Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: UMLS:C0596263 (carcinogenesis)
64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Over the past 10 years, much fascinating information has been obtained concerning the biochemistry, genetics, toxicological implications and molecular genetics of the N-acetylation polymorphism in mice. Using C57BL/6J (B6) mice as representative of rapid acetylation and A/J (A) mice as representing slow acetylation, it has been shown that the polymorphism observed in N-acetyltransferase (NAT) activity in liver also occurs in kidney, bladder, blood, and other tissues. The development of congenic acetylator mouse lines derived from B6 and A, have provided the necessary tools to study the role of the acetylation polymorphism, on either the B6 or A genetic background, free of nearly all other genetic differences between these strains. Eliminating genes which modify and complicate the differences due to the acetylator genes make the congenic lines very useful in toxicology studies, particularly those involving carcinogenesis. The molecular genetic basis of the acetylator polymorphism in B6 and A mice involves two Nat genes. Nat-1 encodes a protein termed NAT1 which is identical in rapid and slow acetylator strains. Nat-2, however, differs between rapid and slow strains by a single nucleotide change in the coding region. The corresponding NAT2 proteins differ by a single change at amino acid 99: an hydrophilic asparagine in rapid acetylator NAT2 to an hydrophobic isoleucine in NAT2 from slow acetylators. The mechanistic basis for the differences between rapid and slow acetylation in mice appears to be that NAT2 from the rapid B6 strain is 15-fold more stable at 37 degrees C and is transcribed/translated with a maximal efficiency twice that of the enzyme from slow acetylator A mice. Results discussed in this review indicate that mice provide an excellent system for studying the N-acetyltransferase polymorphism and also are useful for modelling several aspects of the human N-acetyltransferase polymorphism.
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PMID:Metabolic, molecular genetic and toxicological aspects of the acetylation polymorphism in inbred mice. 130 19

The metabolic activation of the heterocyclic food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) by two human cytochrome P450 monoxygenases (P4501A1 and P4501A2) and two human N-acetyltransferases (NAT1 and NAT2) was investigated. Various combinations of these enzymes were functionally expressed in COS-1 cells. DNA adducts resulting from the activation of IQ were assayed quantitatively by the 32P-postlabeling procedure. The highest adduct frequency was observed in cells expressing both CYP1A2 and NAT2. CYP1A2 in combination with NAT1 was 3-6 times less active. When expressed alone these enzymes gave rise to low adduct frequencies. Experiments with N-acetyl-IQ as substrate suggest that NAT1 and NAT2 in addition to their known role in N-acetylation display arylhydroxamic acid N, O-acetyltransferase (AHAT) activity. Quantitative differences in adduct formation between IQ and N-acetyl-IQ indicated that metabolic activation of these arylamines preferentially occurs by P4501A2-catalyzed N-hydroxylation followed by O-acetylation mediated through NAT1 and/or NAT2. These data, in combination with the known genetic polymorphism of NAT2, may explain the clinical observation that the acetylation polymorphism constitutes a risk factor in the carcinogenic activation of environmental mutagens.
Carcinogenesis 1992 Oct
PMID:The role of the human acetylation polymorphism in the metabolic activation of the food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). 142 30

