Abstract
We studied the role of c-Jun N-terminal kinase (JNK) in human neutrophils stimulated by tumor necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Stimulation of neutrophils with TNF-α and GM-CSF caused phosphorylation of p54 or p46 JNK or both. The phosphorylated p46 JNK band in TNF-α-stimulated neutrophils mobilized faster than that in GM-CSF-stimulated cells. The JNK isoform transcripts expressed in neutrophils were JNK1β1, JNK1β2, JNK2α1, and JNK2α2. The JNK isoforms phosphorylated by TNF-α and GM-CSF stimulation were found to be JNK1 and JNK2, respectively, on the basis of the molecular mass and the capture assay. TNF-α-induced JNK phosphorylation was sustained in the presence of cycloheximide, which was accompanied by accelerated neutrophil apoptosis. The JNK inhibitors (SP600125 and TAT-TI-JIP153–163) suppressed neutrophil apoptosis induced by TNF-α plus cycloheximide, whereas they attenuated the GM-CSF-mediated antiapoptotic effect on neutrophils. The JNK inhibitor did not affect the levels of Mcl-1 and XIAP (antiapoptotic molecules), which were regulated by TNF-α plus cycloheximide and GM-CSF. The JNK inhibitor markedly suppressed TNF-α-induced and GM-CSF-induced superoxide release. These findings suggest that JNK1 and JNK2 are involved in TNF-α-induced neutrophil apoptosis and GM-CSF-mediated antiapoptotic effect on neutrophils, respectively, and both JNK isoforms are involved in TNF-α-induced and GM-CSF-induced superoxide release.