected in increased T(m) values upon adduction. The magnitude of the increased T(m) value is characteristically 2-3 degrees C. The major rotamer of the neutral guanine N7 adduct trans-8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxy aflatoxin B(1) (the FAPY major adduct) exhibits a 15 degrees C increase in T(m) in 5'-d(CTAT(FAPY)GATTCA)-3'-5'-d(TGAATCATAG)-3'. Site-specific mutagenesis experiments reveal the FAPY major adduct induces G-->T mutations in Escherichia coli at a frequency six times higher than that of the cationic adduct (Smela, M. E.; Hamm, M. L.; Henderson, P. T.; Harris, C. M.; Harris, T. M.; Essigmann, J. M. Proc Natl Acad Sci USA, 99, 6655-6660). Thus, the FAPY major lesion may account substantially for the genotoxicity of AFB(1). Structural studies for cationic and FAPY adducts of aflatoxin B(1) suggest both adducts intercalate above the 5'-face of the modified deoxyguanosine and that in each instance the aflatoxin moiety spans the DNA helix. Intercalation of the aflatoxin moiety, accompanied by favorable stacking with the neighboring base pairs, is thought to account for the increased thermal stability of the aflatoxin cationic guanine N7 and the FAPY major adducts. However, the structural basis for the large increase in thermal stability of the FAPY major adduct in comparison to the cationic guanine N7 adduct of aflatoxin B(1) is not well understood. In light of the site-specific mutagenesis studies, it is of considerable interest. For both adducts, the intercalation structures are similar, although improved stacking with neighboring base pairs is observed for the FAPY major adduct. In addition, the presence of the formamido group in the aflatoxin B(1) FAPY major adduct may enhance duplex stability, perhaps via intrastrand sequence-specific hydrogen bonding interactions within the duplex.
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Affiliation(s)
- Indrajit Giri
- Department of Chemistry and Center in Molecular Toxicology, Vanderbilt University, Nashville, TN 37235, USA
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Madden CR, Finegold MJ, Slagle BL. Altered DNA mutation spectrum in aflatoxin b1-treated transgenic mice that express the hepatitis B virus x protein. J Virol 2002; 76:11770-4. [PMID: 12388740 PMCID: PMC136763 DOI: 10.1128/jvi.76.22.11770-11774.2002] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Humans chronically infected with hepatitis B virus (HBV) are at further risk of liver cancer upon exposure to dietary aflatoxin B1 (AFB1), a carcinogenic product of the mold Aspergillus flavus. For the present study, we utilized double-transgenic mice (ATX mice) that express the HBV X protein (HBx) and possess a bacteriophage lambda transgene to evaluate the in vivo effect of HBx expression on AFB1-induced DNA mutations. The expression of HBx correlated with a 24% increase in mutation frequency overall and an approximately twofold increase in the incidence of G/C-to-T/A transversion mutations following AFB1 exposure. These results are consistent with a model in which expression of HBx during chronic HBV infection may contribute to the development of hepatocellular carcinoma following exposure to environmental carcinogens.
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Affiliation(s)
- Charles R Madden
- Department of Molecular Virology and Microbiology. Department of Pathology, Baylor College of Medicine, Houston, Texas 77030, USA
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Niketeghad F, Decker HJ, Caselmann WH, Lund P, Geissler F, Dienes HP, Schirmacher P. Frequent genomic imbalances suggest commonly altered tumour genes in human hepatocarcinogenesis. Br J Cancer 2001; 85:697-704. [PMID: 11531255 PMCID: PMC2364116 DOI: 10.1054/bjoc.2001.1963] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Hepatocellular carcinoma (HCC) is one of the most frequent-occurring malignant tumours worldwide, but molecular changes of tumour DNA, with the exception of viral integrations and p53 mutations, are poorly understood. In order to search for common macro-imbalances of genomic tumour DNA, 21 HCCs and 3 HCC-cell lines were characterized by comparative genomic hybridization (CGH), subsequent database analyses and in selected cases by fluorescence in situ hybridization (FISH). Chromosomal subregions of 1q, 8q, 17q and 20q showed frequent gains of genomic material, while losses were most prevalent in subregions of 4q, 6q, 13q and 16q. Deleted regions encompass tumour suppressor genes, like RB-1 and the cadherin gene cluster, some of them previously identified as potential target genes in HCC development. Several potential growth- or transformation-promoting genes located in chromosomal subregions showed frequent gains of genomic material. The present study provides a basis for further genomic and expression analyses in HCCs and in addition suggests chromosome 4q to carry a so far unidentified tumour suppressor gene relevant for HCC development.
