Neutrophil "priming" induced by orthovanadate: evidence of a role for tyrosine phosphorylation

Reactive oxygen and nitrogen species as signaling molecules regulating neutrophil function

As a cornerstone of the innate immune response, neutrophils are the archetypical phagocytic cell; they actively seek out, ingest, and destroy pathogenic microorganisms. To achieve this essential role in host defense, neutrophils deploy a potent antimicrobial arsenal that includes oxidants, proteinases, and antimicrobial peptides. Importantly, oxidants produced by neutrophils, referred to in this article as reactive oxygen (ROS) and reactive nitrogen (RNS) species, have a dual function. On one hand they function as potent antimicrobial agents by virtue of their ability to kill microbial pathogens directly. On the other hand, they participate as signaling molecules that regulate diverse physiological signaling pathways in neutrophils. In the latter role, ROS and RNS serve as modulators of protein and lipid kinases and phosphatases, membrane receptors, ion channels, and transcription factors, including NF-kappaB. The latter regulates expression of key cytokines and chemokines that further modulate the inflammatory response. During the inflammatory response, ROS and RNS modulate phagocytosis, secretion, gene expression, and apoptosis. Under pathological circumstances such as acute lung injury and sepsis, excess production of ROS may influence vicinal cells such as endothelium or epithelium, contributing to inflammatory tissue injury. A better understanding of these pathways will help identify novel targets for amelioration of the untoward effects of inflammation.

Formyl-Met-Leu-Phe induces calcium-dependent tyrosine phosphorylation of Rel-1 in neutrophils

Chemoattractant priming and activation of PMNs results in changes in cytosolic Ca2+ concentration, tyrosine kinase activity, and gene expression. We hypothesize that the initial signaling for the activation of a 105kDa protein (Rel-1) requires Ca2+-dependent tyrosine phosphorylation. A rapid and time-dependent tyrosine phosphorylation of Rel-1 occurred following formyl-Met-Leu-Phe (fMLP) stimulation of human PMNs at concentrations that primed or activated the NADPH oxidase (10(-9) to 10(-6)M), becoming maximal after 30s. Pretreatment with pertussis toxin (Ptx) or tyrosine kinase inhibitors abrogated this phosphorylation and inhibited fMLP activation of the oxidase. The fMLP concentrations employed also caused a rapid increase in cytosolic Ca2+ but chelation negated the effects, including the cytosolic Ca2+ flux, oxidase activation, and the tyrosine phosphorylation of Rel-1. Conversely, chelation of extracellular Ca2+ decreased the fMLP-mediated Ca2+ flux, had no affect on the oxidase, and augmented tyrosine phosphorylation of Rel-1. Phosphorylation of Rel-1 was inhibited when PMNs were preincubated with a p38 MAP kinase (MAPK) inhibitor (SB203580). In addition, fMLP elicited rapid activation of p38 MAPK which was abrogated by chelation of cytosolic Ca2+. Thus, fMLP concentrations that prime or activate the oxidase cause a rapid Ca2+-dependent tyrosine phosphorylation of Rel-1 involving p38 MAPK activation.

Analysis of selected blood and immune cell responses to carbohydrate-dependent surface binding of proto- and chimera-type galectins

