Dexamethasone promotes DMP1 mRNA expression by inhibiting negative regulation of Runx2 in multipotential mesenchymal progenitor, ROB-C26
Dexamethasone promotes DMP1 mRNA expression by inhibiting negative regulation of Runx2 in multipotential mesenchymal progenitor, ROB-C26
复制标题
DOI：
10.1016/j.cellbi.2007.08.033
复制
发表时间：
2008-02-01
影响因子：
3.9
通讯作者：
Takagi, Minoru
中科院分区：
文献类型：
--
作者：
Mikami, Yoshikazu;Takahashi, Tomihisa;Takagi, Minoru
牙本质基质蛋白1（Dentin matrix protein 1，DMP 1）是一种酸性磷酸化的细胞外蛋白，对牙本质和骨的矿化至关重要，但DMP 1表达调控的确切机制尚不完全清楚。合成糖皮质激素（GC）地塞米松（Dex）促进间充质祖细胞ROB-C26（C26）的早期成骨细胞分化，同时诱导成骨细胞特异性转录因子Runx 2和其他细胞外基质蛋白如骨钙素和骨唾液蛋白（BSP）的表达。我们研究了Dex通过诱导C26细胞中的Runx 2对DMP 1表达的影响。真实的时间RT-PCR结果显示Dex以时间和剂量依赖的方式增加DMP 1 mRNA的表达水平，GC拮抗剂RU 486则显著抑制DMP 1 mRNA的表达水平。此外，Dex增加了6个重复的成骨细胞特异性顺式作用元件2（6 x OSE 2）的荧光素酶活性，这是Runx 2的结合序列，表明Dex通过激活Runx 2刺激DMP 1表达。然而，意想不到的结果表明，外源性Runx 2的过表达抑制了DMP 1 mRNA的表达水平，即使在细胞用Dex处理后，而内源性Runx 2的表达下调增强了Dex诱导的DMP 1 mRNA的表达水平。这些结果表明，大量的外源Runx 2抑制DMP 1的表达，而少量的是更有效的右旋糖酐诱导的DMP 1在C26细胞的表达。因此，Dex可能激活了一些抑制Runx 2对DMP 1表达负作用的因子。由于丝裂原活化蛋白激酶（mitogen-activating protein kinase，MAPK）磷酸酶-1（MKP-1）已被报道通过减少Runx 2磷酸化而影响Dex诱导的成骨细胞分化，因此我们关注MKP-1和DMP 1表达之间的关系。Dex增加MKP-1表达，外源MKP-1的过表达显示6 x OSE的荧光素酶活性显着增加，达到Dex处理的C26细胞中检测到的水平。然而，在C26细胞中没有发现与BSP和OPN不同的诱导性DMP 1 mRNA表达水平。这些结果表明，虽然MKP-1增加Runx 2的DNA结合活性，但DMP 1表达可能需要MKP-1和添加剂因子的协作，以刺激Dex处理的C26细胞的转录后事件中Runx 2介导的DMP 1表达。(C)2007年国际细胞生物学联合会。由爱思唯尔有限公司出版。保留所有权利。
Dentin matrix protein 1 (DMP1) is an acidic phosphorylated extracellular protein and essential for mineralization of dentin and bone; however, the precise mechanism regulating DMP1 expression is not fully understood. A synthetic glucocorticoid (GC), dexamethasone (Dex), promotes an early osteoblast differentiation of a mesenchymal progenitor, ROB-C26 (C26), in parallel with inductive expression of an osteoblast-specific transcription factor, Runx2, and other extracellular matrix proteins such as osteocalcin and bone sialoprotein (BSP). We have examined the effect of Dex on DMP1 expression via induction of Runx2 in C26 cells. Real time RT-PCR showed that Dex increases DMP1 mRNA expression levels at time- and dose-dependent manners and a GC antagonist, RU486, drastically inhibited DMP1 mRNA expression levels. Furthermore, Dex increased the luciferase activity of six-repeated osteoblast-specific cis-acting element 2 (6 x OSE2), which is the binding sequence of Runx2, suggesting that Dex stimulates DMP1 expression via activation of Runx2. However, unexpected results showed that overexpression of exogenous Runx2 depressed DMP1 mRNA expression level, even after cells had been treated with Dex, while downregulated expression of endogenous Runx2 enhanced Dex-induced DMP1 mRNA expression level. These results imply that large amounts of exogenous Runx2 inhibit DMP1 expression, whereas small amounts are more effective for Dex-induced DMP1 expression in C26 cells. Therefore, Dex may activate some factors that inhibit negative action of Runx2 on DMP1 expression. Since mitogen-activating protein kinase (MAPK) phosphatase-1 (MKP-1) has been reported to affect the Dex-induced osteoblast differentiation via decrease of Runx2-phosphorylation, we focus on the relationship between MKP-1 and DMP1 expression. Dex increases MKP-1 expression, and overexpression of exogenous MKP-1 showed significant increase of luciferase activity of 6 x OSE up to the level detected in Dex-treated C26 cells. However, no inductive DMP1 mRNA expression level was found in C26 cells unlike BSP and OPN. These results suggest that although MKP-1 increases DNA-binding activity of Runx2, DMP1 expression may require the collaboration of MKP-1 and additive factors to stimulate Runx2-mediated DMP1 expression in the post-transcriptional event of Dex-treated C26 cells. (C) 2007 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved.