Granulocyte-macrophage colony-stimulating factor stimulates JAK2 signaling pathway and rapidly activates p93fes, STAT1 p91, and STAT3 p92 in polymorphonuclear leukocytes

Application of JAK inhibitors in paradoxical reaction through immune-related dermatoses

Biologics play a positive and effective role in the treatment of immune-related dermatoses. However, many other immune-related diseases have also manifested along with biologics treatment. Paradoxical reaction through immune-related dermatoses refer to the new onset or exacerbation of other immune-mediated dermatoses (mainly psoriasis and atopic dermatitis) after biologics treatment of inflammatory dermatoses (mainly psoriasis and atopic dermatitis), such as new atopic dermatitis (AD) in psoriasis (PsO) treatment and new PsO in AD treatment. A common genetic background and Inflammatory pathway are possible pathogenesis. Faced with paradoxical reactions, the choice of therapy needs to be directed toward therapies effective for both diseases, such as Janus kinase (JAK) inhibitors. The Janus kinase and signal transducer and activator of transcription (JAK-STAT) pathway plays an important role in the inflammatory pathway, and has been widely used in the treatment of AD and PsO in recent years. This article focuses on JAK inhibitors such as tofacitinib, baricitinib, ruxolitinib, Abrocitinib, upadacitinib, and deucravacitinib, to explore the possible application in treatment of paradoxical reactions. Common side effects, baseline risk factors and safety use of JAK inhibitors were discussed.

Messing with βc: A unique receptor with many goals

Our understanding of the biological role of the βc family of cytokines has evolved enormously since their initial identification as bone marrow colony stimulating factors in the 1960's. It has become abundantly clear over the intervening decades that this family of cytokines has truly astonishing pleiotropic capacity, capable of regulating not only hematopoiesis but also many other normal and pathological processes such as development, inflammation, allergy and cancer. As noted in the current pandemic, βc cytokines contribute to the cytokine storm seen in acutely ill COVID-19 patients. Ongoing studies to discover how these cytokines activate their receptor are revealing insights into the fundamental mechanisms that give rise to cytokine pleiotropy and are providing tantalizing glimpses of how discrete signaling pathways may be dissected for activation with novel ligands for therapeutic benefit.

Breast cancer-derived GM-CSF regulates arginase 1 in myeloid cells to promote an immunosuppressive microenvironment

Tumor-infiltrating myeloid cells contribute to the development of the immunosuppressive tumor microenvironment. Myeloid cell expression of arginase 1 (ARG1) promotes a protumor phenotype by inhibiting T cell function and depleting extracellular l-arginine, but the mechanism underlying this expression, especially in breast cancer, is poorly understood. In breast cancer clinical samples and in our mouse models, we identified tumor-derived GM-CSF as the primary regulator of myeloid cell ARG1 expression and local immune suppression through a gene-KO screen of breast tumor cell-produced factors. The induction of myeloid cell ARG1 required GM-CSF and a low pH environment. GM-CSF signaling through STAT3 and p38 MAPK and acid signaling through cAMP were required to activate myeloid cell ARG1 expression in a STAT6-independent manner. Importantly, breast tumor cell-derived GM-CSF promoted tumor progression by inhibiting host antitumor immunity, driving a significant accumulation of ARG1-expressing myeloid cells compared with lung and melanoma tumors with minimal GM-CSF expression. Blockade of tumoral GM-CSF enhanced the efficacy of tumor-specific adoptive T cell therapy and immune checkpoint blockade. Taken together, we show that breast tumor cell-derived GM-CSF contributes to the development of the immunosuppressive breast cancer microenvironment by regulating myeloid cell ARG1 expression and can be targeted to enhance breast cancer immunotherapy.

