Endogenous reactive oxygen intermediates activate tyrosine kinases in human neutrophils

Evaluation of the process for superoxide production by NADPH oxidase in human neutrophils: evidence for cytoplasmic origin of superoxide

We present an up-to-date insight into the function of NADPH oxidase in human neutrophils, the signalling pathways involved in activation of this enzyme and the process of association of its components with the cytoskeleton. We also discuss the functional implications of morphological studies revealing localization of the sites of NADPH oxidase activity. An original model of the process of superoxide (O2*-) production in human neutrophils is shown. Organization of NADPH oxidase is associated with several components. Upon stimulation, tri-phox cytosolic components of NADPH oxidase (p40-phox, p47-phox and p67-phox) bind to actin filaments. This process involves other actin-binding proteins, such as cofilin and coronin. Activated protein kinase C, translocated from the plasma membrane, phosphorylates cytosolic components at a scaffold of cytoskeleton. Subsequently, p40-phox, responsible for maintaining the resting state of NADPH oxidase, is separated from other two cytosolic phox proteins following an attachment of the active form of small GTP-binding protein Rac to p67-phox. Cytosolic duo-phox proteins (p47-phox and p67-phox) conjugate with membrane components (gp91-phox, p22-phox and Rapla) of NADPH oxidase residing within membranes of intracellular compartments. This chain of events triggers production of O2*-. Then, oxidant-producing intracellular compartments associate with the plasma membrane. Eventually, intracellularly produced O2*- is released to the extracellular environment through the orifice formed by fusion of oxidant-producing compartments with the plasma membrane. Intracellular movement of the oxidant-producing compartments may be regulated by myosin light chain kinase. The review emphasizes that functional assembly of NADPH oxidase and, therefore, generation of O2*- is accomplished essentially within the intracellular compartments. Upon neutrophil stimulation, intracellularly generated O2*- is transported to the plasma membrane to be released and to ensure host defense against infection.

Signal transduction pathways activated by engaging immunoglobulin Fc receptors on chicken heterophils

In the present studies, we initiated experiments to identify the signal transduction factors involved in activating phagocytosis, oxidative burst, and degranulation following the binding of IgG-opsonized SE to Fc receptors on the surface of avian heterophils. Peripheral blood heterophils were isolated and exposed to known inhibitors of signal transduction pathways for either 20min (chelerythine, genistein, or verapamil) or 120min (pertussis toxin) at 39 degrees C. The cells were then stimulated for 30min at 39 degrees C with SE opsonized with IgG purified from SE-immune chickens. Phagocytosis, luminol-dependent chemiluminescence (LDCL), and beta-D-glucuronidase release were then evaluated in vitro. The G-protein inhibitor, pertussis toxin, the protein kinase C inhibitor, chelerythine, and the Ca(++) channel blocker, verapamil, markedly reduced phagocytosis in a dose responsive manner. Genistein, a tyrosine kinase inhibitor, had no effect on the phagocytosis of the opsonized SE. Both pertussis toxin (66-98%) and verapamil (47-76%) had marked inhibitory effect on LDCL. Chelerythine (13-25%) and genistein (5-25%) had far less biologically significant effects on LDCL. Neither chelerythine nor genistein had a significant effect on degranulation. Verapamil (2-28%) and pertussis toxin (25-29%) had a moderate inhibitory effect on degranulation stimulated by IgG-opsonized SE. As was found with complement receptor mediated activation of heterophils, the binding of Fc receptors by the IgG-SE complex activated distinct signaling pathways that regulate the functional activities of avian heterophils. Pertussis toxin-sensitive, Ca(++)-dependent, G-proteins and protein kinase C-dependent protein phosphorylation play a major role in the phagocytosis of IgG-opsonized SE. Pertussis toxin-sensitive, Ca(++)-dependent, G-proteins appear to regulate LDCL following Fc receptor binding. The signal transduction inhibitors used in these studies did not affect Fc receptor mediated degranulation by avian heterophils.

Tyrosine phosphorylation regulates manganese superoxide dismutase (MnSOD) RNA-binding protein activity and MnSOD protein expression

All cells tested contain a cytosolic protein that binds to a defined region in the 3' untranslated region of manganese superoxide dismutase (MnSOD) RNA; both the MnSOD RNA-binding protein (MnSOD-BP) and the cis element are required for efficient translation of MnSOD RNA [Chung, D. J., Wright, A. E., and Clerch, L. B. (1997) Biochemistry 37, 16298-16306]. This study was designed to test the hypothesis that MnSOD-BP activity is regulated by phosphorylation. When cell extracts from whole rat lung or a rat lung fibroblast cell line, RFL-6, were treated in vitro with a protein tyrosine phosphatase, there was a 4-fold increase in MnSOD-BP activity indicating that MnSOD-BP activity was upregulated by tyrosine dephosphorylation. RFL-6 cells treated in cell culture with herbimycin A or genistein, inhibitors of protein tyrosine kinase, had significantly more MnSOD-BP activity than cells treated with diluent. In RFL-6 cells treated with herbimycin A, the increase in MnSOD-BP activity was associated with an increase in the level of MnSOD protein without a change in MnSOD mRNA concentration. We propose that the modulation of MnSOD protein expression by the tyrosine phosphorylation state of MnSOD-BP is a potential therapeutic target for increasing MnSOD activity during periods of oxidative stress.

Inhibition of melanogenesis in response to oxidative stress: transient downregulation of melanocyte differentiation markers and possible involvement of microphthalmia transcription factor

H2O2 and other reactive oxygen species are key regulators of many intracellular pathways. Within mammalian skin, H2O2 is formed as a byproduct of melanin synthesis, and following u.v. irradiation. We therefore analyzed its effects on melanin synthesis. The activity of the rate-limiting melanogenic enzyme, tyrosinase, decreased in H2O2-treated mouse and human melanoma cells. This inhibition was concentration- and time-dependent in the B16 melanoma model. Maximal inhibition (50-75%) occurred 8-16 hours after a 20 minute exposure to 0.5 mM H2O2. B16 cells withstand this treatment adequately, as shown by a small effect on glutathione levels and a rapid recovery of basal lipid peroxidation levels. Enzyme activities also recovered, beginning to increase 16-20 hours after the treatment. Inhibition of enzyme activities reflected decreased protein levels. mRNAs for tyrosinase, tyrosinase-related protein 1, dopachrome tautomerase, silver protein and melanocortin 1 receptor also decreased after H2O2 treatment, and recovered at different rates. Downregulation of melanocyte differentiation markers mRNAs was preceded by a decrease in microphthalmia transcription factor (Mitf) gene expression, which was quantitatively similar to the decrease achieved using 12-O-tetradecanoylphorbol-13-acetate. Recovery of basal Mitf mRNA levels was also observed clearly before that of tyrosinase. Therefore, oxidative stress may lead to hypopigmentation by mechanisms that include a microphthalmia-dependent downregulation of the melanogenic enzymes.

A new superoxide-generating oxidase in murine osteoclasts

Superoxide production contributes to osteoclastic bone resorption. Evidence strongly indicates that NADPH oxidase is an enzyme system responsible for superoxide generation in osteoclasts. A membrane-bound subunit, p91, is the catalytic domain of NADPH oxidase. However, osteoclasts from p91 knockout mice still produce superoxide at a rate similar to that observed in wild type mice. This unexpected phenomenon prompted us to examine the osteoclasts for an alternative to the p91-containing oxidase. In this study, the cloning of a NADPH oxidase subunit (Nox 4) with 578 amino acids is reported. Nox 4 has 58% similarity in amino acids with the known p91 subunit of NADPH oxidase. Nox 4 is present and active in osteoclasts. Antisense oligonucleotides of Nox 4 reduced osteoclastic superoxide generation as well as resorption pit formation by osteoclasts. This new oxidase complex was present and functional in osteoclasts from p91 knockout mice, explaining the normal resorptive activity seen in the osteoclasts where no p91 is present.

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

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

Role of oxidants in the signaling pathway of preconditioning

This review focuses on the possible role of reactive oxygen species in the pathogenesis of this phenomenon. Evidence in support of a role of oxidants in preconditioning has come from the observation that administration of oxygen radical scavengers during the reperfusion period following the initial "preconditioning" ischemia could prevent the phenomenon. In addition, a brief exposure to a low, nontoxic dose of oxygen radicals may reproduce the beneficial effects of ischemic preconditioning, thus suggesting that radicals can directly trigger the preconditioning pathway. To explain the effects of oxidants in this setting, it has been suggested that reperfusion after the initial, "preconditioning" ischemic episode results in the generation of relatively low amounts of oxygen radicals, which are insufficient to determine cell necrosis, but nevertheless could modify cellular activities that have been implicated as mediators of the preconditioning phenomenon. Recent evidence suggests that low levels of oxidants may have a modulatory role on several cell functions. Possible mechanisms of oxidant-mediated protection might be protein kinase C and other kinases, ATP-dependent potassium channels, or changes in sulfhydryl group redox state, while an effect on adenosine metabolism, or the induction of myocardial stunning presumably does not contribute to oxidant-mediated preconditioning. Finally, de novo protein synthesis and gene expression, and increased antioxidant defenses might be involved in the late phase of preconditioning. In summary, available data strongly suggest that oxygen radicals might be possible mediators of preconditioning. However, further investigation is required to clearly elucidate their exact role and mechanisms of action.

