Phosphatidylcholine Hydrolysis by Phospholipase D Determines Phosphatidate and Diglyceride Levels in Chemotactic Peptide-stimulated Human Neutrophils

Combined Treatment with KV Channel Inhibitor 4-Aminopyridine and either γ-Cystathionine Lyase Inhibitor β-Cyanoalanine or Epinephrine Restores Blood Pressure, and Improves Survival in the Wistar Rat Model of Anaphylactic Shock

Simple Summary

Allergic diseases are presenting a constant increase all over the world and caused by such different substances as food, drugs, and pollens. Anaphylactic shock is the more severe complication of allergy which can induce death if the treatment is not administered immediately. Some patients do not respond to the recommended treatment, intra venous or intramuscular epinephrine. The pathophysiology of anaphylactic shock is still under investigation. The mediators released after the activation of mast cells and basophiles act on endothelial cells and smooth muscle cells, inducing the vasodilation responsible for hypotension and shock. Nitric oxide and hydrogen sulphide are both intracellular mediators that induce vasodilation. The role of potassium voltage dependent channels is suspected. We aimed to demonstrate the ability of a blocker of potassium voltage dependent channels, 4-aminopyridine, alone or in combination with inhibitors of cystathionine γ-lyase to restore blood pressure and improve survival in an ovalbumin rat anaphylactic shock model. The blockade of potassium voltage dependent channels alone or combined with inhibitors of cystathionine γ-lyase, dl-propargylglycine, or β-cyanoalanine restored blood pressure and improved survival. These findings suggest possible investigative treatment pathways for research concerning epinephrine-refractory anaphylactic shock in patients.

Abstract

The mechanism of anaphylactic shock (AS) remains incompletely understood. The potassium channel blocker 4-aminopyridine (4-AP), the inhibitors of cystathionine γ-lyase (ICSE), dl-propargylglycine (DPG) or β-cyanoalanine (BCA), and the nitric oxide (NO) synthase produce vasoconstriction and could be an alternative for the treatment of AS. The aim of this study was to demonstrate the ability of L-NAME, ICSE alone or in combination with 4-AP to restore blood pressure (BP) and improve survival in ovalbumin (OVA) rats AS. Experimental groups included non-sensitized Wistar rats (n = 6); AS (n = 6); AS (n = 10 per group) treated i.v. with 4-AP (AS+4-AP), epinephrine (AS+EPI), AS+DPG, AS+BCA, or with L-NAME (AS+L-NAME); or AS treated with drug combinations 4-AP+DPG, 4-AP+BCA, 4-AP+L-NAME, or 4-AP+EPI. AS was induced by i.v. OVA (1 mg). Treatments were administered i.v. one minute after AS induction. Mean arterial BP (MAP), heart rate (HR), and survival were monitored for 60 min. Plasma levels of histamine, prostaglandin E2 (PGE2) and F2 (PGF2α), leukotriene B4 and C4, angiotensin II, vasopressin, oxidative stress markers, pH, HCO3, PaO2, PaCO2, and K+ were measured. OVA induced severe hypotension and all AS rats died. Moreover, 4-AP, 4-AP+EPI, or 4-AP+BCA normalized both MAP and HR and increased survival. All sensitized rats treated with 4-AP alone or with 4-AP+BCA survived. The time-integrated MAP “area under the curve” was significantly higher after combined 4-AP treatment with ICSE. Metabolic acidosis was not rescued and NO, ICSE, and Kv inhibitors differentially alter oxidative stress and plasma levels of anaphylactic mediators. The AS-induced reduction of serum angiotensin II levels was prevented by 4-AP treatment alone or in combination with other drugs. Further, 4-AP treatment combined with EPI or with BCA also increased serum PGF2α, whereas only the 4-AP+EPI combination increased serum LTB4. Serum vasopressin and angiotensin II levels were increased by 4-AP treatment alone or in combination with other drugs. Moreover, 4-AP alone and in combination with inhibition of cystathionine γ-lyase or EPI normalizes BP, increases serum vasoconstrictor levels, and improves survival in the Wistar rat model of AS. These findings suggest possible investigative treatment pathways for research into epinephrine-refractory anaphylactic shock in patients.

Interactome analysis of human phospholipase D and phosphatidic acid-associated protein network

Mammalian phospholipase D (PLD) enzyme family consists of six members. Among them, PLD1/2/6 catalyzes phosphatidic acid (PA) production, while PLD3/4/5 has no catalytic activities. Deregulation of the PLD-PA lipid signaling has been associated with various human diseases including cancer. However, a comprehensive analysis of the regulators and effectors for this crucial lipid metabolic pathway has not been fully achieved. Using a proteomic approach, we defined the protein interaction network for the human PLD family of enzymes and PA and revealed diverse cellular signaling events involving them. Through it, we identified PJA2 as a novel E3 ubiquitin ligase for PLD1 involved in control of the PLD1-mediated mammalian target of rapamycin signaling. Additionally, we showed that PA interacted with and positively regulated sphingosine kinase 1. Taken together, our study not only generates a rich interactome resource for further characterizing the human PLD-PA lipid signaling but also connects this important metabolic pathway with numerous biological processes.

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Defining the interactome of human phospholipase D enzymes and phosphatidic acid.

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PJA2 functions as an E3 ubiquitin ligase of phospholipase D1.

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Phosphatidic acid interacts with and positively regulates sphingosine kinase 1.

Phospholipases and the Activation and Priming of Neutrophils by Peritoneal Dialysis Effluent

Objective

To investigate the role of phospholipases during the activation and priming of neutrophil nicotinamide adenine dinucleotide phosphate (NADPH) oxidase by peritoneal dialysis effluent (PDE).

Design

Examine the action of 4-hour dwell PDE upon phospholipase activation in the circulating neutrophils obtained from healthy individuals.

Results

We have previously reported that PDE stimulated superoxide release by the NADPH oxidase of human neutrophils and primed the response to the bacterial peptide, fMLP (fMetLeuPhe). To elucidate the biochemical mechanisms underlying these observations, we have examined the roles of phospholipases (PL) C, D, and A2, whose activation causes the release of a range of intracellular secondary messengers. Following fMLP stimulation, we observed a rapid activation of both PLC and PLD as well as a small but nonsignificant increase in PLA2 activity. Peritoneal dialysis effluent alone failed to stimulate either PLC or PLD, while pre-incubation with PDE had no affect upon fMLP-induced PLC and PLD activation. However, PDE caused a small but nonsignificant increase in PLA2 activity (which was comparable to that observed with fMLP) and primed the fMLP-induced response. In common with a role for PLA2 and the subsequent release of arachidonic acid (AA), we have demonstrated dose-dependent inhibition of PDE-induced superoxide release by the PLA2 inhibitor mepacrine, as well as activation and priming of the fMLP-induced superoxide generation by AA.

Conclusions

These results imply that PDE-induced NADPH-oxidase activation and priming in human neutrophils is mediated via a PLA2-dependent but PLC and PLD-independent mechanism.

Endocannabinoid hydrolysis inhibition unmasks that unsaturated fatty acids induce a robust biosynthesis of 2-arachidonoyl-glycerol and its congeners in human myeloid leukocytes

The endocannabinoid (eCB) 2-arachidonoyl-gycerol (2-AG) modulates immune responses by activating cannabinoid receptors or through its multiple metabolites, notably eicosanoids. Thus, 2-AG hydrolysis inhibition might represent an interesting anti-inflammatory strategy that would simultaneously increase the levels of 2-AG and decrease those of eicosanoids. Accordingly, 2-AG hydrolysis inhibition increased 2-AG half-life in neutrophils. Under such setting, neutrophils, eosinophils, and monocytes synthesized large amounts of 2-AG and other monoacylglycerols (MAGs) in response to arachidonic acid (AA) and other unsaturated fatty acids (UFAs). Arachidonic acid and UFAs were ~1000-fold more potent than G protein-coupled receptor (GPCR) agonists. Triascin C and thimerosal, which, respectively, inhibit fatty acyl-CoA synthases and acyl-CoA transferases, prevented the UFA-induced MAG biosynthesis, implying glycerolipid remodeling. 2-AG and other MAG biosynthesis was preceded by that of the corresponding lysophosphatidic acid (LPA). However, we could not directly implicate LPA dephosphorylation in MAG biosynthesis. While GPCR agonists poorly induced 2-AG biosynthesis, they inhibited that induced by AA by 25%-50%, suggesting that 2-AG biosynthesis is decreased when leukocytes are surrounded by a pro-inflammatory entourage. Our data strongly indicate that human leukocytes use AA and UFAs to biosynthesize biologically significant concentrations of 2-AG and other MAGs and that hijacking the immune system with 2-AG hydrolysis inhibitors might diminish inflammation in humans.

Characterization and quantification of diacylglycerol species in biological extracts after one-step derivatization: a shotgun lipidomics approach

Diacylglycerols (DAGs) are important intermediates of lipid metabolism and cellular signaling. It is well-known that the mass levels of DAG are altered under disease states. Therefore, quantitative analysis of DAGs in biological samples can provide critical information to uncover underlying mechanisms of various cellular functional disorders. Although great efforts on the analysis of individual DAG species have recently been made by utilizing mass spectrometry with or without derivatization, cost-effective and high throughput methodologies for identification and quantification of all DAG species including regioisomers, particularly in an approach of shotgun lipidomics, are still missing. Herein, we described a novel method for directly identifying and quantifying DAG species including regioisomers present in lipid extracts of biological samples after facile one-step derivatization with dimethylglycine based on the principles of multidimensional mass spectrometry-based shotgun lipidomics. The established method provided substantial sensitivity (low limit of quantification at amol/μL), high specificity, and broad linear dynamics range (2500-fold) without matrix effects. By exploiting this novel method, we revealed a 16-fold increase of total DAG mass in the livers of ob/ob mice compared to their wild type controls at 4 months of age (an insulin-resistant state) versus a 5-fold difference between 3 month old mice (with normal insulin). These results demonstrated the importance and power of the method for studying biochemical mechanisms underpinning disease states.

