Mutant E-cadherin breast cancer cells do not display constitutive Wnt signaling

Participation of E-cadherin in the Wnt signaling pathway was suggested beca use of the dual role of beta -catenin in cell adhesion and the Wnt signalin g cascade. Whereas beta -catenin interacts at the cell membrane with the ce ll adhesion protein E-cadherin, in the nucleus it activates Wnt target gene s through formation of transcriptionally active complexes with members of t he Tcf/Lef family of transcription factors. Here, we analyzed by PCR and di rect cycle sequencing 26 human breast cancer cell lines for alterations in the E-cadherin gene. Genetic alterations were identified in eight cell line s. Five cell lines had truncating mutations, whereas three cell lines had i n-frame deletions in the gene transcript and expressed mutant E-cadherin pr oteins at the cell membrane. Involvement of E-cadherin in the Wnt pathway w as evaluated through determination of the activity of a Tcf reporter gene, which had been transiently transfected into 15 breast cancer cell lines. No ne of six E-cadherin mutant cell lines and four cell lines that exhibit tra nscriptional silencing of the E-cadherin gene showed Tcf-mediated transcrip tional activation. E-cadherin wild-type cell line DU4475 exhibited constitu tive Tcf-beta -catenin signaling activity and was found to express truncate d APC proteins. These results indicate that if cellular transformation occu rred through mutation of E-cadherin, it is not mediated via constitutive ac tivation of the Wnt signaling pathway.