Identification of a common signal associated with cellular proliferation stimulated by four haemopoietic growth factors in a highly enriched population of granulocyte/macrophage colony-forming cells

Regulation of granulocyte and macrophage populations of murine bone marrow cells by G-CSF and CD137 protein

Background

Granulocytes and monocytes/macrophages differentiate from common myeloid progenitor cells. Granulocyte colony-stimulating factor (G-CSF) and CD137 (4-1BB, TNFRSF9) are growth and differentiation factors that induce granulocyte and macrophage survival and differentiation, respectively. This study describes the influence of G-CSF and recombinant CD137-Fc protein on myelopoiesis.

Methodology/Principal Findings

Both, G-CSF and CD137 protein support proliferation and survival of murine bone marrow cells. G-CSF enhances granulocyte numbers while CD137 protein enhances macrophage numbers. Both growth factors together give rise to more cells than each factor alone. Titration of G-CSF and CD137 protein dose-dependently changes the granulocyte/macrophage ratio in bone marrow cells. Both factors individually induce proliferation of hematopoietic progenitor cells (lin^-, c-kit⁺) and differentiation to granulocytes and macrophages, respectively. The combination of G-CSF and CD137 protein further increases proliferation, and results in a higher number of macrophages than CD137 protein alone, and a lower number of granulocytes than G-CSF alone demonstrating that CD137 protein-induced monocytic differentiation is dominant over G-CSF-induced granulocytic differentiation. CD137 protein induces monocytic differentiation even in early hematopoietic progenitor cells, the common myeloid progenitors and the granulocyte macrophage progenitors.

Conclusions/Significance

This study confirms earlier data on the regulation of myelopoiesis by CD137 receptor - ligand interaction, and extends them by demonstrating the restriction of this growth promoting influence to the monocytic lineage.

Generation of a conditionally immortalized myeloid progenitor cell line requiring the presence of both interleukin-3 and stem cell factor to survive and proliferate

The H-2Kappab temperature-sensitive (ts) A58 transgenic (Immorto) mouse has been used previously to generate conditionally immortalized cells from a number of tissues. The present study aimed to investigate characteristics of primitive myeloid precursor cells derived from H-2Kappab-tsA58 bone marrow. Cell populations were enriched for granulocyte/macrophage progenitors by centrifugal elutriation, and were cultured in the presence and absence of cytokines at the permissive and restrictive temperatures for the A58 oncogene. Cells derived from H-2Kappab-tsA58 mice required both A58 activation and the growth factors, stem cell factor (SCF) and interleukin-3 (IL-3), for long-term cell survival and growth; cells were maintained for > 300 d in culture under these conditions. IL-3- and SCF-dependent clonal cell lines were derived with a phenotype (lin-, Sca-1+, CD34+, ER-MP 58+, ER-MP 12+, ER-MP 20-) characteristic of primitive myeloid progenitors. These cells differentiated on addition of granulocyte/macrophage colony-stimulating factor (GM-CSF) or macrophage colony-stimulating factor (M-CSF) and acquired mature cell morphology with some upregulation of differentiation markers. In conclusion, the A58 oncogene can immortalize haemopoietic progenitor cells. These cells require two cytokines for growth, IL-3 and SCF; as such, they constitute a useful resource for the study of synergistic interactions between growth factors. The ability to develop monocytic cell characteristics also permits the investigation of cytokine-mediated early haemopoietic progenitor cell development.

Neuropeptide control of bone marrow neutrophil production is mediated by both direct and indirect effects on CFU-GM

Noradrenaline- and peptide-containing nerve fibres project into the bone marrow and terminate in association with stromal cells and within the parenchyma. Peptidergic nerve terminals are also associated with antigen-processing and -presenting cells throughout the body and have been shown to be important in leucocyte trafficking and wound healing, as well as haemopoiesis. Here, we tested the in vivo effects of deleting the peripheral neuropeptide network on haemopoiesis and also investigated whether the target cell population for these substances was myeloid progenitor cells (colony-forming unit-granulocyte/macrophage, CFU-GM). Deletion of the neuropeptides, substance P (SP) and calcitonin gene-related peptide (CGRP) by capsaicin abrogates normal blood cell production. These neuropeptides produced significant stimulation of colony formation from unfractionated bone marrow and elicited production of soluble factors capable of stimulating highly enriched CFU-GM. CGRP also had a direct stimulatory effect on highly enriched CFU-GM. Noradrenaline elicited factors that inhibited colony formation and had no direct effect on CFU-GM. We conclude that the neuropeptides form the positive arm of a neural control system and that noradrenaline acts as a negative regulator.

Flt3 ligand can promote survival and macrophage development without proliferation in myeloid progenitor cells

Flt3 ligand elicits a variety of effects on early hemopoietic progenitors by occupying its cognate receptor, Flt3, a member of the type III tyrosine kinase receptor family. The cytokines macrophage colony-stimulating factor (M-CSF) and stem cell factor (SCF) bind to related members of this tyrosine kinase receptors family, c-fms and c-kit, respectively. The relative effects of the cytokines M-CSF, SCF, and Flt3L on the proliferation and development of the late myeloid progenitors granulocyte-macrophage colony-forming cells (GM-CFC) were investigated. Distinct biologic responses were stimulated by ligand binding to these different tyrosine kinase receptors in enriched GM-CFC. M-CSF stimulated GM-CFC to proliferate and develop into macrophages. SCF, on the other hand, stimulated GM-CFC to develop into neutrophils. Flt3 ligand had a relatively small proliferative effect on enriched GM-CFC compared to SCF and M-CSF and had no ability to either stimulate colony formation or synergize with these two cytokines in promoting DNA synthesis, colony formation, or expansion in liquid culture. Flt3 ligand, however, was capable of maintaining the clonogenic potential of GM-CFC and acted as an anti-apoptotic agent as assessed using the Annexin-V apoptosis assay. GM-CFC cultured in Flt3 ligand eventually formed macrophages and neutrophils in liquid culture. Labeling with the membrane-associated cell tracker dye PKH26 indicated that the majority of the enriched GM-CFC responded to Flt3 ligand by undergoing limited proliferation and macrophage development, whereas other cells survived but did not proliferate and differentiate into macrophages. Thus, Flt3 ligand promoted survival and stimulated development without proliferation in primary-enriched myeloid progenitor cells.

