Tumor necrosis factor-alpha activation of the c-Jun N-terminal kinase pathway in human neutrophils

The intensity and duration of an inflammatory response depends on the balan ce of factors that favor perpetuation versus resolution. At sites of inflam mation, neutrophils adherent to other cells or matrix components are expose d to tumor necrosis factor-alpha (TNF alpha), Although TNF alpha has been i mplicated in induction of pro-inflammatory responses, it may also inhibit t he intensity of neutrophilic inflammation by promoting apoptosis, Since TNF alpha is not only an important activator of the stress-induced pathways le ading to p38 MAPk and c-Jun N-terminal kinase (JNK) but also a potent effec tor of apoptosis, we investigated the effects of TNF alpha on the JNK pathw ay in adherent human neutrophils and the potential involvement of this path way in neutrophil apoptosis. Stimulation with TNF alpha was found to result in beta (2) integrin-mediated activation of the cytoplasmic tyrosine kinas es Pyk2 and Syk, and activation of a three-part MAPk module composed of MEK K1, MKK7, and/or MKK4 and JNK1. JNK activation was attenuated by blocking a ntibodies to beta (2) integrins, the tyrosine kinase inhibitors, genistein, and tyrphostin A9, a Pyk2-specific inhibitor, and piceatannol, a Syk-speci fic inhibitor, Exposure of adherent neutrophils to TNF alpha led to the rap id onset of apoptosis that was demonstrated by augmented annexin V binding and caspase-3 cleavage. TNF alpha -induced increases in annexin V binding t o neutrophils were attenuated by blocking antibodies to beta (2) integrins, and the caspase-3 cleavage was attenuated by tyrphostin A9. Hence, exposur e of adherent neutrophils to TNF alpha leads to utilization of the JNK-sign aling pathways that may contribute to diverse functional responses includin g induction of apoptosis and subsequent resolution of the inflammatory resp onse.