Granulocyte-macrophage colony-stimulating factor (GM-CSF) primes human neutrophils for enhanced phosphatidylcholine breakdown by phospholipase D

GM-CSF has previously been shown to increase human neutrophil phospholipase D (PLD) activity in response to fMLP. To further define the mechanism by which GM-CSF up-regulates PLD activity, we investigated the effect of GM-CSF pretreatment of neutrophils on phosphatidylcholine breakdown in response to a receptor-coupled stimulus N-formyl-methionyl-leucyl-phenylalanine (fMLP) and to a receptor-independent stimulus phorbol-myristate-acetate (PMA). Treatment of 1-0-[³H]alkyl-2-acetyl-sn-glycero-3-phosphocholine-prelabeled human neutrophils with 200 pM GM-CSF for 1 hour at 37°C led to a more rapid and increased accumulation (2–3 fold) of [³H]-alkyl-phosphatidic acid (or [³H]-alkyl-phosphatidylethanol when cells are stimulated in presence of 0.5% ethanol) in response to both fMLP or PMA. The data indicate GM-CSF up-regulates phosphatidylcholine hydrolysis by a PLD by interfering with the excitation-response coupling sequence at a site distal to the fMLP receptor.