Human peripheral eosinophils have a specific mechanism to express gp91-phox, the large subunit of cytochrome b558

A highly sensitive chemiluminescence assay for superoxide detection and chronic granulomatous disease diagnosis

Reactive oxygen species (ROS) produced by neutrophils are crucial for defense against infectious diseases, and the adequate measurement of ROS levels is an important way to evaluate the possibility of infections. The fluorescent probe dihydrorhodamine 123 has been applied exclusively to the measurement of ROS thus far. We developed a novel method for detecting ROS, which utilizes the chemiluminescent probes Luminol and Diogenes. The new method quantitatively detects ROS produced by as few as 10 to 10(4) neutrophils. Furthermore, this method can detect ROS levels in one microliter of whole blood or ROS produced by Epstein-Barr immortalized B lymphocytes. This method will be valuable for prompt diagnosis of neonatal chronic granulomatous diseases in which neutrophils aberrantly produce superoxide.

Hematologically important mutations: X-linked chronic granulomatous disease (third update)

Chronic granulomatous disease (CGD) is an immunodeficiency disorder affecting about 1 in 250,000 individuals. The disease is caused by a lack of superoxide production by the leukocyte enzyme NADPH oxidase. Superoxide is used to kill phagocytosed micro-organisms in neutrophils, eosinophils, monocytes and macrophages. The leukocyte NADPH oxidase is composed of five subunits, of which the enzymatic component is gp91-phox, also called Nox2. This protein is encoded by the CYBB gene on the X chromosome. Mutations in this gene are found in about 70% of all CGD patients. This article lists all mutations identified in CYBB in the X-linked form of CGD. Moreover, apparently benign polymorphisms in CYBB are also given, which should facilitate the recognition of future disease-causing mutations.

Involvement of p38 MAP Kinase in Not Only Activation of the Phagocyte NADPH Oxidase Induced by Formyl-methionyl-leucyl-phenylalanine but Also Determination of the Extent of the Activity

Activated NADPH oxidase in neutrophils produces superoxide. We investigated the role of p38 MAP kinase in activating NADPH oxidase stimulated by the bacteria-derived peptide fMLP. fMLP-stimulated superoxide production was completely abolished by SB203580, a p38 MAP kinase inhibitor, whereas anisomycin, a p38 MAP kinase activator, did not induce superoxide production, indicating that p38 MAP kinase was essential, but not sufficient, for NADPH oxidase activation. Anisomycin pretreatment strongly activated p38 MAP kinase in fMLP-stimulated cells, accompanied by greatly increased superoxide production, suggesting that p38 MAP kinase determines the extent of the fMLP-stimulated NADPH oxidase activity. Furthermore, superoxide production was remarkably reactivated by cytochalasin B addition after fMLP-stimulated production had disappeared, and this was correlated with highly activated p38 MAP kinase. These results suggest that p38 MAP kinase is involved not only in activating NADPH oxidase stimulated by fMLP but also in determining the extent of its activity.

Chronic granulomatous disease presenting with eosinophilic inflammation

Chronic granulomatous disease (CGD), a rare immunodeficiency, typically presents with recurrent infections caused by catalase-positive organisms. We report 2 patients with CGD who presented with eosinophilic inflammatory conditions recognized before the diagnosis of CGD. Both patients had significant urologic disease. Physicians should be aware of the association of CGD with eosinophilic inflammatory conditions.

Divergence of mechanisms regulating respiratory burst in blood and sputum eosinophils and neutrophils from atopic subjects

Eosinophil respiratory burst is an important event in asthma and related inflammatory disorders. However, little is known concerning activation of the respiratory burst NADPH oxidase in human eosinophils. Conversely, neutrophils are known to assemble NADPH oxidase in intracellular and plasma membranes. We hypothesized that eosinophils and neutrophils translocate NADPH oxidase to distinct intracellular locations, consistent with their respective functions in O(2)(-)-mediated cytotoxicity. PMA-induced O(2)(-) release assayed by cytochrome c was 3.4-fold higher in atopic human eosinophils than in neutrophils, although membrane-permeable dihydrorhodamine-123 showed similar amounts of release. Eosinophil O(2)(-) release was dependent on Rac, in that it was 54% inhibited by Clostridium difficile toxin B (400-800 ng/ml). In eosinophils stimulated with PMA, a pronounced shift of cytosolic Rac to p22(phox)-positive plasma membrane was observed by confocal microscopy, whereas neutrophils directed Rac2 mainly to intracellular sites coexpressing p22(phox). Similarly, ex vivo sputum eosinophils from asthmatic subjects exhibited predominantly plasma membrane-associated immunoreactivity for Rac, whereas sputum neutrophils exhibited cytoplasmic Rac2 staining. Thus, activated sputum eosinophils, rather than neutrophils, may contribute significantly to the pathogenesis of asthma by extracellular release of tissue-damaging O(2)(-). Our findings suggest that the differential modes of NADPH oxidase assembly in these cells may have important implications for oxidant-mediated tissue injury.

