1,2-dioctanoyl-sn-glycerol can stimulate neutrophils by different mechanisms. Evidence for a pathway that does not involve phosphorylation of the 47-kDa protein

Neutrophils treated with 1,2-dioctanoyl-sn-glycerol (DiC8) are known to release large quantities of superoxide (O2-) and to exhibit an intense phosphorylation of two proteins with molecular masses of approximately 47 and 49 kDa. In this paper, we report that O2- release from guinea pig cells stimulated with a near optimal amount of DiC8 (2.0 microM) is markedly inhibited (greater than or equal to 70%) by antagonists of protein kinase C (i.e. 150 nM staurosporine; 200 microM 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7], whereas that from cells stimulated with an optimal amount of DiC8 (7.8 microM) is not (approximately 25% inhibition). However, staurosporine (150 nM) effectively reduced the level of phosphorylation of the 47- and the 49-kDa proteins to that observed in unstimulated cells when either amount of DiC8 (i.e. 2.0 or 7.8 microM) was utilized. Thus, neutrophils stimulated with 7.8 microM DiC8 in the presence of staurosporine release large quantities of O2- without an enhanced phosphorylation of the 47- and the 49-kDa proteins. In contrast, these antagonists of protein kinase C effectively blocked O2- release from neutrophils stimulated with an optimal amount of phorbol 12-myristate 13-acetate (PMA), and the percentage of inhibition was not affected by increasing the concentration of PMA 160-fold. These data show that DiC8 and PMA, both activators of protein kinase C, can have distinct effects on O2- release by neutrophils. Moreover, they suggest that DiC8 (or a metabolite) under certain circumstances may function in a stimulatory pathway for O2- release that is independent of protein kinase C. Differences in the morphology of neutrophils stimulated with PMA and DiC8 are presented. Ancillary data on human neutrophils are also provided.

Protein phosphorylation associated with synergistic stimulation of neutrophils

Neutrophils treated with optimal amounts of tumor promoters that activate protein kinase C (e.g. mezerein) release large quantities of superoxide (O2-) and exhibit an intense phosphorylation of two proteins with molecular masses of approximately 47 and 49 kDa. These cells can also be stimulated synergistically to release a comparable amount of O2-. This involves treatment with a suboptimal amount of a tumor promoter and an agent capable of elevating cellular Ca2+. Neutrophils treated in the former fashion exhibit a redistribution of the activity of protein kinase C from a soluble to a particulate fraction that is stable in the presence of Ca2+ chelators, whereas cells stimulated synergistically do not do so to an appreciable extent (Badwey, J. A., Robinson, J. M., Horn, W., Soberman, R. J., Karnovsky, M. J., and Karnovsky, M. L. (1988) J. Biol. Chem. 263, 2779-2786). In this paper, we report that neutrophils stimulated synergistically do exhibit a significant incorporation of 32P into the 47-kDa protein, but with little labeling of the 49-kDa species. This labeling of the 47-kDa protein was greater than the sum of those observed with each agent added separately but was less than that observed in cells stimulated with optimal amounts of tumor promoters alone. An inhibitor of protein kinase C (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine) blocked O2- release and the phosphorylation of the 47-kDa protein under all conditions of stimulation mentioned, whereas an inhibitor of cyclic nucleotide-dependent kinases had no effect on these phenomena. Thus, labeling of the 47-kDa protein can occur in the absence of a "tight" translocation of protein kinase C to membrane and was always observed during synergy. The data support a role for protein kinase C and the 47-kDa phosphoprotein in the synergistic stimulation of neutrophils.

Paradoxical effects of retinal in neutrophil stimulation

Retinal stimulates the activity of phospholipase C and superoxide (O2-) release in neutrophils. The latter response is comparable in magnitude to that observed when phorbol 12-myristate 13-acetate (PMA) is the stimulating agent. Cells treated with retinal, however, do not undergo degranulation, nor do they exhibit the formation of intracellular vesicles, as is commonly observed with other agents (e.g. Lochner, J. E., Badwey, J. A., Horn, W., and Karnovsky, M. L. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 7673-7677). Retinal promotes redistribution of the activity of protein kinase C from a soluble to a particulate fraction in neutrophils, and this redistribution precedes O2- release. Superoxide release stimulated with retinal, however, is largely insensitive to inhibitors of protein kinase C (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7); staurosporine). These compounds substantially block both O2- release and the phosphorylation of two proteins with molecular masses of about 47 and 49 kDa when the stimulus is PMA. The data indicate that retinal and PMA elicit the formation of active protein kinase C complexes of different natures, or that the mechanism of stimulation of O2- release by retinal does not involve this kinase. The significance of these observations to the common use of retinoids as inhibitors of protein kinase C is discussed.

