Nuclear factor-kappaB activates dual inhibition sites in the regulation of tumor necrosis factor-alpha-induced neutrophil apoptosis.

The objective of this study was to elucidate the role of the nuclear factor-kappaB (NF-kappaB) pathway in tumor necrosis factor-alpha (TNF-alpha)-induced neutrophil apoptosis. A single treatment with TNF-alpha produced significant caspase-3 activation in a time- and concentration-dependent manner, while no significant morphological change in neutrophils was observed. After pretreatment of neutrophils with cycloheximide or actinomycin D, TNF-alpha produced morphologically typical apoptosis in a time- and concentration-dependent manner. Similarly, following pretreatment of neutrophils with the specific NF-kappaB inhibitors, pyrrolidine dithiocarbamate or SN50, TNF-alpha also produced neutrophil apoptosis (assessed morphologically). Caspase-3 activation by TNF-alpha was significantly enhanced by pretreatment with both cycloheximide and pyrrolidine dithiocarbamate. TNF-alpha-induced a rapid phosphorylation and degradation of IkappaB-alpha in neutrophils. Furthermore, TNF-alpha increased NF-kappaB DNA binding, which was abolished by pretreatment with pyrrolidine dithiocarbamate. These results indicate that the NF-kappaB pathway is crucial for neutrophil survival against TNF-alpha cell toxicity. Furthermore, it is proposed that NF-kappaB-induced proteins act on dual inhibitory sites, both upstream and downstream of caspase-3, to protect against apoptosis.