Regulation of human neutrophil granule protein expression

Intracellular pools of FcαR (CD89) in human neutrophils are localized in tertiary granules and secretory vesicles, and two FcαR isoforms are found in tertiary granules

The human FcalphaRIota (CD89) is expressed on cells of myeloid lineage and plays an important role in host defense. Neutrophils make up the majority of FcalphaRIota-positive cells. Previous reports suggested that FcalphaR was stored in neutrophil intracellular pools, and it could be mobilized quickly once neutrophils were activated. However, the subcellular localization of FcalphaR in neutrophils has not been defined yet. In this study, we identified that FcalphaR was stored in secretory vesicles and tertiary granules of neutrophils by flow cytometry analysis, ELISA, confocal microscopy, and Western blotting. The molecular mass of FcalphaR in secretory vesicles was different from that in tertiary granules. FcalphaR stored in tertiary granules had a molecular mass of 50-70 kDa, whereas FcalphaR in secretory vesicles and membranes had a molecular mass of 55-75 kDa. After treatment by peptide-N-glycosidase F, an enzyme that removes N-glycosylation, FcalphaR from secretory vesicles and tertiary granules revealed a core protein of 32 kDa, which was the same as the backbone of full length of FcalphaR. A smaller FcalphaR variant with a core protein of 29-30 kDa was found in tertiary granules but not in secretory vesicles. The nature of the small variant is not clear at present and remains to be investigated further.

Growth factor independence-1 (Gfi-1) plays a role in mediating specific granule deficiency (SGD) in a patient lacking a gene-inactivating mutation in the C/EBPepsilon gene

Neutrophil-specific granule deficiency (SGD) is a rare congenital disorder marked by recurrent bacterial infections. Neutrophils from SGD patients lack secondary and tertiary granules and their content proteins and lack normal neutrophil functions. Gene-inactivating mutations in the C/EBPepsilon gene have been identified in 2 SGD patients. Our studies on a third SGD patient revealed a heterozygous mutation in the C/EBPepsilon gene. However, we demonstrate elevated levels of C/EBPepsilon and PU.1 proteins in the patient's peripheral blood neutrophils. The expression of the transcription factor growth factor independence-1 (Gfi-1), however, was found to be markedly reduced in our SGD patient despite the absence of an obvious mutation in this gene. This may explain the elevated levels of both C/EBPepsilon and PU.1, which are targets of Gfi-1 transcriptional repression. We have generated a growth factor-dependent EML cell line from the bone marrow of Gfi-1(+/-) and Gfi-1(+/+) mice as a model for Gfi-1-deficient SGD, and demonstrate that lower levels of Gfi-1 expression in the Gfi-1(+/-) EML cells is associated with reduced levels of secondary granule protein (SGP) gene expression. Furthermore, we demonstrate a positive role for Gfi-1 in SGP expression, in that Gfi-1 binds to and up-regulates the promoter of neutrophil collagenase (an SGP gene), in cooperation with wild-type but not with mutant C/EBPepsilon. We hypothesize that decreased Gfi-1 levels in our SGD patient, together with the mutant C/EBPepsilon, block SGP expression, thereby contributing to the underlying etiology of the disease in our patient.

Herpes virus entry mediator synergizes with Toll-like receptor mediated neutrophil inflammatory responses

In microbial infections polymorphnuclear neutrophils (PMN) constitute a major part of the innate host defence, based upon their ability to rapidly accumulate in inflamed tissues and clear the site of infection from microbial pathogens by their potent effector mechanisms. The recently described transmembrane receptor herpes virus entry mediator (HVEM) is a member of the tumour necrosis factor receptor super family and is expressed on many haematopoietic cells, including T cells, B cells, natural killer cells, monocytes and PMN. Interaction of HVEM with the natural ligand LIGHT on T cells has a costimulatory effect, and increases the bactericidal activity of PMN. To further characterize the function of HVEM on PMN, we evaluated the effect of receptor ligation on human PMN effector functions using an agonistic monoclonal antibody. Here we demonstrate that activation of HVEM causes activation of neutrophil effector functions, including respiratory burst, degranulation and release of interleukin-8 in synergy with ligands for Toll-like receptors or GM-CSF. In addition, stimulation via HVEM enhanced neutrophil phagocytic activity of complement opsonized, but not of non-opsonized, particles. In conclusion, these results indicate a new, as yet unknown, participation of HVEM in the innate immune response and points to a new link between innate and adaptive immunity.