Cell surface glycans present docking sites to endogenous lectins. With growing insight into the diversity of lectin families it becomes important to answer the question on the activity profiles of individual family members. Focusing on galectins (beta-galactoside-binding proteins without Ca(2+)-requirement sharing the jelly-roll-like folding pattern), this study was performed to assess the potency of proto-type galectins (galectins-1 and -7 and CG-16) and the chimera-type galectin-3 to elicit selected cell responses by carbohydrate-dependent surface binding and compare the results. The galectins, except for galectin-1, were found to enhance detergent (SDS)-induced hemolysis of human erythrocytes to different degrees. Their ability to confer increased membrane osmofragility thus differs. Aggregation of neutrophils, thymocytes and platelets was induced by the proto-type galectin-1 but not -7, by CG-16 and also galectin-3. Cell-type-specific quantitative differences and the importance of the fine-specificity of the galectin were clearly apparent. In order to detect cellular responses based on galectin binding and bridging of cells the formation of haptenic-sugar-resistant (HSR) intercellular contacts (an indicator of post-binding signaling) was monitored. It was elicited by CG-16 and galectin-1 but not galectin-3, revealing another level at which activities of individual galectins can differ. Acting as potent elicitor of neutrophil aggregation, CG-16-dependent post-binding effects were further analyzed. Carbohydrate-dependent binding to the neutrophils' surface led to a sustained increase of cytoplasmic Ca2+ concentration in a dose-dependent manner. The ability of CG-16 to activate H2O2 generation by human peripheral blood neutrophils was primed by the Ca(2+)-ionophor ionomycin and by cytochalasin B. In a general context, these results emphasize that--besides plant lectins as laboratory tools--animal lectins can trigger cell reaction cascades, implying potential in vivo relevance for the measured activities. Within the family of galectins, the activity profiles depend on the target cell type and the individual galectin. Notably, proto-type galectins do not necessarily share a uniform capacity as elicitor.

Lipopolysaccharide-binding protein- and CD14-dependent activation of mitogen-activated protein kinase p38 by lipopolysaccharide in human neutrophils is associated with priming of respiratory burst

Neutrophil (PMN) functions can be primed for greatly increased oxidative radical release by exposure to certain agents such as lipopolysaccharide (LPS). Although a variety of signaling pathways involving both tyrosine kinases and mitogen-activated protein (MAP) kinases may be operative, the mechanisms of PMN priming are still not understood. We found that PMN priming was not achieved by treatment of cells with a very low concentration (5 ng/ml) of LPS unless additional "helper" factors were present in plasma (5%). Under these conditions, LPS induced tyrosine phosphorylation of a 38-kDa protein, which was coincident with the MAP kinase p38 action in this situation. LPS-mediated activation of p38 in human PMNs was dependent on the presence of LPS binding protein from plasma and CD14 on the surfaces of the cells. Phosphorylation of p38 was highly correlated with LPS priming of a formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN respiratory burst. Treatment of PMN with the p38-specific inhibitor SB203580 significantly attenuated the respiratory burst in cells primed by LPS and stimulated by fMLP. These results suggest that the LPS signaling pathway leading to p38 activation may be an important mechanism in regulation of PMN priming. The mediator(s) linking CD14 to p38 involves proteins that are functionally sensitive to genistein but insensitive to tyrphostin AG126 and to Src- and Syk-family kinase, protein kinase C, and phosphatidylinositol 3-kinase inhibitors. Elucidating this pathway will provide insight into possible regulation of PMN priming by LPS.

Lipopolysaccharide-binding protein- and CD14-dependent activation of mitogen-activated protein kinase p38 by lipopolysaccharide in human neutrophils is associated with priming of respiratory burst

Neutrophil (PMN) functions can be primed for greatly increased oxidative radical release by exposure to certain agents such as lipopolysaccharide (LPS). Although a variety of signaling pathways involving both tyrosine kinases and mitogen-activated protein (MAP) kinases may be operative, the mechanisms of PMN priming are still not understood. We found that PMN priming was not achieved by treatment of cells with a very low concentration (5 ng/ml) of LPS unless additional "helper" factors were present in plasma (5%). Under these conditions, LPS induced tyrosine phosphorylation of a 38-kDa protein, which was coincident with the MAP kinase p38 action in this situation. LPS-mediated activation of p38 in human PMNs was dependent on the presence of LPS binding protein from plasma and CD14 on the surfaces of the cells. Phosphorylation of p38 was highly correlated with LPS priming of a formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN respiratory burst. Treatment of PMN with the p38-specific inhibitor SB203580 significantly attenuated the respiratory burst in cells primed by LPS and stimulated by fMLP. These results suggest that the LPS signaling pathway leading to p38 activation may be an important mechanism in regulation of PMN priming. The mediator(s) linking CD14 to p38 involves proteins that are functionally sensitive to genistein but insensitive to tyrphostin AG126 and to Src- and Syk-family kinase, protein kinase C, and phosphatidylinositol 3-kinase inhibitors. Elucidating this pathway will provide insight into possible regulation of PMN priming by LPS.

