Activation of human neutrophil NADPH-oxidase in vitro by the catalytic fragment of protein kinase-C

Cell-Free NADPH Oxidase Activation Assays: A Triumph of Reductionism

The superoxide (O₂^·-)-generating NADPH oxidase complex of phagocytes comprises a membrane-associated heterodimeric flavocytochrome, known as cytochrome b ₅₅₈ (consisting of NOX2 and p22^phox) and four cytosolic regulatory proteins, p47^phox, p67^phox, p40^phox, and the small GTPase Rac. Under physiological conditions, in the resting phagocyte, O₂^·- generation is initiated by engagement of membrane receptors by a variety of stimuli, followed by signal transduction sequences leading to the translocation of the cytosolic components to the membrane and their association with the cytochrome, a process known as NADPH oxidase assembly. A consequent conformational change in NOX2 initiates the electron flow along a redox gradient, from NADPH to molecular oxygen (O₂), leading to the one-electron reduction of O₂ to O₂^·-. Historically, methodological difficulties in the study of the assembled complex derived from stimulated cells, due to its lack of stability, led to the design of "cell-free" systems (also known as "broken cells" or in vitro systems). In a major paradigm shift, the cell-free systems have as their starting point NADPH oxidase components derived from resting (unstimulated) phagocytes, or as in the predominant method at present, recombinant proteins representing the components of the NADPH oxidase complex. In cell-free systems, membrane receptor stimulation and the signal transduction sequence are absent, the accent being placed on the actual process of assembly, all of which takes place in vitro. Thus, a mixture of the individual components of the NADPH oxidase is exposed in vitro to an activating agent, the most common being anionic amphiphiles, resulting in the formation of a complex between cytochrome b ₅₅₈ and the cytosolic components and O₂^·- generation in the presence of NADPH. Alternative activating pathways require posttranslational modification of oxidase components or modifying the phospholipid milieu surrounding cytochrome b ₅₅₈. Activation is commonly quantified by measuring the primary product of the reaction, O₂^·-, trapped immediately after its generation by an appropriate acceptor in a kinetic assay, permitting the calculation of rates of O₂^·- production, but numerous variations exist, based on the assessment of reaction products or the consumption of substrates. Cell-free assays played a paramount role in the identification and characterization of the components of the NADPH oxidase complex, the performance of structure-function studies, the deciphering of the mechanisms of assembly, the search for inhibitory drugs, and the diagnosis of various forms of chronic granulomatous disease (CGD).

Cell-free NADPH oxidase activation assays: "in vitro veritas"

The superoxide (O2 (∙-))-generating NADPH oxidase complex of phagocytes comprises a membrane-imbedded heterodimeric flavocytochrome, known as cytochrome b 558 (consisting of Nox2 and p22 (phox) ) and four cytosolic regulatory proteins, p47 (phox) , p67 (phox) , p40 (phox) , and the small GTPase Rac. Under physiological conditions, in the resting phagocyte, O2 (∙-) generation is initiated by engagement of membrane receptors by a variety of stimuli, followed by specific signal transduction sequences leading to the translocation of the cytosolic components to the membrane and their association with the cytochrome. A consequent conformational change in Nox2 initiates the electron "flow" along a redox gradient, from NADPH to oxygen, leading to the one-electron reduction of molecular oxygen to O2 (∙-). Methodological difficulties in the dissection of this complex mechanism led to the design "cell-free" systems (also known as "broken cells" or in vitro systems). In these, membrane receptor stimulation and all or part of the signal transduction sequence are missing, the accent being placed on the actual process of "NADPH oxidase assembly," thus on the formation of the complex between cytochrome b 558 and the cytosolic components and the resulting O2 (∙-) generation. Cell-free assays consist of a mixture of the individual components of the NADPH oxidase complex, derived from resting phagocytes or in the form of purified recombinant proteins, exposed in vitro to an activating agent (distinct from and unrelated to whole cell stimulants), in the presence of NADPH and oxygen. Activation is commonly quantified by measuring the primary product of the reaction, O2 (∙-), trapped immediately after its generation by an appropriate acceptor in a kinetic assay, permitting the calculation of the linear rate of O2 (∙-) production, but numerous variations exist, based on the assessment of reaction products or the consumption of substrates. Cell-free assays played a paramount role in the identification and characterization of the components of the NADPH oxidase complex, the deciphering of the mechanisms of assembly, the search for inhibitory drugs, and the diagnosis of various forms of chronic granulomatous disease (CGD).

