Stress-induced platelet-activating factor synthesis in human neutrophils.
Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF) is a potent inflammatory mediator produced by cells in response to physical or chemical stress. The mechanisms linking cell injury to PAF synthesis are unknown. We used liquid chromatography-tandem mass spectrometry to investigate stress-induced PAF synthesis in human neutrophils. PAF synthesis induced by extracellular pH 5.4 correlated with the activation of a stress-activated kinase, p38 mitogen-activated protein kinase (MAPK), and was blocked by the p38 MAPK inhibitor SB 203580. A key enzyme of PAF synthesis, acetyl-CoA:lysoPAF acetyltransferase, which we have previously shown is a target of p38 MAPK, was also activated in an SB 203580-sensitive fashion. Another MAPK pathway, extracellular signal-regulated kinase-1/2 (ERK-1/2), was also activated. Surprisingly, the pharmacological blockade of the ERK-1/2 pathway with PD 98059 did not block, but rather enhanced, PAF accumulation. Two unexpected actions of PD 98059 may underlie this phenomenon: an augmentation of stress-induced p38 MAPK phosphorylation and an inhibition of PAF catabolism. The latter effect did not appear to be due to a direct inhibition of PAF acetylhydrolase. Finally, similar results were obtained using another form of cellular stress, hypertonic sodium chloride. These data are consistent with a model in which stress-induced PAF accumulation is regulated positively by p38 MAPK and negatively by ERK-1/2. Such a model contrasts with the PAF accumulation induced by other forms of stimulation, which we and others have found is up-regulated by both p38 MAPK and ERK-1/2.
Owen
John S
JS
Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
Baker
Paul R S
PR
O'Flaherty
Joseph T
JT
Thomas
Michael J
MJ
Samuel
Michael P
MP
Wooten
Rhonda E
RE
Wykle
Robert L
RL
D000123:Acetyltransferases / Q000378:metabolism; D002853:Chromatography, Liquid; D004121:Dimethyl Sulfoxide; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D013058:Mass Spectrometry; D009504:Neutrophils / Q000378:metabolism*; D009997:Osmotic Pressure; D018384:Oxidative Stress; D010766:Phosphorylation; D010972:Platelet Activating Factor / Q000096:biosynthesis / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D004791:Enzyme Inhibitors; D007093:Imidazoles; D010972:Platelet Activating Factor; D011725:Pyridines; D000123:Acetyltransferases; C046035:1-alkylglycerophosphocholine acetyltransferase; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580; D004121:Dimethyl Sulfoxide