A1 is a constitutive and inducible Bcl-2 homologue in mature human neutrophils

Pharmacological Induction of Granulocyte Cell Death as Therapeutic Strategy

Apoptosis is central for the maintenance of health. In the immune system, apoptosis guarantees proper development of immune cells and shutdown of immune reactions by the coordinated elimination of activated immune cells. Limitation of the life span of granulocytes is important, as overactivation of these cells is associated with chronic inflammation and collateral tissue damage. Consequently, targeted induction of granulocyte apoptosis may be beneficial in the course of respective immune disorders. Anti-inflammatory drugs such as glucocorticoids and monoclonal antibodies against IL-5Rα exert their function in part by triggering eosinophil apoptosis. Agonistic antibodies targeting Siglec-8 or death receptors are tested (pre)clinically. Moreover, a new class of inhibitors targeting antiapoptotic BCL-2 proteins shows great promise for anticancer treatments. Because of their specificity and tolerable side effects, these so-called BH3 mimetics may be worthwhile to evaluate in inflammatory disorders. Here, we review past and recent data on pharmacological apoptosis induction of granulocytes and highlight respective therapeutic potential.

BCL-XL antagonism selectively reduces neutrophil life span within inflamed tissues without causing neutropenia

Neutrophils help to clear pathogens and cellular debris, but can also cause collateral damage within inflamed tissues. Prolonged neutrophil residency within an inflammatory niche can exacerbate tissue pathology. Using both genetic and pharmacological approaches, we show that BCL-XL is required for the persistence of neutrophils within inflammatory sites in mice. We demonstrate that a selective BCL-XL inhibitor (A-1331852) has therapeutic potential by causing apoptosis in inflammatory human neutrophils ex vivo. Moreover, in murine models of acute and chronic inflammatory disease, it reduced inflammatory neutrophil numbers and ameliorated tissue pathology. In contrast, there was minimal effect on circulating neutrophils. Thus, we show a differential survival requirement in activated neutrophils for BCL-XL and reveal a new therapeutic approach to neutrophil-mediated diseases.

Targeting Bfl-1 via acute CDK9 inhibition overcomes intrinsic BH3-mimetic resistance in lymphomas

BH3 mimetics like venetoclax target prosurvival Bcl-2 family proteins and are important therapeutics in the treatment of hematological malignancies. We demonstrate that endogenous Bfl-1 expression can render preclinical lymphoma tumor models insensitive to Mcl-1 and Bcl-2 inhibitors. However, suppression of Bfl-1 alone was insufficient to fully induce apoptosis in Bfl-1-expressing lymphomas, highlighting the need for targeting additional prosurvival proteins in this context. Importantly, we demonstrated that cyclin-dependent kinase 9 (CDK9) inhibitors rapidly downregulate both Bfl-1 and Mcl-1, inducing apoptosis in BH3-mimetic-resistant lymphoma cell lines in vitro and driving in vivo tumor regressions in diffuse large B-cell lymphoma patient-derived xenograft models expressing Bfl-1. These data underscore the need to clinically develop CDK9 inhibitors, like AZD4573, for the treatment of lymphomas using Bfl-1 as a selection biomarker.

Does Neutrophil Phenotype Predict the Survival of Trauma Patients?

According to the World Health Organization (WHO), trauma is responsible for 10% of deaths and 16% of disabilities worldwide. This is considerably higher than those for malaria, tuberculosis, and HIV/AIDS combined. While the human suffering and death caused by injury is well-recognized, injury has a significant medical care cost. Better prediction of the state of trauma patients in the days immediately after trauma may reduce costs. Traumatic injuries to multiple organs can cause dysfunction in all systems of the body especially the immune system placing patients at high risk of infections and inflammatory complications which are often fatal. Neutrophils are the most abundant leukocyte in the human circulation and are crucial for the prevention of microbial disease. Significant changes in neutrophil functions such as enhanced chemotaxis, Neutrophil extracellular trap (NET)-induced cell death (NETosis), and phagocytosis occur early after injury followed by prolonged functional defects such as phagocytosis, killing mechanisms, and receptor expression. Analysis of these changes may improve the prediction of the patient's condition over time. We provide a comprehensive and up-to-date review of the literature investigating the effect of trauma on neutrophil phenotype with an underlying goal of using this knowledge to examine the predictive potential of neutrophil alterations on secondary complications in patients with traumatic injuries. We conclude that alterations in neutrophil surface markers and functions may be potential biomarkers that predict the outcome of trauma patients.

Inflammation Resolution and the Induction of Granulocyte Apoptosis by Cyclin-Dependent Kinase Inhibitor Drugs

Inflammation is a necessary dynamic tissue response to injury or infection and it's resolution is essential to return tissue homeostasis and function. Defective or dysregulated inflammation resolution contributes significantly to the pathogenesis of many, often common and challenging to treat human conditions. The transition of inflammation to resolution is an active process, involving the clearance of inflammatory cells (granulocytes), a change of mediators and their receptors, and prevention of further inflammatory cell infiltration. This review focuses on the use of cyclin dependent kinase inhibitor drugs to pharmacologically target this inflammatory resolution switch, specifically through inducing granulocyte apoptosis and phagocytic clearance of apoptotic cells (efferocytosis). The key processes and pathways required for granulocyte apoptosis, recruitment of phagocytes and mechanisms of engulfment are discussed along with the cumulating evidence for cyclin dependent kinase inhibitor drugs as pro-resolution therapeutics.

Conditional knockdown of BCL2A1 reveals rate-limiting roles in BCR-dependent B-cell survival

Bcl2 family proteins control mitochondrial apoptosis and its members exert critical cell type and differentiation stage-specific functions, acting as barriers against autoimmunity or transformation. Anti-apoptotic Bcl2a1/Bfl1/A1 is frequently deregulated in different types of blood cancers in humans but its physiological role is poorly understood as quadruplication of the Bcl2a1 gene locus in mice hampers conventional gene targeting strategies. Transgenic overexpression of A1, deletion of the A1-a paralogue or constitutive knockdown in the hematopoietic compartment of mice by RNAi suggested rate-limiting roles in lymphocyte development, granulopoiesis and mast cell activation. Here we report on the consequences of conditional knockdown of A1 protein expression using a reverse transactivator (rtTA)-driven approach that highlights a critical role for this Bcl2 family member in the maintenance of mature B-cell homeostasis. Furthermore, we define the A1/Bim (Bcl-2 interacting mediator of cell death) axis as a target of key kinases mediating B-cell receptor (BCR)-dependent survival signals, such as, spleen tyrosine kinase (Syk) and Brutons tyrosine kinase (Btk). As such, A1 represents a putative target for the treatment of B-cell-related pathologies depending on hyperactivation of BCR-emanating survival signals and loss of A1 expression accounts, in part, for the pro-apoptotic effects of Syk- or Btk inhibitors that rely on the ‘BH3-only' protein Bim for cell killing.

