Non-Cell-Autonomous Activity of the Hemidesmosomal Protein BP180/Collagen XVII in Granulopoiesis in Humanized NC16A Mice

BP180 (also termed type XVII collagen) is a hemidesmosomal protein and plays a critical role in cell-cell matrix adhesion in the skin; however, its other biological functions are largely unclear. In this study, we generated a BP180 functional-deficient mouse strain by deleting its extracellular domain of humanized NC16A (termed ΔNC16A mice). We found that BP180 is expressed by bone marrow mesenchymal stem cells (BM-MSC), and its functional deficiency leads to myeloid hyperplasia. Altered granulopoiesis in ΔNC16A mice is through bone marrow stromal cells evidenced by bone marrow transplantation. Furthermore, the level of G-CSF in bone marrow and circulation were significantly increased in ΔNC16A mice as compared with wild-type mice. The increased G-CSF was accompanied by an increased activation of the NF-κB signaling pathway in bone marrow and BM-MSC of ΔNC16A mice. Blockade of G-CSF restored normal granulopoiesis in ΔNC16A mice. Inhibition of NF-κB signaling pathway significantly reduces the release of G-CSF from ΔNC16A BM-MSC in vitro and the level of serum G-CSF in ΔNC16A mice. To our knowledge, these findings provide the first direct evidence that BP180 plays an important role in granulopoiesis through regulating NF-κB signaling pathway in BM-MSC.

Rational targeting of immunosuppressive neutrophils in cancer

Neutrophils, the most abundant circulating leukocytes in human, play an indispensable role in the innate immune response to microbial infections. However, the contribution of tumor-associated neutrophils (TANs) to cancer progression and tumor immunity has been a matter of debate for decades. A higher neutrophil-to-lymphocyte ratio is associated with adverse overall survival in many solid tumors. Preclinical evidence exists to support both anti-tumor and pro-tumor activities of TANs, and TANs employ diverse mechanisms to influence tumor progression and metastasis. Here, we focus our review on the immunosuppressive mechanism of TANs and highlight how neutrophils can operate to dampen both innate and adaptive immunity to promote tumorigenesis. Here we discuss the intriguing and sometimes controversial connection between TANs and granulocytic/polymorphonuclear myeloid-derived suppressor cells (G/PMN-MDSCs). The molecular mechanisms underlying neutrophils' role in immunosuppression provide potential therapeutic targets for cancer treatment, either as monotherapies or as a part of combinatorial regimens. Therefore, we also highlight a number of neutrophil-targeting approaches that may improve the efficacy of current anticancer therapies, especially cancer immunotherapy. Currently interest is surging in the understanding and targeting of immunosuppressive neutrophils, with the goal of developing novel therapeutic strategies in the battle against cancer.

IFNγ inhibits G-CSF induced neutrophil expansion and invasion of the CNS to prevent viral encephalitis

Emergency hematopoiesis facilitates the rapid expansion of inflammatory immune cells in response to infections by pathogens, a process that must be carefully regulated to prevent potentially life threatening inflammatory responses. Here, we describe a novel regulatory role for the cytokine IFNγ that is critical for preventing fatal encephalitis after viral infection. HSV1 encephalitis (HSE) is triggered by the invasion of the brainstem by inflammatory monocytes and neutrophils. In mice lacking IFNγ (GKO), we observed unrestrained increases in G-CSF levels but not in GM-CSF or IL-17. This resulted in uncontrolled expansion and infiltration of apoptosis-resistant, degranulating neutrophils into the brainstem, causing fatal HSE in GKO but not WT mice. Excessive G-CSF in GKO mice also induced granulocyte derived suppressor cells, which inhibited T-cell proliferation and function, including production of the anti-inflammatory cytokine IL-10. Unexpectedly, we found that IFNγ suppressed G-CSF signaling by increasing SOCS3 expression in neutrophils, resulting in apoptosis. Depletion of G-CSF, but not GM-CSF, in GKO mice induced neutrophil apoptosis and reinstated IL-10 secretion by T cells, which restored their ability to limit innate inflammatory responses resulting in protection from HSE. Our studies reveals a novel, complex interplay among IFNγ, G-CSF and IL-10, which highlights the opposing roles of G-CSF and IFNγ in regulation of innate inflammatory responses in a murine viral encephalitis model and reveals G-CSF as a potential therapeutic target. Thus, the antagonistic G-CSF-IFNγ interactions emerge as a key regulatory node in control of CNS inflammatory responses to virus infection.

Granulocyte colony-stimulating factor blockade enables dexamethasone to inhibit lipopolysaccharide-induced murine lung neutrophils

Glucocorticoids promote neutrophilic inflammation, the mechanisms of which are poorly characterized. Using a lipopolysaccharide (LPS)-induced acute murine lung injury model, we determined the role of granulocyte colony-stimulating factor (G-CSF) in mouse lung neutrophil numbers in the absence and presence of dexamethasone, a potent glucocorticoid. G-CSF was blocked using a neutralizing antibody. Airway neutrophil numbers, cytokine levels, and lung injury parameters were measured. Glucocorticoid treatment maintained LPS-induced airway G-CSF while suppressing TNF and IL-6. The addition of anti-G-CSF antibodies enabled dexamethasone to decrease airway G-CSF, neutrophils, and lung injury scores. In LPS-challenged murine lungs, structural cells and infiltrating leukocytes produced G-CSF. In vitro using BEAS 2B bronchial epithelial cells, A549 lung epithelial cells, human monocyte-derived macrophages, and human neutrophils, we found that dexamethasone and proinflammatory cytokines synergistically induced G-CSF. Blocking G-CSF production in BEAS 2B cells using shRNAs diminished the ability of BEAS 2B cells to protect neutrophils from undergoing spontaneous apoptosis. These data support that G-CSF plays a role in upregulation of airway neutrophil numbers by dexamethasone in the LPS-induced acute lung injury model.

Anti-G-CSF treatment induces protective tumor immunity in mouse colon cancer by promoting protective NK cell, macrophage and T cell responses

Granulocyte colony-stimulating factor (G-CSF) is a cytokine that is highly expressed in human and mouse colorectal cancers (CRC). We previously reported that G-CSF stimulated human CRC cell growth and migration, therefore in this study we sought to examine the therapeutic potential of anti-G-CSF treatment for CRC. G-CSF is known to mobilize neutrophils, however its impact on other immune cells has not been well examined. Here, we investigated the effects of therapeutic anti-G-CSF treatment on CRC growth and anti-tumor immune responses. C57BL/6 mice treated with azoxymethane/dextran sodium sulfate (AOM/DSS) to induce neoplasms were administered anti-G-CSF or isotype control antibodies three times a week for three weeks. Animals treated with anti-G-CSF antibodies had a marked decrease in neoplasm number and size compared to the isotype control group. Colon neutrophil and macrophage frequency were unchanged, but the number of macrophages producing IL-10 were decreased while IL-12 producing macrophages were increased. NK cells were substantially increased in colons of anti-G-CSF treated mice, along with IFNγ producing CD4(+) and CD8(+) T cells. These studies are the first to indicate a crucial role for G-CSF inhibition in promoting protective anti-tumor immunity, and suggest that anti-G-CSF treatment is a potential therapeutic approach for CRC.

