Chibby Is A Weak Regulator Of Beta-Catenin Activity In Gastric Epithelium

The canonical Wnt-beta-catenin pathway is important in normal development. Mutations in beta-catenin or proteins involved with regulating its phosphorylation or localization result in its nuclear accumulation where it activates its target genes and stimulates cell proliferation. This pathway is dysregulated in many different types of cancer, including gastric cancer (GC). Chibby (Cby) is a 14-kDa protein that inhibits beta-catenin localization to the nucleus and represses beta-catenin-induced transcriptional activity. In the current study, we examined the expression and function of Cby in normal and cancerous human gastric tissue. Reverse-transcription polymerase chain reaction and immunohistochemistry revealed that Cby is expressed in human stomach and localized to glandular elements. Immunohistochemical staining intensity of Cby was decreased in GC tissue when compared with normal gastric epithelium. In AGS cells, a human gastric carcinoma cell line, Cby expression was low. Stable AGS cell transfectants overexpressing Cby were prepared. Cby overexpression did not affect proliferation rates or beta-catenin levels. However, confocal microscopy and subcellular fractionation studies revealed that Cby overexpression resulted in a small decrease in nuclear beta-catenin. Moreover, Cby overexpression caused a molecular weight shift in nuclear beta-catenin and resulted in decreased beta-catenin signaling in AGS cells as measured by the TopFlash assay. However, Cby overexpression did not affect c-Myc protein levels. To conclude, Cby expression was decreased in GC samples and Cby expression altered beta-catenin localization in cultured GC cells. However, Cby did not affect cell proliferation rates or beta-catenin-induced protein expression. Cby may be involved in the early events in the pathogenesis of GC.