Lineage-Restricted Expression of Protein Kinase C Isoforms in Hematopoiesis

The pattern of expression of several protein kinase C (PKC) isoforms (, βΙ, δ, ɛ, η, and ζ) during the course of hematopoietic development was investigated using primary human CD34+ hematopoietic cells and stable cell lines subcloned from the growth factor-dependent 32D murine hematopoietic cell line. Each 32D cell clone shows the phenotype and growth factor dependence characteristics of the corresponding hematopoietic lineage. Clear-cut differences were noticed between erythroid and nonerythroid lineages. (1) The functional inhibition of PKC-ɛ in primary human CD34+ hematopoietic cells resulted in a twofold increase in the number of erythroid colonies. (2) Erythroid 32D Epo1 cells showed a lower level of bulk PKC catalytic activity, lacked the expression of ɛ and η PKC isoforms, and showed a weak or absent upregulation of the remaining isoforms, except βΙ, upon readdition of Epo to growth factor-starved cells. (3) 32D, 32D GM1, and 32D G1 cell lines with mast cell, granulo-macrophagic, and granulocytic phenotype, respectively, expressed all the PKC isoforms investigated, but showed distinct responses to growth factor readdition. (4) 32D Epo 1.1, a clone selected for interleukin-3 (IL-3) responsiveness from 32D Epo1, expressed the ɛ isoform only when cultured with IL-3. On the other hand, when cultured in Epo, 32D Epo1.1 cells lacked the expression of both ɛ and η PKC isoforms, similarly to 32D Epo1. (5) All 32D cell lines expressed the mRNA for PKC-ɛ, indicating that the downmodulation of the ɛ isoform occurred at a posttranscriptional level. In conclusion, the PKC isoform expression during hematopoiesis appears to be lineage-specific and, at least partially, related to the growth factor response.

Lineage-Restricted Expression of Protein Kinase C Isoforms in Hematopoiesis

The pattern of expression of several protein kinase C (PKC) isoforms (, βΙ, δ, ɛ, η, and ζ) during the course of hematopoietic development was investigated using primary human CD34+ hematopoietic cells and stable cell lines subcloned from the growth factor-dependent 32D murine hematopoietic cell line. Each 32D cell clone shows the phenotype and growth factor dependence characteristics of the corresponding hematopoietic lineage. Clear-cut differences were noticed between erythroid and nonerythroid lineages. (1) The functional inhibition of PKC-ɛ in primary human CD34+ hematopoietic cells resulted in a twofold increase in the number of erythroid colonies. (2) Erythroid 32D Epo1 cells showed a lower level of bulk PKC catalytic activity, lacked the expression of ɛ and η PKC isoforms, and showed a weak or absent upregulation of the remaining isoforms, except βΙ, upon readdition of Epo to growth factor-starved cells. (3) 32D, 32D GM1, and 32D G1 cell lines with mast cell, granulo-macrophagic, and granulocytic phenotype, respectively, expressed all the PKC isoforms investigated, but showed distinct responses to growth factor readdition. (4) 32D Epo 1.1, a clone selected for interleukin-3 (IL-3) responsiveness from 32D Epo1, expressed the ɛ isoform only when cultured with IL-3. On the other hand, when cultured in Epo, 32D Epo1.1 cells lacked the expression of both ɛ and η PKC isoforms, similarly to 32D Epo1. (5) All 32D cell lines expressed the mRNA for PKC-ɛ, indicating that the downmodulation of the ɛ isoform occurred at a posttranscriptional level. In conclusion, the PKC isoform expression during hematopoiesis appears to be lineage-specific and, at least partially, related to the growth factor response.

Calcium signaling and cytotoxicity

The divalent calcium cation Ca(2+) is used as a major signaling molecule during cell signal transduction to regulate energy output, cellular metabolism, and phenotype. The basis to the signaling role of Ca(2+) is an intricate network of cellular channels and transporters that allow a low resting concentration of Ca(2+) in the cytosol of the cell ([Ca(2+)]i) but that are also coupled to major dynamic and rapidly exchanging stores. This enables extracellular signals from hormones and growth factors to be transduced as [Ca(2+)]i spikes that are amplitude and frequency encoded. There is considerable evidence that a number of toxic environmental chemicals target these Ca(2+) signaling processes, alter them, and induce cell death by apoptosis. Two major pathways for apoptosis will be considered. The first one involves Ca(2+)-mediated expression of ligands that bind to and activate death receptors such as CD95 (Fas, APO-1). In the second pathway, Ca(2+) has a direct toxic effect and its primary targets include the mitochondria and the endoplasmic reticulum (ER). Mitochondria may respond to an apoptotic Ca(2+) signal by the selective release of cytochrome c or through enhanced production of reactive oxygen species and opening of an inner mitochondrial membrane pore. Toxic agents such as the environmental pollutant tributyltin or the natural plant product thapsigargin, which deplete the ER Ca(2+) stores, will induce as a direct result of this effect the opening of plasma membrane Ca(2+) channels and an ER stress response. In contrast, under some conditions, Ca(2+) signals may be cytoprotective and antagonize the apoptotic machinery.