Human bone marrow adipocytes block granulopoiesis through neuropilin-1-induced granulocyte colony-stimulating factor inhibition

Adipocytes are part of hematopoietic microenvironment, even though up to now in humans, their role in hematopoiesis is still questioned. We have previously shown that accumulation of fat cells in femoral bone marrow (BM) coincides with increased expression of neuropilin-1 (NP-1), while it is weakly expressed in hematopoietic iliac crest BM. Starting from this observation, we postulated that adipocytes might exert a negative effect on hematopoiesis mediated through NP-1. To test this hypothesis, we set up BM adipocytes differentiated into fibroblast-like fat cells (FLFC), which share the major characteristics of primitive unilocular fat cells, as an experimental model. As expected, FLFCs constitutively produced macrophage colony stimulating factor and induced CD34(+) differentiation into macrophages independently of cell-to-cell contact. By contrast, granulopoiesis was hampered by cell-to-cell contact but could be restored in transwell culture conditions, together with granulocyte colony stimulating factor production. Both functions were also recovered when FLFCs cultured in contact with CD34(+) cells were treated with an antibody neutralizing NP-1, which proved its critical implication in contact inhibition. An inflammatory cytokine such as interleukin-1 beta or dexamethasone modulates FLFC properties to restore granulopoiesis. Our data provide the first evidence that primary adipocytes exert regulatory functions during hematopoiesis that might be implicated in some pathological processes. Disclosure of potential conflicts of interest is found at the end of this article.

The role of G-CSF and IL-6 in the granulopoiesis-stimulating activity of murine blood serum induced by perorally administered ultrafiltered pig leukocyte extract, IMUNOR®

IMUNOR, a low-molecular weight (< 12 kD) ultrafiltered pig leukocyte extract, has been previously found to have significant stimulatory effects on murine hematopoiesis supressed by ionizing radiation or cytotoxic drugs. This communication shows data on the mechanisms of these effects. Using ELISA assay, significantly increased levels of granulocyte colony-stimulating factor (G-CSF) and interleukin-6 (IL-6) were observed. On the contrary, no detectable levels of granulocyte-macrophage colony-stimulating factor (GM-CFC) and interleukin-3 (IL-3) have been found in blood serum of IMUNOR-treated mice. Incubation of the serum from IMUNOR-treated mice with antibodies against G-CSF caused abrogation of the ability of the sera to stimulate in vitro growth of colonies originating from granulocyte-macrophage progenitor cells (GM-CFC). In contrast, incubation of the serum with antibodies against IL-6 did not change its colony-stimulating activity. It may be inferred from these findings that G-CSF is probably the main cytokine responsible for the granulopoiesis-stimulating effects of IMUNOR. When the serum from IMUNOR-treated mice with G-CSF inactivated by anti-G-CSF antibodies (but with elevated IL-6) was added to cultures of bone marrow cells together with a suboptimum concentration of IL-3, a significant increase in the numbers of GM-CFC colonies was found. Moreover, conjoint inactivation of G-CSF and IL-6 significantly decreased the numbers of GM-CFC colonies in comparison with those observed when only G-CSF was inactivated. This observation strongly suggests that though IMUNOR-induced IL-6 is not able to induce the growth of GM-CFC colonies alone, it is able to potentiate the hematopoiesis-stimulating effect of IL-3. These findings represent a new knowledge concerning the hematopoiesis-stimulating action of IMUNOR, a promising immunomodulatory agent.

Effects of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor on lung cancer: roles of cyclooxygenase-2

We examined the effects of granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) on the lung cancer cell lines PC-9, LA-1 and A549. In addition, we examined if the effects of the cytokines on the cell lines are mediated by activation of cyclooxygenase (COX)-2. The three cell lines did not constitutively produce either G-CSF or GM-CSF. G-CSF did not influence cell growth in the three cell lines, while GM-CSF increased cell growth in the A549 and LA-1 lines. G-CSF and GM-CSF dose-dependently decreased cell death in the three cell lines. RT-PCR demonstrated GM-CSF receptor expression in the three lung cancer cell lines, whereas the G-CSF receptor exists only in the PC-9 line. We suggest that G-CSF might rescue the tumor cells from cytotoxicity due to serum deprivation through cellular pathways independent of the G-CSF receptor. G-CSF and GM-CSF increased cyclooxygenase-2 (COX-2) expression in PC-9 and LA-1 cells whereas they decreased COX-2 expression in A549 cells. The COX-2 inhibitor NS-398 increased cell death in PC-9 and LA-1 cells, whereas it decreased cell death in A549 cells. PC-9 and LA-1 clones transfected with sense G-CSF- or GM-CSF showed an increase in COX-2 expression, while COX-2 expression was decreased in transfected A549 clones. COX-2 expression was increased in anti-sense G-CSF- and GM-CSF-transfected A549 clones. Thus, although COX-2 activation seems to induce different biological behavior depending on the cell type, we propose that G-CSF and GM-CSF might accelerate tumor progression by directly regulating COX-2 expression, independently of an autocrine mechanism.

Granulocyte colony-stimulating factor and its receptor in normal myeloid cell development, leukemia and related blood cell disorders

Granulocyte colony-stimulating factor (G-CSF) is the major hematopoietic cytokine involved in the control of neutrophil production and thus serves as a critical regulator of the innate immunity against bacterial infections. G-CSF is applied on a routine basis in the clinic for treatment of congenital and acquired neutropenias, diseases characterized by a critical shortage of neutrophils, leading to severe opportunistic bacterial infections. Very recently, it has become clear that therapeutic application of G-CSF may not be limited to different types of neutropenia, but may extend to non-hematological conditions, in particular cardiac and brain infarctions. G-CSF drives the proliferation, survival and neutrophilic differentiation of myeloid progenitor cells by activation of a receptor of the hematopoietin receptor superfamily, which subsequently triggers multiple signaling mechanisms. These mechanisms exert positive as well as negative effects on the signaling function of the G-CSF receptor. The integrated output of these signaling pathways provide the appropriate balance needed for accurate production of neutrophils under both steady state and "emergency" conditions. Here we review how these mechanisms are thought to act in concert to meet with these demands and how perturbations in the function of the G-CSF receptor are implicated in various types of myeloid disease.

Importance of recruitment of bone marrow-derived CXCR4+ cells in post-infarct cardiac repair mediated by G-CSF

OBJECTIVE

Granulocyte-colony stimulating factor (G-CSF) accelerates repair following myocardial infarction (MI). Recently, the beneficial effects of post-MI administration of G-CSF were reported to be mediated by direct activation of the Jak-Stat pathway in cardiomyocytes. Our aim was to test the hypothesis that bone marrow-derived cells recruited into the infarcted myocardium are the primary mediators of the beneficial effects by G-CSF.

METHODS AND RESULTS

MI was induced using a 30-min ischemia-reperfusion protocol (day 0) in 40 rabbits treated with G-CSF (10 microg/kg/day from days 3 to 7) or saline. Another 40 rabbits received the same G-CSF or saline protocol but also received AMD3100 (200 microg/kg/day), a specific inhibitor of CXCR4. On day 28 post-MI, left ventricular ejection fractions and end-diastolic dimensions were significantly better in the G-CSF group than in the control saline group, and the scar area/left ventricular wall area ratio was significantly smaller in the G-CSF group. G-CSF administration also led to increased mobilization of CXCR4+ bone marrow cells, including RAM11+ macrophages, into infarcted areas. And within those areas there was significant upregulation of expression of stromal cell-derived factor (SDF)-1, a chemoattractant of circulating CXCR4+ cells, as well as of the collagenase matrix metalloproteinase-1. AMD3100 significantly inhibited all of these beneficial effects of G-CSF, but did not affect the upregulation of SDF-1 or phospho-Stat3.

