Characterization of p31^CTN, a new α-catenin binding protein.

Abstract

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Alpha-catenin plays a crucial role in E-cadherin mediated cell-cell adhesion by coupling the E-cadherin-beta/gamma-catenin complex to the actin cytoskeleton of the cell. Absence or dysfunction of α-catenin leads to an impaired E-cadherin function, and a concomitant loss of epithelial integrity. In addition to the direct binding of α-catenin to α-actinin and actin filaments, other proteins might be involved in the binding to, and signaling via the cytoskeleton. By screening a yeast two hybrid cDNA library using full length α-catenin as a bait, a gene, named p31^CTN, was identified that encodes a 31kDa protein that binds to α-catenin. No sequence homology was found with any protein described so far. To confirm that p31^CTN is a bona fide interactant of α-catenin, co-localization and co-immunoprecipitation were performed using stable p31^CTN transfectants in the human A431 cell line. Furthermore, the effect of ectopic overexpression of p31^CTN on cell migration was studied. Co-immunoprecipitation experiments demonstrated that p31^CTN interacts with α-catenin and the other proteins of the E-cadherin/catenin complex. Furthermore, the p31^CTN protein co-localizes with E-cadherin and α, β and γ-catenin to the cell membrane. Overexpression of p31^CTN resulted in an increased cell migration as determined by a scratch assay, indicating that p31^CTN destabilizes or modulates the E-cadherin/catenin-mediated cell adhesion complex. Interestingly, although p31^CTN was found to be ubiquitously expressed in normal human tissues, a significant upregulation was found in several tumor specimens. In conclusion, p31^CTN is a novel protein that physically interacts with α-catenin. Increased expression of p31^CTN was observed in tumor cells, and in vitro led to an increased cell migration. These data suggest that p31^CTN might be a novel tumor invasion marker.