Phospholipase A2IVα regulates phagocytosis independent of its enzymatic activity

J Biol Chem. 2012 May 11;287(20):16849-59. doi: 10.1074/jbc.M111.309419. Epub 2012 Mar 5.

Abstract

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

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Cell Line, Transformed
  • Cell Membrane / enzymology*
  • Cell Membrane / genetics
  • Fibroblasts / cytology
  • Fibroblasts / enzymology
  • Group IV Phospholipases A2 / genetics
  • Group IV Phospholipases A2 / metabolism*
  • Humans
  • Macrophages / cytology
  • Macrophages / enzymology*
  • Mice
  • Mice, Knockout
  • Mutation, Missense
  • Phagocytosis / drug effects
  • Phagocytosis / physiology*
  • Phagosomes / genetics
  • Phagosomes / metabolism*
  • Protein Structure, Tertiary
  • Protein Transport / drug effects
  • Protein Transport / physiology
  • Pyrrolidines / pharmacology
  • Receptors, IgG / genetics
  • Receptors, IgG / metabolism

Substances

  • Fc gamma receptor IIA
  • Pyrrolidines
  • Receptors, IgG
  • pyrrophenone
  • Group IV Phospholipases A2