Functional role of phosphatidylcholine-specific phospholipase C in regulating leukotriene synthesis and degranulation in human eosinophils.

Phosphatidylinositol-specific phospholipase C (PI-PLC) and cytosolic phospholipase A (cPLA) regulate both eosinophil degranulation and leukotriene (LT) synthesis via PI-PLC-mediated calcium influx and cPLA activation. Phosphatidylcholine-specific phospholipase C (PC-PLC) likely plays a key role in cellular signaling, including the eosinophilic allergic inflammatory response. This study examined the role of PC-PLC in eosinophil LT synthesis and degranulation using tricyclodecan-9-yl-xanthogenate (D609), a PC-specific PLC inhibitor. D609 inhibited N-formyl-met-leu-phe + cytochalasin B (fMLP/B)-induced arachidonic acid (AA) release and leukotriene C (LTC) secretion. However, at concentrations that blocked both AA release and LTC secretion, D609 had no significant inhibitory effect on stimulated cPLA activity. D609 also partially blocked fMLP/B-induced calcium influx, indicating that inhibition of AA release and LTC secretion by D609 is due to inhibition of calcium-mediated cPLA translocation to intracellular membranes, not inhibition of cPLA activity. In addition, D609 inhibited fMLP/B-stimulated eosinophil peroxidase release, indicating that PC-PLC regulates fMLP/B-induced eosinophil degranulation by increasing the intracellular calcium concentration ([Ca]). Overall, our results showed that PC-PLC is critical for fMLP/B-stimulated eosinophil LT synthesis and degranulation. In addition, degranulation requires calcium influx, while PC-PLC regulates LTC synthesis through calcium-mediated cPLA activation.