Cerutti P, Hussain P, Pourzand C, Aguilar F
Department of Carcinogenesis, Swiss Institute for Experimental Cancer Research, Epalinges/Lausanne.
Cancer Res. 1994 Apr 1;54(7 Suppl):1934s-1938s.
Point mutations in ras protooncogenes and in the p53 tumor suppressor gene are common in many forms of human cancer. The identification of carcinogens which are responsible for their induction in humans is of great interest because it may suggest measures for disease prevention. Furthermore, the load of somatic mutations in cancer-related genes in premalignant tissues may become a useful parameter for risk assessment. For the measurement of such mutations, highly sensitive genotypic mutation systems are required which avoid the selection and clonal expansion of cells on the basis of a mutated phenotype. We have developed the restriction fragment length polymorphism/polymerase chain reaction method for genotypic mutation analysis and applied it to the study of the mutability of hot-spot codons in c-H-ras1 and p53 genes with human carcinogens. In particular, we studied the mutability of codons 247-250 of p53 with the mycotoxin aflatoxin B1 (AFB1) in human hepatocytes. AFB1 preferentially induced the transversion of guanosine to thymidine in the third position of codon 249, generating the same mutation which is found in a large fraction of hepatocellular carcinomas from regions of the world with AFB1-contaminated food. Our results are in support of AFB1 as an etiological factor for hepatocellular carcinoma in AFB1-contaminated areas. In an ongoing study we are comparing the load of mutations in hot-spot codon 12 of c-H-ras1 in urinary bladder carcinoma and in normal tissue, by restriction fragment length polymorphism/polymerase chain reaction. We observed moderately elevated abundances of guanosine to thymidine transversions in the middle position of codon 12 in tumor DNA. These results may reflect a mutator phenotype of the tumor tissue or they could be the consequence of the heterogeneity of the biopsies which were analyzed.
ras原癌基因和p53肿瘤抑制基因中的点突变在多种人类癌症中很常见。确定导致这些基因在人类中发生突变的致癌物备受关注，因为这可能提示疾病预防措施。此外，癌前组织中癌症相关基因的体细胞突变负荷可能成为风险评估的有用参数。为了检测此类突变，需要高度敏感的基因型突变系统，该系统可避免基于突变表型对细胞进行选择和克隆扩增。我们开发了用于基因型突变分析的限制性片段长度多态性/聚合酶链反应方法，并将其应用于研究c-H-ras1和p53基因热点密码子与人类致癌物的突变性。特别是，我们研究了黄曲霉毒素B1（AFB1）对人肝细胞中p53基因第247-250密码子的突变性。AFB1优先诱导密码子249第三位的鸟苷向胸苷的颠换，产生与世界上AFB1污染地区大部分肝细胞癌中发现的相同突变。我们的结果支持AFB1作为AFB1污染地区肝细胞癌的病因。在一项正在进行的研究中，我们通过限制性片段长度多态性/聚合酶链反应比较膀胱癌和正常组织中c-H-ras1基因第12位热点密码子的突变负荷。我们观察到肿瘤DNA中密码子12中间位置鸟苷向胸苷颠换的丰度适度升高。这些结果可能反映了肿瘤组织的突变表型，也可能是所分析活检组织异质性的结果。
