NF-κB Signaling Participates in Both RANKL- and IL-4-Induced Macrophage Fusion: Receptor Cross-Talk Leads to Alterations in NF-κB Pathways

NF-kappa B activation is essential for receptor activator for NF-kappa B 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-kappa B. However, we found that IL-4 did not block proximal, canonical NF-kappa B signaling. Instead, we found that IL-4 inhibited alternative NF-kappa B signaling and induced p105/50 expression. Interestingly, in nf kappa b1(-/-) 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-kappa B 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-kappa B inhibitors I kappa B kinase 2 inhibitor and NF-kappa B essential modulator inhibitory peptide. Furthermore, overexpression of p50, p65, p52, and RelB individually in nf kappa b1(-/-) or nf kappa b1(+/+) BMM enhanced both giant osteoclast and MNG formation. Interestingly, knockdown of nf kappa b2 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-kappa B-inducing kinase(-/-) BMM. These results suggest IL-4 influences NF-kappa B pathways by increasing p105/p50 and suppressing RANKL-induced p52 translocation and that NF-kappa B pathways participate in both RANKL- and IL-4-induced giant cell formation. The Journal of Immunology, 2011, 187: 1797-1806.