CATENIN AND CADHERIN SIGNALING IN DEVELOPMENT AND CANCER

β -连环蛋白是钙粘蛋白复合物的一个组成部分，也是Wnt通路中的细胞内信号转导蛋白。β -连环蛋白受APC肿瘤抑制蛋白调控，β -连环蛋白和E-钙粘蛋白的突变与多种形式的癌症有关。该项目的两个总体目标是确定β -连环蛋白信号传导的细胞质调节机制，以及确定钙粘蛋白如何影响β -连环蛋白信号传导、细胞分化和肿瘤细胞生长。β -连环蛋白的核输入对信号传导很重要，并通过一种涉及其与核孔相互作用的新机制发生。研究β -连环蛋白核孔对接机制及Wnt信号通路对其的调控作用。-连环蛋白信号是由一个非常大的蛋白复合物调控的，该蛋白复合物包括APC、轴蛋白和激酶gsk3 β。完整复合物的性质将通过体外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。该复合体也将被纯化，以确定关键的蛋白质成分。此外，我们还将评估最近发现的第二种APC蛋白APC-2在爪蟾胚胎早期β -连环蛋白信号传导中的作用。Cadherin表达通过在质膜上结合β -连环蛋白信号而拮抗β -连环蛋白信号，为细胞粘附变化与基因表达调控提供了一种潜在的机制。我们将探讨钙粘蛋白调控β -连环蛋白信号在爪蟾胚胎神经嵴发育（上皮-间质过渡）中发挥重要作用的可能性。同样，我们将通过实验来确定调节β - catenin信号传导或增强细胞粘附对E-cadherin肿瘤抑制功能的相对贡献。实验还将确定E-cadherin是否可以直接产生介导细胞生长接触抑制的信号。这些实验将有助于我们理解β -连环蛋白介导的信号传导机制，并为细胞粘附、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.