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Affiliation(s)
- F Niketeghad
- Institute of Pathology, University of Cologne, Joseph Stelzmann Str. 9, Cologne, D-50931, Germany
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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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Chao HK, Tsai TF, Lin CS, Su TS. Evidence that mutational activation of the ras genes may not be involved in aflatoxin B(1)-induced human hepatocarcinogenesis, based on sequence analysis of the ras and p53 genes. Mol Carcinog 1999; 26:69-73. [PMID: 10506750 DOI: 10.1002/(sici)1098-2744(199910)26:2<69::aid-mc1>3.0.co;2-a] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Exposure to aflatoxin B(1) (AFB(1)) is one of the risk factors for developing hepatoma. In rats, activation of the ras gene is a prevalent event in AFB(1)-induced hepatocarcinogenesis. It is not clear whether a similar event occurs in humans. By analysis of codon 249 of the p53 gene, six of 36 human hepatoma samples were found to show a G-->T transversion, suggesting that AFB(1) may be a risk factor for hepatocarcinogenesis. However, analysis at codons 12, 13, and 61 in the ras family genes revealed a A-->T transversion at codon 61 of the N-ras gene in a single tumor. Apparently, ras activation is rare in human hepatoma, and the mutation detected might not be induced by AFB(1). This suggests that activation of the ras gene may not be a major event in AFB(1)-related human hepatocarcinogenesis.
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Affiliation(s)
- H K Chao
- Department of Medical Research and Education, Veterans General Hospital-Taipei, Taipei, Taiwan, Republic of China
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McDonagh PD, Judah DJ, Hayes JD, Lian LY, Neal GE, Wolf CR, Roberts GC. Determinants of specificity for aflatoxin B1-8,9-epoxide in alpha-class glutathione S-transferases. Biochem J 1999; 339 ( Pt 1):95-101. [PMID: 10085232 PMCID: PMC1220132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
We have used homology modelling, based on the crystal structure of the human glutathione S-transferase (GST) A1-1, to obtain the three-dimensional structures of rat GSTA3 and rat GSTA5 subunits bound to S-aflatoxinyl-glutathione. The resulting models highlight two residues, at positions 208 and 108, that could be important for determining, either directly or indirectly, substrate specificity for aflatoxin-exo-8,9-epoxide among the Alpha-class GSTs. Residues at these positions were mutated in human GSTA1-1 (Met-208, Leu-108), rat GSTA3-3 (Glu-208, His-108) and rat GSTA5-5 (Asp-208, Tyr-108): in the active rat GSTA5-5 to those in the inactive GSTA1-1; and in the inactive human GSTA1-1 and rat GSTA3-3 to those in the active rat GSTA5-5. These studies show clearly that, in all three GSTs, an aspartate residue at position 208 is a prerequisite for high activity in aflatoxin-exo-8,9-epoxide conjugation, although this alone is not sufficient; other residues in the vicinity, particularly residues 103-112, are important, perhaps for the optimal orientation of the aflatoxin-exo-8,9-epoxide in the active site for catalysis to occur.
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Affiliation(s)
- P D McDonagh
- Centre for Mechanisms of Human Toxicity, University of Leicester, Leicester LE1 9HN, UK
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Stanley LA, Mandel HG, Riley J, Sinha S, Higginson FM, Judah DJ, Neal GE. Mutations associated with in vivo aflatoxin B1-induced carcinogenesis need not be present in the in vitro transformations by this toxin. Cancer Lett 1999; 137:173-81. [PMID: 10374839 DOI: 10.1016/s0304-3835(98)00354-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Ingestion of aflatoxin B1 is implicated in the high incidence of human liver cancers in several developing countries. An association has been detected between human exposure to aflatoxins, and mutations in the third base of codon 249 of the p53 gene in hepatomas. In vitro experiments using human cell line cells and aflatoxin B1 have demonstrated the induction of p53 mutations in codon 249 and adjacent codons. It was therefore of interest to see if this correlation between the in vivo and in vitro situations held for other species. The present study examined a rat liver-derived cell line, transformed in vitro with aflatoxin B1, for the presence of mutations associated with in vivo aflatoxin-induced hepatocarcinogenesis. In an in vivo rodent model systems using the aflatoxin B1-sensitive male F344 rat, previous studies have shown that hepatocarcinogenesis is accompanied by significant incidences of codon 12 mutations in K-ras and codon 13 mutations in N-ras genes, but in contrast to the human, apparently not by mutations in codon 243 of the p53 gene (which corresponds to codon 249 in the human gene). In contrast to the situation in humans, mutation in the third base of codon 243 in the rat would not result in any changes in amino acid sequence, but mutations in codon 250, as seen in in vitro human systems, would be expressed in the rat p53 protein. In the present study, an immortalised, non-transformed liver epithelial cell line derived from a male F344 rat was transformed in vitro by aflatoxin B1 as demonstrated by tumour formation in nude mice. The transformation was dependent on metabolic activation of the aflatoxin B1. Transfection of DNA, extracted from these tumours, into NIH 3T3 fibroblasts conferred a stable, malignant transforming capacity. However, no mutations in codon 12 of the K-ras or codon 13 of the N-ras genes were detected in any of these tumours. These results indicate that in vitro transformation does not necessarily involve the same mutations, as those observed in vivo. Also, no mutations in codon 243 or adjacent codons of the p53 gene, paralleling those observed in the human cell line treated with aflatoxin B1, were detected. The results serve to emphasise the in vivo and in vitro variation in the oncogene activation in the same target organ or cell lines derived from that organ, even when using a single carcinogen activated by a known metabolic pathway.