Arsenite induces apoptosis of murine T lymphocytes through membrane raft-linked signaling for activation of c-Jun amino-terminal kinase

Because of its dual roles in acute toxicity and in therapeutic application in cancer treatment, arsenic has recently attracted a renewed attention. In this study, we report NaAsO(2)-induced signal cascades from the cell surface to the nucleus of murine thymic T lymphocytes that involve membrane rafts as an initial signal transducer. NaAsO(2) induced apoptosis through fragmentation of DNA, activation of caspase, and reciprocal regulation of Bcl-2/Bax with the concomitant reduction of membrane potential. We demonstrated that NaAsO(2)-induced caspase activation is dependent on curcumin-sensitive c-Jun amino-terminal kinase and barely dependent on SB203580-sensitive p38 kinase or PD98059-sensitive extracellular signal-regulated kinase. Additionally, staurosporine, which severely inhibited the activation of mitogen-activated protein (MAP) family kinases and c-Jun, partially blocked the NaAsO(2)-mediated signal for poly(ADP-ribose) polymerase (PARP) degradation. Potentially as the initial cell surface event for intracellular signaling, NaAsO(2) induced aggregation of GPI-anchored protein Thy-1 and superoxide production. This Thy-1 aggregation and subsequent activation of MAP family kinase and c-Jun and the degradation of PARP induced by NaAsO(2) were all inhibited by DTT, suggesting the requirement of interaction between arsenic and protein sulfhydryl groups for those effects. beta cyclodextrin, which sequestrates cholesterol from the membrane rafts, inhibited NaAsO(2)-induced activation of protein tyrosine kinases and MAP family kinases, degradation of PARP, and production of superoxide. In addition, beta cyclodextrin dispersed NaAsO(2)-induced Thy-1 clustering. These results suggest that a membrane raft integrity-dependent cell surface event is a prerequisite for NaAsO(2)-induced protein tyrosine kinase/c-Jun amino-terminal kinase activation, superoxide production, and downstream caspase activation.

Enhancement of T cell receptor signaling by a mild oxidative shift in the intracellular thiol pool

Exposure of T cells to the macrophage products hydrogen peroxide (HP) or L-lactate (LAC) was previously shown to enhance IL-2 production and to modulate glutathione (GSH) status. We now found that 50 microM HP and 30 mM LAC enhanced strongly the transcription from the IL-2 promoter in Jurkat T cells after stimulation with anti-CD28 together with or without anti-CD3 but not with anti-CD3 Abs alone. Therefore, we used anti-CD3 plus anti-CD28-stimulated cells to investigate the effect of the GSH reductase inhibitor 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) on the signal cascade. BCNU enhanced the transcription to a similar extent as HP or LAC. Lowering the intracellular GSH/GSH disulfide ratio by BCNU, HP, or NO resulted in all cases in the fulminant enhancement of Jun-N-terminal kinase and p38 mitogen-activated protein kinase but not extracellular signal-regulated kinase 1/2. Jun-N-terminal kinase and NF-kappaB activation was enhanced through pathways involving Rac, Vav1, PKCTheta, p56(lck), p59(fyn), and IkappaB kinases. In a cell-free system, the autophosphorylation of rFyn was stimulated by GSH disulfide but not by HP. These findings suggest that the oxidation of the cellular thiol pool may play a role as an amplifying mechanism for TCR/CD3 signals in immune responses.

Oxidant stress stimulates phosphorylation of eIF4E without an effect on global protein synthesis in smooth muscle cells. Lack of evidence for a role of H202 in angiotensin II-induced hypertrophy

Reactive oxygen species (ROS) are implicated in the pathogenesis of several proliferative diseases, including atherosclerosis and cancer. Eukaryotic translation initiation factor 4E (eIF4E) plays an important role in cell proliferation and differentiation. To gain insight into molecular mechanisms by which ROS influence the pathogenesis of these diseases, I have studied the effect of H(2)O(2), a ROS, on eIF4E phosphorylation. H(2)O(2) induced eIF4E phosphorylation in a dose- and time-dependent manner in growth-arrested smooth muscle cells (SMC). H(2)O(2)-induced eIF4E phosphorylation occurred on serine residues. PD098059, a specific inhibitor of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase inhibited ERK activities but had no significant effect on eIF4E phosphorylation induced by H(2)O(2). Similarly, SB203580, a specific inhibitor of p38 MAPK, although inhibiting H(2)O(2)-induced p38 MAPK activity, had no effect on H(2)O(2)-induced eIF4E phosphorylation. Calphostin C, a specific inhibitor of protein kinase C, also had no effect on H(2)O(2)-induced eIF4E phosphorylation. In contrast, trifluoperazine, an antagonist of calcium/calmodulin kinases, completely blocked H(2)O(2)-induced eIF4E phosphorylation. In addition, intracellular and extracellular Ca(2+) chelators significantly inhibited H(2)O(2)-induced eIF4E phosphorylation. Despite its ability to induce eIF4E phosphorylation, H(2)O(2) had no significant effect on protein levels and new protein synthesis as compared with control. In contrast, it induced the expression of c-Fos, c-Jun, and HSP70 in a time-dependent manner in SMC. Together, these results suggest that H(2)O(2), a ROS and a cellular oxidant, induces eIF4E phosphorylation in a manner that is dependent on Ca(2+) and Ca(2+)/calmodulin kinases and independent of ERKs, p38 MAPK, and protein kinase C. These results also suggest that enhanced eIF4E phosphorylation by H(2)O(2) appears to be an important event in SMC in response to oxidant stress and that eIF4E phosphorylation may be associated with the translation of a small subset of mRNAs such as c-fos, c-jun, and HSP70 gene mRNAs, whose products may have a critical role in cell survival.

Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B4(LTB4)–induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53lyn, p56lyn, p56/59hck, p55fgr, and p56lck whereas p60src, p62yes, p55blk, and p59fyn were not detected. LTB4 promoted a rapid increase in p53/56lyn activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56lyn in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 μmol/L to 10 μmol/L), which attenuated LTB4-stimulated p53/56lyn activity and the phosphorylation of extracellular signal-regulated kinase–2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB4-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca++-dependent [3H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB4-induced chemotaxis but had no effect on oxidant production or [3H]AA release. Collectively, these results implicate lyn kinase in LTB4-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.

Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B4(LTB4)–induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53lyn, p56lyn, p56/59hck, p55fgr, and p56lck whereas p60src, p62yes, p55blk, and p59fyn were not detected. LTB4 promoted a rapid increase in p53/56lyn activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56lyn in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 μmol/L to 10 μmol/L), which attenuated LTB4-stimulated p53/56lyn activity and the phosphorylation of extracellular signal-regulated kinase–2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB4-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca++-dependent [3H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB4-induced chemotaxis but had no effect on oxidant production or [3H]AA release. Collectively, these results implicate lyn kinase in LTB4-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.

Superoxide generation and tyrosine kinase

NADPH oxidase is a multi-subunit enzyme complex responsible for superoxide generation in many cells, for example, B-lymphocytes and osteoclasts. NADPH oxidase is localized on the cell surface and generates superoxide extracellularly. After synthesis, components of this oxidase are transported to the cell membrane where the functional NADPH oxidase complex is assembled. The mechanism by which the membrane-bound components are transported to the cell surface of osteoclasts remains unclear. In this study, we examined the role of tyrosine kinase activity in the transport of NADPH oxidase components. When B-lymphocytes and osteoclasts were treated with herbimycin A, a specific inhibitor of tyrosine kinase, superoxide production was significantly decreased. The amount of p91, the catalytic subunit of NADPH oxidase, was decreased in the cellular membrane of herbimycin A treated cells compared to untreated controls. Similar results were obtained for the movement of a regulatory subunit of the NADPH oxidase complex, p47, in B-lymphocytes. Thus, inhibition of tyrosine kinase decreases superoxide production by disrupting the translocation of the NADPH oxidase complex.

