Mutations and nuclear accumulation of β-catenin correlate with intestinal phenotypic expression in human gastric cancer

Aims: Abnormal localization of β-catenin is frequently observed in human gastric cancers. The aim of the present study was to evaluate relationships among gastrointestinal differentiation phenotypes, β-catenin localization and mutations of Wnt signalling genes. Methods and results: Seventy-seven regions in 39 gastric adenocarcinomas were classified according to β-catenin localization and gastric and intestinal phenotypes. Cases with membranous β-catenin localization showed a gradual decrease from gastric (G) (55% = 6/11) and gastric-and-intestinal-mixed (GI) (17% = 5/29) to intestinal (I) (0% = 0/21) phenotypes, while those with nuclear localization showed a concomitant increase: 18% (2/11), 41% (12/29), 95% (20/21) and 63% (10/16) for G, GI, I and null type (N), respectively (P < 0.001, membranous versus nuclear localization in G, GI through I). Mutations in exon 3 of the β-catenin gene were found in G (50% = 1/2), GI (67% = 8/12), I (45% = 9/20) and N (0% = 0/10) regions with nuclear β-catenin localization (GI versus N, P < 0.01; I versus N, P < 0.05). Adenomatous polyposis coli (APC) gene mutations were demonstrated only in GI, I and N types, irrespective of β-catenin localization. Molecular analysis of these genes revealed 10 tumours to be heterogeneous out of 16 informative cases (62.5%). Conclusion: Intestinal phenotypic expression is accompanied by a shift from membranous to cytoplasmic/nuclear accumulation of β-catenin. In contrast, N-type regions may progress along a different pathway.