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MESH Headings
- 3T3 Cells
- Aflatoxin B1/toxicity
- Animals
- Blotting, Southern
- Carcinogenicity Tests
- Cell Line
- Cell Transformation, Neoplastic/chemically induced
- Cell Transformation, Neoplastic/genetics
- DNA Mutational Analysis
- Epithelial Cells/drug effects
- Genes, p53/drug effects
- Genes, p53/genetics
- Genes, ras/drug effects
- Genes, ras/genetics
- Liver/chemistry
- Liver/drug effects
- Male
- Mice
- Mice, Nude
- Mutagens/toxicity
- Mutation/drug effects
- Rats
- Rats, Inbred F344
- Sequence Analysis, DNA
- Transfection
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Affiliation(s)
- L A Stanley
- Department of Pharmaceutical Sciences, De Montfort University, Leicester, UK
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28
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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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29
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Kang BS, Ha JY, Lim JC, Lee J, Kim CK, Min KR, Kim Y. Structure of catechol 2,3-dioxygenase gene from Alcaligenes eutrophus 335. Biochem Biophys Res Commun 1998; 245:791-6. [PMID: 9588193 DOI: 10.1006/bbrc.1998.8511] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Catechol 2,3-dioxygenase (C23O), one of extradiol-type dioxygenases cleaving aromatic C-C bond at meta position of dihydroxylated aromatic substrates, catalyzes the conversion of catechol to 2-hydroxymuconic semialdehyde. As our ongoing study to characterize biochemical and genetic properties of the extradiol-type dioxygenases at molecular level, a C23O gene encoded in chromosomal DNA of Alcaligenes eutrophus 335, a strain degrading phenol and p-cresol, was cloned. The C23O gene was localized in an 1.4-kb PstI fragment from A. eutrophus 335, and was expressed in E. coli HB101. The C23O exhibited the highest aromatic ring-fission activity to catechol as a substrate, and its relative activity to other dihydroxylated aromatic substrates was in order of catechol >> 4-methylcatechol > 3-methylcatechol, protocatechuate, 4-chlorocatechol > 3,4-dihydroxy-phenylacetate > 2,3-dihydroxybiphenyl. Nucleotide sequence of the 1.4-kb fragment has revealed that an open reading frame (ORF) corresponding to the C23O gene was composed of 930 base pairs. A putative ribosome-binding sequence of AGGAG was found at about 10 nucleotides upstream the ORF which can encode a polypeptide of molecular weight 34 kDa consisting of 309 amino acid residues. The deduced amino acid sequence of C23O from A. eutrophus 335 exhibited the highest 59% identity with those of corresponding enzymes from Pseudomonas sp. CF600 (p VI150), P. putida HS1 (pDK1), and P. putida PpG7 (NAH7). An alignment of amino acid sequences of extradiol-type dioxygenases including C23O from A. eutrophus 335 has revealed that catalytically and structurally important amino acid residues of the enzymes were conserved during evolution.
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Affiliation(s)
- B S Kang
- College of Pharmacy, Chungbuk National University, Cheongju, Korea
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30
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Hayes JD, Pulford DJ, Ellis EM, McLeod R, James RF, Seidegård J, Mosialou E, Jernström B, Neal GE. Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents: mechanisms of inducible resistance to aflatoxin B1. Chem Biol Interact 1998; 111-112:51-67. [PMID: 9679543 DOI: 10.1016/s0009-2797(97)00151-8] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.