Lipid raft proteome of the human neutrophil azurophil granule

Detergent-resistant membrane domains (DRMs) are present in the membranes of azurophil granules in human neutrophils (Feuk-Lagerstedt et al., J. Leukoc. Biol. 2002, 72, 970). Using a proteomic approach, we have now identified 106 proteins in a DRM preparation from these granule membranes. Among these proteins were the lipid raft structural proteins flotillin-1 and -2, cytoskeletal proteins such as actin, vimentin and tubulin, and membrane fusion promoting proteins like annexins and dysferlin. Our results suggest that the azurophil granule membrane, in similarity to the plasma membrane, is an elaborate structure that takes part in intracellular signaling and functions other than the mere delivery of bactericidal effector molecules to the phagosome.

Down-regulation of RXRalpha expression is essential for neutrophil development from granulocyte/monocyte progenitors

Neutrophil granulocytes (Gs) represent highly abundant and short-lived leukocytes that are constantly regenerated from a small pool of myeloid committed progenitors. Nuclear receptor (NR) family members are ligand-activated transcription factors that play key roles in cellular proliferation and differentiation processes including myelopoiesis. Retinoid X receptor alpha (RXRalpha) represents the predominant NR types I and II homo- and heterodimerization partner in myeloid cells. Here we show that human myeloid progenitors express RXRalpha protein at sustained high levels during macrophage colony-stimulating factor (M-CSF)-induced monopoiesis. In sharp contrast, RXRalpha is down-regulated during G-CSF-dependent late-stage neutrophil differentiation from myeloid progenitors. Down-regulation of RXRalpha is critically required for neutrophil development since ectopic RXRalpha inhibited granulopoiesis by impairing proliferation and differentiation. Moreover, ectopic RXRalpha was sufficient to redirect G-CSF-dependent granulocyte differentiation to the monocyte lineage and to promote M-CSF-induced monopoiesis. Functional genetic interference with RXRalpha signaling in hematopoietic progenitor/stem cells using a dominant-negative RXRalpha promoted the generation of late-stage granulocytes in human cultures in vitro and in reconstituted mice in vivo. Therefore, our data suggest that RXRalpha down-regulation is a critical requirement for the generation of neutrophil granulocytes.

Gelatinase B [matrix metalloproteinase (MMP)-9] and collagenases (MMP-8/-13) are upregulated in cerebrospinal fluid during aseptic and bacterial meningitis in children

We investigated the protein expression of gelatinases [matrix metalloproteinase (MMP)-2 and -9] and collagenases (MMP-8 and -13) in cerebrospinal fluid (CSF) from patients with bacterial (BM, n = 17) and aseptic (AM, n = 14) meningitis. In both, MMP-8 and -9 were increased in 100% of patients, whereas MMP-13 was detectable in 53% and 82% respectively. Three patients with clinical signs of meningitis, without CSF pleocytosis, scored positive for all three MMPs. MMP-8 appeared in two isoforms, granulocyte-type [polymorphonuclear cell (PMN)] and fibroblast/macrophage (F/M) MMP-8. Analysis of kinetic changes from serial lumbar punctures showed that these MMPs are independently regulated, and correlate only partly with CSF cytosis or levels of the endogenous inhibitor, tissue inhibitor of matrix metalloproteinase-1. In vitro, T cells, peripheral blood mononuclear cells (PBMCs) and granulocytes (PMN) release MMP-8 and -9, whereas MMP-13 could be found only in the former two cell types. Using models of exogenous (n-formyl-Met-Leu-Phe, T cell receptor cross-linking) and host-derived stimuli (interleukin-2), the kinetics and the release of the MMP-8, -9 and -13 showed strong variation between these immune cells and suggest release from preformed stocks. In addition, MMP-9 is also synthesized de novo in PBMCs and T cells. In conclusion, invading immune cells contribute only partially to MMPs in CSF during meningitis, and parenchymal cells are an equally relevant source. In this context, in patients with clinical signs of meningitis, but without CSF pleocytosis, MMPs seem to be a highly sensitive marker for intrathecal inflammation. The present data support the concept that broad-spectrum enzyme inhibition targeting gelatinases and collagenases is a potential strategy for adjunctive therapy in infectious meningitis.

