Selectins and chemokines use shared and distinct signals to activate β2 integrins in neutrophils

Rolling neutrophils receive signals while engaging P- and E-selectin and chemokines on inflamed endothelium. Selectin signaling activates beta 2 integrins to slow rolling velocities. Chemokine signaling activates beta 2 integrins to cause arrest. Despite extensive study, key aspects of these signaling cascades remain unresolved. Using complementary in vitro and in vivo assays, we found that selectin and chemokine signals in neutrophils triggered Rap1a-dependent and phosphatidylinositol-4-phosphate 5-kinase gamma (PIP5K gamma 90)-dependent pathways that induce integrin-dependent slow rolling and arrest. Interruption of both pathways, but not either pathway alone, blocked talin-1 recruitment to and activation of integrins. An isoform of PIP5K gamma 90 lacking the talin-binding domain (PIP5K gamma 87) could not activate integrins. Chemokines, but not selectins, used phosphatidylinositol-4,5-bisphosphate 3-kinase gamma (PI3K gamma) in cooperation with Rap1a to mediate integrin-dependent slow rolling (at low chemokine concentrations), as well as arrest (at high chemokine concentrations). High levels of chemokines activated beta 2 integrins without selectin signals. When chemokines were limiting, they synergized with selectins to activate beta 2 integrins.