Cooperation of STAT-1 and IRF-1 in interferon-gamma-induced transcription of the gp91(phox) gene

Interferon (IFN)-gamma induces the expression of the gp91(phox) gene both during myeloid differentiation and also in mature phagocytes through several cis-elements and their binding proteins. To find new cis-elements for this induction, transient expression assays were performed using a reporter gene driven by serially truncated gp91(phox) promoters in U937 cells. The results suggest that a critical cis-element for induction exists in the region from bp -115 to -96 of the promoter. Site-directed mutagenesis showed that a gamma-activated sequence (GAS) element at bp -100 (-100GAS) of the gp91(phox) promoter plays a pivotal role for the IFN-gamma-dependent activity of the bp -115 to +12 region of the gp91(phox) promoter. Electrophoretic mobility shift assays using several GAS competitors and specific antibodies indicated that phosphorylated STAT-1alpha specifically binds to the -100GAS. Site-directed mutagenesis showed that an interferon-stimulated response element (ISRE) at bp -88 (-88ISRE) mediates the induction of the gene by IFN-gamma in cooperation with -100GAS. Electrophoretic mobility shift assay showed that IRF-1 dominantly binds to -88ISRE in an IFN-gamma-dependent fashion. These results demonstrate a new mechanism for IFN-gamma-induced transcription of the gp91(phox) gene by the cooperation of STAT-1alpha and IRF-1 binding to -100GAS and -88ISRE, respectively.

Transcriptional mechanisms regulating myeloid-specific genes

Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.

Mechanisms of expression of NADPH oxidase components in human cultured monocytes: role of cytokines and transcriptional regulators involved

Human blood monocytes lose their capability to produce microbicidal oxidants during culture. We report that this process is associated with decreased gp91phox, p22phox and p47phox expression, release of PU.1 and CP-1 from gp91phox promoter, and PU.1 from p47phox promoter. However, in presence of IFN-gamma or TNF-alpha, the superoxide anion (O(2)(-)) production, the p47phox, gp91phox and p22phox expression, and the binding of PU.1 and CP-1 to DNA are maintained at the high levels observed in blood monocytes. To clarify the role of PU.1 in the expression of NADPH oxidase components, oligonucleotides competing for PU.1-DNA binding were added to cultured monocytes. These oligonucleotides abrogated the maintenance of gp91phox and p22phox expression by IFN-gamma and TNF-alpha, but did not inhibit the effect of these cytokines on p47phox expression and O(2)(-) production. Our results indicate that in monocytes the IFN-gamma- and TNF-alpha-induced expression of gp91phox and p22phox, but not p47phox, requires the binding of PU.1 to gp91phox promoter. However, the preservation of O(2)(-) production by IFN-gamma and TNF-alpha is unrelated to their effect on gp91phox and p22phox expression.

Point mutations in the promoter region of the CYBB gene leading to mild chronic granulomatous disease

Chronic granulomatous disease (CGD) is a clinical syndrome of recurrent bacterial and fungal infections caused by a rare disorder of phagocytic cells. In CGD, the phagocytes are unable to generate oxygen radicals after stimulation of these cells, due to a defect in the NADPH oxidase system. This NADPH oxidase is a multicomponent enzyme of at least four subunits, of which the beta-subunit of cytochrome b558, gp91-phox, is encoded by an X-linked gene (called CYBB). We report here five patients from two families; in each family we found a different mutation in the promoter region of CYBB. Both mutations prevented the expression of gp91-phox in the patients' neutrophils and thus caused inability of these cells to generate oxygen radicals. However, the mutations left the gp91-phox expression and the function of the NADPH oxidase in the patients' eosinophils intact. The relatively mild course of the CGD in these patients can probably be attributed to the fact that the eosinophils have retained their oxidative capacity. Furthermore, our results indicate that neutrophils and eosinophils differ in their regulation of gp91-phox expression.