The peptide Trp-Lys-Tyr-Met-Val-D-Met activates neutrophils through the formyl peptide receptor only when signaling through the formylpeptde receptor like 1 is blocked

Neutrophils express the G protein-coupled N-formyl peptide receptor (FPR) and its homologue FPRL1. The hexapeptide Trp-Lys-Tyr-Met-Val-D-Met-NH2 (WKYMVm) activates HL-60 cells transfected either with FPRL1 or with FPR. The signaling through the stably expressed receptors was inhibited by specific receptor antagonists, cyclosporine H and WRWWWW (WRW4) for FPR and FPRL1, respectively. The neutrophil release of superoxide was used to determine receptor preference, when these cells were triggered with WKYMVm. The response was not affected by the FPR specific antagonist suggesting that no signals are transduced through this receptor. The response was only partly inhibited by WRW4, but this antagonist induced a receptor switch, perceptible as a change in sensitivity to the FPR antagonist. The activity remaining in the presence of WRW4 was inhibited by cyclosporine H. A cell permeable peptide (PBP10) corresponding to the phosphatidyl-inositol-bisphosphate binding region of gelsolin, inhibited the FPRL1-, but not the FPR-induced cellular response and induced the same type of receptor switch. We show that an agonist that has the potential to bind and activate neutrophils through FPRL1 as well as through FPR, uses the latter receptor and its signaling route, only when the activating signal generated through FPRL1 is blocked. The receptor switch is achieved when signaling through FPRL1 is inhibited both by a receptor antagonist, and by an inhibitor operating from the inside of the plasma membrane. The phenomenon described is of general importance for proper interpretation of results generated through the use of different "silencing technologies" in receptor operated signaling transduction research.

PU.1 phosphorylation correlates with hydroquinone-induced alterations in myeloid differentiation and cytokine-dependent clonogenic response in human CD34+ hematopoietic progenitor cells

The transcriptional regulatory factor PU.1 is important for the regulation of a diverse group of hematopoietic and myeloid genes. Posttranslational phosphorylation of PU.1 has been demonstrated in the regulation of a variety of promoters in normal cells. In leukemia cells, differing patterns of PU.1 phosphorylation have been described among acute myelogenous leukemia (AML) subtypes. Therefore, we hypothesized that modulation of PU.1-dependent gene expression might be a molecular mediator of alterations in myeloid cell growth and differentiation that have been demonstrated to be early events in benzene-induced leukemogenesis. We found that freshly isolated human CD34(+) hematopoietic progenitor cells (HPC) exhibit multiple PU.1-DNA binding species that represent PU.1 proteins in varying degrees of phosphorylation states as determined by phosphatase treatment in combination with electrophoretic mobility shift assay (EMSA). Maturation of granulocyte and monocyte lineages is also accompanied by distinct changes in PU.1-DNA binding patterns. Experiments reveal that increasing doses of the benzene metabolite, hydroquinone (HQ) induce a time-and dose-dependent alteration in the pattern of PU.1-DNA binding in cultured human CD34(+) cells, corresponding to hyperphosphorylation of the PU.1 protein. HQ-induced alterations in PU.1-DNA binding are concomitant with a sustained immature CD34(+) phenotype and cytokine-dependent enhanced clonogenic activity in cultured human HPC. These results suggest that HQ induces a dysregulation in the external signals modulating PU.1 protein phosphorylation and this dysregulation may be an early event in the generation of benzene-induced AML.

LL-37, the only human member of the cathelicidin family of antimicrobial peptides

Antimicrobial peptides and their precursor molecules form a central part of human and mammalian innate immunity. The underlying genes have been thoroughly investigated and compared for a considerable number of species, allowing for phylogenetic characterization. On the phenotypical side, an ever-increasing number of very varied and distinctive influences of antimicrobial peptides on the innate immune system are reported. The basic biophysical understanding of mammalian antimicrobial peptides, however, is still very limited. This is especially unsatisfactory since knowledge of structural properties will greatly help in the understanding of their immunomodulatory functions. The focus of this review article will be on LL-37, the only cathelicidin-derived antimicrobial peptide found in humans. LL-37 is a 37-residue, amphipathic, helical peptide found throughout the body and has been shown to exhibit a broad spectrum of antimicrobial activity. It is expressed in epithelial cells of the testis, skin, the gastrointestinal tract, and the respiratory tract, and in leukocytes such as monocytes, neutrophils, T cells, NK cells, and B cells. It has been found to have additional defensive roles such as regulating the inflammatory response and chemo-attracting cells of the adaptive immune system to wound or infection sites, binding and neutralizing LPS, and promoting re-epthelialization and wound closure. The article aims to report the known biophysical facts, with an emphasis on structural evidence, and to set them into relation with insights gained on phylogenetically related antimicrobial peptides in other species. The multitude of immuno-functional roles is only outlined. We believe that this review will aid the future work on the biophysical, biochemical and immunological investigations of this highly intriguing molecule.

