Prostaglandin Levels in Stimulated Macrophages Are Controlled by Phospholipase A₂-activating Protein and by Activation of Phospholipase C and D

Prostaglandins (PG), which are responsible for a large array of biological functions in eukaryotic cells, are produced from arachidonic acid by phospholipases and cyclooxygenase enzymes COX-1 and COX-2. We demonstrated that PG levels in cells were partly controlled by a regulatory protein, phospholipase A₂ (PLA₂)-activating protein (PLAA). Treatment of murine macrophages with lipopolysaccharide, interleukin-1β, and tumor necrosis factor-α increased PLAA levels at early time points (2-30 min), which correlated with an up-regulation in cytosolic PLA₂ and PGE₂ levels. Both COX-2 and secretory PLA₂ were also increased in lipopolysaccharide-stimulated macrophages, however, at later time points of 4-24 h. The role of PLAA in eicosanoid formation in macrophages was confirmed by the use of an antisense plaa oligonucleotide. Within amino acid residues 503-538, PLAA exhibited homology with melittin, and increased PGE ₂ production was noted in macrophages stimulated with melittin. In addition to PLA₂, we demonstrated that activation of phospholipase C and D significantly controlled PGE₂ production. Finally, increased antigen levels of PLAA, COX-2, and phospholipases were demonstrated in biopsy specimens from patients with varying amounts of intestinal mucosal inflammation, which corresponded to increased levels of phospholipase activity. These results could provide a basis for the development of new therapeutic tools to control inflammation.