A regulatory role for ADP-ribosylation factor 6 (ARF6) in activation of the phagocyte NADPH oxidase

In activated neutrophils NADPH oxidase is regulated through various signaling intermediates, including heterotrimeric G proteins, kinases, GTPases, and phospholipases. ADP-ribosylation factor (ARF) describes a family of GTPases associated with phospholipase D (PLD) activation. PLD is implicated in NADPH oxidase activation, although it is unclear whether activation of PLD by ARF is linked to receptor-mediated oxidase activation. We explored whether ARF participates in NADPH oxidase activation by formyl-methionine-leucine-phenylalanine (fMLP) and whether this involves PLD. Using multicolor forward angle light scattering analyses to measure superoxide production in differentiated neutrophil-like PLB-985 cells, we tested enhanced green fluorescent fusion proteins of wild-type ARF1 or ARF6, or their mutant counterparts. The ARF6(Q67L) mutant defective in GTP hydrolysis caused increased superoxide production, whereas the ARF6(T27N) mutant defective in GTP binding caused diminished responses to fMLP. The ARF1 mutants had no effect on fMLP responses, and none of the ARF proteins affected phorbol 12-myristate 13-acetate-elicited oxidase activity. PLD inhibitors 1-butanol and 2, 3-diphosphoglycerate, or the ARF6(N48R) mutant assumed to be defective in PLD activation, blocked fMLP-elicited oxidase activity in transfected cells. The data suggest that ARF6 but not ARF1 modulates receptor-mediated NADPH oxidase activation in a PLD-dependent mechanism. Because PMA-elicited NADPH oxidase activation also appears to be PLD-dependent, but ARF-independent, ARF6 and protein kinase C may act through distinct pathways, both involving PLD.

Genetic, biochemical, and clinical features of chronic granulomatous disease

The reduced nicotinamide dinucleotide phosphate (NADPH) oxidase complex allows phagocytes to rapidly convert O2 to superoxide anion which then generates other antimicrobial reactive oxygen intermediates, such as H2O2, hydroxyl anion, and peroxynitrite anion. Chronic granulomatous disease (CGD) results from a defect in any of the 4 subunits of the NADPH oxidase and is characterized by recurrent life-threatening bacterial and fungal infections and abnormal tissue granuloma formation. Activation of the NADPH oxidase requires translocation of the cytosolic subunits p47phox (phagocyte oxidase), p67phox, and the low molecular weight GT-Pase Rac, to the membrane-bound flavocytochrome, a heterodimer composed of the heavy chain gp91phox and the light chain p22phox. This complex transfers electrons from NADPH on the cytoplasmic side to O2 on the vacuolar or extracellular side, thereby generating superoxide anion. Activation of the NADPH oxidase requires complex rearrangements between the protein subunits, which are in part mediated by noncovalent binding between src-homology 3 domains (SH3 domains) and proline-rich motifs. Outpatient management of CGD patients relies on the use of prophylactic antibiotics and interferon-gamma. When infection is suspected, aggressive effort to obtain culture material is required. Treatment of infections involves prolonged use of systemic antibiotics, surgical debridement when feasible, and, in severe infections, use of granulocyte transfusions. Mouse knockout models of CGD have been created in which to examine aspects of pathophysiology and therapy. Gene therapy and bone marrow transplantation trials in CGD patients are ongoing and show great promise.

Eosinophil-specific regulation of gp91(phox) gene expression by transcription factors GATA-1 and GATA-2

The glycoprotein gp91(phox) is an essential component of the phagocyte NADPH oxidase and is expressed in eosinophils, neutrophils, monocytes, and B-lymphocytes. We previously suggested an eosinophil-specific mechanism of gp91(phox) gene expression. To elucidate the mechanism, we performed functional assays on deletion mutants of the gp91(phox) promoter in various types of gp91(phox)-expressing cells. A 10-base pair (bp) region from bp -105 to -96 of the promoter activated transcription of the gene in eosinophilic cells, but not in neutrophilic, monocytic, or B-lymphocytic cells. A 2-bp mutation introduced into the GATA site spanning bp -101 to -96 (-98GATA site) of the fragment abolished its activity. Gel shift assays using a GATA competitor and specific antibodies demonstrated that both GATA-1 and GATA-2 specifically bound to the -98GATA site with similar affinities. Individual transfection of GATA-1 and GATA-2 into Jurkat cells, which have neither endogenous GATA-1 nor GATA-2, activated the -105/+12 construct in a -98GATA site-dependent manner. Combined transfection of GATA-1 and GATA-2 activated the promoter less than transfection of GATA-1 alone. These results suggest that GATA-1 is an activator and that GATA-2 is a relative competitive inhibitor of GATA-1 in the expression of the gp91(phox) gene in human eosinophils.

