Wnt-LRP interaction in Wnt signal transduction

描述（由申请人提供）： Wnt基因编码一个大家族的分泌信号分子，在动物发育和人类癌症和疾病中发挥重要作用。 关键的Wnt信号通路之一是经典的β-连环蛋白通路。Wnt/b-连环蛋白信号的失调与人类结直肠癌、骨质疏松症和其他类型的疾病有关。Wnt/β-连环蛋白信号传导由两个不同家族的细胞表面受体的Wnt激活启动。一种是卷曲（Fz）蛇形受体家族的成员，另一种是属于LDL受体相关蛋白家族LRP 5或LRP 6的单跨膜受体。Wnt如何导致这两类受体的激活是一个关键但知之甚少的问题。我们发现，Fz和LRP 5/6可以在Wnt存在下形成复合物，并表明Fz-LRP 5/6共受体复合物触发细胞内信号传导。我们还鉴定了Dickkopf-1（Dkk-1），一种已知的Wnt信号传导拮抗剂，作为LRP 5/6的高亲和力配体，并证明Dkk-1破坏Wnt诱导的Fz-LRP 5/6复合物的形成。最近的人类遗传学研究揭示了Wnt、Dkk-1和LRP 5相互作用在骨质疏松症和高骨密度疾病中的重要作用。在本申请中，我们提出了3个具体的目标来研究Wnt信号转导中Wnt、Dkk、Fz和LRP相互作用的分子基础：（1）进一步研究Wnt-LRP 6-Fz相互作用，包括Wnt-LRP配体-受体结合亲和力，鉴定结合LRP或Fz的Wnt亚结构域，以及Wnt-LRP-Fz相互作用的潜在特异性。(2)研究Wnt-LRP和Dkk-LRP相互作用之间的相互作用及其在人类疾病中的参与，包括绘制结合Wnt和/或Dkk-1的LRP结构域，LRP 5和LRP 6之间的相似性和区别，LRP 5突变在人类疾病中的分子基础，以及新型Dkk-1结合蛋白在Dkk-LRP相互作用中的潜在功能。(3)探讨LRP胞内域的信号转导机制，包括关键信号基序的鉴定、LRP功能的磷酸化依赖性调节以及与胞内信号组分的相互作用。我们相信，这项全面的研究将为Wnt-LRP在发育和疾病中的相互作用提供重要的见解。

DESCRIPTION (provided by applicant): Wnt genes encode a large family of secreted signaling molecules that play essential roles in animal development and in human cancer and diseases. One of the key Wnt signaling pathways is the canonical b-catenin pathway. Deregulation of Wnt/b-catenin signaling is linked to human colorectal cancers, osteoporosis, and other types of diseases. Wnt/b-catenin signaling is initiated by Wnt activation of two distinct families of cell surface receptors. One is a member of the Frizzled (Fz) family of serpentine receptors, and the other is a single transmembrane receptor belonging to the LDL receptor related protein family, LRP5 or LRP6. How Wnt leads to the activation of these two classes of receptors is a critical but poorly understood issue. We showed that Fz and LRP5/6 can form a complex in the presence of Wnt, and suggested that the Fz-LRP5/6 co-receptor complex triggers intracellular signaling. We also identified Dickkopf-1 (Dkk-1), a known antagonist for Wnt signaling, as a high affinity ligand for LRP5/6, and demonstrated that Dkk-1 disrupts Wnt-induced Fz-LRP5/6 complex formation. Recent human genetic studies revealed important roles of Wnt, Dkk-1 and LRP5 interactions in osteoporosis and high bone density diseases. In this grant application, we propose 3 specific aims to study the molecular basis for Wnt, Dkk, Fz and LRP interactions in Wnt signal transduction: (1) to further investigate Wnt-LRP6-Fz interaction, including Wnt-LRP ligand-receptor binding affinity, identification of Wnt subdomains that bind either LRP or Fz, and potential specificities of Wnt-LRP-Fz interactions. (2) to investigate the interplay between Wnt-LRP and Dkk- LRP interactions and their involvement in human diseases, including mapping LRP domains that bind Wnt and/or Dkk-1, similarities and distinctions between LRP5 and LRP6, the molecular basis of LRP5 mutations in human diseases, and potential functions of a novel Dkk-1 binding protein in Dkk-LRP interaction. (3) to investigate the signaling mechanism of LRP intracellular domain, including the identification of key signaling motifs, and phosphorylation-dependent regulation of LRP function and interaction with intracellular signaling components. We believe that this comprehensive study will provide significant insights into Wnt-LRP interaction in development and diseases.