Characterization of high affinity neurotensin receptor NTR1 in HL-60 cells and its down regulation during granulocytic differentiation

1. We investigated responses to neurotensin in human promyelocytic leukaemia HL-60 cells. 2. Neurotensin increased the cytosolic calcium concentration ([Ca2+]i) in a concentration-dependent manner and also produced inositol 1,4,5-trisphosphate (InsP3). 3. Among the tested neurotensin analogues, neurotensin 8-13, neuromedin-N, and xenopsin also increased [Ca2+]i, whereas neurotensin 1-11 and neurotensin 1-8 did not elicit detectable responses. 4. SR48692, an antagonist of NTR1 neurotensin receptors, blocked the neurotensin-induced [Ca2+]i increase, whereas levocabastine, which is known as an NTR2 neurotensin receptor antagonist, did not attenuate the neurotensin-evoked effect. 5. The expression of NTR1 neurotensin receptors was confirmed by Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR). 6. During 1.25% dimethylsulfoxide (DMSO)-triggered granulocytic differentiation of HL-60 cells, the neurotensin-induced [Ca2+]i rise became gradually smaller and completely disappeared 4 days after treatment with DMSO. The mRNA level for neurotensin receptors was also decreased after differentiation. 7. The results show that HL-60 cells express NTR1 neurotensin receptors and suggest that granulocytic differentiation involves transcriptional regulation of the receptors resulting in down-regulation of the neurotensin-induced signalling.

Expression of two inward rectifier potassium channels is essential for differentiation of primitive human hematopoietic progenitor cells

A potassium inward rectifier (K(ir)) current was previously shown by us to be induced in primitive hematopoietic progenitor cells, stimulated with the combination of interleukin-3 (IL-3) and stem cell factor (SCF). Biophysical features of whole cell currents implicated the involvement of more than one K(ir) channel type. Employing IL-3 + SCF stimulated human cord blood CD34+38- cells, we isolated and characterized different components of this current. Reverse transcription-polymerase chain reaction (RT-PCR) subcloning identified the expression of a strongly rectifying K(ir) channel (K(ir) 4.3) as well as a weakly rectifying K(ir) channel (K(ir) 1.1) in these cells. Inhibition of the expression of each of the channels suppressed progenitor cell generation by IL-3 and SCF-stimulated CD34+38- cells in 7-day suspension cultures. The variable expression of two essential inward rectifying potassium channels early in the course of hematopoietic progenitor cell differentiation may play a potentially important role in potassium homeostasis in these cells.

Different mechanisms for suppression of apoptosis by cytokines and calcium mobilizing compounds

Overexpression of wild-type p53 in M1 myeloid leukemia cells induces apoptotic cell death that was suppressed by the calcium ionophore A23187 and the calcium ATPase inhibitor thapsigargin (TG). This suppression of apoptosis by A23187 or TG was associated with suppression of caspase activation but not with suppression of wild-type-p53-induced expression of WAF-1, mdm-2, or FAS. In contrast to suppression of apoptosis by the cytokines interleukin 6 (IL-6) and interferon gamma, a protease inhibitor, or an antioxidant, suppression of apoptosis by A23187 or TG required extracellular Ca2+ and was specifically abolished by the calcineurin inhibitor cyclosporin A. IL-6 induced immediate early activation of junB and zif/268 (Egr-1) but A23187 and TG did not. A23187 and TG also suppressed induction of apoptosis by doxorubicin or vincristine in M1 cells that did not express p53 by a cyclosporin A-sensitive mechanism. Suppression of apoptosis by A23187 or TG was not associated with autocrine production of IL-6. Apoptosis induced in IL-6-primed M1 cells after IL-6 withdrawal was not suppressed by A23187 or TG but was suppressed by the cytokines IL-6, IL-3, or interferon gamma. The results indicate that these Ca2+-mobilizing compounds can suppress some pathways of apoptosis suppressed by cytokines but do so by a different mechanism.

An activated protein kinase C alpha gives a differentiation signal for hematopoietic progenitor cells and mimicks macrophage colony-stimulating factor-stimulated signaling events

Highly enriched, bipotent, hematopoietic granulocyte macrophage colony-forming cells (GM-CFC) require cytokines for their survival, proliferation, and development. GM-CFC will form neutrophils in the presence of the cytokines stem cell factor and granulocyte colony-stimulating factor, whereas macrophage colony-stimulating factor leads to macrophage formation. Previously, we have shown that the commitment to the macrophage lineage is associated with lipid hydrolysis and translocation of protein kinase C alpha (PKCalpha) to the nucleus. Here we have transfected freshly prepared GM-CFC with a constitutively activated form of PKCalpha, namely PKAC, in which the regulatory domain has been truncated. Greater than 95% of the transfected cells showed over a twofold increase in PKCalpha expression with the protein being located primarily within the nucleus. The expression of PKAC caused macrophage development even in the presence of stimuli that normally promote only neutrophilic development. Thus, M-CSF-stimulated translocation of PKCalpha to the nucleus is a signal associated with macrophage development in primary mammalian hematopoietic progenitor cells, and this signal can be mimicked by ectopic PKAC, which is also expressed in the nucleus.

Identification of a Serpin Specifically Expressed in Multipotent and Bipotent Hematopoietic Progenitor Cells and in Activated T Cells

We have identified a gene that has a high level of mRNA expression in undifferentiated, multipotential hematopoietic cells (FDCP-Mix) and that downregulates both transcript and protein, as these cells are induced to differentiate into mature myeloid cells. Sequence analysis of this gene has identified it as a serine protease inhibitor EB22/3 (serpin 2A). Constitutive expression of serpin 2A in FDCP-Mix cells was associated with an increase in the clonogenic potential of the cells and with a delay in the appearance of fully mature cells in cultures undergoing granulocyte macrophage differentiation when compared with control cells. Serpin 2A was also found to be expressed in bone marrow-derived bipotent granulocyte macrophage progenitor cells (GM-colony forming cell [CFC]), but not in erythrocyte progenitor cells from day 15 fetal liver. Expression of serpin 2A also showed a marked up regulation during the activation of cytotoxic suppressor CD8+ T cells, with a clear lag between the appearance of transcript and detection of protein.

