CCAAT/Enhancer-binding Protein β Promotes Osteoblast Differentiation by Enhancing Runx2 Activity with ATF4
CCAAT/Enhancer-binding Protein β Promotes Osteoblast Differentiation by Enhancing Runx2 Activity with ATF4
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DOI：
10.1091/mbc.e08-03-0329
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发表时间：
2008-12-01
影响因子：
3.3
通讯作者：
Imamura, Takeshi
中科院分区：
文献类型：
--
作者：
Tominaga, Hiroyuki;Maeda, Shingo;Imamura, Takeshi
虽然CCAAT/增强子结合蛋白β（C/EBP β）参与体外成骨细胞中骨钙素基因的表达，但C/EBP β在骨形成中的生理重要性和分子机制仍有待阐明。特别是，目前尚不清楚C/EBP β在成骨细胞分化过程中是否与其他蛋白质作为同源二聚体或异源二聚体。在这里，从小鼠中删除C/EBP β基因导致骨形成延迟，同时抑制软骨细胞成熟和成骨细胞分化。X型胶原的表达以及软骨细胞肥大在突变骨中被抑制，为C/EBP β在软骨细胞成熟中的可能作用提供了新的见解。在成骨细胞中，荧光素酶报告基因、凝胶位移、DNAP和ChIP分析表明，C/EBP β与活化转录因子4（ATF 4）异二聚化，ATF 4是另一种对成骨细胞成熟至关重要的碱性亮氨酸拉链转录因子。该复合物相互作用并反式激活骨钙素启动子的骨钙素特异性元件1（OSE 1）。C/EBP β还通过增强其相互作用增强了ATF 4和Runx 2对骨钙素启动子反式激活的协同作用。因此，我们的研究结果提供了证据表明，C/EBP β是Runx 2和ATF 4促进成骨细胞成熟的关键辅因子。
Although CCAAT/enhancer-binding protein beta (C/EBP beta) is involved in osteocalcin gene expression in osteoblast in vitro, the physiological importance of and molecular mechanisms governing C/EBP beta in bone formation remain to be elucidated. In particular, it remains unclear whether C/EBP beta acts as a homodimer or a heterodimer with other proteins during osteoblast differentiation. Here, deletion of the C/EBP beta gene from mice resulted in delayed bone formation with concurrent suppression of chondrocyte maturation and osteoblast differentiation. The expression of type X collagen as well as chondrocyte hypertrophy were suppressed in mutant bone, providing new insight into the possible roles of C/EBP beta in chondrocyte maturation. In osteoblasts, luciferase reporter, gel shift, DNAP, and ChIP assays demonstrated that C/EBP beta heterodimerized with activating transcription factor 4 (ATF4), another basic leucine zipper transcription factor crucial for osteoblast maturation. This complex interacted and transactivated osteocalcin-specific element 1 (OSE1) of the osteocalcin promoter. C/EBP beta also enhanced the synergistic effect of ATF4 and Runx2 on osteocalcin promoter transactivation by enhancing their interaction. Thus, our results provide evidence that C/EBP beta is a crucial cofactor in the promotion of osteoblast maturation by Runx2 and ATF4.