Arylamine chemicals inflict a number of toxicities including cancer. Metabolic activation (i.e., oxidation) is required in order to elicit the toxic actions. Acetylation is an important step in the metabolic activation and deactivation of arylamines. N-acetylation forms the amide derivative which is often nontoxic. However, O-acetylation of the N-hydroxyarylamine (following oxidation) yields an acetoxy arylamine derivative which breaks down spontaneously to a highly reactive arylnitrenium ion, the ultimate metabolite responsible for mutagenic and carcinogenic lesions. Human capacity to acetylate arylamine chemicals is subject to a genetic polymorphism. Individuals segregate into rapid, intermediate, or slow acetylator phenotypes by Mendelian inheritance regulated by a single gene encoding for a polymorphic acetyltransferase isozyme (NAT2). Individuals homozygous for mutant alleles are deficient in the polymorphic acetyltransferase and are slow acetylators. A second acetyltransferase isozyme (NAT1) is monomorphic and is not regulated by the acetylator genotype. Several human epidemiological studies suggest an association between slow acetylator phenotype and urinary bladder cancer. In contrast, a few studies suggest a relationship between rapid acetylator phenotype and colorectal cancer. The basis for this paradox may relate to the relative importance of N- versus O-acetylation in the etiology of these cancers. Conclusions drawn from human epidemiological data are often compromised by uncontrolled environmental and other genetic factors. Our laboratory recently completed construction of homozygous rapid, heterozygous intermediate, and homozygous slow acetylator congenic Syrian hamsters to be homologous in greater than 99.975% of their genomes. The availability of these acetylator congenic lines should eliminate genetic variability in virtually all aspects of arylamine carcinogenesis except at the acetylator gene locus. Ongoing studies in these congenic hamster lines should provide unequivocal information regarding the role of genetic acetylator phenotype in susceptibility to arylamine-related cancers.
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PMID:Acetyltransferases and susceptibility to chemicals. 147 Nov 66

Epidemiological studies have shown that there is a significantly greater proportion of the rapid acetylator phenotype in patients with colorectal tumors than in controls; phenotype-related differences in bioactivation of dietary or environmental amines in the intestinal epithelium have been suggested as a mechanism for this effect. In the present study, we have used hepatic and intestinal cytosols to compare N-acetyltransferase (NAT1 and NAT2), O-acetyltransferase (OAT) and arylhydroxamic acid N,O-acyltransferase (AHAT) distribution in rapid and slow acetylator rabbits. The ratio (rapid/slow) for p-aminobenzoic acid acetylation (a selective substrate for NAT1) was 6 in liver, 1.7-2 in small intestine and 1.3-1.5 in large intestine while the ratio of sulfamethazine acetylation (a selective substrate for NAT2) was 150 in liver, 16-22 in small intestine and 1.8-2.5 in large intestine. The ratios (rapid/slow) for DNA binding of N-hydroxy-3,2'-dimethyl-4-aminobiphenyl and N-hydroxy-4-aminobiphenyl (primarily substrates for OAT) were 82-84 in liver, 13-20 in small intestine and 3.8-5.3 in large intestine and for DNA binding of N-hydroxy-2-acetylamidofluorene (a substrate for AHAT), the ratio was 432 in liver, 32-161 in small intestine and 8.8-13.5 in large intestine. The data show also that NAT1 activity is uniformly distributed along the intestinal tract whereas NAT2 activity is highest in the small intestine. In addition, hepatic and intestinal OAT and AHAT but not NAT1 activities in the rabbit intestine are similarly distributed to activities for NAT2, suggesting that NAT2, OAT and AHAT activities are properties of a single protein in the rapid acetylator phenotype. Moreover, OAT and AHAT activities were much higher in tissues from the rapid than the slow phenotype. The data support the hypothesis that phenotype-dependent metabolic activation of N-OH heterocyclic or aromatic amines to reactive acetoxy metabolites may be involved in the etiology of colorectal cancer.
Carcinogenesis 1991 Aug
PMID:Distribution of acetyltransferase activities in the intestines of rapid and slow acetylator rabbits. 186 Jan 67