Identification of a Serpin Specifically Expressed in Multipotent and Bipotent Hematopoietic Progenitor Cells and in Activated T Cells

We have identified a gene that has a high level of mRNA expression in undifferentiated, multipotential hematopoietic cells (FDCP-Mix) and that downregulates both transcript and protein, as these cells are induced to differentiate into mature myeloid cells. Sequence analysis of this gene has identified it as a serine protease inhibitor EB22/3 (serpin 2A). Constitutive expression of serpin 2A in FDCP-Mix cells was associated with an increase in the clonogenic potential of the cells and with a delay in the appearance of fully mature cells in cultures undergoing granulocyte macrophage differentiation when compared with control cells. Serpin 2A was also found to be expressed in bone marrow-derived bipotent granulocyte macrophage progenitor cells (GM-colony forming cell [CFC]), but not in erythrocyte progenitor cells from day 15 fetal liver. Expression of serpin 2A also showed a marked up regulation during the activation of cytotoxic suppressor CD8+ T cells, with a clear lag between the appearance of transcript and detection of protein.

High-level expression of the ER-MP58 antigen on mouse bone marrow hematopoietic progenitor cells marks commitment to the myeloid lineage

Studies on the early events in the differentiation of the nonspecific immune system require the identification and isolation of myeloid-committed progenitor cells. Using the monoclonal antibodies (mAb) ER-MP12 and ER-MP20, generated against immortalized macrophage precursors, we have shown previously that the earliest macrophage colony-stimulating factor (M-CSF)-responsive cells in the bone marrow have the ER-MP12hi 20- phenotype. In addition, we found that the ER-MP12hi 20- subset (comprising about 2 % of total nucleated marrow) contains progenitor cells of all hematopoietic lineages. Aiming at the identification and purification of the myeloid progenitor cells within the ER-MP12hi 20-subset, we used ER-MP58, a marker expressed at high level by all M-CSF-responsive bone marrow progenitors. With this marker the ER-MP12hi 20- cell population could be divided into three subfractions: one with absent or low level ER-MP58 expression, one with intermediate, and one with high ER-MP58 expression. These subfractions were isolated by fluorescence-activated cell sorting and tested in vitro and in vivo for their differentiation capacities. In addition, the expression of ER-MP58 on stem cell subsets was examined in the cobblestone area-forming cell (CAFC) assay. Our data indicate that in the ER-MP12hi 20- subpopulation myeloid-committed progenitors are characterized by high-level expression of the ER-MP58 antigen, whereas cells with other or broader differentiation capacities have an ER-MP58 negative/low or intermediate phenotype. These myeloid-committed progenitors have no significant repopulating ability in vivo, in contrast to the ER-MP58 intermediate cells. Primitive CAFC-28/35, corresponding to cells providing long-term hematopoietic engraftment in vivo, also did not express the ER-MP58 Ag at a high level. Thus, cells committed to the myeloid lineage can be separated from progenitor cells with other differentiation capacities by means of multiparameter cell sorting using ER-MP58 in combination with ER-MP12 and ER-MP20.

Reversal of doxorubicin resistance by the amiloride analogue EIPA in multidrug resistant human colon carcinoma cells

Although multidrug resistance (mdr) may arise through a variety of mechanisms, the most widely studied and accepted form is associated with an increased concentration of P-glycoprotein (P-gp), a 170 kd protein found in the membrane fraction of a number of mammalian cells. Since mdr seems to be related to the ability of resistant cells to extrude drugs and the circumvention of mdr is supposed to be due to the restored ability to accumulate drugs, membrane has been regarded as the crucial site for such a regulation and an important role for membrane ion exchangers has been suggested. The aim of this work was to elucidate whether the Na+/H+ antiporter is involved in the mechanism of regulation and circumvention of mdr and if 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a selective inhibitor of the Na+/H+ exchanger, can modulate the functional expression of the mdr phenotype. The effect of EIPA on doxorubicin (DX) resistant cells (LoVo/DX) obtained from a human colon adenocarcinoma cell line (LoVo) was studied. EIPA at concentrations ranging from 10 to 50 mu M was able to increase the antibiotic cytotoxicity in the resistant Lovo/DX cells. The reversal of DX resistance paralleled an increase of the ability of the cells to accumulate the drug. Both drug loading and sensitivity to the inhibitory effect of DX on cell proliferation were restored by EIPA in a dose-dependent way. These results suggest a new mechanism of mdr reversal and indicate that amiloride and its derivatives may be useful in reversing DX resistance and in enhancing the clinical effectiveness of chemotherapeutics.

Macrophage inflammatory protein-1 alpha mediated growth inhibition in a haemopoietic stem cell line is associated with inositol 1,4,5 triphosphate generation

Macrophage Inflammatory Protein-1 alpha (MIP-1 alpha) can inhibit the proliferation of multipotent haemopoietic cells. Using the FDCP-Mix A4 multipotent stem cell line, MIP-1 alpha was shown to inhibit 1L-3 stimulated cell cycling (assessed using the [3H]-thymidine "suicide" assay). Furthermore, MIP-1 alpha can inhibit 1L-3-stimulated [3H]-thymidine incorporation in FDCP-Mix cells, with half maximal inhibition observed at 3 ng/ml MIP-1 alpha. Prostaglandin E2, but not MIP-1 alpha was able to elevate cyclic AMP levels in FDCP-Mix A4 cells although both agents can cause growth inhibition. However, MIP-1 alpha addition resulted in a pertussis-toxin-insensitive increase in the level of the second messenger inositol 1,4,5 triphosphate (Ins 1,4,5P3). This response was both rapid (maximal at 5 seconds) and transient. A half maximal effect was observed at 5 ng/ml MIP-1 alpha and the dose dependency correlated with that for MIP-1 alpha mediated growth inhibition. A rapid increase in cytosolic Ca2+ levels was also observed in response to MIP-1 alpha. Inositol lipid hydrolysis and an increase in cytosolic Ca2+ (signals normally associated with proliferation) may therefore be implicated in growth inhibitory mechanisms in multipotent cells.

