COMPARISON OF THE ROLES OF MITOGEN-ACTIVATED PROTEIN-KINASE KINASE AND PHOSPHATIDYLINOSITOL 3-KINASE SIGNAL-TRANSDUCTION IN NEUTROPHIL EFFECTOR FUNCTION

Although it is known that many stimuli can activate mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinases (PI3K) in h uman neutrophils, little is known concerning either the mechanisms or function of this activation. We have utilized a selective inhibitor of MAPK kinase (MEK), PD098059, and two inhibitors of PI3K, wortmannin a nd LY294002, to investigate the roles of these kinases in the regulati on of neutrophil effector functions. Granulocyte/macrophage colony-sti mulating factor, platelet-activating factor (PAF) and N-formylmethiony l-leucyl-phenylalanine are capable of activating both p44(ERK1) and p4 2(ERK2) MAPKs and phusphotyrosine-associated PI3K in human neutrophils . The activation of extracellular signal-related protein kinases (ERKs ) is correlated with the activation of p21(ras) by both tyrosine kinas e and G-protein-coupled receptors as measured by a novel assay for GTP loading. Wortmannin and LY294002 inhibit, to various degrees, superox ide generation, neutrophil migration and PAF release. Incubation with PD098059, however, inhibits only the PAF release stimulated by serum-t reated zymosan. This demonstrates that, while neither MEK nor ERK kina ses are involved in the activation of respiratory burst or neutrophil migration, inhibition of PAF release suggests a potential role in the activation of cytosolic phospholipase A(2). PI3K isoforms, however, se em to have a much wider role in regulating neutrophil functioning.