Activation of human neutrophils by Mycobacterium tuberculosis H37Ra involves phospholipase C gamma 2, Shc adapter protein, and p38 mitogen-activated protein kinase

Recent studies have shown that human neutrophils play a significant protective role in mycobacteria infection. When encountered with mycobacteria, neutrophils exhibit the typical early bactericidal responses including phagocytosis and generation of reactive oxygen intermediates (ROI), but the underlying mechanisms are largely unknown. The present study shows that stimulation of neutrophils with an attenuated strain of Mycobacterium tuberculosis H37Ra (Mtb) led to a tyrosine kinase-dependent ROI production in these cells. Stimulation with Mtb induces a rapid and transient tyrosine phosphorylation of several proteins, one of which was identified as phospholipase C gamma 2 (PLC gamma 2). Several tyrosine-phosphorylated proteins were associated with the PLC gamma 2 precipitates from Mtb-stimulated neutrophils, of which pp46 was characterized as the Shc adapter protein. A role for PLC gamma 2-Shc association in the generation of ROI is supported by the observations that stimulation with Mtb causes the activation of p38 mitogen-activated protein kinase (MAPK), a downstream target of the Shc/Ras signaling cascade, and that the effect of genistein on ROI production coincided with its ability to inhibit both PLC gamma 2-Shc association and p38 MAPK activation. Moreover, pretreatment of neutrophils with a PLC inhibitor markedly suppresses the Mtb-stimulated ROI production as well as p38 MAPK activation in these cells. Taken together, these results indicate that stimulation of neutrophils with Mtb triggers the tyrosine phosphorylation of PLC gamma 2 and its association with Shc, and that such association is critical for the Mtb-stimulated ROI production through activating p38 MAPK.

Modulation of human neutrophil responses to CD32 cross-linking by serine/threonine phosphatase inhibitors: cross-talk between serine/threonine and tyrosine phosphorylation

The interplay between serine/threonine and tyrosine phosphorylation was studied in human neutrophils. The direct effects of calyculin and okadaic acid, potent inhibitors of PP1 and PP2A serine/threonine phosphatases, on the patterns of neutrophil phosphorylation, and their effects on the responses of neutrophils to CD32 cross-linking were monitored. After a 2-min incubation with 10-6 M calyculin, a transient tyrosine phosphorylation of a subset of proteins, among which Cbl and Syk, was observed. After a longer incubation (>5 min) with calyculin, concomitant with an accumulation of serine and threonine phosphorylation, neutrophil responses to CD32 cross-linking were selectively altered. Tyrosine phosphorylation of Cbl in response to CD32 cross-linking was inhibited by calyculin, and this inhibition was linked with a slower electrophoretic mobility of Cbl as a consequence of its phosphorylation on serine/threonine residues. However, tyrosine phosphorylation of Syk and of the receptor itself were not affected. Furthermore, the mobilization of intracellular calcium stimulated by CD32 cross-linking was totally abrogated by calyculin. Finally, the stimulation of superoxide production observed in response to CD32 cross-linking was enhanced in calyculin-treated cells. These results suggest that serine/threonine phosphorylation events regulate the signaling pathways activated by CD32 cross-linking in neutrophils and identify a novel mechanism of modulation of the functional responsiveness of human neutrophils to CD32 cross-linking.

Particles binding beta(2)-integrins mediate intracellular production of oxidative metabolites in human neutrophils independently of phagocytosis

Complement-opsonised particles are readily ingested by human neutrophils through a complement receptor-mediated process leading to phagolysosome fusion and production of oxidative metabolites. To investigate the complement receptor 3 (CR3)-associated signal system involved, cells were challenged with protein A-positive, heat-killed Staphylococcus aureus to which antibodies with specificity for the subunits of the beta(2)-integrins, i.e. anti-CD11b (the alpha subunit of CR3) and anti-CD18 (the beta subunit of CR3), were bound through their Fc moiety. Despite not being ingested by the neutrophils, the surface associated anti-CD18- and anti-CD11b-coated particles were able to activate the neutrophil NADPH-oxidase. Also anti-CD11a- (the alpha subunit of LFA-1) and to a lesser extent anti-CD11c- (the alpha subunit of CR4) coated particles were able to trigger the NADPH-oxidase. The NADPH-oxidase was activated without extracellular release of reactive oxygen species. The activity was inhibited by cytochalasin B, suggesting a necessary role for the cytoskeleton in the signalling pathway that activates the oxidase. We show that particle-mediated cross-linking of beta(2)-integrins on the neutrophil surface initiates a signalling cascade, involving cytoskeletal rearrangements, leading to an activation of the NADPH-oxidase without phagosome formation or extracellular release of reactive oxygen species.

Redox regulation of beta2-integrin CD11b/CD18 activation

Although the central role of beta2-integrin CD11b / CD18 in neutrophil functions is well recognized, signaling pathway that regulate integrin activation remain to be elucidated. We analyzed the contribution of oxido-reduction mechanisms in this signaling. Exogenously added H(2)O(2) induced CD11b/CD18-dependent neutrophil adhesion and expression of an integrin activation neoepitope recognized by monoclonal antibody (mAb) clone 24. H(2)O(2)-triggered beta2-integrin activation was inhibited by tyrosine kinase inhibitors and by complexing sulfhydryl groups with phenylarsine oxide (PAO). CD11b/CD18-dependent adhesion and mAb 24 antigen expression triggered by physiological agonists such as TNF-alpha were inhibited by diphenylene iodonium (DPI, an inhibitor of flavoprotein oxidoreductase), by free radical scavengers, by tyrosine kinase inhibitors and by PAO. No inhibition was observed when adhesion was induced by the integrin-activating KIM 185 mAb. Taken together, these results emphasize the importance of an oxidative S-thiolation step(s) in the tyrosine kinase-dependent signaling pathway leading to beta2-integrin activation. H(2)O(2) would directly mediate this oxidative reaction and bypass the initial agonist/receptor pathway to promote integrin-dependent adhesion. The putative oxidase(s) involved in this process is not NADPH oxidase, since adhesion of neutrophils from patients with chronic granulomatous disease was normal and inhibited by scavengers and DPI. These data shed a new light on the regulation of integrin activation required for cell migration into inflamed organs.

CR3, FcgammaRIIA and FcgammaRIIIB induce activation of the respiratory burst in human neutrophils: the role of intracellular Ca(2+), phospholipase D and tyrosine phosphorylation

Human neutrophils express two different types of phagocytic receptors, complement receptors (CR) and Fc receptors. In order to characterize the different signaling properties of each receptor we have used non-adherent human neutrophils and investigated CR3, FcgammaRIIA and FcgammaRIIIB for their signaling capacity. Selective activation of each receptor was achieved by coupling specific antibodies to heat-killed Staphylococcus aureus particles, Pansorbins, through their Fc moiety. Despite the fact that these particles are not phagocytosed, we show that addition of Pansorbins with anti-CD18 antibodies recognizing CR3 induced prominent signals leading to a respiratory burst. Stimulation with anti-FcgammaRIIIB Pansorbins induced about half of the response induced by anti-CR3 Pansorbins, whereas anti-FcgammaRIIA Pansorbins induced an even weaker signal. However, FcgammaRIIA induced strong phosphorylation of p72(syk) whereas FcgammaRIIIB induced only a very weak p72(syk) phosphorylation. During CR3 stimulation no tyrosine phosphorylation of p72(syk) was seen. Both phospholipase D and NADPH oxidase activities were dependent on intracellular calcium. This is in contrast to tyrosine phosphorylation of p72(syk) that occurred even in calcium-depleted cells, indicating that oxygen metabolism does not affect p72(syk) phosphorylation. Inhibitors of tyrosine phosphorylation blocked the respiratory burst induced by both FcgammaRIIA and FcgammaRIIIB as well as CR3. This shows that tyrosine phosphorylation of p72(syk) is an early signal in the cascade induced by FcgammaRIIA but not by CR3.

Angiotensin II activation of insulin-like growth factor 1 receptor transcription is mediated by a tyrosine kinase-dependent redox-sensitive mechanism

We have recently shown that angiotensin II activation of insulin-like growth factor 1 receptor (IGF-1R) transcription is a critical requirement for angiotensin-stimulated vascular smooth muscle cell growth; therefore, we examined the signaling pathway involved. In rat aortic smooth muscle cells, the antioxidants N-acetyl-L-cysteine (5 mmol/L) and pyrrolidine dithiocarbamate (100 micromol/L) completely inhibited angiotensin II-stimulated increases in IGF-1R mRNA and protein levels, suggesting the involvement of reactive oxygen species. Indeed, catalase abolished the Ang II-stimulated increase of IGF-1R protein expression, and accordingly, H(2)O(2) (0.2 mmol/L) or the oxidized products of linoleic acid, hydroperoxyoctadecadienoic acids (10 micromol/L), increased IGF-1R mRNA levels at 3 hours by 74+/-20% and 107+/-22% and increased receptor number at 24 hours by 51+/-6.7% and 55+/-7.4%, respectively. The protein tyrosine kinase inhibitors genistein and tyrphostin A25 also blocked angiotensin II increases in IGF-1R mRNA and protein levels and blocked the ability of hydroperoxyoctadecadienoic acids and H(2)O(2) to increase IGF-1R expression, suggesting that oxidative stress may be an early event in the angiotensin II signaling cascade. Furthermore, calcium chelation inhibited the angiotensin II effect. Transient transfection assays revealed that a (-2350)+640 IGF-1R promoter/luciferase construct was fully responsive to angiotensin II stimulation (127+/-20% increase). Ten millimoles per liter hydroperoxyoctadecadienoic acids and 0.2 mmol/L H(2)O(2) increased luciferase activity by 79+/-8.5% and 63+/-12%, respectively, and 5 mmol/L N-acetyl-L-cysteine blocked the angiotensin II-induced upregulation of luciferase activity by 70%. These data suggest that angiotensin II stimulates IGF-1R gene transcription via calcium-dependent activation of protein tyrosine kinase activity that lies downstream from an oxidant stimulus. These findings provide key insights into the signaling mechanisms whereby angiotensin II exerts its growth-promoting effects on the vasculature.

