Department of Microbiology and Immunology, Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
J Immunol. 2011 Aug 15;187(4):1797-806. doi: 10.4049/jimmunol.1002628. Epub 2011 Jul 6.
NF-κB activation is essential for receptor activator for NF-κB ligand (RANKL)-induced osteoclast formation. IL-4 is known to inhibit the RANKL-induced osteoclast differentiation while at the same time promoting macrophage fusion to form multinucleated giant cells (MNG). Several groups have proposed that IL-4 inhibition of osteoclastogenesis is mediated by suppressing the RANKL-induced activation of NF-κB. However, we found that IL-4 did not block proximal, canonical NF-κB signaling. Instead, we found that IL-4 inhibited alternative NF-κB signaling and induced p105/50 expression. Interestingly, in nfκb1(-/-) bone marrow-derived macrophages (BMM), the formation of both multinucleated osteoclast and MNG induced by RANKL or IL-4, respectively, was impaired. This suggests that NF-κB signaling also plays an important role in IL-4-induced macrophage fusion. Indeed, we found that the RANKL-induced and IL-4-induced macrophage fusion were both inhibited by the NF-κB inhibitors IκB kinase 2 inhibitor and NF-κB essential modulator inhibitory peptide. Furthermore, overexpression of p50, p65, p52, and RelB individually in nfκb1(-/-) or nfκb1(+/+) BMM enhanced both giant osteoclast and MNG formation. Interestingly, knockdown of nfκb2 in wild-type BMM dramatically enhanced both osteoclast and MNG formation. In addition, both RANKL- and IL-4-induced macrophage fusion were impaired in NF-κB-inducing kinase(-/-) BMM. These results suggest IL-4 influences NF-κB pathways by increasing p105/p50 and suppressing RANKL-induced p52 translocation and that NF-κB pathways participate in both RANKL- and IL-4-induced giant cell formation.
NF-κB 的激活对于核因子-κB 配体（RANKL）诱导的破骨细胞形成是必不可少的。已知白细胞介素 4（IL-4）抑制 RANKL 诱导的破骨细胞分化，同时促进巨噬细胞融合形成多核巨细胞（MNG）。有几个研究小组提出，IL-4 抑制破骨细胞生成是通过抑制 RANKL 诱导的 NF-κB 激活来介导的。然而，我们发现 IL-4 并没有阻断近端的、经典的 NF-κB 信号通路。相反，我们发现 IL-4 抑制了替代的 NF-κB 信号通路，并诱导了 p105/50 的表达。有趣的是，在 NF-κB1（-/-）骨髓来源的巨噬细胞（BMM）中，RANKL 或 IL-4 分别诱导的多核破骨细胞和 MNG 的形成均受损。这表明 NF-κB 信号通路在 IL-4 诱导的巨噬细胞融合中也起着重要作用。事实上，我们发现 RANKL 诱导的和 IL-4 诱导的巨噬细胞融合均被 NF-κB 抑制剂 IκB 激酶 2 抑制剂和 NF-κB 必需调节肽抑制。此外，在 NF-κB1（-/-）或 NF-κB1（+/+）BMM 中单独过表达 p50、p65、p52 和 RelB 均可增强巨大多核破骨细胞和 MNG 的形成。有趣的是，在野生型 BMM 中敲低 NF-κB2 可显著增强破骨细胞和 MNG 的形成。此外，在 NF-κB 诱导激酶（-/-）BMM 中，RANKL 和 IL-4 诱导的巨噬细胞融合均受损。这些结果表明，IL-4 通过增加 p105/p50 并抑制 RANKL 诱导的 p52 易位来影响 NF-κB 途径，并且 NF-κB 途径参与了 RANKL 和 IL-4 诱导的巨细胞形成。