Regulation of matrix metalloproteinase-9 (MMP-9) in TNF-stimulated neutrophils: novel pathways for tertiary granule release

Matrix metalloproteinase-9 (MMP-9) is present in the tertiary granules of neutrophils and is rapidly released following stimulation. We examined the pathways that regulate tumor necrosis factor (TNF)-mediated MMP-9 release and found this to be dependent on the TNF receptor I. TNF rapidly activated extracellular signal-regulated kinase and p38 mitogen-activated protein kinases, but neither of these pathways was critical for MMP-9 release. Many neutrophil responses to TNF require beta2-integrin-dependent signaling and subsequent Src family kinase activation. In contrast, we found that MMP-9 release from tertiary granules was only partially affected by blocking beta2-integrin-mediated adhesion. Similarly, blocking Src family kinases with the inhibitor PP2 only attenuated TNF-induced MMP-9 release. Blocking beta2-integrin-mediated adhesion and Src family kinases did not result in additive inhibition of MMP-9 release. In contrast, inhibiting protein kinase C (PKC) with a pan-specific inhibitor blocked greater than 85% of MMP-9 release. Inhibitors against specific PKC isoforms suggested a role for PKC alpha and PKC delta in maximal MMP-9 release. These data suggest that MMP-9 release from tertiary granules uses beta2-integrin-independent signaling pathways. Furthermore, PKC isoforms play a critical role in regulating tertiary granule release.

The proximal promoter of the human cathepsin G gene conferring myeloid-specific expression includes C/EBP, c-myb and PU.1 binding sites

Cathepsin G is a hematopoietic serine protease stored in the azurophil granules of neutrophil granulocytes. The mRNA of cathepsin G is transiently expressed during the promyelocyte stage of neutrophil maturation. The protease plays several roles in inflammatory actions of neutrophils, such as bactericidal effects. A human cathepsin G gene fragment of 6 kb directs a promyelocyte-specific expression in transgenic mice, indicating the presence of necessary cis-acting elements. However, neither the precise architecture of the promoter, nor the trans-acting factors responsible for its activation, have been characterized. In the present work, 2.6 kb upstream of the translation start site of the human cathepsin G gene was cloned. When transfected to monoblast-like U937 or to acute promyelocytic leukemia NB4 cells, both expressing endogenous cathepsin G, the initial 360 bp upstream of the translation start were sufficient to direct a strong expression of a luciferase reporter gene. No expression was observed in erythroid K562 control cells. Further deletions revealed three major regulatory regions containing the consensus binding-sites for the transcription factors C/EBP, c-myb and PU.1. Moreover, a GC-rich region, similar to a cis-element in the proteinase 3 promoter, was identified. Direct binding of the trans-factors C/EBPalpha, C/EBPepsilon, c-myb and PU.1 to the promoter was shown by chromatin immunoprecipitation. The functional significance of the cis-elements was verified by site-directed mutagenesis. Mutations of the putative PU.1 site moderately decreased the activity of the promoter in monoblastic U937 cells, but not in promyelocytic NB4 cells. Separate mutations of the putative C/EBP binding site, c-myb-binding site or the GC-rich element resulted in a dramatically reduced transcriptional activity in both cell lines, suggesting cooperation between corresponding trans-factors.

Proteomic Analysis of Human Neutrophil Granules

Stimulated exocytosis of intracellular granules plays a critical role in conversion of inactive, circulating neutrophils to fully activated cells capable of chemotaxis, phagocytosis, and bacterial killing. The functional changes induced by exocytosis of each of the granule subsets, gelatinase (tertiary) granules, specific (secondary) granules, and azurophil (primary) granules, are poorly defined. To improve the understanding of the role of exocytosis of these granule subsets, a proteomic analysis of the azurophil, specific, and gelatinase granules from human neutrophils was performed. Two different methods for granule protein identification were applied. First, two-dimensional (2D) gel electrophoresis followed by MALDI-TOF MS analysis of peptides obtained by in-gel trypsin digestion of proteins was performed. Second, peptides from tryptic digests of granule membrane proteins were separated by two-dimensional microcapillary chromatography using strong cation exchange and reverse phase microcapillary high pressure liquid chromatography and analyzed with electrospray ionization tandem mass spectrometry (2D HLPC ESI-MS/MS). Our analysis identified 286 proteins on the three granule subsets, 87 of which were identified by MALDI MS and 247 were identified by 2D HPLC ESI-MS/MS. The increased sensitivity of 2D HPLC ESI-MS/MS, however, resulted in identification of over 500 proteins from subcellular organelles contaminating isolated granules. Defining the proteome of neutrophil granule subsets provides a basis for understanding the role of exocytosis in neutrophil biology. Additionally, the described methods may be applied to mobilizable compartments of other secretory cells.

