《分子與細胞生物學》（《Molecular and Cellular Biology》）雜志近日在線發(fā)表了上海生科院生化與細胞所李林研究組的研究論文“The E3 Ubiquitin Ligase ITCH Negatively Regulates Canonical Wnt Signaling by Targeting Dishevelled Protein”,，該研究成果揭示了泛素連接酶ITCH負調(diào)控經(jīng)典Wnt信號途徑的功能作用及其分子機制,。
Wnt信號轉(zhuǎn)導途徑在多細胞真核生物中高度保守，在生物體早期胚胎發(fā)育以及成體病變過程中都發(fā)揮了極其重要的作用,。Dishevelled（Dvl）蛋白是經(jīng)典與非經(jīng)典Wnt信號途徑中的關(guān)鍵分子，在經(jīng)典Wnt信號轉(zhuǎn)導過程中它更是同時在上游和下游發(fā)揮著雙重作用,。雖然Dvl的磷酸化被認為是經(jīng)典Wnt信號激活所必需,，但經(jīng)典Wnt信號轉(zhuǎn)導途徑中Dvl的活性調(diào)節(jié)機制目前尚不完全清楚。
在這項工作中,，李林實驗室的韋韋等人發(fā)現(xiàn)并鑒定了一個特異性針對磷酸化形式Dvl的E3泛素連接酶 ITCH,。與已經(jīng)發(fā)現(xiàn)的其他針對Dvl的E3泛素連接酶不同，ITCH只作用于磷酸化形式的Dvl,，它能夠泛酸化并促使磷酸化形式的Dvl通過蛋白酶體依賴的方式降解,。進一步的工作發(fā)現(xiàn)ITCH能夠以磷酸化Dvl作為靶點在β-catenin上游負調(diào)控經(jīng)典Wnt信號途徑。
這項研究豐富了人們對于Wnt信號轉(zhuǎn)導網(wǎng)絡(luò)的認識,，也為Dvl蛋白在經(jīng)典Wnt信號途徑中的活性以及穩(wěn)定性的調(diào)節(jié)提供了一種新的機制,。另外，雖然ITCH的一些底物被發(fā)現(xiàn)參與腫瘤發(fā)生以及化療敏感等過程,，但是到目前為止,，ITCH與癌癥病理還沒有建立起直接聯(lián)系。這項研究首次把與腫瘤發(fā)生發(fā)展密切相關(guān)的Wnt信號途徑與ITCH聯(lián)系起來,，為該領(lǐng)域的研究提供了新的線索,。
該課題獲得了科技部、基金委項目的經(jīng)費支持,。（生物谷Bioon.com）
doi:10.1128/MCB.00251-12
PMC:
PMID:
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.
