PAPIN

A neural plakophilin-relatedarmadillo repeat protein (NPRAP)/δ-catenin interacts with one of Alzheimer disease-related gene products, presenilin 1. We have previously reported the interaction of NPRAP/δ-catenin with synaptic scaffolding molecule, which is involved in the assembly of synaptic components. NPRAP/δ-catenin also interacts with E-cadherin and β-catenin and is implicated in the organization of cell-cell junctions. p0071, a ubiquitous isoform of NPRAP/δ-catenin, is localized at desmosomes in HeLa and A431 cells and at adherens junctions in Madin-Darby bovine kidney cells. We have identified here a novel protein interacting with NPRAP/δ-catenin and p0071 and named this protein plakophilin-related armadillo repeat protein-interacting PSD-95/Dlg-A/ZO-1 (PDZ) protein (PAPIN). PAPIN has six PDZ domains and binds to NPRAP/δ-catenin and p0071 via the second PDZ domain. PAPIN and p0071 are ubiquitously expressed in various tissues and are localized at cell-cell junctions in normal rat kidney cells and bronchial epithelial cells. PAPIN may be a scaffolding protein connecting components of epithelial junctions with p0071.