《分子与细胞生物学》(《Molecular and Cellular Biology》)杂志近日在线发表了上海生科院生化与细胞所李林研究组的研究论文“The E3 Ubiquitin Ligase ITCH Negatively Regulates Canonical Wnt Signaling by Targeting Dishevelled Protein”,该研究成果揭示了泛素连接酶ITCH负调控经典Wnt信号途径的功能作用及其分子机制。
Wnt信号转导途径在多细胞真核生物中高度保守,在生物体早期胚胎发育以及成体病变过程中都发挥了极其重要的作用。Dishevelled(Dvl)蛋白是经典与非经典Wnt信号途径中的关键分子,在经典Wnt信号转导过程中它更是同时在上游和下游发挥着双重作用。虽然Dvl的磷酸化被认为是经典Wnt信号激活所必需,但经典Wnt信号转导途径中Dvl的活性调节机制目前尚不完全清楚。
在这项工作中,李林实验室的韦韦等人发现并鉴定了一个特异性针对磷酸化形式Dvl的E3泛素连接酶 ITCH。与已经发现的其他针对Dvl的E3泛素连接酶不同,ITCH只作用于磷酸化形式的Dvl,它能够泛酸化并促使磷酸化形式的Dvl通过蛋白酶体依赖的方式降解。进一步的工作发现ITCH能够以磷酸化Dvl作为靶点在β-catenin上游负调控经典Wnt信号途径。
这项研究丰富了人们对于Wnt信号转导网络的认识,也为Dvl蛋白在经典Wnt信号途径中的活性以及稳定性的调节提供了一种新的机制。另外,虽然ITCH的一些底物被发现参与肿瘤发生以及化疗敏感等过程,但是到目前为止,ITCH与癌症病理还没有建立起直接联系。这项研究首次把与肿瘤发生发展密切相关的Wnt信号途径与ITCH联系起来,为该领域的研究提供了新的线索。
该课题获得了科技部、基金委项目的经费支持。(生物谷Bioon.com)
doi:10.1128/MCB.00251-12
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The E3 Ubiquitin Ligase ITCH Negatively Regulates Canonical Wnt Signaling by Targeting Dishevelled Protein
Wei Wei, Meng Li, Jiyong Wang, Fen Nie and Lin Li#
Dishevelled (Dvl) is a key component in the canonical Wnt signaling pathway and becomes hyperphosphorylated upon Wnt stimulation. Dvl is required for LRP6 phosphorylation, which is essential for subsequent steps of signal transduction, such as Axin recruitment and cytosolic β-catenin stabilization. Here, we identify the HECT-containing Nedd4-like ubiquitin E3 ligase ITCH as a new Dvl-binding protein. ITCH ubiquitinates the phosphorylated form of Dvl and promotes its degradation via the proteasome pathway, thereby inhibiting canonical Wnt signaling. Knockdown of ITCH by RNA interference increased the stability of phosphorylated Dvl, and upregulated Wnt reporter gene activity as well as endogenous Wnt target gene expression induced by Wnt stimulation. In addition, we found that both the PPXY motif and the DEP domain of Dvl are critical for its interaction with ITCH, as mutation in the PPXY motif (Dvl2-Y568F) or deletion of the DEP domain led to reduced affinity for ITCH. Consistently, overexpression of ITCH inhibited the wild type Dvl2, but not the Dvl2-Y568F mutant, induced Wnt reporter activity. Moreover, the Y568F mutant, but not the wild type Dvl2, can reverse the ITCH-mediated inhibition of Wnt-induced reporter activity. Collectively, these results indicate that ITCH plays a negative regulatory role in modulating canonical Wnt signaling by targeting the phosphorylated form of Dvl.