Chen B, Liu L, Castonguay A, Maronpot R R, Anderson M W, You M
Department of Pathology, Medical College of Ohio, Toledo 43699.
Carcinogenesis. 1993 Aug;14(8):1603-8. doi: 10.1093/carcin/14.8.1603.
In a previous study, the spectrum of H-ras mutations detected in B6C3F1 mouse liver tumors induced by 5, 50 or 150 mumol/kg body wt of N-nitrosodiethylamine (NDEA) was similar to that in spontaneous B6C3F1 mouse liver tumors, suggesting that activation of the H-ras gene in NDEA-induced mouse liver tumors may not be the direct result of the chemical interaction with the H-ras gene. In the present study, mutations in the H-ras oncogene from B6C3F1 mouse liver tumors induced by 5 or 50 mumol/kg body wt of NDEA were characterized by DNA amplification with polymerase chain reaction (PCR), single-strand conformation of polymorphism (SSCP) and direct sequence analysis. Twenty-one of 66 NDEA-induced B6C3F1 mouse liver tumors contained activated H-ras gene with 2 of 21 having a CG to AT transversion at the first base of codon 61, 17 of 21 having AT to GC transition and 2 of 21 having an AT to TA transversion at the second base of codon 61 in the H-ras gene. The predominant mutation, AT to GC transition (17/21, 81%) is consistent with the formation of O4-ethylthymine adduct, and is distinct from the predominant CG to AT transversion (50%) at the first base of codon 61 detected in H-ras gene from NDEA-induced B6C3F1 mouse liver tumors in a previous study by Stowers et al. Mutations in the K-ras oncogene from 59 A/J mouse lung tumors induced by 0.53 mmol/kg body wt of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were also characterized by using the above mentioned methods. Forty-six of 59 NNK-induced A/J mouse lung tumors contained activated K-ras genes. All 46 (100%) of the activated K-ras gene had GC to AT transitions at the second base of codon 12. The same mutation was observed in 70% (7/10) of the K-ras oncogene from A/J lung tumors induced by 4.8 mmol/kg body wt (given in 21 doses) of NNK. These data suggest that other factors in addition to genotoxic effect might be involved in the induction of rodent tumors by some carcinogens when given at higher doses. Therefore, further studies to compare the dose-dependent differences in the profile of ras mutations induced by chemical carcinogens may help to assess human cancer risk. Mutation(s) in exons 5-8 of the p53 gene was not found in these NDEA-induced mouse liver tumors and NNK-induced mouse lung tumors.
在先前的一项研究中，由5、50或150 μmol/kg体重的N-亚硝基二乙胺（NDEA）诱导的B6C3F1小鼠肝肿瘤中检测到的H-ras基因突变谱与自发的B6C3F1小鼠肝肿瘤中的相似，这表明在NDEA诱导的小鼠肝肿瘤中H-ras基因的激活可能不是与H-ras基因发生化学相互作用的直接结果。在本研究中，通过聚合酶链反应（PCR）进行DNA扩增、单链构象多态性（SSCP）和直接序列分析，对由5或50 μmol/kg体重的NDEA诱导的B6C3F1小鼠肝肿瘤中的H-ras癌基因进行了突变特征分析。在66个NDEA诱导的B6C3F1小鼠肝肿瘤中，有21个含有激活的H-ras基因，其中21个中有2个在密码子61的第一个碱基处发生了CG到AT的颠换，21个中有17个发生了AT到GC的转换，21个中有2个在H-ras基因密码子61的第二个碱基处发生了AT到TA的颠换。主要突变，即AT到GC的转换（17/21，81%）与O4-乙基胸腺嘧啶加合物的形成一致，并且与Stowers等人先前研究中在NDEA诱导的B6C3F1小鼠肝肿瘤的H-ras基因中检测到的密码子61第一个碱基处主要的CG到AT颠换（50%）不同。对由0.53 mmol/kg体重的4-（甲基亚硝基氨基）-1-（3-吡啶基）-1-丁酮（NNK）诱导的59个A/J小鼠肺肿瘤中的K-ras癌基因的突变也使用上述方法进行了特征分析。在59个NNK诱导的A/J小鼠肺肿瘤中，有46个含有激活的K-ras基因。所有46个（100%）激活的K-ras基因在密码子12的第二个碱基处都发生了GC到AT的转换。在由4.8 mmol/kg体重（分21次给药）的NNK诱导的A/J肺肿瘤的K-ras癌基因中，70%（7/10）也观察到了相同的突变。这些数据表明，当以较高剂量给予某些致癌物时，除了遗传毒性作用外，其他因素可能也参与了啮齿动物肿瘤的诱导。因此，进一步研究比较化学致癌物诱导的ras基因突变谱中的剂量依赖性差异可能有助于评估人类癌症风险。在这些NDEA诱导的小鼠肝肿瘤和NNK诱导的小鼠肺肿瘤中未发现p53基因外显子5 - 8中的突变。
