Role of p38 in the priming of human neutrophils by peritoneal dialysis effluent

Peritoneal dialysis effluent (PDE) contains a low-molecular-weight substanc e that is able to prime human neutrophils for the release of arachidonic ac id and superoxide anion. Conventional priming agents, such as tumor necrosi s factor alpha (TNF-alpha), are known to signal via mitogen-activated prote in (MAP) kinases; at least one possible substrate for MAP kinases is cytoso lic phospholipase A(2) (cPLA(2)). Phosphorylation of this enzyme results in arachidonic acid release, and this fatty acid is a potent primer and activ ator of the human neutrophil NADPH oxidase. Because of the striking similar ities between the priming of neutrophils with agents such as TNF-alpha. and PDE, we have investigated the signalling pathways evoked by PDE and explor ed the possibility that cPLA(2) is a target for activated MAP kinases. Our results show that PDE treatment of human neutrophils results in the phospho rylation of the p38 kinase rather than the p42 and p44 kinases. Phosphoryla tion of p38 is transient with maximal activity being observed 1 min after e xposure to PDE. We were unable to demonstrate that activation of p38 result ed in phosphorylation of cPLA(2); furthermore, translocation of this enzyme to a membrane-containing fraction was not enhanced in PDE-treated neutroph ils. Taken together, these data suggest that, in a manner similar to that o f TNF-alpha, PDE primes human neutrophils by the activation of the p38 kina se. However, unlike the cytokine, the activation of this protein does not r esult in phosphorylation or activation of cPLA(2).