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Affiliation(s)
- J D Hayes
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Scotland, UK
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31
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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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32
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Moon J, Kang E, Min KR, Kim CK, Min KH, Lee KS, Kim Y. Characterization of the gene encoding catechol 2,3-dioxygenase from Achromobacter xylosoxidans KF701. Biochem Biophys Res Commun 1997; 238:430-5. [PMID: 9299526 DOI: 10.1006/bbrc.1997.7312] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Catechol 2,3-dioxygenase (C23O) catalyzes a meta cleavage of the aromatic ring in catechol to form 2-hydroxymuconic semialdehyde. A C23O gene was cloned from chromosomal DNA of A. xylosoxidans KF701, a soil bacterium degrading biphenyl, and expressed in E. coli HB101. In substrate specificity to catechol and its analogs, the C23O exhibited the highest aromatic ring-fission activity to catechol, and its relative activity to other dihydroxylated aromatics was 4-chlorocatechol > 4-methylcatechol > 3-methylcatechol >> 2, 3-dihydroxybiphenyl. Aromatic ring-fission activity of the C23O to catechol was about 40-fold higher than that to 2,3-dihydroxybiphenyl. Nucleotide sequence analysis of the C23O gene from A. xylosoxidans KF701 revealed an open reading frame consisting of 924 base pairs, and identified a putative ribosome-binding sequence (AGGTGA) at about 10 nucleotides upstream from the initiation codon. The open reading frame can encode a polypeptide chain with molecular weight of 34 kDa containing 307 amino acid residues. The deduced amino acid sequence of the C23O exhibited the highest homology with that of C23O from Pseudomonas sp. IC with 96% identity, and the least homology with that of C23O from P. putida F1 with 22% identity among reported C23O sequences. Furthermore, comparison of the C23O sequence with other extradiol dioxygenases has led to identification of evolutionally conserved amino acid residues whose possible catalytic and structural roles are proposed.
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Affiliation(s)
- J Moon
- College of Pharmacy, Chungbuk National University, Cheongju, 361-763, Korea
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33
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Oh JM, Kang E, Min KR, Kim CK, Kim YC, Lim JY, Lee KS, Min KH, Kim Y. Structure of catechol 2,3-dioxygenase gene encoded in TOM plasmid of Pseudomonas cepacia G4. Biochem Biophys Res Commun 1997; 234:578-81. [PMID: 9175755 DOI: 10.1006/bbrc.1997.6680] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The catechol 2,3-dioxygenase is an extradiol-type dioxygenase which cleaves the C-C bond at the meta position of catechol to form 2-hydroxymuconic semialdehyde. A catechol 2,3-dioxygenase gene (tomB) in the TOM plasmid of P. cepacia G4 has been cloned and its nucleotide sequence was analyzed. The enzyme gene consisted of 945 base pairs with an ATG initiation codon and a TGA termination codon which can encode a polypeptide of molecular weight 35 kDa containing 314 amino acid residues, and a putative ribosome-binding sequence was identified at approximately 10 nucleotides upstream of the initiation codon. The deduced amino acid sequence of catechol 2,3-dioxygenase from P. cepacia G4 exhibited 79-82% homologies with those of 3-methylcatechol 2,3-dioxygenase of P. putida UCC2 and catechol 2,3-dioxygenase of P. pickettii PKO1.
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Affiliation(s)
- J M Oh
- College of Pharmacy, Chungbuk National University, Cheongju, Korea
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34
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Abstract
Inhalation exposure to the carcinogen aflatoxin B1 (AFB1) in certain occupations is considerable. Because circumstantial epidemiological evidence suggests that AFB1 inhalation may cause primary lung cancer, we investigated AFB1 activation by human lung microsomes. Microsomes were incubated with [3H]AFB1 (124 microM), and activation to the AFB1-8,9-epoxide was measured as the AFB1-glutathione (AFB1-GSH) conjugate by HPLC. The formation of AFB1-GSH was in the range of 0.05-0.073 fmol/mg protein/min. The role of cytochrome P450 (CYP) 3A in this activation was investigated by oxidation of nifedipine (a prototype substrate for CYP 3A), by immunoinhibition, and by immunoblot analysis. Nifedipine oxidation varied from 0.2 to 19.2 pmol/mg protein/min in microsomes from different subjects, but did not correlate with AFB1 activation. Anti-human polyclonal CYP 3A4 IgG inhibited AFB1 activation. CYP 3A isoforms were immunoestimated to be in the range of 0.01-1.90 pmol/mg protein. Neither CYP 1A2 nor associated activity was detected in the lung microsomes. These data indicate that human lung microsomes activate AFB1 to form the exo-AFB1-8,9-epoxide and that CYP(s) of the 3A subfamily may be responsible for this activity. The relatively low amount of AFB1 activation in human lung compared to that in human liver can be explained by the scarcity of CYP-containing cells in the lung. In situ AFB1 activation and resultant carcinogenic risk are distinctly possible in occupational settings where inhalation of AFB1-contaminated dusts occurs.