CONCLUSION

Recruitment of CXCR4+ cells into infarcted myocardial tissues via stimulation of the CXCR4/SDF-1 axis plays a critical role in the beneficial effects of G-CSF.

Effect of imatinib mesylate combined with granulocyte colony-stimulating factor on leukaemic blast cells derived from advanced-stage chronic myelogenous leukaemia patients

Neutropenia is a severe adverse effect that can occur when treating patients with imatinib mesylate for advanced-stage chronic myelogenous leukaemia (CML). Therefore, we evaluated in vitro the combined effect of imatinib and granulocyte colony-stimulating factor (G-CSF) on proliferation and apoptosis of Bcr-Abl-expressing leukaemic cells to infer the safety of G-CSF administration. In KU812 and K562 cell lines, G-CSF neither stimulated their proliferation nor abolished the suppressive effect of imatinib. However, it stimulated the proliferation of blast cells in 2 out of the 5 cases with advanced-stage CML. These in vitro studies appear to provide data for the decision of G-CSF administration in combination with imatinib in the treatment of neutropenic patients with advanced-stage CML.

Prostaglandin E2 stimulates granulocyte colony-stimulating factor production via the prostanoid EP2 receptor in mouse peritoneal neutrophils

G-CSF is a hemopoietic growth factor involved in granulocytic differentiation of progenitor cells. In this study, we investigated the effects of PGE2 on G-CSF production in murine peritoneal neutrophils in vitro and in vivo. PGE2 augmented LPS-primed G-CSF release from peritoneal neutrophils. This augmentation was mimicked by a type E prostanoid receptor (EP)2-selective agonist but not by other EP-specific agonists. Indeed, the effect of PGE2 on G-CSF release was abolished in neutrophils isolated from EP2-deficient mice. PGE2 and an EP2 agonist have the ability to stimulate G-CSF gene expression even in the absence of LPS. In the casein-induced peritonitis model, the appearance of G-CSF in the casein-injected peritoneal cavity associated well with the timing of neutrophil infiltration as well as PGE2 levels in exudates, with a peak value at 6 h postinjection. Inhibition of endogenous PG synthesis by indomethacin resulted in a marked decrease in G-CSF content and neutrophil number in the peritoneal cavity. Moreover, EP2-deficient mice exhibited a strikingly reduced G-CSF content in peritoneal exudates with comparable responses in neutrophil migration and local PGE2 production at 6 h postinjection. These results suggest that the PGE2-EP2 system contributes to the local production of G-CSF during acute inflammation.

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.

FIV-infected cats respond to short-term rHuG-CSF treatment which results in anti-G-CSF neutralizing antibody production that inactivates drug activity

The hematological and virological effects of recombinant human granulocyte colony-stimulating factor (rHuG-CSF) were evaluated in feline immunodeficiency virus (FIV)-infected cats. Six age-matched, FIV-infected cats used in this cross-over study were injected subcutaneously with 5 microg/kg of rHuG-CSF daily for 3 weeks, while six control cats received a placebo. Five of six rHuG-CSF-treated cats had significant increases in neutrophil counts that peaked on days 11-21 of treatment. All rHuG-CSF-treated cats exhibited an increase in myeloid:erythroid ratios of the bone marrow cells without significant changes in lymphocyte, CD4 counts, CD4/CD8 ratios, RBC counts, FIV antibody titers, and FIV loads in peripheral blood, and without clinical and hematological toxicities. Five of six rHuG-CSF-treated cats developed antibodies to rHuG-CSF by 14-21 days of treatment, which correlated with decreasing neutrophil counts and increasing neutralizing antibodies to rHuG-CSF. Three cats re-treated with rHuG-CSF rapidly developed neutralizing antibodies to rHuG-CSF, while one cat also developed neutralizing antibodies to recombinant feline G-CSF (rFeG-CSF). Overall, rHuG-CSF treatment increased neutrophil counts in FIV-infected cats without affecting the infection status of cats. However, long-term use of rHuG-CSF is not recommended in cats because of the neutralizing antibody production to rHuG-CSF that affects the drug activity. In addition, a preliminary finding suggests that repeated treatment cycle can also induce cross-neutralizing antibodies to rFeG-CSF, which may potentially affect the homeostasis of endogenous FeG-CSF.

Regulatory roles of IL-17 and IL-17F in G-CSF production by lung microvascular endothelial cells stimulated with IL-1β and/or TNF-α

The role of the interleukin (IL)-17 family members in the regulation of G-CSF production by lung microvasculature has not been elucidated yet. We therefore investigated the effects of IL-17 and IL-17F on the regulation of G-CSF production by lung microvascular endothelial cells (LMVECs). While a wide range of doses of IL-17 or IL-17F alone did not up-regulate G-CSF production from primary human LMVECs, IL-17 had an enhancing effect on macrophage-derived IL-1beta- and TNF-alpha-induced G-CSF production, whereas IL-17F had an enhancing effect on IL-1beta-induced production, but an inhibitory effect on TNF-alpha-induced secretion. G-CSF production was further enhanced with the combination of three cytokines IL-1beta, TNF-alpha and IL-17. In contrast, three cytokines IL-1beta, TNF-alpha and IL-17F were combined together, G-CSF production was less than that induced by IL-1beta or IL-1beta plus TNF-alpha or IL-17F. Moreover, IL-17 plus Th1 or Th2 cytokine had a modest stimulatory effect on TNF-alpha-induced G-CSF production, whereas IL-17 plus IFN-gamma had an inhibitory effect on IL-1beta-induced release. Similarly, IL-17F plus IL-10, IL-13 or IFN-gamma had an inhibitory effect on IL-1beta-induced production. Our findings indicate that CD4 T cell cytokines IL-17 and IL-17F play a differential regulatory role in G-CSF production by LMVECs stimulated with IL-1beta and/or TNF-alpha, which is also sensitive to Th1 and Th2 cytokine modulation.

Identification in human airways smooth muscle cells of the prostanoid receptor and signalling pathway through which PGE2 inhibits the release of GM-CSF

1. The prostanoid receptor(s) on human airways smooth muscle (HASM) cells that mediates the inhibitory effect of PGE(2) on interleukin (IL)-1 beta-induced granulocyte/macrophage colony-stimulating factor (GM-CSF) release has been classified. 2. IL-1 beta evoked the release of GM-CSF from HASM cells, which was suppressed by PGE(2), 16,16-dimethyl PGE(2) (nonselective), misoprostol (EP(2)/EP(3)-selective), ONO-AE1-259 and butaprost (both EP(2)-selective) with pIC(50) values of 8.61, 7.13, 5.64, 8.79 and 5.43, respectively. EP-receptor agonists that have selectivity for the EP(1)-(17-phenyl-omega-trinor PGE(2)) and EP(3)-receptor (sulprostone) subtypes as well as cicaprost (IP-selective), PGD(2), PGF(2 alpha) and U-46619 (TP-selective) were poorly active or inactive at concentrations up to 10 microM. 3. AH 6809, a drug that can be used to selectively block EP(2)-receptors in HASM cells, antagonised the inhibitory effect of PGE(2), 16,16-dimethyl PGE(2) and ONO-AE1-259 with apparent pA(2) values of 5.85, 6.09 and 6.1 respectively. In contrast, the EP(4)-receptor antagonists, AH 23848B and L-161,982, failed to displace to the right the concentration-response curves that described the inhibition of GM-CSF release evoked by PGE(2) and ONO-AE1-259. 4. Inhibition of GM-CSF release by PGE(2) and 8-Br-cAMP was abolished in cells infected with an adenovirus vector encoding an inhibitor protein of cAMP-dependent protein kinase (PKA) but not by H-89, a purported small molecule inhibitor of PKA. 5. We conclude that prostanoid receptors of the EP(2)-subtype mediate the inhibitory effect of PGE(2) on GM-CSF release from HASM cells by recruiting a PKA-dependent pathway. In addition, the data illustrate that caution should be exercised when using H-89 in studies designed to assess the role of PKA in biological processes.