Phytochemicals Targeting JAK-STAT Pathways in Inflammatory Bowel Disease: Insights from Animal Models

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract that consists of Crohn’s disease (CD) and ulcerative colitis (UC). Cytokines are thought to be key mediators of inflammation-mediated pathological processes of IBD. These cytokines play a crucial role through the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) signaling pathways. Several small molecules inhibiting JAK have been used in clinical trials, and one of them has been approved for IBD treatment. Many anti-inflammatory phytochemicals have been shown to have potential as new drugs for IBD treatment. This review describes the significance of the JAK–STAT pathway as a current therapeutic target for IBD and discusses the recent findings that phytochemicals can ameliorate disease symptoms by affecting the JAK–STAT pathway in vivo in IBD disease models. Thus, we suggest that phytochemicals modulating JAK–STAT pathways are potential candidates for developing new therapeutic drugs, alternative medicines, and nutraceutical agents for the treatment of IBD.

The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects

The growth hormone receptor (GHR), although most well known for regulating growth, has many other important biological functions including regulating metabolism and controlling physiological processes related to the hepatobiliary, cardiovascular, renal, gastrointestinal, and reproductive systems. In addition, growth hormone signaling is an important regulator of aging and plays a significant role in cancer development. Growth hormone activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway, and recent studies have provided a new understanding of the mechanism of JAK2 activation by growth hormone binding to its receptor. JAK2 activation is required for growth hormone-mediated activation of STAT1, STAT3, and STAT5, and the negative regulation of JAK-STAT signaling comprises an important step in the control of this signaling pathway. The GHR also activates the Src family kinase signaling pathway independent of JAK2. This review covers the molecular mechanisms of GHR activation and signal transduction as well as the physiological consequences of growth hormone signaling.

The anti-apoptotic Bcl-2 family protein A1/Bfl-1 regulates neutrophil survival and homeostasis and is controlled via PI3K and JAK/STAT signaling

Neutrophil granulocytes are innate effector cells of the first line of defense against pyogenic bacteria. Neutrophil lifespan is short, is prolonged by pro-inflammatory stimuli, controls functionality of the cells and can determine tissue damage. Experimental analysis of primary neutrophils is difficult because of their short lifespan and lack of possibilities of genetic manipulation. The Hoxb8 system of neutrophil differentiation from immortalized progenitor cells offers the advantage of unlimited production of neutrophils in vitro as well as easy genetic modification. We here use this system to analyze the role of the poorly characterized anti-apoptotic B-cell lymphoma protein 2 (Bcl-2) family member A1/Bfl-1 (Bcl-2-related protein A1) for survival and homeostasis of neutrophils and of neutrophil progenitors. Low constitutive mRNA and protein expression of A1 was detected, while A1 was transiently upregulated early during differentiation. Pro-inflammatory stimuli caused strong, mainly transcriptional, A1 upregulation, in contrast to posttranscriptional regulation of Mcl-1 (induced myeloid leukemia cell differentiation protein). Inhibitor studies showed that phosphoinositide-3 kinase (PI3K)/Akt and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) is required for A1 expression and survival of progenitors and mature neutrophils. ShRNA-mediated constitutive A1 knockdown (KD) impaired maintenance of progenitors. ShRNA experiments further showed that A1 was required early during neutrophil differentiation as well as in mature neutrophils upon pro-inflammatory stimulation. Our data further indicate differential regulation of the two anti-apoptotic proteins A1 and Mcl-1. Relevant findings were confirmed in primary human neutrophils. Our data indicate that A1, in addition to the well-established Mcl-1, substantially contributes to neutrophil survival and homeostasis. A1 may thus be a promising target for anti-inflammatory therapy.

