The biochemical mechanism of Wnt signaling

描述（由申请人提供）：本提案的长期目标是了解Wnt信号以受控方式传输的机制，以及这种机制的破坏如何导致发育缺陷和癌症。分泌信号分子的Wnt家族在动物发育期间的各种组织的分化和图案化中起关键作用。Wnt信号的异常激活也会导致几种癌症。Wnt信号的传递由两种细胞表面受体介导，一种来自Frizzled家族，另一种来自低密度脂蛋白受体相关蛋白（LRP）家族。然而，目前还不清楚Wnt结合如何导致受体的激活以及受体如何向下游传递Wnt信号。该建议将评估Wnt结合诱导的受体聚集激活下游信号传递的假设。为了建立Wnt受体激活的机制，本文提出的研究将采用生物化学和细胞生物学方法来研究在Wnt存在或不存在的情况下受体如何相互作用以及与下游组分相互作用。由于Wnt和Frizzled家族都由大量的家族成员组成，因此仍不清楚单个Wnt如何与各种Frizzled蛋白质实现特异性相互作用。虽然不同的配体-受体对之间的不同亲和力被认为在建立特异性中起决定性作用，但由于缺乏合适的Wnt制剂，这种假设难以测试。为了评估这一假设，该提案将通过采用最近可用的可溶性和活性Wnt制剂来直接测量Wnt-卷曲相互作用的特异性和亲和力。由于Wnts的生化特性的基本知识是必不可少的信号转导机制的阐明，该提案还将确定Wnts的结构和生化特征，重要的是通过诱变，蛋白质纯化和生化表征，其活动。对这一信号通路的全面了解将为开发高度选择性的、基于机制的方法提供重要见解，用于预防、诊断和治疗由异常Wnt功能引起的疾病和癌症。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to understand the mechanisms by which Wnt signals are transmitted in a controlled manner and how disruption of this mechanism leads to developmental defects and cancers. The Wnt family of secreted signaling molecules plays pivotal roles in the differentiation and patterning of various tissues during animal development. Aberrant activation of Wnt signaling also causes several cancers. Transmission of Wnt signals is mediated by two cell surface receptors, one from the Frizzled family and the other from the low-density lipoprotein receptor-related protein (LRP) family. It is, however, unclear how Wnt binding leads to the activation of the receptors and how the receptors transmit the Wnt signal downstream. This proposal will evaluate the hypothesis that receptor clustering induced by Wnt binding activates the downstream signal transmission. To establish the mechanisms of Wnt receptor activation, the investigations proposed here will employ biochemical and cell biological approaches to examine how receptors interact with each other and with downstream components in the presence or absence of Wnts. Since both the Wnt and Frizzled families consist of a large number of family members, it remains unclear how individual Wnts achieve specific interactions with various Frizzled proteins. Although differing affinities among various ligand-receptor pairs are thought to play deciding roles in establishing the specificities, this assumption has been difficult to test due to the lack of suitable Wnt preparations. To evaluate this hypothesis, this proposal will directly measure the specificities and affinities of Wnt-Frizzled interactions by employing soluble and active Wnt preparations that have become available recently. Since a fundamental knowledge of the biochemical properties of Wnts is essential to the elucidation of the signaling mechanism, this proposal will also determine the structural and biochemical features of Wnts important for their activities through mutagenesis, protein purification and biochemical characterization. A complete understanding of this signaling pathway will provide important insights for the development of highly selective, mechanism-based approaches for the prevention, diagnosis, and treatment of diseases and cancers caused by aberrant Wnt functions.