Bacterial phosphatidylcholine-preferring phospholipase C (PC-PLC) has been recognized as a virulence factor and is implicated in the hemolytic and dermonecrotic properties associated with certain organisms. Moreover, recent data suggest that PC-PLC may be an important component in the signal transduction cascade by contributing to diacylglycerol (DAG) mass via the hydrolysis of phosphatidylcholine (PC). We have previously shown that PC-PLC can inhibit superoxide generation in human polymorphonuclear leukocytes (PMN). We now extend these observations and show that the mechanism of PC-PLC inhibition of superoxide generation is reversible inhibition of the membrane component of the NADPH oxidase (in a cell-free system) accompanied by expected generation of DAG and phosporylcholine. Addition of PC reversed the effects of the enzyme. Surprisingly, we also found that phosphatidic acid (PA), the hydrolysis product of phospholipase D, was also produced in intact PMN following PC-PLC exposure. Subsequent addition of the agonist N -formylmethionyl-phenylalanine resulted in further PA production. Restoration of PA in cell-free preparations partially restored superoxide generating capability. We conclude that PC-PLC may enhance bacterial virulence by inhibiting superoxide generation by human PMN, and that this effect is due to direct inhibition of the membrane component of the NADPH oxidase.
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