Autophagy promotes radiation-induced senescence but inhibits bystander effects in human breast cancer cells

Ionizing radiation induces cellular senescence to suppress cancer cell proliferation. However, it also induces deleterious bystander effects in the unirradiated neighboring cells through the release of senescence-associated secretory phenotypes (SASPs) that promote tumor progression. Although autophagy has been reported to promote senescence, its role is still unclear. We previously showed that radiation induces senescence in PTTG1-depleted cancer cells. In this study, we found that autophagy was required for the radiation-induced senescence in PTTG1-depleted breast cancer cells. Inhibition of autophagy caused the cells to switch from radiation-induced senescence to apoptosis. Senescent cancer cells exerted bystander effects by promoting the invasion and migration of unirradiated cells through the release of CSF2 and the subsequently activation of the JAK2-STAT3 and AKT pathways. However, the radiation-induced bystander effects were correlated with the inhibition of endogenous autophagy in bystander cells, which also resulted from the activation of the CSF2-JAK2 pathway. The induction of autophagy by rapamycin reduced the radiation-induced bystander effects. This study reveals, for the first time, the dual role of autophagy in radiation-induced senescence and bystander effects.

Increased reactive oxygen species production and p47phox phosphorylation in neutrophils from myeloproliferative disorders patients with JAK2 (V617F) mutation

Myeloproliferative disorders are associated with increased risk of thrombosis and vascular complications. The pathogenesis of these complications is not completely known. Reactive oxygen species produced by the neutrophil NADPH oxidase could have a role in this process. The aim of this study was to evaluate reactive oxygen species production by neutrophils of myeloproliferative disorder patients. Patients with or without the JAK2 V617F mutation were characterized. Reactive oxygen species production was assessed by chemiluminescence, and phosphorylation of the NADPH oxidase subunit p47phox was analyzed by Western blots. In a comparison of controls and myeloproliferative disorder patients without the JAK2 V617F mutation, reactive oxygen species production by neutrophils from patients with the JAK2 V617F mutation was dramatically increased in non-stimulated and in stimulated conditions. This increase was associated with increased phosphorylation of the p47phox on Ser345 and of the uspstream kinase ERK1/2. In neutrophils from healthy donors, JAK2 can be activated by GM-CSF. GM-CSF-induced p47phox phosphorylation and priming of reactive oxygen species production are inhibited by the selective JAK2 inhibitors AG490 and lestaurtinib (CEP-701), supporting a role for JAK2 in the upregulation of NADPH oxidase activation. These findings show an increase in reactive oxygen species production and p47phox phosphorylation in neutrophils from myeloproliferative disorder patients with the JAK2 V617F mutation, and demonstrate that JAK2 is involved in GM-CSF-induced NADPH oxidase hyperactivation. As neutrophil hyperactivation could be implicated in the thrombophilic status of patients with myeloproliferative disorders, aberrant activation of JAK2 V617F, leading to excessive neutrophil reactive oxygen species production might play a role in this setting.

The role of JAK-STAT signaling in adipose tissue function

Adipocytes play important roles in lipid storage, energy homeostasis and whole body insulin sensitivity. The JAK-STAT (Janus Kinase-Signal Transducer and Activator of Transcription) pathway mediates a variety of physiological processes including development, hematopoiesis, and inflammation. Although the JAK-STAT signaling pathway occurs in all cells, this pathway can mediate cell specific responses. Studies in the last two decades have identified hormones and cytokines that activate the JAK-STAT signaling pathway. These cytokines and hormones have profound effects on adipocytes. The content of this review will introduce the types of adipocytes and immune cells that make up adipose tissue, the impact of obesity on adipose cellular composition and function, and the general constituents of the JAK-STAT pathway and how its activators regulate adipose tissue development and physiology. A summary of the identification of STAT target genes in adipocytes reveals how these transcription factors impact various areas of adipocyte metabolism including insulin action, modulation of lipid stores, and glucose homeostasis. Lastly, we will evaluate exciting new data linking the JAK-STAT pathway and brown adipose tissue and consider the future outlook in this area of investigation. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Constitutive MHC class I molecules negatively regulate TLR-triggered inflammatory responses via the Fps-SHP-2 pathway