Involvement of receptor aggregation and reactive oxygen species in osmotic stress-induced Syk activation in B cells

Syk has been shown to be activated by osmotic stress, however, the mechanisms involved are largely unknown. In this study, we demonstrated that cell shrinkage, rather than osmolarity, was responsible for osmotic stress-induced Syk activation. Osmotic stress-induced Syk activation depended partly upon aggregation of surface receptors. Moreover, intracellular reactive oxygen species were involved in mediating osmotic stress-induced Syk activation, with osmotic stress-induced Syk activation being inhibited by the pretreatment of cells with N-acetyl-cysteine and reduced glutathione. When cells were treated with the combination of sodium chloride and hydrogen peroxide, there was a synergistic activation of Syk. In conclusion, osmotic stress-induced Syk activation required suramin-inhibitable surface receptor aggregation and accumulation of intracellular reactive oxygen species.

Regulation of phospholipase D by phosphorylation-dependent mechanisms

The rapid production of phosphatidic acid following receptor stimulation has been demonstrated in a wide range of mammalian cells. Virtually every cell uses phosphatidylcholine as substrate to produce phosphatidic acid in a controlled reaction catalyzed by specific PLD isoforms. Considerable effort has been directed at studying the regulation of PLD activities and subsequent work has characterized a family of proteins including PLD1 and PLD2. Whereas both PLD enzymes are dependent on phosphatidylinositol 4, 5-bisphosphate for activity only the PLD1 isoform was strongly stimulated by the small GTPases ARF and RhoA and by protein kinase Calpha as well. A role for tyrosine kinase activities in the membrane recruitment of small GTPases, in the synthesis of phosphatidylinositol 4,5-bisphosphate and tyrosine phosphorylation of PLD1 and PLD2 has been uncovered. However, it still not clear exactly how tyrosine phosphorylation of proteins contributes to PLD activation in cells. Here we review the data linking tyrosine phosphorylation of proteins to the activation of PLD and describe recent finding on the sites and possible mechanisms of action of tyrosine kinases in receptor-mediated PLD activation. Finally, a model illustrating the potential complex interplay linking these signaling events with the activation of PLD is presented.

Oxidative stress triggers STAT3 tyrosine phosphorylation and nuclear translocation in human lymphocytes

Oxidizing agents are powerful activators of factors responsible for the transcriptional activation of cytokine-encoding genes involved in tissue injury. In this study we show evidence that STAT3 is a transcription factor whose activity is modulated by H2O2 in human lymphocytes, in which endogenous catalase had previously been inhibited. H2O2-induced nuclear translocation of STAT3 to form sequence-specific DNA-bound complexes was evidenced by immunoblotting of nuclear fractions and electrophoretic mobility shift assays, and vanadate was found to strongly synergize with H2O2. Moreover, anti-STAT3 antibodies specifically precipitated a protein of 92 kDa that becomes phosphorylated on tyrosine upon lymphocyte treatment with H2O2. Phenylarsine oxide, a tyrosine phosphatase inhibitor, and genistein, a tyrosine kinase inhibitor, cooperated and cancelled, respectively, the H2O2-promoted STAT3 nuclear translocation. Evidence is also presented, using Fe2+/Cu2+ ions, that.OH generated from H2O2 through Fenton reactions could be a candidate oxygen reactive species to directly activate STAT3. Present data suggest that H2O2 and vanadate are likely to inhibit the activity of intracellular tyrosine phosphatase(s), leading to enhanced STAT3 tyrosine phosphorylation and hence its translocation to the nucleus. These results demonstrate that the DNA binding activity of STAT3 can be modulated by oxidizing agents and provide a framework to understand the effects of oxidative stress on the JAK-STAT signaling pathway.

Activation of several MAP kinases upon stimulation of rat alveolar macrophages: role of the NADPH oxidase

Zymosan-activated serum (ZAS), a source of C5a, stimulates the rat alveolar macrophages (AM) to release superoxide anion. Here we show that treatment of rat AM with ZAS induced a time-dependent increase in the tyrosine phosphorylation of several proteins (116, 105-110, 82-78, 66-72, 62, 45, 42, and 38 kDa). This increase was sensitive to genistein, a tyrosine kinase inhibitor. ZAS stimulated the tyrosine phosphorylation and activation of three members of a family of serine/threonine kinases known as the mitogen-activated protein kinases (MAPK), i.e., ERK1 and ERK2, as assessed by immunoblotting, immunoprecipitation, and phosphotransferase activity, and p38 MAPK, as determined by immunoblotting with phospho-specific antibodies. In addition, ZAS induced the tyrosine phosphorylation of the SHC proteins and their association with GRB2, suggesting a role for this complex in the activation of the ERK pathway. Addition of extracellular catalase during ZAS stimulation significantly reduced the tyrosine phosphorylation response and the activation of ERK1 and ERK2 and their activator MEK1/2 while it did not affect that of p38 MAPK and MKK3/MKK6. Superoxide dismutase marginally increased the response to ZAS, supporting a role for hydrogen peroxide. In contrast to the results with AM, stimulation of human neutrophils with ZAS in the presence of catalase minimally altered the activation of ERK1 and ERK2. These data show that, in ZAS-stimulated rat AM, activation of the respiratory burst and production of hydrogen peroxide via superoxide dismutation are largely responsible for the activation of the ERK pathway through an upstream target.

Reactive Oxygen Intermediates Enhance Fcγ Receptor Signaling and Amplify Phagocytic Capacity

Receptors for the Fc region of IgG (FcγR) mediate internalization of opsonized particles by human neutrophils (PMN) and mononuclear phagocytes. Cross-linking of FcγR leads to activation of protein tyrosine kinases and phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) within FcγR subunits, both obligatory early signals for phagocytosis. Human PMN constitutively express two structurally distinct FcγR, FcγRIIa and FcγRIIIb, and can be induced to express FcγRI by IFN-γ. We have previously shown that stimulation of PMN through FcγRIIIb results in enhanced FcγRIIa-mediated phagocytic activity that is inhibited by catalase. In the present study, we have tested the hypothesis that reactive oxygen intermediates (ROI) have the capacity to regulate FcγR responses and defined a mechanism for this effect. We show that H2O2 augmented phagocytosis mediated by FcγRIIa and FcγRI in PMN and amplified receptor-triggered tyrosine phosphorylation of FcγR-associated ITAMs and signaling elements. Generation of endogenous oxidants in PMN by cross-linking FcγRIIIb similarly enhanced phosphorylation of FcγRIIa and Syk, a tyrosine kinase required for phagocytic function, in a catalase-sensitive manner. Our results provide a mechanism for priming phagocytes for enhanced responses to receptor-driven effects. ROI generated in an inflammatory milieu may stimulate quiescent cells to rapidly increase the magnitude of their effector function. Indeed, human monocytes incubated in the presence of stimulated PMN showed oxidant-induced increases in FcγRIIa-mediated phagocytosis. Definition of the role of oxidants as amplifiers of FcγR signaling identifies a target for therapeutic intervention in immune complex-mediated tissue injury.

Mediating phosphorylation events in the vanadium-induced respiratory burst of alveolar macrophages

Occupational exposure by inhalation to vanadium-containing particles such as residual oil fly ash results in respiratory tract inflammation. This inflammation, characterized by abundant neutrophilia, appears to be initiated by alveolar macrophages (AMs) encountering particles and the subsequent release of proinflammatory cytokines. Intracellular signaling events in these cells in response to particles or their components are largely unknown. We investigated two immediate responses of AMs to vanadium exposure in vitro, the production of reactive oxygen intermediates (ROI) or respiratory burst (RB), and the tyrosine phosphorylation of cellular proteins. Macrophages exposed in vitro to 100 microM vanadyl chloride/1 microCi 48V incorporated 8.3% of the metal after 30 min. Exposure of AMs to increasing concentrations of sodium metavanadate resulted in a dose-dependent increase in production of ROI as measured by dichlorofluorescin oxidation. The lowest dose yielding a significant response was 50 microM, whereas 1000 microM increased RB activity by 173%. NADPH oxidase inhibitors deoxy-D-glucose (100 mM) and diphenylene iodonium (25 microM) reduced the metavanadate-induced RB by 62 and 71%, respectively, implicating NADPH oxidase as the primary cellular source of ROI. Enhanced cerium chloride oxidation in response to metavanadate localized to the plasma membrane consistent with increased NADPH oxidase activity. Pretreatment of AMs with the epidermal growth factor receptor inhibitor, tryphostin B50 (10 microM), reduced the metavanadate-induced RB, but did not influence overall tyrosine phosphorylation. Metavanadate and H2O2 exposure greatly increased overall tyrosine phosphorylation, yielding a similar but distinguishable pattern of phosphorylation in these cells. These observations demonstrate that in vitro metavanadate exposure regulates two distinct, yet related intracellular signaling pathways important in initiating inflammatory responses in these cells: (1) activation of the NADPH oxidase complex with subsequent increased ROI synthesis, and (2) enhanced tyrosine phosphorylation of cellular proteins.

