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

Derangement of transcription factor profiles during in vitro differentiation of HL60 and NB4 cells

Sequential up- and down-regulation of a handful of critical transcription factors is required for proper neutrophil differentiation. Malfunction of transcription factors may lead to diseases such as acute myeloid leukemia (AML) and specific granule deficiency. In order to understand the molecular background for normal and malignant granulopoiesis, a good model system is required that faithfully mimics the in vivo transcription factor expression profiles. The two human leukemic cell lines HL60 and NB4 have been widely used as model cell lines for these purposes. Differentiation of HL60 and NB4 cells resulted in asynchronous differentiation to morphologically mature neutrophils over a period of 5-7 days. To obtain cell populations of more even maturity, cells at different stages of in vitro differentiation were purified by immunomagnetic isolation. This resulted in three cell populations that could be classified as promyelocytes, myelocytes/metamyelocytes, and mature neutrophils, respectively. Comparison of transcription factor mRNA profiles from these cell populations with those previously seen in normal human bone marrow, demonstrated that although all of the 14 transcription factors described in vivo, could be detected during in vitro differentiation, vast differences in their expression profiles was observed. These data illustrate the limitations of cell lines as models for normal granulopoiesis.

Trans-Repressive Effect of NUP98-PMX1 on PMX1-Regulated c-FOSGene through Recruitment of Histone Deacetylase 1 by FG Repeats

The formation of fusion genes between NUP98 and members of the HOX family represents a critical factor for the genesis of acute leukemia or acute transformation of chronic myeloid leukemia (CML). To gain insights into the molecular mechanisms underlying the leukemogenesis of NUP98-HOX fusion products, we cloned NUP98-PMX1 from a CML-blast crisis patient with t(1;11) as a secondary chromosomal translocation, and functionally studied the fusion products in detail through various molecular and protein biochemical assays. In addition to many interesting features, we have found that the NUP98-PMX1 fusion protein exerts a repressive effect on PMX1 or serum response factor-mediated c-FOS activation, probably through the recruitment of a common corepressor histone deacetylase 1 by FG domains of the NUP98-PMX1 fusion protein. Moreover, we have provided evidence that the FG domains of NUP98-PMX1 and two other NUP98-containing fusion proteins, i.e., NUP98-HOXA9 and NUP98-HOXC11, all exhibit dual binding ability to both CREB binding protein, a coactivator, and histone deacetylase 1, a corepressor. Accordingly, we have hypothesized that this dual binding activity is shared by most, if not all, NUP98-HOX-involved fusion proteins, enabling these fusion proteins to act as both trans-activators and trans-repressors, and contributing to the genesis of acute leukemia or acute transformation of CML.

C/EBPalpha: a tumour suppressor in multiple tissues?

The CCATT/enhancer binding protein alpha, C/EBPalpha, is a key transcription factor involved in late differentiation events of several cell types. Besides acting as a classical transcription factor, C/EBPalpha is also a well-characterized inhibitor of mitotic growth in most cell lines tested. In line with its anti-mitotic properties, C/EBPalpha has been shown to interact with, and alter the activities of, several cell cycle related proteins and a number of models as to the mechanistics of C/EBPalpha-mediated growth repression have been proposed. More recently, several reports have indicated that C/EBPalpha acts as a tumour suppressor in the hematopoietic system and that mutation within C/EBPalpha is sufficient to induce tumourigenesis. Here, we will review these data and probe the possibility that C/EBPalpha also act as a tumour suppressor in other C/EBPalpha-expressing tissues.

p21Waf1 inhibits granulocytic differentiation of 32Dcl3 cells

Defining the molecular mechanisms that prevent myeloid progenitor cells from maturing is important because defects in maturation contribute to the development of myeloproliferative and myelodysplastic diseases. IL-3 is an important developmental factor for myeloid progenitor cells in vivo and is required to maintain the undifferentiated state in the 32Dcl3 cell line. The mechanisms employed by IL-3 to block differentiation, however, are not well understood. 32Dcl3 cells are myeloid progenitor cells of murine origin with high basal levels of p21waf1/cip1 (p21) expression. Our laboratory has previously reported that p21 levels decreased as CD34+-derived myeloid progenitor cells underwent terminal granulopoiesis in vitro. The effect of p21 upon the expression of genes associated with granulocytic differentiation has been unexplored, however. Since IL-3 maintains high levels of p21 in 32Dcl3 cells, we tested the hypothesis that p21 is an inhibitor of myeloid differentiation. Our findings demonstrate that siRNA knockdown of murine p21 is correlated with premature expression of the primary granule proteins myeloperoxidase and proteinase-3, proteins not abundant in cells maintained as myeloblasts by IL-3. Rescue with human p21 in these cells suppressed premature granule protein expression. p21 knockdown was also found to accelerate morphologic granulocytic differentiation in 32Dcl3 cells stimulated with G-CSF. Since high expression levels of p21 and overexpression of the IL-3 receptor have been correlated with poor outcomes in acute myeloid leukemias (AML), differentiation blockade by p21 may be one mechanism that contributes to AML pathogenesis.

