The diacylglycerol kinase inhibitor, R59022, enhances the superoxide generation from human neutrophils induced by stimulation of fMet-Leu-Phe, IgG and C3b receptors

Potential role of diacylglycerol kinases in immune-mediated diseases

The mechanism promoting exacerbated immune responses in allergy and autoimmunity as well as those blunting the immune control of cancer cells are of primary interest in medicine. Diacylglycerol kinases (DGKs) are key modulators of signal transduction, which blunt diacylglycerol (DAG) signals and produce phosphatidic acid (PA). By modulating lipid second messengers, DGK modulate the activity of downstream signaling proteins, vesicle trafficking and membrane shape. The biological role of the DGK α and ζ isoforms in immune cells differentiation and effector function was subjected to in deep investigations. DGK α and ζ resulted in negatively regulating synergistic way basal and receptor induced DAG signals in T cells as well as leukocytes. In this way, they contributed to keep under control the immune response but also downmodulate immune response against tumors. Alteration in DGKα activity is also implicated in the pathogenesis of genetic perturbations of the immune function such as the X-linked lymphoproliferative disease 1 and localized juvenile periodontitis. These findings suggested a participation of DGK to the pathogenetic mechanisms underlying several immune-mediated diseases and prompted several researches aiming to target DGK with pharmacologic and molecular strategies. Those findings are discussed inhere together with experimental applications in tumors as well as in other immune-mediated diseases such as asthma.

Beyond Lipid Signaling: Pleiotropic Effects of Diacylglycerol Kinases in Cellular Signaling

The diacylglycerol kinase family, which can attenuate diacylglycerol signaling and activate phosphatidic acid signaling, regulates various signaling transductions in the mammalian cells. Studies on the regulation of diacylglycerol and phosphatidic acid levels by various enzymes, the identification and characterization of various diacylglycerol and phosphatidic acid-regulated proteins, and the overlap of different diacylglycerol and phosphatidic acid metabolic and signaling processes have revealed the complex and non-redundant roles of diacylglycerol kinases in regulating multiple biochemical and biological networks. In this review article, we summarized recent progress in the complex and non-redundant roles of diacylglycerol kinases, which is expected to aid in restoring dysregulated biochemical and biological networks in various pathological conditions at the bed side.

DGKα in Neutrophil Biology and Its Implications for Respiratory Diseases

Diacylglycerol kinases (DGKs) play a key role in phosphoinositide signaling by removing diacylglycerol and generating phosphatidic acid. Besides the well-documented role of DGKα and DGKζ as negative regulators of lymphocyte responses, a robust body of literature points to those enzymes, and specifically DGKα, as crucial regulators of leukocyte function. Upon neutrophil stimulation, DGKα activation is necessary for migration and a productive response. The role of DGKα in neutrophils is evidenced by its aberrant behavior in juvenile periodontitis patients, which express an inactive DGKα transcript. Together with in vitro experiments, this suggests that DGKs may represent potential therapeutic targets for disorders where inflammation, and neutrophils in particular, plays a major role. In this paper we focus on obstructive respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD), but also rare genetic diseases such as alpha-1-antitrypsin deficiency. Indeed, the biological role of DGKα is understudied outside the T lymphocyte field. The recent wave of research aiming to develop novel and specific inhibitors as well as KO mice will allow a better understanding of DGK's role in neutrophilic inflammation. Better knowledge and pharmacologic tools may also allow DGK to move from the laboratory bench to clinical trials.