Anti-nociceptive and anti-inflammatory activities of (-)-α-bisabolol in rodents

(-)-α-Bisabolol is an unsaturated, optically active sesquiterpene alcohol obtained by the direct distillation of essential oil from plants such as Vanillosmopsis erythropappa and Matricaria chamomilla. (-)-α-Bisabolol has generated considerable economic interest, as it possesses a delicate floral odour and has been shown to have antiseptic and gastroprotective activities. In this study, (-)-α-bisabolol was tested in standardised rodent models by gavage administration at doses of 100 and 200 mg/kg in the models of inflammation and 25 and 50 mg/kg in the models of nociception. In the inflammatory models of paw oedema induced by carrageenan and dextran, the mice treated with (-)-α-bisabolol showed smaller oedemas compared to animals treated only with the vehicle. (-)-α-Bisabolol was capable of reducing paw oedemas induced by 5-HT but not oedemas induced by histamine. (-)-α-Bisabolol demonstrated anti-nociceptive activity in the models of visceral nociception induced by acetic acid and in the second phase of the nociception test induced by the intraplantar administration of formalin. (-)-α-Bisabolol did not have any effect in a thermal nociception model using a hot plate but was able to diminish mechanical inflammatory hypernociception evoked by carrageenan. These findings suggest that the anti-nociceptive action of (-)-α-bisabolol is not linked to a central mechanism but instead is related to the inflammatory process. (-)-α-Bisabolol was able to decrease leukocyte migration, protein extravasations and the amount of TNF-α to the peritoneal cavity in response to carrageenan. Additionally, (-)-α-bisabolol reduced neutrophil degranulation in response to phorbol-myristate-acetate. We demonstrate, for the first time, the peripheral anti-inflammatory and anti-nociceptive activities of (-)-α-bisabolol.

Macrophage inflammatory protein-1 alpha mediated growth inhibition in a haemopoietic stem cell line is associated with inositol 1,4,5 triphosphate generation

Macrophage Inflammatory Protein-1 alpha (MIP-1 alpha) can inhibit the proliferation of multipotent haemopoietic cells. Using the FDCP-Mix A4 multipotent stem cell line, MIP-1 alpha was shown to inhibit 1L-3 stimulated cell cycling (assessed using the [3H]-thymidine "suicide" assay). Furthermore, MIP-1 alpha can inhibit 1L-3-stimulated [3H]-thymidine incorporation in FDCP-Mix cells, with half maximal inhibition observed at 3 ng/ml MIP-1 alpha. Prostaglandin E2, but not MIP-1 alpha was able to elevate cyclic AMP levels in FDCP-Mix A4 cells although both agents can cause growth inhibition. However, MIP-1 alpha addition resulted in a pertussis-toxin-insensitive increase in the level of the second messenger inositol 1,4,5 triphosphate (Ins 1,4,5P3). This response was both rapid (maximal at 5 seconds) and transient. A half maximal effect was observed at 5 ng/ml MIP-1 alpha and the dose dependency correlated with that for MIP-1 alpha mediated growth inhibition. A rapid increase in cytosolic Ca2+ levels was also observed in response to MIP-1 alpha. Inositol lipid hydrolysis and an increase in cytosolic Ca2+ (signals normally associated with proliferation) may therefore be implicated in growth inhibitory mechanisms in multipotent cells.

The Malmö biomarker programme

Evaluation of pro-oxidant/antioxidant dietary factors in relation to individual susceptibility to cancer and cardiovascular disease is justified based on a review of the literature. This working hypothesis is amendable to further scientific validation from biomarkers with end-point sensitivity to oxygen radicals. So far, the biomarker programme developed around this theme may be divided into three distinct classes: (1) Markers of genotoxic exposure estimate DNA damage either directly as a biologically effective dose, or indirectly by estimating aberrant cellular functions that lead to accumulation of DNA damage. The examples included are ADP-ribosylation in mononuclear leucocytes (R. Pero, A. Olsson), oxidative DNA damage (K. Frenkel), gene expression in lymphocytes (S. Garte, G. Cosma), serum alpha macroglobulin (W. Troll) and oxidized DNA damage and repair (N. Christie). (2) Markers of genetic predisposition have been shown to have genetic inheritance patterns that relate to individual susceptibility to cancer or cardiovascular disease. The examples included are glutathione transferase mu phenotyping (R. Pero, J. Seidegård) and poly (ADP-ribose) polymerase pseudogene polymorphism (M. Smulson). (3) Markers of dietary status have been validated to estimate the amount of a particular nutrient or xenobiotic in the diet that has been taken up and metabolized or distributed to body fluids or tissues. The example included here is niacin nutriture (E. Jacobson, M. Jacobson). This biomarker is presented in Section 5 (pp. 59-62) of the Malmö Diet and Cancer Programme Minisymposium reported in this issue of the journal.

