Two transduction sequences are necessary for neutrophil activation by receptor agonists

Abstract

The effects of 17-hydroxywortmannin (HWT), a powerful inhibitor of the respiratory burst associated with phagocytosis (Baggiolini, M., Dewald, B., Schnyder, J., Ruch, W., Cooper, P. H., and Payne, T. G. (1987) Exp. Cell Res. 169, 408-418), were studied in human neutrophils stimulated with chemotactic agonists or phorbol myristate acetate. At nanomolar concentrations HWT inhibited superoxide production and the release of granule contents induced by N-formyl-Met-Leu-Phe, C5a, platelet-activating factor, and leukotriene B4, but not by phorbol myristate acetate, indicating that it interferes with receptor-mediated activation of the neutrophils, without directly affecting protein kinase C (Ca2+/phospholipid-dependent enzyme), the NADPH-oxidase, or the process of granule exocytosis. Moreover, HWT did not influence agonist-induced [Ca2+]i changes, indicating that it does not interfere with the function of agonist receptors, G-proteins or the phosphatidylinositol-specific phospholipase C. By studying the effect of HWT on the respiratory burst elicited in normal and Ca2+-depleted cells by combined stimulation with N-formyl-Met-Leu-Phe and phorbol myristate acetate, evidence was obtained that two transduction sequences, both of which are G-protein-dependent, are necessary for the induction of the response by receptor agonists. One sequence is Ca2+-dependent, HWT-insensitive, and leads to activation of protein kinase C, the other is Ca2+-independent and HWT-sensitive. Ca2+ depletion, which blocks the first, and HWT, which blocks the second, can be used to show that both processes must be functional for the transduction of agonist signals into a respiratory burst response.