Extracellular signal-regulated kinase 1/2-mediated phosphorylation of cytosolic phospholipase A(2) is essential for human eosinophil adhesion to fibronectin

We examined the role of p38, p42, and p44 mitogen-activated protein kinase (MAPK) isoforms and cytosolic phospholipase Az (cPLA(2)) activation in huma n eosinophil adhesion to plate-coated fibronectin (FN), In the control stat e, eosinophil adhesion was maximal, with 10 mug/ml FN at 30 min, and decrea sed after 60-90 min. Western blot analysis demonstrated that p44/42 MAPK (e xtracellular signal-regulated kinase (ERK)1/2) and cPLA(2) were phosphoryla ted during adhesion to FN, whereas p38 MAPK phosphorylation was unchanged, Preincubation of eosinophils with U0126 or PD98059, two structurally unrela ted MAPK kinase inhibitors, or arachidonic trifluoromethyl ketone, a cPLA(2 ) inhibitor, blocked eosinophil adhesion to FN, By contrast, eosinophil adh esion was unaffected by SB203580, a p38 MAPK inhibitor. Pretreatment of eos inophils with okadaic acid, a serine/threonine phosphatase inhibitor, at th e concentrations that induced ERK1/2 and cPLA(2) phosphorylation caused an increase in maximal eosinophil adhesion to FN for >60 min. MAPK kinase inhi bition but not p38 inhibition also blocked FN-mediated F-actin redistributi on in eosinophils and prevented cPLA(2) phosphorylation caused by adhesion to FN. These results demonstrate that ERK1/2 mediating cPLA(2) activation i s essential for eosinophil adhesion to FN.