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Affiliation(s)
- J D Kelly
- Program in Toxicology and Molecular Biology, Utah State University, Logan 84322-4620, USA
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35
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Nelson E. Laboratory probing of oncogenes from human liquid and solid specimens as markers of exposure to toxicants. Crit Rev Toxicol 1996; 26:483-549. [PMID: 8891429 DOI: 10.3109/10408449609037476] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Recent discoveries regarding the mechanistic role of oncogenes and tumor suppressor genes in cancer development have opened a new era of molecular diagnosis. It has been observed repeatedly that genetic lesions serve as tumor markers in a broad variety of human cancers. The ras gene family, consisting of three related genes, H-ras, K-ras, and N-ras, acquires transforming activity through amplification or mutation in many tissues. If not all, then most types of human malignancies have been found to contain an altered ras gene. Because the ras oncogenes actively participate in both early and intermediate stages of cancer, several highly specific and sensitive approaches have been introduced to detect these genetic alterations as biomarkers of exposure to carcinogens. There is also mounting evidence that implicate chemical-specific alterations of the p53 tumor suppressor gene detected in most human tumors. Therefore, it seems a reliable laboratory approach to identify both altered p53 and ras genes as biomarkers of human chronic or intermittent exposure to toxicants in a variety of occupational settings.
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Affiliation(s)
- E Nelson
- Toxicology Laboratory, University Medical Center, Essen, Germany
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36
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Bailey EA, Iyer RS, Harris TM, Essigmann JM. A viral genome containing an unstable aflatoxin B1-N7-guanine DNA adduct situated at a unique site. Nucleic Acids Res 1996; 24:2821-8. [PMID: 8759017 PMCID: PMC146009 DOI: 10.1093/nar/24.14.2821] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A problem that has hindered the study of the biological properties of certain DNA adducts, such as those that form at the N7 atoms of purines, is their extreme chemical lability. Conditions are described for the construction of a single-stranded genome containing the chemically and thermally labile 8,9-dihydro-8- (N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N7-Gua) adduct, the major DNA adduct of the potent liver carcinogen aflatoxin B1 (AFB1). A 13mer oligonucleotide, d(CCTCTTCGAACTC), was allowed to react with the exo-8,9-epoxide of AFB1 to form an oligonucleotide containing a single AFB1-N7-Gua (at the underlined guanine). This modified 13mer was 5'-phosphorylated and ligated into a gap in an M13 bacteriophage genome generated by annealing a 53mer uracil-containing scaffold to M13mp7L2 linearized by EcoRI. Following ligation, the scaffold was enzymatically removed with uracil DNA glycosylase and exonuclease III. The entire genome construction was complete within 3 h and was carried out at 16 degrees C, pH 6.6, conditions determined to be optimal for AFB1-N7-Gua stability. Characterization procedures indicated that the AFB1-N7-Gua genome was approximately 95% pure with a small (5%) contamination by unmodified genome. This construction scheme should be applicable to other chemically or thermally unstable DNA adducts.
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Affiliation(s)
- E A Bailey
- Department of Chemistry, Whitaker College of Health Science and Technology, Massachusetts Institute of Technology, Cambridge 02139, USA
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37
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Bailey EA, Iyer RS, Stone MP, Harris TM, Essigmann JM. Mutational properties of the primary aflatoxin B1-DNA adduct. Proc Natl Acad Sci U S A 1996; 93:1535-9. [PMID: 8643667 PMCID: PMC39975 DOI: 10.1073/pnas.93.4.1535] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The mutagenic activity of the major DNA adduct formed by the liver carcinogen aflatoxin B1 (AFB1) was investigated in vivo. An oligonucleotide containing a single 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N7-Gua) adduct was inserted into the single-stranded genome of bacteriophage M13. Replication in SOS-induced Escherichia coli yielded a mutation frequency for AFB1-N7-Gua of 4%. The predominant mutation was G --> T, identical to the principal mutation in human liver tumors believed to be induced by aflatoxin. The G --> T mutations of AFB1-N7-Gua, unlike those (if the AFB1-N7-Gua-derived apurinic site, were much more strongly dependent on MucAB than UmuDC, a pattern matching that in intact cells treated with the toxin. It is concluded that the AFB1-N7-Gua adduct, and not the apurinic site, has genetic requirements for mutagenesis that best explain mutations in aflatoxin-treated cells. While most mutations were targeted to the site of the lesion, a significant fraction (13%) occurred at the base 5' to the modified guanine. In contrast, the apurinic site-containing genome gave rise only to targeted mutations. The mutational asymmetry observed for AFB1-N7-Gua is consistent with structural models indicating that the aflatoxin moiety of the aflatoxin guanine adduct is covalently intercalated on the 5' face of the guanine residue. These results suggest a molecular mechanism that could explain an important step in the carcinogenicity of aflatoxin B1.
