INVOLVEMENT OF NUCLEAR FACTOR-KAPPA-B IN PLATELET-ACTIVATING FACTOR-MEDIATED TUMOR-NECROSIS-FACTOR-ALPHA EXPRESSION

Tumor necrosis factor (TNF)-alpha and platelet-activating factor (PAF) are important mediators of inflammatory reactions, and their release is controlled by a positive feedback network. However, the regulatory mechanisms underlying the interaction of these two molecules are unkno wn. Within 10 min of the injection of lipopolysaccharide (LPS) into C5 7BL/6 mice, effects inducible by PAF such as anaphylactic shock-like s ymptoms, disseminated intravascular coagulation, and hemorrhage in ren al medullae were observed, and all these pathological changes were pre vented by the PAF antagonist, BN 50739. The plasma level of PAF after LPS injection reached a peak at 5 min. TNF-alpha gene expression was e vident 20 min after LPS injection and was maximal at 40 min, and the l evel of serum TNF-alpha reached a peak at 1 h. Pretreatment with BN 50 739 inhibited LPS-induced TNF-alpha gene expression and protein synthe sis in a dose-dependent manner. Injection of PAF or treatment of the m acrophage cell line, J774A.1, with PAF activated the transcription fac tor, nuclear factor (NF)-chi B, which is essential for inducible TNF-a transcription. The activation of NF-chi B by PAF preceded the LPS-med iated TNF-a gene expression. Pretreatment with BN 50739 inhibited LPS- induced mobilization of NF-chi B in a dose-dependent manner in vivo as well as in vitro. These data suggest that PAF, which is released imme diately or shortly after LPS injection, induces the expression of TNF- alpha through the activation of NF-chi B.