Apoptosis in the haemopoietic system

Our previous studies have shown that haemopoietic stem cells undergo apoptotic death as a consequence of growth factor withdrawal. In this paper we review the new data that has accumulated since this observation and compare it with older data from the 'pre-apoptotic' age. Models of erythropoiesis and granulopoiesis that incorporate apoptosis as a normal physiological process controlling homeostasis are examined. The converse to cell death is cell survival, and we describe experiments which suggest that haemopoietic growth factors can not only act as mitogenic or differentiation stimuli but also act as survival signals. We, and others, have proposed that these growth factor-induced survival signals act through the membrane bound polypeptide receptors and share common features of signal transduction with proliferative responses. Enforced expression of bcl-2 in haemopoietic stem cells is able to overcome apoptosis following the withdrawal of growth factor, and the cells commit into different lineage differentiation programmes. Such cells spontaneously differentiate without cell division, suggesting a stochastic model of haemopoiesis in which the major role of haemopoietic growth factors is to suppress apoptosis and act as mitogens. We review the evidence that the underlying causes of some haematological diseases may be associated with change in the balance between cell survival and death.

Suppression of apoptosis allows differentiation and development of a multipotent hemopoietic cell line in the absence of added growth factors

In the absence of growth factors, hemopoietic cells die rapidly by the process of apoptosis. Transfection of the human bcl-2 gene into an interleukin-3 (IL-3)-dependent, multipotent hemopoietic cell line allowed these cells to survive in the absence of IL-3, both in serum-containing and serum-deprived conditions, and this survival was accompanied by multilineage differentiation. Moreover, single cell experiments showed that differentiation could occur in the absence of cell division. While these data do not rule out the possibility that growth factors can influence the lineage choice of multipotent cells, they suggest that exposure to growth factors may not be obligatory for the differentiation of stem cells. The data also support the hypothesis that differentiation is intrinsically determined and that the role of the hemopoietic growth factors is enabling rather than inductive.

Role of aberrant sialylation of chronic myeloid leukemia granulocytes on binding and signal transduction by chemotactic peptides and colony stimulating factors

Chronic myelogenous leukemia (CML) granulocytes exhibit a number of characteristics attributable to immature granulocytes, including marked increases in cell surface sialylation of glycoproteins which may be due, at least in part, to an increased activity of cytidine 5'-monophosphate-N-acetylneuraminic acid:Ga1 beta 1-3Ga1NAc alpha(2-3)-sialyltransferase (EC 2.4.99.4), and perhaps to altered activity of other glycosyltransferases and sialidases. This aberrant sialylation of CML granulocytes contributes to the decreased binding of the synthetic chemotactic peptide, formyl Met Leu Phe (fMLP), to the surface of CML granulocytes which leads to a rapid, transient increase in cytosolic free calcium ([Ca2+]i), an integral step in the biochemical cascade leading to cell activation. To determine if the decrease in binding of fMLP to CML granulocytes translates into a functional deficit, we measured fMLP-induced increases in [Ca2+]i. Compared to normal granulocytes, fMLP-induced increases in [Ca2+]i were markedly decreased in CML granulocytes. After sialidase treatment, a significant augmentation in fMLP-induced increases in [Ca2+]i was noted in CML granulocytes, indicating that the decreased signalling may be a consequence of aberrant sialylation. To determine if the effects of aberrant sialylation also alters the binding of endogenous polypeptide mediators, we determined the effect of desialylation of CML and normal granulocytes on binding of the colony stimulating factor for granulocytes and monocytes (GM-CSF), which plays a role in differentiation and proliferation of myeloid-lineage cells. As with fMLP binding, we also showed that the binding of GM-CSF to CML granulocytes, but not normal granulocytes, was markedly increased after sialidase treatment. Similarly, binding of GM-CSF to undifferentiated HL-60 cells was markedly increased after sialidase treatment. Therefore, we have demonstrated that aberrant sialylation of CML granulocytes not only alters the binding of fMLP and GM-CSF to their receptor(s), but may also alter signal transduction. Thus, aberrant glycosylation of CML granulocytes may reduce the binding of hematopoietic growth factors, which in turn may be responsible for the immature phenotype of CML granulocytes.

Tyrosine phosphorylation and intracellular alkalinization are early events in human neutrophils stimulated by tumor necrosis factor, granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor

Tumor necrosis factor (TNF), granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte CSF (G-CSF) primed human neutrophils for enhanced release of superoxide in time- and dose-dependent manners. The priming effects of these cytokines were detected at 3 min and maximal at 10 min of preincubation. The potency of the maximal effect was TNF > GM-CSF > G-CSF. Exposure of human neutrophils to TNF, GM-CSF and G-CSF resulted in tyrosine phosphorylation of a 42-kDa protein and intracellular alkalinization in a dose-dependent manner. The dose-response curves for triggering of tyrosine phosphorylation and intracellular alkalinization by each cytokine were similar to those for priming the cells. The potency of the maximal effect on tyrosine phosphorylation was TNF > GM-CSF > G-CSF, whereas that on intracellular alkalinization was GM-CSF > TNF > G-CSF. Tyrosine phosphorylation was detected at 3 min and maximal at 5-10 min after stimulation with each cytokine. Tyrosine phosphorylation induced by TNF declined at 20-40 min, whereas that induced by GM-CSF or G-CSF was maintained for at least 40 min. Intracellular alkalinization induced by each cytokine required a lag time of 3-5 min and was sustained for at least 40 min. Tyrosine phosphorylation preceded or occurred concomitantly with intracellular alkalinization and priming of the cells. These findings indicate that tyrosine phosphorylation and intracellular alkalinization are early events in human neutrophils stimulated by TNF, GM-CSF and G-CSF, and that these early events may, at least in part, mediate activation or priming of human neutrophils by these cytokines.

