Tsukiyama Tadasuke, Fukui Akimasa, Terai Sayuri, Fujioka Yoichiro, Shinada Keisuke, Takahashi Hidehisa, Yamaguchi Terry P, Ohba Yusuke, Hatakeyama Shigetsugu
Department of Biochemistry, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, Japan.
Laboratory of Tissue and Polymer Sciences, Division of Advanced Interdisciplinary Science, Faculty of Advanced Life Science, Hokkaido University, Sapporo, Hokkaido, Japan.
Mol Cell Biol. 2015 Jun 1;35(11):2007-23. doi: 10.1128/MCB.00159-15. Epub 2015 Mar 30.
Wnt signaling pathways are tightly regulated by ubiquitination, and dysregulation of these pathways promotes tumorigenesis. It has been reported that the ubiquitin ligase RNF43 plays an important role in frizzled-dependent regulation of the Wnt/β-catenin pathway. Here, we show that RNF43 suppresses both Wnt/β-catenin signaling and noncanonical Wnt signaling by distinct mechanisms. The suppression of Wnt/β-catenin signaling requires interaction between the extracellular protease-associated (PA) domain and the cysteine-rich domain (CRD) of frizzled and the intracellular RING finger domain of RNF43. In contrast, these N-terminal domains of RNF43 are not required for inhibition of noncanonical Wnt signaling, but interaction between the C-terminal cytoplasmic region of RNF43 and the PDZ domain of dishevelled is essential for this suppression. We further show the mechanism by which missense mutations in the extracellular portion of RNF43 identified in patients with tumors activate Wnt/β-catenin signaling. Missense mutations of RNF43 change their localization from the endosome to the endoplasmic reticulum (ER), resulting in the failure of frizzled-dependent suppression of Wnt/β-catenin signaling. However, these mutants retain the ability to suppress noncanonical Wnt signaling, probably due to interaction with dishevelled. RNF43 is also one of the potential target genes of Wnt/β-catenin signaling. Our results reveal the molecular role of RNF43 and provide an insight into tumorigenesis.
Wnt信号通路受到泛素化的严格调控，这些通路的失调会促进肿瘤发生。据报道，泛素连接酶RNF43在Wnt/β-连环蛋白通路的卷曲蛋白依赖性调控中起重要作用。在此，我们表明RNF43通过不同机制抑制Wnt/β-连环蛋白信号和非经典Wnt信号。抑制Wnt/β-连环蛋白信号需要细胞外蛋白酶相关（PA）结构域与卷曲蛋白的富含半胱氨酸结构域（CRD）以及RNF43的细胞内环状结构域之间相互作用。相比之下，RNF43的这些N端结构域对于抑制非经典Wnt信号并非必需，但RNF43的C端细胞质区域与散乱蛋白的PDZ结构域之间的相互作用对于这种抑制至关重要。我们进一步揭示了在肿瘤患者中鉴定出的RNF43细胞外部分的错义突变激活Wnt/β-连环蛋白信号的机制。RNF43的错义突变使其定位从内体转变为内质网（ER），导致卷曲蛋白依赖性抑制Wnt/β-连环蛋白信号失败。然而，这些突变体保留了抑制非经典Wnt信号的能力，这可能是由于与散乱蛋白相互作用所致。RNF43也是Wnt/β-连环蛋白信号的潜在靶基因之一。我们的结果揭示了RNF43的分子作用，并为肿瘤发生提供了深入见解。
