Regulation of E-cadherin/catenin association by tyrosine phosphorylation

Alteration of cadherin-mediated cell-cell adhesion is frequently associated to tyrosine phosphorylation of p120- and β-catenins. We have examined the role of this modification in these proteins in the control of β-catenin/E-cadherin binding using in vitro assays with recombinant proteins. Recombinant pp60(c-src) efficiently phosphorylated both catenins in vitro, with stoichiometries of 1.5 and 2.0 mol of phosphate/mol of protein for β-catenin and p120-catenin, respectively. pp60(c-src) phosphorylation had opposing effects on the affinities of β-catenin and p120 for the cytosolic domain of E-cadherin; it decreased (in the case of β-catenin) or increased (for p120) catenin/E-cadherin binding. However, a role for p120- catenin in the modulation of β-catenin/E-cadherin binding was not observed, since addition of phosphorylated p120-catenin did not modify the affinity of phosphorylated (or unphosphorylated) β-catenin for E-cadherin. The phosphorylated Tyr residues were identified as Tyr-86 and Tyr-654. Experiments using point mutants in these two residues indicated that, although Tyr-86 was a better substrate for pp60(c-src), only modification of Tyr-654 was relevant for the interaction with E-cadherin. Transient transfections of different mutants demonstrated that Tyr-654 is phosphorylated in conditions in which adherens junctions are disrupted and evidenced that binding of β-catenin to E-cadherin in vivo is controlled by phosphorylation of β-catenin Tyr-654.