Evidence for a Synergistic Role of Two Types of Human Tumor Necrosis Factor Receptors for the Ligand-Dependent Activation of the Nuclear Transcription Factor NF-κB

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Abstract
Tumor necrosis factor (TNF) is a multipotential cytokine that interacts with a wide variety of cells through two distinct receptors, referred to as the p60 and p80 receptors. Why there are two distinct receptors for the same ligand and whether these receptors mediate their signal independently or synergistically is not known. We examined the role of these two receptors in the ligand-dependent activation of a transcriptional factor, NF-κB, an early response (5–15 min) to TNF in human myeloid ML-1a cells. By using receptor type-specific antibodies, these cells were found to express almost equal amounts of both receptors. TNF-dependent activation of NF-κB could be blocked partially by both anti-p60 and anti-p80, suggesting that TNF mediates its effect independently through the p60 and p80 receptors. In comparison, the activation of NF-κB by lymphotoxin (LT), which shares receptors with TNF, was completely blocked by anti-p60, whereas anti-p80 had no effect. Anti-p60 but not anti-p80 by itself was found to activate NF-κB in a dose-dependent manner, but on a molar basis anti-p60 was found to be 100 times less potent than TNF. Interestingly, even though anti-p80 by itself was inactive, it potentiated the effect of anti-p60 synergistically, suggesting an interaction between the two types of TNF receptor. Thus, overall these results demonstrate that the two forms of TNF receptors could mediate their signal in both an independent and synergistic manner and that TNF mediates its signal through both forms of receptors, whereas LT mediates its signal through the p60 receptor.