The metabolic activation and detoxification pathways associated with the carcinogenic aromatic amines provide an extraordinary model of polymorphisms that can modulate human urinary bladder carcinogenesis. In this study, the metabolic N-acetylation of p-aminobenzoic acid (PABA) to N-acetyl-PABA (NAT1 activity) and of sulfamethazine (SMZ) to N-acetyl-SMZ (NAT2 activity), as well as the O-acetylation of N-hydroxy-4-aminobiphenyl (OAT activity; catalyzed by NAT1 and NAT2), were measured in tissue cytosols prepared from 26 different human bladder samples; then DNA was isolated for determination of NAT1 and NAT2 genotype and for analyses of carcinogen-DNA adducts. Both PABA and OAT activities were detected, with mean activities +/- SD of 2.9 +/- 2.3 nmol/min/mg protein and 1.4 +/- 0.7 pmol bound/mg DNA/min/mg protein, respectively. However, SMZ activities were below the assay limits of detection (< 10 pmol/min/mg protein). The levels of putative carcinogen-DNA adducts were quantified by 32P-postlabeling and averaged 2.34 +/- 2.09 adducts/10(8) deoxyribonucleotide phosphate (dNp). Moreover, the DNA adduct levels in these tissues correlated with their NAT1-dependent PABA activities (r = 0.52; P < 0.01) but not with their OAT activities. Statistical and probit analyses indicated that this NAT1 activity was not normally distributed and appeared bimodal. Applying the NAT1:OAT activity ratios (N:O ratio) allowed arbitrary designation of rapid and slow NAT1 phenotypes, with a cutpoint near the median value. Within each of these subgroups, NAT1 correlated with OAT (P < 0.05); DNA adduct levels were elevated 2-fold in individuals with the rapid NAT1 or NAT1/OAT phenotype. Examination of DNA sequence polymorphisms in the NAT1 gene by PCR have demonstrated that an NAT1 polyadenylation polymorphism is associated with differences in tissue NAT1 enzyme activity; accordingly, NAT1 activity in the bladder of individuals with the heterozygous NAT1*10 allele was 2-fold higher than in subjects homozygous for the putative wild-type NAT1*4 allele. Likewise, DNA adduct levels in the mucosa of the urinary bladder were found to be 2-fold (P < 0.05) higher in individuals with the heterozygous NAT1*10 allele (3.5 +/- 2.1 adducts/10(8) dNp) as compared to NAT1*4 homozygous (1.8 +/- 1.9 adducts/10(8) dNp). Thus, these data provide strong support for the hypothesis that NAT1 activity in the urinary bladder mucosa represents a major bioactivation step that converts urinary N-hydroxy arylamines to reactive N-acetoxy esters that form covalent DNA adducts.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Role of aromatic amine acetyltransferases, NAT1 and NAT2, in carcinogen-DNA adduct formation in the human urinary bladder. 758 81

Heterocyclic aromatic amines formed during the cooking of meat and meat-derived products can be activated to reactive metabolites which bind to DNA, induce mutations and cause tumors in animals. A principal route of metabolic activation is N-oxidation to hydroxylamines, and their subsequent activation by acetyltransferase-catalyzed O-acetylation. We have used mutagenicity assays to study O-acetylation of heterocyclic arylhydroxylamines by the two isozymes of human N-acetyltransferase, NAT1 and NAT2, expressed in Salmonella typhimurium. N-Acetylation was also examined, using an HPLC method. In addition, Salmonella strains with endogenous acetyltransferase and lacking this activating activity were used. Hydroxylamines of nine heterocyclic aromatic amines, IQ, isoIQ, MeIQ, MeIQx, NI, PhIP, Glu-P-1, Glu-P-2, and Trp-P-2 were generated in situ by rat liver S9 mix. The strains expressing human NAT1 and lacking acetyltransferase activity showing little or no ability to activate these substrates. The strains expressing human NAT2 and Salmonella acetyltransferase supported to different extents the activation of all the compounds except PhIP and Trp-P-2. N-Acetylation of IQ, MeIQx and PhIP was slow or not detectable. In conclusion, human NAT2 but not NAT1 can O-acetylate heterocyclic hydroxylamines. NAT2 probably plays a key role in the genotoxic effects of the above heterocyclic amines except for PhIP and Trp-P-2, which have NAT2-independent mutagenic activity.
Carcinogenesis 1995 Mar
PMID:Metabolic activation of heterocyclic aromatic amines catalyzed by human arylamine N-acetyltransferase isozymes (NAT1 and NAT2) expressed in Salmonella typhimurium. 769 26