Haemopoietic stem cell development to neutrophils is associated with subcellular redistribution and differential expression of protein kinase C subspecies

Multipotential FDCP-Mix A4 (A4) cells can be induced either to self-renew or to differentiate and develop into mature neutrophils in liquid culture, depending on the haemopoietic growth factors with which they are cultured. When cultured in low concentrations of interleukin 3 (IL-3, 1 unit/ml)) plus Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) and Granulocyte-CSF (G-CSF), A4 cells proliferate with accompanying development to form cells which resemble mature, postmitotic neutrophils. The presence of high concentrations of IL-3 (100 units/ml) blocks the development of A4 cells even in the presence of GM-CSF plus G-CSF. A4 cell development to neutrophils is accompanied by major changes in the expression of protein kinase C (PKC) subspecies in these cells. The predominant subspecies present in multipotent A4 cells, as judged by direct chromatographic analysis, was the type III enzyme (alpha) subspecies, whereas in mature A4 cell neutrophils, the type II (beta I + beta II) enzymes were predominant. Phorbol esters added to immature A4 cells resulted in a proliferative response, but when added to postmitotic A4 cells resembling neutrophils they elicited a large increase in reactive oxygen intermediate production. This suggests that the type III (alpha) subspecies may mediate proliferative responses in stem cells, whilst the type II (beta I + beta II) enzymes are more important for the mature cell functions of postmitotic neutrophils. In cultures containing IL-3 (100 units/ml) both the type III, and also the type II subspecies were predominantly membrane-associated for prolonged periods (> 24 hours).(ABSTRACT TRUNCATED AT 250 WORDS)

Examination of the role of the proteolytically-activated form of protein kinase C in the differentiation of human haemopoietic cells

In neutrophils, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) induced the translocation of the Ca(++)- and phospholipid-dependent protein kinase, protein kinase C (PK-C) from the soluble to the particulate fraction. At the same time there was a corresponding increase in the amount of Ca(++)- and phospholipid-independent protein kinase activity recovered in the soluble fraction. This soluble Ca(++)- and phospholipid-independent protein kinase presumably reflects proteolytic activation of the particulate associated PK-C. Bone marrow and undifferentiated HL-60 cells also translocated PK-C to the particulate fraction in response to TPA but did not accumulate the soluble Ca(++)- and phospholipid-independent form of the enzyme. Similar results were obtained using HL-60 cells induced to differentiate with dimethyl sulphoxide (DMSO), recombinant human granulocyte-macrophage colony-stimulating factor (rh GM-CSF) or 1 alpha,25-dihydroxyvitamin D3. There was also no significant change in either the number or time of expression of differentiation-specific cell surface antigens observed on HL-60 cells induced to differentiate with either DMSO, 1 alpha,25-dihydroxyvitamin D3 or TPA in the presence of cyclosporin A, an agent reported to inhibit the proteolytic breakdown of PK-C to the Ca(++)- and phospholipid-independent form. Likewise, cyclosporin A did not affect the rate of extent of differentiation of primary bone marrow cell cultures. These results suggest that the proteolytically activated and phospholipid-independent form of PK-C is probably not involved in haemopoietic cell differentiation.

Purification of PKC-I, an endogenous protein kinase C inhibitor, and types II and III protein kinase C isoenzymes from human neutrophils

Human neutrophil protein kinase C (PKC) activity is inhibited by an endogenous protein found primarily in the pellet fraction from homogenized specific granules, which was both heat- and proteinase-sensitive [Balazovich, Smolen & Boxer (1986) J. Immunol. 137, 1665-1673]. We now report that two PKC isoenzymes and the endogenous PKC inhibitor, which we named PKC-I, were purified from human neutrophils. A neutrophil soluble fraction that was subjected to DEAE-Sephacel chromatography yielded highly enriched PKC because, by definition, enzymic activity was strictly dependent on Ca2+ and phosphatidylserine. Hydroxyapatite chromatography resolved two peaks of PKC activity. Type II and Type III PKC isoenzymes were each identified on Western blots by using isoenzyme-specific monoclonal antibodies. Unlike rat brain, from which PKC isoenzymes were also purified, Type I PKC was not detected in human neutrophils. Western blots indicated that both Type II and Type III PKC isoenzymes had molecular masses near 80 kDa. In agreement with other reports, PKC was autophosphorylated in vitro. PKC-I, an endogenous neutrophil inhibitor of PKC, was purified to apparent homogeneity by DEAE-Sephacel and S-400 Sephacel chromatography. PKC-I had a molecular mass of 41 kDa. PKC-I inhibited purified PKC activity stimulated by 1,2-diacylglycerols in a concentration-dependent manner, and inhibited PKC-dependent phosphorylation of proteins present in neutrophil cytosol.

