ACTIVATION OF THE RESPIRATORY BURST AND TYROSINE PHOSPHORYLATION OF PROTEINS IN HUMAN NEUTROPHILS - NO DIRECT RELATIONSHIP AND INVOLVEMENT OF PROTEIN-KINASE C-DEPENDENT AND C-INDEPENDENT SIGNALING PATHWAYS

Human neutrophils maximally stimulated with the optimal concentration (100 ng/ml) of phorbol myristate acetate (PMA), a direct activator of protein kinase C (PKC), for 5 min at 37 degrees C did not respond with superoxide (O-2(-)) release to the later addition of PMA itself or th e Ca2+ ionophore ionomycin. However, these cells did respond with enha nced release of O-2(-) to the later addition of N-formyl-methionyl-leu cyl-phenylalanine (FMLP) or concanavalin A (Con A). In these PMA-pretr eated cells, an increase in cytoplasmic free Ca2+ ([Ca2+](i)) induced by ionomycin was unaffected, whereas that induced by FMLP was inhibite d by 50-60% and that induced by Con A was completely abolished. A 42-k Da protein was predominantly and consistently tyrosine-phosphorylated by FMLP, PMA and ionomycin with the different kinetics according to th e stimuli. The dose-response curves showed that tyrosine phosphorylati on and O-2(-) release were stimulated in parallel by PMA, whereas tyro sine phosphorylation and an increase in [Ca2+](i), but not O-2(-) rele ase, were stimulated in parallel by FMLP or ionomycin, The potency of inducing tyrosine phosphorylation was ionomycin > FMLP = PMA, whereas the potency of triggering of O-2(-) release was PMA > ionomycin = FMLP . UCN-01, a PKC inhibitor, inhibited O-2(-) release and tyrosine phosp horylation induced by PMA, but not by FMLP or ionomycin. In contrast, pertussis toxin inhibited O-2(-) release and tyrosine phosphorylation induced by FMLP, but not by PMA. Tyrosine kinase inhibitors (erbstatin and genistein) inhibited O-2(-) release induced by FMLP, but not by P MA. However, both tyrosine kinase inhibitors did not impair FMLP- or P MA-induced tyrosine phosphorylation of a 42-kDa protein. Increased tyr osine phosphorylation of a 42-kDa protein was also detected in immatur e myeloid cells (HL-60 cells) stimulated by PMA, but not by ionomycin. These findings suggest that FMLP and Con A trigger the respiratory bu rst in human neutrophils by activating the definite pathway which incl ude other signals than activation of PKC and an increase in [Ca2+](i); tyrosine phosphorylation of a 42-kDa protein is induced by the PKC-de pendent and independent mechanisms according to the stimuli, and the P KC-independent and ionomycin-sensitive mechanism is inoperative in HL- 60 cells; and tyrosine phosphorylation of a 42-kDa protein is unlikely to be causally related to activation of the respiratory burst.