Lipid phosphate phosphatase 3 participates in transport carrier formation and protein trafficking in the early secretory pathway

The inhibition of phosphatidic acid phosphatase (PAP) activity by propanolol indicates that diacylglycerol (DAG) is required for the formation of transport carriers at the Golgi and for retrograde trafficking to the ER. Here we report that the PAP2 family member lipid phosphate phosphatase 3 (LPP3, also known as PAP2b) localizes in compartments of the secretory pathway from ER export sites to the Golgi complex. The depletion of human LPP3: (i) reduces the number of tubules generated from the ER-Golgi intermediate compartment and the Golgi, with those formed from the Golgi being longer in LPP3-silenced cells than in control cells; (ii) impairs the Rab6-dependent retrograde transport of Shiga toxin subunit B from the Golgi to the ER, but not the anterograde transport of VSV-G or ssDsRed; and (iii) induces a high accumulation of Golgi-associated membrane buds. LPP3 depletion also reduces levels of de novo synthesized DAG and the Golgi-associated DAG contents. Remarkably, overexpression of a catalytically inactive form of LPP3 mimics the effects of LPP3 knockdown on Rab6-dependent retrograde transport. We conclude that LPP3 participates in the formation of retrograde transport carriers at the ER-Golgi interface, where it transitorily cycles, and during its route to the plasma membrane.

Discovery of phosphatidylcholines and sphingomyelins as biomarkers for ovarian endometriosis

BACKGROUND

Current non-invasive diagnostic methods for endometriosis lack sensitivity and specificity. In search for new diagnostic biomarkers for ovarian endometriosis, we used a hypothesis-generating targeted metabolomics approach.

METHODS

In a case-control study, we collected plasma of study participants and analysed their metabolic profiles. We selected a group of 40 patients with ovarian endometriosis who underwent laparoscopic surgery and a control group of 52 healthy women who underwent sterilization at the University Clinical Centre Ljubljana, Slovenia. Over 140 targeted analytes included glycerophospholipids, sphingolipids and acylcarnitines. The analytes were quantified by electrospray ionization tandem mass spectrometry. For assessing the strength of association between the metabolite or metabolite ratios and the disease, we used crude and adjusted odds ratios. A stepwise logistic regression procedure was used for selecting the best combination of biomarkers.

RESULTS

Eight lipid metabolites were identified as endometriosis-associated biomarkers due to elevated levels in patients compared with controls. A model containing hydroxysphingomyelin SMOH C16:1 and the ratio between phosphatidylcholine PCaa C36:2 to ether-phospholipid PCae C34:2, adjusted for the effect of age and the BMI, resulted in a sensitivity of 90.0%, a specificity of 84.3% and a ratio of the positive likelihood ratio to the negative likelihood ratio of 48.3.

CONCLUSIONS

Our results suggest that endometriosis is associated with elevated levels of sphingomyelins and phosphatidylcholines, which might contribute to the suppression of apoptosis and affect lipid-associated signalling pathways. Our findings suggest novel potential routes for therapy by specifically blocking highly up-regulated isoforms of phosphpolipase A2 and lysophosphatidylcholine acyltransferase 4.

Roles of phospholipase D in phorbol myristate acetate-stimulated neutrophil respiratory burst

The phorbol myristate acetate (PMA) stimulated nutrophil respiratory burst has been considered to simply involve the activation of protein kinase C (PKC). However, the PLD activity was also increased by 10-fold in human neutrophils stimulated with 100 nM PMA. Unexpectedly, U73122, an inhibitor of phospholipase C, was found to significantly inhibit PMA-stimulated respiratory burst in human neutrophils. U73122 at the concentrations, which were sufficient to inhibit the respiratory burst completely, caused partial inhibition of the PLD activity but no inhibition on PKC translocation and activation, suggesting that PLD activity is also required in PMA-stimulated respiratory burst. Using 1-butanol, a PLD substrate, to block phosphatidic acid (PA) generation, the PMA-stimulated neutrophil respiratory burst was also partially inhibited, further indicating that PLD activation, possibly its hydrolytic product PA and diacylglycerol (DAG), is involved in PMA-stimulated respiratory burst. Since GF109203X, an inhibitor of PKC that could completely inhibit the respiratory burst in PMA-stimulated neutrophils, also caused certain suppression of PLD activation, it may suggest that PLD activation in PMA-stimulated neutrophils might be, to some extent, PKC dependent. To further study whether PLD contributes to the PMA stimulated respiratory burst through itself or its hydrolytic product, 1,2-dioctanoyl-sn-glycerol, an analogue of DAG , was used to prime cells at low concentration, and it reversed the inhibition of PMA-stimulated respiratory burst by U73122. The results indicate that U73122 may act as an inhibitor of PLD, and PLD activation is required in PMA-stimulated respiratory burst.

Phospholipid synthesis participates in the regulation of diacylglycerol required for membrane trafficking at the Golgi complex

The lipid metabolite diacylglycerol (DAG) is required for transport carrier biogenesis at the Golgi, although how cells regulate its levels is not well understood. Phospholipid synthesis involves highly regulated pathways that consume DAG and can contribute to its regulation. Here we altered phosphatidylcholine (PC) and phosphatidylinositol synthesis for a short period of time in CHO cells to evaluate the changes in DAG and its effects in membrane trafficking at the Golgi. We found that cellular DAG rapidly increased when PC synthesis was inhibited at the non-permissive temperature for the rate-limiting step of PC synthesis in CHO-MT58 cells. DAG also increased when choline and inositol were not supplied. The major phospholipid classes and triacylglycerol remained unaltered for both experimental approaches. The analysis of Golgi ultrastructure and membrane trafficking showed that 1) the accumulation of the budding vesicular profiles induced by propanolol was prevented by inhibition of PC synthesis, 2) the density of KDEL receptor-containing punctated structures at the endoplasmic reticulum-Golgi interface correlated with the amount of DAG, and 3) the post-Golgi transport of the yellow fluorescent temperature-sensitive G protein of stomatitis virus and the secretion of a secretory form of HRP were both reduced when DAG was lowered. We confirmed that DAG-consuming reactions of lipid synthesis were present in Golgi-enriched fractions. We conclude that phospholipid synthesis pathways play a significant role to regulate the DAG required in Golgi-dependent membrane trafficking.

Procoagulant and prothrombotic activation of human erythrocytes by phosphatidic acid

Increased phosphatidic acid (PA) and phospholipase D (PLD) activity are frequently observed in various disease states including cancers, diabetes, sepsis, and thrombosis. Previously, PA has been regarded as just a precursor for lysophosphatidic acid (LPA) and diacylglycerol (DAG). However, increasing evidence has suggested independent biological activities of PA itself. In the present study, we demonstrated that PA can enhance thrombogenic activities in human erythrocytes through phosphatidylserine (PS) exposure in a Ca2+-dependent manner. In freshly isolated human erythrocytes, treatment of PA or PLD induced PS exposure. PA-induced PS exposure was not attenuated by inhibitors of phospholipase A2or phosphatidate phosphatase, which converts PA to LPA or DAG. An intracellular Ca2+increase and the resultant activation of Ca2+-dependent PKC-α appeared to underlie the PA-induced PS exposure through the activation of scramblase. A marginal decrease in flippase activity was also noted, contributing further to the maintenance of exposed PS on the outer membrane. PA-treated erythrocytes showed strong thrombogenic activities, as demonstrated by increased thrombin generation, endothelial cell adhesion, and erythrocyte aggregation. Importantly, these procoagulant activations by PA were confirmed in a rat in vivo venous thrombosis model, where PA significantly enhanced thrombus formation. In conclusion, these results suggest that PA can induce thrombogenic activities in erythrocytes through PS exposure, which can increase thrombus formation and ultimately contribute to the development of cardiovascular diseases.

Phospholipase D in the Golgi apparatus

Phospholipase D has long been implicated in vesicle formation and vesicular transport through the secretory pathway. The Golgi apparatus has been shown to exhibit a plethora of mechanisms of vesicle formation at different stages to accommodate a wide variety of cargo. Phospholipase D has been found on the Golgi apparatus and is regulated by ADP-ribosylation factors which are themselves regulators of vesicle trafficking. Moreover, the product of phospholipase D activity, phosphatidic acid, as well as its degradation product diacylglycerol, have been implicated in vesicle fission and fusion events. Here we summarize recent advances in the understanding of the role of phospholipase D at the Golgi apparatus.

Phosphatidic acid regulation of phosphatidylinositol 4-phosphate 5-kinases

Phosphatidic acid (PA) production by receptor-stimulated phospholipase D is believed to play an important role in the regulation of cell function. The second messenger function of PA remains to be elucidated. PA can bind and affect the activities of different enzymes and here we summarise the current status of activation of Type I phosphatidylinositol 4-phosphate 5-kinase by PA. Type 1 phosphatidylinositol 4-phosphate 5-kinase is also regulated by ARF proteins as is phospholipase D and we discuss the contributions of ARF and PA towards phosphatidylinositol(4,5)bisphosphate synthesis at the plasma membrane.

