Axin-mediated CKI phosphorylation of β-catenin at Ser 45:: a molecular switch for the Wnt pathway
Axin-mediated CKI phosphorylation of β-catenin at Ser 45:: a molecular switch for the Wnt pathway
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DOI：
10.1101/gad.230302
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发表时间：
2002-05-01
影响因子：
10.5
通讯作者：
Alkalay, I
中科院分区：
文献类型：
--
作者：
Amit, S;Hatzubai, A;Alkalay, I
Wnt途径通过β-连环蛋白-TCF/LEF转录复合物控制许多发育过程。该途径的失调导致β-连环蛋白在细胞核中的异常积累，通常导致癌症。正常情况下，胞质β-连环蛋白与APC和轴蛋白结合，并被GSK-3 β持续磷酸化，标志着它被蛋白酶体降解。Wnt信号被认为阻止GSK-3 β磷酸化β-连环蛋白，从而使其稳定。然而，Wilt的作用机制尚未得到解决。在这里，我们研究β-连环蛋白磷酸化和降解的Wnt途径的调节。使用质谱和磷酸肽特异性抗体，我们表明，轴蛋白和酪蛋白激酶I（CKI）的复合物诱导β-连环蛋白磷酸化在一个单一的网站：丝氨酸45（S45）。免疫纯化的轴蛋白和重组CKI在体外使β-连环蛋白在S45磷酸化; CKI抑制剂在体内抑制这种磷酸化。CKI磷酸化为GSK-3 β创造了一个引发位点，并且是启动β-连环蛋白磷酸化-降解级联反应所必需和充分的。Wnt 3A信号传导和Dvl过表达抑制S45磷酸化，从而阻止级联反应的启动。因此，一个单一的CKI依赖性磷酸化事件作为Wnt途径的分子开关。
The Wnt pathway controls numerous developmental processes via the beta-catenin-TCF/LEF transcription complex. Deregulation of the pathway results in the aberrant accumulation of beta-catenin in the nucleus, often leading to cancer. Normally, cytoplasmic beta-catenin associates with APC and axin and is continuously phosphorylated by GSK-3beta, marking it for proteasomal degradation. Wnt signaling is considered to prevent GSK-3beta from phosphorylating beta-catenin, thus causing its stabilization. However, the Wilt mechanism of action has not been resolved. Here we study the regulation of beta-catenin phosphorylation and degradation by the Wnt pathway. Using mass spectrometry and phosphopeptide-specific antibodies, we show that a complex of axin and casein kinase I (CKI) induces beta-catenin phosphorylation at a single site: serine 45 (S45). Immunopurified axin and recombinant CKI phosphorylate beta-catenin in vitro at S45; CKI inhibition suppresses this phosphorylation in vivo. CKI phosphorylation creates a priming site for GSK-3beta and is both necessary and sufficient to initiate the beta-catenin phosphorylation-degradation cascade. Wnt3A signaling and Dvl overexpression suppress S45 phosphorylation, thereby precluding the initiation of the cascade. Thus, a single, CKI-dependent phosphorylation event serves as a molecular switch for the Wnt pathway.