Cytokine-induced myeloid differentiation is dependent on activation of the MEK/ERK pathway

The intracellular signaling pathways that mediate cytokine-induced granulocytic and monocytic differentiation are incompletely understood. In this study, we examined the importance of the MEK/ERK signal transduction pathway in granulocyte-colony stimulating factor (G-CSF)-induced granulocytic differentiation of murine 32 Dc l3 cells, and in interleukin-6 (IL-6)-induced monocytic differentiation of murine M1 cells. Induction of granulocytic differentiation with G-CSF, or monocytic differentiation with IL-6, led to rapid and sustained activation of the MEK-1/-2 and ERK-1/-2 enzymes. Inhibition of the MEK/ERK pathway by pretreatment with the MEK inhibitor U 0126 dramatically attenuated G-CSF-induced granulocytic differentiation and IL-6-induced monocytic differentiation. Inhibition of MEK/ERK signaling also significantly reduced cytokine-induced DNA binding activities of STAT 3 and PU.1, transcription factors that have been implicated in myeloid differentiation. Additionally, interleukin-3, which inhibits G-CSF-induced differentiation of 32 Dc l3 cells, also inhibited the ability of G-CSF to stimulate prolonged MEK/ERK activation. Thus, the opposing actions of different hematopoietic cytokines on myeloid progenitors may be mediated at the level of MEK/ERK activation. Taken together, these studies demonstrate an important requirement for MEK/ERK activation during cytokine-induced granulocytic and monocytic differentiation.

On mouse and man: neutrophil gelatinase associated lipocalin is not involved in apoptosis or acute response

Neutrophil gelatinase-associated lipocalin (NGAL) is a siderphore binding molecule present in the specific granules of neutrophils and induced in a variety of epithelial cells during inflammation. Its mouse orthologue, 24p3, is also an acute phase protein synthesized in the liver and adipose tissue during inflammation. 24p3 has recently been implicated in apoptosis of myeloid cells. We investigated whether similar features are characteristics of NGAL. First, isolated normal myeloid bone marrow cells were incubated with NGAL for 6 and 24 hr and analyzed for apoptosis by annexin V binding and by propidium iodide labeling. We found no indication that NGAL induces significant apoptosis in myeloid cells. Second, a human sepsis model where normal volunteers were given endotoxin 2 ng/kg intravenously, showed no evidence that NGAL is an acute phase protein. The plasma level of NGAL reflected the number of circulating neutrophils and was completely different from the kinetics of C-reactive protein. We thus conclude that major differences exist between mouse and man with regards to the role of this lipocalin in myelopoiesis and inflammation.

Decreased expression of CCAAT/enhancer binding protein zeta (C/EBPzeta) in patients with different myeloid diseases

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that have been implicated in diverse cellular functions such as cellular differentiation and proliferation, and inflammatory processes. C/EBPzeta, also known as GADD153, CHOP10, and DDIT3 has been found associated with the development of myxoid liposarcoma and the progression of melanoma. To investigate the correlation of C/EBPzeta transcript levels with the development of leukemia, samples from 187 patients with myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), and chronic myeloid leukemia (CML) were examined for C/EBPzeta mRNA using real-time quantitative PCR (RQ-PCR). RQ-PCR analysis demonstrated the median levels of C/EBPzeta were significantly decreased in MDS, AML, and CML patients compared with normal controls (1.40, 0.96, 2.60 versus 14.69, P<0.0001). Significant differences were also observed between patients with CML and with AML or MDS. These results suggest that the insufficient dosage of C/EBPzeta might be involved in the development of leukemia.