Protein kinase C involved in zymosan-induced release of arachidonic acid and superoxide but not in calcium ionophore-elicited arachidonic acid release or formation of prostaglandin E2 from added arachidonate

Zymosan and phorbol ester induced in liver macrophages the release of arachidonic acid, prostaglandin E2, and superoxide; the calcium ionophore A 23187 elicited a release of arachidonic acid and prostaglandin E2 but not of superoxide, and exogenously added arachidonic acid led to the formation of prostaglandin E2 only. The zymosan- and phorbol-ester-induced release of arachidonic acid, prostaglandin E2, and superoxide was dose-dependently inhibited by staurosporine and K252a, two inhibitors of protein kinase C, and by pretreatment of the cells with phorbol ester which desensitized protein kinase C. The release of arachidonic acid or prostaglandin E2 following the addition of A 23187 or arachidonic acid was not affected by these treatments. Zymosan and phorbol ester but not A 23187 or arachidonic acid induced a translocation of protein kinase C from the cytosol to membranes in intact cells. These results demonstrate an involvement of protein kinase C in the zymosan- and phorbol-ester-induced release of arachidonic acid, prostaglandin E2, and superoxide; the release of arachidonic acid and prostaglandin E2 elicited by A 23187 and the formation of prostaglandin E2 from exogenously added arachidonic acid, however, is independent of an activation of protein kinase C.

Nuclear protein kinases in rat liver: evidence for increased histone H1 phosphorylating activity during liver regeneration

Comparison of protein kinase activity in normal and regenerating rat liver nuclei indicates that exogenous histone H1 is hyperphosphorylated in 22-h regenerating nuclei. The protein kinase involved is not sensitive to protein kinase A inhibitor, is inhibited by staurosporine and by an anti-PKC polyclonal antibody, utilizes only ATP, and also phosphorylates the C-terminal fragment of histone H1. These data suggest that protein kinase C is responsible for the observed effects, in agreement with the presence of this enzyme in normal and regenerating nuclei demonstrated by immunoblotting.

Protein kinase C and T cell activation

Understanding the intracellular mechanisms by which binding of ligands, such as hormones and growth factors, to their specific receptors elicits the appropriate cellular response has long been a topic of great interest. Considerable excitement was generated when it was recognised that several receptor-ligand interactions operate via the hydrolysis of inositol phospholipids. This yields, at least, two 'second messengers', namely, inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], which causes the release of Ca2+ from intracellular stores, and 1,2-diacylglycerol (ac2Gro), which activates the serine/threonine-specific enzyme, protein kinase C(PKC), reviewed in [1] and [2]. The pertinent question that follows is, how do PKC activation and elevation of the intracellular Ca2+ concentration evoke cell responses? In this review, attention has been focused on PKC, and the consequences of its activation in resting human T cells. Evidence that PKC activity is, at least partially, responsible for activation of resting human T cells will be examined, and some of the more recent research investigating how PKC activation elicits this cell response will be described.

Involvement of protein kinase C in activation of human granulocytes and peritoneal macrophages by type 1 fimbriated (mannose specific) Escherichia coli

Specific binding of bacteria to phagocytic cells mediated by antibody and complement (opsonins) or by lectin-carbohydrate interactions is required for their efficient uptake and killing by opsonophagocytosis or lectinophagocytosis, respectively (Ofek and Sharon, Infect. Immun. 56, 539, 1988). An early step in these processes is activation of the phagocytes by the bound bacteria, as evidenced by appearance of an oxidative burst. Previous work has shown that protein kinase C (PKC) is involved in activation of human granulocytes by opsonized Escherichia coli. In the present study, we used three inhibitors of PKC to examine the possible involvement of the enzyme in activation of human granulocytes and peritoneal macrophages by type 1 fimbriated (mannose-specific) Escherichia coli in the absence of opsonins. Activation, as measured by chemiluminescence, was completely inhibited by sphingosine (50 microM) and only partially (50%) by 100 microM H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine]; in both cases it was fully reversible. The third inhibitor, K252a, also inhibited almost completely the activation at 1 microM. The inhibitors acted similarly on activation of the phagocytic cells by opsonized bacteria or by phorbol-12-myristate-13-acetate (0.1 microM). Down regulation of the kinase, by pretreatment of the human granulocytes or macrophages with a high concentration (1.6 microM) of phorbol myristate acetate, abolished their ability to respond to stimulation by the bacteria. Our findings provide evidence for the involvement of PKC in the activation of phagocytic cells by type 1 fimbriated bacteria.