Role of Humoral Factors in the Regulation of Hemopoiesis during Immobilization Stress

Experiments were performed on CBA/CaLac mice with hyperplasia of hemopoiesis induced by 10-h immobilization. Erythropoietic and colony-stimulating activity increased under the influence of hemopoietic growth factors and other humoral substances, which plays a major role in the increase in bone marrow cellularity during immobilization stress. Erythropoietin stimulated proliferation of erythroid colony-forming units, while granulocyte colony-stimulating factor accelerated maturation of granulocyte precursors.

Neutrophil elastase enzymatically antagonizes the in vitro action of G-CSF: implications for the regulation of granulopoiesis

There is evidence that neutrophil production is a balance between the proliferative action of granulocyte-colony-stimulating factor (G-CSF) and a negative feedback from mature neutrophils (the chalone). Two neutrophil serine proteases have been implicated in granulopoietic regulation: pro-proteinase 3 inhibits granulocyte macrophage-colony-forming unit (CFU-GM) growth, and elastase mutations cause cyclic and congenital neutropenia. We further studied the action of the neutrophil serine proteases (proteinase 3, elastase, azurocidin, and cathepsin G) on granulopoiesis in vitro. Elastase inhibited CFU-GM in methylcellulose culture. In serum-free suspension cultures of CD34+ cells, elastase completely abrogated the proliferation induced by G-CSF but not that of GM-CSF or stem cell factor (SCF). The blocking effect of elastase was prevented by inhibition of its enzymatic activity with phenylmethylsulfonyl fluoride (PMSF) or heat treatment. When exposed to enzymatically active elastase, G-CSF, but not GM-CSF or SCF, was rapidly cleaved and rendered inactive. These results support a role for neutrophil elastase in providing negative feedback to granulopoiesis by direct antagonism of G-CSF.

G-CSF-stimulated neutrophils are a prominent source of functional BLyS

B lymphocyte stimulator (BLyS) is a novel member of the TNF ligand superfamily that is important in B cell maturation and survival. We demonstrate that human neutrophils, after incubation with G-CSF or, less efficiently, IFN gamma, express high levels of BLyS mRNA and release elevated amounts of biologically active BLyS. In contrast, surface expression of the membrane-bound BLyS was not detected in activated neutrophils. Indeed, in neutrophils, uniquely among other myeloid cells, soluble BLyS is processed intracellularly by a furin-type convertase. Worthy of note, the absolute capacity of G-CSF-stimulated neutrophils to release BLyS was similar to that of activated monocytes or dendritic cells, suggesting that neutrophils might represent an important source of BLyS. In this regard, we show that BLyS serum levels as well as neutrophil-associated BLyS are significantly enhanced after in vivo administration of G-CSF in patients. In addition, serum obtained from two of these patients induced a remarkable accumulation of neutrophil-associated BLyS in vitro. This effect was neutralized by anti-G-CSF antibodies, indicating that G-CSF, present in the serum, stimulated neutrophils to produce BLyS. Collectively, our findings suggest that neutrophils, through the production of BLyS, might play an unsuspected role in the regulation of B cell homeostasis.

Production of granulocyte colony-stimulating factor in the nonspecific acute phase response enhances host resistance to bacterial infection

Mice mounting an acute phase response, induced by sterile inflammation after a single s.c. injection of casein 24 h beforehand, were remarkably protected against lethal infection with Gram-positive or Gram-negative bacteria. This was associated with enhanced early clearance of bacteremia, greater phagocytosis and oxidative burst responses by neutrophils, and enhanced recruitment of neutrophils into tissues compared with control, nonacute phase mice. Casein-induced inflammation was also associated with increased concentrations of G-CSF in serum, and administration of neutralizing Ab to this cytokine completely abrogated protection against Escherichia coli infection after casein pretreatment. Injection of recombinant murine G-CSF between 3 and 24 h before infection conferred the same protection as casein injection. In contrast, the casein-induced acute phase response affected neither serum values of TNF-alpha, IL-1 beta, or IL-6 after E. coli infection nor susceptibility to LPS toxicity. Furthermore, protection against infection was unaffected in IL-1R knockout mice, which have deficient acute phase plasma protein responses, or after nonspecific inhibition of acute phase protein synthesis by D-galactosamine or specific depletion of complement C3 by cobra venom factor. Increased production of G-CSF in the acute phase response is thus a key physiological component of host defense, and pretreatment with G-CSF to prevent bacterial infection in at-risk patients now merits further study, especially in view of increasing bacterial resistance to antibiotics.

STAT3 is a negative regulator of granulopoiesis but is not required for G-CSF-dependent differentiation

STAT3 has been described as an essential component of G-CSF-driven cell proliferation and granulopoiesis. This notion was tested by conditional gene ablation in transgenic mice. Contrary to expectation, granulocytes developed from STAT3 null bone marrow progenitors, and STAT3 null neutrophils displayed mature effector functions. Rather than a deficit in granulopoiesis, mice lacking STAT3 in their hematopoietic progenitors developed neutrophilia, and bone marrow cells were hyperresponsive to G-CSF stimulation. These studies provide direct evidence for STAT3-independent granulopoiesis and suggest that STAT3 directs a negative feedback loop necessary for controlling neutrophil numbers, possibly through induced expression of the signaling inhibitor, SOCS3.

Somatostatin modulates G-CSF-induced but not interleukin-3-induced proliferative responses in myeloid 32D cells via activation of somatostatin receptor subtype 2

INTRODUCTION

Somatostatin, originally identified as a peptide involved in neurotransmission, functions as an inhibitor of multiple cellular responses, including hormonal secretion and proliferation. Somatostatin acts through activation of G-protein-coupled receptors of which five subtypes have been identified. We have recently established that human CD34/c-kit expressing hematopoietic progenitors and acute myeloid leukemia (AML) cells exclusively express SSTR2. A major mechanism implicated in the antiproliferative action of somatostatin involves activation of the SH2 domain-containing protein tyrosine phosphatase SHP-1. While 0.1-1 x 10(-9) M of somatostatin, or its synthetic stable analog octreotide, can inhibit G-CSF-induced proliferation of AML cells, little or no effects are seen on GM-CSF- or IL-3-induced responses.

MATERIALS AND METHODS

To study the mechanisms underlying the antiproliferative responses of myeloblasts to somatostatin, clones of the IL-3-dependent murine cell line 32D that stably express SSTR2 and G-CSF receptors were generated.

RESULTS

Similar to AML cells, octreotide inhibited G-CSF-induced but not IL-3-induced proliferative responses of 32D[G-CSF-R/SSTR2] cells. Somatostatin induced SHP-1 activity and inhibited G-CSF-induced, but not IL-3-induced, activation of the signal transducer and activator of transcription proteins STAT3 and STAT5.

CONCLUSION

Based on these data and previous results, we propose a model in which recruitment and activation of the tyrosine phosphatase SHP-1 by SSTR2 is involved in the selective negative action of somatostatin on G-CSF-R signaling.