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Affiliation(s)
- E A Bailey
- Department of Chemistry, Whitaker College of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, 02139, USA
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38
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De Benedetti V, Bennett WP, Greenblatt MS, Harris CC. p53 tumor suppressor gene: Implications for iatrogenic cancer and cancer therapy. ACTA ACUST UNITED AC 1996. [DOI: 10.1002/(sici)1096-911x(1996)27:1+<2::aid-mpo2>3.0.co;2-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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39
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Saracco G. Primary liver cancer is of multifactorial origin: importance of hepatitis B virus infection and dietary aflatoxin. J Gastroenterol Hepatol 1995; 10:604-8. [PMID: 8963039 DOI: 10.1111/j.1440-1746.1995.tb01354.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Primary liver cancer has a variable incidence worldwide, occurring most frequently in South-East Asia and China, which indicates that environmental factors are important in its aetiology. Although hepatitis B virus and chemical agents are the major risk factors for primary liver cancer, current evidence strongly suggests that it is of multifactorial origin. Aflatoxins are thought to be important because they are common food contaminants and are potent liver carcinogens in a wide variety of animal species. Evidence for the possible interactions between aflatoxin and hepatitis B infection, and their effects on the prevalence of primary liver cancer, is obtained from animal data and epidemiological studies. The risk of developing primary liver cancer following exposure to hepatitis B infection and aflatoxin is shown to be increased and the possible molecular mechanisms involved are discussed.
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Affiliation(s)
- G Saracco
- Dipartimento di Gastroenterologia, Ospedale Molinette, Torino, Italy
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40
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41
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Chatterjee D, Liu CJ, Northey D, Teicher BA. Molecular characterization of the in vivo alkylating agent resistant murine EMT-6 mammary carcinoma tumors. Cancer Chemother Pharmacol 1995; 35:423-31. [PMID: 7850925 DOI: 10.1007/s002800050257] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The expression of several early-response genes and genes associated with malignant disease was assessed in the EMT-6/parent tumor and the EMT-6/CTX and EMT-6/CDDP in vivo resistant tumor lines growing as tumors or as monolayers in culture. In the absence of treatment the levels of mRNA for the genes c-jun, c-fos, c-myc, Ha-ras and p53 were increased in the EMT-6/CTX and EMT-6/CDDP as compared with the EMT-6/parent tumor, whereas the expression of erb-2 was similar in all three tumors. Although the cells from each of the three tumors show increased expression of early response genes after exposure to cisplatin (CDDP; 100 microM, 2 h) or 4-Hydroxyperoxycyclophosphamide (4-HC; 100 microM, 2 h) in culture, in mRNA extracted from tumor tissue these changes are absent or very small. Both C-jun and erb-2 were detectable in liver. There was increased expression of both of these genes in the livers of tumor-bearing animals as compared with non-tumor-bearing animals. The highest expression of both c-jun and erb-2 occurred in the livers of animals bearing the EMT-6/CDDP tumor. Treatment of the animals with CDDP or cyclophosphamide, in general, resulted in increased expression of both genes at 6 h post treatment. The increased expression of these genes may impart metabolic changes in the tumors and/or hosts that contribute to the resistance of these tumors to specific antitumor alkylating agents.
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MESH Headings
- Alkylating Agents/toxicity
- Animals
- Blotting, Northern
- Cisplatin/pharmacology
- DNA Probes
- Drug Resistance, Multiple/genetics
- Female
- Gene Expression Regulation, Neoplastic/drug effects
- Gene Expression Regulation, Neoplastic/genetics
- Genes, erbB-2/genetics
- Genes, fos/genetics
- Genes, jun/genetics
- Genes, myc/genetics
- Genes, ras/genetics
- Image Processing, Computer-Assisted
- Liver/drug effects
- Liver/metabolism
- Mammary Neoplasms, Experimental/genetics
- Mammary Neoplasms, Experimental/metabolism
- Mice
- Mice, Inbred BALB C
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Tumor Cells, Cultured
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Affiliation(s)
- D Chatterjee
- Dana-Farber Cancer Institute, Joint Center for Radiation Therapy, Boston, MA 02115
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42
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McMahon G. The genetics of human cancer: implications for ecotoxicology. ENVIRONMENTAL HEALTH PERSPECTIVES 1994; 102 Suppl 12:75-80. [PMID: 7713039 PMCID: PMC1566737 DOI: 10.1289/ehp.94102s1275a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The study of human cancers has provided evidence that malignant progression is associated with genetic change. It has been suggested that some genetic alterations in tumors may be the result of direct or indirect processes related to environmental chemical exposure. This hypothesis has been supported by genetic evidence in liver tumors which has associated aflatoxin B1 exposure with the detection of inactivating DNA mutations within the human p53 tumor suppressor gene. The detection of activating ras oncogene mutations at high frequency in liver tumors of feral fish suggest that the survey of mutations in genes, such as p53 or other genes, might provide a genetic signature for specific chemical exposure in tissues of aquatic animals derived from environmentally damaged sites.