Roles of reactive oxygen species: signaling and regulation of cellular functions

Reactive oxygen species (ROS) are the side products (H2O2, O2.-, and OH.) of general metabolism and are also produced specifically by the NADPH oxidase system in most cell types. Cells have a very efficient antioxidant defense to counteract the toxic effect of ROS. The physiological significance of ROS is that ROS at low concentrations are able to mediate cellular functions through the same steps of intracellular signaling, which are activated by natural stimuli. Moreover, a variety of natural stimuli act through the intracellular formation of ROS that change the intracellular redox state (oxidation-reduction). Thus, the redox state is a part of intracellular signaling. As such, ROS are now considered signal molecules at nontoxic concentrations. Progress has been achieved in studying the oxidative activation of gene transcription in animal cells and bacteria. Changes in the redox state of intracellular thiols are considered to be an important mechanism that regulates cell functions.

Src-family kinase-p53/ Lyn p56 plays an important role in TNF-alpha-stimulated production of O2- by human neutrophils adherent to fibrinogen

Stimulation of neutrophil function by TNFalpha is largely dependent on beta2 integrins. It has also been proposed that src-family kinases are involved in this process. However, the functions of src-like kinases in human neutrophils still remain to be determined. In the present study, we used the new src-family kinase specific inhibitor PP1 [4-Amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] to investigate the role src-kinases play in TNFalpha stimulation of neutrophil function. Our results demonstrated that, in neutrophils adherent to fibrinogen, PP1 inhibited TNFalpha-stimulated superoxide production and protein tyrosine phosphorylation in a dose-dependent manner. In in vitro kinase assays, PP1 profoundly inhibited the activation of p53/56lyn but not p59hck or p72syk. Only slight inhibition was found of p58c-fgr. These data indicate that p53/56lyn plays an important role in TNFalpha-mediated stimulation of PMN function.

Involvement of reactive oxygen species produced via NADPH oxidase in tyrosine phosphorylation in human B- and T-lineage lymphoid cells

In several human B- and T-lymphoid cell lines, reactive oxygen species (ROS) were produced in a time- and dose-dependent manner in response to menadione (vitamin K3) and anti-Fas (CD95/APO-1) mAb when ROS formation was determined by a chemiluminescence-based method. The ROS evoked by menadione and anti-Fas could be first observed as rapidly as within 20 seconds after the stimulation, reaching a maximum within 5-10 min, and declining slowly thereafter. Both menadione and anti-Fas also induced increased tyrosine phosphorylation of multiple cellular proteins whose pattern was similar to that observed upon hydrogen peroxide treatment. For each agent, the kinetics of the increased tyrosine phosphorylation was similar to that of ROS production, and an NADPH oxidase inhibitor, diphenyleneiodonium, prevented both of these two events. Our results suggest a close link between ROS production and tyrosine phosphorylation induced by divergent extracellular stimuli and the possible role of NADPH oxidase or its related enzyme.

ROS stimulate reorganization of mesangial cell-collagen gels by tyrosine kinase signaling

Reactive oxygen species (ROS) initiate multiple pathological and physiological cellular responses, including tyrosine phosphorylation of proteins. In this study, we investigated the effects of ROS on cell-extracellular matrix interactions utilizing the floating three-dimensional collagen gel assay. Exposure of mesangial cells grown in three-dimensional culture to H2O2, 3-amino-1,2,4-triazole (a catalase inhibitor), or puromycin is associated with gel reorganization accompanied by tyrosine phosphorylation of multiple proteins, including focal adhesion kinase (FAK). Neutrophils cocultured with mesangial cells in three-dimensional culture also induce mesangial cell-collagen gel reorganization and initiate tyrosine phosphorylation of a similar set of proteins. Collectively, these results show that ROS of either endogenous or exogenous origin can modulate mesangial cell-extracellular matrix interactions through initiation of a phosphotyrosine kinase signaling cascade. Consequently, ROS may play a role as signaling molecules that regulate mesangial cell-extracellular matrix interactions in both physiological and pathological conditions.

Redox regulation of cellular signalling

Extracellular stimuli elicit a variety of responses, such as cell proliferation and differentiation, through the cellular signalling system. Binding of growth factors to the respective receptor leads to the activation of receptor tyrosine kinases, which in turn stimulate downstream signalling systems such as mitogen-activated protein (MAP) kinases, phospholipase Cgamma (PLCgamma) and phosphatidylinositol 3-kinase. These biochemical reactions finally reach the nucleus, resulting in gene expression mediated by the activation of several transcription factors. Recent studies have revealed that cellular signalling pathways are regulated by the intracellular redox state. Generation of reactive oxygen species (ROS), such as H2O2, leads to the activation of protein tyrosine kinases followed by the stimulation of downstream signalling systems including MAP kinase and PLCgamma. The activation of PLCgamma by oxidative radical stress elevates the cellular Ca2+ levels by flux from the intracellular Ca2+ pool and from the extracellular space. Such reactions in the upstream signalling cascade, in concert, result in the activation of several transcription factors. On the other hand, reductants generally suppress the upstream signalling cascade resulting in the suppression of transcription factors. However, it is well known that cysteine residues in a reduced state are essential for the activity of many transcription factors. In fact, in vitro, oxidation of NFkappaB results in its activation, whereas reductants promote its activity. Thus, cellular signalling pathways are generally subjected to dual redox regulation in which redox has opposite effects on upstream signalling systems and downstream transcription factors. Not only are the cellular signalling pathways subjected to redox regulation, but also the signalling systems regulate the cellular redox state. When cells are activated by extracellular stimuli, the cells produce ROS, which in turn stimulate other cellular signalling pathways, indicating that ROS act as second messengers. It is thus evident that there is cross talk between the cellular signalling system and the cellular redox state. Cell death and life also are subjected to such dual redox regulation and cross talk. Death signals induce apoptosis through the activation of caspases in the cells. Oxidative radical stress induces the activation of caspases, whereas the oxidation of caspases results in their inactivation. Furthermore, some cell-death signals induce the production of ROS in the cells, and the ROS produced in turn stimulate the cell-death machinery. All this evidence shows that the cell's fate is determined by cross talk between the cellular signalling pathways and the cellular redox state through a complicated regulation mechanism.

Pseudomonas pyocyanin increases interleukin-8 expression by human airway epithelial cells

Pseudomonas aeruginosa, an opportunistic human pathogen, causes acute pneumonia in patients with hospital-acquired infections and is commonly associated with chronic lung disease in individuals with cystic fibrosis (CF). Evidence suggests that the pathophysiological effects of P. aeruginosa are mediated in part by virulence factors secreted by the bacterium. Among these factors is pyocyanin, a redox active compound that increases intracellular oxidant stress. We find that pyocyanin increases release of interleukin-8 (IL-8) by both normal and CF airway epithelial cell lines and by primary airway epithelial cells. Moreover, pyocyanin synergizes with the inflammatory cytokines tumor necrosis factor alpha and IL-1alpha. RNase protection assays indicate that increased IL-8 release is accompanied by increased levels of IL-8 mRNA. The antioxidant n-acetyl cysteine, general inhibitors of protein tyrosine kinases, and specific inhibitors of mitogen-activated protein kinases diminish pyocyanin-dependent increases in IL-8 release. Conversely, inhibitors of protein kinases C (PKC) and PKA have no effect. In contrast to its effects on IL-8 expression, pyocyanin inhibits cytokine-dependent expression of the monocyte/macrophage/T-cell chemokine RANTES. Increased release of IL-8, a potent neutrophil chemoattractant, in response to pyocyanin could contribute to the marked infiltration of neutrophils and subsequent neutrophil-mediated tissue damage that are observed in Pseudomonas-associated lung disease.

Reactive oxygen species activate focal adhesion kinase, paxillin and p130cas tyrosine phosphorylation in endothelial cells

Reactive oxygen species (ROS), particularly hydroxyl radical (HO*), increase neutrophil adherence to hypoxanthine-xanthine oxidase (HX-XO)-treated human umbilical vein endothelial cells (HUVEC) in culture. This adherence is inhibited by the tyrosine kinase inhibitors genistein (30 microM) and herbimycin A (0.9 microM), suggesting the involvement of tyrosine kinase. Phosphorylation of several HUVEC proteins in the range of 120-130 and 70 kDa was found to depend on the XO concentration and stimulation time. This phosphorylation was inhibited by the antioxidants dimethylthiourea (DMTU, 0.75 to 7.5 mM) and pentoxifylline (Ptx, 0.1 mM), and by the iron chelators desferrioxamine (DF, 1 mM) and hydroxybenzyl ethylene diamine (HBED, 0.5 mM), suggesting the involvement of HO*. Three tyrosine-phosphorylated proteins, focal adhesion kinase (p125FAK), paxillin (PAX) and p130cas were isolated and characterized by immunoprecipitation and western blotting. Antioxidants and iron chelators reduced their phosphorylation. HUVEC treated with ROS for 15 min showed actin stress fiber formation. Cytochalasin D (5 microM) inhibited tyrosine phosphorylation and PMN-HUVEC adherence, showing the importance of cytoskeleton integrity in these two functions. In conclusion, HO*, which is involved in increased PMN-HUVEC adhesion, also increases tyrosine phosphorylation on three major cytoskeleton proteins which seem to play a role in this adhesion.