Activation of extracellular signal-related protein kinases 1 and 2 of the mitogen-activated protein kinase family by lipopolysaccharide requires plasma in neutrophils from adults and newborns

Neutrophils exposed to low concentrations of gram-negative lipopolysaccharide (LPS) become primed and have an increased oxidative response to a second stimulus (e.g., formyl-methionyl-leucyl-phenylalanine [fMLP]). In studies aimed at understanding newborn sepsis, we have shown that neutrophils of newborns are not primed in response to LPS. To further understand the processes involved in LPS-mediated priming of neutrophils, we explored the role of extracellular signal-related protein kinases (ERK 1 and 2) of the mitogen-activated protein kinase family. We found that LPS activated ERK 1 and 2 in cells of both adults and newborns and that activation was plasma dependent (maximal at > or =5%) through LPS-binding protein. Although fibronectin in plasma is required for LPS-mediated priming of neutrophils of adults assessed by fMLP-triggered oxidative burst, it was not required for LPS-mediated activation of ERK 1 and 2. LPS-mediated activation was dose and time dependent; maximal activation occurred with approximately 5 ng of LPS per ml and at 10 to 40 min. We used the inhibitor PD 98059 to study the role of ERK 1 and 2 in the LPS-primed fMLP-triggered oxidative burst. While Western blotting showed that 100 microM PD 98059 completely inhibited LPS-mediated ERK activation, oxidative response to fMLP by a chemiluminescence assay revealed that the same concentration inhibited the LPS-primed oxidative burst by only 40%. We conclude that in neutrophils, LPS-mediated activation of ERK 1 and 2 requires plasma and that this activation is not dependent on fibronectin. In addition, we found that the ERK pathway is not responsible for the lack of LPS priming in neutrophils of newborns but may be required for 40% of the LPS-primed fMLP-triggered oxidative burst in cells of adults.

Deficiency of Src homology 2-containing phosphatase 1 results in abnormalities in murine neutrophil function: studies in motheaten mice

Neutrophils, an essential component of the innate immune system, are regulated in part by signaling pathways involving protein tyrosine phosphorylation. While protein tyrosine kinase functions in regulating neutrophil behavior have been extensively investigated, little is known about the role for specific protein tyrosine phosphatases (PTP) in modulating neutrophil signaling cascades. A key role for Src homology 2 domain-containing phosphatase 1 (SHP-1), a PTP, in neutrophil physiology is, however, implied by the overexpansion and inappropriate activation of granulocyte populations in SHP-1-deficient motheaten (me/me) and motheaten viable (me(v)/me(v)) mice. To directly investigate the importance of SHP-1 to phagocytic cell function, bone marrow neutrophils were isolated from both me/me and me(v)/me(v) mice and examined with respect to their responses to various stimuli. The results of these studies revealed that both quiescent and activated neutrophils from motheaten mice manifested enhanced tyrosine phosphorylation of cellular proteins in the 60- to 80-kDa range relative to that detected in wild-type congenic control neutrophils. MOTHEATEN: neutrophils also demonstrated increased oxidant production, surface expression of CD18, and adhesion to protein-coated plastic. Chemotaxis, however, was severely diminished in the SHP-deficient neutrophils relative to control neutrophils, which was possibly attributable to a combination of defective deadhesion and altered actin assembly. Taken together, these results indicate a significant role for SHP-1 in modulating the tyrosine phosphorylation-dependent signaling pathways that regulate neutrophil microbicidal functions.

