DEMONSTRATION OF RAS AND P53 GENE-MUTATIONS IN CARCINOMAS IN THE FORESTOMACH AND INTESTINE AND SOFT-TISSUE SARCOMAS INDUCED BY N-METHYL-N-NITROSOUREA IN THE RAT

The presence of ras family and p53 gene mutations in rat forestomach, intestine and liver tumors and soft tissue sarcomas induced by N-methy l-N-nitrosourea (MNU) was examined using polymerase chain reaction-sin gle strand conformation polymorphism (PCR-SSCP) followed by direct seq uencing analysis. In the forestomach squamous cell carcinomas (SCC), H a-ras and p53 mutations were detected in 2 (40%) and 4 (80%) of 5 case s, respectively. The figures for Ki-ras and p53 gene mutations in aden ocarcinomas of the large and small intestines were 3 (18.8%) and 5 (31 .3%) of 16 cases. Soft tissue sarcomas in different sites were found t o have mutations of Ki-ras in 7 (23.3%) and of p53 in 9 (30%) of 30 ca ses. One forestomach SCC and 2 soft tissue sarcomas had double p53 mut ations in different exons. Single cases of forestomach SCC and intesti nal adenocarcinoma had mutations in both Ki-ras and p53 genes. No muta tions were found in counterpart benign tumors or hepatocellular adenom as. The p53 mutation spectrum revealed preferential clustering within exon 8 for the forestomach SCCs, and exons 5 and 8 for the intestinal adenocarcinomas, whereas the distribution was evenly spread through ex ons 5 to 8 in soft tissue sarcomas. All the detected ras or p53 mutati ons were G:C to A:T transitions. These results indicate firstly that s pecific Ki-ras, Ha-ras and p53 gene mutations in MNU-induced lesions a re related to particular alkylation sites (G:C to A:T transitions) and secondly, although not essential, Ki-ras, Ha-ras or p53 gene mutation s may be involved in the progression stage of forestomach, intestine a nd soft tissue neoplasms induced by MNU.