A1/Bfl-1 in leukocyte development and cell death

The function of the anti-apoptotic Bcl-2 family member Bcl2a1/Bfl-1/A1 is poorly understood due to the lack of appropriate loss-of-function mouse models and redundant effects with other Bcl-2 pro-survival proteins upon overexpression. Expression analysis of A1 suggests predominant roles in leukocyte development, their survival upon viral or bacterial infection, as well as during allergic reactions. In addition, A1 has been implicated in autoimmunity and the pathology and therapy resistance of hematological as well as solid tumors that may aberrantly express this protein. In this review, we aim to summarize current knowledge on A1 biology, focusing on its role in the immune system and compare it to that of other pro-survival Bcl-2 proteins.

Decreased neutrophil apoptosis in quiescent ANCA-associated systemic vasculitis

Background

ANCA-Associated Systemic Vasculitis (AASV) is characterized by leukocytoclasis, accumulation of unscavenged apoptotic and necrotic neutrophils in perivascular tissues. Dysregulation of neutrophil cell death may contribute directly to the pathogenesis of AASV.

Methods

Neutrophils from Healthy Blood Donors (HBD), patients with AASV most in complete remission, Polycythemia Vera (PV), Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA) and renal transplant recipients (TP) were incubated in vitro, and the rate of spontaneous apoptosis was measured by FACS. Plasma levels of cytokines and sFAS were measured with cytometric bead array and ELISA. Expression of pro/anti-apoptotic factors, transcription factors C/EBP-α, C/EBP-β and PU.1 and inhibitors of survival/JAK2-pathway were measured by real-time-PCR.

Results

AASV, PV and RA neutrophils had a significantly lower rate of apoptosis compared to HBD neutrophils (AASV 50±14% vs. HBD 64±11%, p<0.0001). In RA but not in AASV and PV, low apoptosis rate correlated with increased plasma levels of GM-CSF and high mRNA levels of anti-apoptotic factors Bcl-2A1 and Mcl-1. AASV patients had normal levels of G-CSF, GM-CSF and IL-3. Both C/EBP-α, C/EBP-β were significantly higher in neutrophils from AASV patients than HBD. Levels of sFAS were significantly higher in AASV compared to HBD.

Conclusion

Neutrophil apoptosis rates in vitro are decreased in AASV, RA and PV but mechanisms seem to differ. Increased mRNA levels of granulopoiesis-associated transcription factors and increased levels of sFAS in plasma were observed in AASV. Additional studies are required to define the mechanisms behind the decreased apoptosis rates, and possible connections with accumulation of dying neutrophils in regions of vascular lesions in AASV patients.

Constitutive neutrophil apoptosis: regulation by cell concentration via S100 A8/9 and the MEK-ERK pathway

Programmed cell death (PCD) is a fundamental mechanism in tissue and cell homeostasis. It was long suggested that apoptosis regulates the cell number in diverse cell populations; however no clear mechanism was shown. Neutrophils are the short-lived, first-line defense of innate immunity, with an estimated t = 1/2 of 8 hours and a high turnover rate. Here we first show that spontaneous neutrophil constitutive PCD is regulated by cell concentrations. Using a proteomic approach, we identified the S100 A8/9 complex, which constitutes roughly 40% of cytosolic protein in neutrophils, as mediating this effect. We further demonstrate that it regulates cell survival via a signaling mechanism involving MEK-ERK via TLR4 and CD11B/CD18. This mechanism is suggested to have a fine-tuning role in regulating the neutrophil number in bone marrow, peripheral blood, and inflammatory sites.

CBLB613: a TLR 2/6 agonist, natural lipopeptide of Mycoplasma arginini , as a novel radiation countermeasure

To date, there are no safe and effective drugs available for protection against ionizing radiation damage. Therefore, a great need exists to identify and develop non-toxic agents that will be useful as radioprotectors or postirradiation therapies under a variety of operational scenarios. We have developed a new pharmacological agent, CBLB613 (a naturally occurring Mycoplasma-derived lipopeptide ligand for Toll-like receptor 2/6), as a novel radiation countermeasure. Using CD2F1 mice, we investigated CBLB613 for toxicity, immunogenicity, radioprotection, radiomitigation and pharmacokinetics. We also evaluated CBLB613 for its effects on cytokine induction and radiation-induced cytopenia in unirradiated and irradiated mice. The no-observable-adverse-effect level of CBLB613 was 1.79 mg/kg and 1 mg/kg for single and repeated doses, respectively. CBLB613 significantly protected mice against a lethal dose of (60)Co γ radiation. The dose reduction factor of CBLB613 as a radioprotector was 1.25. CBLB613 also mitigated the effects of (60)Co γ radiation on survival in mice. In both irradiated and unirradiated mice, the drug stimulated induction of interleukin-1β (IL-1β), IL-6, IL-10, IL-12, keratinocyte-derived chemokine, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor-1α. CBLB613 also reduced radiation-induced cytopenia and increased bone marrow cellularity in irradiated mice. Our immunogenicity study demonstrated that CBLB613 is not immunogenic in mice, indicating that it could be developed as a radioprotector and radiomitigator for humans against the potentially lethal effects of radiation exposure.

NO signaling in exercise training-induced anti-apoptotic effects in human neutrophils

Short-lived neutrophils play a predominant role in innate immunity, the effects of exercise training on neutrophil survival is unclear. In this study, we investigated the underlying mechanisms of training effects on human neutrophil apoptosis. Healthy male subjects were trained on a cycling ergometer for 8 weeks and followed by 4 weeks of detraining. Blood neutrophils were collected before exercise, after training, and after detraining. Comparing with pre-exercise specimens, neutrophils collected after training showed reduced apoptosis rate, which partially returned after detraining. Various intracellular proteins, including iNOS, Mcl-1, A1, Grp78, and IL-8, were upregulated by training, and they remained high after detraining. Upregulated iNOS was closely correlated with these anti-apoptotic molecules in neutrophils. Furthermore, the possible mechanism by which iNOS suppressed apoptosis was explored. Neutrophil apoptosis was accelerated by blocking and retarded by stimulating the endogenous iNOS activity. As an anti-apoptosis mediator of NO signaling, the Mcl-1 level dropped by depletion of the major NO downstream molecule cGMP and such loss of Mcl-1 was avoidable when supplying exogenous NO. Upon activation of NO-cGMP signaling, neutrophils held increased Mcl-1 expression and delayed apoptosis. Collectively, our results suggested that exercise training may retard neutrophil apoptosis by upregulating the iNOS-NO-cGMP-Mcl-1 pathway.

Butyrate and propionate induced activated or non-activated neutrophil apoptosis via HDAC inhibitor activity but without activating GPR-41/GPR-43 pathways

OBJECTIVE

Decreased neutrophil apoptosis is implicated in persistent inflammation resulting in systemic inflammatory response syndrome and multiple organ dysfunctions syndromes. Short-chain fatty acids (SCFAs) may be a candidate to control neutrophil apoptosis because SCFAs are normally produced in the gut and related products have been approved for human use. We investigated the effects of SCFAs on apoptosis of activated and non-activated neutrophils and their mechanisms.

