Expression of beta-catenin and gamma-catenin in epithelial tumor cell lines and characterization of a unique cell line.

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