Requirement of JNK-mediated phosphorylation for translocation of group IVA phospholipase A2 to phagosomes in human macrophages

Abstract

Eicosanoids are a broad family of lipids that play a critical role in host defense against bacterial and fungal infections. The first enzyme in the metabolic pathway for the generation of eicosanoids is group IVA phospholipase A2, also known as cytosolic phospholipase A2 (cPLA2 ). During phagocytosis, cPLA2 has been found to translocate to the phagosome, although the molecular mechanism involved in such a translocation has not been elucidated. By using enhanced GFP-tagged proteins we show in this work that a nonphosphorylatable cPLA2 mutant (S505A) does not translocate to the phagosomes, but a mutant that mimics phosphorylation on Ser505 (S505E) does it so readily. During phagocytosis, endogenous cPLA2 is phosphorylated at Ser505, and inhibitors of JNK, but not of other related kinases such as p38 or the extracellular-regulated kinases 1 and 2, completely block such a phosphorylation. Inhibition of JNK activity also inhibits the translocation of cPLA2 to phagosomal membranes, as well as arachidonic acid release to the extracellular medium. Moreover, the S505E mutant makes the enzyme refractory to JNK inhibition, translocating normally to phagosomal membranes. Collectively, these data support a key role for JNK-mediated cPLA2 phosphorylation at Ser505 in the sequence of events leading to translocation and activation of the enzyme to phagosomal membranes in human macrophages.