METHODS

Purified neutrophils obtained from healthy volunteers were preincubated for 1 h with or without the G-protein receptor (GPR) inhibitor pertussis toxin (100 ng/mL) or U-73122 (50 ng/mL), extracellular signal-related protein kinase inhibitor PD98059 (10 microM), mitogen-activated protein kinase (MAPK) p38 inhibitor SB203580 (25 microM), Jun kinase inhibitor-I (2 microM), caspase-3 and -7 inhibitor Z-VAD-FMK (100 microM), caspase-8 inhibitor Z-IETD-FMK (50 microM), or caspase-9 inhibitor Z-LEHD-FMK (50 microM). The cells were then cultured with or without SCFAs or trichostatin A, a typical histone deacetylase inhibitor, in the presence or absence of lipopolysaccharide (1 microg/mL) or tumor necrosis factor-alpha (100 ng/mL). Neutrophil apoptosis was assessed by annexin V staining using flow cytometry. The GPR-41 and -43 and apoptosis-related proteins (bax, mcl-1, a1) mRNA were measured by quantitative real-time polymerase chain reaction and the expression of acetylated histone H3 was determined by western blot.

RESULTS

The caspase inhibitors inhibited butyrate- and propionate-induced neutrophil apoptosis treated or untreated with lipopolysaccharide or tumor necrosis factor-alpha, whereas GPR and MAPK inhibitors had no effect. The mRNA expressions of GPR-43 and a1 protein were reduced by butyrate and propionate. The expressions of acetylated histone H3 were induced by butyrate and propionate.

CONCLUSION

These results suggest that butyrate and propionate increase apoptosis of neutrophils irrespective of their activation state, by factors other than GPRs and MAPKs, and their mechanisms likely relate to their histone deacetylase inhibition activity, which may control a1 mRNA expression.

Calcium pyrophosphate dihydrate crystal-induced inhibition of neutrophil apoptosis: involvement of Bcl-2 family members

INTRODUCTION

The inflammation associated with calcium pyrophosphate dihydrate (CPPD) crystal-induced arthritis arises from the activation of neutrophils with crystals in the synovial joint. Furthermore, constitutive neutrophil apoptosis is inhibited by this interaction with CPPD so that the lifetime of the cells and the duration of the inflammatory response are extended. The objective of this study was to investigate the role of bcl-2 protein family members in the CPPD-induced prosurvival response.

METHODS

Apoptosis was measured using DNA fragmentation and Caspase 3 assays. The expression and activation levels of the bcl-2 protein family members A1, Mcl-1, Bcl-xl, Bim, Bad and Bax-alpha were measured using western blot analysis.

RESULTS

The prosurvival proteins Mcl-1 and Bcl-xl were both found to be strongly expressed but unaffected by CPPD-induced neutrophil activation over 3 h. The expression of proapoptotic proteins Bim and Bax-alpha was found to decrease over the time course of a 3 h incubation of neutrophils with CPPD crystals (but not the bacterial chemoattractant fMLP). Furthermore, expression of the unphosphorylated (active, proapoptotic) form of Bim was dominant in control cells at 0.5 h, whereas the status of this protein switched to the phosphorylated form following cell activation by both CPPD and fMLP. For CPPD (but not fMLP) this phosphorylation effect reversed over a 3 h incubation.

CONCLUSION

Upon stimulation by CPPD crystals, the expression of both Bim and Bax-alpha decreased after 3 h suggesting a reduced proapoptotic effect of these proteins so that the static expression of the prosurvival proteins Bcl-xl and Mcl-1 might allow for a temporary shift in the balance to a prosurvival state of the cells. Because a sudden (but transient) increase in the phosphorylated form of Bim was observed in CPPD-stimulated neutrophils it is possible that this species might act as a signaling intermediate, resulting in the observed downregulation of Bax-alpha.

Neutrophil apoptosis and the resolution of infection

Polymorphonuclear leukocytes (PMNs) are the most abundant white cell in humans and an essential component of the innate immune system. PMNs are typically the first type of leukocyte recruited to sites of infection or areas of inflammation. Ingestion of microorganisms triggers production of reactive oxygen species and fusion of cytoplasmic granules with forming phagosomes, leading to effective killing of ingested microbes. Phagocytosis of bacteria typically accelerates neutrophil apoptosis, which ultimately promotes the resolution of infection. However, some bacterial pathogens alter PMN apoptosis to survive and thereby cause disease. Herein, we review PMN apoptosis and the ability of microorganisms to alter this important process.

Changes in gene expression of granulocytes during in vivo granulocyte colony-stimulating factor/dexamethasone mobilization for transfusion purposes

The treatment of healthy donors with granulocyte colony-stimulating factor (G-CSF) and dexamethasone results in sufficient numbers of circulating granulocytes to prepare granulocyte concentrates for clinical purposes. Granulocytes obtained in this way demonstrate relatively normal functional behavior combined with a prolonged life span. To study the influence of mobilizing agents on granulocytes, we used oligonucleotide microarrays to identify genes that are differentially expressed in mobilized granulocytes compared with control granulocytes. More than 1000 genes displayed a differential expression pattern, with at least a 3-fold difference. Among these, a large number of genes was induced that encode proteins involved in inflammation and the immune response, such as C-type lectins and leukocyte immunoglobulin-like receptors. Because mobilized granulocytes have a prolonged life span, we focused on genes involved in the regulation of apoptosis. One of the most prominent among these was CAST, the gene encoding calpastatin. Calpastatins are the endogenous inhibitors of calpains, a family of calcium-dependent cysteine proteases recently shown to be involved in neutrophil apoptosis. Transcriptional activity of the CAST gene was induced by G-CSF/dexamethasone treatment both in vivo and in vitro, whereas the protein expression of CAST was stabilized during culture. These studies provide new insight in the genotypic changes as well as in the regulation of the immunologic functions and viability of mobilized granulocytes used for clinical transfusion purposes.

IL-3 induces a Pim1-dependent antiapoptotic pathway in primary human basophils

The contribution of basophils in allergic disease and other Th2-type immune responses depends on their persistence at sites of inflammation, but the ligands and molecular pathways supporting basophil survival are largely unknown. The comparison of rates of apoptosis and of the expression of antiapoptotic proteins in different human granulocyte types revealed that basophils have a considerably longer spontaneous life span than neutrophils and eosinophils consistent with high levels of constitutive Bcl-2 expression. Interleukin-3 (IL-3) is the only ligand that efficiently protects basophils from apoptosis as evidenced by screening a large number of stimuli. IL-3 up-regulates the expression of the antiapoptotic proteins cIAP2, Mcl-1, and Bcl-X(L) and induces a rapid and sustained de novo expression of the serine/threonine kinase Pim1 that closely correlates with cytokine-enhanced survival. Inhibitor studies and protein transduction of primary basophils using wild-type and kinase-dead Pim1-Tat fusion-proteins demonstrate the functional importance of Pim1 induction in the IL-3-enhanced survival. Our data further indicate that the antiapoptotic Pim1-mediated pathway operates independently of PI3-kinase but involves the activation of p38 MAPK. The induction of Pim1 leading to PI3-kinase-independent survival as described here for basophils may also be a relevant antiapoptotic mechanism in other terminally differentiated leukocyte types.

