Diacylglycerol kinase inhibitor R59022 and stimulated neutrophil responses

Antineutrophil Cytoplasm Antibody–Stimulated Neutrophil Adhesion Depends on Diacylglycerol Kinase–Catalyzed Phosphatidic Acid Formation

Patients with certain forms of systematic vasculitis, such as Wegener's granulomatosis, have circulating antineutrophil cytoplasmic antibodies (ANCA). These inappropriately stimulate circulating neutrophils adhere to and thereby obstruct small vessels. This, together with ANCA-induced degranulation and an oxidative burst, leads to local tissue damage. The signaling pathways that are activated by ANCA IgG are distinct from those that are involved in normal neutrophil activation. This study shows that diacylglycerol kinase is selectively activated by ANCA and that the generated phosphatidic acid is responsible for promoting neutrophil adhesion, in part through integrin activation. The data presented point to diacylglycerol kinase alpha as a novel but selective target for the development of drugs to treat this potentially fatal disorder.

Differentiation of HL-60 cells to granulocytes involves regulation of select diacylglycerol kinases (DGKs)

Diacylglycerol Kinases (DGKs) are a family of enzymes that regulate the levels of different pools of diacylglycerol (DAG), affecting DAG-mediated signal transduction. Since DAG is known to play several important regulatory roles in granulocyte physiology, we investigated the expression pattern of DGK isoforms throughout differentiation of HL-60 cells to granulocytes. HL-60 cells were incubated with 1.25% dimethyl-sulfoxide (DMSO) to initiate differentiation and total RNA isolated at different time points. DGK expression was assessed through Northern blot, end-point PCR, and real-time PCR. The non-selective inhibitors R59022 and R59949 were used to block DGK at different time points throughout differentiation. CD11b and GPI-80, reactive oxygen species (ROS) generation, changes in the cell cycle, and apoptosis were used as markers of differentiation. Of the nine isoforms of DGK evaluated (alpha, delta, epsilon, gamma, zeta, beta, theta;, iota, eta), only five (alpha, delta, epsilon, gamma, and zeta) were expressed in HL-60 cells. DGKalpha was virtually absent in non-differentiated cells, but was markedly upregulated throughout differentiation. The other isoforms (delta, epsilon, gamma, and zeta) were expressed in undifferentiated HL-60 cells but were substantially decreased throughout differentiation. Non-selective blocking of DGK with R59022 and R59949 led to acceleration of differentiation, reducing the time necessary to observe upregulation of CD11b, GPI-80 and generation of ROS by 50%. Likewise, the cell cycle was disrupted when DGK isoforms were inhibited. These results provide evidence that DGK levels are dynamically regulated throughout differentiation and that expression of DGKs play an important regulatory function during the differentiation of neutrophils.

A molecular defect in intracellular lipid signaling in human neutrophils in localized aggressive periodontal tissue damage

Host defense mechanisms are impaired in patients with congenital neutrophil (polymorphonuclear neutrophils (PMN)) defects. Impaired PMN chemotaxis is observed in localized aggressive periodontitis (LAP), a familial disorder characterized by destruction of the supporting structures of dentition. In the present studies, we sought evidence for molecular events underlying this aberrant human PMN phenotype. To this end, PMN transendothelial migration and superoxide anion generation were assessed with LAP patients and asymptomatic family members, as well as patients with other chronic mucosal inflammation. PMN from LAP patients showed decreased transmigration across vascular endothelial monolayers (18 +/- 12% of control, n = 4) and increased superoxide anion generation (358 +/- 37%, p = 0.003). Gene expression was analyzed using oligonucleotide microarrays and fluorescence-based kinetic PCR. cDNA microarray and kinetic-PCR analysis revealed diminished RNA expression of leukocyte-type diacylglycerol (DAG) kinase alpha in PMN from LAP patients (4.6 +/- 1.7 relative units, n = 6, p = 0.007) compared with asymptomatic individuals (51 +/- 27 relative units, n = 7). DAG kinase activity was monitored by DAG phosphorylation and individual DAG molecular species were quantified using liquid chromatography and tandem mass spectrometry-based lipidomics. DAG kinase activity was also significantly decreased (73 +/- 2%, p = 0.007) and correlated with increased accumulation of 1,2-diacyl-sn-3-glycerol substrates (p = 0.01). These results implicate defects in both PMN transendothelial migration and PMN DAG kinase alpha signaling as disordered functions in LAP. Moreover, they identify a potential molecular lesion in PMN signal transduction that may account for their aberrant responses and tissue destruction in this disease.