GM-CSF triggers a rapid, glucose dependent extracellular acidification by TF-1 cells: evidence for sodium/proton antiporter and PKC mediated activation of acid production

The extracellular acidification rate of the human bone marrow cell line, TF-1, increases rapidly in response to a bolus of recombinant granulocyte-macrophage colony stimulating factor (GM-CSF). Extracellular acidification rates were measured using a silicon microphysiometer. This instrument contains micro-flow chambers equipped with potentiometric sensors to monitor pH. The cells are immobilized in a fibrin clot sandwiched between two porous polycarbonate membranes. The membranes are part of a disposable plastic "cell capsule" that fits into the microphysiometer flow chamber. The GM-CSF activated acidification burst is dose dependent and can be neutralized by pretreating the cytokine with anti-GM-CSF antibody. The acidification burst can be resolved kinetically into at least two components. A rapid component of the burst is due to activation of the sodium/proton antiporter as evidenced by its elimination in sodium-free medium and in the presence of amiloride. A slower component of the GM-CSF response is a consequence of increased glycolytic metabolism as demonstrated by its dependence on D-glucose as a medium nutrient. Okadaic acid (a phospho-serine/threonine phosphatase inhibitor), phorbol 12-myristate 13-acetate (PMA, a protein kinase C (PKC) activator), and ionomycin (a calcium ionophore) all produce metabolic bursts in TF-1 cells similar to the GM-CSF response. Pretreatment of TF-1 cells with PMA for 18 h resulted in loss of the GM-CSF acidification response. Although this treatment is reported to destroy protein kinase activity, we demonstrate here that it also down-regulates expression of high-affinity GM-CSF receptors on the surface of TF-1 cells. In addition, GM-CSF driven TF-1 cell proliferation was decreased after the 18 h PMA treatment. Short-term treatment with PMA (1-2 h) again resulted in loss of the GM-CSF acidification response, but without a decrease in expression of high-affinity GM-CSF receptors. Evidence for involvement of PKC in GM-CSF signal transduction was obtained using calphostin C, a specific inhibitor of PKC, which inhibited the GM-CSF metabolic burst at a subtoxic concentration. Genistein and herbimycin A, tyrosine kinase inhibitors, both inhibited the GM-CSF response of TF-1 cells, but only at levels high enough to also inhibit stimulation by PMA. These results indicate that GM-CSF activated extracellular acidification of TF-1 cells is caused by increases in sodium/proton antiporter activity and glycolysis, through protein kinase signalling pathways which can be both activated and down-regulated by PMA.

Haemopoietic stem cell development to neutrophils is associated with subcellular redistribution and differential expression of protein kinase C subspecies

Multipotential FDCP-Mix A4 (A4) cells can be induced either to self-renew or to differentiate and develop into mature neutrophils in liquid culture, depending on the haemopoietic growth factors with which they are cultured. When cultured in low concentrations of interleukin 3 (IL-3, 1 unit/ml)) plus Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) and Granulocyte-CSF (G-CSF), A4 cells proliferate with accompanying development to form cells which resemble mature, postmitotic neutrophils. The presence of high concentrations of IL-3 (100 units/ml) blocks the development of A4 cells even in the presence of GM-CSF plus G-CSF. A4 cell development to neutrophils is accompanied by major changes in the expression of protein kinase C (PKC) subspecies in these cells. The predominant subspecies present in multipotent A4 cells, as judged by direct chromatographic analysis, was the type III enzyme (alpha) subspecies, whereas in mature A4 cell neutrophils, the type II (beta I + beta II) enzymes were predominant. Phorbol esters added to immature A4 cells resulted in a proliferative response, but when added to postmitotic A4 cells resembling neutrophils they elicited a large increase in reactive oxygen intermediate production. This suggests that the type III (alpha) subspecies may mediate proliferative responses in stem cells, whilst the type II (beta I + beta II) enzymes are more important for the mature cell functions of postmitotic neutrophils. In cultures containing IL-3 (100 units/ml) both the type III, and also the type II subspecies were predominantly membrane-associated for prolonged periods (> 24 hours).(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular signalling events stimulated by myeloid haemopoietic growth factors

In haemopoietic cells, proliferation, commitment to development, lineage restriction and survival via suppression of apoptosis can all be controlled by haemopoietic growth factors. The mechanisms underlying the regulation of these events can now be studied since recombinant forms of most of these haemopoietic growth factors are now available. Recent advances in cell purification techniques and the development of multipotent cell lines (see Spangrude et al, 1988; Whetton, 1990; Heyworth et al, 1988, 1990a; Jones et al, 1990) have provided suitable cell populations on which to study the cellular signalling events associated with differentiation and lineage restriction. This process has started with the elucidation of the structure and expression of many of the myeloid growth factor receptors, which should now facilitate progress in the study of the signal transduction mechanisms these growth factors employ. Another important facet of these studies will be to determine whether a single growth factor with multiple target cell types, ranging from multipotent cells to postmitotic cells (e.g. neutrophils), employs distinct signalling mechanisms depending on the target cell in question. The cellular signalling events elicited by each of these growth factors and the ways in which they can regulate the transcriptional activation of genes associated with specific developmental events are going to be key areas of haemopoietic research in the next few years.

