Kinase pathways in chemoattractant-induced degranulation of neutrophils: The role of p38 mitogen-activated protein kinase activated by Src family kinases

The aim of the present study was to investigate the role of tyrosine phosph orylation pathways in fMLP-induced exocytosis of the different secretory co mpartments (primary and secondary granules, as well as secretory vesicles) of neutrophils, Genistein, a broad specificity tyrosine kinase inhibitor, b locked the exocytosis of primary and secondary granules, but had only a mar ginal effect on the release of secretory vesicles. Genistein also inhibited the phosphorylation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinases (MAPK), raising the possibility that inh ibition of ERK and/or p38 MAPK might be responsible for the effect of the d rug on the degranulation response. Indeed, SB203580, an inhibitor of p38 MA PK, decreased the release of primary and secondary granules, but not that o f secretory vesicles. However, blocking the ERK pathway with PD98059 had no effect an any of the exocytic responses tested. PP1, an inhibitor of Src f amily kinases, also attenuated the release of primary and secondary granule s, and neutrophils from mice deficient in the Src family kinases Hck, Fgr, and Lyn were also defective in secondary granule release. Furthermore, acti vation of p38 MAPK was blocked by both PP1 and the hck(-/-)fgr(-/-)lyn(-/-) mutation, Taken together, our data indicate that fMLP-induced degranulatio n of primary and secondary granules of neutrophils is mediated by p38 MAPK activated via Src family tyrosine kinases, Although piceatannol, a reported ly selective inhibitor of Syk, also prevented degranulation and activation of p38 MAPK, no fMLP-induced phosphorylation of Syk could be observed, rais ing doubts about the specificity of the inhibitor.