Aggregation of granulocyte colony stimulating factor under physiological conditions: characterization and thermodynamic inhibition

We have investigated the aggregation of recombinant human granulocyte colony stimulating factor (rhGCSF), a protein that rapidly aggregates and precipitates at pH 6.9 and 37 degrees C. We observed that native monomeric rhGCSF reversibly forms a dimer under physiological conditions and that this dimeric species does not participate in the irreversible aggregation process. Sucrose, a thermodynamic stabilizer, inhibits the aggregation of rhGCSF. We postulate that sucrose acts by reducing the concentration of structurally expanded species, consistent with the hypothesis that preferential exclusion favors most compact species in the native state ensemble. Thermodynamic stability data from unfolding curves and hydrogen-deuterium exchange experimental results support the above hypothesis. Thus, the strategy of stabilizing the native state of the protein under physiological conditions using thermodynamic stabilizers, especially ligands binding with high affinity to the native state, is expected to protect against protein aggregation occurring under such nonperturbing solution conditions.

Increased granulopoiesis through interleukin-17 and granulocyte colony-stimulating factor in leukocyte adhesion molecule-deficient mice

Many mutant mice deficient in leukocyte adhesion molecules display altered hematopoiesis and neutrophilia. This study investigated whether peripheral blood neutrophil concentrations in these mice are elevated as a result of accumulation of neutrophils in the circulation or altered hematopoiesis mediated by a disrupted regulatory feedback loop. Chimeric mice were generated by transplanting various ratios of CD18(+/+) and CD18(-/-) unfractionated bone marrow cells into lethally irradiated wild-type mice, resulting in approximately 0%, 10%, 50%, 90%, or 100% CD18 null neutrophils in the blood. The presence of only 10% CD18(+/+) neutrophils was sufficient to prevent the severe neutrophilia seen in mice reconstituted with CD18(-/-) bone marrow cells. These data show that the neutrophilia in CD18(-/-) mice is not caused by enhanced neutrophil survival or the inability of neutrophils to leave the vascular compartment. In CD18(-/-), CD18(-/-)E(-/-), CD18(-/-)P(-/-), EP(-/-), and EPI(-/-) mice, levels of granulocyte colony-stimulating factor (G-CSF) and interleukin-17 (IL-17) were elevated in proportion to the neutrophilia seen in these mice, regardless of the underlying mutation. Antibiotic treatment or the propensity to develop skin lesions did not correlate with neutrophil counts. Blocking IL-17 or G-CSF function in vivo significantly reduced neutrophil counts in severely neutrophilic mice by approximately 50% (P <.05) or 70% (P <.01), respectively. These data show that peripheral blood neutrophil numbers are regulated by a feedback loop involving G-CSF and IL-17 and that this feedback loop is disrupted when neutrophils cannot migrate into peripheral tissues.

Ectopic expression of interferon regulatory factor-1 potentiates granulocytic differentiation

Numerous transcription factors allow haematopoietic cells to respond to lineage- and stage-specific cytokines and to act as their effectors. It is increasingly evident that the interferon regulatory factor-1 (IRF-1) transcription factor can selectively regulate different sets of genes depending on the cell type and/or the nature of cellular stimuli, evoking distinct responses in each. In the present study, we investigated mechanisms underlying the differentiation-inducing properties of granulocytic colony-stimulating factor (G-CSF) and whether IRF transcription factors are functionally relevant in myeloid differentiation. Both normal human progenitors and murine 32Dcl3 myeloblasts induced to differentiate along the granulocytic pathway showed an up-regulation of IRF-1 expression. Ectopic expression of IRF-1 did not abrogate the growth factor requirement of 32Dcl3 cells, although a small percentage of cells that survived cytokine deprivation differentiated fully to neutrophils. Moreover, in the presence of G-CSF, granulocytic differentiation of IRF-1-expressing cells was accelerated, as assessed by morphology and expression of specific differentiation markers. Down-modulation of c-Myb protein and direct stimulation of lysozyme promoter activity by IRF-1 were also observed. Conversely, constitutive expression of IRF-2, a repressor of IRF-1 transcriptional activity, completely abrogated the G-CSF-induced neutrophilic maturation. We conclude that IRF-1 exerts a pivotal role in granulocytic differentiation and that its induction by G-CSF represents a limiting step in the early events of differentiation.

Cyclophosphamide stimulates lung fibroblasts to release neutrophil and monocyte chemoattractants

Cyclophosphamide is an alkylating antineoplastic agent used in several conditions. However, little is known about the mechanism of its pulmonary toxicity. In the present study, we determined that human lung fibroblasts release activity for neutrophils and monocytes in response to cyclophosphamide in a dose- and time-dependent manner. Checkerboard analysis revealed that both neutrophil and monocyte activities were chemotactic. The release of chemotactic activity was inhibited by lipoxygenase inhibitors and cycloheximide. Molecular-sieve column chromatography revealed that both neutrophil (NCA) and monocyte (MCA) chemotactic activities had multiple peaks. NCA was inhibited by a leukotriene B4receptor antagonist and anti-interleukin-8 and anti-granulocyte colony-stimulating factor antibodies. MCA was attenuated by a leukotriene B4receptor antagonist and anti-monocyte chemoattractant protein-1 and anti-granulocyte-macrophage colony-stimulating factor antibodies. The concentrations of interleukin-8, granulocyte colony-stimulating factor, monocyte chemoattractant protein-1, and granulocyte-macrophage colony-stimulating factor significantly increased in response to cyclophosphamide. These data suggest that lung fibroblasts may modulate inflammatory cell recruitment into the lung by releasing NCA and MCA in response to cyclophosphamide.

Prolonged neutropenia in a novel mouse granulocyte colony-stimulating factor neutralizing auto-immunoglobulin G mouse model

Therapeutic use of recombinant human cytokines in humans can result in the generation of drug-specific antibodies. To predetermine the maximum potential effects of a granulocyte colony-stimulating factor (G-CSF) neutralizing auto-immunoglobulin G (auto-IgG) response during recombinant human G-CSF therapy, we developed a mouse model of mouse G-CSF (mG-CSF) neutralizing auto-IgG response. Mice were immunized and boosted with mG-CSF chemically conjugated to either keyhole limpet hemocyanin or ovalbumin on an alternating schedule. Sera were analyzed for mG-CSF-specific titers and full blood counts were performed on a Technicon H-1E. On day 252, tissues were collected for histology. IgG was protein A affinity purified from pooled mG-CSF autoimmune sera. Mice immunized with mG-CSF conjugates produced mG-CSF-specific auto-IgG responses that lasted for the length of the study. Significant neutropenia (p(max) < 0.004) was concurrent with the rise in mG-CSF-specific IgG titers. However, neutrophil counts remained at approximately 20% of preimmunization levels through day 252. Endogenous mG-CSF neutralizing auto-IgG had no significant effect on hemoglobin, erythrocyte, lymphocyte, eosinophil, basophil, and platelet counts, and had minor, transient, or no effects on monocyte counts. Bone marrow colony assays from mG-CSF autoimmune mice demonstrated no significant effect of G-CSF neutralization on the numbers or proliferative capacity of preneutrophil lineage progenitors. Purified IgG from mG-CSF autoimmune mice neutralized mG-CSF in vitro. High-titer G-CSF neutralizing auto-IgG in adult mice partially inhibited steady-state granulopoiesis and had little or no effect on steady-state levels of other hematopoietic cells.