PU.1-mediated transcriptional regulation of prophenin-2 in primary bone marrow cells

Prophenin-2 (PF-2) is a cathelicidin, 97-amino-acid antimicrobial protein stored in neutrophil secondary granules. PF-2 is expressed specifically in porcine immature myeloid cells; however, little is known about its regulation. In this study, we characterized the 5' regulatory regions of the PF-2 gene to understand the molecular mechanisms regulating its expression. Using bioinformatic approaches, site-directed mutagenesis, and transactivation experiments, we found that the PF-2 gene was regulated by transcription factor PU.1. In addition, PF-2 expression also is regulated by the cytokines GM-CSF and IL-3. Taken together, these results identify cis- and trans-acting factors involved in the regulation of PF-2 and clarify mechanisms of cathelidicin gene regulation.

Proteinase-3 induces procaspase-3 activation in the absence of apoptosis: potential role of this compartmentalized activation of membrane-associated procaspase-3 in neutrophils

In the present study, we provide evidence that procaspase-3 is a novel target of proteinase 3 (PR3) but not of human neutrophil elastase (HNE). Human mast cell clone 1 (HMC1) and rat basophilic leukemia (RBL) mast cell lines were transfected with PR3 or the inactive mutated PR3 (PR3S203A) or HNE cDNA. In both RBL/PR3 and HMC1/PR3, a constitutive activity of caspase-3 was measured with DEVD substrate, due to the direct processing of procaspase-3 by PR3. No caspase-3 activation was observed in cells transfected with the inactive PR3 mutant or HNE. Despite the high caspase-3 activity in RBL/PR3, no apoptosis was detected as demonstrated by an absence of 1) phosphatidylserine externalization, 2) mitochondria cytochrome c release, 3) upstream caspase-8 or caspase-9 activation, or 4) DNA fragmentation. In vitro, purified PR3 cleaved procaspase-3 into an active 22-kDa fragment. In neutrophils, the 22-kDa caspase-3 activation fragment was present only in resting neutrophils but was absent after apoptosis. The 22 kDa fragment was specific of myeloid cells because it was absent from resting lymphocytes. This 22-kDa fragment was not present when neutrophils were treated with pefabloc, an inhibitor of serine proteinase. Like in HMC1/PR3, the 22-kDa caspase-3 fragment was restricted to the plasma membrane compartment. Double immunofluorescence labeling after streptolysin-O permeabilization further showed that PR3 and procaspase-3 could colocalize in an extragranular compartment. In conclusion, our results strongly suggest that compartmentalized PR3-induced caspase-3 activation might play specific functions in neutrophil survival.

Prodefensins are matrix proteins of specific granules in human neutrophils

Defensins are potent antimicrobial and proinflammatory peptides. The human neutrophil defensins human neutrophil peptide (HNP)-1-3 are synthesized as 94 amino acide (aa) preproHNPs, which are converted to 75 aa proHNPs by cotranslational removal of a 19 aa endoplasmic reticulum signal peptide. At the promyelocytic stage of myelopoiesis, proHNPs are further proteolytically modified and accumulate in azurophil granules as 29-30 aa HNPs. In contrast, proHNPs produced by more mature myeloid cells are not subjected to proteolytic cleavage and undergo a high degree of constitutive exocytosis. The proHNPs are devoid of antimicrobial potential, and the significance of their secretion is unknown. To investigate whether mature neutrophils contain proHNPs, we developed antibodies against proHNP-1 by DNA immunization of rabbits. In addition, antibodies against the 45 aa proHNP pro-piece were raised by conventional immunization procedures. These antibodies allowed detection of proHNPs in homogenates of peripheral blood neutrophils. The proHNPs were isolated by affinity chromatography, and their identity was confirmed by mass spectrometry and N-terminal aa sequence analysis. Finally, the neutrophil proHNPs were identified as novel matrix proteins of specific granules by subcellular fractionation experiments, release studies, and immunoelectron microscopy. Thus, human neutrophils not only store large amounts of mature defensins in azurophil granules but also contain a more easily mobilized reservoir of unprocessed prodefensins in specific granules.

