Department of Molecular Genetics, School of Dentistry and Dental Research Institute, BK21 Program, Seoul National University, Seoul 110-749, Republic of Korea.
J Biol Chem. 2010 Nov 19;285(47):36410-9. doi: 10.1074/jbc.M110.142307. Epub 2010 Sep 17.
Runx2 is a critical transcription factor for osteoblast differentiation. Regulation of Runx2 expression levels and transcriptional activity is important for bone morphogenetic protein (BMP)-induced osteoblast differentiation. Previous studies have shown that extracellular signal-regulated kinase (Erk) activation enhances the transcriptional activity of Runx2 and that BMP-induced Runx2 acetylation increases Runx2 stability and transcriptional activity. Because BMP signaling induces Erk activation in osteoblasts, we sought to investigate whether BMP-induced Erk signaling regulates Runx2 acetylation and stability. Erk activation by overexpression of constitutively active MEK1 increased Runx2 transcriptional activity, whereas U0126, an inhibitor of MEK1/2, suppressed basal Runx2 transcriptional activity and BMP-induced Runx2 acetylation and stabilization. Overexpression of constitutively active MEK1 stabilized Runx2 protein via up-regulation of acetylation and down-regulation of ubiquitination. Erk activation increased p300 protein levels and histone acetyltransferase activity. Knockdown of p300 using siRNA diminished Erk-induced Runx2 stabilization. Overexpression of Smad5 increased Runx2 acetylation and stabilization. Erk activation further increased Smad-induced Runx2 acetylation and stabilization, whereas U0126 suppressed these functions. On the other hand, knockdown of Smad1 and Smad5 by siRNA suppressed both basal and Erk-induced Runx2 protein levels. Erk activation enhanced the association of Runx2 with p300 and Smad1. Taken together these results indicate that Erk signaling increases Runx2 stability and transcriptional activity, partly via increasing p300 protein levels and histone acetyltransferase activity and subsequently increasing Runx2 acetylation by p300. In addition to the canonical Smad pathway, a BMP-induced non-Smad Erk signaling pathway cooperatively regulates osteoblast differentiation partly via increasing the stability and transcriptional activity of Runx2.
Runx2 是成骨细胞分化的关键转录因子。Runx2 表达水平和转录活性的调节对于骨形态发生蛋白（BMP）诱导的成骨细胞分化非常重要。先前的研究表明，细胞外信号调节激酶（Erk）的激活增强了 Runx2 的转录活性，并且 BMP 诱导的 Runx2 乙酰化增加了 Runx2 的稳定性和转录活性。由于 BMP 信号在成骨细胞中诱导 Erk 激活，我们试图研究 BMP 诱导的 Erk 信号是否调节 Runx2 乙酰化和稳定性。通过过表达组成型激活的 MEK1 激活 Erk 可增加 Runx2 的转录活性，而 MEK1/2 的抑制剂 U0126 则抑制基础 Runx2 的转录活性以及 BMP 诱导的 Runx2 乙酰化和稳定。组成型激活的 MEK1 通过上调乙酰化和下调泛素化来稳定 Runx2 蛋白。Erk 激活增加了 p300 蛋白水平和组蛋白乙酰转移酶活性。使用 siRNA 敲低 p300 减少了 Erk 诱导的 Runx2 稳定。Smad5 的过表达增加了 Runx2 的乙酰化和稳定。Erk 激活进一步增加了 Smad 诱导的 Runx2 乙酰化和稳定，而 U0126 则抑制了这些功能。另一方面，siRNA 敲低 Smad1 和 Smad5 抑制了基础和 Erk 诱导的 Runx2 蛋白水平。Erk 激活增强了 Runx2 与 p300 和 Smad1 的结合。总之，这些结果表明 Erk 信号通过增加 p300 蛋白水平和组蛋白乙酰转移酶活性，随后通过 p300 增加 Runx2 乙酰化，从而增加 Runx2 的稳定性和转录活性。除了经典的 Smad 途径外，BMP 诱导的非 Smad Erk 信号途径通过增加 Runx2 的稳定性和转录活性，部分协同调节成骨细胞分化。
