Smad4 and β-catenin co-activators functionally interact with lymphoid-enhancing factor to regulate graded expression of Msx2
Smad4 and β-catenin co-activators functionally interact with lymphoid-enhancing factor to regulate graded expression of Msx2
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DOI：
10.1074/jbc.m305472200
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发表时间：
2003-12-05
影响因子：
4.8
通讯作者：
Sirard, C
中科院分区：
文献类型：
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作者：
Hussein, SM;Duff, EK;Sirard, C
最近的体内证据表明，Wnt信号通过调节骨形态发生蛋白(BMP)水平，进而影响MSX基因的表达，在决定干细胞在外胚层和神经脊中的命运中发挥核心作用。然而，作为细胞命运关键调节因子的MSX基因表达调控的分子机制尚未阐明。在这里，我们在小鼠胚胎干细胞中表明，MSX2的BMP依赖的激活是通过在两个Smad结合元件上协同结合Smad4和在两个Lef1/Tcf结合部位协同结合淋巴增强因子(Lef1)来介导的。Lef1可以与Smad4和Smad1协同激活MSX2启动子，该转录复合体组装在内源性启动子上以响应BMP2。Wnt/β-catenin信号通路可以通过Lef1与其启动子的结合激活MSX2，并与BMP2协同激活MSX2的表达，可能是通过增强p300/cAMP反应元件结合蛋白结合蛋白辅助因子的募集。有趣的是，在Smad4缺失的胚胎干细胞中，或者当Smad结合元件发生突变但在各种BMP拮抗剂存在的情况下持续存在时，MSX2的Wnt/β-catenin依赖的激活是有缺陷的，这表明Smad4在没有BMP自分泌环的情况下参与了Wnt/β-catenin信号的转导。染色质免疫沉淀分析表明，内源性Smad4，而不是Smad1，是响应β-连环素激活的Lef1转录复合体的一部分，排除了BMP信号在这一反应中的任何含义。我们认为，Wnt信号通路不仅通过调节BMP水平，而且还通过直接协同调节BMP靶基因来决定细胞命运。
Recent in vivo evidence suggests that Wnt signaling plays a central role in determining the fate of stem cells in the ectoderm and in the neural crest by modulating bone morphogenetic protein (BMP) levels, which, in turn, influence Msx gene expression. However, the molecular mechanism regulating the expression of the Msx genes as key regulators of cell fate has not been elucidated. Here we show in murine embryonic stem cells that BMP-dependent activation of Msx2 is mediated via the cooperative binding of Smad4 at two Smad binding elements and of lymphoid enhancing factor (Lef1) at two Lef1/TCF binding sites. Lef1 can synergize with Smad4 and Smad1 to activate Msx2 promoter, and this transcriptional complex is assembled on the endogenous promoter in response to BMP2. The Wnt/beta-catenin signaling pathway can activate Msx2 via the binding of Lef1 to its promoter and synergizes with BMP2 to activate Msx2 expression, possibly via enhanced recruitment of the p300/cAMP-response element-binding protein-binding protein co-factor. Interestingly, the Wnt/beta-catenin- dependent activation of Msx2 was defective in Smad4-deficient embryonic stem cells or when Smad binding elements were mutated but persisted in the presence of various BMP antagonists, indicating that Smad4 was involved in transducing the Wnt/beta-catenin signals in the absence of a BMP autocrine loop. A chromatin immunoprecipitation analysis revealed that endogenous Smad4, but not Smad1, was part of the Lef1 transcriptional complex in response to beta-catenin activation, dismissing any implication of BMP signaling in this response. We propose that Wnt signaling pathway could dictate cell fate not only by modulating BMP levels but also by directly regulating cooperatively BMP-target genes.