Phospholipase C, phosphatidylinositol 3-kinase, and intracellular [Ca(2+)] mediate the activation of chicken HD11 macrophage cells by CpG oligodeoxynucleotide

The activation of phospholipases is one of the earliest key events in receptor-mediated cellular responses to a number of extracellular signaling molecules. Oligodeoxynucleotides containing CpG motifs (CpG ODN) mimic microbial DNA and are immunostimulatory to most vertebrate species. In the present study, we used the production of nitric oxide (NO) as an indicator to evaluate the involvement of the signaling cascades of phospholipases and phosphatidylinositol 3-kinase (PI3K) in the activation of chicken HD11 macrophage cells by CpG ODN. Using selective inhibitors, we have identified the involvement of phosphatidylinositol (PI)-phospholipase C (PI-PLC), but not phosphatidylcholine (PC)-phospholipase C (PC-PLC) and PC-phospholipase D (PC-PLD), in CpG ODN-induced NO production in HD11 cells. Preincubation with PI-PLC selective inhibitors (U-73122) completely abrogated CpG ODN-induced NO production in HD11 cells, whereas PC-PLC inhibitor (D609) and PC-PLD inhibitor (n-butanol) had no inhibitory effects. Additionally, inhibition of PI3K and protein kinase C (PKC) with selective inhibitors and chelation of intracellular [Ca(2+)] also significantly attenuated NO production in CpG ODN-activated HD11 cells. Our results demonstrate that PI-PLC, PI3 K, PKC, and intracellular [Ca(2+)] are important components of the CpG ODN-induced signaling pathway that leads to the production of NO in avian macrophage cells.

CCR5 signaling through phospholipase D involves p44/42 MAP-kinases and promotes HIV-1 LTR-directed gene expression

The chemokine receptor CCR5 plays an important role as an entry gate for the human immunodeficiency virus-1 (HIV-1) and for viral postentry events. Among signal transducers used by chemoattractant receptors, the phosphatidylcholine-specific phospholipase D (PLD) produces large amounts of second messengers in most cell types. However, the relevance of PLD isoforms to CCR5 signaling and HIV-1 infection process remains unexplored. We show here that CCR5 activation by MIP-1beta in HeLa-MAGI cells triggered a rapid and substantial PLD activity, as assessed by mass choline production. This activity required the activation of ERK1/2-MAP kinases and involved both PLD1 and PLD2. MIP-1beta also promoted the activation of an HIV-1 long terminal repeat (LTR) by the transactivator Tat in HeLa P4.2 cells through a process involving ERK1/2. Expression of wild-type and catalytically inactive PLDs dramatically boosted and inhibited the LTR activation, respectively, without altering Tat expression. Wild-type and inactive PLDs also respectively potentiated and inhibited HIV-1(BAL) replication in MAGI cells. Finally, in monocytic THP-1 cells, antisense oligonucleotides to both PLDs dramatically inhibited the HIV-1 replication. Thus, PLD is activated downstream of ERK1/2 upon CCR5 activation and plays a major role in promoting HIV-1 LTR transactivation and virus replication, which may open novel perspectives to anti-HIV-1 strategies.

Involvement of phosphatidylcholine-selective phospholipase C in activation of mitogen-activated protein kinase pathways in imidazoline receptor antisera-selected protein

Imidazoline receptor antisera-selected protein (IRAS) is considered as a candidate for the I1-imidazoline receptor (I1R), but the signaling pathway mediated by IRAS remains unknown. In our study, the signal transduction pathways of IRAS were investigated in CHO cells stably expressing IRAS (CHO-IRAS), and compared to the native I1R signaling pathways. Rilmenidine or moxonidine (10 nM-100 microM), I1R agonists, failed to stimulate [35S]-GTPgammaS binding in CHO-IRAS cell membrane preparations, suggesting that G protein may not be involved in IRAS signaling pathway. However, incubation of CHO-IRAS with rilmenidine or moxonidine for 5 min could induce an upregulation of phosphatidylcholine-selective phospholipase C (PC-PLC) activity, and an increase in the accumulation of diacylglycerol (DAG), the hydrolysate of PC-PLC, in a concentration-dependent manner. The elevated activation of PC-PLC by rilmenidine or moxonidine (100 nM) could be blocked by efaroxan, a selective I1R antagonist. Cells treated with rilmenidine or moxonidine showed an increased level of extracellular signal-regulated kinase (ERK) phosphorylation in a concentration-dependent manner, which could be reversed by efaroxan or D609, a selective PC-PLC inhibitor. These results suggest that the signaling pathway of IRAS in response to I1R agonists coupled with the activation of PC-PLC and its downstream signal transduction molecule, ERK. These findings are similar to those in the signaling pathways of native I1R, providing some new evidence for the relationship between I1R and IRAS.

Involvement of phosphatidylinositol-phospholipase C in immune response to Salmonella lipopolysacharide in chicken macrophage cells (HD11)

The activation of phospholipases is one of the earliest key events in receptor-mediated cellular responses to a number of extracellular signaling molecules. Lipopolysaccharide (LPS) is a principle component of the outer membrane of Gram-negative bacteria and a prime target for recognition by the innate immune system. In the present study, we evaluated the role of specific phospholipase in the activation of a chicken macrophage cell line HD11 by LPS. Activation of HD11 cells by LPS results in induction of nitric oxide (NO). Using selective inhibitors, we have identified that phosphatidylinositol (PI)-phospholipase C (PI-PLC), but not phosphatidylcholine (PC)-phospholipase C (PC-PLC) nor PC-phospholipase D (PC-PLD), was required for LPS-induced NO production. Preincubation with PI-PLC selective inhibitors (U-73122 and ET-18-OCH3) abrogated LPS-induced NO production in HD11 cells, whereas PC-PLC inhibitor (D609), phosphatide phosphohydrolase inhibitor (propranolol), and PC-PLD inhibitor (n-butanol) had no inhibitory effects. We also showed that inhibition of protein kinase C (PKC) by selective inhibitors Ro 31-8220 and calphostin C and chelating intracellular Ca2+ by BAPTA-AM significantly reduced NO production in LPS-stimulated HD11 cells. Our results demonstrate that PI-PLC plays a critical role, most likely through activation of PKC pathway, in TLR4 mediated immune responses of avian macrophage cells to LPS.

Lipid mediators as agonists for the resolution of acute lung inflammation and injury

Resolution of acute lung inflammation and injury is an active process; it is not merely the absence of proinflammatory signals. Restoration of homeostasis is coordinated by specific mediators and cellular events. In response to injury and inflammatory stimuli, infiltrating leukocytes and tissue-resident cells interact to generate lipoxins (LXs), which are bioactive eicosanoids derived from arachidonic acid. In contrast to proinflammatory leukotrienes and prostaglandins, LXs display potent antiinflammatory actions. LXA(4) interacts with a G protein-coupled receptor, termed ALX, that transduces counter-regulatory signals in part via intracellular polyisoprenyl phosphate remodeling. Presqualene diphosphate (PSDP) is a polyisoprenyl phosphate in human neutrophils that is rapidly converted to presqualene monophosphate (PSMP) upon cell activation. PSDP, but not PSMP, directly inhibits phospholipase D, phosphoinositol-3 kinase, and superoxide anion generation. LXs block PSDP turnover in neutrophil membranes to prevent proinflammatory responses. Hence, LX and polyisoprenyl phosphate signaling provide a counter-regulatory circuit to promote resolution of acute lung inflammation. LXA(4) and PSDP mimetics have been prepared with potent protective actions in murine models of asthma and acute lung injury.

Phospholipase D1 Regulates Phagocyte Adhesion

Adhesion is a fundamental cellular response that is essential to the physiologic processes of development, differentiation, proliferation, and motility, as well as to the pathology of inflammation, transformation, and metastasis. Adhesion of phagocytic leukocytes is a critical modulator of antimicrobial and cytotoxic functions, including the respiratory burst, secretion, and apoptosis. Because phospholipase D (PLD) is linked to several signaling pathways implicated in these processes, we tested the hypothesis that PLD regulates phagocyte adhesion. Adhesion of primary human neutrophils and monocyte-derived macrophages to fibronectin was accompanied by marked stimulation of PLD activity. Similarly, adhesion of both human (PLB, THP-1) and murine (RAW) myeloid-macrophage cell lines to fibronectin, fibrinogen, collagen, or plastic resulted in significant activation of PLD. Stimulation of PLD activity was rapid and persisted for at least 90 min. Confocal microscopy indicated that PLD1 exhibited partial colocalization with actin filaments at the adherent interface, in proximity to the focal adhesion protein, paxillin. Reductions in PLD activity by chemical inhibitors or specific short-interfering RNA-induced knockdown of PLD1 resulted in significant inhibition of phagocyte adhesion and was accompanied by reductions in total cellular F-actin. These data support the hypotheses that adhesion stimulates PLD activity, and that PLD1 regulates the initial stages of phagocyte adhesion. Stimulation of PLD activity may promote adhesion-dependent phagocyte effector responses.