Induction of interleukin-8 by ozone is mediated by tyrosine kinase and protein kinase A, but not by protein kinase C

Ozone is one of the most common air pollutants humans routinely inhale. We have previously shown that in vitro ozone exposure induces the DNA-binding activities of NF-kappaB and NF-IL6 as well as the expression of interleukin 8 in respiratory epithelial cells. In this study, we investigated intracellular signaling steps mediating ozone-induced inflammatory mediator release. A549 cells, a type II like alveolar epithelial cell line, were exposed in vitro to air or 0.1 ppm of ozone in the presence of several kinase inhibitors. Exposure to ozone increased interleukin 8 expression and transcription factor activities in a protein tyrosine kinase (PTK)-dependent and protein kinase A (PKA)-dependent, yet protein kinase C (PKC)-independent, manner. Furthermore, ozone-induced PTK and PKA activities but failed to induce PKC activity. In addition, our results suggest that ozone-induced PTK and PKA activities were reactive oxygen intermediate dependent and occurred in parallel, because specific inhibitors for PTK and PKA failed to block the other kinase's activity. These results indicate that PTK and PKA activities are early events in the signal transduction cascade mediating the ozone-induced activation of NF-kappaB and NF-IL6 as well as the release of interleukin 8.

Serum factors and the cellular redox status regulate cellular responsiveness to MHC class II-triggered homotypic B cell adhesion

Cross-linking the major histocompatibility complex (MHC) class II (MHC-II) by their cognate ligands including mAb induces homotypic cell adhesion. It has been shown that merely surface MHC-II expression is insufficient to induce the response. We found that MHC-II-triggered cell adhesion in human B cell lines was absent when serum was removed from medium. Even in the presence of serum, the response was prevented when cells were treated with the glutathione synthesis inhibitor, buthionine sulfoximine, an irreversible catalase inhibitor, aminotriazole, and H2O2. Flow cytometrical analysis showed that these changes in cellular responsiveness were unlikely to be merely the result of altered surface Ag expression. In addition, the response was independent of the two major lymphocyte adhesion receptors, LFA-1 and intercellular adhesion molecule-1 (ICAM-1). These findings suggest that serum- and redox-sensitive intracellular events regulate cellular responsiveness to MHC-II-triggered LFA-1/ICAM-1-independent cell adhesion independently of differentiation.

Increased tyrosine phosphorylation of band 3 in hemoglobinopathies

In order to investigate the tyrosine phosphorylation of band 3, we performed immunoblotting of intact red cells using anti-phosphotyrosine antibody of 21 patients with sickle cell disorders (11 SS, 5 Sbeta, 5 SC), 7 patients with beta thalassemias (5 beta thal intermedia, 2 deltabeta thal), 10 normal controls, and 1 patient with hereditary spherocytosis. They had not received transfusion for the last 4 months and all were clinically stable. Our results showed an increased tyrosine phosphorylation of two proteins, in the 100 and 80 kD regions, in sickle cell and beta-thalassemic red cells when compared to the normal controls and to the patient with hereditary spherocytosis. Immunoprecipitation of the lysed red cells with anti-band 3 antibody and immunoblotting with anti-phosphotyrosine antibody confirmed that the 100 kD tyrosine phosphorylated protein was band 3. In the sickle cell disease group, the band 3 tyrosine phosphorylation varied from 2- to 10-fold increase compared to control (x +/- SD; SS = 7.8- +/- 2.7-fold; SC = 3.8- +/- 1.3-fold; Sbeta = 5.2- +/- 2.0-fold). It was also higher in the beta-thalassemic group (beta-thal = 4.3- +/- 3.7-fold). There was no significant difference in tyrosine phosphorylation among the various groups tested, except when we compared the phosphorylation in intact red cells of patients with sickle cell anemia and hemoglobinopathy SC (U = 6, P < 0.02). The tyrosine phosphorylation of band 3 was increased in hemoglobinopathies even in the absence of high reticulocyte count. At least two mechanisms might be involved in the increased tyrosine phosphorylation of band 3 in these hemoglobin disorders, probably related to the endogenous reactive oxygen intermediates generated by the abnormal erythrocyte: an inhibition of protein tyrosine phosphatase activity or an activation of the protein tyrosine kinase p72syk.

Natural resistance to intracellular parasites: a study by two-dimensional gel electrophoresis coupled with multivariate analysis

Natural resistance to Mycobacterium bovis bacillus Calmette-Guérin (BCG) is determined by the Bcg gene (Nramp1), which is exclusively expressed by mature macrophages. The Nramp1 gene is a dominant autosomal gene that has two allelic forms; r confers resistance and s confers susceptibility to infection with intracellular pathogen. Although the wide range of pleiotropic immunological effects of the Nramp1 gene has been described, the exact mechanism of its action remains elusive. In this study we searched for differentially expressed proteins that might provide clues in the studies on Nramp1 gene function. We performed two-dimensional gel electrophoresis of cellular proteins prepared from a B10R macrophage line derived from mice carrying the r allele of the Nramp1 gene, B10S macrophages carrying the s allele, and B10R-Rb macrophages transfected with Nramp1-ribozyme. The classification of protein patterns and selection of distinct proteins characteristic of r or s allele-carrying macrophages was performed using the principal component analysis. We found differential expression of four proteins with the following isoelectric point/molecular weight (pI/Mr) in B10R macrophages compared to B10S and B10R-Rb macrophages: 6.6/25, 7.0/22, 9.1/31.5, and 5.3/8.5. The protein 7.0/22 has been identified as Mn-superoxide dismutase and the best candidate for protein p6.6/25 seems to be Bcl-2 according to the immunoblot analysis. When the splenic macrophages carrying the r or s allele were analyzed, the changes in relative abundance for proteins 6.6/25 and p7.0/22 were satisfactorily reproduced. Overall, the two identified proteins are important in the regulation of intracellular redox balance and the regulation of apoptosis in macrophages, respectively. Our findings may suggest their possible biological role in the innate immunity against intracellular pathogens.

Involvement of reactive oxygen intermediates in lectin-induced protein-tyrosine phosphorylation of Syk in THP-1 cells

Oxidative stress (H2O2) has been shown to be associated with tyrosine phosphorylation and activation of protein-tyrosine kinase Syk. In the present study, we examined the possibility that reactive oxygen intermediates (ROI) were involved in concanavalin A (Con A)-induced tyrosine phosphorylation in THP-1 cells. Rapid tyrosine phosphorylations of Syk, Fc gamma receptor(s) and phospholipase C gamma 2 (PLC gamma 2) were induced by Con A treatment in THP-1 cells. Pretreatment of cells with antioxidants N-acetylcysteine (NAC) and glutathione (GSH) almost completely blocked tyrosine phosphorylations of Syk, Fc gamma receptor(s) and PLC gamma 2. In addition, THP-1 cells showed significant levels of ROI from the early period of Con A treatment and the levels of ROI were inhibited by antioxidant treatment. These data suggest that ROI have an important role in Con A-induced protein-tyrosine kinase(s) signaling pathways.

Hydroxyl radical as a potential intracellular mediator of polymorphonuclear neutrophil apoptosis

We investigated reactive oxygen species (ROS) involvement in polymorphonuclear neutrophilic leukocyte (neutrophil) apoptosis triggering. Neutrophils were incubated with xanthine oxidase (XO), which produces superoxide anion (O2.-) and hydrogen peroxide (H2O2) or glucose oxidase (GO), which produces only H2O2. Both XO and GO accelerated apoptosis when compared to spontaneously aged neutrophils. Catalase inhibited both spontaneous apoptosis and XO- or GO-accelerated apoptosis, but superoxide dismutase did not. Hydrogen peroxide can enter the cell, thus generating intracellular oxidation, which was observed by flow cytometry. Furthermore, the intracellular reduced glutathione content fell in the presence of XO or GO; however, apoptosis was not accelerated in the presence of buthionine sulfoximine (BSO), suggesting that the fall in glutathione in the presence of XO or GO is a consequence of oxidative stress but not a trigger of apoptosis. Hydrogen peroxide can react with iron to form hydroxyl radicals (HO.); we observed that two iron chelators, deferoxamine and hydroxybenzyl ethylenediamine (HBED), both inhibited spontaneous and accelerated apoptosis, suggesting that HO. may mediate neutrophil apoptosis.