ATP- and EGF-stimulated phosphatidulinositol synthesis by two different pathways, phospholipase D and diacylglycerol kinase, in A-431 epidermoid carcinoma cells

The [(3)H]inositol incorporation into the membrane fraction of A-431 human epidermoid carcinoma cells was markedly increased by stimulation of the cells with either epidermal growth factor (EGF), ATP, bradykinin, or a calcium ionophore A23187 in the presence of 1 mM extracellular calcium ions; most incorporated [(3)H]inositol was found to have accumulated as phosphatidylinositol (PI). The EGF- and ATP-stimulated PI synthesis was inhibited by two protein kinase C inhibitors, staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), and an intracellular calcium chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA/AM), but not by the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). Pretreatment of cells with pertussis toxin (IAP, islet-activating protein) inhibited the PI synthesis, [Ca(2+)]i elevation, and inositol trisphosphate (IP(3)) production by ATP, suggesting that the phospholipase C(PLC) system coupled with IAP-sensitive G protein is involved in the ATP-stimulated PI synthesis. On the other hand, the ATP stimulation increased the release of [(3)H]choline and [(32)P)phosphatidic acid (PA) from radiolabeled cells, and such release was not inhibited by IAP. In the presence of n-butyl alcohol, which prevents the production of PA by generation of phosphatidylbutanol, the ATP-stimulated PI synthesis was reduced. Because n-butyl alcohol did not inhibit IP(3) production and [Ca(2+)]i elevation, this fact suggests that the lAP-insensitive PLD system is involved in the ATP-stimulated PI synthesis. In A-431 cells, the stimulation of P(2)-purinergic receptors appears to activate the IAP-sensitive PLC system and IAP-insensitive PLD system, both of which are essential for the stimulation of PI synthesis. The present results imply the general prospect that ligand stimulation, which mobilizes second messengers and consumes their precursors, simultaneously provokes the pathway to synthesize and salvage the second messenger precursors as well.

Neutrophil chemotaxis induced by the diacylglycerol kinase inhibitor R59022

The diacylglycerol kinase inhibitor R59022 induced chemotaxis in neutrophils. The response to R59022 was primarily chemotactic and only very little chemokinetic. Pretreatment with the protein kinase C inhibitors staurosporine and AMG-C16 inhibited chemotaxis induced by R59022 indicating the involvement of protein kinase C. In contrast, chemotaxis induced by fMet-Leu-Phe was only slightly inhibited by staurosporine and AMG16. The effects of R59022 were comparable to the effects of the protein kinase C activators DiC8 and PMA and suggest an involvement of protein kinase C. Pretreatment with pertussis toxin inhibited R59022-induced migration, fMet-Leu-Phe-induced migration, and random migration. GTP gamma S, which stimulates migration of electropermeabilized neutrophils by itself, causes an additive increase of migration in electropermeabilized neutrophils stimulated with a suboptimal concentration R59022, but causes a synergistic increase of migration in cells stimulated with a suboptimal concentration fMet-Leu-Phe. The effects of GTP gamma S on migration are completely inhibited by AMG-C16. This suggests that the GTP-binding protein involved in R59022-activated migration is the G protein that is associated with random migration.

Mechanism and regulation of neutrophil priming by platelet-activating factor

Although a weak direct stimulus of superoxide anion (O2-) production, platelet-activating factor (PAF) markedly enhances responses to chemotactic peptides (such as n-formyl-met-leu-phe, FMLP) and phorbol esters (such as phorbol myristate acetate, PMA) in human neutrophils. The mechanism of priming was explored first through inhibition of steps in the signal transduction pathway at and following PAF receptor occupation. Priming was not altered by pertussis toxin or intracellular calcium chelation, but the PAF receptor antagonist WEB 2086 and the protein kinase C (PKC) inhibitors sphinganine and staurosporine significantly inhibited the primed response. In order to study the regulation of PAF priming, the effect of PAF alone was desensitized by exposure to escalating doses of PAF prior to exposure to the secondary stimuli. The priming effect of PAF was not desensitized under these conditions. The role of PKC in desensitization was also studied. Prior exposure to PAF also desensitized the increase in membrane PKC activity evoked by a single concentration of PAF. However, when the PAF response was desensitized, PKC priming of the response to FMLP or PMA still occurred, suggesting that PKC activity may play a role in the maintenance of the primed state despite PAF desensitization. These data suggest that: (1) PAF priming is receptor- and PKC-mediated but is independent of pertussis toxin-inhibitable G-proteins or intracellular calcium, (2) during migration in vivo, neutrophils may be desensitized to the direct effects of PAF but maintain the capacity for enhanced responses to other stimuli, (3) desensitization of PAF-induced particulate PKC activity also occurs, but PAF primes PKC activity despite PAF desensitization, and (4) distinct mechanisms govern the direct and priming effects of PAF on oxidative metabolism.