Characterization of serotonin 5-HT2C receptor signaling to extracellular signal-regulated kinases 1 and 2

Serotonin 5-HT2C receptors (5-HT(2C)Rs) are almost exclusively expressed in the CNS, and implicated in disorders such as obesity, depression, and schizophrenia. The present study investigated the mechanisms governing the coupling of the 5-HT(2C)R to the extracellular signal-regulated kinases (ERKs) 1/2, using a Chinese hamster ovary (CHO) cell line stably expressing the receptor at levels comparable to those found in the brain. Using the non-RNA-edited isoform of the 5-HT(2C)R, constitutive ERK1/2 phosphorylation was observed and found to be modulated by full, partial and inverse agonists. Interestingly, agonist-directed trafficking of receptor stimulus was also observed when comparing effects on phosphoinositide accumulation and intracellular Ca2+ elevation to ERK1/2 phosphorylation, whereby the agonists, [+/-]-2,5-dimethoxy-4-iodoamphetamine (DOI) and quipazine, showed reversal of efficacy between the phosphoinositide/Ca2+ pathways, on the one hand, and the ERK1/2 pathway on the other. Subsequent molecular characterization found that 5-HT-stimulated ERK1/2 phosphorylation in this cellular background requires phospholipase D, protein kinase C, and activation of the Raf/MEK/ERK module, but is independent of both receptor- and non-receptor tyrosine kinases, phospholipase C, phosphoinositide 3-kinase, and endocytosis. Our findings underscore the potential for exploiting pathway-selective receptor states in the differential modulation of signaling pathways that play prominent roles in normal and abnormal neuronal signaling.

Blockade of rapid versus prolonged extracellularly regulated kinase 1/2 activation has differential effects on insulin-induced gene expression

In the present work, insulin's regulation of expression of activating transcription factor 3 (ATF-3), the putative transcription factor proline-rich induced protein (Pip)92, and insulin-inducible gene-1 (Insig-1) (an ER resident protein involved in regulation of sterol-responsive element-binding protein 1 activation) have been examined in a liver-derived cell line (rat H4IIE hepatoma cells). We report that: 1) insulin-induced transcription of ATF-3, Pip92, and Insig-1 required MEK-ERK activation; 2) insulin-induced transcription of ATF-3 and Pip92 reached maximum levels within 15 min and was blocked by wortmannin but not LY294002; 3) in contrast, the maximum level of insulin-induced transcription of Insig-1 was delayed and was not blocked by either wortmannin or LY294002; 4) insulin activated ERK1/2 in two distinct phases, a rapid peak and a later plateau; 5) the delayed plateau phase of insulin-induced ERK1/2 activation was partially phosphatidylinositol 3-OH-kinase dependent; and 6) however, the rapid, insulin-induced peak of ERK1/2 activation was blocked by wortmannin but not LY294002.

Role of phospholipase D and diacylglycerol in activating constitutive TRPC-like cation channels in rabbit ear artery myocytes

Previously we have described a constitutively active Ca2+-permeable non-selective cation channel in freshly dispersed rabbit ear artery myocytes that has similar properties to canonical transient receptor potential (TRPC) channel proteins. In the present study we have investigated the transduction pathways responsible for stimulating constitutive channel activity in these myocytes. Application of the pharmacological inhibitors of phosphatidylcholine-phospholipase D (PC-PLD), butan-1-ol and C2 ceramide, produced marked inhibition of constitutive channel activity in cell-attached patches and also butan-1-ol produced pronounced suppression of resting membrane conductance measured with whole-cell recording whereas the inactive isomer butan-2-ol had no effect on constitutive whole-cell or channel activity. In addition butan-1-ol had no effect on channel activity evoked by the diacylglycerol (DAG) analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG). Inhibitors of PC-phospholipase C (PC-PLC) and phospholipase A2 (PLA2) had no effect on constitutive channel activity. Application of a purified PC-PLD enzyme and its metabolite phosphatidic acid to inside-out patches markedly increased channel activity. The phosphatidic acid phosphohydrolase (PAP) inhibitor dl-propranolol also inhibited constitutive and phosphatidic acid-induced increases in channel activity but had no effect on OAG-evoked responses. The DAG lipase and DAG kinase inhibitors, RHC80267 and R59949 respectively, which inhibit DAG metabolism, produced transient increases in channel activity which were mimicked by relatively high concentrations (40 microm) of OAG. The protein kinase C (PKC) inhibitor chelerythrine did not prevent channel activation by OAG but blocked the secondary inhibitory response of OAG. It is proposed that endogenous DAG is involved in the activation of channel activity and that its effects on channel activity are concentration-dependent with higher concentrations of DAG also inhibiting channel activity through activation of PKC. This study indicates that constitutive cation channel activity in ear artery myocytes is mediated by DAG which is generated by PC-PLD via phosphatidic acid which represents a novel activation pathway of cation channels in vascular myocytes.

Involvement of phospholipase A2 and lipoxygenase in lipopolysaccharide-induced inducible nitric oxide synthase expression in glial cells

The present study underlines the importance of phospholipase A2 (PLA2)- and lipoxygenase (LO)-mediated signaling processes in the regulation of inducible nitric oxide synthase (iNOS) gene expression. In glial cells, lipopolysaccharide (LPS) induced the activities of PLA2 (calcium-independent PLA2; iPLA2 and cytosolic PLA2; cPLA2) as well as gene expression of iNOS. The inhibition of cPLA2 by methyl arachidonyl fluorophosphates (MAFP) or antisense oligomer against cPLA2 and inhibition of iPLA2 by bromoenol lactone reduced the LPS-induced iNOS gene expression and NFkappaB activation. In addition, the inhibition of LO by nordihydroguaiaretic acid (NDGA; general LO inhibitor) or MK886 (5-LO inhibitor), but not baicalein (12-LO inhibitor), completely abrogated the LPS-induced iNOS expression. Because NDGA could abrogate the LPS-induced activation of NFkappaB, while MK886 had no effect on it, LO-mediated inhibition of iNOS gene induction by LPS may involve an NFkappaB-dependent or -independent (by 5-LO) pathway. In contrast to LO, however, the cyclooxygenase (COX) may not be involved in the regulation of LPS-mediated induction of iNOS gene because COX inhibition by indomethacin (general COX inhibitor), SC560 (COX-1 inhibitor), and NS398 (COX-2 inhibitor) affected neither the LPS-induced iNOS expression nor activation of NFkappaB. These results indicate a role for cPLA2 and iPLA2 in LPS-mediated iNOS gene induction in glial cells and the involvement of LO in these reactions.

Lysophosphatidic acid increases phosphatidic acid formation, phospholipase D activity and degranulation by human neutrophils

I-oleoyl-sn-glycero-3-phosphate, a lysophosphatidic acid (LPA), in serum is a biologically active lipid and has multiple functions depending on the cell types. Several studies have shown that LPA stimulates phospholipase D (PLD) activity in fibroblasts and prostate cancer cells in culture. PLD plays a central role in regulating neutrophil functions. One of the functions of the lipid product, phosphatidic acid (PA), of PLD action in neutrophils is to promote degranulation. In the present study, we examined the effect of LPA on PLD activity and degranulation by human neutrophils. The results show that exogenous LPA increased PA formation, PLD activity and degranulation by human neutrophils in a time and concentration dependent manner. These findings suggest that LPA released from activated platelets during blood clotting may participate in bacterial killing and wound healing process. On the other hand, augmented LPA production might be involved in inflammation, causing damage of the host tissues.

Angiotensin II-induced Akt activation through the epidermal growth factor receptor in vascular smooth muscle cells is mediated by phospholipid metabolites derived by activation of phospholipase D

Angiotensin II (Ang II) activates cytosolic Ca(2+)-dependent phospholipase A(2) (cPLA(2)), phospholipase D (PLD), p38 mitogen-activated protein kinase (MAPK), epidermal growth factor receptor (EGFR) and Akt in vascular smooth muscle cells (VSMC). This study was conducted to investigate the relationship between Akt activation by Ang II and other signaling molecules in rat VSMC. Ang II-induced Akt phosphorylation was significantly reduced by the PLD inhibitor 1-butanol, but not by its inactive analog 2-butanol, and by brefeldin A, an inhibitor of the PLD cofactor ADP-ribosylation factor, and in cells infected with retrovirus containing PLD(2) siRNA or transfected with PLD(2) antisense but not control LacZ or sense oligonucleotide. Diacylglycerol kinase inhibitor II diminished Ang II-induced and diC8-phosphatidic acid (PA)-increased Akt phosphorylation, suggesting that PLD-dependent Akt activation is mediated by PA. Ang II-induced EGFR phosphorylation was inhibited by 1-butanol and PLD(2) siRNA and also by cPLA(2) siRNA. In addition, the inhibitor of arachidonic acid (AA) metabolism 5,8,11,14-eicosatetraynoic acid (ETYA) reduced both Ang II- and AA-induced EGFR transactivation. Furthermore, ETYA, cPLA(2) antisense, and cPLA(2) siRNA attenuated Ang II-elicited PLD activation. p38 MAPK inhibitor SB202190 [4-(4-flurophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole] reduced PLD activity and EGFR and Akt phosphorylation elicited by Ang II. Pyrrolidine-1, a cPLA(2) inhibitor, and cPLA(2) siRNA decreased p38 MAPK activity. These data indicate that Ang II-stimulated Akt activity is mediated by cPLA(2)-dependent, p38 MAPK regulated PLD(2) activation and EGFR transactivation. We propose the following scheme of the sequence of events leading to activation of Akt in VSMC by Ang II: Ang II-->cPLA(2)-->AA-->p38 MAPK-->PLD(2)-->PA-->EGFR-->Akt.

