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 Nmethyl‐N‐nitrosourea (MNU) was examined using polymerase chain reaction‐single strand conformation polymorphism (PCR‐SSCP) followed by direct sequencing analysis. In the forestomach squamous cell carcinomas (SCC), Ha‐ros and p53 mutations were detected in 2 (40%) and 4 (80%) of 5 cases, respectively. The figures for Ki‐ras and p53 gene mutations in adenocarcinomas 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 to have mutations of Ki‐ras in 7 (23.3%)and of p53 in 9 (30%) of 30 cases. One forestomach SCC and 2 soft tissue sarcomas had double p53 mutations in different exons. Single cases of forestomach SCC and intestinal adenocarcinoma had mutations in both Ki‐ras and p53 genes. No mutations were found in counterpart benign tumors or hepatocellular adenomas. 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 exons 5 to 8 in soft tissue sarcomas. All the detected ras or p53 mutations were G:C to A:T transitions. These results indicate firstly that specific Ki‐ras, Ha‐ras and p53 gene mutations in MNU‐induced lesions are related to particular alkylation sites (G:C to A:T transitions) and secondly, although not essential, Ki‐ras, Ha‐ras or p53 gene mutations may be involved in the progression stage of forestomach, intestine and soft tissue neoplasms induced by MNU.