Evaluation of electrochemiluminescent technology for inhibitors of granulocyte colony-stimulating factor receptor binding

An electrochemiluminescent (ECL) assay was developed to identify compounds that inhibit the interaction of granulocyte colony-stimulating factor (GCSF) with its recombinant human receptor. The ECL technology uses a tris-(bipyridine) chelate of ruthenium, which, in the presence of excess tripropylamine, undergoes a redox reaction cycle to produce light. Paramagnetic beads with primary antibody were coated with secondary anti-GCSF receptor antibody, which were then bound with GCSF receptor. These samples were incubated with ruthenylated GCSF in the presence and absence of test compounds. The bead density, receptor and ligand concentrations, and incubation time were optimized in the assay. A set of mixed compound plates was screened to examine the feasibility of using this technology in high throughput screening. The results from this format were found to be comparable to the assay performed using a time-resolved fluorescence format.

The colony-stimulating factors and collagen-induced arthritis: exacerbation of disease by M-CSF and G-CSF and requirement for endogenous M-CSF

There is increasing evidence that the colony-stimulating factors (CSFs) may play a part in chronic inflammatory autoimmune diseases, such as rheumatoid arthritis (RA). We examined the involvement of macrophage CSF (M-CSF or CSF-1) and granulocyte CSF (G-CSF) in collagen-induced arthritis (CIA), a murine model of RA. Daily injections of M-CSF or G-CSF, 20-24 days postprimary immunization with type II collagen, exacerbated disease symptoms in suboptimally immunized DBA/1 mice. Support for the involvement of endogenous M-CSF in CIA was obtained by studies in which neutralizing monoclonal antibody reduced the severity of established CIA and also by studies showing the resistance of M-CSF-deficient op/op mice to CIA induction. These studies show that M-CSF and G-CSF can be proinflammatory in CIA and provide evidence that macrophage- and granulocyte-lineage cells can exacerbate CIA. Our results also show that M-CSF-dependent cells are essential for CIA development, suggesting M-CSF may be a suitable target for therapeutic intervention in RA.

Bradykinin stimulates lung fibroblasts to release neutrophil and monocyte chemotactic activity

Activation of the kallikrein-kinin system in lung injury has long been recognized. However, the effects of bradykinin (BK) on human lung fibroblasts (HLF) remain to be elucidated. We determined whether BK stimulates HLF to release chemotactic activity for neutrophils and monocytes (NCA and MCA, respectively). We evaluated HLF supernatant fluids for chemotactic activity through a blind-well chamber technique. HLF released NCA and MCA in a dose- and time-dependent manner in response to BK. The release of chemotactic activity was inhibited by lipoxygenase inhibitors and cycloheximide. Molecular sieve column chromatography revealed that both NCA and MCA had multiple chemotactic peaks. NCA was inhibited by a leukotriene (LT) B(4) receptor antagonist and by antibodies to interleukin (IL)-8 and granulocyte colony-stimulating factor (G-CSF). MCA was attenuated by the LTB(4) receptor antagonist and by antibodies to monocyte chemoattractant protein-1 (MCP-1), granulocyte-macrophage colony-stimulating factor (GM-CSF), and transforming growth factor (TGF)-beta. Both the LTB(4) receptor antagonist and these antibodies inhibited chemotactic activity of the molecular weights corresponding to MCP-1, GM-CSF, and TGF-beta, separated by column chromatography. The concentrations of IL-8, G-CSF, MCP-1, GM-CSF, and TGF-beta in supernatant fluids increased significantly in a time-dependent manner in response to BK. The receptors responsible for the release of NCA, MCA, and individual chemokines included both BKB(1) and BKB(2) receptors. These data suggest that BK may stimulate lung fibroblasts to release inflammatory cytokines, which may modulate lung inflammation.

Effects of saiboku-to on the survival of human eosinophils

In recent years, bronchial asthma has come to be regarded as a chronic inflammatory disease of the respiratory tract, with mast cells, lymphocytes and eosinophils playing important roles in its pathogenesis. Proteins contained in eosinophil granules, especially major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN) and eosinophil peroxidase (EPO), can cause tissue injury. When stimulated, eosinophils release mediators such as leukotriene C4 (LTC4) and platelet activating factors (PAF). Thus, they are recognized as effector cells that are actively involved in the development of allergic inflammation. In this study, eosinophils from healthy volunteers were used to investigate the effects of Saiboku-to on eosinophils whose survival had been prolonged through stimulation with eosinophil-activating cytokines such as interleukin (IL)-3, IL-5 and granulocyte macrophage colony stimulating factors (GM-CSF). As a result, the cytokine-enhanced survival of eosinophils was significantly shortened by the addition of Saiboku-to. These findings suggest that Saiboku-to has the potential to inhibit allergic responses by directly affecting eosinophils which are related to allergic inflammation.

Suppression of G-CSF-mediated Stat signalling by IL-3

G-CSF-induced myeloid differentiation of 32Dcl3 murine myeloblast cells is antagonized by concurrent exposure to interleukin-3 (IL-3) or by oncogenic transformation of 32Dcl3 by src- or abl-oncogenes which render the cells IL-3-independent. Recent reports have linked G-CSF-mediated differentiation to the ability of G-CSF to activate Stat3. We hypothesized that IL-3 suppresses 32Dcl3 differentiation in part through disruption of G-CSF-Stat signalling. We report that IL-3 inhibited the ability of G-CSF to induce Stat3 DNA binding. Moreover, we find that G-CSF activation of Stat3 binding to DNA is biphasic, peaking at 15-30 min and again at 6-8 h; both peaks are inhibited by IL-3. Transformation of 32Dcl3 cells by the v-abl oncogene leads to constitutive Stat3 activation and distinctive Stat-DNA-binding patterns which are not affected by G-CSF. Cross-modulation of Stat pathway signalling could be a physiologic mechanism for establishing a hierarchy of growth factor effects upon a cell exposed at once to multiple cytokines.

Suppression of the granulocyte colony-stimulating factor response to Escherichia coli challenge by alcohol intoxication

Alcohol's suppressive effects on polymorphonuclear leukocyte (PMN) production and function increases host susceptibility to a wide variety of infections and impairs the ability of these effector cells to seek and destroy invading pathogens. Granulocyte colony-stimulating factor (G-CSF), an important regulator of PMN production and function, is known to be increased in the plasma during infectious episodes. In previous studies we found acute alcohol intoxication to suppress the tumor necrosis factor-alpha (TNF alpha) response to in vivo challenges with bacteria or lipopolysaccharide. The present study was initiated to determine the impact of alcohol intoxication on the plasma G-CSF response to gram-negative infection. For this purpose, rats received an intravenous challenge of Escherichia coli (10(6) CFU) 30 min after an intraperitoneal injection of ethanol (5.5 g/kg) or an equivalent volume of saline (control). Ethanol-intoxicated rats had a greater 48 hr mortality to live E. coli injection than did unintoxicated animals (45% vs. 8%). Despite an increased bacterial burden in both the lung and liver at 24 hr after initiating E. coli infection in alcohol-intoxicated animals, PMN tissue recruitment, indexed as myeloperoxidase activity, did not differ between control and alcohol-treated rats. Moreover, alcohol suppressed blood PMN phagocytic capacity to a greater extent in animals given alcohol than controls at 5 and 24 hr after initiating infection. In control animals after intravenous E. coli injection, bioactive G-CSF increased in plasma and peaked near 300 ng/ml at 8 hr. In rats pretreated with alcohol, the plasma G-CSF response was markedly suppressed in response to intravenous E. coli (p < 0.05). In a second experiment, neutralization of the E. coli-induced plasma TNF alpha response by pretreatment with anti-TNF alpha antibody similarly inhibited the plasma G-CSF response. These results support the postulate that alcohol-induced inhibition of TNF alpha directly contributes to the adverse effects of alcohol on PMN function by suppressing the normal autocrine amplification pathway responsible for G-CSF production.

