Pharmacological glucocorticoids (GCs) inhibit bone formation, leading to osteoporosis. GCs inhibit bone morphogenetic protein-2 (Bmp2) expression, and rhBMP-2 restores mineralization in GC-arrested osteoblast cultures. To better understand how GCs regulate BMPs, we investigated Bmp transcription, as well as rhBMP-induced Smad and alkaline phosphatase (ALP) activity. Bmp2 cis-regulatory regions were analyzed by reporter plasmids and LacZ-containing bacterial artificial chromosomes. We found that GCs inhibited Bmp2 via a domain > 50 kb downstream of the coding sequence. Bmp expression was evaluated by RT-PCR; whereas GCs strongly inhibited Bmp2, Bmp4 was abundantly expressed and resistant to GCs. Both rhBMP-2 and rhBMP-4 restored mineralization in GC-arrested cultures; rhBMP-2 was 5-fold more effective when dosing was based on ALP activation, however, the rhBMPs were equipotent when dosing was based on Smad transactivation. In conclusion, GCs regulate Bmp2 via a far-downstream domain, and activation of Smad, not ALP, best predicts the pro-mineralization potential of rhBMPs.

中文翻译：

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糖皮质激素抑制的 MC3T3-E1 成骨细胞中 BMP-2 与 BMP-4 的表达和活性：Smad 信号传导，而不是碱性磷酸酶活性，预测矿化的拯救。

药理糖皮质激素 (GCs) 抑制骨形成，导致骨质疏松症。GCs 抑制骨形态发生蛋白-2 (Bmp2) 表达，rhBMP-2 恢复 GC 阻止的成骨细胞培养物中的矿化。为了更好地了解 GC 如何调节 BMP，我们研究了 Bmp 转录以及 rhBMP 诱导的 Smad 和碱性磷酸酶 (ALP) 活性。Bmp2 顺式调控区域通过报告质粒和含 LacZ 的细菌人工染色体进行分析。我们发现 GC 通过编码序列下游 > 50 kb 的域抑制 Bmp2。通过RT-PCR评估Bmp表达；GCs 强烈抑制 Bmp2，而 Bmp4 大量表达并且对 GCs 有抗性。rhBMP-2 和 rhBMP-4 在 GC 抑制的培养物中恢复矿化；当给药基于 ALP 激活时，rhBMP-2 的有效性提高 5 倍，然而，当给药基于 Smad 反式激活时，rhBMPs 是等效的。总之，GCs 通过远下游域调节 Bmp2，Smad 而非 ALP 的激活最能预测 rhBMPs 的促矿化潜力。