INTERCADHERIN INTERACTIONS IN EPITHELIAL CELLS

e -钙粘蛋白属于经典钙粘蛋白的多基因家族，在称为粘附连接的特殊细胞间连接中充当结构跨膜元件。基于e -钙粘蛋白的黏附对上皮组织的正常发育和维持至关重要。然而，尽管它们很重要，但人们对这些连接的分子机制知之甚少。目前的建议是基于我们的发现，e -钙粘蛋白可以自结合形成三种不同的复合物暴露在细胞表面。其中两种配合物，即e -钙粘蛋白分子通过残基Trp156形成二聚体的侧向配合物（Trp156依赖的侧向配合物）和反平行（粘附）配合物，已经通过晶体学分析进行了预测。鉴定的第三个复合物是外侧不依赖trp156的复合物。它是由从培养基中消耗细胞外Ca2+离子引起的。重要的是，只有黏附复合物的形成取决于细胞质e -钙粘蛋白结构域。此外，表皮生长因子（EGF）强烈增加这些复合物的数量。这三种不同的复合体很可能代表了粘附体连接组装的连续步骤。那么，本提案的主要目标就是评估这一假设。为此，我们将研究这些配合物对粘附结组装的贡献。将评估侧向trp156依赖性复合物和连环蛋白在粘合复合物形成中的作用。我们将确定哪些e -钙粘蛋白的决定因素参与了Trp156不依赖的相互作用。此外，我们计划研究是否通过点突变或特定肽来失活这个决定因素，影响粘附复合物聚集成粘附连接。建议的最后一部分集中在了解EGF对粘接复合物形成的影响。在这个提议中描述的实验将进一步我们的理解负责上皮形态发生的分子机制。

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.