β-Catenin gene alteration in glandular stomach adenocarcinomas in N-methyl-N-nitrosourea-treated and Helicobacter pylori-infected Mongolian gerbils

The goal of this study was to elucidate whether β-catenin gene mutations might contribute to glandular stomach carcinogenesis in Helicobacter pylori (H.pylori)-infected Mongolian gerbils. Firstly, exon 3 of gerbil β-catenin cDNA, a mutation hot spot, was cloned and sequenced and found to have 89.3% homology with the human form and 95.5% with the rat and mouse forms. Peptide sequence in this region was shown to be 100% conserved in these mammals. Then, 45 stomach adenocarcinomas induced with N-methyl-N-nitrosourea (MNU) plus H. pylori infection and 7 induced with MNU alone were examined for β-catenin expression by immunohistochemistry and for DNA mutations using a combination of microdissection and PCR-single strand conformation polymorphism analysis. One gastric cancer in the MNU+H. pylori group (2.2%) displayed nuclear (N) β-catenin localization, 3 (6.7%) showed cytoplasmic (C) distribution in local regions, and 41 (91.1%) demonstrated cell membrane (M) localization. Tumors induced by MNU alone showed only membranous β-catenin localization (7/7). Analysis of exon 3 of the β -catenin gene demonstrated all tumors with membrane or cytoplasmic staining as well as surrounding normal mucosa (S) to feature wild-type β-catenin. In contrast, the lesion with nuclear staining had a missense mutation at codon 34 [GAC (Gly)→GAA (Glu)] in exon 3 (1/ 1=100%, N vs. M, P<0.05; and N vs. S, P<0.05). In conclusion, these results suggest that β-catenin may not be a frequent target for mutation in stomach carcinogenesis in MNU+H. pylori-treated gerbils.