Phospholipase A₂IVα regulates phagocytosis independent of its enzymatic activity

Group IVα phospholipase A₂ (PLA₂IVα) is a lipolytic enzyme that catalyzes the hydrolysis of membrane phospholipids to generate precursors of potent inflammatory lipid mediators. Here, the role of PLA₂IVα in Fc receptor (FcR)-mediated phagocytosis was investigated, demonstrating that PLA₂IVα is selectively activated upon FcR-mediated phagocytosis in macrophages and that it rapidly translocates to the site of the nascent phagosome. Moreover, pharmacological inhibition of PLA₂IVα by pyrrophenone reduces particle internalization by up to 50%. In parallel, fibroblasts from PLA ₂IVα knock-out mice overexpressing FcγRIIA and able to internalize IgG-opsonized beads show 50% lower phagocytosis, compared with wild-type cells, and transfection of PLA₂IVα fully recovers this impaired function. Interestingly, transfection of the catalytically inactive deleted PLA₂IVαmutant (PLA₂IVα(1-525) ) and point mutant (PLA₂IVα- S228C) also promotes recovery of this impaired function. Finally, transfection of the PLA₂IVα C2 domain (which is directly involved in PLA₂IVα membrane binding), but not of PLA₂IVα-D43N (which cannot bind to membranes), rescues FcR-mediated phagocytosis. These data unveil a new mechanism of action for PLA₂IVα, which demonstrates that the membrane binding, and not the enzymatic activity, is required for PLA ₂IVα modulation of FcR-mediated phagocytosis.