title: Role of cytosolic phospholipase A2 in arachidonic acid release of rat-liver macrophages: regulation by Ca2+ and phosphorylation.
abstract: In this study we have verified the existence of a cytosolic phospholipase A2 (cPLA2) in rat-liver macrophages. Stimulation of these cells with phorbol 12-myristate 13-acetate (PMA), zymosan and lipopolysaccharide (LPS), but not with the Ca(2+)-ionophore A23187, leads to phosphorylation of cPLA2 and activation of mitogen-activated protein (MAP) kinase, supporting the hypothesis that MAP kinase is involved in cPLA2 phosphorylation. We show furthermore, that the tyrosine kinase inhibitor genistein prevents the LPS- but not the PMA- or zymosan-induced phosphorylation of cPLA2 and activation of MAP kinase, indicating that tyrosine kinases participate in LPS- but not in PMA- and zymosan-induced cPLA2 phosphorylation and MAP kinase activation. Phosphorylation of cPLA2 does not strongly correlate with stimulation of the arachidonic acid (AA) cascade: (1) A23187, a potent stimulator of AA release, fails to induce cPLA2 phosphorylation; (2) withdrawal of extracellular Ca2+, which inhibits PMA-stimulated AA release (Dieter, Schulze-Specking and Decker (1988) Eur. J. Biochem. 177, 61-67), has no effect on PMA-induced phosphorylation of cPLA2; (3) LPS induces cPLA2 phosphorylation within minutes, whereas increased AA release upon treatment with LPS is detectable for the first time after 4 h; and (4) genistein, which prevents LPS-induced cPLA2 phosphorylation, does not inhibit AA release in response to LPS. From these data we suggest that a rise in intracellular Ca2+, but not phosphorylation of cPLA2, is essential for activation of the AA cascade in rat-liver macrophages.
authors.affiliation: Biochemical Institute, University of Freiburg, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Ambs
authors.forename: M
authors.initials: M
authors.lastname: Baccarini
authors.forename: E
authors.initials: E
authors.lastname: Fitzke
authors.forename: P
authors.initials: P
authors.lastname: Dieter
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology*; D004789:Enzyme Activation; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008099:Liver / Q000166:cytology*; D008264:Macrophages / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015054:Zymosan / Q000494:pharmacology
chemical_list: D008070:Lipopolysaccharides; D016718:Arachidonic Acid; D000001:Calcimycin; D015054:Zymosan; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D013755:Tetradecanoylphorbol Acetate