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. Pep‐tide 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 mis‐sense 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.