Granulocyte colony-stimulating factor delays neutrophil apoptosis by inhibition of calpains upstream of caspase-3

Neutrophils have a very short life span and undergo apoptosis within 24 hours after leaving the bone marrow. Granulocyte colony-stimulating factor (G-CSF) is essential for the recruitment of fresh neutrophils from the bone marrow but also delays apoptosis of mature neutrophils. To determine the mechanism by which G-CSF inhibits neutrophil apoptosis, the kinetics of neutrophil apoptosis during 24 hours in the absence or presence of G-CSF were analyzed in vitro. G-CSF delayed neutrophil apoptosis for approximately 12 hours and inhibited caspase-9 and -3 activation, but had virtually no effect on caspase-8 and little effect on the release of proapoptotic proteins from the mitochondria. However, G-CSF strongly inhibited the activation of calcium-dependent cysteine proteases calpains, upstream of caspase-3, via apparent control of Ca(2+)-influx. Calpain inhibition resulted in the stabilization of the X-linked inhibitor of apoptosis (XIAP) and hence inhibited caspase-9 and -3 in human neutrophils. Thus, neutrophil apoptosis is controlled by G-CSF after initial activation of caspase-8 and mitochondrial permeabilization by the control of postmitochondrial calpain activity.

The dual effects of TNFalpha on neutrophil apoptosis are mediated via differential effects on expression of Mcl-1 and Bfl-1

Neutrophils have a very short half-life in the circulation, undergoing rapid death by apoptosis, but a number of agents can either delay or accelerate the rate at which these cells undergo death. TNFalpha can exert opposing, concentration-dependent effects on neutrophils to either accelerate their apoptosis or enhance their survival. We show that TNFalpha greatly increases the rate of turnover of Mcl-1, an antiapoptotic protein that plays a key role in neutrophil survival. In contrast to Mcl-1 turnover in control- or granulocyte-macrophage colony-stimulating factor (GM-CSF)-treated neutrophils that occurs via the proteasome, TNFalpha-accelerated Mcl-1 turnover occurs via activation of caspases. Mcl-1-depleted cells thus have accelerated rates of apoptosis. While TNFalpha had no effect on MCL-1 transcription, it induced expression of another antiapoptotic molecule, BFL-1. Low concentrations of TNFalpha (<or=1 ng/mL) stimulated BFL-1 expression, whereas higher concentrations (>or=10 ng/mL) triggered caspase-dependent acceleration of Mcl-1 turnover. These opposing effects on 2 separate antiapoptotic systems of neutrophils explain the divergent effects of TNFalpha on neutrophil apoptosis and have important implications for understanding how TNFalpha may affect immune function in inflammatory diseases.

Age-related impairment of GM-CSF-induced signalling in neutrophils: role of SHP-1 and SOCS proteins

Functional activities of mature human neutrophils are strongly influenced by the pro-inflammatory cytokine granulocyte macrophage-colony stimulating factor (GM-CSF). Accordingly, a defective response to GM-CSF might have dramatic consequences for neutrophil functions and the host defence against infections. Such an event is most likely to occur in senescence. A number of studies have, in fact, reported an impairment of the GM-CSF capacity to prime and/or to activate respiratory burst, as well as to delay apoptotic events, in neutrophils from elderly individuals. In the last 2 decades many efforts have been made to explore at molecular levels the mechanism underlying these defects. Recent studies let us depict a scenario in which an increased activity of inhibitory molecules, such as Src homology domain-containing protein tyrosine phosphatase-1 (SHP-1) and suppressors of cytokine signalling (SOCS), is responsible for the age-related failure of GM-CSF to stimulate neutrophil functions via inhibition of Lyn-, phosphoinositide 3-kinase (PI3-K)/extracellular signal-regulated kinase (ERK)- and signal transducers and activators of transcription (STAT)-dependent pathways. The control of SHP-1 and/or SOCS activity might therefore be an important therapeutic target for the restoration of normal immune responses during senescence.

Effects of whole-body gamma irradiation and 5-androstenediol administration on serum G-CSF

5-Androstenediol (5-AED) is a natural circulating adrenocortical steroid hormone that interconverts in vivo with other members of the 5-androstene family of steroids: dehydroepiandrosterone and 5-androstenetriol. These steroids stimulate immune responses and resistance to infection. 5-AED has been identified as a systemic radiation countermeasure that enhances survival in mice exposed to gamma irradiation and ameliorates radiation-induced neutropenia in mice and nonhuman primates. 5-AED mitigates radiation-induced decreases in platelets, natural killer (NK) cells, red blood cells, and monocytes. Administration of 5-AED causes functional activation of circulating granulocytes (phagocytic ability), monocytes (oxidative burst), and NK cells (surface CD11b expression). The effects of 5-AED on survival and hematological parameters are consistent with induction of hematopoietic cytokines. To test this hypothesis, we measured serum cytokines by ELISA, Luminex, and a cytokine array. A cytokine array was used for 62 different cytokines, chemokines, growth factors, and soluble receptors. 5-AED caused significant increases in circulating granulocyte colony-stimulating factor (G-CSF) in irradiated and unirradiated animals as observed with ELISA and Luminex. The cytokine array results suggest induction of G-CSF and additional cytokines, and related molecules. Since G-CSF is an important hematopoietic cytokine, the results support our hypothesis that the previously observed increases in numbers of hematopoietic progenitors, circulating innate immune cells and platelets, and functional activation of granulocytes, monocytes, and NK cells result from a cytokine cascade induced by 5-AED.

Glucocorticoid modulation of Bcl-2 family members A1 and Bak during delayed spontaneous apoptosis of bovine blood neutrophils

Neutrophils are critical for innate immune defense against microbial invasion but can also cause inflammatory tissue damage if their life span is not tightly regulated. Antiinflammatory glucocorticoids delay spontaneous apoptosis in human, rodent, and bovine neutrophils, but mechanisms involved are unknown. We hypothesized here that glucocorticoids delay neutrophil apoptosis by altering expression of key Bcl-2 apoptosis regulatory proteins, A1 and Bak, via activation of the cell's glucocorticoid receptors. To test this hypothesis, isolated bovine blood neutrophils were exposed to dexamethasone with and without glucocorticoid receptor antagonism (RU486) and aged ex vivo over 0-24 h for assessment of various spontaneous apoptosis pathway indicators and A1 and Bak abundance. Results show that dexamethasone preserved neutrophil mitochondrial membrane integrity, delayed caspase-9 activation, and reduced the rate of spontaneous apoptosis. Also, dexamethasone increased A1 and decreased Bak mRNA abundance. RU486 pretreatment of the cells abrogated each of these dexamethasone effects. Dexamethasone-induced increases in A1 mRNA were reflected in A1 protein increases, which also were observed in circulating neutrophils of dexamethasone-treated animals. Bak protein decreases were observed in neutrophils of the dexamethasone-treated animals but not in isolated neutrophils, suggesting that stimuli additional to (and perhaps regulated by) glucocorticoid are required to affect Bak protein expression changes in neutrophils. Collectively, our results are unique in demonstrating a mechanism behind glucocorticoid regulation of spontaneous apoptosis and implicate steroid receptor activation and subsequent regulation of A1 and Bak as contributors to mitochondrial membrane stability, reduced caspase-9 activity, and delayed apoptosis in bovine neutrophils exposed to glucocorticoids.