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Affiliation(s)
- G McMahon
- SUGEN, Inc., Redwood City, CA 94063, USA
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43
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Abstract
Some of the multiple factors involved in the molecular pathogenesis of hepatocellular carcinoma have been elucidated in recent years but no clear picture of how and in what sequence these factors interact at the molecular level has emerged yet. Transformation of hepatocytes to the malignant phenotype may occur irrespective of the aetiological agent through a pathway of chronic liver injury, regeneration and cirrhosis. The activation of cellular oncogenes, the inactivation of tumour suppressor genes and overexpression of certain growth factors contribute to the development of HCC. There is increasing evidence that the hepatitis B virus may play a direct role in the molecular pathogenesis of HCC. Aflatoxins have been shown to induce specific mutations of the p53 tumour suppressor gene thus providing a clue to how an environmental factor may contribute to tumour development at the molecular level.
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Affiliation(s)
- D Moradpour
- Molecular Hepatology Laboratory, Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown 02129, USA
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44
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Hayes J, Nguyen T, Judah D, Petersson D, Neal G. Cloning of cDNAs from fetal rat liver encoding glutathione S-transferase Yc polypeptides. The Yc2 subunit is expressed in adult rat liver resistant to the hepatocarcinogen aflatoxin B1. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32050-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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45
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Tokusashi Y, Fukuda I, Ogawa K. Absence of p53 mutations and various frequencies of Ki-ras exon 1 mutations in rat hepatic tumors induced by different carcinogens. Mol Carcinog 1994; 10:45-51. [PMID: 8185829 DOI: 10.1002/mc.2940100108] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Mutations of p53 and Ki-ras exon 1 were investigated in rat hepatic lesions induced by four kinds of hepatocarcinogenic protocols: continuous feeding of 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB), daily intraperitoneal injection of aflatoxin B1 (AFB1), and the Solt and Farber regimen (Nature 236:701-703, 1976), in which diethylnitrosamine (DEN) or nitrosomethylurea (NMU) was used as initiating agents. DNA from microdissected tissue sections was amplified by the polymerase chain reaction (PCR) directly using primers for p53 exons 5-8 and Ki-ras exon 1 and analyzed for mutations by denaturing gradient gel electrophoresis (DGGE) or constant denaturant gel electrophoresis (CDGE). One or both of the p53 PCR primers were located within introns to prevent amplifying the p53 processed pseudogenes. In a total of 59 hepatocellular carcinomas (HCCs), no p53 aberrations were detected, indicating that p53 mutations are not very important in rat hepatic carcinogenesis. On the other hand, Ki-ras codon 12 mutations were found at low frequency in HCCs, hyperplastic foci, and cholangiofibroses induced by 3'-Me-DAB and by AFB1 but not in the lesions induced by the Solt and Farber regimen. Although Ki-ras codon 12 mutations are generally infrequent in rat hepatic tumors, their incidence thus appears to vary depending on the carcinogen used for their induction.
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Affiliation(s)
- Y Tokusashi
- Department of Pathology, Asahikawa Medical College, Japan
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46
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Tabor E. Tumor suppressor genes, growth factor genes, and oncogenes in hepatitis B virus-associated hepatocellular carcinoma. J Med Virol 1994; 42:357-65. [PMID: 8046425 DOI: 10.1002/jmv.1890420406] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A series of changes in the genes that control hepatocyte growth, or interference with the protein products of these genes, appears to have an important role in the etiology of hepatocellular carcinoma (HCC). Mutations of the p53 tumor suppressor gene have been identified in 30-50% of HCC patients in some geographic areas. Abnormalities of the RB tumor suppressor gene have been found in 20-25% of HCCs, including 80-86% of HCCs with p53 mutations. Overexpression of transforming growth factor alpha (TGF-alpha), insulin-like growth factor II (IGF-II), and the oncogenes N-ras, c-myc, and c-fos have been found in high percentages of HCC patients. The cumulative effect of these changes may be more important than the order in which they occur. Some of these changes may explain the mechanism(s) by which the hepatitis B virus participates in the development of HCC.
