Matsuo Koichi, Galson Deborah L, Zhao Chen, Peng Lan, Laplace Catherine, Wang Kent Z Q, Bachler Marcus A, Amano Hitoshi, Aburatani Hiroyuki, Ishikawa Hiromichi, Wagner Erwin F
Department of Microbiology and Immunology, School of Medicine, Keio University, Tokyo 160-8582, Japan.
J Biol Chem. 2004 Jun 18;279(25):26475-80. doi: 10.1074/jbc.M313973200. Epub 2004 Apr 8.
Osteoclasts are specialized macrophages that resorb bone. Mice lacking the AP-1 component c-Fos are osteopetrotic because of a lack of osteoclast differentiation and show an increased number of macrophages. The nature of the critical function of c-Fos in osteoclast differentiation is not known. Microarray analysis revealed that Nfatc1, another key regulator of osteoclastogenesis, was down-regulated in Fos(-/-) osteoclast precursors. Chromatin immunoprecipitation assay showed that c-Fos bound to the Nfatc1 and Acp5 promoters in osteoclasts. In vitro promoter analyses identified nuclear factor of activated T-cells (NFAT)/AP-1 sites in the osteoclast-specific Acp5 and Calcr promoters. Moreover, in Fos(-/-) precursors gene transfer of an active form of NFAT restored transcription of osteoclast-specific genes in the presence of receptor activator of the NF-kappaB ligand (RANKL), rescuing bone resorption. In the absence of RANKL, however, Fos(-/-) precursors were insensitive to NFAT-induced osteoclastogenesis unlike wild-type precursors. These data indicate that lack of Nfatc1 expression is the cause of the differentiation block in Fos(-/-) osteoclast precursors and that transcriptional induction of Nfatc1 is a major function of c-Fos in osteoclast differentiation.
破骨细胞是负责吸收骨质的特化巨噬细胞。缺乏AP-1成分c-Fos的小鼠因破骨细胞分化缺失而患骨石化症，且巨噬细胞数量增多。c-Fos在破骨细胞分化中的关键功能本质尚不清楚。微阵列分析显示，破骨细胞生成的另一个关键调节因子Nfatc1在Fos(-/-)破骨细胞前体中表达下调。染色质免疫沉淀试验表明，c-Fos在破骨细胞中与Nfatc1和Acp5启动子结合。体外启动子分析在破骨细胞特异性Acp5和Calcr启动子中鉴定出活化T细胞核因子（NFAT）/AP-1位点。此外，在Fos(-/-)前体中，活性形式的NFAT基因转移在存在核因子κB受体激活剂配体（RANKL）的情况下恢复了破骨细胞特异性基因的转录，挽救了骨吸收。然而，在没有RANKL的情况下，与野生型前体不同，Fos(-/-)前体对NFAT诱导的破骨细胞生成不敏感。这些数据表明，Nfatc1表达缺失是Fos(-/-)破骨细胞前体分化阻滞的原因，且Nfatc1的转录诱导是c-Fos在破骨细胞分化中的主要功能。