Overexpression of CCAAT Displacement Protein Represses the Promiscuously Active Proximal gp91phox Promoter

CCAAT displacement protein (CDP) is a transcriptional repressor that restricts expression of the gp91phox gene to mature myeloid cells. CDP interacts with multiple sites within the −450 to +12 bp human gp91phox promoter, and down-regulation of CDP DNA-binding activity is required for induction of gp91phox transcription in mature phagocytes. Truncation of the gp91phox promoter to −102 to +12 bp removes 4 CDP-binding sites and reveals a promiscuous promoter activity that is active in some nonphagocytic cells. A cis-element at −90 bp is required for derepressed transcription and serves as a binding site for multiple transcriptional activators. We now report that this element also serves as a binding site for CDP. The affinity of CDP for this element is relatively weak compared with upstream CDP-binding sites within the promoter, consistent with the promiscuous transcriptional activity exhibited by the −102 to +12 bp gp91phox promoter fragment. Further analysis of the proximal promoter reveals an additional weak-affinity CDP-binding site centered at approximately −20 bp. Overexpression of cloned CDP represses the −102 to +12 bp gp91phox promoter, indicating that these proximal CDP-binding sites are functionally significant. The constellation of transcriptional activators and a repressor that interacts with the −90 bp cis-element is identical to that observed for a promoter element at −220 bp, reflecting the highly modular organization of the gp91phoxpromoter. These studies illustrate the complex interplay between transcriptional activators and a repressor that contribute to the myeloid-restricted expression of the gp91phox gene.

Overexpression of CCAAT Displacement Protein Represses the Promiscuously Active Proximal gp91phox Promoter

CCAAT displacement protein (CDP) is a transcriptional repressor that restricts expression of the gp91phox gene to mature myeloid cells. CDP interacts with multiple sites within the −450 to +12 bp human gp91phox promoter, and down-regulation of CDP DNA-binding activity is required for induction of gp91phox transcription in mature phagocytes. Truncation of the gp91phox promoter to −102 to +12 bp removes 4 CDP-binding sites and reveals a promiscuous promoter activity that is active in some nonphagocytic cells. A cis-element at −90 bp is required for derepressed transcription and serves as a binding site for multiple transcriptional activators. We now report that this element also serves as a binding site for CDP. The affinity of CDP for this element is relatively weak compared with upstream CDP-binding sites within the promoter, consistent with the promiscuous transcriptional activity exhibited by the −102 to +12 bp gp91phox promoter fragment. Further analysis of the proximal promoter reveals an additional weak-affinity CDP-binding site centered at approximately −20 bp. Overexpression of cloned CDP represses the −102 to +12 bp gp91phox promoter, indicating that these proximal CDP-binding sites are functionally significant. The constellation of transcriptional activators and a repressor that interacts with the −90 bp cis-element is identical to that observed for a promoter element at −220 bp, reflecting the highly modular organization of the gp91phoxpromoter. These studies illustrate the complex interplay between transcriptional activators and a repressor that contribute to the myeloid-restricted expression of the gp91phox gene.

Elf-1 and PU.1 Induce Expression of gp91phox Via a Promoter Element Mutated in a Subset of Chronic Granulomatous Disease Patients

The cytochrome b heavy chain (gp91phox) is the redox center of the NADPH-oxidase and is highly expressed in mature myeloid cells. Point mutations at −57, −55, −53, and −52 bp of the gp91phox promoter have been detected in patients with chronic granulomatous disease (CGD; Newburger et al,J Clin Invest 94:1205, 1994; and Suzuki et al, Proc Natl Acad Sci USA 95:6085, 1998). We report that Elf-1 and PU.1,ets family members highly expressed in myeloid cells, bind to this promoter element. Either factor trans-activates the −102 to +12 bp gp91phox promoter when overexpressed in nonhematopoietic HeLa cells or the PLB985 myeloid cell line. However, no synergy of gp91phox promoter activation occurs when both Elf-1 and PU.1 are overexpressed. Introduction of the −57 bp or −55 bp CGD mutations into the gp91phoxpromoter significantly reduces the binding affinity of Elf-1 and PU.1 and also reduces the ability of these factors to trans-activate the promoter. These results indicate that Elf-1 and PU.1 contribute to directing the lineage-restricted expression of the gp91phox gene in phagocytes and that failure of these factors to effectively interact with this promoter results in CGD.

