No involvement of β-catenin gene mutation in gastric carcinomas induced by N-methyl-N-nitrosourea in male F344 rats

The agent N-methyl-N-nitrosourea (MNU) is a direct acting carcinogen and induces well-differentiated adenocarcinoma on the rat gastric mucosa. In this study, 27 histopathologically verified gastric carcinomas induced in male F344 rats were analyzed for mutations in the N-terminal phosphorylation sites (codons 1–51) of the β-catenin gene by using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) assays. In parallel studies, the specific localization of the β-catenin protein was also examined by immunohistochemical analysis. No mutations in the β-catenin gene were found in any of 27 gastric carcinomas induced by MNU. Immunohistochemical analysis resulted in the β-catenin protein to be localized in the plasma membrane but cytoplasmic and/or nuclear accumulation of β-catenin was not identified in any of these carcinomas. These results suggest that mutations in the β-catenin gene are less contributory to the development of rat gastric carcinomas induced by MNU. This animal model may provide a system for evaluating the mechanism of human gastric carcinogenesis that is not associated with β-catenin gene mutations.