Cytokine signals through STAT3 promote expression of granulocyte secondary granule proteins in 32D cells

OBJECTIVE

In a previous study, we showed that activation of a transfected human erythropoietin receptor (EPOR) in the murine myeloid cell line 32D resulted in the development of morphologic features of granulocytic differentiation and expression of the neutrophil primary granule protein myeloperoxidase. We now studied if EPOR signaling could also mediate secondary granule protein gene expression and investigated the signal transduction requirements for induction of secondary granule gene expression in 32D cells.

MATERIALS AND METHODS

Wild-type and variant 32D cells expressing normal or chimeric EPORs or receptors for granulocyte colony-stimulating factor (G-CSFRs) were stimulated with EPO or G-CSF and the expression of granulocyte-specific genes was analyzed by Northern blot analysis. To determine the signaling mechanisms required for secondary granule protein gene induction, the activation of STAT pathways following growth factor stimulation was studied by Western blot analysis.

RESULTS

We found that EPO treatment of 32D cells engineered to express EPOR did not result in induction of the secondary granule protein genes encoding lactoferrin and 24p3 lipocalin, the mouse homolog of human N-Gal, or the myeloid transcription factor C/EBPepsilon. Replacement of the intracellular domain of EPOR with the intracellular domain of G-CSFR in a chimeric receptor was associated with EPO-mediated induction of lactoferrin, 24p3 lipocalin, and C/EBPepsilon genes. We found that STAT3 phosphorylation was mediated by the intracellular domain of G-CSFR, but not EPOR. Replacement of one or two of the STAT5 binding sites in the intracytoplasmic domain of the EPOR with STAT3 binding sites resulted in EPO-mediated STAT3 activation and a marked increase in the expression of the 24p3 lipocalin gene. Knockdown of STAT3 protein levels with siRNA caused significant decrease in 24p3 lipocalin gene induction.

CONCLUSION

These results indicate that EPOR signaling cannot substitute for G-CSFR signaling to stimulate secondary granule protein gene expression in 32D cells. In addition, STAT3 is a critical mediator of 24p3 lipocalin gene expression in these cells.

Human neutrophil collagenase expression is C/EBP-dependent during myeloid development

OBJECTIVE

Human neutrophil collagenase (HNC) is one of several secondary granule proteins (SGP) expressed late in the myeloid maturation pathway. SGPs are encoded by unlinked and functionally diverse genes that are hypothesized to be coordinately regulated at the transcriptional level and demonstrate uniform dysregulation in leukemic cells. In support of the hypothesis that tissue and stage-specific expression of SGP genes is regulated by shared factor(s), we sought to identify factors responsible for positive regulation of the SGP genes.

METHODS

Using 5' deletion analysis, we identified a minimal HNC promoter located within the first 193 bp upstream of the transcription start site. Three CCAAT enhancer binding protein (C/EBP) sites were identified within this region and their functional importance was confirmed by mutational analysis, gel retardation, and oligonucleotide pulldown assays. Using chromatin immunoprecipitation (ChIP), we demonstrated that C/EBPalpha binds to the SGP gene promoters lactoferrin and HNC in nonexpressing cells. Upon induction of maturation, C/EBPalpha binds to these promoters and this binding correlates with the expression of both SGP genes.

CONCLUSION

We conclude that in the later stages of myeloid development, SGP genes are coordinately upregulated, and that members of the C/EBP family of transcription factors, in particular C/EBPalpha and C/EBPepsilon, play specific and unique roles in upregulating their expression.