Pentoxifylline decreases neutrophil respiratory bursts in patients with stable angina

We estimated the effect of pentoxifylline (PTX) on the respiratory burst (examined by chemiluminescence method) of unprimed and primed neutrophils with tumor necrosis factor-alpha (TNF-alpha) in patients with stable angina pectoris. Chemiluminescence of non-stimulated as well as formyl-methionyl-leucyl-phenylalanine (fMLP) and phorbol myristate acetate (PMA) stimulated neutrophils was measured. We studied 45 patients with stable angina subjected to percutaneous transluminal coronary angioplasty (PTCA) procedure, who were randomly divided into two groups. The study group consisted of 24 patients who were administered pentoxifylline orally, and the control group consisted of 21 patients without pentoxifylline administration. Blood samples for examination were collected from the coronary sinus and peripheral vein just before the PTCA procedure. Pentoxifylline decreased the respiratory burst of non-stimulated and fMLP-stimulated neutrophils without affecting the chemiluminescence of PMA stimulated neutrophils. Moreover, pentoxifylline diminished the chemiluminescence non-stimulated and stimulated by fMLP but not by PMA of TNF-alpha primed neutrophils. We presume that administration of PTX in stable angina patients may have a beneficial effect.

CD45 modulation of CXCR1 and CXCR2 in human polymorphonuclear leukocytes

All leukocytes express the cell surface glycoprotein CD45, which has intrinsic intracellular protein tyrosine phosphatase activity. CD45 is known to play a regulatory role in activation-induced signaling in lymphocytes; however, little is known of its role in non-lymphoid leukocytes. Therefore, we examined the potential effect of CD45 on chemokine-induced signaling in human neutrophils (polymorphonuclear cells, PMN). Treating isolated PMN for 2 h with an anti-CD45RB antibody (Bra11) down-modulated expression of the chemokine receptors CXCR1 and CXCR2 to 44 +/- 10% and 47 +/- 9% of their respective controls. The tyrosine kinase inhibitors genistein and herbimycin A significantly inhibited the Bra11-induced down-modulation of CXCR1 and CXCR2. Furthermore, Bra11-treated PMN were functionally inhibited in their capacity to exhibit IL-8-induced transient intracellular Ca2+ increases. Selected targeting of CXC receptors is indicated by the fact that N-formyl-Met-Leu-Phe (fMLP) receptor expression and function were not lost following Bra11 treatment. The effect of Bra11 on IL-8-mediated function and receptor expression was paralleled by decreased tyrosine phosphorylation of a 54- to 60-kDa protein. These findings indicate that CD45 can act to modulate PMN responses to chemokines; thus agents regulating CD45 can potentially modulate leukocyte traffic and may represent a novel therapeutic approach towards the treatment of inflammatory diseases.

Lipopolysaccharide-induced priming of the human neutrophil is not associated with a change in phosphotyrosine phosphatase activity

The activation of the neutrophil respiratory burst is a two-step process involving an initial 'priming' phase followed by a 'triggering' event. The biochemical mechanisms which underlie these events are yet to be fully elucidated, but the evidence suggests a crucial role for stimulus-induced tyrosine phosphorylation. The enhanced tyrosine phosphorylation observed upon triggering primed cells may reflect an increase in tyrosine kinase activity or a reduction in the levels of the opposing phosphotyrosine phosphatases (PTPases). We have investigated the latter by examining the possibility that lipopolysaccharide (LPS)-induced priming of the neutrophil respiratory burst involves the suppression of cellular PTPase activity. Purified human neutrophils were incubated for 60 min with and without LPS. Priming of the respiratory burst was confirmed by fMet-Leu-Phe-induced cytochrome c reduction. The level of PTPase activity was assessed by dephosphorylation of [32P]RR-src peptide as substrate. Pretreatment of human neutrophils with 200 ng/ml LPS induced a 2.9 +/- 0.3 (mean +/- SEM, n = 3, P = 0.022) fold increase in the fMet-Leu-Phe-triggered respiratory burst. In the same cells, LPS did not induce a significant change in the total cellular PTPase activity (1.02 +/- 0.02-fold, mean +/- SEM, n = 3, P = 0.63). Similarly, stimulation of neutrophils with fMet-Leu-Phe or phorbol myristate acetate did not significantly affect the cellular PTPase activity (P = 0.94 and 0.68, respectively). Our results suggest that suppression of PTPase activity is not the mechanism underlying the priming and/or triggering of the neutrophil respiratory burst.