Control of aldosterone secretion: a model for convergence in cellular signaling pathways

Aldosterone secretion by glomerulosa cells is stimulated by angiotensin II (ANG II), extracellular K(+), corticotrophin, and several paracrine factors. Electrophysiological, fluorimetric, and molecular biological techniques have significantly clarified the molecular action of these stimuli. The steroidogenic effect of corticotrophin is mediated by adenylyl cyclase, whereas potassium activates voltage-operated Ca(2+) channels. ANG II, bound to AT(1) receptors, acts through the inositol 1,4,5-trisphosphate (IP(3))-Ca(2+)/calmodulin system. All three types of IP(3) receptors are coexpressed, rendering a complex control of Ca(2+) release possible. Ca(2+) release is followed by both capacitative and voltage-activated Ca(2+) influx. ANG II inhibits the background K(+) channel TASK and Na(+)-K(+)-ATPase, and the ensuing depolarization activates T-type (Ca(v)3.2) Ca(2+) channels. Activation of protein kinase C by diacylglycerol (DAG) inhibits aldosterone production, whereas the arachidonate released from DAG in ANG II-stimulated cells is converted by lipoxygenase to 12-hydroxyeicosatetraenoic acid, which may also induce Ca(2+) signaling. Feedback effects and cross-talk of signal-transducing pathways sensitize glomerulosa cells to low-intensity stimuli, such as physiological elevations of [K(+)] (< or =1 mM), ANG II, and ACTH. Ca(2+) signaling is also modified by cell swelling, as well as receptor desensitization, resensitization, and downregulation. Long-term regulation of glomerulosa cells involves cell growth and proliferation and induction of steroidogenic enzymes. Ca(2+), receptor, and nonreceptor tyrosine kinases and mitogen-activated kinases participate in these processes. Ca(2+)- and cAMP-dependent phosphorylation induce the transfer of the steroid precursor cholesterol from the cytoplasm to the inner mitochondrial membrane. Ca(2+) signaling, transferred into the mitochondria, stimulates the reduction of pyridine nucleotides.

A requirement for calcium-independent phospholipase A2 in thrombin-induced arachidonic acid release and growth in vascular smooth muscle cells

Thrombin is a potent mitogen for vascular smooth muscle cells (VSMC). To understand its mitogenic signaling events, we have studied the role of calcium-independent phospholipase A2 (iPLA2). Without affecting its levels, thrombin increased iPLA2 activity in a time-dependent manner in VSMC. Thrombin also induced arachidonic acid release and DNA synthesis by about 2-fold as compared with control. Down-regulation of iPLA2 activity by its specific inhibitor, bromoenol lactone, or its expression by antisense oligonucleotides, significantly reduced thrombin-induced arachidonic acid release and DNA synthesis in VSMC. To learn the mechanism of thrombin-stimulated iPLA2 activity, we next tested the role of p38 MAPK. Thrombin stimulated p38 MAPK phosphorylation and activity in a time-dependent manner in VSMC. Inhibition of p38 MAPK activity by SB203580 and SB202190 resulted in decreased iPLA2 activity, arachidonic acid release, and DNA synthesis induced by thrombin in VSMC. Together, these results for the first time demonstrate that iPLA2 plays a role in thrombin-induced arachidonic acid release and growth in VSMC and that these responses are mediated by p38 MAPK.

Investigation of the cellular mechanism of inhibition of formyl-methionyl-leucyl-phenylalanine-induced superoxide anion generation in rat neutrophils by 2-benzyloxybenzaldehyde

The inhibition of formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O2(.-)) generation by 2-benzyloxybenzaldehyde (CCY1a) was investigated in rat neutrophils, and the underlying mechanism of this inhibition was assessed. CCY1a concentration-dependently inhibited O2(.-) generation (IC(50)=18.5+/-4.3 microM). In cell-free systems, CCY1a failed to alter O2(.-) generation during dihydroxyfumaric acid autoxidation, in phorbol 12-myristate 13-acetate (PMA)-activated neutrophil particulate NADPH oxidase preparations, or during arachidonic acid-induced NADPH oxidase activation. CCY1a increased cellular cyclic AMP (cAMP) levels in a time- and concentration-dependent manner, and this cAMP-elevating effect was inhibited by the adenylyl cyclase inhibitor 9-(tetrahydro-2'-furyl)adenine (SQ22536), adenosine deaminase (ADA), and the adenosine receptor antagonist 8-(p-sulfophenyl)theophylline. In neutrophils, inhibition of O2(.-) generation by CCY1a was partially reversed by the protein kinase A inhibitor (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-l][1,6]benzodiazocine-10-carboxylic acid, hexyl ester (KT5720). CCY1a did not affect fMLP-induced p38 mitogen-activated protein kinase phosphorylation, but concentration-dependently attenuated the phosphorylation of extracellular signal-regulated kinase (ERK) and Akt (IC(50) about 31.3 and 19.4 microM, respectively). The plateau phase, but not the initial spike, of fMLP-induced [Ca2+](i) changes was inhibited by CCY1a in a concentration-dependent manner. CCY1a inhibition of Ca2+ entry, ERK, and Akt phosphorylation was not prevented by SQ22536 or ADA. fMLP-induced phospholipase D (PLD) activation was inhibited by CCY1a (IC(50)=13.9+/-2.0 microM). ADA and KT5720 did not prevent the inhibition of PLD activation by CCY1a. Collectively, these results indicate that the inhibition by CCY1a of fMLP-induced O2(.-) generation in rat neutrophils can probably be attributed to the increase in cAMP levels, and to the blockade of Ca2+ entry, suppression of Akt, and PLD activation via cAMP-independent mechanisms.

Induction of 5-lipoxygenase activation in polymorphonuclear leukocytes by 1-oleoyl-2-acetylglycerol

1,2-Diacylglycerols (DAGs) can prime polymorphonuclear leukocytes (PMNL) for enhanced release of arachidonic acid (AA) and generation of 5-lipoxygenase (5-LO) products upon subsequent agonist stimulation. Here, we demonstrate that in isolated human PMNL, 1-oleoyl-2-acetylglycerol (OAG) functions as a direct agonist stimulating 5-LO product formation (up to 42-fold). OAG caused no release of endogenous AA, but in the presence of exogenous AA, the magnitude of 5-LO product synthesis induced by OAG was comparable to that obtained with the Ca(2+)-ionophore A23187. Interestingly, OAG-induced 5-LO product synthesis was not connected with increased 5-LO nuclear membrane association. Examination of diverse glycerides revealed that the sn-2-acetyl-group is important, thus, also 1-O-hexadecyl-2-acetylglycerol (EAG) stimulated 5-LO product formation (up to 8-fold). Treatment of PMNL with OAG did not alter the mobilization of Ca(2+) but removal of intracellular Ca(2+) abolished the upregulatory OAG effects. Notably, the PKC activator phorbol-myristate-acetate hardly increased 5-LO product synthesis and PKC inhibitors failed to suppress the effects of OAG. Although OAG rapidly activated p38 MAPK and p42/44(MAPK), which can stimulate 5-LO for product synthesis, specific inhibitors of these kinases could not prevent 5-LO activation by OAG. Together, OAG acts as a direct agonist for 5-LO product synthesis in PMNL stimulating 5-LO by novel undefined mechanisms.

Involvement of nuclear factor-kappaB in lipoteichoic acid-induced cyclooxygenase-2 expression in RAW 264.7 macrophages

We have investigated the role of protein kinase C (PKC) and nuclear factor-kappaB (NF-kappaB) in cyclooxygenase-2 (COX-2) expression caused by Staphylococcus aureus lipoteichoic acid in RAW 264.7 macrophages. A phosphatidylcholine-phospholipase C (PC-PLC) inhibitor (D-609) and a phosphatidylinositol-phospholipase C (PI-PLC) inhibitor (U-73122) attenuated lipoteichoic acid-induced COX-2 expression, while a phosphatidate phosphohydrolase inhibitor (propranolol) had no effect. Two PKC inhibitors (Go 6976 and Ro 31-8220) and the NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC), also attenuated lipoteichoic acid-induced COX-2 expression. Lipoteichoic acid resulted in a decrease in PKC activity in the cytosol and an increase in PKC activity in membranes. The lipoteichoic acid-induced translocation of p65 NF-kappaB from the cytosol to the nucleus was inhibited by D-609, U-73122, Go 6976, Ro 31-8220, and PDTC, but not by propranolol. The results suggested that lipoteichoic acid might have activated PC-PLC and PI-PLC to induce PKC activation, which in turn initiated NF-kappaB activation, and finally induced COX-2 expression in RAW 264.7 macrophages.

Mechanism of endothelin-1-induced cytosolic Ca(2+) mobility in cultured H9c2 myocardiac ventricular cells

The effect of endothelin-1 (ET-1) on the intracellular free Ca(2+) ([Ca(2+)](i)) mobility in cultured H9c2 myocardiac ventricular cells was studied after loading with fura-2-AM. In Ca(2+)-containing buffer, ET-1 induced [Ca(2+)](i) rise from 10(-7) to 10(-9) M. ET-1 induced [Ca(2+)](i), which was composed of a first small peak and a secondary persistent plateau. In Ca(2+)-free buffer, pretreatment with 10(-7) M ET-1 inhibited the thapsigargin and carbonylcyanide m-chlorophenylhydrazone (CCCP)-induced [Ca(2+)](i) increase. Meanwhile, pretreatment with thapsigargin and CCCP also inhibited ET-1-induced [Ca(2+)](i) rise. In Ca(2+)-containing buffer, the ET(A) receptor antagonist (BQ123) completely abolished the secondary rising peak and plateau. Conversely, the ET(B) receptor antagonist (BQ788) completely inhibited the first small peak and secondary peak plateau. Nifedipine and La(3+) also abolished the 10(-7) M ET-1-induced [Ca(2+)](i) in the first rising peak. The internal Ca(2+) release induced by ET-1 was inhibited by U73122 (phospholipase C inhibitor), propranolol (phospholipase D inhibitor) and aristolochic acid (phospholipase A2 inhibitor). After incubation of 10(-7) M ET-1 in Ca(2+)-free buffer, the addition of 5 mM CaCl(2) increased Ca(2+) influx, implying that release of Ca(2+) from internal stores further induces capacitative Ca(2+) entry. Taken together, these results suggest that both ET(A) and ET(B) receptors are involved in ET-1-induced [Ca(2+)](i) rise in H9c2 myocardiac ventricular cells. Whereas ET(B) receptor seems to mediate the initial Ca(2+) influx via L-type Ca(2+) channel, ET(A) receptor appears to be involved in the subsequent Ca(2+) release from endoplasmic reticulum and mitochondria Ca(2+) stores.