Cyclooxygenase-independent effects of non-steroidal anti-inflammatory drugs on the neutrophil respiratory burst

A range of 12 non-steroidal anti-inflammatory drugs (NSAIDs), including members from each of the main chemical groups, were examined for their effects on the oxidative burst induced by the receptor stimulus, platelet-activating factor, and the two post-receptor stimuli, fluoride and dioctanoylglycerol. It was found that the NSAIDs fell into three categories: (1) those that increased the stimulated superoxide (O2-) response, (2) those that had no effect and (3) those that decreased O2- production. All the drugs were without effect in unstimulated cells. The mode of action of those drugs that caused enhancement of the O2- response is unlikely to be due to an inhibition of the cyclooxygenase pathway of arachidonate metabolism as not all NSAIDs caused the enhancement. This data could have clinical implications for the therapy of inflammatory disorders such as rheumatoid arthritis, in that those NSAIDs which cause an increased O2- response, while providing temporary relief of symptoms, could be exacerbating the underlying inflammatory condition and associated tissue damage.

A novel conformationally restricted protein kinase C inhibitor, Ro 31-8425, inhibits human neutrophil superoxide generation by soluble, particulate and post-receptor stimuli

A novel, bis-indolylmaleimide, Ro 31-8425, bearing a conformationally restricted side chain, inhibits protein kinase C isolated from rat brain and human neutrophils with a high degree of selectivity over cAMP-dependent kinase and Ca2+/calmodulin-dependent kinase. It also inhibits phorbol ester-induced intracellular events known to be mediated by protein kinase C (p47 phosphorylation in intact platelets, CD3 and CD4 down-regulation in T-cells). Ro 31-8425 inhibited superoxide generation in human neutrophils activated by both receptor stimuli (formyl-methionyl-leucylphenylalanine, opsonized zymosan, IgG and heat aggregated IgG) and post-receptor stimuli (1,2-dioctanoylglycerol and fluoride). The compound also blocked antigen driven, but not IL-2 induced, T-cell proliferation. These results support a central role for protein kinase C in the activation of the respiratory burst and antigen-driven T-cell proliferation.

Cytosolic rat brain synapsin I is a diacylglycerol kinase

The phosphorylation of diacylglycerol (DG), a reaction catalyzed by DG kinase, may be critical in the termination of effector-induced signals mediated by protein kinase C. Synapsin I is a principal target of intracellular protein kinases and is thought to be involved in the release of neurotransmitter from axon terminals. We present several lines of evidence which indicate that rat brain synapsin, in addition to this role, may function as a DG kinase. Purified rat brain DG kinase was digested with trypsin, which produced three major fragments whose sequence was identical to three regions in synapsin I. Using a rabbit anti-synapsin polyclonal antiserum, the elution profile of synapsin immunoreactivity coincided exactly with that of DG kinase activity in column fractions from the final step in the DG kinase purification procedure. As is the case with synapsin, the purified enzyme was a strongly basic protein with an isoelectric point greater than 10.0. Finally, incubating the DG kinase with highly purified bacterial collagenase, an enzyme that partially degrades the proline- and glycine-rich synapsin, resulted in the simultaneous loss of DG kinase activity and synapsin immunoreactivity. We conclude that cytosolic rat brain synapsin is capable of functioning as a DG kinase.

