INHIBITION OF TYROSINE PHOSPHORYLATION BY WORTMANNIN IN HUMAN NEUTROPHILS - DISSOCIATION FROM ITS INHIBITORY EFFECTS ON PHOSPHOLIPASE-D

BACKGROUND: Recent studies have indicated that the regulation of the a ctivation of human neutrophils depends on tyrosine phosphorylation and on phospholipase D. Furthermore, a tentative causal relationship betw een these two signalling pathways has been indirectly implied derived through the use of inhibitors of tyrosine kinases. The fungal metaboli te, wortmannin is at present the only compound known to inhibit the re ceptor-mediated activation of phospholipase D in human neutrophils. It s mechanism of action is presently unknown. EXPERIMENTAL DESIGN: The a bility of peripheral blood neutrophils to respond to various agonists with an increase in activity of phospholipase D and an enhancement of tyrosine phosphorylation in the absence or presence of wortmannin was monitored. RESULTS: Wortmannin was found to inhibit the stimulation of tyrosine phosphorylation by fMet-Leu-Phe, and by the inflammatory mic rocrystals monosodium urate and calcium pyrophosphate dihydrate. This effect of wortmannin was not secondary to inhibition of phospholipase D as U73122, a previously described phospholipase C inhibitor, was als o found to inhibit phospholipase D without affecting tyrosine phosphor ylation. CONCLUSIONS: The results make it likely that one of the earli est sites of action of wortmannin in human neutrophils is at the level of tyrosine phosphorylation which then exerts a modulatory influence on the activation of phospholipase D.