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Affiliation(s)
- E Tabor
- National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
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47
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Robinson WS. Molecular events in the pathogenesis of hepadnavirus-associated hepatocellular carcinoma. Annu Rev Med 1994; 45:297-323. [PMID: 8198385 DOI: 10.1146/annurev.med.45.1.297] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Chronic hepadnavirus infection is associated with hepatocellular carcinoma (HCC) in natural hosts such as humans, woodchucks, and Beechey ground squirrels. Several possible oncogenic mechanisms have been identified, including a potential role of the hepadnavirus x (hbx) gene, which transactivates transcription regulated by certain cis-acting sequences, e.g. regulatory sequences of the hepatitis B virus (HBV) and heterologous regulatory sequences of other viruses and cellular genes. The oncogenic potential of hbx is suggested by the observation of HCCs in hbx transgenic mice, the oncogenic transformation of cells expressing hbx in culture, and the transactivation of oncogenes c-myc and c-jun by hbx. Cis-activation of cellular oncogenes N-myc and c-myc by viral promoter insertion has been a common finding in woodchuck hepatitis virus (WHV)-associated HCCs of woodchucks. No such cis-activation of any cellular gene has been shown in virus-associated HCCs of ground squirrels or humans. Amplification and overexpression of the c-myc gene has been a common finding in HCCs of ground squirrels, and is rare in woodchuck or human HCCs. Point mutations in the p53 gene and allelic deletion of p53 have been common findings in human HCCs, but have not been found in HCCs in woodchucks and have been found rarely in ground squirrels. How each of these genetic changes in the different hosts contributes to HCC remains to be determined, but apparently different changes in different HCCs of hepadnavirus-infected hosts suggest that several separate genetic events may contribute to the development of HCC. These events may differ in each host, and some may not result from a direct virus-specific mechanism. Chronic hepadnavirus infection is often associated with chronic necroinflammatory liver disease and cirrhosis, a pathologic process common to several other risk factors for HCC. This suggests that this pathologic process (necroinflammatory disease) may be hepatocarcinogenic regardless of the inciting agent. Thus hepadnavirus infection may play an important role in the development of HCC by causing chronic hepatitis and HCC with the same mechanisms by which other risk factors for HCC cause chronic necroinflammatory liver disease and HCC.
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Affiliation(s)
- W S Robinson
- Stanford University School of Medicine, California 94305
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48
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Lehman TA, Greenblatt M, Bennett WP, Harris CC. Mutational spectrum of the p53 tumor suppressor gene: clues to cancer etiology and molecular pathogenesis. Drug Metab Rev 1994; 26:221-35. [PMID: 8082567 DOI: 10.3109/03602539409029793] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- T A Lehman
- Laboratory of Human Carcinogenesis, National Cancer Institute, Bethesda, Maryland 20892
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49
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Schirmacher P, Rogler CE, Dienes HP. Current pathogenetic and molecular concepts in viral liver carcinogenesis. VIRCHOWS ARCHIV. B, CELL PATHOLOGY INCLUDING MOLECULAR PATHOLOGY 1993; 63:71-89. [PMID: 8094924 DOI: 10.1007/bf02899246] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Hepatocellular carcinoma (HCC) is one of the most frequent malignancies in humans and in most cases a consequence of chronic infection of the liver by hepatotropic viruses (Hepatitis B Virus (HBV) and possibly Hepatitis C Virus (HCV)). Formation of HCC results from a stepwise process involving different preneoplastic lesions that reflect multiple genetic events, like protooncogene activation, tumor suppressor gene inactivation, and growth factor over- or reexpression. Recent investigations have gained new insights into how these factors are activated and may interact. In addition, improved knowledge of the molecular biology of HBV has led to better understanding of its pleiotropic effects on induction and progression in hepatocarcinogenesis.
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Affiliation(s)
- P Schirmacher
- Institute of Pathology, University Hospital, Mainz, Federal Republic of Germany
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50
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Soman NR, Wogan GN. Activation of the c-Ki-ras oncogene in aflatoxin B1-induced hepatocellular carcinoma and adenoma in the rat: detection by denaturing gradient gel electrophoresis. Proc Natl Acad Sci U S A 1993; 90:2045-9. [PMID: 8446626 PMCID: PMC46017 DOI: 10.1073/pnas.90.5.2045] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Sequence alterations in the exon 1 region of the rat c-Ki-ras gene were studied in DNA isolated from aflatoxin B1 (AFB1)-induced rat liver carcinomas and precursor lesions appearing 56 weeks after administration of the carcinogen. To detect the mutations with high sensitivity, DNA samples were analyzed by using polymerase chain reaction (PCR) amplification in conjunction with allele-specific oligonucleotide (ASO) hybridization together with a modified PCR-G+C clamp-denaturing gradient gel electrophoresis (DGGE) method. Mutations in the Ki-ras gene were present in all adenomas and carcinomas examined. The predominant mutation observed was a G.C-to-A.T base transition in codon 12 (GGT to GAT). Also present, but at low frequency, was a G.C-to-T.A base transversion in the same codon (GGT to TGT). In addition, 20% of the samples contained a G.C-to-T.A transversion in the second base position of codon 12 (GGT to GTT), a mutation not previously observed in AFB1-induced rat liver tumors. These results confirm and extend our previous findings that Ki-ras mutation is a prevalent event in hepato-cellular carcinogenesis induced in Fischer 344 rats by AFB1. The modified DGGE method described is applicable to the screening of multiple mutations in neoplastic lesions with high fidelity and sensitivity.
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Affiliation(s)
- N R Soman
- Division of Toxicology, Whitaker College of Health Sciences and Technology, Cambridge, MA
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