Okadaic acid, an inhibitor of type 1 and type 2A phosphatases, modulates the activation of phospholipase D in formyl peptide- and mastoparan-stimulated human neutrophils.
The activation of phospholipase D (PLD) induced by formyl peptides (fMLP), as evaluated by production of tritiated phosphatidylethanol (PEt) and phosphatidic acid (PA) in polymorphonuclear leukocytes (PMN), was markedly enhanced (50-125%) by low okadaic acid concentrations (0.25-0.5 microM) but inhibited by higher concentrations (2-3 microM), although the drug caused protein hyperphosphorylation. Both effects of okadaic acid were amplified when PLD activation was primed with cytochalasin B. Stimulation of PMN with mastoparan, a wasp venom toxin that activates Pertussis toxin(PTX)-sensitive G proteins, resulted in a weak calcium-dependent production of PEt which was respectively enhanced and inhibited by okadaic acid (1-2 microM) in unprimed and cytochalasin-primed PMN. The results show that low okadaic acid concentrations primed fMLP-mediated activation of PLD, in keeping with a down-regulatory role of protein phosphatases. The contrasting effects of okadaic acid in mastoparan-stimulated PMN further suggest that protein phosphatases may regulate the generation of second messengers through alteration of major signaling events at/or downstream of PTX-sensitive G proteins (Gi).
Djerdjouri
B
B
Laboratoire d'Hématologie, INSERM U294, CHU Xavier Bichat, Paris, France.
Pedruzzi
E
E
Hakim
J
J
Périanin
A
A
D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004988:Ethers, Cyclic / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D019319:Okadaic Acid; D010455:Peptides; D010739:Phospholipase D / Q000097:blood*; D010743:Phospholipids / Q000096:biosynthesis / Q000097:blood; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010750:Phosphoproteins / Q000097:blood / Q000302:isolation & purification; D014862:Wasp Venoms / Q000494:pharmacology*
D004988:Ethers, Cyclic; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010743:Phospholipids; D010750:Phosphoproteins; D014862:Wasp Venoms; D019319:Okadaic Acid; D009240:N-Formylmethionine Leucyl-Phenylalanine; C037500:mastoparan; D010749:Phosphoprotein Phosphatases; D010739:Phospholipase D