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The canonical Wnt–β‐catenin pathway is important in normal development. Mutations in β‐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 β‐catenin localization to the nucleus and represses β‐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 β‐catenin levels. However, confocal microscopy and subcellular fractionation studies revealed that Cby overexpression resulted in a small decrease in nuclear β‐catenin. Moreover, Cby overexpression caused a molecular weight shift in nuclear β‐catenin and resulted in decreased β‐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 β‐catenin localization in cultured GC cells. However, Cby did not affect cell proliferation rates or β‐catenin‐induced protein expression. Cby may be involved in the early events in the pathogenesis of GC. Chibby (Cby) is a 14‐kDa protein that inhibits β‐catenin localization to the nucleus and represses β‐catenin‐induced transcriptional activity. Cby expression was decreased in gastric cancer (GC) tissue and Cby expression altered β‐catenin localization in cultured GC cells. However, Cby did not affect cell proliferation rates or β‐catenin‐induced protein expression. [ABSTRACT FROM AUTHOR]

Helicobacter pylori colonizes the human stomach by infecting gastric epithelial cells. It is the primary cause of peptic ulcer disease and gastric cancer (GC). Cytotoxin-associated gene A (CagA) is a virulence factor produced by H. pylori. Strains positive for the CagA protein are associated with more severe gastric diseases. The 3' region of the cagA gene exhibits heterogeneity with respect to tyrosine phosphorylation motifs (EPIYA) and CagA multimerization motifs (CM). CagA proteins are categorized as either Western or Eastern based on EPIYA sequences. CM motifs are also identified as Western and Eastern based on CM sequences identified in Western and East Asian countries. It has been suggested that CagA proteins possessing an Eastern CM type are associated with less severe gastric disorders. In the present study, the effects of two CagA peptides with different CM motifs on cell function were compared: CagA with a Western and Eastern CM motif (CagA-WE), and CagA with two Western CM motifs (CagA-WW). CagA sequences were fused with green fluorescent protein (GFP) to form GFP-CagA fusion proteins. GFP-CagA and GFP control constructs were transfected into human gastric adenocarcinoma cells (AGS). GFP-CagA expression was verified by immunoblotting and immunofluorescence. The results demonstrated that, following 18 h, the CagA-WE-transfected cells were less adherent compared with the CagA-WW transfected cells. CagA has also been reported to cause cell elongation in AGS cells. In the current study, cell elongation was more frequent in the CagA-WW-transfected cells compared with the CagA-WE transfected cells (8.34 vs. 3.97% cells, respectively). The CagA peptides did not affect proliferation or apoptosis rates. These results suggest that different CM motif types may affect CagA virulence. [ABSTRACT FROM AUTHOR]