Selectivity of the diacylglycerol kinase inhibitor 3-[2-(4-[bis-(4-fluorophenyl)methylene]-1-piperidinyl)ethyl]-2, 3-dihydro-2-thioxo-4(1H)quinazolinone (R59949) among diacylglycerol kinase subtypes

Diacylglycerol kinases (DGKs) attenuate diacylglycerol-induced protein kinase C activation during stimulated phosphatidylinositol turnover. This reaction also initiates phosphatidylinositol resynthesis. Two agents, 3-(2-(4-[bis-(4-fluorophenyl)methylene]-1-piperidinyl)ethyl)-2,3-dihydro -2-thioxo-4(1H)quinazolinone (R59949) and 6-(2-(4-[(4-fluorophenyl)phenylmethylene]-1-piperidinyl)ethyl)-7-m ethyl-5H-thiazolo(3,2-a)pyrimidin-5-one (R59022), inhibit diacylglycerol phosphorylation in several systems. To examine the mechanism of this effect, we developed a mixed micelle method suitable for in vitro study of DGK inhibition. Animal cells express multiple DGK isoforms. In a survey of DGK isotypes, these agents selectively inhibited Ca2+-activated DGKs. R59949 was the more selective of the two. To map the site of interaction with the enzyme, a series of DGKalpha deletion mutants were prepared and examined. Deletion of the Ca2+-binding EF hand motif, which is shared by Ca2+-activated DGKs, had no effect on inhibition. Consistent with this observation, inhibition kinetics were noncompetitive with Ca2+. A construct expressing only the catalytic domain was also inhibited by R59949. Studies of substrate kinetics demonstrated that MgATP potentiated R59949 inhibition, indicating synergy of inhibitor and MgATP binding. These results indicate that R59949 inhibits DGKalpha by binding to its catalytic domain.

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.

Activation of neutrophil migration by dioctanoyl-sn-glycerol and fMet-Leu-Phe is controlled by different pathways

Migration activated by fMet-Leu-Phe is inhibited by GTP[S] and is little affected by protein kinase C inhibitors. We investigated the effects of GTP[S] and the protein kinase C inhibitor AMG-C16 on dioctanoyl-sn-glycerol (DiC8)-activated migration of rabbit neutrophils and compared them with the effects on fMet-Leu-Phe-activated migration and random migration. GTP[S] did not inhibit DiC8-activated migration or random migration but inhibited fMet-Leu-Phe-activated migration. AMG-C16 gave a strong inhibition of DiC8-activated migration but had only a small effect on fMet-Leu-Phe-activated migration and random migration. When fMet-Leu-Phe and DiC8 were added together in suboptimal concentrations an additive effect was found. Pretreatment with the diacylglycerol kinase inhibitor R59022 enhanced random migration. The enhancement was completely inhibited by AMG-C16 and was unaffected by GTP[S]. These findings suggest that DiC8-activated migration and fMet-Leu-Phe-activated migration are controlled by different pathways.

Role of tumor necrosis factor-alpha in Sneddon-Wilkinson subcorneal pustular dermatosis. A model of neutrophil priming in vivo

A patient with IgG-kappa-associated subcorneal pustular dermatosis (Sneddon-Wilkinson disease) refractory to dapsone, etretinate, and plasma exchange was successfully treated with corticosteroids. A study of neutrophils from both blood and pustules was carried out before and during treatment. Levels of tumor necrosis factor-alpha were measured in serum, pustules, content, and supernatant of monocytes. The results suggest that a hyperactivation of neutrophils in the skin is due at least partly to excessive production of tumor necrosis factor-alpha.

Phosphatidic acid accumulation and catecholamine release in adrenal chromaffin cells: stimulation by high potassium and by nicotine, and effect of a diacylglycerol kinase inhibitor R 59 022

Using primary cultures of bovine adrenal chromaffin cells labelled with 32Pi, we show that stimulation with bradykinin, nicotine, or a depolarising concentration of potassium stimulates the accumulation of [32P]phosphatidic acid. The effects of nicotine and potassium are smaller than the effect of bradykinin, and are dependent entirely on extracellular calcium. The diacylglycerol kinase inhibitor R 59 022 attenuates the formation of phosphatidic acid by nicotine and depolarising concentrations of potassium. This inhibitor also blocks the nicotine and potassium stimulation of noradrenaline release from chromaffin cells. Using 45Ca2+ influx studies, we show that the nicotine-evoked calcium influx is also attenuated by R 59 022. These observations contrast with those in another report in which we showed that bradykinin stimulation of either [32P]phosphatidic acid accumulation or noradrenaline release is not affected by R 59 022. It is likely that the calcium influx produced by nicotine and depolarising potassium is blocked by R 59 022 by a mechanism that is independent of its ability to block diacylglycerol kinase. The nicotine- and potassium-stimulated [32P]phosphatidic acid accumulation is a consequence of this calcium influx and presumably reflects calcium activation of either phospholipase C or phospholipase D.