PGF(2alpha)-induced contraction of cat esophageal and lower esophageal sphincter circular smooth muscle

Lower esophageal sphincter (LES) tone depends on PGF(2alpha) and thromboxane A(2) acting on receptors linked to G(i3) and G(q) to activate phospholipases and produce second messengers resulting in muscle contraction. We therefore examined PGF(2alpha) signal transduction in circular smooth muscle cells isolated by enzymatic digestion from cat esophagus (Eso) and LES. In Eso, PGF(2alpha)-induced contraction was inhibited by antibodies against the alpha-subunit of G(13) and the monomeric G proteins RhoA and ADP-ribosylation factor (ARF)1 and by the C3 exoenzyme of Clostridium botulinum. A [(35)S]GTPgammaS-binding assay confirmed that G(13), RhoA, and ARF1 were activated by PGF(2alpha). Contraction of Eso was reduced by propranolol, a phospholipase D (PLD) pathway inhibitor and by chelerythrine, a PKC inhibitor. In LES, PGF(2alpha)-induced contraction was inhibited by antibodies against the alpha-subunit of G(q) and G(i3), and a [(35)S]GTPgammaS-binding assay confirmed that G(q) and G(i3) were activated by PGF(2alpha). PGF(2alpha)-induced contraction of LES was reduced by U-73122 and D609 and unaffected by propranolol. At low PGF(2alpha) concentration, contraction was blocked by chelerythrine, whereas at high concentration, contraction was blocked by chelerythrine and CGS9343B. Thus, in Eso, PGF(2alpha) activates a PLD- and protein kinase C (PKC)-dependent pathway through G(13), RhoA, and ARF1. In LES, PGF(2alpha) receptors are coupled to G(q) and G(i3), activating phosphatidylinositol- and phosphatidylcholine-specific phospholipase C. At low concentrations, PGF(2alpha) activates PKC. At high concentration, it activates both a PKC- and a calmodulin-dependent pathway.

Mechanism of angiotensin II-induced phospholipase D activation in bovine adrenal glomerulosa cells

Based on previous data demonstrating activation of phospholipase D (PLD) in response to angiotensin II (AngII), we have hypothesized a role for PLD in mediating aldosterone secretion from bovine adrenal glomerulosa cells. In this study we demonstrate that a PLD-generated signal(s) is required for the AngII-elicited secretory response, since interfering with lipid second messenger formation using a primary alcohol inhibited AngII-induced aldosterone secretion, but not that elicited by incubation with a hydrophilic cholesterol analog, 22(R)-hydroxycholesterol, which bypasses signaling pathways. Three mechanisms for hormonal activation of PLD have been described in other systems: direct receptor coupling, activation through protein kinase C (PKC) and a combination of these two mechanisms. Our results indicate that the PKC activator, phorbol 12-myristic 13-acetate (PMA), is able to activate PLD, and that receptor engagement is apparently not necessary for PLD activation in response to this agent. Maximal doses of AngII and PMA produced no additive effect on PLD activation, suggesting that these two agents function through a common PKC pathway. This interpretation was confirmed by the ability of a PKC inhibitor, Gö 6976, to inhibit partially AngII-induced PLD activation. Finally, treatment with the calcium ionophores A23187 or ionomycin or the calcium channel agonist BAY K8644 had no effect on PLD activity. Likewise, inhibiting calcium influx with high-dose nitrendipine affected neither basal PLD activity nor that stimulated by AngII. Thus, our results suggest a role for PKC, independent of calcium influx, in mediating AngII-induced PLD activation in glomerulosa cells.

Differential regulation of neutrophil phospholipase d activity and degranulation

One of the proposed functions of phosphatidic acid (PA) formation from phospholipase D (PLD) activation in neutrophils is to promote degranulation induced by receptor agonists. The present study shows that the time course and dose response of PA formation and degranulation induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) differed. PLD activation and degranulation also exhibited different dose response to genistein and epigallocatechin gallate (EGCG), inhibitors of protein tyrosine kinases. Genistein inhibited PLD activity with an IC(50) value of 12.2 microM in fMLP- and 107 microM in phorbol myristate acetate (PMA)-stimulated cells. It required higher concentrations of genistein to inhibit degranulation than to inhibit PLD activity induced by fMLP. EGCG in the range of 40-400 microM had no effect on PLD activity but it inhibited the release of beta-glucuronidase and elastase by fMLP-stimulated cells. These results demonstrate differential regulation of PLD activity and degranulation of primary granules by genistein and EGCG in fMLP-stimulated neutrophils.

Sensitization of human neutrophil defense activities through activation of platelet-activating factor receptors by ginkgolide B, a bioactive component of the Ginkgo biloba extract EGB 761

Ginkgolide B (GKB, BN 52021) was described as a platelet-activating factor (Paf) receptor antagonist. However, it is not known whether all GKB biological effects are mediated through Paf receptor antagonism only. To gain insight into the drug mode of action, we investigated here the effects of GKB per se on functional and signaling activities in human polymorphonuclear leukocytes (PMN). Treatment of PMN with GKB (0.5-12 microM) stimulates a rapid and weak production of reactive oxygen species determined by chemiluminescence. ROS production required the activation of protein kinase C (PKC), tyrosine kinases and p38 mitogen-activated protein kinase as indicated by inhibitory effects of, respectively, GF 109203X (IC(50) of 0.5 microM), genistein (IC(50) of 0.5 microM) and SB 203580 (IC(50) of 0.2 microM) or SB 202190 (IC(50) of 1.1 microM). GKB stimulated a Pertussis toxin-sensitive PLD activity assessed by the formation of tritiated phosphatidic acid and choline. By contrast, GKB did prevent the Paf-mediated PLD activity and CL response (IC(50) of 2 microM). Interestingly, both GKB and Paf-induced CL response were prevented by selective Paf antagonists such as CV 6209 or WEB 2086 indicating that GKB may directly activate Paf receptors. Finally, GKB potentiated the CL response induced by fMet-Leu-Phe and zymosan. These results show that GKB is the first partial agonist of the Paf receptor described so far capable of priming the polymorphonuclear leukocyte function.

Inhibition of superoxide anion generation by YC-1 in rat neutrophils through cyclic GMP-dependent and -independent mechanisms

3-(5'-Hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), a soluble guanylyl cyclase (sGC) activator, inhibited formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O(2)*(-)) generation and O(2) consumption in rat neutrophils (IC(50) values of 12.7+/-3.1 and 17.7+/-6.9 microM, respectively). Inhibition of O(2)*(-) generation by YC-1 was partially reversed by the cyclic GMP-lowering agent 6-anilinoquinoline-5,8-quinone (LY83583) and by the Rp isomer of 8-(4-chlorophenylthio)guanosine-3',5'-monophosphorothioate (Rp-8-pCPT-cGMPS), a cyclic GMP-dependent protein kinase inhibitor. In cell-free systems, YC-1 failed to alter O(2)*(-) generation during dihydroxyfumaric acid autoxidation, phorbol 12-myristate 13-acetate (PMA)-activated neutrophil particulate NADPH oxidase preparation, and arachidonic acid-induced NADPH oxidase activation. YC-1 increased cellular cyclic GMP levels through the activation of sGC and the inhibition of cyclic GMP-hydrolyzing phosphodiesterase activity. The plateau phase, but not the initial spike, of fMLP-induced [Ca(2+)](i) changes was inhibited by YC-1 (IC(50) about 15 microM). fMLP- but not PMA-induced phospholipase D activation was inhibited by YC-1 (IC(50) about 28 microM). Membrane-associated ADP-ribosylation factor and Rho A in cell activation was also reduced by YC-1 at a similar concentration range. Neither cytosolic protein kinase C (PKC) activity nor PKC membrane translocation was altered by YC-1. YC-1 did not affect either fMLP-induced phosphatidylinositol 3-kinase activation or p38 mitogen-activated protein kinase phosphorylation, but slightly attenuated the phosphorylation of extracellular signal-regulated kinase. Collectively, these results indicate that the inhibition of the fMLP-induced respiratory burst by YC-1 is mediated by cyclic GMP-dependent and -independent signaling mechanisms.