Phosphorylation of both 47 and 49kDa proteins accompanies superoxide release by neutrophils

Neutrophils stimulated with activators of protein kinase C (i.e., 4 beta-phorbol 12-myristate 13-acetate; sn-1,2-dioctanoylglycerol) exhibit a dramatic, dose-dependent incorporation of 32P[Pi] into two proteins with molecular weights of ca. 47 and 49kDa. Proteins of the same molecular weights are also labelled when the cells are stimulated with a chemotactic peptide. However, with the latter stimulus, labelling of the 47kDa species is transient whereas that of the 49kDa entity persists. Labelling of both proteins always accompanied the release of O2-stimulated by these agents. The kinetics of labelling are compatible with the involvement of both phosphoproteins in the stimulation of these cells.

Respiratory burst oxidase activation can be dissociated from phosphatidylinositol bisphosphate degradation in a cell-free system from human neutrophils

Activation of the respiratory burst oxidase in cell-free preparations from 32P-labeled neutrophils was compared with changes in levels of radioactively labeled phosphoinositides in the same preparations. With membrane particles, treatment with sodium dodecyl sulfate (SDS) in the presence of cytosol led to activation of the oxidase without an alteration in levels of labeled phosphatidylinositol 4,5-bisphosphate (PIP2) or phosphatidylinositol 4-phosphate (PIP). Conversely, solubilization of the membrane particles with deoxycholate resulted in loss of nearly 98% of the radioactive PIP2 without activation of the oxidase. In this solubilized preparation, the oxidase could subsequently be fully activated by SDS in the presence of cytosol, even though the labeled PIP2 was almost totally depleted. Two PIP2-derived second messengers, diacylglycerol and inositol 1,4,5-trisphosphate, as well as the protein kinase C activator phorbol myristate acetate (PMA), failed to activate the oxidase. These results suggest that in a cell-free preparation from human neutrophils, detergent-mediated activation of the respiratory burst oxidase is independent of changes in the levels of phosphoinositides or phosphoinositide-derived second messengers.

Second messengers involved in superoxide production by neutrophils. Function and metabolism

The second messengers that initiate superoxide production by phagocytic leukocytes are reviewed with emphasis on the interactions of these compounds. Enzymes that control the production of the messengers are described.

Synergistic stimulation of neutrophils. Possible involvement of 5-hydroxy-6,8,11,14-eicosatetraenoate in superoxide release

Neutrophils stimulated with optimal amounts of tumor-promoters that activate protein kinase C (e.g. mezerein, phorbol 12,13-dibutyrate) are known to release large quantities of superoxide: approximately 40-50 nmol O2-/min/10(7) cells. Previous studies have shown that treatment of neutrophils with the calcium ionophore A23187, or with 5-hydroxy-6,8,11,14-eicosatetraenonate (5-HETE), dramatically increased the ability of these cells to release O2- in response to suboptimal concentrations of the stimulants mentioned. In this manuscript, we provide data relevant to the basis of this augmentation of O2- release. The synergy with ionophore A23187 exhibited a partial requirement for extracellular Ca2+, whereas that with 5-HETE exhibited a near absolute requirement for that cation. Neutrophils stimulated with optimal amounts of tumor-promoters are known to exhibit a redistribution of protein kinase C activity from the soluble to a particulate fraction. A redistribution of kinase activity was not observed in cells stimulated synergistically. On the other hand, ionophore A23187 and 5-HETE increased the binding of a suboptimal amount of [3H] phorbol 12,13-dibutyrate to intact neutrophils by approximately 25 and 50%, respectively. Inhibitors of protein kinase C (i.e. sphingosine, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine) substantially blocked O-2 release from neutrophils stimulated either synergistically or with optimal levels of tumor-promoters. These data suggest a role for 5-HETE in modulating O-2 release by neutrophils and are discussed in relation to models of the interactions of protein kinase C with membranes.

Cell surface dynamics of neutrophils stimulated with phorbol esters or retinoids

Neutrophils undergo rapid morphological changes as well as metabolic perturbations when stimulated with certain phorbol esters. Stimulated cells initially exhibit pronounced projections emanating from the cell bodies, followed by rounding of the cells, reduction in granule number, and the appearance of intracellular vesicles. We show these vesicles to be derived, at least in part, from the plasmalemma. The experimental approach involved labeling stimulated and unstimulated cells with native ferritin and cationized ferritin, along with the cytochemical localization of ecto-5'-nucleotidase. The labeling patterns of the vesicles indicate that these structures are involved in both phorbol ester-stimulated adsorptive and fluid-phase endocytosis. Neutrophils stimulated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) exhibit two distinct rates of superoxide release in which the second, prolonged level is approximately 50% of the initial rate. All-trans-retinal, which we have recently shown to stimulate O2- release but not granule exocytosis or cell vesiculation, induces a single prolonged rate of maximal O2- release. Neutrophils treated with both all-trans-retinal and TPA exhibit only a single sustained rate of maximal O2- release similar to that observed with all-trans-retinal alone. Moreover, treatment of cells with all-trans-retinal blocks the vesiculation of neutrophils induced by TPA in a dose-dependent manner. This observation provides a possible explanation for the differences in the kinetics of superoxide release.

