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-kappaB, mitogen-activated protein kinases, and apoptosis. LPS activated NF-kappaB by 3-4-fold in wt cells but by 9-10-fold in p60(-/-), p80(-/-), and p60(-/-) p80(-/-) macrophages. These results correlated with the IkappaBalpha kinase activation, which is needed for NF-kappaB 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.