A rise in ionized calcium activates the neutrophil NADPH-oxidase but is not sufficient to directly translocate cytosolic p47phox or p67phox to b cytochrome containing membranes

Neutrophil production of reactive oxygen species is dependent on an assembly process that involves a translocation of the cytosolic NADPH-oxidase components (p47phox; p67phox; Rac2) to a b cytochrome containing membrane. Based on the fact that an intracellular Ca2+ rise can activate the oxidase without any extracellular release of reactive oxygen species, we suggest that the oxidase can be assembled in a membrane distinct from the plasma membrane. Disintegrated cells were used to monitor Ca2+ dependent membrane binding of neutrophil cytosolic proteins. Membranes containing the b cytochrome part of the oxidase, i.e., specific granules and plasma membranes/secretory vesicles, were used in the translocation experiments. Several cytosolic proteins were found to translocate to specific granules as well as the plasma membranes/secretory vesicles, one of them being annexin I. Using antibodies in the blotting assay against the cytosolic oxidase components p47phox and p67phox, we could show that no Ca2+ dependent translocation of these cytosolic proteins occur to neither of the b cytochrome containing membranes.

Influence of tyrosine phosphorylation on protein interaction with FcgammaRIIa

The cytoplasmic tail of Fc(gamma)RIIa present on human neutrophils shares with other antigen receptors a common amino acid sequence called ITAM (Immunoreceptor Tyrosine-based Activation Motif). After receptor ligation, the tyrosine residues within this motif become phosphorylated. We prepared a recombinant fusion protein of the cytoplasmic tail of Fc(gamma)RIIa (containing the ITAM) with glutathione-S-Transferase (GST-CT) to characterize the phosphorylation of Fc(gamma)RIIa and its ability to interact with other proteins involved in signal transduction. The GST-CT became phosphorylated in the presence of Lyn, Hck and Syk (immunoprecipitated from human neutrophils), but not in the presence of Fgr. Of the active kinases, only Lyn (mainly present in the membrane fraction) was found to associate with the GST-CT in the absence of ATP. This association was also observed in immunoprecipitates of Fc(gamma)RIIa from resting neutrophils, suggesting that Lyn might be the kinase responsible for the initial Fc(gamma)RIIa phosphorylation. Moreover, we observed specific association of Syk and the p85 subunit of PI 3-kinase after incubation of the GST-CT with neutrophil cytosol. This interaction was dependent on tyrosine phosphorylation of the GST-CT. Substitution of 269Tyr by Phe almost completely abolished tyrosine phosphorylation of the fusion protein. Substitution of either 253Tyr or 269Tyr eliminated Syk binding, but only 253Tyr appeared to be essential for p85 binding. We hypothesize that, upon activation, the membrane-associated Lyn is responsible for the initial tyrosine phosphorylation of Fc(gamma)RIIa, thus creating a docking site for Syk and PI 3-kinase.

Induction of tyrosine phosphorylation and Na+/H+ exchanger activation during shrinkage of human neutrophils

The ubiquitous isoform of the Na+/H+ exchanger (NHE1) is essential for the regulation of cellular volume. The underlying molecular mechanism, which is poorly understood, was studied in human polymorphonuclear leukocytes (PMN). Suspension of PMN in hypertonic media induced rapid cellular shrinkage and activation of NHE1, which is measurable as a cytosolic alkalinization. Concomitantly, hypertonic stress also induced extensive tyrosine phosphorylation of several proteins. Pretreatment of PMN with genistein, a tyrosine kinase inhibitor, prevented not only the tyrosine phosphorylation in response to a hypertonic shock but also the activation of NHE1. The signal elicited by hyperosmolarity that induces activation of tyrosine kinases and NHE1 was investigated. Methods were devised to change medium osmolarity without altering cell volume and vice versa. Increasing medium and intracellular osmolarity in normovolemic cells failed to activate tyrosine kinases or NHE1. However, shrinkage of cells under iso-osmotic conditions stimulated both tyrosine phosphorylation and NHE1 activity. These findings imply that cells detect alterations in cell size but not changes in osmolarity or ionic strength. The identity of the proteins that were tyrosine-phosphorylated in response to cell shrinkage was also investigated. Unexpectedly, the mitogen-activated protein kinases SAPK, p38, erk1, and erk2 were not detectably phosphorylated or activated. In contrast, the tyrosine kinases p59(fgr) and p56/59(hck) were phosphorylated and activated upon hypertonic challenge. We propose that cells respond to alterations in cell size, but not to changes in osmolarity, with increased tyrosine phosphorylation, which in turn leads to the activation of NHE1. The resulting changes in ion content and cytosolic pH contribute to the restoration of cell volume in shrunken cells.

Effects of respiratory burst inhibitors on nitric oxide production by human neutrophils

Human neutrophils (PMN) activated by N-formylmethionyl-leucyl-phenylalanine (fMLP) simultaneously release nitric oxide (.NO), superoxide anion (O2.-) and its dismutation product, hydrogen peroxide (H2O2). To assess whether .NO production shares common steps with the activation of the NADPH oxidase, PMN were treated with inhibitors and antagonists of intracellular signaling pathways and subsequently stimulated either with fMLP or with a phorbol ester (PMA). The G-protein inhibitor, pertussis toxin (1-10 micrograms/ml) decreased H2O2 yield without significantly changing .NO production in fMLP-stimulated neutrophils; no effects were observed in PMA-activated cells. The inhibition of tyrosine kinases by genistein (1-25 micrograms/ml) completely abolished H2O2 release by fMLP-activated neutrophils; conversely, .NO production increased about 1.5- and 3-fold with fMLP and PMA, respectively. Accordingly, orthovanadate, an inhibitor of phosphotyrosine phosphatase, markedly decreased .NO production and increased O2.- release. On the other hand, inhibition of protein kinase C with staurosporine and the use of burst antagonists like adenosine, cholera toxin or dibutyryl-cAMP diminished both H2O2 and .NO production. The results suggest that the activation of the tyrosine kinase pathway in stimulated human neutrophils controls positively O2.- and H2O2 generation and simultaneously maintains .NO production in low levels. In contrast, activation of protein kinase C is a positive modulator for O2.- and .NO production.

Preservation of the pattern of tyrosine phosphorylation in human neutrophil lysates

Activation of various cell types by different agonists is known to stimulate a transient increase in the level of tyrosine phosphorylation of certain cellular proteins. Such phosphorylation is essential for mediating signalling by these agonists. The preservation of the tyrosine phosphorylation of proteins in lysates has proven to be a difficult task in neutrophils because of their large arsenal of proteases and phosphatases. Here we describe a technique that we found useful for preserving the tyrosine phosphorylation of cellular proteins. The technique depends on the denaturing lysis of neutrophils followed by the removal of the denaturing agents using Sephadex columns. Preparing neutrophil lysates by this technique has proven to be reliable in terms of maintaining the stability of the tyrosine phosphorylated proteins of various molecular weights and their subsequent immunoprecipitation and identification.

Transfection and expression of MnSOD cDNA decreases tumor malignancy of human oral squamous carcinoma SCC-25 cells

Overexpression of human manganese-containing superoxide dismutase (MnSOD) activity has been demonstrated to suppress malignancy in human melanoma and breast carcinoma cells in vitro and in vivo. To study its effects on human oral squamous carcinoma cells, stable transfection and expression of MnSOD in SCC-25 cells have been conducted. The MnSOD-overexpressing cell clones were shown to have approximately two- to five-fold increased MnSOD activity compared to the wild-type parental- or vector control-transfected cell clones, respectively. Plating efficiency with different concentrations of serum was decreased in the high MnSOD activity cell clones. Soft agar assays demonstrated that the clonogenic fractions of high-expressing MnSOD clones were dramatically reduced. When inoculated in nude mice, tumor growth was markedly inhibited in MnSOD overexpressing cell clones compared with the wild-type or vector control transfected cell lines. Thus, gene therapy of human oral cancer by increasing the expression of MnSOD activity in target cells might be used to prevent or reduce human oral tumor malignancy.

Protein tyrosine kinase activity is required for oxidant-induced extracellular signal-regulated protein kinase activation and c-fos and c-jun expression

Hydrogen peroxide stimulated tyrosine phosphorylation of several proteins in growth-arrested vascular smooth muscle cells (VSMC). One of these proteins was identified as fibroblast growth factor receptor type I (FGFR1). In addition, induced tyrosine phosphorylation of FGFR1 by hydrogen peroxide resulted in complex formation with Grb2. Hydrogen peroxide also caused a time-dependent activation of extracellular signal-regulated protein kinases (ERKs; p42&p44) group of mitogen-activated protein kinases (MAPKs) in VSMC. The time courses of the hydrogen peroxide-stimulated FGFR1 tyrosine phosphorylation and ERKs activation were followed by induced expression of c-fos and c-jun. Genistein, a potent inhibitor of protein tyrosine kinases, significantly blunted the hydrogen peroxide-induced FGFR1 tyrosine phosphorylation, ERKs activation and c-fos and c-jun expression. PD98059, a specific inhibitor of MEK1, attenuated the hydrogen peroxide-induced ERKs activation and c-fos and c-jun expression. Together, these results suggest that oxidants such as hydrogen peroxide stimulate tyrosine phosphorylation of receptor tyrosine kinases and these, in turn, mediate the down-stream signalling events including the recruitment of Grb2 by the receptor, activation of ERKs and induction of c-fos and c-jun expression.

