PHOSPHATIDYLINOSITOL 3-KINASE MEDIATES CHEMOATTRACTANT-STIMULATED, CD11B CD18-DEPENDENT CELL-CELL ADHESION OF HUMAN NEUTROPHILS - EVIDENCE FOR AN ERK-INDEPENDENT PATHWAY/

We examined the role of phosphatidylinositol 3-kinase (PI 3-K) in FMLP -stimulated cell-cell adhesion of human neutrophils, The specific PI 3 -K inhibitors wortmannin and LY294002 inhibited neutrophil homotypic a ggregation stimulated by chemoattractants such as FMLP (50% inhibitory concentration (IC50) approximate to 11 nM and 13 mu M, respectively) but not PMA. Wortmannin also inhibited FMLP-stimulated adhesion of neu trophils to human endothelial cell monolayers, suggesting a common sig naling pathway for homotypic and heterotypic adhesion. Neither CD11b/C D18 expression nor expression of an activation-specific epitope of CD1 1b/CD18 was affected by wortmannin in FMLP-stimulated cells. Moreover, wortmannin also inhibited the aggregation of egranulate neutrophil cy toplasts that lack the capacity for CD11b/CD18 up-regulation. Although wortmannin inhibited neutrophil lysosomal enzyme release, it had no e ffect on FMLP-stimulated up-regulation of CD35 in intact neutrophils, suggesting discrepant signaling pathways for specific granule degranul ation and secretory vesicle release, Aggregation of human neutrophils is associated with activation of the mitogen-activated protein kinases Erk1 and -2, and Erk is activated in response to PI 3-K in some cell types. However, wortmannin inhibited FMLP stimulation of neutrophil Er k only at concentrations (IC50 greater than or equal to 1 mu M) incons istent with an effect on PI 3-K. Our data indicate that PI 3-K mediate s neutrophil adhesion by a mechanism independent of CD11b/CD18 up-regu lation, suggesting that PI 3-K acts either parallel to, or downstream of, Erk.