Ionomycin causes activation of p38 and p42/44 mitogen-activated protein kinases in human neutrophils

Many receptor-linked agents that prime or activate the NADPH oxidase in pol ymorphonuclear neutrophils (PMNs) elicit changes in cytosolic Ca2+ concentr ation and activate mitogen-activated protein (MAP) kinases. To investigate the role of Ca2+ in the activation of p38 and p42/44 MAP kinases, we examin ed the effects of the Ca2+-selective ionophore ionomycin on priming and act ivation of the PMN oxidase. Ionomycin caused a rapid rise in cytosolic Ca2 that was due to both a release of cytosolic Ca2+ stores and Ca2+ influx. I onomycin also activated (2 muM) and primed (20-200 nM) the PMN oxidase. Dua l phosphorylation of p38 MAP kinase and phosphorylation of its substrate ac tivating transcription factor-2 were detected at ionomycin concentrations t hat prime or activate the PMN oxidase, while dual phosphorylation of p42/44 MAP kinase and phosphorylation of its substrate Elk-1 were elicited at 0.2 -2 muM. SB-203580, a p38 MAP kinase antagonist, inhibited ionomycin-induced activation of the oxidase (68 +/- 8%, P< 0.05) and tyrosine phosphorylatio n of 105- and 72-kDa proteins; conversely, PD-98059, an inhibitor of MAP/ e xtracellular signal-related kinase 1, had no effect. Treatment of PMNs with thapsigargin resulted in priming of the oxidase and activation of p38 MAP kinase. Chelation of cytosolic but not extracellular Ca2+ completely inhibi ted ionomycin activation of p38 MAP kinase, whereas chelation of extracellu lar Ca2+ abrogated activation of p42/44 MAP kinase. These results demonstra te the importance of changes in cytosolic Ca2+ for MAP kinase activation in PMNs.