E-selectin engages PSGL-1 and CD44 through a common signaling pathway to induce integrin α_Lβ₂-mediated slow leukocyte rolling

In inflamed venules, neutrophils rolling on E-selectin induce integrin α_Lβ₂-dependent slow rolling on intercellular adhesion molecule-1 by activating Src family kinases (SFKs), DAP12 and Fc receptor-γ (FcRγ), spleen tyrosine kinase (Syk), and p38. E-selectin signaling cooperates with chemokine signaling to recruit neutrophils into tissues. Previous studies identified P-selectin glycoprotein ligand-1 (PSGL-1) as the essential E-selectin ligand and Fgr as the only SFK that initiate signaling to slow rolling. In contrast, we found that E-selectin engagement of PSGL-1 or CD44 triggered slow rolling through a common, lipid raft - dependent pathway that used the SFKs Hck and Lyn as well as Fgr. We identified the Tec kinase Bruton tyrosine kinase as a key signaling intermediate between Syk and p38. E-selectin engagement of PSGL-1 was dependent on its cytoplasmic domain to activate SFKs and slow rolling. Although recruiting phosphoinositide-3-kinase to the PSGL-1 cytoplasmic domain was reported to activate integrins, E-selectin-mediated slow rolling did not require phosphoinositide-3-kinase. Studies in mice confirmed the physiologic significance of these events for neutrophil slow rolling and recruitment during inflammation. Thus, E-selectin triggers common signals through distinct neutrophil glycoproteins to induce α_Lβ₂-dependent slow rolling.