Hein D W, Doll M A, Rustan T D, Gray K, Feng Y, Ferguson R J, Grant D M
Department of Pharmacology and Toxicology, University of North Dakota School of Medicine, Grand Forks 58202-9037.
Carcinogenesis. 1993 Aug;14(8):1633-8. doi: 10.1093/carcin/14.8.1633.
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.
N-乙酰转移酶（NAT2）基因位点的一种基因多态性可将个体分为快速、中间或慢速乙酰化代谢型，该基因编码多态性N-乙酰转移酶（NAT2）。快速和慢速乙酰化代谢型均与某些与芳胺暴露相关的靶器官癌症发病率增加有关，这表明乙酰化在芳胺致癌物的激活和失活过程中均发挥作用。另一个基因（NAT1）编码一种不同的乙酰转移酶同工酶（NAT1），该同工酶不存在经典的乙酰化多态性。为了评估NAT1和NAT2激活和失活芳胺致癌物的相对能力，我们分别测试了在大肠杆菌XA90菌株DMG100和DMG200中表达的重组人NAT1和NAT2催化多种碳环和杂环芳胺致癌物的N-乙酰化（失活）和O-乙酰化（激活）的能力。NAT1和NAT2均催化了所测试的17种芳胺中每种的N-乙酰化反应。对于杂环芳胺，如2-氨基-3-甲基-咪唑并[4,5-f]喹啉（IQ），尤其是那些对外环氨基有空间位阻的（如IQ），NAT1和NAT2的N-乙酰化速率相当低。对于碳环芳胺，如4-氨基联苯和β-萘胺，NAT2的表观亲和力显著高于NAT1（P<0.05）。NAT1/NAT2活性比和清除率计算表明，多态性NAT2在碳环芳胺致癌物的N-乙酰化过程中起重要作用。NAT1和NAT2均催化N-羟基-2-氨基芴和N-羟基-4-氨基联苯的依赖于乙酰辅酶A的O-乙酰化反应，生成DNA加合物。NAT1以低速率催化对氧磷抗性、分子内N,O-乙酰转移酶介导的N-羟基-2-乙酰氨基芴和N-羟基-4-乙酰氨基联苯的激活；在对氧磷存在的情况下，未轻易检测到NAT2的催化作用。总之，这些研究强烈表明，人类乙酰化多态性通过NAT2的多态性表达影响芳胺致癌物的代谢激活（O-乙酰化）和失活（N-乙酰化）。这些发现为人类流行病学研究提供了机制支持，这些研究表明快速和慢速乙酰化代谢型均与与芳胺暴露相关的癌症之间存在关联。
