Peroxynitrite induces integrin‐dependent adhesion of human neutrophils to endothelial cells via activation of the Raf‐1/MEK/Erk pathway

ABSTRACT Accumulating evidence suggests that enhanced peroxynitrite (ONOO‐) formation occurs during inflammation. We have studied the impact and the mechanisms of ONOO‐ action on expression of adhesion molecules on human neutrophils and coronary artery endothelial cells (HCAEC) and binding of neutrophils to HCAEC. Addition of ONOO‐ (0.1 to 200 µΜ) to isolated neutrophils resulted in a concentration‐dependent down‐regulation of L‐selectin expression, and up‐regulation of CD11b/CD18 expression. ONOO‐ stimulation of Erk activity was accompanied by activation of Ras, Raf‐1 and MEK (mitogen‐activated protein kinase kinase), and was sensitive to the MEK inhibitor PD 98059. We have observed a tight association between Erk activation and changes in CD11b/CD18 expression. ONOO‐ also evoked activation of neutrophil p38 MAPK. Neither ONOO‐‐induced up‐regulation of CD11b/CD18 expression nor Erk activation was affected by SB 203580, a selective inhibitor of p38 MAPK. ONOO‐ by itself had little effect on expression of ICAM‐1 and E‐selectin on HCAEC, whereas it markedly enhanced attachment of neutrophils to lipopolysaccharide‐activated HCAEC only when it was added together with neutrophils. Increases in neutrophil adhesion evoked by ONOO‐ were blocked by an anti‐CD18 monoclonal antibody. These data suggest that ONOO‐ activates Erk in neutrophils via the Ras/Raf‐1/MEK signal transduction pathway, leading to up‐regulation of surface expression of CD11b/CD18 and consequently to increased neutrophil adhesion to endothelial cells.