Cellular localization of the inhibitory action of abruquinone A against respiratory burst in rat neutrophils

1. The possible mechanisms of action of the inhibitory effect of abruquinone A on the respiratory burst in rat neutrophils in vitro was investigated. 2. Abruquinone A caused an irreversible and a concentration-dependent inhibition of formylmethionylleucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2.-) generation with IC50 values of 0.33 +/- 0.05 microgram ml-1 and 0.49 +/- 0.04 microgram ml-1, respectively. 3. Abruquinone A also inhibited O2 consumption in neutrophils in response to fMLP/CB and PMA. However, abruquinone A did not scavenge the generated O2.- in xanthine-xanthine oxidase system and during dihydroxyfumaric acid (DHF) autoxidation. 4. Abruquinone A inhibited both the transient elevation of [Ca2+]i in the absence of [Ca2+]o (IC50 7.8 +/- 0.2 micrograms ml-1) and the generation of inositol trisphosphate (IP3) (IC50 10.6 +/- 2.0 micrograms ml-1) in response to fMLP. 5. Abruquinone A did not affect the enzyme activaties of neutrophil cytosolic protein kinase C (PKC) and porcine heart protein kinase A (PKA). 6. Abruquinone A had no effect on intracellular guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels but decreased the adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 7. The cellular formation of phosphatidic acid (PA) and phosphatidylethanol (PEt) induced by fMLP/ CB was inhibited by abruquinone A with IC50 values of 2.2 +/- 0.6 micrograms ml-1 and 2.5 +/- 0.3 micrograms ml-1, respectively. Abruquinone A did not inhibit the fMLP/CB-induced protein tyrosine phosphorylation but induced additional phosphotyrosine accumulation on proteins of 73-78 kDa in activated neutrophils. 8. Abruquinone A inhibited both the O2.- generation in PMA-activated neutrophil particulate NADPH oxidase (IC50 0.6 +/- 0.1 microgram ml-1) and the iodonitrotetrazolium violet (INT) reduction in arachidonic acid (AA)-activated cell-free system (IC50 1.5 +/- 0.2 micrograms ml-1) 9. Collectively, these results indicate that the inhibition of respiratory burst in rat neutrophils by abruquinone A is mediated partly by the blockade of phospholipase C (PLC) and phospholipase D (PLD) pathways, and by suppressing the function of NADPH oxidase through the interruption of electron transport.

Syk-dependent and -independent signaling cascades in B cells elicited by osmotic and oxidative stress

It was found that Syk protein-tyrosine kinase is rapidly activated in B cells after H2O2 treatment (oxidative stress) or increased extracellular NaCl concentration (osmotic stress) as well as in response to B cell receptor activation. In this study we examined the involvement of Syk in responses elicited by these types of extracellular stress, particularly Ca2+ responses and c-Jun amino-terminal kinase (JNK) activation, using a chicken B cell line, DT40, as well as the DT40-derived mutant DT40/Syk(-), which does not express Syk. Osmotic stress evokes increases in [Ca2+]i by stimulating an extracellular Ca2+ influx in both DT40 and DT40/Syk(-) cells. In comparison, oxidative stress elicits an increase in [Ca2+]i by stimulating both an extracellular Ca2+ influx and Ca2+ release from internal stores in DT40 cells, but this Ca2+ response is partially abolished in DT40/Syk(-) cells, indicating that the oxidative stress-induced Ca2+ response is at least partly dependent on Syk. Interestingly, the depletion of Ca2+ results in a significantly decreased level of Syk activation in DT40 cells stimulated by oxidative but not osmotic stress. Furthermore, JNK is activated to different extents by these two types of stress. The extent of JNK activation in DT40/Syk(-) cells in response to osmotic stress is comparable to that observed in DT40 cells. Intriguingly, oxidative stress-induced JNK activation is significantly compromised in DT40/Syk(-) cells. Collectively, these results indicate that both the Ca2+ response and JNK activity induced by oxidative stress are partly dependent on Syk, whereas those induced by osmotic stress are independent of Syk.

Absence of respiratory burst in X-linked chronic granulomatous disease mice leads to abnormalities in both host defense and inflammatory response to Aspergillus fumigatus

Mice with X-linked chronic granulomatous disease (CGD) generated by targeted disruption of the gp91phox subunit of the NADPH-oxidase complex (X-CGD mice) were examined for their response to respiratory challenge with Aspergillus fumigatus. This opportunistic fungal pathogen causes infection in CGD patients due to the deficient generation of neutrophil respiratory burst oxidants important for damaging A. fumigatus hyphae. Alveolar macrophages from X-CGD mice were found to kill A. fumigatus conidia in vitro as effectively as alveolar macrophages from wild-type mice. Pulmonary disease in X-CGD mice was observed after administration of doses ranging from 10(5) to 48 spores, none of which produced disease in wild-type mice. Higher doses produced a rapidly fatal bronchopneumonia in X-CGD mice, whereas progression of disease was slower at lower doses, with development of chronic inflammatory lesions. Marked differences were also observed in the response of X-CGD mice to the administration of sterilized Aspergillus hyphae into the lung. Within 24 hours of administration, X-CGD mice had significantly higher numbers of alveolar neutrophils and increased expression of the proinflammatory cytokines IL-1 beta and TNF-alpha relative to the responses seen in wild-type mice. By one week after administration, pulmonary inflammation was resolving in wild-type mice, whereas X-CGD mice developed chronic granulomatous lesions that persisted for at least six weeks. This is the first experimental evidence that chronic inflammation in CGD does not always result from persistent infection, and suggests that the clinical manifestations of this disorder reflect both impaired microbial killing as well as other abnormalities in the inflammatory response in the absence of a respiratory burst.

Regulation of Src homology 2-containing tyrosine phosphatase 1 during activation of human neutrophils. Role of protein kinase C

The tyrosine phosphorylation of several proteins induced in neutrophils by soluble and particulate stimuli is thought to be crucial for initiating antimicrobial responses. Although activation of tyrosine kinases is thought to mediate this event, the role of tyrosine phosphatases in the initiation and modulation of neutrophil responses remains largely undefined. We investigated the role of Src homology 2-containing tyrosine phosphatase 1 (SHP-1; also known as protein tyrosine phosphatase 1C (PTP1C), hematopoetic cell phosphatase, PTP-N6, and SHPTP-1), a phosphatase expressed primarily in hemopoietic cells, in the activation of human neutrophils. SHP-1 mRNA and protein were detected in these cells, and the enzyme was found to be predominantly localized to the cytosol in unstimulated cells. Following stimulation with neutrophil agonists such as phorbol ester, chemotactic peptide, or opsonized zymosan, a fraction of the phosphatase redistributed to the cytoskeleton. Agonist treatment also induced significant decreases (30-60%) in SHP-1 activity, which correlated temporally with increases in the cellular phosphotyrosine content. Phosphorylation of SHP-1 on serine residues was associated with the inhibition of its enzymatic activity, suggesting a causal relationship. Accordingly, both the agonist-evoked phosphorylation of SHP-1 and the inhibition of its catalytic activity were blocked by treatment with bisindolylmaleimide I, a potent and specific inhibitor of protein kinase C (PKC) activity. Immunoprecipitated SHP-1 was found to be phosphorylated efficiently by purified PKC in vitro. Such phosphorylation also caused a decrease in the phosphatase activity of SHP-1. Together, these data suggest that inhibition of SHP-1 by PKC-mediated serine phosphorylation plays a role in facilitating the accumulation of tyrosine-phosphorylated proteins following neutrophil stimulation. These findings provide a new link between the PKC and tyrosine phosphorylation branches of the signaling cascade that triggers antimicrobial responses in human neutrophils.

Hck is activated by opsonized zymosan and A23187 in distinct subcellular fractions of human granulocytes

Regulation of neutrophil responses is known to involve tyrosine phosphorylation. Hck, a major neutrophil protein-tyrosine kinase, becomes expressed during differentiation of human promyelocytic NB4 cells into neutrophil-like cells. Hck is mainly localized in a secretory granule-enriched cell fraction, but it is also present in a granule-free membrane fraction and the cytosol. Hck is rapidly and transiently activated upon stimulation of differentiated NB4 cells or human neutrophils with serum-opsonized zymosan or the calcium ionophore A23187, but not by phorbol 12-myristate 13-acetate. In NB4 cells, Hck is also weakly activated by fMet-Leu-Phe. Cell fractionation showed that opsonized zymosan and A23187 induce Hck activation in distinct subcellular fractions. Both stimuli activate Hck in the secretory granule-enriched fraction, but only A23187 activates the kinase in the granule-free membrane fraction. Our results suggest that Hck might regulate early signal transduction events induced by opsonized zymosan and A23187, and that the different subcellular fractions of Hck might serve discrete functions, one of which could be regulation of the degranulation response.