Survival of the myeloid progenitor cell line FDC-P1 is prolonged by interferon-gamma or interleukin-4

Continuous proliferation of the immortalized myeloid progenitor cell line FDC-P1 depends on stimulation with either interleukin-3 (IL-3) or granulocyte-macrophage colony stimulating factor (GM-CSF). Two other cytokines, interferon-gamma (IFN-gamma) and IL-4, were found to prolong FDC-P1 survival for several days. Surviving cells incorporated [3H]thymidine and a minority completed up to 3 cell divisions before dying. This transient proliferative response was a direct effect of IFN-gamma and IL-4 since these cytokines did not induce production of detectable IL-3 or GM-CSF and the response was unaffected by cell concentration. IL-6, a constitutive product of FDC-P1 cells whose secretion was increased by IL-3, GM-CSF and IL-4 but not by IFN-gamma, was not responsible for the proliferative response. FDC-P1 lines that constitutively expressed the cell cycle-associated oncogene myc or the survival-associated oncogene bcl-2 also responded only transiently to IFN-gamma or IL-4, indicating that expression of these genes did not complement the signals delivered by IFN-gamma or IL-4. By contrast, the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) prolonged survival of FDC-P1 cells on its own and potentiated the response to IFN-gamma or IL-4, although the combination of stimuli did not support long-term growth. It is concluded that IFN-gamma and IL-4 trigger only some of the signalling events that lead to mitogenesis; these events are complemented by stimulation with PMA but additional signals are required for sustained proliferation.

Signalling through CSF receptors

The finely regulated process of blood cell formation is under the control of a family of glycoprotein hormones, known as colony-stimulating factors (CSFs), and their receptors. The complexity of the intracellular mechanisms involved in the action of such factors has been appreciated only recently. In this review, Gino Vairo and John Hamilton discuss the biochemistry of CSF action and its relevance to growth control, and examine the possibility that different CSFs may use common control pathways within the one cell type.

GM-CSF and phorbol esters modulate GM-CSF receptor expression by independent mechanisms

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) (0.1 nM) down-modulates its receptor in IL-3/GM-CSF dependent M-07e cells, in KG-1 cells and normal granulocytes, whereas phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) (2 nM) down-modulates the GM-CSF receptor in M-07e cells and granulocytes but not in KG-1 cells. As data analysis shows by nonlinear regression, the decreased binding ability depends on a reduction of the binding sites with no significant change of their dissociation constant. To gain insight into the mechanisms involved in the GM-CSF receptor regulation, we investigated the role of protein kinase C (PKC). GM-CSF, unlike TPA, was unable to activate PKC in all the cells studied. Moreover, unlike TPA, GM-CSF was still able to down-modulate its receptor in cells where PKC was inhibited by 1-(5-isoquinolonesulphonyl)-2-methylpiperazine (H7) and staurosporine or in cells where PKC was exhausted by prolonged incubation with 1 microM TPA. Finally, the receptor re-expression rate was accelerated by protein kinases inhibitors. These results, taken together, indicate the presence of a PKC-dependent and -independent down-modulation mechanism and a negative role of the endogeneous protein kinases in GM-CSF receptor re-expression.

Expression of the GM-CSF gene after retroviral transfer in hematopoietic stem cell lines induces synchronous granulocyte-macrophage differentiation

Multipotent murine stem cell lines (FDC-Pmix) depend on IL-3 for self-renewal and proliferation and can be induced to differentiate into multiple hematopoietic lineages. Single FDC-Pmix cells infected with retroviral vectors expressing GM-CSF are induced to differentiate into granulocytes and macrophages. This results in a complete loss of clonogenic cells if IL-3 is not exogenously supplied; however, multipotent variants can be selected that do not terminally differentiate if cells are kept in the presence of IL-3. Unidirectional and synchronous granulocyte and macrophage differentiation accompanied with loss of self-renewal capacity is induced when IL-3 is removed. Our data indicate that activation of the GM-CSF receptor induces differentiation of stem cells by an instructive mechanism that can be blocked by the activated IL-3 receptor. A model of how receptors can induce proliferation and cell-specific differentiation by two separate pathways is discussed.

Interactions of dimethyl sulfoxide and granulocyte-macrophage colony-stimulating factor on the cell cycle kinetics and phosphoproteins of G1-enriched HL-60 cells: evidence of early effects on lamin B phosphorylation

We have found that GM-CSF and DMSO have antagonistic effects on the proliferation but not maturation of asynchronously growing HL-60 cells such that growth in the presence of both more closely resembles normal hematopoiesis (Brennan et al., J. Cell Physiol. 132:246, 1987). Studies were undertaken to determine whether or not the agents affected the same mitogenic pathway and locus in the cell cycle. HL-60 populations containing at least 90% G1 cells were obtained by centrifugal elutriation, exposed to 100 u/ml recombinant human GM-CSF and/or 0-1.25% DMSO, and phosphoprotein changes quantified on autoradiograms of [32P]-orthophosphate-labeled cell proteins separated by giant 2-D gel electrophoresis. Results were correlated with 1) intracellular pH, determined by measurement of BCECF fluorescence; 2) [32P]-orthophosphate uptake; 3) cell cycle progression, determined by flow quantitation of DNA content in mithramycin or propidium iodide-stained cells; and 4) growth, determined by cell volume and concentration. GM-CSF stimulated and DMSO inhibited the GM-CSF-stimulated phosphorylation of 1 protein (approximately 65 kDa, p.i. 5.6) within 2 min of exposure. These effects were sustained through G1, not associated with changes in intracellular pH, and preceded similar antagonistic effects on phosphate uptake (15-30 minutes), cell volume change (16-24 hr), and cell concentration increase (28-32 hr). GM-CSF accelerated and DMSO inhibited G1 to S transit with the most marked antagonism observed in the second cycle following synchronization (28 to 40 hrs). Cell maturation (morphology, NBT reduction) was dominated by DMSO and not antagonized by GM-CSF. We have identified p65 as the nuclear intermediate filament protein, lamin B, on the basis of its locus on gels and its binding of a monoclonal antibody to intermediate filaments and antiserum to human lamin B on immunoblots. These studies suggest that at least part of the GM-CSF-DMSO antagonism is exerted through the same mitogenic pathway, that a major locus of cytokinetic effect is on G1 to S transit, and that nuclear envelope protein phosphorylation is an important early event.