Influence of bradykinin on diacylglycerol and phosphatidic acid accumulation in cultured bovine adrenal chromaffin cells

Earlier studies have shown that bradykinin stimulated release of catecholamines from chromaffin cells by an influx of calcium through dihydropyridine-insensitive channels, and also that bradykinin stimulated (poly)phosphoinositide hydrolysis. To investigate membrane-bound second messengers in chromaffin cells, and to elucidate any role these may play in stimulus-secretion coupling, we have studied the influence of bradykinin on diacylglycerol and phosphatidic acid (PA). Using equilibrium labelling of primary cultures of chromaffin cells with [3H]arachidonic acid or [3H]glycerol, we found no influence of bradykinin (10 nM) on labelled diacylglycerol formation, either in the presence or absence of inhibitors of diacylglycerol lipase or kinase. However, when we used cells prelabelled with 32Pi for 2.5 h, we found that bradykinin produced a substantial stimulation of label found in PA, with an EC50 value of about 1 nM. This bradykinin stimulation of [32P]PA formation was only partially dependent on extracellular calcium, in contrast to the smaller response to nicotine, which was completely dependent on extracellular calcium. Short (10 min) pretreatment with tetradecanoylphorbol acetate (TPA) almost completely eliminated the bradykinin-stimulated formation of inositol phosphates, but failed to affect bradykinin stimulation of label in PA, suggesting that PA production in response to bradykinin is not downstream of phospholipase C activation. TPA alone failed to stimulate [32P]PA substantially, whereas long-term (24 or 48 h) treatment with TPA failed to attenuate the response to bradykinin. Diacylglycerol kinase inhibitors were also without effect on the bradykinin stimulation of [32P]PA. These results suggest that bradykinin stimulates PA production by a mechanism independent of the activation of protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystal-induced neutrophil activation. I. Initiation and modulation of calcium mobilization and superoxide production by microcrystals

The effects of monosodium urate and calcium pyrophosphate dihydrate crystals on the levels of cytoplasmic free calcium and on the oxidative burst in normal human blood neutrophils were examined. The pattern of sensitivity to granulocyte-macrophage colony-stimulating factor, colchicine, cytochalasin B, pertussis toxin, diglyceride kinase, and protein kinase C inhibitors differentiated the mechanism(s) of neutrophil activation by the crystals from that involved in the responses to soluble chemotactic factors and indicated that individual crystals can use several activation pathways.

Influence of phorbol esters, and diacylglycerol kinase and lipase inhibitors on noradrenaline release and phosphoinositide hydrolysis in chromaffin cells

1. We have investigated the modification of catecholamine efflux and inositol phosphate formation in cultured adrenal chromaffin cells by tetradecanoyl phorbol acetate (TPA) and inhibitors of diacylglycerol kinase (R 59,022) and diacylglycerol lipase (RG 80267), the two principal pathways of diacylglycerol metabolism. 2. TPA (1 nM to 1 microM) elicited a slow, calcium-dependent, sustained release of noradrenaline, which was partially blocked by the dihydropyridine calcium channel blocker (-)-202,791 and potentiated by the channel enhancer (+)-202,791. 3. R 59,022 enhanced noradrenaline efflux at 30 and 50 microM, while the lipase inhibitor RG 80267 failed to elicit release. 4. Neither R 59,022 nor RG 80267 affected bradykinin- or histamine-stimulated release, but both drugs substantially attenuated nicotine- and high K(+)-stimulated release. 5. Pretreatment for 10 min with TPA (but not the relatively inactive 4-methoxy TPA) or the non-phorbol protein kinase C stimulator mezerein potently inhibited bradykinin- and histamine-stimulated accumulation of total [3H]-inositol phosphate; inhibition of [3H]-inositol phosphate formation was also seen with 24 h TPA treatment. 6. Neither R 59,022 nor RG 80267, separately or together, affected bradykinin-stimulated [3H]-inositol phosphate formation. 7. Thus while the mechanism exists for inhibition of formation of inositol phosphates by stimulation of protein kinase C, these studies failed to show that this mechanism is activated by agonists acting on phospholipase C linked receptors.

