Phospholipase D is involved in cytosolic phospholipase A₂‐dependent selective release of arachidonic acid by fMLP‐stimulated rat neutrophils

Abstract

The production of phosphatidic acid (PA) from phosphoAbstract When rat polymorphonuclear neutrophils (PMN) were treated with N-formyI-Met-Leu-Phe (fMLP), the release lipase D (PLD)-catalyzed hydrolysis of phosphatidylcholine is of araehidonie acid in preference to other fatty acids was a rapid and widespread response of cells stimulated with diobserved. Levels of arachidonic acid reached a plateau within verse agonists, and is implicated in a broad spectrum of 5 rain, and were accompanied by an ,-~ 4-fold increase in in vitro physiological and pathological processes, such as exocytosis, phospholipase (PL) A2 and PLD activities in PMN lysates, mitogenesis, oncogenesis and inflammation (reviewed in [4]). Treatment of PMN with ethanol (an inhibitor of PLD-mediatedThere are also several lines of evidence to suggest that arachiphosphatidic acid formation), propranolol (a phosphatiflic acid donic acid release correlates with PLD activation. Arachidonphosphatase inhibitor), or 4-bromophenaeylbromide (a PLA2 ic acid release by activated cells is reported to be accompanied inhibitor), each suppressed fMLP-stimulated araehidonate reby the increase in PLD activity and inhibition of PLD by lease. Treatment with RHC-80267 (a diaeylglyeerol lipase ethanol is associated with the decrease in arachidonic acid inhibitor), however, had no such effect. The eytosolie PLA2 release [5][6][7][8][9][10]. To account for these observations, some inves-(ePLA2) inhibitor, araehidonoyl trifluoromethyl ketone, suppressed PLA2 activity in PMN homogenates and araehidonate tigators have proposed that the PA generated by the PLD release by fMLP-treated PMN. These results suggest that reaction is converted to diacylglycerol (DG) by PA phosphatfMLP-elicited arachidonate release is mediated by cPLA2 but ase, and that arachidonic acid is released from DG by DG not diacylglycerol lipase, and that the activation of cPLA2 is lipase [6,7]. In contrast to this 'indirect' model for arachidonic downstream of the PLD-dependent signaling pathway, acid release via DG, other investigators have proposed that arachidonic acid is 'directly' released from phospholipids by

Independent Functioning of Cytosolic Phospholipase A2 and Phospholipase D1 in Trp-Lys-Tyr-Met-Val-D-Met-Induced Superoxide Generation in Human Monocytes

“…The introduction of a combination of PA and DAG reconstituted full cPLA 2 activity in permeabilized human PMN cells, while addition of either PA or DAG alone evoked only partial activation of cPLA 2 , suggesting that PLD acts as an upstream regulator in the induction of PLA 2 activity. Fujita et al showed that treatment of neutrophils with ethanol (PA acceptor) or propranolol (PA phosphohydrolase inhibitor) suppressed the FMLP-stimulated AA release, and they suggested that cPLA 2 may be downstream of the PLD-dependent signaling pathway in FMLP-stimulated neutrophils (45). In this study we demonstrated that the inhibition of PA production via a transphosphatidylation reaction in the presence of a primary alcohol does not affect the WKYMVm-induced cPLA 2 activation (Fig.…”

“…(44). Treatment of neutrophils with ethanol, an inhibitor of PA formation by PLD, suppressed FMLP-stimulated AA release, suggesting that PLD acts upstream of PLA 2 in neutrophils (45). However, the interrelationship between PLA 2 and PLD in the context of superoxide generation has not been studied extensively in human monocytes.…”

Functional crosstalk between phospholipase D2 and signaling phospholipase A2/cyclooxygenase‐2‐mediated prostaglandin biosynthetic pathways

“…Several lines of evidence have suggested a functional correlation between PLA 2 and PLD enzymes during cell activation [24–30]. We [24] and others [25–27] have reported that stimulus‐induced AA release, which appears to be mediated by cPLA 2 , is suppressed by pharmacological inhibition of PLD. Moreover, PLD 2 , not PLD 1 , activity has been reported to be modulated by cPLA 2 or its reaction products [28–30].…”

Lack of Alpha-Synuclein Modulates Microglial Phenotype In Vitro

“…Butanol Attenuated Increased Protein Levels of cPLA 2 and Cox-2 But Not PLD2 in Snca -/-Microglia Because cPLA2 and subsequent arachidonic acid metabolism by enzymes like Cox-2 have been demonstrated to be downstream of PLD activity in immune cells [38,39] it was possible that changes in PLD activity might be autoregulating PLD2 expression and feed-forward regulating the increases in cPLA 2 or Cox-2 protein levels. To assess whether the changes in protein levels were due to PLD activity, PLD-mediated generation of phosphatidic acid was attenuated by treating cells with increasing concentrations of butanol [40,41].…”