Osteopontin Signals through Calcium and Nuclear Factor of Activated T Cells (NFAT) in Osteoclasts A NOVEL RGD-DEPENDENT PATHWAY PROMOTING CELL SURVIVAL
Osteopontin Signals through Calcium and Nuclear Factor of Activated T Cells (NFAT) in Osteoclasts A NOVEL RGD-DEPENDENT PATHWAY PROMOTING CELL SURVIVAL
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DOI：
10.1074/jbc.m111.295048
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发表时间：
2011-11-18
影响因子：
4.8
通讯作者：
Dixon, S. Jeffrey
中科院分区：
文献类型：
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作者：
Tanabe, Natsuko;Wheal, Benjamin D.;Dixon, S. Jeffrey
骨桥蛋白 (OPN) 是一种整合素结合细胞外基质糖蛋白，可增强破骨细胞活性；然而，其作用机制却难以捉摸。 Ca2+ 依赖性转录因子 NFATc1 对于破骨细胞分化至关重要。我们评估了 OPN 对 NFATc1 的影响，NFATc1 在激活后易位到细胞核。将新生兔和大鼠的破骨细胞铺在盖玻片上，盖玻片不包被或包被 OPN 或牛白蛋白。 OPN 提高了显示核 NFATc1 的破骨细胞的比例。含有 RGD 的整合素阻断肽可阻止 OPN 诱导的 NFATc1 易位。此外，缺乏 RGD 的突变 OPN 无法诱导 NFATc1 易位。因此，NFATc1 的激活依赖于整联蛋白通过 RGD 的结合。使用荧光成像，发现 OPN 可以增加表现出胞质 Ca2+ 短暂升高（振荡）的破骨细胞的比例。 OPN 还可以增强破骨细胞的存活率。细胞内 Ca2+ 螯合剂 1,2-双（O-氨基苯氧基）乙烷-N,N,N',N'-四乙酸 (BAPTA) 抑制 Ca2+ 振荡，并抑制 OPN 诱导的 NFATc1 易位和存活增加。此外，一种特异性的细胞渗透性 NFAT 激活肽抑制剂可阻断 OPN 对 NFATc1 易位和破骨细胞存活的影响。这是 OPN 激活 NFATc1 并通过 Ca2+-NFAT 依赖性途径增强破骨细胞存活的首次证明。 NFATc1 活性增加和破骨细胞存活率提高可能是 OPN 对体内破骨细胞功能的刺激作用的原因。
Osteopontin (OPN), an integrin-binding extracellular matrix glycoprotein, enhances osteoclast activity; however, its mechanisms of action are elusive. The Ca2+-dependent transcription factor NFATc1 is essential for osteoclast differentiation. We assessed the effects of OPN on NFATc1, which translocates to nuclei upon activation. Osteoclasts from neonatal rabbits and rats were plated on coverslips, uncoated or coated with OPN or bovine albumin. OPN enhanced the proportion of osteoclasts exhibiting nuclear NFATc1. An RGD-containing, integrin-blocking peptide prevented the translocation of NFATc1 induced by OPN. Moreover, mutant OPN lacking RGD failed to induce translocation of NFATc1. Thus, activation of NFATc1 is dependent on integrin binding through RGD. Using fluorescence imaging, OPN was found to increase the proportion of osteoclasts exhibiting transient elevations in cytosolic Ca2+ (oscillations). OPN also enhanced osteoclast survival. The intracellular Ca2+ chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) suppressed Ca2+ oscillations and inhibited increases in NFATc1 translocation and survival induced by OPN. Furthermore, a specific, cell-permeable peptide inhibitor of NFAT activation blocked the effects of OPN on NFATc1 translocation and osteoclast survival. This is the first demonstration that OPN activates NFATc1 and enhances osteoclast survival through a Ca2+-NFAT-dependent pathway. Increased NFATc1 activity and enhanced osteoclast survival may account for the stimulatory effects of OPN on osteoclast function in vivo.