Differential activation by fMet-Leu-Phe and phorbol ester of a plasma membrane phosphatidylcholine-specific phospholipase D in human neutrophil

Abstract

Signal transduction involving phosphatidylcholine hydrolysis has been investigated in human neutrophils (PMN) after in situ generation of [3H]alkylacyl-sn-glycero-3-phosphocholine ([3H]alkylacyl-GPC) by cell incubation with [3H]alkylacetyl-GPC. When PMN were stimulated with the chemotactic peptide N-formyl-Met-Leu-Phe(fMLP) or phorbol myristate acetate (PMA) in the presence of cytochalasin B, both 1-O-alkyl-2-acyl-sn-glycero-3-phosphate (PA) and 1-O-alkyl-2-acyl-sn-glycerol (AAG) were generated. On addition of the agonists in the presence of ethanol, phosphatidylethanol (PEt) [corrected] was formed with a concomitant decrease in PA and AAG. These results indicate the presence of a phospholipase D (PLD) acting on phosphatidylcholine in human PMN. The kinetics of hydrolysis were quite different according to the stimulus. Whereas fMLP induced a maximum rise in PA and AAG at 30-45 s, these products began to appear only after 1 min upon cell incubation with PMA. Similar amounts of products were formed at 1 min with fMLP and only at 5 min with PMA. Although similar time courses of PA generation were obtained in the absence of cytochalasin B, AAG were no longer involved and therefore cannot account for intracellular second messenger under physiological conditions. Subcellular distribution studies demonstrated the exclusive location of PA and PEt [corrected] in the plasma membrane. The possible involvement of PA in respiratory burst activation is discussed.