Isolation of novel proteins that regulate the Wnt signaling pathway

在这个项目中，我们已经确定了三个新的蛋白质来调节Wnt信号通路。它们是轴蛋白结合蛋白、DVL结合蛋白和β-连环蛋白结合蛋白，我们分别将它们命名为Axam、IDAX和DUPLIN。Axam在N端有核定位信号(NLS)，在其中心区有Axin结合区。此外，Axam与SENP1的催化结构域有很高的同源性，SENP1是一种相扑专一性的蛋白酶。的确，Axam显示出脱氨基活性。Axam促进哺乳动物细胞中β-连环蛋白的降解，并抑制非洲爪哇胚胎中轴的形成。Axam的催化失活突变体降低了这些活性。因此，SUMO可能参与了Wnt信号转导途径。IDAX与其他蛋白质没有任何同源性。IDAX通过抑制β与Axin的结合，抑制Wnt依赖的DVL-catenin的积聚和轴突的形成。Duplin在其C-颤动区含有NLS和β-连环蛋白结合区。虽然Duplin抑制了β依赖的Tcf的激活和轴的形成，但缺乏NLS的Duplin突变体失去了这些活性，这表明Duplin必须位于细胞核中才能发挥其功能。综上所述，Axam、IDAX和Duplin是Wnt信号通路的负调控因子。这些新分子在人类癌症中的突变筛查仍有待澄清。

We have identified three novel proteins that regulate the Wnt signaling pathway in this project. They are Axin-binding, Dvl-binding, and β-catenin-binding proteins, and we designated them Axam, Idax, and Duplin, respectively. Axam has nuclear localization signal (NLS) at the N-terminus and Axin-binding domain in its central region. Furthermore, Axam shares high homology with the catalytic domain of Senp1, which is a SUMO specific protease. Indeed, Axam showed an desumoylation activity. Axam stimulated degradation of β-catenin in mammalian cells and inhibited axis formation in Xenopus embryos. Catalyticaly inactive mutant of Axam reduced these activity. Therefore, sumoylation may be involved in the Wnt signaling pathway. Idax does not share any homology with other proteins. Idax suppressed Wnt dependent β-catenin accumulation and axis formation by inhibiting the binding of Dvl to Axin. Duplin has NLS and β-catenin-binding domain in its C-treminus. Although Duplin inhibited β-catenin-dependent Tcf activation and axis formation, the Duplin mutant that lacks NLS lost these activities, suggesting that Duplin must be in the nucleus to exert its functions. Taken together, Axam, Idax, and Duplin act as a negative regulator of the Wnt signaling pathway. Screening of mutations of these novel molecules in human cancers remains to be clarified.