Ep-CAM: A Homophilic Cell-Cell Adhesion Molecule with EGF-like Domains

Abstract

Ep-CAM is a recently identified Ca²⁺-independent, homophilic cell-cell adhesion molecule of epithelial cells. This transmembrane glycoprotein has a molecular weight of only 40kD, which is unusually small for an adhesion protein. The extracellular domain of Ep-CAM contains two EGF-like domains followed by a cysteine-poor region- structural features that set Ep-CAM apart from the four main groups of cell adhesion molecules- cadherins, integrins, selectins and adhesion molecules of the immunoglobulin superfamily. Ep-CAM is abundantly expressed in simple, transitional and some pseudostratified epithelia, but not in squamous epithelia, where the de novo expression of this molecule is often associated with proliferative/neoplastic changes. Ep-CAM is not expressed in cell types of nonepithelial origin. The exact biological role of the Ep-CAM molecule is still unknown, but the evidence so far suggests involvement in regulation of cell-cell interactions, segregation of cell types, tissue pattern formation, and support of tissue architecture.