Differential activation of human neutrophil cytosolic and secretory phospholipase a2 's during priming by 1,2-DIACYL- And 1O-ALKYL-2-Acylglycerols

Diglycerides may act as signaling molecules during inflammation and can prime cellular responses. Both 1,2-diacylglycerol (AAG) and ether linked 1-0-alkyl-2acylglycerol (EAG) prime neutrophil functions, especially the fMLP stimulated oxidative burst and arachidonic acid release. The increased AA release results from priming of phospholipase A2. Two calcium dependent phospholipase A2's have been described recently in leukocytes. They are a cytosolic phosphoprotein (cPLA2) and a low molecular weight secretory PLA2 (sPLA2). We hypothesized that AAG, a kinase activator, would activate the cPLA2 by phosphorylation. EAG is not a kinase activator and was expected to act independently of cPLA2. We recently found sPLA2 secretion can be primed by cytokines such as TNF, thus we hypothesized that EAG primed neutrophil AA release similarly may occur via activation of sPLA2. When neutrophils were primed with 5-20 &iM AAG, a shift was observed in cPLA2 migration on SDS/PAGE gels, consistent with phosphorylation of the protein. At 20 nM AAG, 86% of cPLA2 was phosphorylated. This gel shift was not activated by EAG. AAG also caused a parallel increase in enzymatic activity of cPLA2 (172+28% of resting cytosolic activity) whereas EAG did not. However, both EAG and AAG caused direct secretion of sPLA2, while only EAG further primed sPLA2 secretion upon stimulation of cells with fMLP. In summary, diglycerides can differentially activate cPLA2 (induced by AAG) and cause secretion of sPLA2 (by EAG and AAG). Also, priming by diglycerides may be kinase dependent (cPLA2) or kinase independent (sPLA2).

Duke Scholars

Author Andrew Benjamin Nixon Medicine, Medical Oncology