Cyclic AMP delays neutrophil apoptosis via stabilization of Mcl-1

Human neutrophils underwent spontaneous apoptosis, which was accompanied by degradation of Mcl-1, but not other anti-apoptotic molecules (cIAP1, cIAP2, A1, survivin and Bcl-2). Spontaneous neutrophil apoptosis and Mcl-1 degradation were prevented by cyclic AMP (cAMP) agonists (dibutyryl cAMP and prostaglandin E(1)), and the effects of cAMP agonists on neutrophils were highly resistant to cycloheximide, a protein synthesis inhibitor, although slight increase in Mcl-1 mRNA expression was induced by cAMP agonists. Proteasome inhibitors (epoxomicin and lactacystin) also prevented spontaneous neutrophil apoptosis and Mcl-1 degradation to the same extent as cAMP agonists, and no additive effect was obtained by combination of cAMP agonists and proteasome inhibitors. These findings suggest that cAMP agonists, like proteasome inhibitors, delay neutrophil apoptosis primarily via stabilization of Mcl-1.

BCL2 family of apoptosis-related genes: functions and clinical implications in cancer

One of the most effective ways to combat different types of cancer is through early diagnosis and administration of effective treatment, followed by efficient monitoring that will allow physicians to detect relapsing disease and treat it at the earliest possible time. Apoptosis, a normal physiological form of cell death, is critically involved in the regulation of cellular homeostasis. Dysregulation of programmed cell death mechanisms plays an important role in the pathogenesis and progression of cancer as well as in the responses of tumours to therapeutic interventions. Many members of the BCL2 (B-cell CLL/lymphoma 2; Bcl-2) family of apoptosis-related genes have been found to be differentially expressed in various malignancies, and some are useful prognostic cancer biomarkers. We have recently cloned a new member of this family, BCL2L12, which was found to be differentially expressed in many tumours. Most of the BCL2 family genes have been found to play a central regulatory role in apoptosis induction. Results have made it clear that a number of coordinating alterations in the BCL2 family of genes must occur to inhibit apoptosis and provoke carcinogenesis in a wide variety of cancers. However, more research is required to increase our understanding of the extent to which and the mechanisms by which they are involved in cancer development, providing the basis for earlier and more accurate cancer diagnosis, prognosis and therapeutic intervention that targets the apoptosis pathways. In the present review, we describe current knowledge of the function and molecular characteristics of a series of classic but also newly discovered genes of the BCL2 family as well as their implications in cancer development, prognosis and treatment.

Lipopolysaccharide signaling in endothelial cells

Sepsis is the systemic immune response to severe bacterial infection. The innate immune recognition of bacterial and viral products is mediated by a family of transmembrane receptors known as Toll-like receptors (TLRs). In endothelial cells, exposure to lipopolysaccharide (LPS), a major cell wall constituent of Gram-negative bacteria, results in endothelial activation through a receptor complex consisting of TLR4, CD14 and MD2. Recruitment of the adaptor protein myeloid differentiation factor (MyD88) initiates an MyD88-dependent pathway that culminates in the early activation of nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases. In parallel, a MyD88-independent pathway results in a late-phase activation of NF-kappaB. The outcome is the production of various proinflammatory mediators and ultimately cellular injury, leading to the various vascular sequelae of sepsis. This review will focus on the signaling pathways initiated by LPS binding to the TLR4 receptor in endothelial cells and the coordinated regulation of this pathway.

Role of mitochondria as the gardens of cell death

Mitochondria play a crucial role in regulating cell death, which is mediated by outer membrane permeabilization in response to death triggers such as DNA damage and growth factor deprivation. Mitochondrial membrane permeabilization induces the release of cytochrome c, Smac/DIABLO, and AIF, which are regulated by proapoptotic and antiapoptotic proteins such as Bax/Bak and Bcl-2/xL in caspase-dependent and caspase-independent apoptosis pathways. Mitochondrial dysfunction is mediated in two ways. The first is by increased calcium in mitochondria derived from endoplasmic reticulum (ER); this calcium increase is regulated by Bcl-2 and Bax through the ER-mitochondria connection and the unfolded protein response in the ER. The second is by the lysosomal enzyme cathepsin, which activates Bid through lysosome-mitochondria cross-signaling. The genomic responses in intracellular organelles after DNA damage are controlled and amplified in the cross-signaling via mitochondria; such signals induce apoptosis, autophagy, and other cell death pathways. This review discusses the recent advancements in understanding the molecular mechanism of mitochondria-mediated cell death.

Inhibition of neutrophil apoptosis by TLR agonists in whole blood: involvement of the phosphoinositide 3-kinase/Akt and NF-kappaB signaling pathways, leading to increased levels of Mcl-1, A1, and phosphorylated Bad

Using flow cytometry, we investigated the effect of TLR agonists on human polymorphonuclear neutrophil (PMN) apoptosis in whole blood. LPS (TLR4), peptidoglycan (TLR2), R-848 (TLR7/8), and CpG-DNA (TLR9) were equally effective at delaying spontaneous apoptosis of PMN, while PamCSK4 (TLR1/2), macrophage-activating lipopeptide-2 (TLR2/6), flagellin (TLR5), and loxoribine (TLR7) were less effective or inactive. TLR agonists found to delay apoptosis also extended the functional life span of PMN. Analysis of signaling pathways revealed that the antiapoptotic effect of TLR agonists required NF-kappaB and PI3K activation. Furthermore, analysis of intact cells by flow cytometry showed that TLR agonists delaying PMN apoptosis increased phosphorylation of Akt, a major target of PI3K. This effect was associated with a PI3K-dependent increase in heat shock protein 27 phosphorylation, which has been reported to play a key role in PMN survival. Finally, the TLR-induced delay in PMN apoptosis was associated with increased levels of Mcl-1 and A1, which are antiapoptotic members of the Bcl-2 family. These effects were reversed by PI3K and NF-kappaB inhibitors, respectively. TLR activation also led to PI3K-dependent phosphorylation of the proapoptotic protein Bad. Taken together, our results strongly suggest a role of NF-kappaB and PI3K in TLR-induced PMN survival, leading to modulation of Bcl-2 family molecules.

Leukocyte apoptosis and its significance in sepsis and shock

Sepsis and multiple organ failure continue to be significant problems among trauma, burn, and the critically ill patient population. Thus, a number of laboratories have focused on understanding the role of altered apoptotic cell death in contributing to immune and organ dysfunction seen in sepsis and shock. Immune cells that undergo altered apoptotic changes include neutrophils, macrophages, dendritic cells, as well as various lymphocyte populations. Evidence of epithelial as well as endothelial cell apoptotic changes has also been reported. Although mediators such as steroids, tumor necrosis factor, nitric oxide, C5a, and Fas ligand (FasL) appear to contribute to the apoptotic changes, their effects are tissue- and cell population-selective. As inhibiting Fas-FasL signaling (e.g., gene deficiency, Fas fusion protein, or Fas short interfering RNA administration), caspase inhibition (caspase mimetic peptides), and/or the overexpression of downstream antiapoptotic molecules (e.g., Bcl-2, Akt) improve survival of septic mice, it not only demonstrates the pathological significance of this process but points to novel targets for the treatment of sepsis.

