Evidence that genetic deletion of the TNF receptor p60 or p80 in macrophages modulates RANKL-induced signaling

In the current report, we investigated the possibility of a cross-talk between receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor α (TNF-α) using macrophage cell lines derived from wild-type mice and from mice with genetic deletion of the type 1 TNF receptor (p60 ^-/-), the type 2 TNF receptor (p80^-/-), or both receptors (p60^-/-p80^-/-). Deletion of TNF receptors sensitized the cells to RANKL-induced NF-κB activation, in order from least to most sensitive of p60^-/- less than p80^-/- less than p60 ^-/- p80^-/-. The effect on nuclear factor-κB (NF-κB) activation correlated with RANKL-induced IκBα kinase activation. Deletion of both TNF receptors also potentiated RANKL-induced c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1 and 2 (ERK1/2), and p38 mitogen-activated protein kinase (MAPK) activations in a dose- and time-dependent manner. Nitric oxide (NO) production and expression of inducible NO synthase (iNOS) and cyclooxygenase 2 (COX-2) induced by RANKL was also maximally induced in double knock-out cells. RANKL had no effect on the proliferation of wild-type cells, but deletion of TNF receptors induced growth modulatory effects. We also found that tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), which mediates RANKL signaling, was constitutively bound to RANK in TNF receptor-deleted cells but not in wild-type cells, and this binding was enhanced by RANKL. Overall our results show that RANKL signaling is modulated by the TNF receptors and thus provide evidence of cross-talk between the receptors of 2 cytokines.