The transcriptional program of terminal granulocytic differentiation

To characterize the transcriptional program that governs terminal granulocytic differentiation in vivo, we performed comprehensive microarray analyses of human bone marrow populations highly enriched in promyelocytes (PMs), myelocytes/metamyelocytes (MYs), and neutrophils (bm-PMNs). These analyses identified 11 310 genes involved in differentiation, of which 6700 were differentially regulated, including previously unidentified effector proteins and surface receptors of neutrophils. Differentiation of PMs toward MYs was accompanied by a marked decline of proliferative and general cellular activity as defined by down-regulation of E2 promoter binding factor (E2F) target genes; cyclin dependent kinases 2, 4, and 6; and various metabolic, proteasomal, and mitochondrial genes. Expression patterns of apoptosis genes indicated death control by the p53 pathway in PMs and by death receptor pathways in bm-PMNs. Effector proteins critical for host defense were expressed successively throughout granulocytic differentiation, whereas receptors and receptor ligands essential for the activation of the host defense program were terminally up-regulated in bm-PMNs. The up-regulation of ligand-receptor pairs, which are defined inducers as well as target genes of nuclear factor-κB (NF-κB), suggests a constitutive activation of NF-κB in bm-PMNs by autocrine loops. Overall, these results define a granulocytic differentiation model governed by a highly coordinated fail-safe program, which promotes completion of differentiation before cells gain responsiveness toward activating stimuli that accompany infections. (Blood. 2005; 105:1785-1796)

Regulation of the neutrophil-mediated inflammatory response to infection

Human polymorphonuclear leukocytes (PMNs) are the first line of defense against invading microorganisms and contribute significantly to inflammation. Recent evidence suggests that resolution of neutrophil-mediated inflammation is facilitated by an apoptosis differentiation program, a final stage of transcriptionally regulated PMN maturation that is accelerated significantly by phagocytosis.

Evidence for expression of early myeloid antigens in mature, non-blast myeloid cells in myelodysplasia

Myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell disorders with frequent cytogenetic abnormalities. They can arise de novo or be related to therapy. Although blasts in MDS have been studied extensively, there is little information available on the mature, non-blast myeloid cells (NBMCs). We used a retrospective case-control study design. NBMC populations in MDS (48 cases) and in tumor-free control (12 cases) bone marrow samples were analyzed using multiparameter flow cytometry for mean side scatter (SSC) channel number and for expression of aberrant cell surface antigens. MDS cases were stratified on the basis of cytogenetic abnormalities. We report that NBMCs in MDS with normal karyotype expressed significantly higher HLA-DR than controls (P = 0.034). NBMCs in MDS cases with cytogenetic abnormalities and with > or =5% marrow blasts, compared with controls, had significantly higher CD34 and higher HLA-DR but lower CD10 and lower SSC mean channel number. CD34 expression in NBMCs was significantly greater in therapy-related MDS compared with de novo MDS ( P = 0.01), although the presence of cytogenetic abnormalities was not different ( P > 0.05). These data suggest that bone marrow, mature, NBMCs have phenotypic changes in MDS that are not seen in normal controls.

Reactivation of formyl peptide receptors triggers the neutrophil NADPH-oxidase but not a transient rise in intracellular calcium

In neutrophils, coupling of chemoattractants to their cell surface receptor at low temperature (<or=15 degrees C) leads to receptor deactivation/desensitization without any triggering of the superoxide anion-generating NADPH-oxidase. We show that the deactivated formyl peptide receptors (FPRs) can be reactivated/resensitized by the cytoskeleton-disrupting drug cytochalasin B. Such cytoskeleton-dependent receptor reactivation occurs also with the closely related receptors FPR-like-1 and C5aR but not with the receptors for interleukin-8 and platelet-activating factor. The reactivation state was further characterized with FPR as a model. The signals generated by receptor reactivation induced superoxide production that was terminated in 5-8 min, after which the neutrophils entered a new state of homologous deactivation. FPR antagonists were potent inhibitors of the superoxide production induced by the reactivated receptors, suggesting that the occupied receptors turn into an actively signaling state when the cytoskeleton is disrupted. The signals generated by the reactivated receptor were pertussis toxin-sensitive, indicating involvement of a G-protein. However, no transient elevation of intracellular Ca2+ accompanies the NADPH-oxidase activation. This was not due to a general down-regulation of phospholipase C/Ca2+ signaling, and despite the fact that no intracellular Ca2+ transient was generated, protein kinase C still appeared to be involved in the response. Further, phosphatidylinositol 3-kinase, mitogen-activated protein kinase, and MEK all participated in the generation of second messengers from the reactivated receptors.