To determine which of the N-acetyltransferase (NAT) alleles [monomorphic (NAT1) or polymorphic (NAT2)] are expressed in the target cells for arylamine carcinogenesis, namely normal human uroepithelial cells, cDNA was prepared from cellular RNA and amplified by polymerase chain reaction (PCR), using upstream primer 1 comprising the 5' end (nt 47-68) and either downstream primers 2 (nt 908-889) or 3 (nt 953-931) corresponding with the 3' end. With primers 1 and 2, selective for NAT1, a characteristic 861 bp DNA fragment was obtained, whereas with primers 1 and 3, selective for NAT2, a characteristic 907 bp fragment was formed. Similarly, the PCR-amplified cDNA products from the SV40-immortalized human uroepithelial cell line were also found to contain both NAT1 and NAT2. Restriction fragment length polymorphism (RFLP) analysis with HincII (digesting NAT2 to produce 659 bp and 248 bp fragments) and HindIII (digesting NAT1 to produce a 786 bp fragment) further confirmed the authenticity of the NAT alleles. Furthermore, the NAT genotypes of 38 individuals were determined by PCR amplification of lymphocyte DNA and subsequent RFLP analysis using TaqI, KpnI and BamHI. The genotypes were compared to their in vivo acetylator phenotypes which were determined by measuring 5-acetylamino-6-formylamino-3-methyluracil and 1-methylxanthine in urine following administration of caffeine. A good correlation between the genotype and phenotype was obtained in the study population and the frequency of NAT2 allele distribution was M1 > wild-type > M2 > M3. These results suggest that susceptibility to arylamine-induced bladder cancer might be influenced by both hepatic and bladder NAT and that the NAT genotype might be a useful biomarker for screening high risk individuals for bladder cancer resulting from exposure to arylamines.
Carcinogenesis 1994 Dec
PMID:Expression of N-acetyltransferase (NAT) in cultured human uroepithelial cells. 800 Dec 35

A genetic polymorphism at the NAT2 gene locus, encoding for polymorphic N-acetyltransferase (NAT2), segregates individuals into rapid, intermediate or slow acetylator phenotypes. Both rapid and slow acetylator phenotypes have been associated with increased incidence of cancer in certain target organs related to arylamine exposure, suggesting a role for acetylation in both the activation and deactivation of arylamine carcinogens. A second gene (NAT1) encodes for a different acetyltransferase isozyme (NAT1) that is not subject to the classical acetylation polymorphism. In order to assess the relative ability of NAT1 and NAT2 to activate and deactivate arylamine carcinogens, we tested the capacity of recombinant human NAT1 and NAT2, expressed in Escherichia coli XA90 strains DMG100 and DMG200 respectively, to catalyze the N-acetylation (deactivation) and O-acetylation (activation) of a variety of carbocyclic and heterocyclic arylamine carcinogens. Both NAT1 and NAT2 catalyzed the N-acetylation of each of the 17 arylamines tested. Rates of N-acetylation by NAT1 and NAT2 were considerably lower for heterocyclic arylamines such as 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), particularly those (e.g. IQ) with steric hindrance to the exocyclic amino group. For carbocyclic arylamines such as 4-aminobiphenyl and beta-naphthylamine, the apparent affinity was significantly (P < 0.05) higher for NAT2 than NAT1. NAT1/NAT2 activity ratios and clearance calculations suggest a significant role for the polymorphic NAT2 in the N-acetylation of carbocyclic arylamine carcinogens. Both NAT1 and NAT2 catalyzed acetyl coenzyme A-dependent O-acetylation of N-hydroxy-2-aminofluorene and N-hydroxy-4-aminobiphenyl to yield DNA adducts. NAT1 catalyzed paraoxon-resistant, intramolecular N,O-acetyltransferase-mediated activation of N-hydroxy-2-acetylaminofluorene and N-hydroxy-4-acetylaminobiphenyl at low rates; catalysis by NAT2 was not readily detectable in the presence of paraoxon. In summary these studies strongly suggest that the human acetylation polymorphism influences both the metabolic activation (O-acetylation) and deactivation (N-acetylation) of arylamine carcinogens via polymorphic expression of NAT2. These findings lend mechanistic support for human epidemiological studies suggesting associations between both rapid and slow acetylator phenotype and cancers related to arylamine exposure.
Carcinogenesis 1993 Aug
PMID:Metabolic activation and deactivation of arylamine carcinogens by recombinant human NAT1 and polymorphic NAT2 acetyltransferases. 835 47

