Expression of β-catenin and γ-catenin in epithelial tumor cell lines and characterization of a unique cell line

In addition to its structural role, β-catenin has recently been identified as an oncogene, while its homologue γ-catenin (plakoglobin) seems to suppress tumorigenicity. Twenty-five epithelial tumor cell lines were screened; 18 expressed both β- and γ-catenin, two expressed neither protein, four showed β- but not γ-catenin expression, while only one cell line showed γ- but not β-catenin expression. As per literature search, the cell line expressing γ- but not β-catenin appeared to be unique. This cell line, SKBR-3, is a human breast cancer cell line which does not express β-catenin or E-cadherin protein. There is, however, expression of β-catenin, but not E-cadherin, mRNA. In order to determine the mechanism for this unique expression pattern, SKBR-3 cells were transfected with E-cadherin which resulted in expression of β-catenin protein. Immunofluorescent staining of the E-cadherin transfected SKBR-3 cells revealed β-catenin in the adherens junctions while transfection with just an epitope tagged (VSV) β-catenin showed expression only in the nucleus. Double transfection with E-cadherin and VSV β-catenin showed the β-catenin in the adherens junction of the E-cadherin transfected cells. These results indicate that the mechanism for the lack of β-catenin expression in the SKBR-3 cell line is possibly post-translational degradation and that when E-cadherin is transfected into these cells, the β-catenin is stabilized in the adherens junction and not degraded. This cell line should be of interest to those studying the role of the homologues, β- and γ-catenin, in cancer pathogenesis.