High expression of Bcl-xL in delayed apoptosis of canine neutrophils induced by lipopolysaccharide

The expression of Bcl-2 family members, Bcl-xL, Bcl-2, Mcl-1 and Bax was investigated in delayed apoptosis of canine neutrophils induced by lipopolysaccharide (LPS). Apoptotic cell rates in neutrophils stimulated by LPS (100 ng/ml) were measured at 24 h incubation by TUNEL assay. The incidence of apoptotic neutrophils stimulated by LPS at 24 h incubation was 17.0+/-2% and that in non-stimulated neutrophils was 29.9+/-3%. By real-time quantitative PCR analysis, it was indicated that Bcl-xL and Bax levels in canine neutrophils were significantly affected by LPS stimulation. The levels of Bcl-xL, Bcl-2, Mcl-1 and Bax transcripts at 9 h incubation in neutrophils stimulated by LPS (100 ng/ml) were increased by about 80.4-, 1.9-, 1.4- and 5.3-folds, in comparison to those in non-stimulated neutrophils, respectively. These results indicated that Bcl-xL was proved have an important role in the inhibition of canine neutrophil apoptosis by LPS.

Heterogeneous expression pattern of pro- and anti-apoptotic factors in myeloid progenitor cells of patients with severe congenital neutropenia treated with granulocyte colony-stimulating factor

Apoptosis is accelerated in the myeloid progenitor cells of patients with severe congenital neutropenia (CN). Granulocyte colony-stimulating factor (G-CSF) increases neutrophil numbers in most CN patients. The effect of G-CSF on apoptosis in CN was analysed by apoptosis rate and expression of anti- and pro-apoptotic factors. G-CSF-treated patients showed higher apoptosis frequency, lower expression of bcl-2 and bcl-xL, but higher expression of bfl-1/A1 and mcl-1. Caspase 9 was highly expressed in patients and controls after G-CSF administration. Thus, G-CSF acts on apoptosis regulation, but additional mechanisms leading to the increase of neutrophil numbers must be assumed.

Molecular cloning of canine Mcl-1 gene and its expression in tumor cell lines

The canine Mcl-1 gene was cloned and sequenced. Canine Mcl-1 clone was 2694 base pairs in length and encoded 350 amino acids. The predicted amino acid sequence was 87.7%, 77.1% and 75.7% homologous to predicted human, mouse and rat Mcl-1, respectively. RT-PCR analysis revealed that canine Mcl-1 mRNA was expressed in PBMCs (peripheral blood mononuclear cells), bone marrow cells, MDCK (Madin-Darby canine kidney) and GL-1 (canine B cell leukemia) whereas undetectable in CL-1 (canine T cell lymphoma) cell line.

Up-regulation of Bfl-1/A1 via NF-κB activation in cisplatin-resistant human bladder cancer cell line

The potent anti-cancer agent cis-diamminedichloroplatinum (II) (cisplatin) is currently used for treating bladder cancer. However, clinical use of this drug for long periods is often limited because of the appearance of cisplatin-resistant bladder tumor cells. We employed the method of a differential display reverse transcriptase polymerase chain reaction to identify the differentially expressed genes in the parental human bladder cancer cell line, T24 and three cisplatin-resistant cell lines. We report here that cisplatin-resistant cell lines overexpress Bcl-2 family protein Bcl-2-related gene expressed in fetal liver (Bfl-1)/A1 as compared with their parental cell. Cisplatin and gamma-irradiation induced expression of Bfl-1/A1 in T24R2 cells but not in T24 cells. Among Bcl-2 family members, Bfl-1/A1 showed the most significant alteration of the expression level in resistant cells. The nuclear translocation of nuclear factor-kappaB (NF-kappaB) by cisplatin and gamma-irradiation selectively occurred in T24R2 cells. Mitochondrial depolarization and cell death by cisplatin were also prevented in T24R2 cells. Moreover, Bfl-1/A1 inhibited cisplatin- and TNF-alpha-induced apoptosis in BOSC23 cells. Our findings suggest that the induction of Bfl-1/A1 by NF-kappaB may be important in controlling resistance to cisplatin responses in bladder tumor cells.

Cytoprotective response of A1, a Bcl-2 homologue expressed in mature human neutrophils and promyelocytic HL-60 cells, to oxidant stress-induced cell death

The ability to generate reactive oxidative intermediates is one of the quintessential properties of mature human neutrophils. Endogenously generated oxidants have been shown to be an important mechanism underlying neutrophil cell death. In acute lung inflammation, newly recruited neutrophils further encounter external oxidants, including reactive oxygen and nitrogen intermediates. In our present study, we showed that A1, a constitutive and inducible Bcl-2 homologue expressed in mature circulating human neutrophils, might confer the protection from hydrogen peroxide (H(2)O(2))- and peroxynitrite (ONOO)-induced cell death. Utilizing the myeloid precursor cell line, HL-60, we further examined the hypothesis that A1 was capable of conferring cytoprotective activity against these oxidative stresses. Whereas the control-transfected HL-60 cells expressed small amounts of A1 and were sensitive to the biologically relevant, cell death-inducing oxidants, H(2)O(2) and ONOO, the stable transfectants that overexpressed A1 were significantly more tolerant. Furthermore, there was a correlation between the level of A1 expression and the antiapoptotic activity. Thus, our results suggest a cytoprotective role of A1 in mature human neutrophils under oxidant stresses in host defense and inflammation.

Transmigration across a lung epithelial monolayer delays apoptosis of polymorphonuclear leukocytes

BACKGROUND

Suppression of polymorphonuclear leukocyte (PMNL) apoptosis may cause or exaggerate acute lung injury that is associated with the acute respiratory distress syndrome. We hypothesized that transepithelial migration would modulate PMNL apoptosis.

METHOD

PMNLs that were freshly purified from normal volunteers were allowed to migrate across transwell membranes alone or coated with monolayers of human lung epithelial cells in response to chemoattractants (interleukin-8, formyl-methionylleucylphenylalanine and leukotriene B(4)). We assessed for migration efficiency, apoptosis, and functional activity of the PMNLs. Changes in the expression of genes modulating PMNL apoptosis were examined with messenger RNA and protein analyses.

RESULTS

Transepithelial migration caused a significant decrease in the percentage of apoptotic PMNLs (interleukin-8; from 31% to 16% at 8 hours; P<.01). This apoptotic delay was sustained to at least 20 hours that was associated with prolongation of PMNL functional activity and independent of chemoattractant-type. Gene and protein expression levels of the antiapoptotic proteins Mcl-1 and 14-3-3 zeta were either augmented or preserved by interleukin-8 treatment alone and after transepithelial migration.

CONCLUSION

Our data reveal, for the first time, the important role of transepithelial migration in the modulation of PMNL apoptosis and may provide insights into possible novel targets for the regulation of PMNL apoptosis during lung inflammation and injury.

Control of apoptosis in the immune system: Bcl-2, BH3-only proteins and more

Apoptotic cell death plays a critical role in the development and functioning of the immune system. During differentiation, apoptosis weeds out lymphocytes lacking useful antigen receptors and those expressing dangerous ones. Lymphocyte death is also involved in limiting the magnitude and duration of immune responses to infection. In this review, we describe the role of the Bcl-2 protein family, and to a lesser extent that of death receptors (members of the tumor necrosis factor receptor family with a death domain), in the control of lymphoid and myeloid cell survival. We also consider the pathogenic consequences of failure of apoptosis in the immune system.