The molecular mechanisms that fine-tune Toll-like receptor (TLR)-triggered innate inflammatory responses remain to be fully elucidated. Major histocompatibility complex (MHC) molecules can mediate reverse signaling and have nonclassical functions. Here we found that constitutively expressed membrane MHC class I molecules attenuated TLR-triggered innate inflammatory responses via reverse signaling, which protected mice from sepsis. The intracellular domain of MHC class I molecules was phosphorylated by the kinase Src after TLR activation, then the tyrosine kinase Fps was recruited via its Src homology 2 domain to phosphorylated MHC class I molecules. This led to enhanced Fps activity and recruitment of the phosphatase SHP-2, which interfered with TLR signaling mediated by the signaling molecule TRAF6. Thus, constitutive MHC class I molecules engage in crosstalk with TLR signaling via the Fps-SHP-2 pathway and control TLR-triggered innate inflammatory responses.

The NADPH oxidase cytosolic component p67phox is constitutively phosphorylated in human neutrophils: Regulation by a protein tyrosine kinase, MEK1/2 and phosphatases 1/2A

Neutrophils play a key role in host defense and inflammation through the production of superoxide anion and other reactive oxygen species (ROS) by the enzyme complex NADPH oxidase. The cytosolic NADPH oxidase component, p67phox, has been shown to be phosphorylated in human neutrophils but the pathways involved in this process are largely unknown. In this study, we show that p67phox is constitutively phosphorylated in resting human neutrophils and that neutrophil stimulation with PMA further enhanced this phosphorylation. Inhibition of the constitutively active serine/threonine phosphatases type 1 and type 2A (PP1/2A) by calyculin A resulted in the enhancement of p67phox phosphorylation. Constitutive and calyculin A-induced phosphorylation of p67phox was completely inhibited by the protein tyrosine kinase inhibitor genistein and partially inhibited by the MEK1/2 inhibitor PD98059, but was unaffected by GF109203X, wortmannin and SB203580, inhibitors of PKC, PI3K and p38MAP kinase, respectively. Two-dimensional phosphopeptide mapping revealed that constitutive and calyculin A-induced p67phox phosphorylation occurred on the same major sites. Interestingly, calyculin A enhanced formyl-Met-Leu-Phe (fMLP)-induced superoxide production, while genistein inhibited this process. Taken together, these results suggest that (i) p67phox undergoes a continual cycle of phosphorylation/dephosphorylation in resting cells; (ii) p67phox phosphorylation is controlled by MEK1/2 and an upstream tyrosine kinase; (iii) PP1/2A directly or indirectly antagonize this process. Thus, these pathways could play a role in regulating ROS production by human neutrophils at inflammatory sites.

Secretion of MIP-1β and MIP-1α by CD8(+) T-lymphocytes correlates with HIV-1 inhibition independent of coreceptor usage

CD8(+) T-lymphocytes can utilize noncytolytic mechanisms to suppress HIV-1 replication through the secretion of soluble factors. The secretion of MIP-1β, MIP-1α, IP-10, MIG, IL-1α, and interferon gamma correlated most strongly with soluble noncytolytic suppression (p<0.0001). Since the noncytolytic response is impaired by histone hyperacetylation, we examined the ability of histone hyperacetylation to alter the expression of immune-related genes. MIP-1α and IP-10 were also among the genes that were down-regulated by histone hyperacetylation. We define a multifactorial cytokine profile of CD8(+) T-lymphocytes capable of mediating noncytolytic suppression of CXCR4-tropic HIV-1 replication.

Anti-inflammatory activity and neutrophil reductions mediated by the JAK1/JAK3 inhibitor, CP-690,550, in rat adjuvant-induced arthritis

Background

The Janus kinase (JAK) family of tyrosine kinases includes JAK1, JAK2, JAK3 and TYK2, and is required for signaling through Type I and Type II cytokine receptors. CP-690,550 is a potent and selective JAK inhibitor currently in clinical trials for rheumatoid arthritis (RA) and other autoimmune disease indications. In RA trials, dose-dependent decreases in neutrophil counts (PBNC) were observed with CP-690,550 treatment. These studies were undertaken to better understand the relationship between JAK selectivity and PBNC decreases observed with CP-690,550 treatment.

