Regulation of β-Catenin Structure and Activity by Tyrosine Phosphorylation

Abstract

β-Catenin plays a dual role as a key effector in the regulation of adherens junctions and as a transcriptional coactivator. Phosphorylation of Tyr-654, a residue placed in the last armadillo repeat of β-catenin, decreases its binding to E-cadherin. We show here that phosphorylation of Tyr-654 also stimulates the association of β-catenin to the basal transcription factor TATAbinding protein. The structural bases of these different affinities were investigated. Our results indicate that the β-catenin C-terminal tail interacts with the armadillo repeat domain, hindering the association of the armadillo region to the TATA-binding protein or to Ecadherin. Phosphorylation of β-catenin Tyr-654 decreases armadillo-C-terminal tail association, uncovering the last armadillo repeats. In a C-terminal-depleted β-catenin, the presence of a negative charge at Tyr-654 does not affect the interaction of the TATA-binding protein to the armadillo domain. However, in the case of E-cadherin, the establishment of ion pairs dominates its association with β-catenin, and its binding is greatly dependent on the absence of a negative charge at Tyr-654. Thus, phosphorylation of Tyr-654 blocks the Ecadherin-β-catenin interaction, even though the steric hindrance of the C-tail is no longer present. These results explain how phosphorylation of β-catenin in Tyr-654 modifies the tertiary structure of this protein and the interaction with its different partners.