Neutrophil apoptosis pathways and their modifications in inflammation

Neutrophils are constantly produced in large numbers in the bone marrow, and the same numbers of cells need to die within a defined time period in order to keep cellular homeostasis under physiologic conditions. Changing the rate of apoptosis rapidly changes cell numbers in such systems. For instance, in many bacterial and autoimmune inflammatory diseases, delayed apoptosis is one important mechanism for neutrophil accumulation. Excessive production of granulocyte/macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF), two important neutrophil survival factors, is often observed in such inflammatory responses. Cytokine withdrawal, as it occurs in the resolution phase of inflammation, leads to the induction of apoptosis. Moreover, neutrophil apoptosis can be accelerated both in the presence and in the absence of survival factors by activation of distinct members of the tumor necrosis factor/nerve growth factor receptor family. This review focuses on recently published work regarding signaling pathways that regulate neutrophil apoptosis.

Expression of Bcl-2 on leukocytes in prostatic fluid from patients with acute and chronic prostatitis

In our continuing investigation to clarify the significance of leukocytosis and its prolongation in prostatic fluid (PF) from prostatitis patients, we investigated whether expression of the antiapoptotic gene Bcl-2 on leukocytes in prostatic fluid has any relation with prolonged leukocytosis in prostatitis. The subjects were eight patients with acute bacterial prostatitis (ABP) and eight with nonbacterial prostatitis (NBP) with a history of more than 2 years. Twelve micrograms of protein obtained from leukocytes in PF were subjected to Western blot analysis. Bcl-2 was expressed in seven of eight (87.5%) and six of eight (75.0%) patients with NBP and ABP, respectively. Quantitative density analysis of the Bcl-2 band did not show any statistically significant differences between patients with NBP and those with ABP. These results suggest that the expression of antiapoptotic Bcl-2 on leukocytes in PF is not a cause of leukocyte longevity in long-term prostatitis.

Modulation of constitutive and delayed apoptosis by brefeldin A in human neutrophils

Neutrophil apoptosis is a constitutive process that can be enhanced or delayed by various stimuli. In this study, the effect of brefeldin A (BFA), which affects the biological process of secretion, on constitutive and delayed apoptosis of neutrophils was investigated. Neutrophil apoptosis was determined after culturing for 20 h in vitro by morphological changes, annexin V staining, and DNA electrophoresis. BFA dose-dependently increased the constitutive apoptotic rate of neutrophils. The delay of apoptosis induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) and lipopolysaccharide (LPS) was also blocked by BFA. However, this effect of BFA was less marked when neutrophils were treated with dexamethasone, interleukin-8 (IL-8), or dibutyryl cAMP (dbcAMP). Moreover, the delay of neutrophil apoptosis induced by rottlerin, a specific inhibitor of protein kinase C (PKC)-delta, was significantly abrogated by BFA. Although BFA-induced apoptosis was not blocked by the caspase-3 inhibitor, zDEVD-fmk, myeloid cell leukemia-1 (Mcl-1) expression levels were downregulated by BFA. These results suggest that derangement of vesicular protein transport may be involved in the apoptosis of neutrophils, and that the action of BFA on apoptosis is dependent on changes in the expression of Mcl-1.

Apoptosis: programmed cell death at a molecular level

OBJECTIVES

To characterize cell surface receptors, their ligands, and their proteins in the 2 major pathways of apoptosis; the components that promote/suppress these interactions; the noninflammatory removal of apoptotic bodies by dendritic cells; and methods of assay in studies of cell death. To describe: how deregulation of apoptosis may contribute to autoimmunity, cancer, and neurodegenerative disorders and strategies some viruses have evolved that interfere with the host's apoptotic pathways.

METHODS

The authors reviewed and compiled literature on the extrinsic (tumor necrosis factor [TNF] receptor superfamily and ligands) and intrinsic (mitochondria-associated) apoptotic pathways, the pro- and antiapoptotic proteins of the B-cell follicular lymphoma (Bcl)-2 family, the nuclear factor (NF)-kappaB family of proteins, commonly used laboratory methods to distinguish apoptosis from necrosis, the recognition and removal by phagocytosis of apoptotic cells by dendritic cells, and viral strategies to avoid a host's apoptotic response.

RESULTS

The 2 major pathways of apoptosis are (1). FasL and other TNF superfamily ligands induce trimerization of cell-surface death receptors and (2). perturbated mitochondria release cytochrome c, the flavoprotein apoptosis-inducing factor, and second mitochondria-derived activator of caspases/DIABLO (a protein that directly neutralizes inhibitors of apoptotic proteins and activates proteases). Catalytically inactive cysteine proteases, called caspases, and other proteases are activated, ultimately leading to cell death with characteristic cellular chromatin condensation and DNA cleavage to fragments of approximately 180 bp. The inhibitory/promoting action of Bcl-2 family members is involved in the release of cytochrome c, an essential factor for the mitochondrial-associated pathway. A balance between inhibition/promotion determines a cell's fate. The NF-kappaB family in the cytoplasm of cells activates various genes carrying the NF-kappaB response element, such as members of the inhibitor of apoptotic proteins family. A few of the more common methods to detect apoptotic cell death are described, which use immunochemical, morphologic and flow cytometric methods, and genetic markers. Exposed phosphatidylserine at the outer leaflet of the plasma membrane of the apoptotic cell serves as a possible receptor for phagocytosis by immature dendritic cells. These cells phagocytize both apoptotic and necrotic cells, but only the latter induce maturation to become fully functional antigen-presenting cells. Viral inhibitors of apoptosis allow increased virus replication in cells, possibly resulting in their oncogenicity.

CONCLUSIONS

Balanced apoptosis is crucial in development and homeostasis, and all multicellular organisms have a physiologically programmed continuum of pathways to apoptotic cell death. Further studies of the control at the molecular level of key components and promoters/suppressors of apoptosis may provide better approaches to treatment of autoimmune diseases, malignancies, and neurodegenerative disorders. Many important questions remain regarding the advantages of modifying apoptotic programs in clinical situations.

Microarray analysis of lipopolysaccharide-treated human neutrophils

Neutrophils respond to infection by degranulation, release of reactive oxygen intermediates, and secretion of chemokines and cytokines; however, activation of neutrophil transcriptional machinery has been little appreciated. Recent findings suggest that gene expression may represent an additional neutrophil function after exposure to lipopolysaccharide (LPS). We performed microarray gene expression analysis of 4,608 mostly nonredundant genes on LPS-stimulated human neutrophils. Analysis of three donors indicated some variability but also a high degree of reproducibility in gene expression. Twenty-eight verifiable, distinct genes were induced by 4 h of LPS treatment, and 13 genes were repressed. Genes other than cytokines and chemokines are regulated; interestingly, genes involved in cell growth regulation and survival, transcriptional regulation, and interferon response are among those induced, whereas genes involved in cytoskeletal regulation are predominantly repressed. In addition, we identified monocyte chemoattractant protein-1 as a novel LPS-regulated chemokine in neutrophils. Included in these lists are five clones with no defined function. These data suggest molecular mechanisms by which neutrophils respond to infection and indicate that the transcriptional potential of neutrophils is greater than previously thought.

