From the Division of Molecular Signaling and Biochemistry and.
J Biol Chem. 2014 Mar 14;289(11):7349-61. doi: 10.1074/jbc.M113.538314. Epub 2014 Jan 31.
The alternative nuclear factor-κB (NF-κB) pathway, mainly the RelB-p52 heterodimer, plays important roles in bone metabolism through an unknown mechanism. We have previously reported that alymphoplasia (aly/aly) mice, which lack active NF-κB-inducing kinase (NIK), show mild osteopetrosis due to the inhibition of osteoclastogenesis. p100 retains RelB in the cytoplasm and inhibits RANKL-induced osteoclastogenesis in aly/aly cells. Furthermore, the overexpression of RelB in aly/aly cells rescues RANKL-induced osteoclastogenesis by inducing p100 processing. In contrast, the overexpression of p65 in aly/aly cells has no effect. However, the overexpression of RelB fails to rescue RANKL-induced osteoclastogenesis in the presence of p100ΔGRR, which cannot be processed to p52, suggesting that p100 processing is a key step in RelB-rescued, RANKL-induced osteoclastogenesis in aly/aly cells. In this study, Cot (cancer Osaka thyroid), an MAP3K, was up-regulated by RelB overexpression. Analysis of the Cot promoter demonstrated that p65 and RelB bound to the distal NF-κB-binding site and that RelB but not p65 bound to the proximal NF-κB-binding site in the Cot promoter. The knocking down of Cot expression significantly reduced the RANKL-induced osteoclastogenesis induced by RelB overexpression. The phosphorylation of IKKα at threonine 23 and its kinase activity were indispensable for the processing of p100 and osteoclastogenesis by RelB-induced Cot. Finally, constitutively activated Akt enhanced osteoclastogenesis by RelB-induced Cot, and a dominant-negative form of Akt significantly inhibited it. Taken together, these results indicate that the overexpression of RelB restores RANKL-induced osteoclastogenesis by activation of Akt/Cot/IKKα-induced p100 processing.
替代核因子-κB（NF-κB）途径，主要是 RelB-p52 异二聚体，通过未知机制在骨代谢中发挥重要作用。我们之前曾报道过，缺乏活性 NF-κB 诱导激酶（NIK）的无淋巴发育不良（aly/aly）小鼠由于破骨细胞生成受到抑制而表现出轻度骨质增生。p100 将 RelB 保留在细胞质中，并抑制 aly/aly 细胞中 RANKL 诱导的破骨细胞生成。此外，RelB 在 aly/aly 细胞中的过表达通过诱导 p100 加工来挽救 RANKL 诱导的破骨细胞生成。相比之下，p65 在 aly/aly 细胞中的过表达没有影响。然而，在不能加工为 p52 的 p100ΔGRR 存在的情况下，RelB 的过表达无法挽救 RANKL 诱导的破骨细胞生成，表明 p100 加工是 RelB 挽救的关键步骤，在 aly/aly 细胞中，RANKL 诱导的破骨细胞生成。在这项研究中，Cot（癌症大阪甲状腺），一种 MAP3K，被 RelB 的过表达上调。Cot 启动子的分析表明，p65 和 RelB 结合到远端 NF-κB 结合位点，而 RelB 但不是 p65 结合到 Cot 启动子中的近端 NF-κB 结合位点。Cot 表达的敲低显著降低了由 RelB 过表达诱导的 RANKL 诱导的破骨细胞生成。RelB 诱导的 Cot 诱导的 p100 加工和破骨细胞生成所必需的 IKKα 丝氨酸 23 的磷酸化及其激酶活性。最后，激活的 Akt 增强了由 RelB 诱导的 Cot 引起的破骨细胞生成，而 Akt 的显性失活形式显著抑制了它。总之，这些结果表明，RelB 的过表达通过激活 Akt/Cot/IKKα 诱导的 p100 加工来恢复 RANKL 诱导的破骨细胞生成。