Diacylglycerol and phosphatidate production and the exocytosis of the sperm acrosome

We have investigated the production of diacylglycerol (DAG) and phosphatidate (PtdOH) during the exocytosis of the sperm acrosome. Ram spermatozoa treated with Ca2+ and the ionophore A23187 experienced a rapid breakdown of the polyphosphoinositides (PPIs), and a rise in [32P]Pi-labelled PtdOH and DAG mass; PtdOH mass, however, was unaffected. Treatment with Ca2+/A23187 and the DAG kinase inhibitor R59022 resulted in a dose-dependent increase in DAG mass and a concomitant decrease in [32P]PtdOH; such treatment showed a dose-dependent stimulation of acrosomal exocytosis. Pre-incubation with exogenous PtdOHs before stimulation with Ca2+/A23187 did not affect the time-course of exocytosis, whereas treatment with Ca2+/A23187 and exogenous DAGs (dioctanoylglycerol, oleoyl-acetyl-glycerol, or dioleoylglycerol) resulted in a dose-dependent stimulation of acrosomal exocytosis. Our results suggest that DAG, rather than PtdOH, is the important metabolite generated upon PPI hydrolysis; however, since spermatozoa lack protein kinase C, the target of DAG in most cells, a role for DAG in acrosomal exocytosis is as yet unclear.

The effect of new potent selective inhibitors of protein kinase C on the neutrophil respiratory burst

New potent inhibitors of protein kinase C were found to inhibit protein kinase C isolated from rat brain and human neutrophils, with a large degree of selectivity over cAMP-dependent kinase and Ca2+/calmodulin-dependent kinase. These novel compounds were potent inhibitors of the fluoride, diC8- and formyl-methionyl-leucyl-phenylalanine-mediated respiratory bursts in intact neutrophils. The opsonized zymosan-stimulated burst was only marginally affected by the compounds. These results differ from those obtained in studies with H7 and CI, (which are less potent and less specific protein kinase C inhibitors) and are consistent with the hypothesis that protein kinase C has a role in the transduction mechanism for the neutrophil oxidative burst stimulated with fluoride, formyl-methionyl-leucyl-phenylalanine and diC8.

Key role of diacylglycerol-mediated 12-lipoxygenase product formation in angiotensin II-induced aldosterone synthesis

We have shown earlier that the 12-lipoxygenase product of arachidonic acid (AA), 12-hydroxyeicosatetraenoic acid (12-HETE), plays an important role in mediating angiotensin II (AII)-induced aldosterone secretion (J. Clin. Invest. (1987) 80, 1763). In the present study, we have evaluated whether diacylglycerol (DG) is the source of arachidonic acid giving rise to this 12-HETE. Treatment of rat adrenal glomerulosa cells with a DG lipase inhibitor, RHC 80267, which prevents conversion of DG to AA and HETEs, blocked AII-induced aldosterone and 12-HETE formation. In contrast, a DG kinase inhibitor, R59022, which prevents conversion of DG to phosphatidic acid, potentiated AII-induced aldosterone and 12-HETE formation. These two inhibitors block DG metabolism which would be expected to lead to increased DG levels and protein kinase C activity and AII-induced steroidogenesis. However, only R59022 potentiated AII action while RHC 80267 was inhibitory. This suggests that conversion of DG to AA and 12-HETE is important for AII action. Further proof for this was obtained by measuring [3H]AA-labeled DG levels. The combination of the inhibitors significantly potentiated AII-induced DG formation even though this same combination was inhibitory on AII-induced aldosterone and 12-HETE. Thus, the inhibitory effect of RHC 80267 is due to blockade of AA release and not of DG formation. These results suggest that DG plays a dual role in AII action, both as an activator of protein kinase C and as a source of AA for 12-HETE formation.

