The Armadillo Family Protein p0071 Is a VE-cadherin- and Desmoplakin-binding Protein*

Abstract

p0071, a member of the armadillo protein family, localizes to both adherens junctions and desmosomes in epithelial cells and exhibits homology to the adherens junction protein p120 and the desmosomal protein plakophilin-1. p0071 is also present at dermal microvascular endothelial intercellular junctions and colocalizes with VE-cadherin, an endothelium-specific cadherin that associates with both actin and intermediate filament networks. To define the role of p0071 in junction assembly, p0071 was tested for interactions with other components of the endothelial junctional complex. In transient expression assays, p0071 colocalized with and formed complexes with both VE-cadherin and desmoplakin. Deletion analysis using the yeast two-hybrid system revealed that the armadillo repeat domain of p0071 bound directly to VE-cadherin. Site-directed mutagenesis experiments demonstrated that p0071 and p120 bound to the same region on the cytoplasmic tail of VE-cadherin and that overexpression of p0071 could displace p120 from intercellular junctions. In contrast to VE-cadherin, desmoplakin was found to associate with the non-armadillo head domain of p0071. Cotransfections and triple-label immunofluorescence analysis revealed that VE-cadherin colocalization with desmoplakin in transfected COS cells required p0071, suggesting that p0071 may couple VE-cadherin to desmoplakin. Based on previous findings that both VE-cadherin and desmoplakin play central roles in vasculogenesis, these new results suggest that p0071 may play an important role in endothelial junction assembly and in the morphogenic events associated with vascular remodeling.