Regulation of polymorphonuclear leukocyte degranulation and oxidant production by ceramide through inhibition of phospholipase D

Exogenous C(2)-ceramide has been shown to inhibit polymorphonuclear leukocyte (PMN) phagocytosis through inhibition of phospholipase D (PLD) and downstream events, including activation of extracellular signal-regulated kinases 1 and 2, leading to the hyphothesis that the sphingomyelinase pathway is involved in termination of phagocytosis. Here it is postulated that increased PLD activity generating phosphatidic acid and diacylglycerol (DAG) is essential for superoxide release and degranulation and that ceramide, previously shown to be generated during PMN activation, inhibits PLD activation, thereby leading to inhibition of PMN function. When PMNs were primed with granulocyte colony-stimulating factor (G-CSF) and then activated with N-formyl-methionyl-leucyl-phenylalanine (FMLP), C(2)-ceramide (10 microM) completely inhibited release of superoxide, lactoferrin, and gelatinase; the DAG analog sn-1,2-didecanoylglycerol (DiC10) (10 microM) restored oxidase activation and degranulation in the ceramide-treated cells. Similarly, C(2)-ceramide inhibited oxidase activity and degranulation of PMNs treated with cytochalasin B followed by FMLP, and DiC10 restored function. In contrast, C(2)-ceramide did not inhibit phosphorylation of p47phox or p38 mitogen-activated protein kinase, or translocation of p47phox, PLD-containing organelles, adenosine diphosphate-ribosylation factor 1, RhoA, protein kinase C (PKC)-beta or PKC-alpha to the plasma membrane in G-CSF or cytochalasin B-treated, FMLP-activated PMNs. PLD activity increased by 3-fold in G-CSF-primed PMNs stimulated by FMLP and by 30-fold in cytochalasin B-treated PMNs stimulated by FMLP. Both PLD activities were completely inhibited by 10 microM C(2)-ceramide. In conclusion, superoxide, gelatinase, and lactoferrin release require activation of the PLD pathway in primed PMNs and cytochalasin B-treated PMNs. Ceramide may affect protein interactions with PLD in the plasma membrane, thereby attenuating PMN activation.

Cellular mechanisms of inhibition of superoxide anion generation in rat neutrophils by the synthetic isoquinoline DMDI

This study was undertaken to assess the cellular localization of the inhibitory effect of a chemically synthetic isoquinoline compound 1-(3',4'-dimethoxybenzyl)-6,7-dichloroisoquinoline (DMDI) on the formyl-methionyl-leucyl-phenylalanine (fMLP)-induced respiratory burst in rat neutrophils. The DMDI concentration dependently inhibited the superoxide anion (O(2)(*-)) generation and O(2) consumption (IC(50) 12.2+/-4.9 and 15.2+/-8.4 microM, respectively) of neutrophils. DMDI did not scavenge the O(2)(*-) generated during the autoxidation of dihydroxyfumaric acid in a cell-free system. DMDI did not elevate cellular cyclic AMP levels. Inhibition of O(2)(*-) generation by DMDI in neutrophils was not reversed by a cyclic AMP-dependent protein kinase inhibitor, (8R,9S,11S)-(-)-9-hydroxy-9-hexoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a,g]cycloocta[cde]trinden-1-one (KT5720). The DMDI concentration dependently inhibited the late plateau phase but not the initial spike of fMLP-induced [Ca(2+)](i) changes in the presence of extracellular Ca(2+). However, DMDI had no effect on the fMLP-induced [Ca(2+)](i) changes in the absence of extracellular Ca(2+). In addition, DMDI did not affect the fMLP-stimulated phosphatidylinositol 3-kinase (PI3-kinase) activation. DMDI produced a concentration-dependent reduction in the formation of phosphatidic acid and phosphatidylethanol in the presence of ethanol from fMLP-stimulated neutrophils (IC(50) 13.3+/-4.0 and 9.4+/-4.3 microM, respectively). On the basis of the immunoblot analysis of the phosphorylation of the mitogen-activated protein (MAP) kinase, DMDI attenuated the fMLP-stimulated MAP kinase phosphorylation in a similar concentration range. Collectively, these results indicate that the inhibition of the respiratory burst by DMDI in rat neutrophils is mediated through the blockade of phospholipase D and MAP kinase signaling pathways.

Regulation of Salmonella-induced neutrophil transmigration by epithelial ADP-ribosylation factor 6

Salmonella typhimurium elicits an acute inflammatory response in the host intestinal epithelium, characterized by the movement of polymorphonuclear leukocytes (PMN) across the epithelial monolayer to the intestinal lumen. It was recently shown that SipA, a protein secreted by S. typhimurium, is necessary and sufficient to drive PMN transmigration across model intestinal epithelia (Lee, C. A., Silva, M., Siber, A. M., Kelly, A. J., Galyov, E., and McCormick, B. A. (2000) Proc. Natl. Acad Sci. USA 97, 12283-12288). However, the epithelial factors responsible for this process have not been identified. Here, for the first time, we demonstrate that S. typhimurium-induced PMN transmigration across Madin-Darby canine kidney-polarized monolayers is regulated by the GTPase ARF6. Apically added S. typhimurium promoted the translocation of ARF6 and its exchange factor ARNO to the apical surface. Overexpression of a dominant-negative mutant of ARF6 inhibited Salmonella-induced PMN transmigration, which was due to a reduction in apical release of the PMN chemoattractant PEEC (pathogen-elicited epithelial chemoattractant), without affecting bacterial internalization. Furthermore, ARF6 and its effector phospholipase D (PLD) were both required for bacteria-induced translocation of protein kinase C (PKC) to membranes. These results describe a novel signal transduction pathway, in which Salmonella initiates an ARF6- and PLD-dependent lipid signaling cascade that, in turn, directs activation of PKC, release of PEEC, and subsequent transepithelial PMN movement.

Induction of cyclooxygenase-2 protein by lipoteichoic acid from Staphylococcus aureus in human pulmonary epithelial cells: involvement of a nuclear factor-kappa B-dependent pathway

1. This study investigated the role of protein kinase C (PKC) and transcription factor nuclear factor-kappaB (NF-kappaB) in cyclooxygenase-2 (COX-2) expression caused by lipoteichoic acid (LTA), a cell wall component of the gram-positive bacterium Staphylococcus aureus, in human pulmonary epithelial cell line (A549). 2. LTA caused dose- and time-dependent increases in COX-2 expression and COX activity, and a dose-dependent increase in PGE(2) release in A549 cells. The LTA-induced increases in COX-2 expression and COX activity were markedly inhibited by dexamethasone, actinomycin D or cyclohexamide, but not by polymyxin B, which binds and inactivates endotoxin. 3. The phosphatidylcholine-phospholipase C (PC-PLC) inhibitor (D-609) and the phosphatidate phosphohydrolase inhibitor (propranolol) reduced the LTA-induced increases in COX-2 expression and COX activity, while phosphatidylinositol-phospholipase C inhibitor (U-73122) had no effect. The PKC inhibitors (Go 6976, Ro 31-8220 and GF 109203X) and NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC), also attenuated the LTA-induced increases in COX-2 expression and COX activity. 4. Treatment of A549 cells with LTA caused an increase in PKC activity in the plasma membrane; this stimulatory effect was inhibited by D-609, propranolol, or Go 6976, but not by U-73122. 5. Exposure of A549 cells to LTA caused a translocation of p65 NF-kappaB from the cytosol to the nucleus and a degradation of IkappaB-alpha in the cytosol. Treatment of A549 cells with LTA caused NF-kappaB activation by detecting the formation of NF-kappaB-specific DNA-protein complex in the nucleus; this effect was inhibited by dexamethasone, D-609, propranolol, Go 6976, Ro 31-8220, or PDTC. 6. These results suggest that LTA might activate PC-PLC and phosphatidylcholine-phospholipase D to induce PKC activation, which in turn initiates NF-kappaB activation, and finally induces COX-2 expression and PGE(2) release in human pulmonary epithelial cell line.

Molecular characterization of a phosphatidylcholine-hydrolyzing phospholipase C

While searching for a phospholipase C (PLC) specific for phosphatidylcholine in mammalian tissues, we came across such an activity originating from a contamination of Pseudomonas fluorescens. This psychrophilic bacterium was found to contaminate placental extracts upon processing in the cold. The secreted phosphatidylcholine-hydrolyzing PLC was purified by a combination of chromatographic procedures. As substrates, the enzyme preferred dipalmitoyl-phosphatidylcholine and 1-palmitoyl-2-arachidonoyl-phosphatidylcholine over phosphatidylinositol. The active enzyme is a monomer of approximately 40 kDa. As for other bacterial PLCs, the enzyme requires Ca2+ and Zn2+ for activity; dithiothreitol affected the activity due to its chelation of Zn2+, but this inhibition could be compensated for by addition of ZnCl2. The compound D609, described to selectively inhibit phosphatidylcholine-specific PLCs, caused half-inhibition of the P. fluorescens enzyme at approximately 420 microM, while 50-fold lower concentrations similarly affected PLCs from Bacillus cereus and Clostridium perfringens. Partial peptide sequences obtained from the pure P. fluorescens enzyme after tryptic cleavage were used to clone a DNA fragment of 3.5 kb from a P. fluorescens gene library prepared from our laboratory isolate. It contains an ORF of 1155 nucleotides encoding the PLC. There is no significant sequence homology to other PLCs, suggesting that the P. fluorescens enzyme represents a distinct subclass of bacterial PLCs. The protein lacks cysteine residues and consequently contains no disulfide bonds. Interestingly, P. fluorescens reference strain DSMZ 50090 is devoid of the PLC activity described here as well as of the relevant coding sequence.