The effect of putative protein kinase C inhibitors, K252a and staurosporine, on the human neutrophil respiratory burst activated by both receptor stimulation and post-receptor mechanisms

1. Two compounds, reported to be potent inhibitors of protein kinase C (PKC), K252a and staurosporine, have been examined in order to gain further information as to the possible role played by PKC in the signal transduction sequence of the neutrophil respiratory burst as determined by superoxide (O2-) production. 2. A number of stimuli were used in the study, some acting at receptors i.e. fMet-Leu-Phe (fMLP), opsonized zymosan and heat-aggregated IgG (HAGG), one acting on a G-protein, fluoride, and two direct PKC activators, dioctanoylglycerol (diC8) and phorbol myristate acetate (PMA). 3. K252a and staurosporine inhibited the respiratory burst with all the stimuli but the order of agonist sensitivity was very different with the two inhibitors. 4. For K252a-induced inhibition of O2- release, the order of potency was fluoride greater than fMLP, HAGG greater than opsonized zymosan greater than PMA, DiC8. For staurosporine-induced inhibition of O2- release, the order of potency changed to fluoride greater than DiC8, PMA greater than HAGG, fMLP greater than opsonized zymosan. The significance of this unexpected difference in relative rank order of potency is discussed with reference to the reported mechanism of action of the two inhibitors and the events involved in the oxidative burst. 5. Staurosporine at low concentrations increased the fMLP-stimulated O2- response by 100%, the maximum effect occurring at 35 nM. 6. To the extent that the compounds used are specific inhibitors of PKC, these findings support a role for the enzyme PKC in stimulus-activation coupling in O2- generation with all the stimuli used in this study.

The activation of gold complexes by cyanide produced by polymorphonuclear leukocytes--II. Evidence for the formation and biological activity of aurocyanide

Experiments have been conducted to investigate a possible mechanism which might explain why aurothiomalate (Autm), a gold complex used in the treatment of rheumatoid arthritis, is active in vivo but not in vitro, by testing the hypothesis that Autm is converted to aurocyanide by activated polymorphonuclear leukocytes (PMN) which generate cyanide from thiocyanate, an anion which is present in plasma at concentrations ranging from 20 to 200 microM. Two-stage experiments were conducted in which PMN, in the first stage, were activated by opsonized zymosan in the presence of Autm both with and without thiocyanate. Then, in the second stage, the effect of the drugs on superoxide (O2-) production stimulated by a further addition of zymosan was measured. Autm at concentrations of 10 and 100 microM decreased O2- production if thiocyanate was present, but not if it was absent. By contrast, preformed aurocyanide at 10 and 100 microM decreases O2- production by PMN stimulated by opsonized zymosan both in the presence and absence of thiocyanate. Changes in the ultraviolet spectra of the supernatants of PMN indicated that aurocyanide was formed by activated PMN in the presence of thiocyanate but not in its absence.

Diacylglycerol kinase: a key modulator of signal transduction?

Diacylglycerol kinase (DGK) plays a central role in the metabolism of diacylglycerol released as a second messenger in agonist-stimulated cells. The major purified form of the enzyme (80 kDa DGK) is highly abundant in lymphocyte cytosol and may become membrane-associated via phosphorylation by protein kinase C. In addition, there are several kinase subspecies immunologically distinct from the 80 kDa enzyme, which differ markedly in their responses to several compounds such as sphingosine and R59022. Thus, further work on each enzyme species is needed to define the function of DGK in stimulated cells.

Different effects of sphingosine, R59022 and anionic amphiphiles on two diacylglycerol kinase isozymes purified from porcine thymus cytosol

Porcine thymus cytosol contains two immunologically distinct forms of diacylglycerol kinase (DGK) [Yamada, K. and Kanoh, H. (1988) Biochem. J. 255, 601-608]. These 2 DGK species, having apparent molecular masses of 80 and 150 kDa, were purified from the thymus cytosol. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the 150-kDa DGK gave 2 polypeptide bands of 50 and 75 kDa, whereas the 80-kDa DGK yielded a single protein band. The 80-kDa DGK was markedly activated by 10-20 microM sphingosine as well as by the known anionic activators such as phosphatidylserine and deoxycholate. In contrast, the 150-kDa DGK was fully active in the absence of the anionic activators and was strongly inhibited by sphingosine (IC50, 20 microM). The putative DGK inhibitor R59022 inhibited the 80-kDa DGK (IC50, 10 microM), but had little effect on the 150-kDa form. It is therefore clear that in the thymus cytosol there are at least 2 DGK isozymes operating under different control mechanisms.

