Canonical WNT signaling promotes osteogenesis by directly stimulating Runx2 gene expression
Canonical WNT signaling promotes osteogenesis by directly stimulating Runx2 gene expression
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DOI：
10.1074/jbc.m500608200
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发表时间：
2005-09-30
影响因子：
4.8
通讯作者：
Lian, JB
中科院分区：
文献类型：
--
作者：
Gaur, T;Lengner, CJ;Lian, JB
典型WNT信号所需的蛋白质的激活和无效突变都揭示了这一途径对正常骨骼发育的重要性。然而，WNT信号促进骨形成细胞分化的组织特异性转录机制尚未确定。在这里，我们提出了一个假设，即典型WNT信号和骨相关转录因子RUNX2/CBFA1/ AML3是成骨细胞分化开始所需途径的功能相关成分。我们的研究结果表明，在WNT信号激活和高骨量表型的SFRP1（分泌卷曲相关蛋白-1）-null小鼠的骨骼中，t细胞因子(TCF)-1、Runx2和Runx2靶基因骨钙素的表达显著增加。我们通过突变分析证明，响应典型WNT信号的功能性TCF调控元件位于Runx2基因的启动子中（- 97至- 93）。通过染色质免疫沉淀，发现β -连环蛋白和TCF1向内源性Runx2基因募集。TCF1与典型WNT蛋白的共表达导致Runx2启动子活性激活2-5倍，内源性mRNA在小鼠多能间充质细胞和骨祖细胞中诱导7-8倍。这种增强被SFRP1废除了。综上所述，我们的研究结果为典型WNT信号直接调控Runx2提供了证据，并表明Runx2是β -catenin/TCF1刺激骨形成的靶点。我们认为WNT/TCF1信号通路与骨形态发生蛋白/转化生长因子- β信号通路一样，激活间充质细胞Runx2基因表达，控制成骨细胞分化和骨骼发育。
Both activating and null mutations of proteins required for canonical WNT signaling have revealed the importance of this pathway for normal skeletal development. However, tissue-specific transcriptional mechanisms through which WNT signaling promotes the differentiation of bone-forming cells have yet to be identified. Here, we address the hypothesis that canonical WNT signaling and the bone-related transcription factor RUNX2/CBFA1/ AML3 are functionally linked components of a pathway required for the onset of osteoblast differentiation. Our findings show that, in bone of the SFRP1 ( secreted frizzled-related protein-1)-null mouse, which exhibits activated WNT signaling and a high bone mass phenotype, there is a significant increase in expression of T-cell factor (TCF)-1, Runx2, and the RUNX2 target gene osteocalcin. We demonstrate by mutational analysis that a functional TCF regulatory element responsive to canonical WNT signaling resides in the promoter of the Runx2 gene ( - 97 to - 93). By chromatin immunoprecipitation, recruitment of beta-catenin and TCF1 to the endogenous Runx2 gene is shown. Coexpression of TCF1 with canonical WNT proteins resulted in a 2-5-fold activation of Runx2 promoter activity and a 7-8-fold induction of endogenous mRNA in mouse pluripotent mesenchymal and osteoprogenitor cells. This enhancement was abrogated by SFRP1. Taken together, our results provide evidence for direct regulation of Runx2 by canonical WNT signaling and suggest that Runx2 is a target of beta-catenin/TCF1 for the stimulation of bone formation. We propose that WNT/TCF1 signaling, like bone morphogenetic protein/transforming growth factor-beta signaling, activates Runx2 gene expression in mesenchymal cells for the control of osteoblast differentiation and skeletal development.