INTERCADHERIN INTERACTIONS IN EPITHELIAL CELLS

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E-cadherin belongs to a multigene family of classic cadherins that serve as structural transmembrane elements in specialized intercellular junctions termed adherens junctions. E-cadherin-based adhesion is critical for normal development and maintenance of epithelial tissue. Despite their importance, however, little is known about the molecular mechanisms involved in the assembly of these junctions. The present proposal is based on our finding that E-cadherin can self- associate to form three distinct complexes exposed on the cell surface. Two of these complexes, the lateral complex in which E-cadherin molecules form dimers via residue Trp156 (Trp156-dependent lateral complex), and the antiparallel (adhesive) complex have been predicted by crystallographic analysis. The third complex identified is the lateral Trp156-independent complex. It is triggered by a depletion of extracellular Ca2+ ions from culture medium. Importantly, only the formation of adhesive complexes depends on cytoplasmic E-cadherin domain. Furthermore, epidermal growth factor (EGF) strongly increases the amount of these complexes. It is likely that the three distinct complexes represent consecutive steps in adherens junction assembly. The broad goal then, of the present proposal is to evaluate this hypothesis. To this end, we will study the contribution of each of these complexes to adherens junction assembly. The role of the lateral Trp156-dependent complexes and catenins in the formation of the adhesive complexes will be evaluated. We will identify which determinant of E-cadherin is involved in Trp156- independent interactions. Also, we plan to examine whether inactivation of this determinant by point mutations, or by specific peptides, affects clustering of the adhesive complexes into adherens junctions. The final part of the proposal is focused on understanding the effect of EGF on the adhesive complex formation. The experiments described in this proposal will further our understanding of the molecular mechanisms responsible for epithelial morphogenesis.