Diacylglycerol kinase inhibitors R59022 and dioctanoylethylene glycol potentiate the respiratory burst of neutrophils by raising cytosolic Ca2+

The diacylglycerol kinase inhibitors, R59022 and dioctanoylethylene glycol (diC8-eg), potentiate stimulation of the respiratory burst by the chemotactic tripeptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) in human neutrophils. However, in contrast to the potentiation observed in intact cells, neither R59022 nor diC8-eg enhanced the effect of fMLP on O2 consumption in electropermeabilized neutrophils, under conditions where cytosolic [Ca2+] was held constant using EGTA. In unstimulated, intact cells treatment with the diacylglycerol kinase inhibitors elicited an increase in cytosolic Ca2+ ([Ca2+]i). The results suggest that enhancement of the respiratory burst by diC8-eg and R59022 is mediated by a rise in [Ca2+]i, rather than by inhibition of diacylglycerol kinase.

Phosphorylation of diacylglycerol kinase in vitro by protein kinase C

We investigated the effects of enzyme phosphorylation in vitro on the properties of diacylglycerol kinase. Diacylglycerol kinase and protein kinase C, both present as Mr-80,000 proteins, were highly purified from pig thymus cytosol. Protein kinase C phosphorylated diacylglycerol kinase (up to 1 mol of 32P/mol of enzyme) much more actively than did cyclic AMP-dependent protein kinase. Phosphorylated and non-phosphorylated diacylglycerol kinase showed a similar pI, approx. 6.8. Diacylglycerol kinase phosphorylated by either protein kinase C or cyclic AMP-dependent protein kinase was almost exclusively associated with phosphatidylserine membranes. In contrast, soluble kinase consisted of the non-phosphorylated form. The catalytic properties of the lipid kinase were not much affected by phosphorylation, although phosphorylation-linked binding with phosphatidylserine vesicles resulted in stabilization of the enzyme activity.

Increased protein synthesis response to insulin in fibroblasts treated with the diacylglycerol kinase inhibitor R59022

Insulin stimulated protein synthesis in quiescent 3T3 fibroblasts. This effect of the hormone was greater in the presence of the diacylglycerol kinase inhibitor R59022 (10(-5) M) over a range of insulin concentrations from 1 microU to 1 mU/ml; R59022 increased the sensitivity of cells to insulin. The amount of radioactive diacylglycerol recovered from cells prelabelled with [3H]glycerol was increased transiently in response to insulin; the response was larger and prolonged in cells given the kinase inhibitor. The results (i) support the hypothesis that diacylglycerol production is part of the signal pathway by which insulin stimulates protein synthesis and (ii) suggest that inhibition of diacylglycerol breakdown leads to increased sensitivity to the hormone.

Activation of the respiratory burst oxidase in neutrophils: on the role of membrane-derived second messengers, Ca++, and protein kinase C

A major bactericidal mechanism of neutrophils involves activation of the respiratory burst oxidase to generate superoxide (O2-). The oxidase is activated rapidly, often within a minute, in response to extracellular signals such as chemoattractants, inflammatory mediators, and invading microorganisms. Increasing evidence indicates that lipases also respond rapidly, releasing potent regulatory molecules from progenitor lipids. Released molecules include potential regulators of protein kinase C--diacylglycerol (DAG), arachidonate, and sphingosine--and levels of one of these, DAG, frequently correlate with O2- production. In this author's view, the available data implicate DAG and protein kinase C as key factors in the regulation of the respiratory burst. Herein, the array of activating agonists, the generation and function of some lipid-derived mediators, and evidence pertaining to the participation of protein kinase C are reviewed.

