Froment O, Boivin S, Barbin A, Bancel B, Trepo C, Marion M J
Institut National de la Santé et de la Recherche Médicale, Unité 271, Hepatitis Research Unit, Lyon, France.
Cancer Res. 1994 Oct 15;54(20):5340-5.
Vinyl chloride is a DNA-damaging carcinogen which induces liver angiosarcomas in humans and animals. Activation of the Ki-ras 2 gene by a GC-->AT transition at the second base of codon 13 in human liver angiosarcomas associated with occupational exposure to vinyl chloride has been reported recently. In order to compare the molecular pathways of carcinogenesis in humans and animals, Sprague-Dawley rats were exposed to vinyl chloride and hepatic tumors, including two hepatocellular carcinomas and five liver angiosarcomas, were investigated for mutations at codons 12, 13 and 61 of the Ha-ras, Ki-ras and N-ras genes. High molecular weight DNA was amplified by the polymerase chain reaction and point mutations were analyzed by allele specific oligonucleotide hybridization, direct sequencing of polymerase chain reaction products and sequencing after cloning. None of the tumors exhibited a mutation in codons 12, 13 and 61 of the Ki-ras gene, nor in codons 12 of the Ha-ras gene or 61 of the N-ras gene. However, an activating AT-->TA transversion at base 2 of codon 61 of the Ha-ras gene was detected in the two hepatocellular carcinomas. Mutations involving codon 13 (GGC-->GAC) and codon 36 (ATA-->CTA) of the N-ras A gene were detected in two liver angiosarcomas, suggesting that the nature of the ras gene affected by a given carcinogen depends on host factors specific to cell types. Several additional base pair substitutions were found in exon 1 of the N-ras B and C sequences. NIH 3T3 transfection assays and Southern blot analysis of DNA from transformed NIH 3T3 cells confirmed the presence of a dominant activated N-ras gene. These results emphasize the differences in the molecular pathways leading to tumors in humans and rats and within a given species between different cell types.
氯乙烯是一种能损伤DNA的致癌物，可在人类和动物体内诱发肝血管肉瘤。最近有报道称，职业性接触氯乙烯的人类肝血管肉瘤中，Ki-ras 2基因在密码子13的第二个碱基处发生了GC→AT转换从而被激活。为了比较人类和动物的致癌分子途径，将斯普拉格-道利大鼠暴露于氯乙烯环境中，并对包括2例肝细胞癌和5例肝血管肉瘤在内的肝脏肿瘤进行了Ha-ras、Ki-ras和N-ras基因密码子12、13和61处的突变研究。通过聚合酶链反应扩增高分子量DNA，并通过等位基因特异性寡核苷酸杂交、聚合酶链反应产物直接测序以及克隆后测序来分析点突变。所有肿瘤在Ki-ras基因的密码子12、13和61处均未出现突变，在Ha-ras基因的密码子12或N-ras基因的密码子61处也未出现突变。然而，在2例肝细胞癌中检测到Ha-ras基因密码子61的第2个碱基处发生了激活型AT→TA颠换。在2例肝血管肉瘤中检测到N-ras A基因涉及密码子13（GGC→GAC）和密码子36（ATA→CTA）的突变，这表明受特定致癌物影响的ras基因的性质取决于细胞类型特有的宿主因素。在N-ras B和C序列的外显子1中还发现了几个额外的碱基对替换。NIH 3T3转染试验以及对转化的NIH 3T3细胞DNA的Southern印迹分析证实了显性激活的N-ras基因的存在。这些结果强调了人类和大鼠以及同一物种内不同细胞类型之间导致肿瘤的分子途径的差异。
