Recently, data which prove that Writ pathway activation may be an early event in multistep carcinogenesis in the stomach have been accumulating. We examined the effect of flavanone against beta-catenin/Tef signaling in AGS gastric cancer cells. Reporter gene assay showed that flavanone inhibited beta-catenin/Tcf signaling efficiently. In addition, the inhibition of beta-catenin/Tcf signaling by flavanone in HEK293 cells transiently transfected with constitutively mutant beta-catenin gene, whose product is not phosphorylated by GSK3 beta, indicates that its inhibitory mechanism was related to beta-catenin itself or downstream components. To investigate the precise inhibitory mechanism, we performed immunofluorescence, Western blot, and EMSA. As a result, our data revealed that there is no change of beta-catenin distribution and of nuclear beta-catenin levels through flavanone. In addition, the binding of Tcf complexes to DNA is not influenced by flavanone. The beta-catenin/Tcf transcriptional target gene cyclinD1 was downregulated by flavanone. These data suggest that flavanone inhibits the transcription of beta-catenin/Tcf responsive genes, by modulating Tcf activity without disrupting beta-catenin/Tcf complex formation. (c) 2005 Elsevier Inc. All rights reserved.