Relationship of phospholipase C- and phospholipase D-mediated phospholipid remodeling pathways to respiratory burst activation in human neutrophils stimulated by Candida albicans hyphae

Abstract

Neutrophil (PMN) oxidant release, a key component of defenses against disseminated candidiasis, was preceded by oxidant generation after stimulation by Candida albicans hyphae. Opsonized or unopsonized hyphae triggered phospholipase D (PLD) activation within 5 or 30 s, respectively, forming 1-O-alkyl-phosphatidic acid (alkyl-PA) or 1-O-alkyl-phosphatidyl-ethanol in the presence of ethanol. Ethanol, which competitively lowers phosphatidic acid (PA) production, caused dose-dependent inhibition of superoxide (O2-) generation after hyphal stimulation but altered neither baseline-unstimulated O2- production nor responses to phorbol myristate acetate. PA rises evoked by unopsonized hyphae began 2 min before significant O2- release, also preceding both phospholipase C activation and cytosolic Ca2+ rises. Diacylglycerol (DAG) rose in two distinct phases after stimulation by opsonized or unopsonized hyphae, peaking briefly after 60 or 120 s, respectively, followed by prolonged secondary rises. Initial DAG rises preceded inositol triphosphate elevations evoked by unopsonized hyphae. Though PA rose before DAG, no dephosphorylation of PA to form 1-O-alkyl-DAG was noted. Propranalol, which increases PA accumulation by inhibiting PA phosphohydrolase, lowered PMN O2- responses to hyphae. Early DAG rises temporally overlapped respiratory burst initiation but PMN responses to hyphae were unchanged by a DAG kinase inhibitor, R59022, which blocks phosphorylation of DAG to PA and enhances DAG accumulation. Thus, neither PA nor DAG accumulation individually accounted for triggering PMN O2- responses to hyphae. PLD activation and PA production may facilitate PMN fungicidal responses to hyphae but play an indirect role in initiating the respiratory burst.

Physiological Role for Phosphatidic Acid in the Translocation of the Novel Protein Kinase C Apl II in Aplysia Neurons

“…28,2008 TRANSLOCATION MECHANISM OF A NOVEL PROTEIN KINASE C 4731 nPKCs. One recent study by Melowic and colleagues (27) reported that the deletion of the C2 domain of PKC greatly enhanced its affinity to PS/DAG-containing membranes.…”

“…1A and B). Furthermore, translocation to DiC8-PA did not require PA to be converted to DAG, because the addition of DiC8-PA in the presence of propranolol, which inhibits DAG formation from PA by inhibiting phosphatidate phosphohydrolase (20,22,28), did not affect translocation (data not shown).…”

A Phosphatidic Acid-activated Protein Kinase and Conventional Protein Kinase C Isoforms Phosphorylate p22 , an NADPH Oxidase Component

“…1) that includes activation of phospholipases, generation of lipid second messengers, and the activation of protein kinases. One of the phospholipases activated in response to many physiological agonists of neutrophils is phospholipase D (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). Phospholipase D cleaves neutrophil phospholipids to form phosphatidic acid (PA), 1 which can then be converted to diacylglycerol by PA phosphohydrolase.…”