Bone acidic glycoprotein-75 delineates the extracellular sites of future bone sialoprotein accumulation and apatite nucleation in osteoblastic cultures
Bone acidic glycoprotein-75 delineates the extracellular sites of future bone sialoprotein accumulation and apatite nucleation in osteoblastic cultures
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DOI：
10.1074/jbc.m312409200
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发表时间：
2004-06-11
影响因子：
4.8
通讯作者：
Gorski, JP
中科院分区：
文献类型：
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作者：
Midura, RJ;Wang, AM;Gorski, JP
在UMR成骨细胞培养中加入有机磷源激活矿化程序，其中BSP定位于细胞外基质位置，羟基磷灰石晶体随后成核(Wang, a ., Martin， J. a ., Lembke， L. a ., and Midura， R. J. (2000) J. Biol。化学，275,11082-11091)。本研究首次发现了新的细胞外球形结构，称为生物矿化灶（BMF），它含有骨酸性糖蛋白-75 （BAG-75）、骨唾液蛋白（BSP）和碱性磷酸酶，它们是UMR模型中羟基磷灰石晶体初始成核的唯一位点。重要的是，在没有添加磷酸盐的情况下，达到融合后的UMR培养包含两个大小的种群，形态上可识别的BMF前体富含BAG-75（直径15-25和150-250）。较小群体的形状和大小与通过纯化BAG-75蛋白自结合在体外组装的结构相似(Gorski， J. P., Kremer， E. A., Chen， Y., Ryan， S., Fullenkamp， C., Delviscio， J., Jensen， K., and McKee， M. D. (1997) J. Cell。生物化学。64,547-564)。添加有机磷后，BSP在这些含bag -75的BMF前体中积累，随后发生羟基磷灰石晶体成核。总之，BAG-75是最早可检测的生物标志物，可准确预测UMR培养中新生生物矿化的细胞外位点。我们假设BAG-75可能在BMF前体的组装和其他蛋白质（如碱性磷酸酶和BSP）的募集中发挥关键的结构作用。此外，我们提出了一个假设的机制，其中BAG-75和BSP在BMF内磷灰石成核中发挥积极作用。
Addition of an organophosphate source to UMR osteoblastic cultures activates a mineralization program in which BSP localizes to extracellular matrix sites where hydroxyapatite crystals are subsequently nucleated (Wang, A., Martin, J. A., Lembke, L. A., and Midura, R. J. (2000) J. Biol. Chem. 275, 11082-11091). This study identifies for the first time novel extracellular spherical structures, termed biomineralization foci (BMF), containing bone acidic glycoprotein-75 (BAG-75), bone sialoprotein (BSP), and alkaline phosphatase that are the exclusive sites of initial nucleation of hydroxyapatite crystals in the UMR model. Importantly, in the absence of added phosphate, UMR cultures after reaching confluency contain two size populations of morphologically identifiable BMF precursors enriched in BAG-75 (15-25 and 150-250 mum in diameter). The shape and size of the smaller population are similar to structures assembled in vitro through self-association of purified BAG-75 protein (Gorski, J. P., Kremer, E. A., Chen, Y., Ryan, S., Fullenkamp, C., Delviscio, J., Jensen, K., and McKee, M. D. (1997) J. Cell. Biochem. 64, 547-564). After organophosphate addition, BSP accumulates within these BAG-75-containing BMF precursors, with hydroxyapatite crystal nucleation occurring subsequently. In summary, BAG-75 is the earliest detectable biomarker that accurately predicts the extracellular sites of de novo biomineralization in UMR cultures. We hypothesize that BAG-75 may perform a key structural role in the assembly of BMF precursors and the recruitment of other proteins such as alkaline phosphatase and BSP. Furthermore, we propose a hypothetical mechanism in which BAG-75 and BSP function actively in nucleation of apatite within BMF.