Cytokine‐mediated cPLA2phosphorylation 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 Ca2+‐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 cPLA2phosphorylation 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 cPLA2phosphorylation, 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 cPLA2phosphorylation. Mutation of tyrosine residues 577 and 612 resulted in a delayed cPLA2phosphorylation similar to the pharmacological ERK inhibition. Furthermore, inhibition of p38 MAPK in cells bearing the double mutant βc577/612 completely abrogated GM‐CSF‐induced cPLA2phosphorylation. We conclude that GM‐CSF can mediate cPLA2phosphorylation through the redundant activation of both p38 and ERK MAP kinases.