Cadherin transfection of Xenopus XTC cells downregulates expression of substrate adhesion molecules

Cadherins are discussed not in terms of their adhesive function but rather as morphoregulatory proteins. Changes in gene expression following cadherin transfection of cells in culture or by overexpression in embryos have, until now, not been reported. We established a protocol for stable transfection of Xenopus XTC cells and generated cells bearing high levels of membrane-integrated mouse uvomorulin (E-cadherin) or Xenopus XB-cadherin. These cell lines showed drastically impaired substrate adhesion on fibronectin and laminin. In immunoblot and radioimmunoprecipitation experiments, we found that fibronectin and alpha 3/beta 1 integrin are downregulated. The reduced amounts of proteins result from a decrease of the respective mRNAs as proven by RNase protection assays. Coprecipitations revealed that transfected cadherin molecules are complexed with alpha-catenin and beta-catenin at plasma membranes. However, the alpha-catenin present in the XB-cadherin complex differs immunologically from that found in the uvomorulin complex. When a truncated form of XB-cadherin lacking 38 of the most C-terminal amino acids was expressed in XTC cells, complex formation with endogenous catenins was abolished. In these transfectants, substrate adhesion was not affected. These results prove that complex formation of transfected cadherins in XTC cells with endogenous beta-catenin correlates with altered synthesis of certain substrate adhesion molecules.