Genetic deletion of the tumor necrosis factor receptor p60 or p80 sensitizes macrophages to lipopolysaccharide-induced nuclear factor-κB, mitogen-activated protein kinases, and apoptosis

Whether deletion of tumor necrosis factor (TNF) receptor 1 or 2 affects lipopolysaccharide (LPS)-mediated signaling is not understood. In this report, we used macrophages derived from wild type (wt) mice and from mice null for the type 1 receptor (p60^-/-), the type 2 receptor (p80^-/-), or both (p60^-/- p80^-/-) to investigate the effect of these receptors on LPS-mediated activation of NF-κB, mitogen-activated protein kinases, and apoptosis. LPS activated NF-κB by 3-4-fold in wt cells but by 9-10-fold in p60^-/-, p80^-/-, and p60^-/- p80^-/- macrophages. These results correlated with the IκBα kinase activation, which is needed for NF-κB activation. LPS-induced cyclooxygenase-2 and inducible NO synthase proteins and NO production were maximum in p60^-/- p80^-/- macrophages and minimum in wt cells. LPS activated C-Jun N-terminal kinase, p38^MAPK, and extracellular signal-regulated kinase in wt cells, but the levels were much higher in p60^-/-, p80^-/-, and p60^-/- p80^-/- cells. LPS-induced cytotoxicity, poly(ADP-ribose) polymerase cleavage, and annexin V staining were also highest in p60^-/- p80^-/- cells and lowest in wt cells. The difference in LPS signaling was unrelated to the expression of LPS receptors, CD14, or toll-like receptor 4. Overall, our studies indicate that deletion of either of the TNF receptors sensitizes the macrophages to LPS and provide evidence for cross-talk between TNF and LPS signaling.