A mutation in alpha-catenin disrupts adhesion in clone A cells without perturbing its actin and beta-catenin binding activity.

Cadherin mediated cell-cell adhesion requires cytoplasmic connections to the cytoskeleton mediated by alpha-catenin. Original descriptions of the catenins, as well as our own in vitro studies, have suggested that this connection was mediated by the interaction of alpha-catenin to actin. Loss of adhesion in the human colon carcinoma cell line "Clone A" is the result of an internal deletion mutation of 158 residues near the N-terminus of the protein resulting in an 80 kD mutated protein. Transfection of these cells with the full length protein restores the normal adhesive phenotype. We have characterized this mutant protein in efforts to understand the normal function of alpha-catenin and, in particular, the region deleted in the Clone A mutant. Co-precipitation experiments using whole cell lysates indicate that the mutant form of alpha-catenin binds beta-catenin and plakoglobin, and can form a structural complex with E-cadherin via these interactions. Actin co-sedimentation assays show that the recombinant mutant binds and bundles F-actin and binds both actin and beta-catenin simultaneously, as seen with wild type alpha-catenin. These results suggest that the stabilization of the E-cadherin-catenin complex may be mediated by factors beyond its direct interaction with actin. We conclude that a region near the N-terminus of alpha-catenin mediates additional interactions between the adhesive complex and the cytoskeleton that are critical for functional adhesion.