Cloning and characterization of a new armadillo family member, p0071, associated with the junctional plaque: evidence for a subfamily of closely related proteins

Abstract

Cell contacts of the adherens type are organized around transmembrane proteins of the cadherin family. Whereas the extracellular domains mediate homophilic interactions between cadherins of neighbouring cells the cytoplasmic domains organize a set of proteins into the junctional plaque. Among these junctional plaque proteins are members of the armadillo gene family, beta-catenin, plakoglobin (gamma-catenin), B6P/plakophilin and p120. These proteins are assumed to play a key role in cell cell signalling through intercellular junctions. Here we report cloning of a cDNA encoding a new armadillo family member, p0071, closely related to p120 and B6P/plakophilin and more distantly related to armadillo, plakoglobin, beta-catenin and other members of the gene family. The deduced amino acid sequence encodes a basic protein of 1,211 amino acids with a central armadillo repeat region which is conserved in sequence and organization of its ten individual motifs between p120, B6P/plakophilin and p0071. In contrast the end domains of the three proteins are variable in size and sequence. The RNA coding for p0071 is expressed in all tissues examined. Using antibodies generated against the armadillo repeat region of the protein we show that p0071 is localized at cell-cell borders and is expressed in the desmosomal plaque of some cultured epithelial cells. The protein seems to be an accessory component of the desmosomal plaque as well as of other adhesion plaques and might be involved in regulating junctional plaque organization and cadherin function. Our data provide evidence for a subfamily of armadillo related proteins that share not only structural features but also have in common their localisation in the junctional plaque. We therefore suggest that family members exert similar functions and might be involved in cell signalling through cell contacts.