ABSTRACT
Desmosomes and adherens junctions constitute the main adhesive junctions between epithelial cells. Adherens junctions are specialized regions of the plasma membrane where the transmembrane cell adhesion molecule E-cadherin recognizes and binds the E-cadherin present on neighboring cells in a Ca2+-dependent manner. E-cadherin is a 120 kDa transmembrane glycoprotein, from which an extracellular 80 kDa tryptic fragment can be released in the presence of Ca2+. The cDNA of E-cadherin encodes a signal peptide at the ammo-terminus, a large extracellular domain with five repeated domains important in Ca2+-binding, a single transmembrane sequence, and a 15 kDa cytoplasmic domain (Takeichi, 1991). The cytoplasmic portion of E-cadherin is associated with a group of proteins, named catenins, which mediate interactions with the microfilament network. This interaction is essential for the integrity of adherens junctions. E-cadherin binds directly to β-catenin, which binds to α-catenin, and α-catenin connects the complex to the cytoskeleton. γcatenin (plakoglobin) is related to β-catenin, and interacts in a similar manner with E-cadherin and α-catenin (Huelsken et al., 1994; Naethke et al., 1994).