The Drosophila lymph gland as a developmental model of hematopoiesis

Drosophila hematopoiesis occurs in a specialized organ called the lymph gland. In this systematic analysis of lymph gland structure and gene expression, we define the developmental steps in the maturation of blood cells (hemocytes) from their precursors. In particular, distinct zones of hemocyte maturation, signaling and proliferation in the lymph gland during hematopoietic progression are described. Different stages of hemocyte development have been classified according to marker expression and placed within developmental niches: a medullary zone for quiescent prohemocytes, a cortical zone for maturing hemocytes and a zone called the posterior signaling center for specialized signaling hemocytes. This establishes a framework for the identification of Drosophila blood cells, at various stages of maturation, and provides a genetic basis for spatial and temporal events that govern hemocyte development. The cellular events identified in this analysis further establish Drosophila as a model system for hematopoiesis.

Transcriptional regulation in myelopoiesis: Hematopoietic fate choice, myeloid differentiation, and leukemogenesis

Myeloid cells (granulocytes and monocytes) are derived from multipotent hematopoietic stem cells. Gene transcription plays a critical role in hematopoietic differentiation. However, there is no single transcription factor that is expressed exclusively by myeloid cells and that, alone, acts as a "master" regulator of myeloid fate choice. Rather, myeloid gene expression is controlled by the combinatorial effects of several key transcription factors. Hematopoiesis has traditionally been viewed as linear and hierarchical, but there is increasing evidence of plasticity during blood cell development. Transcription factors strongly influence cellular lineage during hematopoiesis and expression of some transcription factors can alter the fate of developing hematopoietic progenitor cells. PU.1 and CCAAT/enhancer-binding protein alpha (C/EBPalpha) regulate expression of numerous myeloid genes, and gene disruption studies have shown that they play essential, nonredundant roles in myeloid cell development. They function in cooperation with other transcription factors, co-activators, and co-repressors to regulate genes in the context of chromatin. Because of their essential roles in regulating myeloid genes and in myeloid cell development, it has been hypothesized that abnormal expression of PU.1 and C/EBPalpha would contribute to aberrant myeloid differentiation, i.e. acute leukemia. Such a direct link has been elusive until recently. However, there is now persuasive evidence that mutations in both PU.1 and C/EBPalpha contribute directly to development of acute myelogenous leukemia. Thus, normal myeloid development and acute leukemia are now understood to represent opposite sides of the same hematopoietic coin.

Induction of CCAAT/enhancer binding protein-delta by cytokinins, but not by retinoic acid, during granulocytic differentiation of human myeloid leukaemia cells

Cytokinins, purine derivatives that act as hormones to control many processes in plants, are very effective at inducing the granulocytic differentiation of human myeloid leukaemia cells. Isopentenyladenine (IPA), a potent cytokinin, significantly induced the expression of CCAAT/enhancer-binding protein (C/EBP)delta, but not C/EBP alpha protein, whereas all-trans retinoic acid, a well-known inducer of granulocytic differentiation, induced C/EBP alpha but not C/EBP delta protein. Antisense oligonucleotide for C/EBP delta, but not C/EBP alpha or C/EBP beta, effectively suppressed IPA-induced differentiation, suggesting that the expression of C/EBP delta protein is necessary for cytokinin-induced differentiation. Although C/EBP alpha is known to be crucial for granulocytic differentiation, the function of C/EBP delta has not been well documented in the regulation of haematopoiesis. The role of C/EBP delta in the granulocytic differentiation of myeloid leukaemia cells is discussed.

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)

Neutrophils and keratinocytes in innate immunity--cooperative actions to provide antimicrobial defense at the right time and place

The human neutrophil is a professional phagocyte of fundamental importance for defense against microorganisms, as witnessed by the life-threatening infections occurring in patients with neutropenia or with defects that result in decreased microbicidal activity of the neutrophil. Likewise, the skin and mucosal surfaces provide important barriers against infections. Traditionally, these major defense systems, the epithelial cells and the neutrophils, have been viewed as limited in their armory: The epithelial cells provide defense by constituting a physical barrier, and the neutrophils provide instant delivery of preformed antimicrobial substances or on-the-spot assembly of the multicomponent reduced nicotinamide adenine dinucleotide phosphate oxidase from stored components for the generation of reactive oxygen metabolites. Recent research has shown that epithelial cells are highly dynamic and able to generate antimicrobial peptides in response not only to microbial infection itself but more importantly, to the growth factors that are called into play when the physical barrier is broken, and the risk of microbial infection is imminent. Likewise, the neutrophil changes its profile of actively transcribed genes when it diapedeses into wounded skin. This results in generation of signaling molecules, some of which support the growth and antimicrobial potential of keratinocytes and epithelial cells. This paper will highlight some recent advances in this field.

