Donnelly P J, Devereux T R, Foley J F, Maronpot R R, Anderson M W, Massey T E
Department of Pharmacology and Toxicology, Queen's University, Kingston, Ontario, Canada.
Carcinogenesis. 1996 Aug;17(8):1735-40. doi: 10.1093/carcin/17.8.1735.
In addition to being a potent hepatocarcinogen, aflatoxin B1 (AFB1) is a pulmonary carcinogen in experimental animals and epidemiological studies have shown an association between AFB1 exposure and lung cancer in humans. Since point mutations at codons 12, 13 and 61 of the K-ras protooncogene are often implicated in chemically induced mouse lung tumors and in human lung adenocarcinomas, we undertook an investigation of the role of K-ras activation in AFB1-induced pulmonary carcinogenesis. Female AC3F1 (A/J x C3H/HeJ) mice were treated with AFB1 (150 mg/kg i.p., divided into 24 doses over 8 weeks), and 6-14 months after the completion of dosing mice were killed and pulmonary adenomas and carcinomas removed. Of the 76 AFB1-induced lung tumors analyzed by single strand conformation polymorphism (SSCP) and direct sequencing, 75 possessed K-ras codon 12 mutations (46 GTT, 14 GAT, 13 TGT and 2 TTT; normal, GGT) and one had a GGC-->CGC mutation in codon 13. The observation that K-ras mutations occurred only at G:C base pairs is in agreement with N7-guanine being the primary site of AFB1-DNA adduct formation and with guanine residues being targets for AFB1-induced oxidative DNA damage via formation of 8-hydroxydeoxyguanosine (8-OHdG). The AFB1-specific nature of the observed K-ras mutation spectrum and the fact that 100% of the tumor samples examined contained K-ras mutations is consistent with K-ras activation being an early, critical event in AFB1-induced pulmonary carcinogenesis in AC3F1 mice. The parental origin of the observed K-ras mutations was determined by allele-specific PCR amplification of AFB1-induced lung tumor DNA followed by SSCP analysis. In the vast majority of tumors (73/76), the mutated K-ras allele was derived from the lung tumor susceptible A/J parent. This finding supports the existence of a link between K-ras and differences in mouse lung tumor susceptibility.
黄曲霉毒素B1（AFB1）不仅是一种强效的肝癌致癌物，在实验动物中还是一种肺癌致癌物，并且流行病学研究已表明人类接触AFB1与肺癌之间存在关联。由于K-ras原癌基因第12、13和61密码子处的点突变常与化学诱导的小鼠肺肿瘤以及人类肺腺癌有关，我们对K-ras激活在AFB1诱导的肺癌发生中的作用进行了研究。用AFB1（150mg/kg腹腔注射，在8周内分成24剂）处理雌性AC3F1（A/J×C3H/HeJ）小鼠，给药结束后6至14个月处死小鼠，并切除肺腺瘤和癌。通过单链构象多态性（SSCP）和直接测序分析的76个AFB1诱导的肺肿瘤中，75个具有K-ras第12密码子突变（46个GTT、14个GAT、13个TGT和2个TTT；正常为GGT），1个在第13密码子处有GGC→CGC突变。K-ras突变仅发生在G:C碱基对的观察结果与N7-鸟嘌呤作为AFB1-DNA加合物形成的主要位点以及鸟嘌呤残基作为通过形成8-羟基脱氧鸟苷（8-OHdG）而受到AFB1诱导的氧化性DNA损伤的靶点一致。观察到的K-ras突变谱的AFB1特异性以及所检测的肿瘤样本100%都含有K-ras突变这一事实，与K-ras激活是AC3F1小鼠中AFB1诱导的肺癌发生中的一个早期关键事件相一致。通过对AFB1诱导的肺肿瘤DNA进行等位基因特异性PCR扩增，随后进行SSCP分析，确定了观察到的K-ras突变的亲本来源。在绝大多数肿瘤（73/76）中，突变的K-ras等位基因来自肺肿瘤易感的A/J亲本。这一发现支持了K-ras与小鼠肺肿瘤易感性差异之间存在联系。