Essential role for the BH3-only protein Bim but redundant roles for Bax, Bcl-2, and Bcl-w in the control of granulocyte survival

Programmed cell death of granulocytes is one of the mechanisms that limit inflammatory responses. Members of the Bcl-2 protein family are essential regulators of apoptosis induced by growth factor withdrawal or cytotoxic stress. We have used gene-targeted and transgenic mice to investigate the roles of the prosurvival molecules Bcl-2 and Bcl-w and their proapoptotic relatives Bax and Bim in spontaneous and stress-induced apoptosis of granulocytes from bone marrow or the peritoneum. Bim deficiency, like Bcl-2 overexpression, rendered granulocytes resistant to cytokine withdrawal and cytotoxic drugs, but absence of Bax alone had no protective effect. Loss of Bcl-2 or Bcl-w did not increase the sensitivity of granulocytes to any of these apoptotic stimuli, but Bcl-2 was essential for the in vitro survival of myeloid progenitors under conditions of cytokine withdrawal where cell death was mediated, in part, by Bim. Granulocyte colony-stimulating factor (G-CSF), a key survival factor for granulocytes, enhanced viability of cells lacking bcl-2, bcl-w, bax, or bim, indicating that none of these genes alone is the essential target of this cytokine's prosurvival function. Expression analysis of proapoptotic Bcl-2 family members in granulocytes revealed that the BH3-only protein Bmf is induced upon cytokine withdrawal. These results indicate that the BH3-only protein Bim and possibly also Bmf are critical initiators of spontaneous and drug-induced apoptosis of granulocytes, whereas Bcl-2, Bcl-w, and Bax act in a redundant manner in regulating granulocyte survival and death, respectively.

Colony-stimulating factors for the management of neutropenia in cancer patients

Neutropenia and its subsequent infectious complications represent the most common dose-limiting toxicity of cancer chemotherapy. Febrile neutropenia (FN) occurs with common chemotherapy regimens in 25 to 40% of treatment-naive patients, and its severity depends on the dose intensity of the chemotherapy regimen, the patient's prior history of either radiation therapy or use of cytotoxic treatment, and comorbidities. The occurrence of FN often causes subsequent chemotherapy delays or dose reductions. It may also lengthen hospital stay, increase monitoring, diagnostic and treatment costs, and reduce patient quality of life. A decade after their introduction, colony-stimulating factors (CSFs) such as granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are now an integral part of the prevention of potentially life-threatening FN; however, only G-CSF has US Food and Drug Administration approval for use in chemotherapy-induced neutropenia. These adjunctive agents accelerate formation of neutrophils from committed progenitors, thereby reducing the duration and severity of neutropenia. Important uses of CSFs in oncology are prevention of FN after chemotherapy, treatment of febrile neutropenic episodes and support following bone marrow transplantation, and collection of CSF-mobilised peripheral blood progenitor cells. G-CSF is used more frequently than GM-CSF for all of these indications because of fewer associated adverse effects. Clinical trials to date have not demonstrated a significant effect on overall survival or disease-free survival, which is most likely to be due to small sample size and lack of power to prove effect. However, they have demonstrated clinical utility in allowing the delivery of planned chemotherapy dose on schedule, an important clinical goal especially in curative tumour settings. The high cost of these agents limits their widespread use. Current American Society of Clinical Oncology guidelines recommend primary prophylaxis, or first cycle use, with CSFs being confined to patients with > or = 40% risk of FN, which may include elderly patients and other high-risk patients. In addition to the risk of FN, primary prophylaxis should also be considered if the patient has risk factors that place them in the Special Circumstances category. These risk factors may include decreased immune function in patients who are already at an increased risk of infection and pre-existing neutropenia due to disease, extensive prior chemotherapy, or previous irradiation to the pelvis or other areas containing large amounts of bone marrow. Future studies are needed to better define the patients most likely to benefit from CSF therapy, both for prophylaxis and as an adjunct to antibiotics for treatment of FN. Other potential uses include combination therapy with stem cell factors and other cytokines to boost progenitor cell development, maintaining dose intensity of salvage therapy in metastatic cancer patients, and application in patients with pneumonia, Crohn's fistulas, diabetic foot infections and a variety of other infectious conditions.

Expression of the inhibitor of apoptosis (IAP) family members in human neutrophils: up-regulation of cIAP2 by granulocyte colony-stimulating factor and overexpression of cIAP2 in chronic neutrophilic leukemia

Human neutrophils were found to express members of the inhibitor of apoptosis (IAP) family, namely cellular IAP1 (cIAP1), cIAP2, and X-linked IAP. Among these members, cIAP2 expression was selectively up-regulated by stimulation with granulocyte colony-stimulating factor (G-CSF), but not with granulocyte-macrophage CSF. The increased expression of cIAP2 mRNA was detected as early as 30 minutes after in vitro stimulation with G-CSF, and the elevated level of cIAP2 protein was detected at 1 hour. The elevated level of cIAP2 protein was also detected in peripheral blood neutrophils obtained from healthy donors receiving G-CSF administration. G-CSF-induced up-regulation of cIAP2 mRNA and protein, phosphorylation of signal transducer and activator of transcription 3 (STAT3), and the antiapoptotic effects were inhibited by pretreatment of cells with AG490, a specific inhibitor of Janus kinase 2 (JAK2). Mature neutrophils from a patient with chronic neutrophilic leukemia exhibited remarkable overexpression of cIAP2 mRNA and prolongation of survival, whereas cIAP2 mRNA expression and survival in mature neutrophils from patients with chronic myelogenous leukemia were essentially similar to those in normal neutrophils. These findings suggest that cIAP2 expression is up-regulated by G-CSF through activation of the JAK2-STAT3 pathway, and increased expression of cIAP2 protein may contribute to G-CSF-mediated antiapoptosis. In addition, overexpression of cIAP2 may be partly responsible for sustained neutrophilia at least in some cases of chronic neutrophilic leukemia.

Antiapoptotic effect of granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, and cyclic AMP on human neutrophils: protein synthesis-dependent and protein synthesis-independent mechanisms and the role of the Janus kinase-STAT pathway

Spontaneous neutrophil apoptosis during culture was delayed by granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), or dibutyryl-cyclic adenosine monophosphate (cAMP), whereas apoptosis was accelerated by cycloheximide or actinomycin D. G-CSF-mediated antiapoptosis was completely abolished by cycloheximide or actinomycin D, whereas GM-CSF-mediated antiapoptosis was not completely abolished by these inhibitors. Antiapoptosis induced by dibutyryl-cAMP was highly resistant to cycloheximide, and that induced by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone was unaffected by cycloheximide. G-CSF- and GM-CSF-mediated antiapoptosis and phosphorylation of signal transducer and activator of transcription 3 (STAT3) and STAT5 were inhibited by AG490, an inhibitor of Janus kinase. The level of Mcl-1 protein was not associated with neutrophil apoptosis. The results suggest that (a) neutrophil survival in the resting state is primarily regulated by the constitutive synthesis of antiapoptotic proteins; (b) the prevention of spontaneous apoptosis is mediated through the protein synthesis-dependent and/or protein synthesis-independent mechanisms according to the stimuli used; and (c) the Janus kinase-STAT pathway is involved in G-CSF- and GM-CSF-mediated antiapoptosis.