Takai H, Kanematsu M, Yano K, Tsuda E, Higashio K, Ikeda K, Watanabe K, Yamada Y
Department of Geriatric Research, National Institute for Longevity Sciences, Obu, Aichi 474-8522, Japan.
J Biol Chem. 1998 Oct 16;273(42):27091-6. doi: 10.1074/jbc.273.42.27091.
Osteoprotegerin (OPG)/osteoclastogenesis inhibitory factor (OCIF) is a recently identified cytokine that belongs to the tumor necrosis factor receptor superfamily and regulates bone mass by inhibiting osteoclastic bone resorption. The present study was undertaken to determine whether OPG/OCIF is produced in bone microenvironment and how the expression is regulated. A transcript for OPG/OCIF at 3.1 kilobases was detected in bone marrow stromal cells (ST2 and MC3T3-G2/PA6) as well as in osteoblastic cells (MC3T3-E1). Transforming growth factor-beta1 (TGF-beta1) markedly increased the steady-state level of OPG/OCIF mRNA in a dose-dependent manner, while TGF-beta1 suppressed the mRNA expression of tumor necrosis factor-related activation-induced cytokine (TRANCE)/receptor activator of NF-kappaB ligand (RANKL), a positive regulator of osteoclastogenesis to which OPG/OCIF binds. The effect of TGF-beta1 on the expression of OPG/OCIF mRNA was transient, with a peak level at 3-6 h. The up-regulation of OPG/OCIF mRNA by TGF-beta1 in ST2 cells did not require de novo protein synthesis and involved both a transcriptional and a post-transcriptional mechanism. Western blot analysis and an enzyme-linked immunosorbent assay revealed that TGF-beta1 significantly increased the secretion of OPG/OCIF protein by ST2 cells at 6-24 h. In murine bone marrow cultures, TGF-beta1 markedly inhibited the formation of tartrate-resistant acid phosphatase-positive multinucleated osteoclast-like cells in the presence of 1,25-dihydroxyvitamin D3, whose effect was significantly reversed by a neutralizing antibody against OPG/OCIF. These results suggest that TGF-beta1 negatively regulates osteoclastogenesis, at least in part, through the induction of OPG/OCIF by bone marrow stromal cells and that the balance between OPG/OCIF and TRANCE/RANKL in local environment may be an important determinant of osteoclastic bone resorption.
骨保护素（OPG）/破骨细胞生成抑制因子（OCIF）是最近发现的一种细胞因子，属于肿瘤坏死因子受体超家族，通过抑制破骨细胞介导的骨吸收来调节骨量。本研究旨在确定OPG/OCIF是否在骨微环境中产生以及其表达是如何调控的。在骨髓基质细胞（ST2和MC3T3-G2/PA6）以及成骨细胞（MC3T3-E1）中检测到了3.1千碱基的OPG/OCIF转录本。转化生长因子-β1（TGF-β1）以剂量依赖的方式显著增加OPG/OCIF mRNA的稳态水平，而TGF-β1抑制肿瘤坏死因子相关激活诱导细胞因子（TRANCE）/核因子κB受体激活剂配体（RANKL）的mRNA表达，RANKL是一种破骨细胞生成的正向调节因子，OPG/OCIF可与之结合。TGF-β1对OPG/OCIF mRNA表达的影响是短暂的，在3 - 6小时达到峰值水平。TGF-β1在ST2细胞中对OPG/OCIF mRNA的上调不需要从头合成蛋白质，涉及转录和转录后机制。蛋白质免疫印迹分析和酶联免疫吸附测定显示，TGF-β1在6 - 24小时显著增加ST2细胞分泌OPG/OCIF蛋白。在小鼠骨髓培养中，TGF-β1在1,25 - 二羟维生素D3存在的情况下显著抑制抗酒石酸酸性磷酸酶阳性多核破骨细胞样细胞的形成，其作用被抗OPG/OCIF中和抗体显著逆转。这些结果表明，TGF-β1至少部分地通过骨髓基质细胞诱导OPG/OCIF来负向调节破骨细胞生成，并且局部环境中OPG/OCIF与TRANCE/RANKL之间的平衡可能是破骨细胞介导的骨吸收的重要决定因素。
