CYTOSOLIC PHOSPHOLIPASE A(2) AND ITS MODE OF ACTIVATION IN HUMAN NEUTROPHILS BY OPSONIZED ZYMOSAN - CORRELATION BETWEEN 42 44 KDA MITOGEN-ACTIVATED PROTEIN-KINASE, CYTOSOLIC PHOSPHOLIPASE A(2) AND NADPH OXIDASE/

The role of cytosolic phospholipase A(2) (cPLA(2)) and its mode of act ivation by opsonized zymosan (OZ) was studied in human neutrophils in comparison with activation by PMA. The activation of cPLA(2) by 1 mg/m l OZ or 50 ng/ml PMA is evidenced by its translocation to the membrane fractions on stimulation. This translocation is consistent with dithi othreitol (DTT)-resistant phospholipase A(2) (PLA(2)) activity detecte d in the membranes of activated cells. Neutrophils stimulated by eithe r OZ or PMA exhibited an immediate stimulation of extracellular-signal -regulated kinases (ERKs). The inhibition of ERKs, DTT-resistant PLA(2 ) and NADPH oxidase activities by the MAP kinase kinase inhibitor PD-9 8059 indicates that ERKs mediate the activation of cPLA(2), and NADPH oxidase stimulated by either OZ or PMA. The protein kinase C (PKC) inh ibitor GF-109203X inhibited epidermal growth factor receptor peptide k inase activity, the release of [H-3]arachidonic acid, DTT-resistant PL A(2) activity and superoxide generation induced by PMA, but did not in hibit any of these activities induced by OZ. PKC activity was similarl y inhibited by GF-109203X in membrane fractions separated from neutrop hils stimulated by either PMA or OZ. In the presence of the tyrosine k inase inhibitor genistein, ERKs, PLA(2) and NADPH oxidase activities w ere inhibited in cells stimulated by OZ, whereas they were hardly affe cted in cells stimulated by PMA. The results suggest that the activati on of cPLA(2) by PMA or OZ is mediated by ERKs. Whereas PMA stimulates ERKs activity through a PKC-dependent pathway, signal transduction st imulated by OZ involves tyrosine kinase activity leading to activation of ERKs via a PKC-independent pathway.