Phorbol myristate acetate induces neutrophil death through activation of p38 mitogen-activated protein kinase that requires endogenous reactive oxygen species other than HOCl.

Stimulation of normal mouse neutrophils with phorbol 12-myristate 13-acetate resulted in an acceleration of chromatin condensation and phosphatidylserine externalization that was not associated with caspase-3 activation. Caspase-independent death was completely inhibited by GF109203X and SB202190, specific inhibitors for protein kinase C and p38 mitogen-activated protein kinase respectively. Activation of p38 mitogen-activated protein kinase was completely suppressed by GF109203X, indicating that this enzyme is regulated by protein kinase C. On the other hand, cell death was abolished in NADPH oxidase-deficient neutrophils lacking superoxide production. Of note, p38 mitogen-activated protein kinase was activated by phorbol 12-myristate 13-acetate in normal and myeloperoxidase-deficient neutrophils lacking production of HOCl, whereas no activation was observed in NADPH oxidase-deficient neutrophils. These results strongly suggest that activation of p38 mitogen-activated protein kinase is regulated by endogenously generated superoxide or its metabolites other than HOCl, a critical regulator of inducer-stimulated death of neutrophils.