Role of protein kinase C in the regulation of cytosolic Ca2+ in A431 cells: separation of growth factor and bradykinin pathways

Calcium signaling systems in nonexcitable cells involve activation of Ca2+ entry across the plasma membrane and release from intracellular stores as well as activation of Ca2+ pumps and inhibition of passive Ca2+ pathways to ensure exact regulation of free cytosolic Ca2+ concentration [( Ca2+]i). A431 cells loaded with fura-2 cells were used as a model system to examine regulation of Ca2+ entry and intracellular release. Epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha) both stimulated Ca2+ entry and release while bradykinin appeared only to release Ca2+ from intracellular stores. The possible role of protein kinase C (PKC) in modulating the [Ca2+]i response to these agonists was examined by four methods. Low concentrations of TPA (2 x 10(-10) M) had no effect on Ca2+ release due to EGF, TGR-alpha or bradykinin but resulted in a rapid return of [Ca2+]i to baseline levels for EGF or TGF-alpha. Addition of the PKC inhibitor staurosporine (1 and 10 nM) completely inhibited the action of TPA on EGF-induced [Ca2+]i changes. An inhibitor of diglyceride kinase (R59022) mimicked the action of TPA. Down-regulation of PKC by overnight incubation with 0.1 or 1 microM TPA produced the converse effect, namely prolonged Ca2+ entry following stimulation with EGF or TGF-alpha. To show that one effect of TPA was on Ca2+ entry, fura-2 loaded cells were suspended in Mn2+ rather than Ca2+ buffers. Addition of EGF or TGF-alpha resulted in Ca2+ release and Mn2+ entry. TPA but not the inactive phorbol ester, 4-alpha-phorbol-12,13-didecanoate, inhibited the Mn2+ influx. Thus, PKC is able to regulate Ca2+ entry due to EGF or TGF-alpha in this cell type. A431 cells treated with higher concentrations of TPA (5 x 10(-8) M) inhibited not only Ca2+ entry but also Ca2+ release due to EGF/TGF-alpha but had no effect on bradykinin-mediated Ca2+ release, suggesting differences in the regulation of the intracellular stores responsive to these two classes of agonists. Furthermore, sequential addition of EGF or TGF-alpha gave a single transient of [Ca2+]i, showing a common pool of Ca2+ for these agonists. In contrast, sequential addition of EGF (or TGF-alpha) and bradykinin resulted in two [Ca2+]i transients equal in size to those obtained with a single agonist.(ABSTRACT TRUNCATED AT 400 WORDS)

The diacylglycerol kinase inhibitor, R59022, potentiates cholecystokinin-induced enzyme secretion from rabbit pancreatic acini

The putative inhibitor of diacylglycerol kinase activity, 6-(2-[(4-fluorophenyl)phenylmethylene]-1-piperidinyl)-ethyl-7-meth yl-5H- thiazolo[3,2-a]pyrimidin-5-one (R59022), markedly potentiated cholecystokinin-C-terminal-octapeptide(CCK-8-)stimulated enzyme secretion from isolated rabbit pancreatic acini. Maximal potentiation occurred when acini were stimulated in the presence of 5-10 microM R59022. Potentiation depended both on the concentration of R59022 and CCK-8. No potentiation was observed when acini were half-maximally stimulated, whereas the secretory response to maximal and supramaximal concentrations of secretagogue was increased by 50-60%. R59022 alone had no effect on basal enzyme secretion and the drug did not potentiate the secretory response to the Ca2+ ionophore A23187 or to the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate. Moreover, no increase in basal secretion was observed when acini were incubated in the presence of both R59022 and forskolin. These observations strongly suggest that receptor-mediated activation of the inositol phospholipid pathway is required for R59022-induced potentiation. R59022 inhibited the CCK-8-stimulated incorporation of 32Pi into phosphatidic acid dose dependently, without affecting the CCK-8-stimulated hydrolysis of 32P-labelled phosphatidylinositol 4,5-bisphosphate. This is consistent with an inhibitory effect of R59022 on acinar cell diacylglycerol kinase activity. The potentiating effect of R59022 was mimicked by 12-O-tetradecanoylphorbol 13-acetate added simultaneously with CCK-8. Therefore, it is concluded that in the presence of 5-10 microM R59022 the receptor-mediated increase in acinar cell diacylglycerol content is enhanced leading to enhanced activation of protein kinase C and to potentiation of the secretory response. The fact that the secretory response to maximal and supramaximal concentrations of CCK-8 is potentiated by R59022 suggests that at these concentrations of secretagogue the diacylglycerol/protein kinase C branch of the signal-transduction route is rate-limiting.

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.

Protein kinases in neutrophils: a review

In chemotactic factor-stimulated neutrophils, rapid increases of intracellular levels of cyclic AMP, calcium, and diacylglycerol have been observed and may be linked to protein kinase activation. The study of the physiological role and regulation of protein kinases in the neutrophil and the identification of their substrates has provided valuable information on the molecular mechanism of neutrophil activation. The focus of this review is on those aspects of protein kinases that are relevant to neutrophil activation and on the substrate proteins for these protein kinases. The possible role of protein phosphorylation in neutrophil function is also discussed.