Platelet-activating factor synergizes with phorbol myristate acetate in activating phospholipase D in the human promonocytic cell line U937. Evidence for different mechanisms of activation.
The activation of phospholipase D by platelet-activating factor (PAF) in the human promonocytic cell line U937 has been investigated. In cells prelabeled with [3H]palmitic acid, addition of PAF or phorbol 12-myristate 13-acetate (PMA) induced the synthesis of [3H]phosphatidylethanol, indicating phospholipase D activation. When U937 cells were preincubated for 5 min with PMA, and then stimulated with PAF, formation of phosphatidylethanol was greatly enhanced. In contrast, under the same experimental conditions PMA treatment blocked completely the PAF-induced inositol phosphates formation in cells prelabeled with [3H]inositol. Thus, PMA treatment demonstrates that phospholipase D activation can occur independently from phosphoinositide-specific phospholipase C activation during PAF stimulation in U937 cells. On the other hand, the data herein presented suggest that influx of external calcium is required for phospholipase D activation by PAF, as assessed by complete inhibition of the enzyme activity by chelation of extracellular calcium or by treatment with the calcium channel blocker verapamil. Based on these findings, a hypothetical model for phospholipase D activation is discussed.
Balsinde
J
J
Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
Mollinedo
F
F
D001381:Azepines / Q000494:pharmacology; D002460:Cell Line; D004075:Diglycerides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020404:Glycerophospholipids; D006801:Humans; D007700:Kinetics; D009000:Monocytes; D010712:Phosphatidic Acids / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000378:metabolism / Q000502:physiology*; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014230:Triazoles / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D001381:Azepines; D004075:Diglycerides; D020404:Glycerophospholipids; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D014230:Triazoles; C051521:phosphatidylethanol; C039351:platelet activating factor receptor; C052518:WEB 2086; D010738:Type C Phospholipases; D010739:Phospholipase D; D013755:Tetradecanoylphorbol Acetate