Neutralization of G-CSF inhibits ILK-induced heterophil influx: granulocyte-colony stimulating factor mediates the Salmonella enteritidis-immune lymphokine potentiation of the acute avian inflammatory response

Hematopoietic colony stimulating factors (CSF) regulate the growth and development of phagocytic cell progenitors and also augment functional activation of phagocytes. Granulocyte-CSF (G-CSF) is the CSF that acts specifically upon granulocyte progenitor cells and mature granulocytes. We have shown that lymphokines (ILK) from T cells of birds immunized against Salmonella enteritidis (SE) induce a granulocytic (PMN) inflammatory response in chicks challenged with SE. This inflammatory response was characterized by: (a) a dramatic emigration of granulocytic cells from the bone marrow into the peripheral blood, (b) an enhancement of the biological functions of the circulating PMNs, and (c) a directed influx of these activated PMNs to the site of bacterial invasion. In the current study, we determined the presence of G-CSF in ILK by Western blot analysis using a goat polyclonal antihuman G-CSF antibody (Ab). Using this Ab, we then evaluated the role of G-CSF in the ILK-induced protective inflammatory response in chickens against SE. Pretreatment of ILK with the Ab totally abolished the colony-stimulating activity of the ILK. Furthermore, Ab treatment of ILK resulted in: (a) an elimination of the ILK-induced peripheral blood heterophilia with a dramatic inhibition of ILK-mediated protection against SE organ invasion and (b) an elimination of accumulation of inflammatory PMNs in the peritoneum with subsequent decrease in the survival rate of chicks challenged i.p. with SE. Taken together these studies demonstrate for the first time the contribution of G-CSF to avian PMN activation and the immunoprophylaxis of SE infection by ILK in neonatal chickens.

Protein tyrosine kinases in granulocyte colony stimulating factor receptor signal transduction, myeloid cell proliferation, and neutrophil activation

Granulocyte colony-stimulating factor (G-CSF) plays an important role in the growth and maturation of granulocytic precursor cells. Although the interaction between G-CSF and its receptor (G-CSF-R) is an obligatory event during proliferation and differentiation of myeloid cells, the signal transduction mechanisms leading to these effects are not completely known. We investigated the kinetics of protein tyrosine kinase (PTK) activation in G-CSF-R signal transduction in myeloid leukemic cell lines and peripheral blood neutrophils. G-CSF treatment of myeloid cell-lines (HL-60, KG-1, NFS-60) and neutrophils resulted in a rapid increase in PTK activity. This induction was inhibited by an anti-G-CSF monoclonal antibody and various PTK-specific inhibitors. PTK activity was important for proliferation of myeloid cells; its inhibition resulted in decreased proliferation and clonogenicity of these cells. PTK-induction was not involved in G-CSF-R expression, internalization or recycling, but was partially responsible for up-regulation of CD11b expression on neutrophils. In contrast to neutrophilic cell-lines, the myelo-monocytic cell lines (U-937, WEHI-3B) showed no change in PTK levels in response to G-CSF. The results indicate that the G-CSF-R-mediated PTK up-regulation may be a neutrophil-lineage-restricted signal, and that PTK may play an important role in the proliferation of neutrophil-precursors and functional activation of mature neutrophils.

Expression of the activated (Y501-F501) hck tyrosine kinase in 32Dcl3 myeloid cells prolongs survival in the absence of IL-3 and blocks granulocytic differentiation in response to G-CSF

The hematopoietic cell kinase (hck), a member of the src family of intracellular, membrane-associated protein tyrosine kinases, is primarily expressed in mature granulocytes and monocyte/macrophages. Hck kinase activity plays an essential role in macrophage activation and may be an important signaling molecule in granulocytes. To examine the potential role of hck in hematopoietic differentiation pathways, retroviral vectors were used to express wild-type and mutant forms of p59hck in the hck-negative, interleukin-3 (IL-3) -dependent murine myeloid cell line, 32Dcl3. Constitutive expression of an activated form of hck markedly prolonged the viability of 32Dcl3 cells in the absence of IL-3 but failed to abrogate the requirement for IL-3 for proliferation. Moreover, enforced expression of the activated hck kinase (and less so, the wild-type kinase) blocked granulocytic differentiation of 32Dcl3 cells in response to granulocyte colony-stimulating factor. These findings indicate that up-regulation of hck expression is not required for (and may interfere with) granulocytic differentiation.

Granulocyte colony-stimulating factor-stimulated proliferation of myeloid cells: mode of cell cycle control by a range of inhibitors

The myeloid cell line, NFS-60, is dependent on granulocyte colony-stimulating factor (G-CSF) or interleukin-3 (IL-3) for survival and growth. Long-term G-CSF-dependent proliferation was found to be completely inhibited by interferon-gamma (IFN-gamma), cyclic AMP, and dimethylamiloride and partially inhibited by IFN-alpha and lipopolysaccharide. With the exception of IFN-gamma, these agents exhibited a corresponding pattern of inhibition of DNA synthesis in quiescent NFS-60 cells stimulated with G-CSF. IFN-gamma was only a weak inhibitor of DNA synthesis, suggesting that it may act at a later stage to block proliferation. The addition of G-CSF to NFS-60 cells resulted in phosphorylation of the retinoblastoma protein (pRB) and activation of E2F DNA binding activity. The inhibitors were found to suppress the phosphorylation of pRB, lead to the production of higher order E2F complexes, and suppress the expression of c-myc and proliferating cell nuclear antigen (PCNA) to an extent that correlated with their ability to block DNA synthesis. These findings are consistent with the notion that the ratio of free/bound E2F binding activity is critical in controlling cell cycle progression through G1 to S-phase in these cells.

Transcriptional activation potential of normal and tumor-associated myb isoforms does not correlate with their ability to block GCSF-induced terminal differentiation of murine myeloid precursor cells

The myb gene has been shown to be an important regulator of hematopoietic cell proliferation, differentiation and apoptosis. Activation of the myb gene into an oncogenic form has involved structural alterations to the coding sequences. Thus, the v-myb gene encoded by the Avian Myeloblastosis Virus, is truncated at both the 5' and 3' ends. Additionally, tumor cells containing rearrangements in the myb locus, such as the ABPL tumors or NFS60 tumor cell line have recently been shown to display a heterogeneity of structure. In this study, we examined the growth and differentiation properties of clonal cell lines derived from 32Dcl3 which harbor myb transgenes; derived from v-myb, and the ABPL-1, ABPL-2, ABPL-4 and NFS-60 cell lines. Retroviral vectors containing the appropriate myb cDNAs were produced, transfected into packaging cell lines, and the viruses were used to generate the 32D derivative cell clones. Abrogation of IL-3 dependence was never observed in any cell line. Expression of c-myb, ABPL-1-myb and ABPL-2-myb isoforms in 32D cells resulted in a block to their ability to terminally differentiate into granulocytes at the pro-myelocytic stage. However, expression of ABPL-4-myb or NFS60-myb in these cells failed to result in a similar effect. These cells differentiated into granulocytes in the presence of G-CSF, albeit more slowly than control 32Dcl3 cells. We also examined the ability of various Myb-isoforms to transactivate transcription of reporter genes containing Myb-binding elements in their promoter/enhancer sequences, to determine whether the phenotypic effects produced by these various isoforms correlate with their ability to transactivate transcription. Our results show that while v-myb and c-myb transactivated transcription equally well, the NFS60-myb exhibited the highest levels of transcriptional transactivation. The ABPL-1, ABPL-2 and ABPL-4-myb isoforms showed very low levels of transcriptional transactivation potential with the same reporter genes. These results suggest that the ability of various Myb-isoforms to transactivate transcription does not by itself correlate with their ability to induce a block to G-CSF-induced terminal differentiation of myeloid precursor cells.

