IQGAP2蛋白在介导R-spondin影响小肠干细胞稳态的作用

The intestine epithelial renewal is driven by the intestinal stem cells (ISCs) localized at the base of crypts. Several pathways have been shown to tightly control the fate determination of ISCs, such as EGF signaling, Wnt signaling, BMP signaling, Notch signaling and others. R-spondin (RSPO) is regarded to promote the classical Wnt/-catenin signaling. However, in the in vitro organoids culture, Wnt cannot replace RSPO, and the function of RSPO is not clear. IQGAP2 is considered as a tumor-suppressor in the gastric cancer, liver cancer and cervical cancer. However, its function in ISCs still remains unknown. In this project, based on our preliminary results that RSPO could downregulate IQGAP2, by combining multi-discipline approaches and mouse models, we will explore how RSPO regulates IQGAP2 and how IQGAP2 may affect the self-renewal and differentiation of ISCs. We anticipate that our research would provide a better understanding of the mechanism underlying the role of RSPO in the self-renewal and differentiation of ISCs, lay a foundation for its potential applications in regenerative medicine, and provide a basis and new ideas for colorectal cancer therapy.

作为维持小肠上皮细胞快速持续更新的来源，小肠干细胞受微环境多种信号通路的协同调控，如EGF信号通路、Wnt/R-spondin（RSPO）信号通路和BMP信号通路等。目前，关于R-spondin的研究多集中在经典的Wnt信号通路中。然而，在体外类器官培养中，Wnt3a无法完全取代RSPO，关于RSPO的功能也尚不清晰。在胃癌、肝癌和宫颈癌等疾病中，IQGAP2蛋白被认为是抑癌基因而发挥作用，但其在小肠干细胞中的作用和机制仍未被研究。基于前期RSPO可以下调IQGAP2蛋白水平的数据，在本项目中，我们整合分子生物学、细胞生物学和小鼠模型等，深入研究RSPO调控IQGAP2蛋白的分子机制，阐述IQGAP2蛋白影响小肠干细胞自我更新和分化的调控机制和生理意义。全面探索RSPO在肠干细胞中发挥的非Wnt信号通路的作用机制，将其利用到再生医学领域，为干细胞过度增殖引起的肠癌提供重要基础和全新思路。

作为维持小肠上皮细胞快速持续更新的来源，小肠干细胞受微环境EGF信号通路、Wnt/R-spondin（RSPO）信号通路和BMP等多种信号通路的协同调控。目前，关于R-spondin的研究多集中在经典的Wnt信号通路中，然而，在体外类器官培养中，Wnt3a无法完全取代RSPO，此外，关于RSPO的功能也尚不清晰。在胃癌、肝癌和宫颈癌等疾病中，IQGAP2蛋白被认为是抑癌基因而发挥作用，但其在小肠干细胞中的作用和机制仍未被研究。在本项目中，我们整合分子生物学、细胞生物学和小鼠模型等，发现Iqgap2敲除可以上调肠干细胞数目和自我更新能力，并抵御DSS及辐照带来的应激损伤。机制上，我们发现RSPO可通过与RNF43/ZNRF3相互作用泛素化降解IQGAP2蛋白，从而令隐窝区域处于低IQGAP2表达水平。同时，IQGAP2通过与激活型AKT互作进而抑制p-AKT从而抑制了肠干细胞的数目和自我更新能力，全面阐述RSPO-IQGAP2蛋白-肠干细胞关系轴中影响小肠干细胞自我更新和分化的调控机制和生理意义。本项目全面探索了RSPO在肠干细胞中发挥的非Wnt信号通路的作用机制，为干细胞过度增殖引起的肠癌提供重要基础和全新思路。