Negative Regulation of Myeloid Cell Proliferation and Function by the SH2 Domain-Containing Tyrosine Phosphatase-1

The SH2 domain containing tyrosine phosphatase SHP-1 has been implicated in the regulation of a multiplicity of signaling pathways involved in hemopoietic cell growth, differentiation, and activation. A pivotal contribution of SHP-1 in the modulation of myeloid cell signaling cascades has been revealed by the demonstration that SHP-1 gene mutation is responsible for the overexpansion and inappropriate activation of myelomonocytic populations in motheaten mice. To investigate the role of SHP-1 in regulation of myeloid leukocytes, an HA epitope-tagged dominant negative (interfering) SHP-1 (SHP-1C453S) was expressed in the myelo-monocytic cell line U937 using the pcDNA3 vector. Overexpression of this protein in SHP-1C453S transfectants was demonstrated by Western blot analysis and by detection of decreased specific activity. Growth, proliferation, and IL-3-induced proliferative responses were substantially increased in the SHP-1C453S-overexpressing cells relative to those in control cells. The results of cell cycle analysis also revealed that the proportion of cells overexpressing SHP-1C453S in S phase was greater than that of control cells. The SHP-1C453S-expressing cells also displayed diminished rates of apoptosis as detected by flow cytometric analysis of propidium iodide-stained cells and terminal deoxynucleotidyltransferase-mediated fluorescein-dUTP nick end-labeling assay. While motility and phagocytosis were not affected by SHP-1C453S overexpression, adhesion and the oxidative burst in response to PMA were enhanced in the SHP-1C453S compared with those in the vector alone transfectants. Taken together, these results suggest that SHP-1 exerts an important negative regulatory influence on cell proliferation and activation while promoting spontaneous cell death in myeloid cells.

Stimulation of primed neutrophils by soluble immune complexes: priming leads to enhanced intracellular Ca2+ elevations, activation of phospholipase D, and activation of the NADPH oxidase

Soluble immune complexes activate a rapid burst of reactive oxidant secretion from neutrophils that have previously been primed with GM-CSF. Binding of these complexes to the cell surface of unprimed neutrophils results in the generation of intracellular Ca2+ transients, but the NADPH oxidase fails to become activated. No phospholipase D activity was observed following the addition of soluble immune complexes to unprimed cells. Upon priming with GM-CSF, the intracellular Ca2+ signal generated following soluble complex binding was greatly extended and phospholipase D was activated: there was also increased phosphorylation of proteins on tyrosine residues and the NADPH oxidase was activated. When Ca2+ influx was prevented, this phospholipase D activity was not observed. This primed oxidase activity was completely inhibited by erbstatin. Treatment of unprimed neutrophils with pervanadate (to inhibit protein tyrosine phosphatases) mimicked the effects of priming in that pervanadate-treated neutrophils secreted reactive oxidants in response to soluble immune complexes. The data indicate that during priming a new signaling pathway is activated that involves Ca2+ influx, phosphorylation on tyrosine residues, phospholipase D activity, and NADPH oxidase activation.

The regulation by phosphorylation of 'priming' of phospholipase A2 activity in the neutrophil model system, differentiated HL60 cells

1 Differential HL60 cells have been utilized as a model system to examine the 'priming' of neutrophil phospholipase A2 activity. In control cells activation of phospholipase A2 by a 5 min stimulation with the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (100 nM) was essentially undetectable. When cells were primed by preincubation with 5 microns cytochalasin B for 5 min arachidonate release, a measure of phospholipase A2 activation, was observed within 20 s. 2 Priming by cytochalasin B did not involve or require a change in intracellular free calcium concentration. 3 Priming was associated with an increase in general protein tyrosine phosphorylation and could also be induced by the receptor tyrosine kinase agonist granulocyte macrophage colony-stimulating factor (GM-CSF, 20 ng ml-1) and be mimicked by treatment with the phosphotyrosine phosphatase inhibitor perhydrovanadate (0.5 mM). However, increase in MAP kinase activity was not involved in the priming process. 4 Western blot analysis demonstrated that phospholipase A2 was phosphorylated in both control and primed cells, but that an increase in the amount of membrane associated enzyme was found in the primed cells. 5 Thus priming appears to be due to membrane association of the phospholipase and this may be regulated by tyrosine kinase activities.