Ca2+-induced contraction of cat esophageal circular smooth muscle cells

ACh-induced contraction of esophageal circular muscle (ESO) depends on Ca2+ influx and activation of protein kinase Cepsilon (PKCepsilon). PKCepsilon, however, is known to be Ca2+ independent. To determine where Ca2+ is needed in this PKCepsilon-mediated contractile pathway, we examined successive steps in Ca2+-induced contraction of ESO muscle cells permeabilized by saponin. Ca2+ (0.2-1.0 microM) produced a concentration-dependent contraction that was antagonized by antibodies against PKCepsilon (but not by PKCbetaII or PKCgamma antibodies), by a calmodulin inhibitor, by MLCK inhibitors, or by GDPbetas. Addition of 1 microM Ca2+ to permeable cells caused myosin light chain (MLC) phosphorylation, which was inhibited by the PKC inhibitor chelerythrine, by D609 [phosphatidylcholine-specific phospholipase C inhibitor], and by propranolol (phosphatidic acid phosphohydrolase inhibitor). Ca2+-induced contraction and diacylglycerol (DAG) production were reduced by D609 and by propranolol, alone or in combination. In addition, contraction was reduced by AACOCF(3) (cytosolic phospholipase A(2) inhibitor). These data suggest that Ca2+ may directly activate phospholipases, producing DAG and arachidonic acid (AA), and PKCepsilon, which may indirectly cause phosphorylation of MLC. In addition, direct G protein activation by GTPgammaS augmented Ca2+-induced contraction and caused dose-dependent production of DAG, which was antagonized by D609 and propranolol. We conclude that agonist (ACh)-induced contraction may be mediated by activation of phospholipase through two distinct mechanisms (increased intracellular Ca2+ and G protein activation), producing DAG and AA, and activating PKCepsilon-dependent mechanisms to cause contraction.

Resveratrol inhibits the formation of phosphatidic acid and diglyceride in chemotactic peptide- or phorbol ester-stimulated human neutrophils

Resveratrol (trans-3,5,4'-trihydroxystilbene, Res) is a naturally occurring antioxidant found in grape berry skins and red wine. It has anti-inflammatory effects. In this study, we examined the effect of Res on the formation of phosphatidic acid (PA) and diglyceride (DG), in human neutrophils stimulated by formyl-methionyl-leucyl-phenylalanine (fMLP) or by phorbol 12-myristate 13-acetate (PMA). We measured the masses of PA and DG by using a nonradioactive method. Our results showed that Res inhibited the formation of PA in a concentration dependent manner with an IC(50) value of 42.4 and 60.9 microM in fMLP- and PMA-stimulated cells, respectively. Res also suppressed the formation of phosphatidylethanol (PEt), thereby implying inhibition of phospholipase D (PLD) activity. In addition, Res inhibited the formation of both diacylglycerol (DAG) and ether-linked acylglycerol (EAG) induced by fMLP and by PMA. Our results suggest that Res inhibition of PLD activity may contribute to its anti-inflammatory effects.

Phosphatidic acid regulates tyrosine phosphorylating activity in human neutrophils: enhancement of Fgr activity

In human neutrophils, the activation of phospholipase D and the Tyr phosphorylation of proteins are early signaling events upon cell stimulation. We found that the pretreatment of neutrophils with ethanol (0.8%) or 1-butanol (0.3%), which results in the accumulation of phosphatidylalcohol at the expense of phosphatidic acid (PA), decreased the phorbol myristate acetate-stimulated Tyr phosphorylation of endogenous proteins (42, 115 kDa). When neutrophil cytosol was incubated in the presence or absence of PA, these and other endogenous proteins became Tyr-phosphorylated in a PA-dependent manner. In contrast, phosphatidylalcohols exhibited only 25% (phosphatidylethanol) or 5% (phosphatidylbutanol) of the ability of PA to stimulate Tyr phosphorylation in the cell-free assay. Similarly, other phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine, phosphatidylinositol, polyphosphoinositides, and sphingosine 1-phosphate) showed little ability to stimulate Tyr phosphorylation. These data suggest that PA can function as an intracellular regulator of Tyr phosphorylating activity. Gel filtration chromatography of leukocyte cytosol revealed a peak of PA-dependent Tyr phosphorylating activity distinct from a previously described PA-dependent phosphorylating activity (Waite, K. A., Wallin, R., Qualliotine-Mann, D., and McPhail, L. C. (1997) J. Biol. Chem. 272, 15569-15578). Among the protein Tyr kinases expressed in neutrophils, only Fgr eluted exclusively in the peak of PA-dependent Tyr phosphorylating activity. Importantly, Fgr isolated from unstimulated neutrophil lysates showed increased activity in the presence of PA but not phosphatidylbutanol. Moreover, the pretreatment of neutrophils with 1-butanol decreased Fgr activity in cells stimulated with formyl-methionyl-leucyl phenylalanine plus dihydrocytochalasin B. Together, these results suggest a new second messenger role for PA in the regulation of Tyr phosphorylation.

Overexpression of phospholipase D1 in human breast cancer tissues

Phospholipase D (PLD) catalyzes the hydrolysis of phosphatidylcholine (PC) to produce phosphatidic acid (PA) and choline. PLD is a major enzyme implicated in important cellular processes, such as cell proliferation. We designed this study to investigate the expression of PLD in human breast carcinomas and non-malignant tissues using RT-PCR, Western blot analysis, immunohistochemistry and an Arf-dependent PLD activity assay. We examined about 550 bp of PCR product and 120 kDa of PLD protein. Our results showed that PLD protein and mRNA levels were overexpressed in 14 of 17 breast cancer tissues. We also observed increased expression by immunohistochemistry and Arf-dependent PLD activity in microsomes of human breast tumors, which correlated well with PLD expression. PLD expression was elevated in human breast tumors compared with normal breast tissues. These results implicate a possible role of PLD in human breast tumorigenesis and suggest that PLD may be useful as a marker for malignant disease in the breast.

Phospholipase D and priming of the respiratory burst by H(2)O(2) in NR8383 alveolar macrophages

Previous investigation showed that preincubation within a range of nontoxic H(2)O(2) concentrations enhanced subsequently stimulated superoxide production by rat alveolar macrophages in response to various stimuli. In the present study, the NR8383 rat alveolar macrophage cell line was used to further investigate the priming effect of H(2)O(2). Using nitroblue tetrazolium, which formed an insoluble formazan when reduced by superoxide, modulation of the respiratory burst was visualized in a cell population exposed to a concentration gradient of H(2)O(2) before stimulation. This model system illustrates how H(2)O(2) may constitute a signaling molecule for a feed-forward regulation of the respiratory burst during inflammation. n-Butanol, which allows consumption of phosphatidic acid by the transphosphatidylation reaction, and propanolol, which inhibits phosphatidic acid phosphohydrolase, were used to investigate the possible involvement of phospholipase D in this phenomenon. These two agents were found to inhibit the basal adenosine diphosphate-stimulated respiratory burst. Inhibition of the H(2)O(2)-enhanced respiratory burst was equally or slightly less effective when expressed as percentage of controls. Furthermore, phospholipase D was not activated by H(2)O(2) concentrations that enhance superoxide production. Thus, phospholipase D does not mediate the enhancement of the respiratory burst by H(2)O(2), although it may be activated by high concentrations of this hydroperoxide.

Actin assembly at membranes controlled by ARF6

The small GTPase, ADP-ribosylation factor-6 (ARF6), has been implicated in regulating membrane traffic and remodeling cortical F-actin. Using real-time video analysis of actin assembly in living cells, we investigated the function and mechanism of ARF6 in control of actin assembly. Expression of an activated form of ARF6 that mimicks the GTP-bound form of the GTPase induced actin assembly resulting in the movement of vesicle-like particles, some of which contain markers for pinosomes. Activated ARF6 also stimulated actin assembly at foci on the ventral surface of the cell and stimulated fluid phase pinocytosis. Particle motility induced by ARF6 involved Arp2/3 complex, tyrosine kinase activity, phospholipase D (PLD) and D3-phosphoinositides, but not phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). We conclude that ARF6 regulates actin assembly for pinosome motility and at foci on the ventral cell surface.

Phosphorylation of p22phox is mediated by phospholipase D-dependent and -independent mechanisms. Correlation of NADPH oxidase activity and p22phox phosphorylation

Human neutrophils participate in the host innate immune response, partly mediated by the multicomponent superoxide-generating enzyme NADPH oxidase. A correlation between phosphorylation of cytosolic NADPH oxidase components and enzyme activation has been identified but is not well understood. We previously showed that p22(phox), the small subunit of the membrane-bound oxidase component flavocytochrome b(558), is an in vitro substrate for both a phosphatidic acid-activated kinase and conventional protein kinase C isoforms (Regier, D. S., Waite, K. A., Wallin, R., and McPhail, L. C. (1999) J. Biol. Chem. 274, 36601-36608). Here we show that several neutrophil agonists (phorbol myristate acetate, opsonized zymosan, and N-formyl-methionyl-leucyl-phenylalanine) induce p22(phox) phosphorylation in intact neutrophils. To determine if phospholipase D (PLD) is needed for p22(phox) phosphorylation, cells were pretreated with ethanol, which reduces phosphatidic acid production by PLD in stimulated cells. Phorbol myristate acetate-induced phosphorylation of p22(phox) and NADPH oxidase activity were not reduced by ethanol. In contrast, ethanol reduced both activities when cells were stimulated by N-formyl-methionyl-leucyl-phenylalanine or opsonized zymosan. Varying the time of stimulation with opsonized zymosan showed that the phosphorylation of p22(phox) coincides with NADPH oxidase activation. GF109203X, an inhibitor of protein kinase C and the phosphatidic acid-activated protein kinase, decreased both p22(phox) phosphorylation and NADPH oxidase activity in parallel in opsonized zymosan-stimulated cells. Stimulus-induced phosphorylation of p22(phox) was on Thr residue(s), in agreement with in vitro results. Overall, these data show that NADPH oxidase activity and p22(phox) phosphorylation are correlated and suggest two mechanisms (PLD-dependent and -independent) by which p22(phox) phosphorylation occurs.