Identification of a Novel β-Catenin-Interacting Protein

Abstract

Cadherin is a well-known cell–cell adhesion molecule, and it binds to β-catenin, which in turn binds to α-catenin. However, little is known about the regulatory mechanism underlying the cadherin-mediated cell–cell adhesion. Here we purified two novel β-catenin-interacting proteins with molecular masses of 180 kDa (p180) and 150 kDa (p150) from bovine brain cytosol by using glutathione S-transferase (GST)–β-catenin affinity column chromatography. Mass spectral analysis revealed p180 to be identical to KIAA0313 which has a putative Rap1 guanine nucleotide exchange factor (GEF) domain and p150 to be the same as KIAA0705 which has a high degree of sequence similarity to the synaptic scaffolding molecule (S-SCAM), which binds β-catenin and KIAA0313 in the yeast two-hybrid system and overlay assay, respectively (Ide et al., Biochem. Biophys. Res. Commun. 256, 456–461, 1999; Ohtsuka et al., Biochem. Biophys. Res. Commun. 265, 38–44, 1999). β-Catenin was coimmunoprecipitated with KIAA0313 in Madin–Darby canine kidney II (MDCKII) cells, bovine brain cytosol, and EL cells. KIAA0313 and β-catenin were partly colocalized at sites of cell–cell contact in MDCKII cells. Taken together, our data suggest that KIAA0313 associates with β-catenin through KIAA0705 in vivo at sites of cell–cell contact.