Phosphorylation of TCF Proteins by Homeodomain-interacting Protein Kinase 2
Phosphorylation of TCF Proteins by Homeodomain-interacting Protein Kinase 2
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DOI：
10.1074/jbc.m110.185280
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发表时间：
2011-04-08
影响因子：
4.8
通讯作者：
Sokol, Sergei Y.
中科院分区：
文献类型：
--
作者：
Hikasa, Hiroki;Sokol, Sergei Y.
Wnt信号通路在胚胎发育过程中的细胞增殖、形态发生和细胞命运特化中发挥重要作用。根据共识观点，Wnt途径阻止了含有负调节因子Axin和糖原合成酶激酶3（GSK 3）的蛋白质复合物对关键信号传导组分β-连环蛋白的降解。稳定的β-连环蛋白与TCF蛋白结合并进入细胞核以促进靶基因表达。本研究检测了HIPK 2（bar下的同源域相互作用蛋白激酶（2））在体内调节非洲爪蟾胚胎中不同TCF蛋白的参与。我们发现TCF家族成员LEF 1，TCF 4和TCF 3在Wnt 8刺激和HIPK 2过表达后在胚胎外胚层磷酸化。我们还发现，TCF 3磷酸化是由典型的Wnt配体，LRP 6，和显性失活突变体的轴蛋白和GSK 3，表明这一过程中共享相同的上游调控β-连环蛋白的稳定。HIPK 2依赖性磷酸化导致LEF 1、TCF 4和TCF 3在体内从靶启动子上解离。这一结果为HIPK 2在Wnt信号传导中的上下文依赖性功能提供了机制解释; HIPK 2通过磷酸化转录抑制因子TCF 3上调转录，但通过磷酸化转录激活因子LEF 1抑制转录。最后，我们表明，在HIPK 2介导的磷酸化，TCF 3被替换为积极作用的TCF 1在靶启动子。这些观察结果强调了Wnt/HIPK 2依赖的TCF磷酸化的关键作用，并表明TCF转换是脊椎动物胚胎中Wnt靶基因激活的重要机制。
Wnt pathways play essential roles in cell proliferation, morphogenesis, and cell fate specification during embryonic development. According to the consensus view, the Wnt pathway prevents the degradation of the key signaling component beta-catenin by the protein complex containing the negative regulators Axin and glycogen synthase kinase 3 (GSK3). Stabilized beta-catenin associates with TCF proteins and enters the nucleus to promote target gene expression. This study examines the involvement of HIPK2 (homeodomain-interacting protein kinase (2) under bar) in the regulation of different TCF proteins in Xenopus embryos in vivo. We show that the TCF family members LEF1, TCF4, and TCF3 are phosphorylated in embryonic ectoderm after Wnt8 stimulation and HIPK2 overexpression. We also find that TCF3 phosphorylation is triggered by canonical Wnt ligands, LRP6, and dominant negative mutants for Axin and GSK3, indicating that this process shares the same upstream regulators with beta-catenin stabilization. HIPK2-dependent phosphorylation caused the dissociation of LEF1, TCF4, and TCF3 from a target promoter in vivo. This result provides a mechanistic explanation for the context-dependent function of HIPK2 in Wnt signaling; HIPK2 up-regulates transcription by phosphorylating TCF3, a transcriptional repressor, but inhibits transcription by phosphorylating LEF1, a transcriptional activator. Finally, we show that upon HIPK2-mediated phosphorylation, TCF3 is replaced with positively acting TCF1 at a target promoter. These observations emphasize a critical role for Wnt/HIPK2-dependent TCF phosphorylation and suggest that TCF switching is an important mechanism of Wnt target gene activation in vertebrate embryos.