ABSENCE OF P53 GENE-MUTATIONS IN RAT COLON CARCINOMAS INDUCED BY AZOXYMETHANE

The K-ras and p53 genes are two of the most frequently mutated genes f ound in the human colonic tumors. Since azoxymethane (AOM) induced rat colonic neoplasms are similar to human colonic tumors in their histol ogical features and proliferation characteristics, the rat has been us ed as an experimental model to study the pathogenesis of colon cancer in humans. Although the presence of K-ras point mutations has been rep orted in AOM induced rat colonic tumors, there are no reports describi ng the frequency for mutation of the p53 gene in these tumors. In this study, colon adenocarcinomas induced in rats by AOM were examined for the presence of point mutations in exons 5-8 of the p53 gene, using a combination of single strand conformation (SSCP) analysis, immunohist ochemistry and direct DNA sequencing. SSCP analysis showed no differen ces in banding patterns between the normal mucosa and any of the 20 ad enocarcinomas analyzed, Nuclear p53 immunoreactivity was absent in all tumors examined. Since p53 point mutations predominate in malignant c olonic tumors, five adenocarcinomas with the greatest local invasivene ss were analyzed by direct DNA sequencing of exons 5-8 of the p53 gene . Direct DNA sequencing did not reveal mutations in any of the adenoca rcinomas analyzed, within the coding region of p53 gene that were sequ enced. The results from the present study indicate that point mutation s in the p53 gene, at least in the coding region (exons 5-8) are not i nvolved in the development of colon cancer induced by AOM in the rat.