all-trans-Retinal stimulates superoxide release and phospholipase C activity in neutrophils without significantly blocking protein kinase C

all-trans-Retinal was previously shown to stimulate high levels of superoxide release by guinea pig neutrophils. When the cells, previously labeled with [3H]inositol, are treated with all-trans-retinal, they exhibit a decrease in the levels of [3H]inositol phospholipids and an increase in the accumulation of [3H]inositol phosphates. The maximal accumulation of inositol phosphates and the optimal rate of superoxide release occurred together at approximately 7 min after stimulation. The levels of [3H]inositol phosphates accumulated were comparable to those observed when the cells were stimulated with a chemotactic peptide. In direct measurements, using concentrations that stimulate intact cells maximally, all-trans-retinal was found not to inhibit protein kinase C from the cytosol of neutrophils significantly. This contrasts with the situation with this kinase obtained from other sources. These observations represent additional effects of vitamin A on cells.

Retinoids stimulate the release of superoxide by neutrophils and change their morphology

All-trans-retinal stimulated the release of superoxide by human and guinea pig neutrophils 63 +/- 14 SD and 53 +/- 5 SD nmol of O2-/min/10(7) cells, respectively. Superoxide release by unstimulated cells was negligible. All-trans-retinal also induced morphological changes (i.e., evaginations) in these cells. Other retinoids were effective in instigating these phenomena. The similarities of these effects to those instigated by cis-unsaturated fatty acids (Badwey, J.A., et al., 1984, J. Biol. Chem., 259:7870-7877) are discussed in light of possible mechanisms.

Release of superoxide and change in morphology by neutrophils in response to phorbol esters: antagonism by inhibitors of calcium-binding proteins

The ability of phorbol derivatives to function as stimulating agents for superoxide (O2-) release by guinea pig neutrophils has been evaluated and compared to the known ability of each compound to activate protein kinase C. Those that activate the kinase also stimulate O2- release, while those that are inactive with respect to the kinase have no effect on O2- release. The same correlation was observed with respect to the ability of phorbol esters to induce morphological changes in neutrophils, i.e., vesiculation and reduction in granule content. Certain phenothiazines and naphthalene sulfonamides that are known antagonists of calcium-binding proteins blocked both phorbol ester-induced O2- release and morphological changes in these cells.

Studies on the mechanism of superoxide release from human neutrophils stimulated with arachidonate

cis-Unsaturated fatty acids stimulate release of superoxide (O-2) by human neutrophils (Badwey, J. A., Curnutte, J. T., Robinson, J. M., Berde, C. B., Karnovsky, M. J., and Karnovsky, M. L. (1984) J. Biol. Chem. 259, 7870-7877). The rate of O-2 release due to arachidonate (105 +/- 24 S.D., nmol of O-2/min/10(7) cells) was comparable to optimal values obtained with other stimuli. Antagonists of calcium-binding proteins (i.e. phenothiazines, naphthalene sulfonamides) inhibited the release of O-2 in a fashion compatible with the involvement of calmodulin in these phenomena. Synthetic substrates for and an inhibitor of chymotrypsin-like proteases (e.g. N-benzoyl-L-tyrosine ethyl ester, L-1-tosylamido-2-phenylethyl chloromethyl ketone) also blocked O-2 release. Antagonists of calcium-binding proteins and of proteases were effective in this context with neutrophils stimulated with a variety of agents. The implications of these data for recent reports concerning the mechanism of action of cis-unsaturated fatty acids on phagocytes is discussed.

Superoxide release by neutrophils: synergistic effects of a phorbol ester and a calcium ionophore

Exposure to combined suboptimal concentrations of 4 beta-phorbol 12-myristate 13-acetate and the calcium ionophore A23187 stimulates superoxide release from guinea pig neutrophils to rates ca. 3.5-fold greater than the sum of the rates elicited by each of the agents added separately. This effect was largely dependent upon the presence of calcium in the extracellular medium. The data are discussed in relation to recent reports concerning the interactions of phorbol-esters with cells and the mechanism of activation of superoxide release by neutrophils.

