Direct Interaction of Tumor Suppressor CEACAM1 with Beta Catenin: Identification of Key Residues in the Long Cytoplasmic Domain

Abstract

CEACAM1-4L (carcinoembryonic antigen cell adhesion molecule 1, with 4 extracellular Ig-like domains and a long, 71 amino acid cytoplasmic domain) is expressed in epithelial cells and activated T-cells, but is down-regulated in most epithelial cell cancers and T-cell leukemias. A highly conserved sequence within the cytoplasmic domain has ca 50% sequence homology with Tcf-3 and −4, transcription factors that bind β-catenin, and to a lesser extent (32% homology), with E-cadherin that also binds β-catenin. We show by quantitative yeast two-hybrid, BIAcore, GST-pull down, and confocal analyses that this domain directly interacts with β-catenin, and that H-469 and K-470 are key residues that interact with the armadillo repeats of β-catenin. Jurkat cells transfected with CEACAM1-4L have 2-fold less activity in the TOPFLASH reporter assay, and in MCF7 breast cancer cells that fail to express CEACAM1, transfection with CEACAM1 and growth in Ca²⁺ media causes redistribution of β-catenin from the cytoplasm to the cell membrane, demonstrating a functional role for the long cytoplasmic domain of CEACAM1 in regulation of β-catenin activity.