Clonogenicity, gene expression and phenotype during neutrophil versus erythroid differentiation of cytokine-stimulated CD34+human marrow cellsin vitro

With the objective to correlate clonogenicity, gene expression and phenotype during differentiation, human bone marrow CD34(+) cells were cultured in vitro to stimulate erythroid or neutrophil development, and sorted into five subpopulations according to their surface expression of CD15/CD33 and blood group antigen A/CD117 respectively. Sorted cells were cultured in methylcellulose and analysed by real-time reverse transcription polymerase chain reaction for expression of neutrophil and erythroid marker genes. Surface expression of CD15 coincided with restriction to neutrophil/monocyte differentiation and A antigen with restriction to erythroid differentiation. GATA-2 mRNA was down-regulated during both neutrophil and erythroid maturation, whereas GATA-1, SCL, ABO, erythropoietin receptor, Kell, glycophorin A, beta-globin and alpha-haemoglobin stabilizing protein were up-regulated during erythroid differentiation and silenced during neutrophil differentiation. CCAAT/enhancer-binding protein (C/EBP)-alpha, PU.1, granulocyte colony-stimulating factor receptor, PR3, C/EBP-epsilon and lactoferrin were sequentially expressed during neutrophil differentiation but rapidly down-regulated during the early erythroid stages. Nuclear factor erythroid-derived 2 (NF-E2) and glycophorin C were expressed both during neutrophil and erythroid differentiation. Our data support the notion of early expression of several lineage-associated genes prior to actual lineage commitment, defined by surface expression of CD15 and A antigen as markers for definitive neutrophil/monocyte and erythroid differentiation respectively. Previous findings, primarily from cell lines and mouse models, have been extended to adult human haematopoiesis.

Expression and regulation of NFAT (nuclear factors of activated T cells) in human CD34+cells: down-regulation upon myeloid differentiation

The calcineurin-dependent, cyclosporin A (CsA)-sensitive transcription factor nuclear factor of activated T cells (NFAT) represents a group of proteins, which is well-characterized as a central regulatory element of cytokine expression in activated T cells. In contrast, little is known about the expression or function of NFAT family members in myeloid cells; moreover, it is unclear whether they are expressed by hematopoietic stem/progenitor cells. Here, we show that NFATc2 (NFAT1) is expressed at high levels in CD34+ cells and megakaryocytes but not in cells committed to the neutrophilic, monocytic, or erythroid lineages. Cytokine-induced in vitro differentiation of CD34+ cells into neutrophil granulocytes results in the rapid suppression of NFATc2 RNA and protein. NFATc2 dephosphorylation/rephosphorylation as well as nuclear/cytoplasmic translocation in CD34+ cells follow the same calcineurin-dependent pattern as in T lymphocytes, suggesting that NFATc2 activation in these cells is equally sensitive to inhibition with CsA. Finally, in vitro proliferation, but not differentiation, of CD34+ cells cultured in the presence of fms-like tyrosine kinase 3 ligand (FLT3L), stem cell factor, granulocyte macrophage-colony stimulating factor (GM-CSF), interleukin-3, and G-CSF is profoundly inhibited by treatment with CsA in a dose-dependent manner. These results suggest a novel and unexpected role for members of the NFAT transcription factor family in the hematopoietic system.

Core-binding factors in hematopoiesis and immune function

Core binding factors are heterodimeric transcription factors containing a DNA binding Runx1, Runx2, or Runx3 subunit, along with a non DNA binding CBF beta subunit. All four subunits are required at one or more stages of hematopoiesis. This review describes the role of Runx1 and CBF beta in the initiation of hematopoiesis in the embryo, and in the emergence of hematopoietic stem cells. We also discuss the later stages of hematopoiesis for which members of the core binding factor family are required, as well as the recently described roles for these proteins in autoimmunity.