The in vivo profile of transcription factors during neutrophil differentiation in human bone marrow

In vivo distribution of myeloid transcription factors during granulopoiesis was investigated by Northern and Western blotting in 3 neutrophil precursor populations from human bone marrow: immature (myeloblasts [MBs] and promyelocytes [PMs]); intermediate mature (myelocytes [MCs] and metamyelocytes [MMs]); and mature neutrophil cells (band cells [BCs] and segmented neutrophil cells [SCs]). Nonneutrophil cells were removed with magnetic-bead-coupled antibodies against CD2, CD3, CD14, CD19, CD56, CD61, glycophorin-A, and CD49d (BCs/SCs) before RNA and protein extraction. Polymorphonuclear neutrophils (PMNs) from peripheral blood depleted with anti-CD49d antibodies were also included. Expression of acute myeloid leukemia 1b (AML-1b), c-myb, GATA-1, and CCAAT/enhancer binding protein gamma (C/EBP-gamma) was seen primarily in MBs/PMs, and little expression was found in more mature cells. The level of C/EBP-alpha was constant in the bone marrow-derived cells and decreased in PMNs. C/EBP-epsilon was found primarily in MCs/MMs and was almost absent in more mature cells. Expression of C/EBP-beta, C/EBP-delta, and C/EBP-zeta was observed from the MC/MM stage onward, with peak levels in the most mature cells. The amount of PU.1 increased throughout maturation whereas the level of Elf-1 reached a nadir in MCs/MMs The PU.1 coactivator c-jun and c-jun's dimerization partner c-fos were both detectable in MCs/MMs and increased in amount with maturity. CCAAT displacement protein (CDP) was found at comparable levels at all stages of differentiation. This demonstrates a highly individualized expression of the transcription factors, which can form the basis for the heterogeneous expression of granule proteins during granulopoiesis and cell cycle arrest in metamyelocytes.

Immunity and mastitis. Some new ideas for an old disease

The biggest challenge for host immune defense against mastitis-causing bacteria in dairy cows is to quickly recruit large enough numbers of opsonizing molecules and mature neutrophils into milk such that intramammary pathogens are cleared before they multiply significantly and the inflammatory response gets out of control. Currently, this challenge is best facilitated when established mastitis control procedures are practiced on the farm, including proper hygiene, milking procedures, and regular administration of approved mastitis vaccines. However, mastitis is still a significant problem. New animal functional genomics research is beginning to allow scientists to solve the puzzle of mastitis susceptibility. Results of this type of research offer the hope of giant leaps toward a clear identification of molecular genetic variation and potential gene targets for therapies and immune manipulations that could significantly reduce the risk of clinical mastitis in traditionally susceptible cows.

Dysregulation of transcriptions in primary granule constituents during myeloid proliferation and differentiation in patients with severe congenital neutropenia

We examined the expression of granule constituent genes in myeloid progenitor cells during proliferation and differentiation in patients with severe congenital neutropenia (SCN). The heterozygous mutation of the neutrophil elastase gene was identified in two of four patients. The CD34+/granulocyte-colony stimulating factor receptor (G-CSFR)+ cells of SCN patients showed defective responsiveness to G-CSF in serum-deprived culture. The CD34+/G-CSFR+ cells expressed low levels of the granule constituent mRNAs. The transcription levels of primary granule enzyme genes in CD34+/G-CSFR+ cells were gradually enhanced and then decreased when cells were induced toward myeloid lineage with G-CSF in normal subjects. However, the primary up-regulation and the following down-regulation of these enzyme transcriptions were not clearly observed in SCN patients. No differences in expressions of the lactoferrin gene were seen between normal subjects and patients with SCN. We hypothesize that the abnormal regulation of the transcription in primary granule constituents might involve the defective proliferation and differentiation of myeloid cells in patients with SCN.

Intrinsic requirement for zinc finger transcription factor Gfi-1 in neutrophil differentiation

We report essential roles of zinc finger transcription factor Gfi-1 in myeloid development. Gene-targeted Gfi-1(-/-) mice lack normal neutrophils and are highly susceptible to abscess formation by gram-positive bacteria. Arrested, morphologically atypical, Gr1(+)Mac1(+) myeloid cells expand with age in the bone marrow. RNAs encoding primary but not secondary or tertiary neutrophil (granulocyte) granule proteins are expressed. The atypical Gr1(+)Mac1(+) cell population shares characteristics of both the neutrophil and macrophage lineages and exhibits phagocytosis and respiratory burst activity. Reexpression of Gfi-1 in sorted Gfi-1(-/-) progenitors ex vivo rescues neutrophil differentiation in response to G-CSF. Thus, Gfi-1 not only promotes differentiation of neutrophils but also antagonizes traits of the alternate monocyte/macrophage program.