INTEGRIN-DEPENDENT HOMOTYPIC ADHESION OF NEUTROPHILS - ARACHIDONIC-ACID ACTIVATES RAF-1 MEK/ERK VIA A 5-LIPOXYGENASE-DEPENDENT PATHWAY/

AA stimulates integrin-dependent neutrophil adhesion, a critical early step in acute inflammation. However, neither the signaling pathway(s) of AA-stimulated adhesion, nor whether AA acts directly or through th e generation of active metabolites, has been elucidated. Previously, w e have observed a tight association between neutrophil Erk activation and homotypic adhesion in response to chemoattractants acting through G protein-linked receptors, We now report a similar association betwee n homotypic adhesion and Erk activation in response to AA, Erk activat ion was cyclooxygenase independent and required AA metabolism to 5(S)- hydroperoxyeicosatetraenoic acid (5-HpETE) via 5-lipoxygenase, but not the further lipoxygenase-dependent metabolism of 5-HpETE to leukotrie nes, AA stimulation of Erk was accompanied by Raf-1 activation and was sensitive to inhibitors of Raf-1 and Mek. Whereas activation of Erk b y AA was pertussis toxin sensitive, [H-3]-AA binding to neutrophils wa s not saturable, suggesting that an AA metabolite activates a G protei n. Consistent with this hypothesis, Erk activation by 5(S)-hydroxyeico satetraenoic acid (5-HETE; lipoxygenase-independent metabolite of 5-Hp ETE) was also pertussis toxin sensitive. These data suggest that a 5-l ipoxygenase metabolite of AA, e.g., 5-HETE, is released from AA-treate d cells to engage a plasma membrane-associated, pertussis toxin-sensit ive, G protein-linked receptor, leading to activation of Erk and adhes ion via the Raf-1/Mek signal transduction pathway.