Localization of serglycin in human neutrophil granulocytes and their precursors

Serglycin is a major proteoglycan of hematopoietic cells. It is thought to play a role in the packaging of granule proteins in human neutrophil granulocytes. The presence of serglycin in myeloid cells has been demonstrated only at the transcriptional level. We generated a polyclonal antibody against recombinant human serglycin. Here, we show the localization of serglycin in humans during neutrophil differentiation. Immunocytochemistry revealed serglycin immunoreactivity in the Golgi area of promyelocytes (PM) and myelocytes (MC), as well as in a few band cells and mature neutrophil granulocytes. Granular staining was detected near the Golgi apparatus in some of the PM, and the major part of the cytoplasm was negative. Immunoelectron microscopy showed serglycin immunoreactivity located to the Golgi apparatus and a few immature granules of PM and MC. The decreasing level of serglycin protein during myeloid differentiation coincided with a decrease of mRNA expression, as evaluated by Northern blotting. Subcellular fractions of neutrophil granulocytes were obtained. Serglycin immunoreactivity was detected in the fraction containing Golgi apparatus, plasma membrane, and secretory vesicles by Western blotting and enzyme-linked immunosorbent assay. Serglycin was not detected in subcellular fractions containing primary, secondary, or tertiary granules. Together, these findings indicate that serglycin is located to the Golgi apparatus and a few immature granules during neutrophil differentiation. This is consistent with a function for serglycin in formation of granules in neutrophil granulocytes. Our findings contrast the view that native serglycin is present in mature granules and plays a role in packaging and regulating the activity of proteolytic enzymes there.

pDP4, a novel glycoprotein secreted by mature granulocytes, is regulated by transcription factor PU.1

The transcription factor PU.1 (Spi-1) is a well-characterized regulator of myeloid and lymphoid development. However, its role in mature functional cells is poorly studied. Here we report the characterization of the novel murine gene pDP4 (PU.1 difference product 4), which is absent from fetal livers of PU.1-deficient mice. pDP4 is transcribed as a single 3.2-kb mRNA with a 1518-base pair open reading frame encoded by 5 exons on chromosome 14. pDP4 expression is strongest in small intestine and bone marrow, in which it is expressed predominately in mature neutrophils. Interestingly, however, pDP4 expression is markedly down-regulated in neutrophils of the peripheral blood and peritoneum. The pDP4 gene encodes a secreted 57-kDa glycoprotein with an olfactomedin-like C-terminus. PU.1 binds to a functional site within the pDP4 promoter, and pDP4 expression in myeloid cells is strictly dependent on PU.1 and the presence of this site. In conclusion, we have identified a novel PU.1-regulated extracellular glycoprotein of the olfactomedin-like family with a possible role in neutrophilic trafficking.

AML1/RUNX1 increases during G1 to S cell cycle progression independent of cytokine-dependent phosphorylation and induces cyclin D3 gene expression

AML1/RUNX1, a member of the core binding factor (CBF) family stimulates myelopoiesis and lymphopoiesis by activating lineage-specific genes. In addition, AML1 induces S phase entry in 32Dcl3 myeloid or Ba/F3 lymphoid cells via transactivation. We now found that AML1 levels are regulated during the cell cycle. 32Dcl3 and Ba/F3 cell cycle fractions were prepared using elutriation. Western blotting and a gel shift/supershift assay demonstrated that endogenous CBF DNA binding and AML1 levels were increased 2-4-fold in S and G(2)/M phase cells compared with G(1) cells. In addition, G(1) arrest induced by mimosine reduced AML1 protein levels. In contrast, AML1 RNA did not vary during cell cycle progression relative to actin RNA. Analysis of exogenous Myc-AML1 or AML1-ER demonstrated a significant reduction in G(1) phase cells, whereas levels of exogenous DNA binding domain alone were constant, lending support to the conclusion that regulation of AML1 protein stability contributes to cell cycle variation in endogenous AML1. However, cytokine-dependent AML1 phosphorylation was independent of cell cycle phase, and an AML1 mutant lacking two ERK phosphorylation sites was still cell cycle-regulated. Inhibition of AML1 activity with the CBFbeta-SMMHC or AML1-ETO oncoproteins reduced cyclin D3 RNA expression, and AML1 bound and activated the cyclin D3 promoter. Signals stimulating G(1) to S cell cycle progression or entry into the cell cycle in immature hematopoietic cells might do so in part by inducing AML1 expression, and mutations altering pathways regulating variation in AML1 stability potentially contribute to leukemic transformation.

A panorama of lineage-specific transcription in hematopoiesis

The hematopoietic system consists of more than ten differentiated cell types, all of which are derived from a single type of hematopoietic stem cell. The accessibility and interest of this system have made it a model for understanding normal and abnormal differentiation of mammalian cells. Newer techniques have generated a mass of data that requires integrative approaches for analysis and interpretation. The traditional view of the differentiation program holds that a small number of regulators are involved in each stage of cell specification. However, this may not be the case. Recent analyses have shown that almost all substantial subsets of genes, including the set of broadly expressed transcription factors, are expressed in patterns that are unique for each lineage. Further, much of this difference between lineages can be captured in two-dimensional graphs. Understanding the biologic significance, mechanisms and constraints underlying these differences is a challenge for experimentalists and computational biologists alike.

