Wnt signaling

描述（由申请人提供）：Wnt信号因其在胚胎发育和肿瘤发生中的调节作用而闻名。第一个Wnt基因是通过其在小鼠中诱导乳腺肿瘤的能力被鉴定出来的。目前的研究表明，Wnt信号在许多不同类型的肿瘤中都存在。典型Wnt信号通路由典型Wnt与LDL受体相关蛋白（LRP） 5/6和卷曲蛋白（Fz）组成的受体复合物结合而引发，最终导致-catenin的稳定和基因转录的激活。尽管我们对Wnt信号机制的理解取得了显著进展，但仍存在重大差距。其中包括Wnt调控LRP磷酸化的机制、早期细胞内事件以及Wnt共受体Fz和下游信号分子disheveled （Dvl）参与Wnt/2-catenin信号通路的生化基础。通过筛选人类激酶的siRNA文库，我们发现了一组可以抑制典型Wnt信号传导的磷脂酰亚脂（PtdIns）激酶siRNA。我们继续证明Wnt3a可以诱导哺乳动物细胞中PtdIns (4,5) P2的积累，这取决于Fz和Dvl。我们还发现PtdIns (4,5) P2是wnt3a诱导的典型信号事件所必需的。此外，我们发现异三聚体G蛋白可能参与wnt调控的PtdIns (4,5) P2的形成。此外，我们有初步结果支持PtdIns (4,5)P2调节LRP磷酸化的两种可能机制。综上所述，我们推测Wnt3a可能通过Fz、Dvl和G激活PtdIns激酶，刺激PtdIns (4,5)P2的形成，进而刺激LRP5/6的磷酸化，这是一个早期的Wnt信号事件。特别地，在本应用中，我们将：1)研究Wnt3a诱导PtdIns (4,5)P2形成的机制。2)研究PtdIns (4,5)P2调控LRP磷酸化的机制。公共卫生相关性：细胞-细胞通讯对包括人类在内的多细胞生物的正常功能至关重要。这个过程中的问题会导致包括肿瘤发生在内的各种病理状况。本研究计划旨在了解细胞间通讯的关键分子之一Wnt蛋白如何调控细胞功能，以及该机制的缺陷如何导致疾病。

DESCRIPTION (provided by applicant): Wnt signaling is known for its roles in regulation of embryonic development and in tumorigenesis. The first Wnt gene was identified by virtue of its ability to induce mammary tumors in mice. Studies have now implicated Wnt signaling in many different types of tumors. The best characterized Wnt signaling pathway, the canonical Wnt signaling pathway, is initiated by the binding of canonical Wnts to their receptor complexes consisting of the LDL receptor-related protein (LRP) 5/6 and frizzled (Fz) proteins, which eventually leads to the stabilization of -catenin and activation of gene transcription. Despite remarkable advances in our understanding of Wnt signaling mechanisms, significant gaps still remain. These include the mechanism by which Wnt regulates LRP phosphorylation, an early intracellular event and the biochemical basis for the involvement of Wnt co-receptor Fz and downstream signaling molecule Dishevelled (Dvl) in the Wnt/2-catenin signaling pathway. By screening a siRNA library for human kinases, we identified a group of phosphatidylinositide (PtdIns) kinase siRNAs that could inhibit canonical Wnt signaling. We went on demonstrating that Wnt3a could induce the accumulation of PtdIns (4,5) P2 in mammalian cells, which depends on both Fz and Dvl. We also showed that PtdIns (4,5) P2 is required for Wnt3a-induced canonical signaling events. Moreover, we found that there is possible involvement of heterotrimeric G proteins in Wnt-regulated PtdIns (4,5) P2 formation. Furthermore, we have preliminary results to support the two possible mechanisms by which PtdIns (4,5)P2 may regulate LRP phosphorylation. Putting all of these together, we hypothesize that Wnt3a may, via Fz, Dvl and G, activate PtdIns kinases to stimulate the formation of PtdIns (4,5)P2, which in turn stimulates the phosphorylation of LRP5/6, an early Wnt signaling event. Specially, in this application we will: 1) Investigate the mechanisms by which Wnt3a induces the formation of PtdIns (4,5)P2. 2) Investigate the mechanisms by which PtdIns (4,5)P2 regulates LRP phosphorylation. PUBLIC HEALTH RELEVANCE: Cell-cell communication is essential for normal functions of multi-cellular organisms including human. Problems in this process would lead to various pathological conditions including tumorigenesis. This research proposal is to understand how the Wnt protein, one of the key molecules in cell-cell communication, regulate cellular functions and how the defects in this mechanism would cause diseases.