Tumor Necrosis Factor Receptor-associated Factor 6 Is an Intranuclear Transcriptional Coactivator in Osteoclasts
Tumor Necrosis Factor Receptor-associated Factor 6 Is an Intranuclear Transcriptional Coactivator in Osteoclasts
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DOI：
10.1074/jbc.m802525200
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发表时间：
2008-11-07
影响因子：
4.8
通讯作者：
Teitelbaum, Steven L.
中科院分区：
文献类型：
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作者：
Bai, Shuting;Zha, Jikun;Teitelbaum, Steven L.
肿瘤坏死因子受体相关因子6（TRAF 6）与NF-κ B受体激活因子（RANK）的胞质结构域相关，是介导破骨细胞生成的信号复合物的重要组成部分。然而，TRAF 6的骨诱导活性由于其与四个半LIM结构域2（FHL 2）的结合而减弱，所述FHL 2在细胞质中充当衔接蛋白，在细胞核中充当转录调节因子。我们发现TRAF 6也定位于破骨细胞的细胞核中，但不是它们的骨髓巨噬细胞前体，破骨细胞核内丰度通过RANK配体（RANKL）特异性增加。TRAF 6核定位需要FHL 2，并且在fhl 2（-/-）破骨细胞中减少。TRAF 6与破骨细胞核中的转录因子RUNX 1相互作用，表明其具有转录活性。FHL 2也与RUNX 1结合，但仅在TRAF 6存在时才这样做。重要的是，TRAF 6识别破骨细胞核中的FHL 2和RUNX 1，并且这三种分子形成DNA结合复合物，其识别并反式激活fhl 2启动子中的RUNX 1反应元件。最后，TRAF 6及其近端激活因子RANKL聚泛素化FHL 2，促进其蛋白酶体降解。这些观察结果表明，TRAF 6通过胞浆内隔离FHL 2以钝化RANK激活并作为促进FHL 2表达的转录复合物的组分来负调节破骨细胞形成的反馈机制。
Tumor necrosis factor receptor-associated factor 6 (TRAF6) associates with the cytoplasmic domain of receptor activator of NF-kappa B (RANK) and is an essential component of the signaling complex mediating osteoclastogenesis. However, the osteoclastic activity of TRAF6 is blunted by its association with four and half LIM domain 2 (FHL2), which functions as an adaptor protein in the cytoplasm and transcriptional regulator in the nucleus. We find that TRAF6 also localizes in the nuclei of osteoclasts but not their bone marrow macrophage precursors and that osteoclast intranuclear abundance is specifically increased by RANK ligand (RANKL). TRAF6 nuclear localization requires FHL2 and is diminished in fhl2(-/-) osteoclasts. Suggesting transcriptional activity, TRAF6 interacts with the transcription factor RUNX1 in the osteoclast nucleus. FHL2 also associates with RUNX1 but does so only in the presence of TRAF6. Importantly, TRAF6 recognizes FHL2 and RUNX1 in osteoclast nuclei, and the three molecules form a DNA-binding complex that recognizes and transactivates the RUNX1 response element in the fhl2 promoter. Finally, TRAF6 and its proximal activator, RANKL, polyubiquitinate FHL2, prompting its proteasomal degradation. These observations suggest a feedback mechanism whereby TRAF6 negatively regulates osteoclast formation by intracytoplasmic sequestration of FHL2 to blunt RANK activation and as a component of a transcription complex promoting FHL2 expression.