ICAM-1-activated Src and eNOS signaling increase endothelial cell surface PECAM-1 adhesivity and neutrophil transmigration

Polymorphonuclear neutrophil (PMN) extravasation requires selectin-mediated tethering, intercellular adhesion molecule-1 (ICAM-1)-dependent firm adhesion, and platelet/endothelial cell adhesion molecule 1 (PECAM-1)-mediated transendothelial migration. An important unanswered question is whether ICAM-1 - activated signaling contributes to PMN transmigration mediated by PECAM-1. We tested this concept and the roles of endothelial nitric oxide synthase (eNOS) and Src activated by PMN ligation of ICAM-1 in mediating PECAM-1-dependent PMN transmigration. We observed that lung PMN infiltration in vivo induced in carrageenan-injectedWTmice was significantly reduced in ICAM-1^-/- and eNOS^-/- mice. Crosslinking WT mouse ICAM-1 expressed in human endothelial cells (ECs), but not the phospho-defective Tyr⁵¹⁸Phe ICAM-1 mutant, induced SHP-2-dependent Src Tyr⁵³⁰ dephosphorylation that resulted in Src activation. ICAM-1 activation also stimulated phosphorylation of Akt (p-Ser⁴⁷³) and eNOS (p-Ser¹¹⁷⁷), thereby increasing NO production. PMN migration across EC monolayers was abolished in cells expressing the Tyr⁵¹⁸Phe ICAM-1 mutant or by pretreatment with either the Src inhibitor PP2 or eNOS inhibitor L-NAME. Importantly, phospho-ICAM-1 induction of Src signaling induced PECAM-1 Tyr ⁶⁸⁶ phosphorylation and increased EC surface anti-PECAM-1 mAb-binding activity. These results collectively show that ICAM-1-activated Src and eNOS signaling sequentially induce PECAM-1 - mediated PMN transendothelial migration. Both Src and eNOS inhibition may be important therapeutic targets to prevent or limit vascular inflammation.