CADHERIN TRANSFECTION OF XENOPUS XTC CELLS DOWN-REGULATES EXPRESSION OF SUBSTRATE ADHESION MOLECULES

Cadherins are discussed not in terms of their adhesive function but ra ther as morphoregulatory proteins. Changes in gene expression followin g cadherin transfection of cells in culture or by overexpression in em bryos have, until now, not been reported. We established a protocol fo r stable transfection of Xenopus XTC cells and generated cells bearing high levels of membrane-integrated mouse uvomorulin (E-cadherin) or X enopus XB-cadherin. These cell lines showed drastically impaired subst rate adhesion on fibronectin and laminin. In immunoblot and radioimmun oprecipitation 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 tru ncated form of XB-cadherin lacking 38 of the most C-terminal amino aci ds was expressed in XTC cells, complex formation with endogenous caten ins was abolished, In these transfectants, substrate adhesion was not affected. These results prove that complex formation of transfected ca dherins in XTC cells with endogenous beta-catenin correlates with alte red synthesis of certain substrate adhesion molecules.