Mechanism and regulation of neutrophil priming by platelet-activating factor.
Although a weak direct stimulus of superoxide anion (O2-) production, platelet-activating factor (PAF) markedly enhances responses to chemotactic peptides (such as n-formyl-met-leu-phe, FMLP) and phorbol esters (such as phorbol myristate acetate, PMA) in human neutrophils. The mechanism of priming was explored first through inhibition of steps in the signal transduction pathway at and following PAF receptor occupation. Priming was not altered by pertussis toxin or intracellular calcium chelation, but the PAF receptor antagonist WEB 2086 and the protein kinase C (PKC) inhibitors sphinganine and staurosporine significantly inhibited the primed response. In order to study the regulation of PAF priming, the effect of PAF alone was desensitized by exposure to escalating doses of PAF prior to exposure to the secondary stimuli. The priming effect of PAF was not desensitized under these conditions. The role of PKC in desensitization was also studied. Prior exposure to PAF also desensitized the increase in membrane PKC activity evoked by a single concentration of PAF. However, when the PAF response was desensitized, PKC priming of the response to FMLP or PMA still occurred, suggesting that PKC activity may play a role in the maintenance of the primed state despite PAF desensitization. These data suggest that: (1) PAF priming is receptor- and PKC-mediated but is independent of pertussis toxin-inhibitable G-proteins or intracellular calcium, (2) during migration in vivo, neutrophils may be desensitized to the direct effects of PAF but maintain the capacity for enhanced responses to other stimuli, (3) desensitization of PAF-induced particulate PKC activity also occurs, but PAF primes PKC activity despite PAF desensitization, and (4) distinct mechanisms govern the direct and priming effects of PAF on oxidative metabolism.
Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2588.
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Gay
D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D019852:Diacylglycerol Kinase; D006801:Humans; D066298:In Vitro Techniques; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000502:physiology*; D037342:Pertussis Toxin; D010770:Phosphotransferases / Q000037:antagonists & inhibitors; D010972:Platelet Activating Factor / Q000494:pharmacology*; D010980:Platelet Membrane Glycoproteins; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011744:Pyrimidinones / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D014230:Triazoles / Q000494:pharmacology; D010738:Type C Phospholipases / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D001381:Azepines; D002614:Chelating Agents; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011744:Pyrimidinones; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D013844:Thiazoles; D014230:Triazoles; D010566:Virulence Factors, Bordetella; C039351:platelet activating factor receptor; C052518:WEB 2086; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000584:Amiloride; C047505:R 59022; D037342:Pertussis Toxin; D010770:Phosphotransferases; D019852:Diacylglycerol Kinase; D011493:Protein Kinase C; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium