Uncoupling of XB/U-cadherin-catenin complex formation from its function in cell-cell adhesion.

Xenopus XB/U-cadherin forms functional complexes with mouse alpha- and beta-catenins and p120(cas) when expressed in murine L-TK- fibroblasts. These cells were stably transfected with cDNAs encoding different cytoplasmic XB/U-cadherin mutants, each partially deleted in the different parts of the 38 most carboxyl-terminal amino acids. The binding of p120(cas) was not affected by carboxyl-terminal deletions, confirming its binding to a region more amino-terminal and distinct from the catenins. alpha- and beta-catenins associate with truncated XB/U-cadherins if either 19 amino acid half of the cadherin 38 amino acid tail is present, indicating that the site of catenin interaction is upstream of the deletions. However, for adhesive function of XB/U-cadherin constructs, the most carboxyl-terminal 19 amino acids are essential; if these amino acids are deleted, cadherin-catenin complexes unable to mediate cell-cell adhesion are formed. Nonadhesive complexes are solubilized by mild detergent, whereas functional complexes are stable. Provided that detergent stability of cadherin-catenin complexes is taken as a measure of their cytoskeletal association, our results give first evidence that cytoskeletal stabilization occurs independent of cadherin-catenin complex formation and requires the 19-amino acid cadherin carboxyl terminus.