Comparative analysis of armadillo family proteins in the regulation of A431 epithelial cell junction assembly, adhesion and migration

p0071 is an armadillo family protein related to both the adherens junction protein p120ctn and to the desmosomal proteins plakophilins 1-3. p0071 assembles into both adherens junctions and desmosomes, suggesting that this protein may regulate the balance between adherens junction and desmosome formation. Furthermore, this subfamily of proteins may also regulate cell functions directly influenced by intercellular junctions, including the strength of cell adhesion and the ability of cells to migrate. These possibilities were tested by expressing exogenous p0071 in A431 epithelial cells and monitoring the effects on adhesive junction assembly in comparison to other closely related armadillo family proteins. In this model system, p0071 specifically enhanced adherens junction assembly but dramatically compromised desmosome assembly, resulting in keratin filament retraction from regions of cell-cell contact. Protein interaction studies revealed that p0071 bound to the first 160 amino-terminal residues of desmoplakin and also interacted directly with plakoglobin, suggesting that p0071 may regulate desmosome assembly by controlling plakoglobin availability. Using an in vitro assay to measure the strength of cell-cell contacts, both plakophilin-1 and p120ctn were found to increase the strength of adhesion. Interestingly, p0071 expression caused no overall changes in adhesive strength, but dramatically inhibited the ability of A431 cells to close an in vitro wound. These results suggest that p120ctn/plakophilin family proteins interact with intercellular junction binding partners to differentially modulate the adhesive and migratory behavior of epithelial cells.