ERBIN associates with p0071, an armadillo protein, at cell-cell junctions of epithelial cells

Background: ERBIN, an ErbB2 receptor-interacting protein, belongs to a recently described family of proteins termed the LAP [leucine-rich repeats and PSD-95/dLg-A/ZO-1 (PDZ) domains] family which has essential roles in establishment of cell polarity. Results: To identify new ERBIN-binding proteins, we screened a yeast two-hybrid library, using the carboxyl-terminal fragment of ER-BIN containing PDZ domain as the bait, and we isolated p0071 (also called plakophilin-4) as an ERBIN-interacting protein. p0071 is a member of the p120 catenin family, which are defined as proteins with 10 armadillo repeats, and localizes along the cell-cell border. The ERBIN PDZ domain binds the COOH-terminus of p0071 containing the PDZ domain-binding sequence. Endogenous ER-BIN was co-immunoprecipitated with p0071. In fully polarized Madin-Darby canine kidney (MDCK) cells, ERBIN co-localized largely with beta-catenin and partly with desmoplakin along the lateral plasma membrane domain. At these cell-cell contact regions, ERBIN co-localizes with p0071. Over-expression of the dominant active forms of Cdc42, Rac1 or RhoA, Rho family small GTPases, resulted in a marked accumulation of ER-BIN at the cell-cell contacts of MDCK and HeLa cells. Conclusion: These results show that ERBIN interacts in vivo with p0071 and that it may be involved in the organization of adherens junctions and the desmosomes of epithelia. In addition, we demonstrated that the subcellular localization of ER-BIN might be regulated by Rho family small GTPases.