Effects of free fatty acids on release of superoxide and on change of shape by human neutrophils. Reversibility by albumin

Release of superoxide from human neutrophils was stimulated by cis-unsaturated fatty acids (e.g. arachidonate, linoleate). All the saturated and trans-unsaturated fatty acids tested were ineffective in this context. Binding of linoleate to neutrophils was biphasic and could be resolved into a linear and a saturable component. The extent of linoleate binding to the saturable component correlated strongly with the amount of O-2 released (r = 0.96). Palmitate, a saturated fatty acid, exhibited only linear binding to neutrophils and the binding was similar to the linear component of linoleate binding. All cis-unsaturated fatty acids tested decreased the fluorescence polarization of cis- and trans-parinaric acid used as membrane probes in suspensions of neutrophils, whereas the saturated fatty acid, myristate, increased the polarization. Fatty acids which stimulated O-2 release induced morphological changes (i.e. evaginations) in neutrophils, whereas the inactive fatty acids did not affect the cellular morphology. Effects on both the cell morphology and superoxide release were reversed by treatment of the cells with delipidated albumin. These data are discussed in relation to recent reports concerning the effects of free fatty acids on various biochemical systems.

Determinants of the production of active oxygen species by granulocytes and macrophages

Under certain conditions, phagocytic leukocytes generate considerable quantities of superoxide and hydrogen peroxide, as well as small quantities of hydroxyl radical and singlet oxygen. These activated forms of oxygen are involved in the antibacterial, antiparasitic and antitumour functions of the cells. Important factors in the production of the different oxygen species are the nature of the stimulant and the animal species from which the cells are derived; in addition, macrophages exist in various metabolically modulated states within the organism. The oxidases involved in this process are localized in the leukocyte plasmalemma, where they catalyse the oxidation of reduced pyridine nucleotides; a cytochrome may also be involved in the electron transport. Other oxidases are also present in certain species; for example, guinea pig cells contain aldehyde oxidase. Active forms of oxygen can attack bacteria and other foreign bodies inside the phagocytic vacuole or outside the cell. Peroxidase may play a critical role, chiefly in granulocytes. In this kind of multienzyme system, it is self evident that different genetic defects can lead to the same phenotypic end results, e.g. Chronic Granulomatous Disease in children, and other biochemical disorders.

Properties of NADH-cytochrome-b5 reductase from human neutrophils

An NADH-ferricyanide reductase activity of ca. 170 nmole ferricyanide reduced/min/10(7) cells is present in the membrane fraction of human neutrophils. This membrane-bound activity constitutes ca. 85% of the total NADH-ferricyanide reductase activity that is present in these cells. The enzyme(s) readily utilize(s) purified cytochrome-b5 from beef liver as an electron acceptor. No other physiologic electron acceptors tested (e.g., ubiquinone-30, menadione) were active. The specificities of electron donors (e.g., NADH congruent to deamino-NADH much greater than NADPH) and acceptors (e.g., Fe(CN)6-3 greater than 2,6-dichlorophenol-indophenol much greater than O2) for the enzyme(s) in unfractionated membranes, along with action of inhibitors (e.g., ADP, p-chloromercuribenzoate) and the pH optimum, indicate that virtually all of the membrane-bound ferricyanide reductase activity in these cells is NADH-cytochrome-b5 reductase. This reductase, however, is only slightly solubilized (ca. 10%) by a phosphate buffer extraction procedure that is effective with the liver enzyme.

Comparative biochemical and cytochemical studies on superoxide and peroxide in mouse macrophages

Maximal rates of superoxide (O-2) release, and the cytochemical locales of peroxide staining in resident, elicited, and activated macrophages have been determined. Macrophages elicited into the peritoneum with either casein (1.2% w/v) or proteose-peptone (10.0% w/v) release about twice as much O-2 as macrophages activated by infection of the animals with either Listeria monocytogenes, or Bacille Calmette-Guerin (BCG) followed by immune boosting with Purified Protein Derivative (PPD) (i.e., about 35 vs. 14-18 nmol O-2/min/10(7) cells). Macrophages elicited with thioglycollate (3.0% w/v) and resident macrophages produce negligible amounts of O-2 upon stimulation with PMA. These data are compared with those reported by other investigators who used different procedures. A cytochemical procedure for localizing peroxide has been modified for use with murine macrophages. No production of H2O2 by macrophages is detected cytochemically in the absence of stimulation. Upon exposure to PMA, resident macrophages are still largely unresponsive. Approximately 20% of the casein elicited macrophages and BCG-PPD activated macrophages exhibit H2O2 staining, which is largely restricted to the cytoplasmic vesicles and channels induced by PMA in these cells. The only exception to this staining pattern is a small population (about 2%) of activated macrophages which exhibits H2O2 staining in the cytoplasmic vesicles and channels and on the plasmalemma as well.