CATENIN AND CADHERIN SIGNALING IN DEVELOPMENT AND CANCER

β-连环蛋白是钙粘蛋白粘附蛋白复合物的组分，也是Wnt途径中的细胞内信号转导蛋白。 β-连环蛋白由APC肿瘤抑制蛋白调节，并且β-连环蛋白和E-钙粘蛋白两者的突变涉及许多形式的癌症。 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，并确定钙粘蛋白如何影响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于信号传导很重要，并且通过一种涉及其与核孔相互作用的新机制发生。 我们将研究β-连环蛋白核孔对接的机制及其通过Wnt信号通路的调节。β-连环蛋白信号由一个非常大的蛋白质复合物调节，该蛋白质复合物包括APC、轴蛋白和激酶GSK 3 β。 将使用体外β-连环蛋白信号传导测定、磷酸化测定和β-连环蛋白相互作用分析来研究完整复合物的性质。 还将纯化复合物以鉴定关键蛋白质组分。此外，最近确定的第二APC蛋白，APC-2，在早期非洲爪蟾胚胎β-连环蛋白信号的作用将进行评估。钙粘蛋白表达通过将β-连环蛋白结合在质膜上来拮抗β-连环蛋白信号传导，提供了将细胞粘附的变化与基因表达的调节偶联的潜在机制。钙粘蛋白调节β-连环蛋白信号传导的可能性在非洲爪蟾胚胎神经嵴的发育中起重要作用，这是一种上皮-间充质转化，将被探讨。 类似地，将进行实验以确定调节β-连环蛋白信号传导或增强细胞粘附对E-钙粘蛋白的肿瘤抑制功能的相对贡献。 还将进行实验以确定E-钙粘蛋白是否可以直接产生介导细胞生长的接触抑制的信号。这些实验将帮助我们理解β-连环蛋白介导的信号转导机制，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.