Phosphotyrosine phosphatase activity in the macrophage is enhanced by lipopolysaccharide, tumor necrosis factor alpha, and granulocyte/macrophage-colony stimulating factor: correlation with priming of the respiratory burst

Tyrosine phosphorylation is now recognised as a key event in the activation of the macrophage respiratory burst. Since vanadate, a phosphotyrosine phosphatase (PTP) inhibitor is able to enhance the respiratory burst, we proposed that agents which prime the macrophage for enhance respiratory burst activity may do so by suppressing cellular PTP activity. The level of PTP activity in murine bone marrow-derived macrophages (BMM) was assessed by the ability of cell lysates to dephosphorylate 32P-labelled RR-src peptide. In contrast to our hypothesis, pretreatment of BMM with bacterial lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF alpha) or granulocyte/macrophage-colony stimulating factor (GMCSF), agents which prime for enhanced respiratory burst activity, was found to dramatically increase the level of cellular PTP activity. The time-course for this increase correlated well with the time course of priming by these agents. In addition, colony stimulating factor-1, a cytokine which does not prime the macrophage respiratory burst, did not enhance PTP levels. The physiological relevance of the increased PTP activity was further supported by confirming it was active against endogenous tyrosine phosphorylated substrates. Interestingly, phorbol myristate acetate and zymosan, agents which trigger the macrophage respiratory burst, were found to inhibit the PTP activity of BMM. Our results demonstrate the regulation of cellular PTP activity by priming agents and further highlight the importance of tyrosine phosphorylation and dephosphorylation events in the regulation of macrophage function.

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.

Pentoxifylline inhibits tumor necrosis factor alpha-induced priming of human neutrophils

The study was designed to study the effect of pentoxifylline PTX on the chemiluminescence responses of neutrophils and on tumor necrosis factor-alpha (TNF-alpha)-induced priming of neutrophils. The results demonstrate that TNF-alpha stimulated the respiratory burst by neutrophils and primed them for enhanced response to fMLP but not to PMA. The effect of TNF-alpha on the oxygen metabolism of neutrophils was inhibited when cells were treated with PTX. This reaction was dose-dependent. Additionally, the inhibiting influence of PTX on the chemiluminescence response of neutrophils was observed.

Neutrophil priming: the cellular signals that say 'amber' but not 'green'

One of the most intriguing gaps in our understanding of how neutrophils work concerns the mechanism by which the oxidase response in these cells is 'primed'. In the primed state, there is no increase in oxidase activity, yet subsequent stimulation provokes a response that is larger than in nonprimed, activated cells. Thus, neutrophils exist in one of three states: quiescent, primed or active. Individual primed cells may be thought of as being 'ready to go' but awaiting further stimulus before the oxidase response is elicited. The primed neutrophils are thus held at 'amber', awaiting 'green' before activity is triggered. Here, Maurice Hallett and Darren Lloyds suggest a molecular basis for the signals that say 'amber' but not 'green'.

Development of oxidase 'priming' in maturing HL60 cells: correlation with protein expression and tyrosine phosphorylation

The mechanisms involved in 'priming' of the oxidase response of neutrophils are unknown. Two major problems are encountered in using circulating neutrophils; firstly, prior exposure to circulating 'priming' cytokines cannot be controlled and secondly, non-intentional 'priming' during cell separation can occur. In this study, these problems were avoided by differentiating the promyeloid leukaemic cell line, HL60, towards granulocytes using dibutyrl cyclic AMP, to produce a 'virgin cell' model system. We have demonstrated that the ability of substance P to both prime the oxidase response and induce tyrosine phosphorylation increased during differentiation. The major tyrosine-phosphorylated protein, with molecular weight of 74 kDa, was not recognised by anti-c-raf1 antibodies. Furthermore, c-raf1 expression rapidly declined during HL60 cell granulocytic differentiation. This data shows that although there was no simple relationship between c-raf quantity and priming, the data were consistent with tyrosine phosphorylation of a 74 kDa protein being important for oxidase 'priming'.