Expression and role in growth regulation of tumour necrosis factor receptors p55 and p75 in acute myeloblastic leukaemia cells

Tumour necrosis factor (TNF)-alpha exerts multiple effects on human acute myeloblastic leukaemia (AML) cells in vitro, including (1) synergistic stimulation of proliferation with interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF); (2) inhibition of granulocyte-CSF (G-CSF) and stem cell factor (SCF)-induced growth; (3) suppression of multiplication of clonogenic leukaemic cells; (4) induction of autocrine growth. Recently, two distinct TNF receptors (TNF-Rs), TNF-Rp55 and TNF-Rp75, have been identified. In this study we show that both receptors are expressed on freshly isolated AML blasts, with p75 being the predominant TNF-receptor type. This study investigates the roles of these two receptors in TNF-alpha-driven growth regulation of AML blasts in vitro. Using a receptor-specific antibody, it is shown that both receptor types participate in TNF-alpha-mediated stimulation of GM-CSF/IL-3-induced proliferation and in TNF-alpha-induced autocrine growth. In contrast, the TNF-alpha-triggered growth inhibition (antiproliferation) and the potent suppression of G-CSF- and SCF-induced proliferation exclusively result from activation of TNF-Rp55. Taken together, these results suggest that the proliferative effects of TNF-alpha on AML blasts are mediated through both p55 and p75 TNF receptors, whereas the TNF-alpha-signalled growth inhibition is exclusively transduced via TNF-Rp55.

All-trans retinoic acid directly inhibits granulocyte colony-stimulating factor-induced proliferation of CD34+ human hematopoietic progenitor cells

In this study we examine the effects of retinoids on purified CD34+ human hematopoietic progenitor cells. All-trans retinoic acid inhibited granulocyte colony-stimulating factor (G-CSF)-induced proliferation of CD34+ cells in short-term liquid cultures in a dose-dependent fashion with maximal inhibition of 72% at a concentration of retinoic acid of 1 mumol/L. Although no significant effects were observed on granulocyte-macrophage CSF (GM-CSF)--interleukin-3--or stem cell factor (SCF)-induced proliferation, the combinations of G-CSF and each of these cytokines were all inhibited. Moreover, retinol (3 mumol/L) and chylomicron remnant retinyl esters (0.1 mumol/L) in concentrations normally found in human plasma also had inhibitory effects. Single-cell experiments showed that the effects of retinoic acid were directly mediated. Retinoids also significantly inhibited G-CSF-induced colony formation in semisolid medium, with 88% inhibition observed at a concentration of retinoic acid of 1 mumol/L. However, we did not observe any effects of retinoic acid on G-CSF-induced differentiation as assessed by morphology and flowcytometry. Similar to previous findings using total bone marrow mononuclear cells, we observed a stimulation of GM-CSF-induced colony formation after 14 days. We also observed a stimulatory effect of low doses of retinoic acid (30 nmol/L) on blast-cell colony formation on stromal cell layers. Taken together, the data indicate that vitamin A present in human plasma has inhibitory as well as stimulatory effects on myelopoiesis.

Pharmacological effects of recombinant human granulocyte colony-stimulating factor modified by polyethylene glycol on anticancer drug-induced neutropenia in mice

1. To clarify the pharmacological effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) conjugated to polyethylene glycol (PEG), its effects on the number of circulating neutrophils in mice made neutropenic by cyclophosphamide (CPA) or 5-fluorouracil (5-FU) were compared with rhG-CSF lacking PEG. 2. In normal mice, PEG-conjugated rhG-CSF (PEG-rhG-CSF, 10 micrograms protein/kg) induced an increase in neutrophils which lasted for 72 h after injection whereas the effect of rhG-CSF (10 micrograms protein/kg) disappeared by 24 h after injection. 3. In CPA or 5-FU-induced neutropenic mice, PEG-rhG-CSF inhibited neutropenia or accelerated recovery from neutropenia and its potency was higher than that of rhG-CSF. 4. These results indicate that PEG-rhG-CSF has a longer duration of action than rhG-CSF and is more effective in the recovery from neutropenia.

v-myb blocks granulocyte colony-stimulating factor-induced myeloid cell differentiation but not proliferation

To understand the effects of v-myb expression on mammalian hematopoietic cell differentiation, we have constructed a retroviral vector which can efficiently express v-myb gene product in mammalian cells. Infection of interleukin-3-dependent murine progenitor cell line 32D Cl3, which undergoes terminal differentiation to mature granulocytes in the presence of granulocyte colony-stimulating factor (GCSF), with this recombinant retrovirus does not abrogate its requirement of interleukin-3 for growth. However, expression of v-myb in these cells blocks their ability to differentiate in response to GCSF. Instead, the v-myb-infected cells proliferate indefinitely in the presence of GCSF. 32D Cl3 cells infected with empty vector carrying only the neomycin resistance gene responded to the addition of GCSF in a manner identical to that of the uninfected cells and underwent terminal differentiation into granulocytes. These results suggest that oncogenic forms of myb gene bring about transformation by blocking the differentiation signal derived by cytokines while promoting the proliferative signal transduction pathways.

Gamma-interferon interrupts growth stimulation in chronic myelogenous leukemia established by endogenous granulocyte colony-stimulating factor

We have previously shown that maturing neoplastic cells from patients with stable phase chronic myelogenous leukemia (SP CML) constitutively produce granulocyte colony-stimulating factor (G-CSF) and are also receptive for this molecule. G-CSF functions as an endogenous growth factor in SP CML, and thus is responsible for divisions in maturing leukemic cells leading to an expansion of the compartment of mature cells. In the investigations to be reported below, the effects of various hematopoietic inhibitor molecules on the expression of the G-CSF gene by SP CML bone marrow cells enriched for promyelocytes/myelocytes were examined at the mRNA and protein level. We show that exposure of SP CML bone marrow promyelocytes/myelocytes to recombinant human (rh) interferon (IFN)-gamma but not to rh IFN-alpha, rh tumor necrosis factor (TNF)-alpha, and rh lymphotoxin (LT) leads to downregulation of G-CSF expression and interruption of the G-CSF-mediated endogenous growth stimulation. The action of G-CSF takes place at the posttranscriptional level and involves an acceleration of decay of steady-state levels of G-CSF transcripts in the malignant cell population.

Tetracycline and 13-cis-retinoic acid inhibit production and activity of granulocyte activating factor (GAF) from Propionibacterium acnes

The aim of this study was to evaluate different treatment schedules on release or activity of a granulocyte activating factor (GAF) from Propionibacterium acnes. Incubation of P. acnes in physiological saline (30 min, 37 degrees C) resulted in release of a soluble factor that elicited considerable chemiluminescence response and chemotactic stimulus on human granulocytes. Pretreatment of the microorganisms with subinhibitory concentrations of tetracycline or incubation of granulocytes with 13-cis-retinoic acid significantly reduced the activating potency of GAF on these phagocytic cells. Since GAF was considered to be one of the stimuli for inflammation in acne vulgaris, administration of tetracycline and 13-cis-retinoic acid appears to be an adequate therapy.