The role of acetylation in the genotoxicity of the heterocyclic amine, batracylin, was evaluated in Salmonella typhimurium strains expressing various levels of N- and O-acetyltransferase activity. A significant correlation was observed between batracylin-induced mutagenicity and bacterial N-acetyltransferase activity. Strains with the greatest capacity for N-acetylating batracylin (YG 1012 and YG 1024) were the most sensitive to the mutagenic effects of the drug. The number of revertants/nmol batracylin and the formation of acetylbatracylin were approximately 50-fold greater in YG 1024 compared to TA 98 which expresses endogenous levels of N-acetyltransferase. A similar response was observed with strains YG 1012 and TA 1538. Strains (TA 98/1,8-DNP6 or TA 1538/1,8-DNP6) which lack the ability to N-acetylate batracylin were the least sensitive to the mutagenic effects of the drug. At 1 microgram/plate of batracylin, the number of revertants in TA 1538 and TA 98 was 4-fold higher than that observed in TA 1538/1,8-DNP6 and TA 98/1,8-DNP6. To determine if batracylin was a substrate for human N-acetyltransferases, assays were performed in bacteria expressing NAT1 or NAT2. Both strains were capable of N-acetylating batracylin. The strain expressing NAT2 (DJ 460) formed a significantly greater amount of acetylbatracylin, as well as batracylin-induced revertants, compared to the strain expressing NAT1 (DJ 400). These results demonstrate that the mutagenicity of batracylin is directly related to N-acetyltransferase activity. Data obtained in bacteria expressing either human NAT1 and NAT2 show that batracylin is capable of being bioactivated by both human enzymes. In addition, the higher enzyme activity and mutagenicity in bacteria expressing NAT2 suggests that batracylin is a substrate of this enzyme in humans.
Carcinogenesis 1996 Jan
PMID:The role of acetylation in the mutagenicity of the antitumor agent, batracylin. 856 19

Genes for the 290 amino acid, 33-34 kDa cytosolic acetyltransferases (NAT1* and NAT2*) from rat and hamster were cloned and expressed in Escherichia coli. Active clones were selected by a simple visual test for their ability to decolorize 4-aminoazobenzene in bacterial medium by acetylation. These recombinant acetyltransferases were analyzed for: (i) N-acetyltransferase, which was assayed by the rate of acetyl coenzyme A-dependent N-acetylation of 2-aminofluorene (2-AF) or 4-aminoazobenzene (AAB); (ii) arylhydroxamic acid acyltransferase, assayed by N,O-acyltransfer with N-hydroxy-N-acetyl-2-aminofluorene. Both NAT2s showed first order increases in N-acetylation rates with increasing 2-AF or AAB concentrations between 5 and 100 microM, with apparent K(m) values of 22-32 and 62-138 microM respectively. Although under the same conditions the N-acetylation rates for the two NAT1s declined by > 50%, below 5 microM 2-AF or AAB, the NAT rate data fit Michaelis-Menten kinetics, and the apparent K(m) values were 0.2-0.9 microM. For N,O-acyltransferase, the apparent K(m) values of the NAT1s were approximately 6 microM, while the K(m) values of the NAT2s were approximately 20- to 70-fold higher. SDS-PAGE/Western blot analysis of the recombinant acetyltransferases gave apparent relative molecular weights (MWr) of approximately 31 kDa for both NAT1s and rat NAT2 and approximately 29 kDa for hamster NAT2. Comparable MWr values were observed for native hamster liver NAT1 and NAT2 and for rat NAT1 under the same conditions. Although we did not detect NAT2-like activity in rat liver cytosol previously, the present data show that the rat NAT2* gene does code for a functional acetyltransferase, with properties similar to those of hamster liver NAT2. The data also indicate that at low substrate concentrations, NAT1 would apparently play the predominant role in vivo in N-acetylation and N,O-acyltransfer of aromatic amine derivatives, including their metabolic activation to DNA-reactive agents.
Carcinogenesis 1996 Aug
PMID:Recombinant rat and hamster N-acetyltransferases-1 and -2: relative rates of N-acetylation of arylamines and N,O-acyltransfer with arylhydroxamic acids. 876 33


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