Cytokine-mediated cPLA2 phosphorylation is regulated by multiple MAPK family members

Cytosolic phospholipase A2 (cPLA2) plays a critical role in various neutrophil functions including the generation of leukotrienes and platelet-activating factor release. Enzyme activity is regulated both by translocation to the membrane in a Ca^(2+) -dependent manner and serine phosphorylation by members of the mitogen-activated protein kinase (MAPK) family. In this report, we have investigated the role of granulocyte/macrophage colony-stimulating factor (GM-CSF)- mediated signalling pathways in the regulation of cPLA2. GM- CSF-induced cPLA2 phosphorylation was not affected by pharmacological inhibition of p38 MAPK, phosphatidylinositol 3-kinase or Src. However, inhibition of extracellular signal- regulated kinase (ERK) MAPK activation resulted in a partial inhibition of cPLA2 phosphorylation, revealed in a slower onset of phosphorylation. A cell line stably transfected with the GM- CSF receptor was used to further analyze GM-CSF-mediated cPLA2 phosphorylation. Mutation of tyrosine residues 577 and 612 resulted in a delayed cPLA2 phosphorylation similar to the pharmacological ERK inhibition. Furthermore, inhibition of p38 MAPK in cells bearing the double mutant ßc577/612 completely abrogated GM-CSF-induced cPLA2 phosphorylation. We con- clude that GM-CSF can mediate cPLA2 phosphorylation through the redundant activation of both p38 and ERK MAP kinases