Serum-free culture of enriched murine haemopoietic stem cells. II: Effects of growth factors and haemin on development

A serum-free culture system was used to determine the effects of growth factors on the clonogenic development of a population of cells highly enriched for multipotential day 12 spleen colony forming cells (CFU-S) (FACS-BM). Under these conditions, interleukin-3 (IL-3) was found to be primarily a proliferative stimulus, the progenitor cells developing in the clonal assay systems produced colonies of morphologically undifferentiated cells for up to 20 days. No such induction of proliferation without maturation was observed with other growth factors (eg. granulocyte-macrophage colony stimulating factor (GM-CSF)). However, combinations of IL-3 plus secondary growth factors such as GM-CSF, macrophage colony stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF) or interleukin-1 (IL-1) led to the formation of colonies containing mature haemopoietic cells of the granulocytic, megakaryocytic or monocytic lineages. In contrast, erythroid development did not occur unless the protoporphyrin, haemin, was added to the cultures. Under these conditions mature erythroid cells were produced in cultures containing either IL-3 or GM-CSF (with or without erythropoietin (epo)). In replating experiments it was determined that the FACS-BM cells were able to generate large numbers of clonogenic cells for up to 30-40 free cultures. Such cultures, therefore, may be useful for investigating the biological and basis of the generation of clonogenic cells and of haemopoietic cell differentiation and development in response to growth factors.

Development of multipotential haemopoietic stem cells to neutrophils is associated with increased expression of receptors for granulocyte macrophage colony-stimulating factor: altered biological responses to GM-CSF during development

Interleukin-3 (IL-3) dependent multipotent haemopoietic stem cells FDCP-Mix A4 (A4) were induced to differentiate and develop into mature neutrophils in response to Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) plus granulocyte CSF (G-CSF). This resulted in an increase in cell number over seven days of culture, following which the cells lost the ability to undergo further proliferation. The effect of GM-CSF on these cells has been assessed at various stages of development. Clonogenic cells, able to respond to GM-CSF, were generated only at days 3, 4 post-induction. From day 5 onwards, mature post-mitotic neutrophils are produced and clonogenic cells are lost. Loss of proliferative potential, in response to GM-CSF, was confirmed using [3H]-thymidine incorporation. Receptors for GM-CSF, were also measured during development using [125I]-GM-CSF binding assays. Although the dissociation constant for GM-CSF binding sites did not vary considerably, the number of such sites increased dramatically from about 20 (day 0, when the cells have a primitive morphology) to about 1000 by day 6 (when the cells are predominantly mature neutrophils). GM-CSF-stimulated Na+/H+ antiport activation was also determined. Although few GM-CSF receptors are expressed at day 0, there is a significant response (63% of maximal) to GM-CSF in terms of intracellular alkalinisation: this response increased markedly until, by day 4 (700 GM-CSF binding sites/cell), there is a maximal activation of the antiport by GM-CSF. By day 7 (greater than 900 GM-CSF binding sites/cell), however, there is significant reduction in activation of the Na+/H+ antiport by GM-CSF. Nonetheless, increased viability of these mature cells is still seen in response to GM-CSF. These results suggest that not only does expression of GM-CSF receptors alter during development of multipotential cells to mature neutrophils, but that these receptors are coupled to different intracellular effector mechanisms as the cells progressively mature.

Evidence for a role of the Na+/H+ exchanger in the colony-stimulating-factor-induced ornithine decarboxylase activity and proliferation of the human cell line M-07e

The subclone M-07e, derived from the interleukin-3 (IL-3)-responsive human myeloid cell line M-07, is strictly dependent on either IL-3 or granulocyte-macrophage-colony-stimulating factor (GM-CSF) for its growth and survival. This cell line may be regarded as a candidate model to investigate the poorly understood events triggered by growth factors binding to human hemopoietic cells. Both IL-3 and GM-CSF induce in M-07e cells an increase of ornithine decarboxylase (ODC) activity, which reaches its maximum at 24-30 h and fully depends on de novo protein synthesis. The growth factors do not elicit translocation of protein kinase C to the membrane; thus a role of the kinase in ODC induction is ruled out. An amiloride-inhibitable Na+/H+ exchanger is present in the membrane of M-07e cells; its apparent Km for extracellular Na+ is 47.77 mM; and its activity is greatly enhanced when the cytoplasm is acidified. Growth-factor-evoked ODC activation and DNA synthesis are blocked in a dose- and time-dependent manner when M-07e cells are incubated with ethylisopropylamiloride, a specific inhibitor of Na+/H+ exchanger. The exchanger does not appear to be directly activated by IL-3 or GM-CSF, but its operation is strictly required for the biological effects of these growth factors on M-07e cell line.

Models of haemopoiesis

To date, various models have been proposed to explain the diversification of haemopoietic stem cells along one of at least six pathways of differentiation. Consideration of evidence for and against particular models leads to the conclusion that a precise lineage map for the haemopoietic system is, as yet, unavailable. However, recently available cell and molecular biology techniques provide the means to resolve this problem.