Inhibition of GSK3 phosphorylation of beta-catenin via phosphorylated PPPSPXS motifs of Wnt coreceptor LRP6.
Inhibition of GSK3 phosphorylation of beta-catenin via phosphorylated PPPSPXS motifs of Wnt coreceptor LRP6.
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DOI：
10.1371/journal.pone.0004926
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发表时间：
2009
期刊：
影响因子：
3.7
通讯作者：
He X
中科院分区：
文献类型：
--
作者：
Wu G;Huang H;Garcia Abreu J;He X
Wnt/β-catenin信号通路在细胞的增殖和分化中起着重要作用，而β-catenin蛋白水平的失控导致了多种类型的人类癌症。在Wnt的激活下，Wnt共受体低密度脂蛋白受体相关蛋白6(LRP6)被糖原合成酶激酶3(GSK3)和酪蛋白激酶1(CK1)磷酸化，导致支架蛋白Axin被募集到LRP6中。其结果是抑制了β-连环蛋白的磷酸化，稳定了β-连环蛋白。然而，LRP6的磷酸化以及随后的LRP6-Axin相互作用如何导致GSK3抑制β-连环蛋白的磷酸化还不完全清楚。在本研究中，我们利用重组蛋白在体外重组了GSK3和CK1对轴蛋白依赖的β-连环蛋白的磷酸化，发现磷酸化的PPPSPXS多肽以序列和磷酸化依赖的方式直接抑制β-连环蛋白的磷酸化。这种磷酸化的PPPSPXS基序对β-连环蛋白在Ser33/Ser37/Thr41位的磷酸化具有直接和特异性的抑制作用，而对β-Catenin在Ser45位的CK1磷酸化没有抑制作用，并且这种抑制作用不依赖于轴蛋白功能。我们还发现，磷酸化的PPPSPXS多肽能够激活Wnt/β-catenin信号，并在非洲爪哇胚胎中诱导轴复制，这可能是通过体内抑制GSK3来实现的。基于这些观察，我们提出了一个工作模型，即轴突募集到磷酸化的LRP6将GSK3置于多个磷酸化的PPPSPXS基序附近，从而直接抑制GSK3对β-连环蛋白的磷酸化。这个模型提供了一个可能的机制，部分解释了Wnt激活的LRP6抑制β-连环蛋白磷酸化的原因。
The Wnt/β-catenin signaling pathway plays essential roles in cell proliferation and differentiation, and deregulated β-catenin protein levels lead to many types of human cancers. On activation by Wnt, the Wnt co-receptor LDL receptor related protein 6 (LRP6) is phosphorylated at multiple conserved intracellular PPPSPXS motifs by glycogen synthase kinase 3 (GSK3) and casein kinase 1 (CK1), resulting in recruitment of the scaffolding protein Axin to LRP6. As a result, β-catenin phosphorylation by GSK3 is inhibited and β-catenin protein is stabilized. However, how LRP6 phosphorylation and the ensuing LRP6-Axin interaction lead to the inhibition of β-catenin phosphorylation by GSK3 is not fully understood. In this study, we reconstituted Axin-dependent β-catenin phosphorylation by GSK3 and CK1 in vitro using recombinant proteins, and found that the phosphorylated PPPSPXS peptides directly inhibit β-catenin phosphorylation by GSK3 in a sequence and phosphorylation-dependent manner. This inhibitory effect of phosphorylated PPPSPXS motifs is direct and specific for GSK3 phosphorylation of β-catenin at Ser33/Ser37/Thr41 but not for CK1 phosphorylation of β-catenin at Ser45, and is independent of Axin function. We also show that a phosphorylated PPPSPXS peptide is able to activate Wnt/β-catenin signaling and to induce axis duplication in Xenopus embryos, presumably by inhibition of GSK3 in vivo. Based on these observations, we propose a working model that Axin recruitment to the phosphorylated LRP6 places GSK3 in the vicinity of multiple phosphorylated PPPSPXS motifs, which directly inhibit GSK3 phosphorylation of β-catenin. This model provides a possible mechanism to account, in part, for inhibition of β-catenin phosphorylation by Wnt-activated LRP6.
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影响因子：
56.9
作者：
Behrens, J;Jerchow, BA;Birchmeier, W
通讯作者：
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影响因子：
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作者：
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DOI：
10.1073/pnas.96.11.6273
发表时间：
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影响因子：
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作者：
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通讯作者：
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作者：
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