GATA-3 represses gp91phox gene expression in eosinophil-committed HL-60-C15 cells

To study the regulatory mechanism of gp91phox gene expression in eosinophils, we transiently transfected eosinophil-committed HL-60-C15 cells with gp91phox promoter constructs, and identified a negative element from bp -267 to -246 of the gp91phox gene, the deletion of which caused an 83% increase in promoter activity. Electrophoresis mobility shift assays demonstrated GATA-3 binds to the GATA consensus site from bp -256 to -250. An 81% increment in promoter activity was obtained when a mutation was introduced in the GATA-3 binding site of the bp -267 to +12 construct, which is comparable to that of the bp -245 to +12 construct. We therefore conclude that GATA-3 specifically binding to the GATA site negatively regulates the expression of the gene in HL-60-C15 cells.

PU.1 as an essential activator for the expression of gp91(phox) gene in human peripheral neutrophils, monocytes, and B lymphocytes

We have reported a deficiency of a 91-kDa glycoprotein component of the phagocyte NADPH oxidase (gp91(phox)) in neutrophils, monocytes, and B lymphocytes of a patient with X chromosome-linked chronic granulomatous disease. Sequence analysis of his gp91(phox) gene revealed a single-base mutation (C --> T) at position -53. Electrophoresis mobility-shift assays showed that both PU.1 and hematopoietic-associated factor 1 (HAF-1) bound to the inverted PU.1 consensus sequence centered at position -53 of the gp91(phox) promoter, and the mutation at position -53 strongly inhibited the binding of both factors. It was also indicated that a mutation at position -50 strongly inhibited PU.1 binding but hardly inhibited HAF-1 binding, and a mutation at position -56 had an opposite binding specificity for these factors. In transient expression assay using HEL cells, which express PU.1 and HAF-1, the mutations at positions -53 and -50 significantly reduced the gp91(phox) promoter activity; however, the mutation at position -56 did not affect the promoter activity. In transient cotransfection study, PU.1 dramatically activated the gp91(phox) promoter in Jurkat T cells, which originally contained HAF-1 but not PU.1. In addition, the single-base mutation (C --> T) at position -52 that was identified in a patient with chronic granulomatous disease inhibited the binding of PU.1 to the promoter. We therefore conclude that PU.1 is an essential activator for the expression of gp91(phox) gene in human neutrophils, monocytes, and B lymphocytes.

Interferon regulatory factor-2 directs transcription from the gp91phox promoter

Repressor elements in the gp91(phox) promoter are necessary to restrict tissue-specific transcription to mature phagocytes. Deletion of these elements leads to significant promoter activity in cell lines such as HEL and K562 that do not normally express gp91(phox). The -100 to +12 base pair gp91(phox) promoter region is sufficient to direct maximal de-repressed transcription in these cells. However, promoter activity is dramatically decreased following a 16-base pair truncation that deletes an interferon-stimulated response element. This element interacts with IRF-1 and IRF-2, members of the interferon regulatory factor family of transcription factors. In addition, this promoter region is bound by a factor with properties similar to BID, a DNA-binding protein that also interacts with three upstream sites within the gp91(phox) promoter. Transient transfection studies using mutated promoters indicate that both the IRF and BID binding sites are required for maximal gp91(phox) promoter activity. Overexpression of IRF-1 or IRF-2 in K562 cells leads to transactivation of gp91(phox) promoter constructs, which is dependent on the presence of an intact IRF binding site. IRF-2 predominates in macrophages that express the gp91(phox) gene as well as in HEL and K562 cells. We conclude that IRF-2 and BID activate gp91(phox) promoter activity in the absence of transcriptional repression.

CCAAT displacement protein competes with multiple transcriptional activators for binding to four sites in the proximal gp91phox promoter

CCAAT displacement protein (CDP) competes with transcriptional activating proteins for binding to each of four elements within the myeloid-specific gp91(phox) promoter. CDP exhibits the strongest affinity for a site centered at -110 base pairs (bp) of the promoter and progressively weaker affinities for three more distal binding sites. CDP binding to each site is down-regulated during terminal phagocytic differentiation, coincident with induction of gp91(phox) expression. Deletion of the high affinity CDP-binding site at -110 bp leads to inappropriate gp91(phox) promoter activity in HeLa, K562, and HEL cells. An overlapping binding site for the CCAAT box-binding factor CP1 is required for derepressed promoter activity in HeLa and K562 cells, but is dispensable in HEL cells, indicating that different cell types require distinct cis-elements for gp91(phox) promoter activity. Derepressed gp91(phox) promoter activity is further increased upon removal of a second CDP-binding site centered at -150 bp, revealing that CDP represses gp91(phox) expression via multiple cis-elements. We present a model in which restriction of gp91(phox) expression to mature myeloid cells involves competition between transcriptional activators and repressors for binding to multiple sites within the promoter.