Soluble E-selectin acts in synergy with platelet-activating factor to activate neutrophil β2-integrins -: Role of tyrosine kinases and Ca2+ mobilization

Selectins play a critical role in neutrophil recruitment to sites of inflammation, in tethering and rolling of neutrophils on vascular endothelium, as well as triggering beta(2)-integrin-mediated adhesion. We have previously demonstrated potential pro-inflammatory effects of soluble E-selectin upon neutrophil effector functions, using a soluble recombinant molecule (E-zz), which increased beta(2)-integrin-mediated adhesion, decreased beta(2)-integrin-dependent migration, and triggered reactive oxygen species generation and release. In this study, we have examined the intracellular signals following neutrophil activation by soluble E-selectin, We show that exposure of neutrophils to E-selectin and platelet-activating factor (PAF) in combination induced a synergistic effect upon beta(2)-integrin-mediated adhesion. Although soluble E-selectin did not induce Ca2+ mobilization in neutrophils by itself, elevation of intracellular Ca2+ was specifically prolonged in response to PAF but not leukotriene B-4 or N-formyl-Met-Leu-Phe. The prolonged Ca2+ mobilization observed in the presence of E-selectin was dependent on Ca2+ influx from intracellular stores rather than influx of extracellular Ca2+ through SKF 96365-sensitive channels. The specific alteration of Ca2+ mobilization reported here appears not to have a role in the synergistic effects of E-selectin and PAF upon neutrophil O-2(.) release but may be involved in augmentation of beta(2)-integrin-mediated adhesion.