F9 teratocarcinoma cells in which β-catenin and/or plakoglobin genes are knocked-out were generated and investigated in an effort to define the role of β-catenin and plakoglobin in cell adhesion. Loss of β-catenin expression only did not affect cadherin-mediated cell adhesion activity. Loss of both β-catenin and plakoglobin expression, however, severely affected the strong cell adhesion activity of cadherin. In β-catenin-deficient cells, the amount of plakoglobin associated with E-cadherin dramatically increased. In β-catenin/plakoglobin-deficient cells, the level of E-cadherin and α-catenin markedly decreased. In these cells, E-cadherin formed large aggregates in cytoplasm and membrane localization of α-catenin was barely detected. These data confirmed that β-catenin or plakoglobin is required for α-catenin to form complex with E-cadherin. It was also demonstrated that plakoglobin can compensate for the absence of β-catenin. Moreover it was suggested that β-catenin or plakoglobin is required not only for the cell adhesion activity but also for the stable expression and cell surface localization of E-cadherin.
2005 by Japan Society for Cell Biology