Diacylglycerol kinase inhibitor R59022 and stimulated neutrophil responses

The generation of phosphatidic acid in neutrophils stimulated by the chemotactic factor formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe) is inhibited by the diacylglycerol kinase inhibitor R59022. Superoxide generation produced by fMet-Leu-Phe, leukotriene B4, platelet-activating factor, or phorbol 12-myristate 13-acetate can be greatly increased in neutrophils pretreated with R59022. The potentiation occurs in the presence or absence of cytochalasin B and is evident in the absence of extracellular calcium. In addition, where the superoxide generated by fMet-Leu-Phe is not inhibited by the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), the increase by R59022 is diminished by this compound. Unlike cytochalasin B, R59022 does not affect the increase in cytoskeletal actin produced by fMet-Leu-Phe or platelet-activating factor nor does it decrease the basal level. Furthermore, the basal intracellular concentration of free calcium, but not the rise produced by fMet-Leu-Phe or platelet-activating factor, is elevated by R59022. The data presented here suggest that the potentiation by R59022 of the oxidative burst is most likely mediated through protein kinase C.

The diacylglycerol kinase inhibitor R 59022 potentiates bombesin stimulation of protein kinase C activity and DNA synthesis in Swiss 3T3 cells

Addition of the inhibitor of diacylglycerol kinase R 59022 to quiescent Swiss 3T3 cells potentiated protein kinase C activation by the neuropeptide bombesin, a potent mitogen for these cells. This was detected as a marked shift in the dose-response relationship for bombesin-stimulated phosphorylation of a Mr 80,000 protein, which is a major, specific substrate of protein kinase C. R 59022 also promoted the inhibition of [125I]epidermal growth factor binding induced by bombesin, an effect mediated by protein kinase C. A salient feature of our results is that R 59022, at concentrations that enhanced the activation of protein kinase C in intact cells (4-6 microM), potentiated long-term mitogenesis elicited by bombesin. Thus, R 59022 may be a valuable tool for elucidating the contribution of the protein kinase C pathway in mitogenesis.

The effect of inhibition of both diacylglycerol metabolism and phospholipase A2 activity on superoxide generation by human neutrophils

A 'cocktail' consisting of an inhibitor of diacylglycerol kinase (R59022, 10 microM), an inhibitor of diacylglycerol lipase (RHC80267, 10 microM), and an inhibitor of phospholipase A2 (either 100 microM indomethacin, or 100 microM sodium meclofenamate) markedly enhanced superoxide production by human neutrophils stimulated with post-receptor stimuli, fluoride and gamma-hexachlorocyclohexane. On the other hand, the response to the C3b/Fc receptor stimulus, opsonized zymosan, was marginally decreased whilst that to the Fc receptor stimulus, aggregated IgG, was virtually unaffected. Since the inhibitors used are deemed to inhibit the main routes of arachidonate production, these results call into question the role of arachidonate in the transduction of O2- generation by post-receptor stimuli, but support a role for arachidonate in receptor-mediated transduction.

[3H]phosphatidic acid formed in response to FMLP is not inhibited by R59 022, a diacylglycerol kinase inhibitor

R59 022 has been suggested to function as a selective inhibitor of diacylglycerol kinase in platelets and erythrocyte membranes. In the present study we have studied the effect of this drug on [3H]diacylglycerol and [3H]phosphatidic acid formed in response to FMLP in human neutrophils. Our results indicate that R59 022 (50 microM) itself (without any stimulus) caused a significant hydrolysis of [3H]phosphatidylinositol (6-7%), which resulted in an accumulation of [3H]diacylglycerol and [3H]phosphatidic acid. On the other hand, R59 022 at lower concentrations (10 microM) exhibited a biphasic response on the time-dependent formation of [3H]phosphatidic acid in response to FMLP. [3H]phosphatidic acid formed at 30 sec and 60 sec after stimulation with FMLP was neither inhibited nor stimulated whereas the amount of [3H]phosphatidic acid formed at 2 min and 3 min was significantly higher than that obtained with FMLP alone. Our results demonstrate that the increased formation of diacylglycerol and phosphatidic acid in response to FMLP in the presence of R59 022 is likely due to the activation of phospholipase C and/or D rather than the inhibition of DG kinase. We therefore conclude that R59 022 is relatively nonspecific and can affect several other enzymes involved in the agonist-stimulated turnover of phospholipids.

