Department of Biomedical Sciences, Baylor College of Dentistry, Texas A&M Health Science Center, Dallas, TX 75246, USA.
Dev Dyn. 2012 Nov;241(11):1708-15. doi: 10.1002/dvdy.23858. Epub 2012 Sep 17.
Supernumerary teeth are often observed in patients suffering from cleidocranial dysplasia due to a mutation in Runx2 that results in haploinsufficiency. However, the underlying molecular mechanisms are poorly defined. In this study, we assessed the roles of Runx2 and its functional antagonist Twist1 in regulating fibroblast growth factor (FGF) signaling using in vitro biochemical approaches.
We showed that Twist1 stimulated Fgfr2 and Fgf10 expression in a mesenchymal cell line and that it formed heterodimers with ubiquitously expressed E12 (together with E47 encoded by E2A gene) and upregulated Fgfr2 and Fgf10 promoter activities in a dental mesenchyme-derived cell line. We further demonstrated that the bHLH domain of Twist1 was essential for its synergistic activation of Fgfr2 promoter with E12 and that the binding of E12 stabilized Twist1 by preventing it from undergoing lysosomal degradation. Although Runx2 had no apparent effects on Fgfr2 and Fgf10 promoter activities, it inhibited the stimulatory activity of Twist1 on Fgfr2 promoter.
These findings suggest that Runx2 haploinsufficiency might result in excessive unbound Twist1 that can freely bind to E12 and enhance FGF signaling, thereby promoting the formation of extra teeth.
由于 Runx2 基因突变导致单倍体不足，患有颅锁骨发育不全症的患者常观察到额外牙齿。然而，其潜在的分子机制尚不清楚。在这项研究中，我们使用体外生化方法评估了 Runx2 及其功能拮抗剂 Twist1 在调节成纤维细胞生长因子 (FGF) 信号中的作用。
我们表明 Twist1 在间充质细胞系中刺激 Fgfr2 和 Fgf10 的表达，并与广泛表达的 E12（与 E2A 基因编码的 E47 一起）形成异二聚体，并在上皮间充质衍生细胞系中上调 Fgfr2 和 Fgf10 启动子活性。我们进一步证明 Twist1 的 bHLH 结构域对于其与 E12 协同激活 Fgfr2 启动子是必不可少的，并且 E12 的结合通过防止 Twist1 发生溶酶体降解来稳定 Twist1。虽然 Runx2 对 Fgfr2 和 Fgf10 启动子活性没有明显影响，但它抑制了 Twist1 对 Fgfr2 启动子的刺激活性。
这些发现表明，Runx2 单倍体不足可能导致过多未结合的 Twist1 自由结合 E12 并增强 FGF 信号，从而促进额外牙齿的形成。
