CATENIN AND CADHERIN SIGNALING IN DEVELOPMENT AND CANCER

β-连环蛋白是钙粘附素黏附蛋白复合体的组成部分，也是Wnt途径中的一种细胞内信号转导蛋白。β-连环蛋白受APC肿瘤抑制蛋白的调节，而β-连环蛋白和E-钙粘蛋白的突变都与多种形式的癌症有关。该项目的两个总体目标是确定β-连环蛋白信号的细胞质调节机制，以及确定钙粘附素如何影响β-连环蛋白信号、细胞分化和肿瘤细胞生长。β-连环蛋白的核输入对信号转导很重要，并且通过一种新的机制发生，涉及到它与核孔的相互作用。将研究β-连环蛋白核孔对接的机制以及Wnt信号通路对其的调节。β-连环蛋白信号受一个非常大的蛋白质复合体的调控，该复合体包括APC、Axin和激酶GSK3β。完整复合体的性质将通过体外β-连环蛋白信号分析、磷酸化分析和β-连环蛋白相互作用分析来研究。该复合体还将被提纯，以确定关键的蛋白质成分。此外，最近发现的第二个APC蛋白，APC-2，在非洲爪哇早期胚胎的β-连环蛋白信号转导中的作用将被评估。钙粘附素的表达通过将其结合在质膜上来拮抗β-连环素信号，提供了一种潜在的机制，将细胞黏附的变化与基因表达的调节结合在一起。钙粘附素对β-连环蛋白信号的调节在非洲爪哇胚胎神经脊的发育中发挥重要作用的可能性将被探索，这是一种上皮向间充质的转变。同样，将进行实验以确定调节β-连环蛋白信号或增强细胞黏附对E-钙粘附素的肿瘤抑制功能的相对贡献。还将进行实验，以确定E-钙粘附素是否可以直接产生信号，介导接触抑制细胞生长。这些实验应该有助于我们理解β-连环蛋白介导的信号传递机制，并为细胞黏附、组织形态发生和肿瘤生长之间的关系提供见解。

Beta-catenin is a component of the cadherin adhesion protein complex and an intracellular signal transducing protein in the Wnt pathway. Beta-catenin is regulated by the APC tumor suppressor protein, and mutations in both beta-catenin and E- cadherin are implicated in many forms of cancer. The two overall objectives of the project are to determine the mechanism underlying the cytoplasmic regulation of beta-catenin signaling, and to determine how cadherins affect beta-catenin signaling, cell differentiation, and tumor cell growth. Nuclear import of beta-catenin is important for signaling and occurs by a novel mechanism involving its interaction with the nuclear pore. The mechanism of beta-catenin nuclear pore docking and its regulation by the Wnt signaling pathway will be studied. Beta-catenin signaling is regulated by a very large protein complex that includes APC, axin, and the kinase GSK3beta. The properties of the intact complex will be studied using an in vitro beta-catenin signaling assay, phosphorylation assays, and analyses of beta-catenin interactions. The complex will also be purified in order to identify key protein components. Furthermore, the role of a recently identified second APC protein, APC-2, in beta-catenin signaling in the early Xenopus embryo will be evaluated. Cadherin expression antagonizes beta-catenin signaling by binding it up at the plasma membrane, providing a potential mechanism to couple changes in cell adhesion to regulation of gene expression. The possibility that cadherin regulation of beta-catenin signaling plays an important role in development of the neural crest in the Xenopus embryo, an epithelial-mesenchymal transition, will be explored. Similarly, experiments will be done to determine the relative contributions of regulating beta- catenin signaling or enhancing cell adhesion to the tumor suppressor function of E-cadherin. Experiments will also be performed to determine whether E-cadherin can directly generate signals that mediate contact inhibition of cell growth. These experiments should help us understand the mechanisms of beta-catenin-mediated signaling and provide insights into the relationships between cell adhesion, tissue morphogenesis, and tumor growth.