The actions of inhibitors of diacylglycerol kinase and diacylglycerol lipase on histamine release from rat peritoneal mast cells

1. RHC 80267 and R59 022 are selective inhibitors of diacylglycerol (DAG) lipase and DAG kinase enzymes respectively. These inhibitors were examined with regard to their effects on oleoylacetylglycerol (OAG)-and anti-IgE- induced histamine secretion in rat peritoneal mast cells. 2. RHC 80267, 10 microM and R59 022, 50 microM both enhanced OAG-induced histamine release by 30% and 40% respectively. 3. In the concentration range 3-30 microM, R59 022 enhanced anti-IgE-induced histamine release by up to about 40%, whereas RHC 80267 was without effect. 4. The enhancement of anti-IgE-induced histamine release by R59 022 is consistent with a role for protein kinase C in transducing immunological signals to rat peritoneal mast cells. 5. The lack of effect of RHC 80267 in this situation may indicate that in the mast cell, DAG kinase is more active than DAG lipase in degrading physiological levels of DAG.

The diacylglycerol kinase inhibitor R59022 potentiates superoxide production but not secretion induced by fMet-Leu-Phe: effects of leupeptin and the protein kinase C inhibitor H-7

The addition of low concentrations of the chemotactic factor fMet-Leu-Phe to rabbit neutrophils in the absence of cytochalasin B produces very little superoxide. This level of superoxide can be greatly increased in neutrophils pretreated for 30 min with 10 microM of the diacyl-glycerol kinase inhibitor R59022. This potentiation occurs also in the presence of cytochalasin B. In addition, while the small level of superoxide generated by fMet-Leu-Phe is not inhibited by the protein kinase C inhibitor 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine (H-7), the increase by R59022 is completely abolished by this compound. In addition, this increase can be potentiated further by leupeptin. Unlike superoxide generation, the release of lysozyme or N-acetyl-beta-glucosaminidase produced by fMet-Leu-Phe is not stimulated by R59022. The results presented here suggest that stimulation of the oxidative burst requires the generation and the maintenance of a sufficient amount of diacylglycerol and/or the rearrangement of the cytoskeleton such as the inhibition of actin polymerization. Furthermore, the membrane-associated form of protein kinase C is the one responsible for the activation of the oxidative burst. The relationship between protein kinase C activation and the stimulated oxidative burst and the physiological role of chemotactic factors in the functions of the neutrophils are discussed.

Comparison of the effects of indomethacin, RHC80267 and R59022 on superoxide production by 1,oleoyl-2,acetyl glycerol and A23187 in human neutrophils

1 Indomethacin (10(-4)M) causes marked augmentation of O-2 release from human neutrophils when these are stimulated by either 1,oleoyl-2,acetylglycerol or the divalent cation ionophore, A23187, the concentration-response curve for each agent being shifted to the left and the maximum response to each increased. 2 The diacylglycerol kinase inhibitor, R59022 (10(-5)M) has effects very similar to those of indomethacin on both the 1,oleoyl-2,acetylglycerol-induced and the A23187-induced concentration-response curves for O-2 generation. 3 The diacylglycerol lipase inhibitor, RHC80267 (10(-5 M) on the other hand, has a similar effect to indomethacin on 1,oleoyl-2,acetylglycerol-induced O2- generation but, unlike indomethacin, has no effect on A23187-induced O2- generation. Comparison of the effects of these three agents provides a clue to the locus of the action of indomethacin in increasing superoxide release, suggesting that it may act as a diacylglycerol kinase inhibitor. A component of diacylglycerol lipase inhibition may also be present. It is suggested that these results could have relevance for the use of indomethacin as an anti-inflammatory agent in chronic rheumatoid diseases.