Department of Orthopaedic Surgery and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, United States.
Bone and Mineral Division, Department of Medicine, Washington University School of Medicine, St. Louis, United States.
Elife. 2020 Mar 23;9:e56095. doi: 10.7554/eLife.56095.
Inflammatory osteolysis is governed by exacerbated osteoclastogenesis. Ample evidence points to central role of NF-κB in such pathologic responses, yet the precise mechanisms underpinning specificity of these responses remain unclear. We propose that motifs of the scaffold protein IKKγ/NEMO partly facilitate such functions. As proof-of-principle, we used site-specific mutagenesis to examine the role of NEMO in mediating RANKL-induced signaling in mouse bone marrow macrophages, known as osteoclast precursors. We identified lysine (K)270 as a target regulating RANKL signaling as K270A substitution results in exuberant osteoclastogenesis in vitro and murine inflammatory osteolysis in vivo. Mechanistically, we discovered that K270A mutation disrupts autophagy, stabilizes NEMO, and elevates inflammatory burden. Specifically, K270A directly or indirectly hinders binding of NEMO to ISG15, a ubiquitin-like protein, which we show targets the modified proteins to autophagy-mediated lysosomal degradation. Taken together, our findings suggest that NEMO serves as a toolkit to fine-tune specific signals in physiologic and pathologic conditions.
炎症性骨溶解受破骨细胞生成加剧所控制。大量证据表明 NF-κB 在这种病理反应中起核心作用,但支持这些反应特异性的精确机制仍不清楚。我们提出支架蛋白 IKKγ/NEMO 的基序部分促进了这些功能。作为原理验证,我们使用定点诱变来研究 NEMO 在介导 RANKL 诱导的信号转导中的作用,RANKL 诱导的信号转导在已知的破骨细胞前体细胞小鼠骨髓巨噬细胞中起作用。我们确定赖氨酸 (K)270 是调节 RANKL 信号转导的靶点,因为 K270A 取代导致体外破骨细胞生成旺盛和体内炎症性骨溶解。在机制上,我们发现 K270A 突变会破坏自噬,稳定 NEMO,并增加炎症负担。具体而言,K270A 直接或间接阻碍 NEMO 与 ISG15(一种泛素样蛋白)的结合,我们表明该蛋白将修饰后的蛋白靶向自噬介导的溶酶体降解。总之,我们的发现表明 NEMO 可作为在生理和病理条件下微调特定信号的工具包。
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