A SHORT CORE REGION OF E-CADHERIN IS ESSENTIAL FOR CATENIN BINDING AND IS HIGHLY PHOSPHORYLATED

Classical cadherins associate with three cytoplasmic proteins, termed alpha,- beta- and gamma-catenin. This association mediates the attachm ent of cadherins to the microfilament network, which is believed to be of major importance for cadherin function. Deletion of the carboxyter minal 72-amino acid residues of E-cadherin had been previously shown t o prevent catenin binding. Here we have analyzed additional mutants of E-cadherin with deletions within this region and identified a core re gion of 30 amino acids (E-cadherin pos. 832-862) essential for the int eraction with catenins. Phosphorylation analysis of wild-type and muta nt E-cadherin indicates that the catenin-binding domain is highly phos phorylated. In particular, the 30 amino acid region contains 8 serine residues which are well conserved among cadherins. To elucidate whethe r phosphorylation might be important for cadherin-catenin complex form ation, site-directed mutagenesis experiments were performed. Partial s ubstitutions of up to 5 of the 8 serine residues in the cluster had no influence on E-cadherin-catenin complex formation and E-cadherin medi ated cell adhesion, although phosphorylation of E-cadherin was reduced . In contrast, substitution of the whole serine cluster completely abo lished phosphorylation and affected complex formation with catenins. T hese results suggest that E-cadherin-catenin interaction may be regula ted by phosyhorylation of the catenin-binding domain, which might repr esent one molecular mechanism to regulate cadherin mediated cell adhes ion.