End-stage differentiation of neutrophil granulocytes in vivo is accompanied by up-regulation of p27kip1 and down-regulation of CDK2, CDK4, and CDK6

The in vivo expression profiles of cell-cycle proteins regulating G1-to-S-phase transition were determined in three neutrophil precursor populations from human bone marrow: myeloblasts (MBs) and promyelocytes (PMs); myelocytes (MCs) and metamyelocytes (MMs); and band cells (BCs) and segmented neutrophil cells (SCs) and in mature polymorphonuclear neutrophils (PMNs) from peripheral blood. Complete cell-cycle arrest was observed in BCs/SCs and PMNs. Cyclins D1, D2, and D3 were found to be down-regulated during granulopoiesis, whereas a slight increase of cyclin E was seen. In contrast, cyclin-dependent kinase (CDK)2, -4, and -6 were down-regulated from the MC/MM stages and onward. The transcript levels of CDK2, -4, and -6 were concurrently down-regulated. As the only CDK inhibitor, p27kip1 protein and mRNA expression were up-regulated in MCs/MMs and reached peak levels in PMNs. Protein expression of retinoblastoma protein and the related pocket proteins p107 and p130 was down-regulated from the MC/MM stages and onward. This is the first report to describe expression levels of cell-cycle proteins during granulopoiesis in vivo, and it strongly contrasts the observations made in cell-culture systems in vitro.

Neutrophil granules and secretory vesicles in inflammation

The neutrophil is a major effector cell of innate immunity. Exocytosis of granules and secretory vesicles plays a pivotal role in most neutrophil functions from early activation to the destruction of phagocytosed microorganisms. Neutrophil granules contain a multitude of antimicrobial and potentially cytotoxic substances that are delivered to the phagosome or to the exterior of the cell following degranulation. This review summarises current knowledge of granule biology and highlights the effects of neutrophil degranulation in the acute inflammatory response.

Three novel Bid proteins generated by alternative splicing of the human Bid gene

Bid, a BH3-only Bcl-2 protein, is activated by proteolytic cleavage exposing the BH3 domain, which then induces apoptosis by interacting with pro-apoptotic Bcl-2 family proteins (e.g. Bax and Bak) at the mitochondrial surface. The arrangement of domains within Bid suggested that Bid function might be regulated in part by alternative splicing. We have determined the gene structure of human Bid and identified a number of novel exons. We have also demonstrated endogenous mRNA and protein expression for three novel isoforms of Bid, generated using these exons. Bid(S) contains the N-terminal regulatory domains of Bid without the BH3 domain; Bid(EL) corresponds to full-length Bid with additional N-terminal sequence; and Bid(ES) contains only the Bid sequence downstream of the BH3 domain. Expression of these isoforms is regulated during granulocyte maturation. In functional studies Bid(EL) induces apoptosis, whereas Bid(S) abrogates the pro-apoptotic effects of truncated Bid and inhibits Fas-mediated apoptosis. Bid(ES) induces apoptosis but is also able to partially inhibit the pro-apoptotic effects of truncated Bid. These three novel endogenously expressed isoforms of Bid are distinct in their expression, their cellular localization, and their effects upon cellular apoptosis. Differential expression of these novel Bid isoforms may regulate the function of Bid following cleavage and thus influence the fate of cells exposed to a range of pro-apoptotic stimuli.

Tissue expression of copines and isolation of copines I and III from the cytosol of human neutrophils

Copines are a recently identified group of proteins characterized by two Ca(2+)-binding C2-domains at the N terminus and an A-domain at the C terminus. Although pEST sequences indicate the existence of at least seven copines in man, only copines I, III, and VI have been identified at protein level. Here, we describe the isolation of copines I and III in the cytosol of human neutrophils by use of Ca(2+)-induced hydrophobic chromatography. This is the first demonstration that copines are coexpressed in the same cell. We found that copine III exists in the cytosol of human neutrophils as a monomer with a blocked N terminus. Copines I and III undergo conformational changes upon Ca(2+) binding that lead to exposure of hydrophobic patches. Examination of RNA from 68 human tissues demonstrated that copines I-III are ubiquitously expressed whereas copines IV-VII each has a more restricted and individual expression profile. Expression of copines I-III was also demonstrated in neutrophil precursors from bone marrow. Copine I was uniformly expressed at all stages of neutrophil differentiation, whereas copine II and even more so, copine III were expressed in the more immature neutrophil precursors, which indicates an individual function of these copines.