The regulation of neutrophil phospholipase A₂ by granulocyte-macrophage colony-stimulating factor and its role in priming superoxide production

Experiments were performed to investigate the relative role of phospholipase A₂ (PLA₂) in the activation and cytokine-mediated priming of neutrophil superoxide production. PLA₂ activity was measured with a radiometric assay which discriminates between PLA₂ and the downstream enzyme, 5-lipoxygenase. In cells that had not been primed by prior incubation with granulocyte-macrophage colony stimulating factor (GM-CSF). PLA₂ and NADPH oxidase were differentially stimulated by the chemotactic peptide N-formyl-met-leu-phe (FMLP), calcium ionophore, or phorbol ester. In addition, inhibition of PLA₂ by mepacrine (0-100 μmol/l) did not concomitantly inhibit FMLP-stimulated superoxide production. These findings suggest that the activity of PLA₂ and NADPH oxidase may be uncoupled in the unprimed cell. In cells preincubated with GM-CSF, time- and dose-dependent priming of FMLP-stimulated PLA₂ responses were observed and inhibition of PLA₂ by mepacrine was accompanied by the inhibition of FMLP-stimulated superoxide production down to the level of unprimed cells. The effect of mepacrine was not due to inhibition of FMLP receptor expression. These data suggest that a mepacrine-sensitive PLA₂ may have a role in the GM-CSF mediated priming of superoxide production. Using ionophore-stimulated PLA₂ activity as a model, we showed that Bordetella pertussis toxin did not inhibit GM-CSF mediated priming, demonstrating that a pertussis-sensitive GTP-binding protein does not mediate signal transduction from the GM-CSF receptor to PLA₂. The tyrosine kinase inhibitor, genistein, selectively inhibited GM-CSF primed but not unprimed PLA₂ activity, demonstrating that GM-CSF-mediated priming requires tyrosine kinase activity.