Methods

Potency and selectivity of CP-690,550 for mouse, rat and human JAKs was evaluated in a panel of in vitro assays. The effect of CP-690,550 on granulopoiesis from progenitor cells was also assessed in vitro using colony forming assays. In vivo the potency of orally administered CP-690,550 on arthritis (paw edema), plasma cytokines, PBNC and bone marrow differentials were evaluated in the rat adjuvant-induced arthritis (AIA) model.

Results

CP-690,550 potently inhibited signaling through JAK1 and JAK3 with 5-100 fold selectivity over JAK2 in cellular assays, despite inhibiting all four JAK isoforms with nM potency in in vitro enzyme assays. Dose-dependent inhibition of paw edema was observed in vivo with CP-690,550 treatment. Plasma cytokines (IL-6 and IL-17), PBNC, and bone marrow myeloid progenitor cells were elevated in the context of AIA disease. At efficacious exposures, CP-690,550 returned all of these parameters to pre-disease levels. The plasma concentration of CP-690,550 at efficacious doses was above the in vitro whole blood IC50 of JAK1 and JAK3 inhibition, but not that of JAK2.

Conclusion

Results from this investigation suggest that CP-690,550 is a potent inhibitor of JAK1 and JAK3 with potentially reduced cellular potency for JAK2. In rat AIA, as in the case of human RA, PBNC were decreased at efficacious exposures of CP-690,550. Inflammatory end points were similarly reduced, as judged by attenuation of paw edema and cytokines IL-6 and IL-17. Plasma concentration at these exposures was consistent with inhibition of JAK1 and JAK3 but not JAK2. Decreases in PBNC following CP-690,550 treatment may thus be related to attenuation of inflammation and are likely not due to suppression of granulopoiesis through JAK2 inhibition.

Prospect of JAK2 inhibitor therapy in myeloproliferative neoplasms

The discovery of the Janus kinase (JAK)2 V617F mutation in patients with myeloproliferative neoplasms was a major milestone in understanding the biology of those disorders. Several groups simultaneously reported on the high incidence of this mutation in patients with myeloproliferative neoplasms: almost all patients with polycythemia vera harbor the mutation and about 50% of patients with essential thrombocythemia and primary myelofibrosis have the mutation, making the development of JAK2 tyrosine kinase inhibitors an attractive therapeutic goal. In addition, inhibition of JAK2 kinase may have a therapeutic role in other hematologic malignancies, such as chronic myeloid leukemia or lymphoma. A number of molecules that inhibit JAK2 kinase have been described in the literature, and several are being evaluated in a clinical setting. Here, we summarize current clinical experience with JAK2 inhibitors.

Specific tyrosine phosphorylation of focal adhesion kinase mediated by Fer tyrosine kinase in suspended hepatocytes

Cell adhesion to the extracellular matrix (ECM) can activate signaling via focal adhesion kinase (FAK) leading to dynamic regulation of cellular morphology. Mechanistic basis for the lack of effective intracellular signaling by non-attached epithelial cells is poorly understood. To examine whether signaling in suspended cells is regulated by Fer cytoplasmic tyrosine kinase, we investigated the effect of ectopic Fer expression on signaling in suspended or adherent hepatocytes. We found that ectopic Fer expression in Huh7 hepatocytes in suspension or on non-permissive poly-lysine caused significant phosphorylation of FAK Tyr577, Tyr861, or Tyr925, but not Tyr397 or Tyr576. Fer-mediated FAK phosphorylation in suspended cells was independent of c-Src activity or growth factor stimulation, but dependent of cortactin expression. Consistent with these results, complex formation between FAK, Fer, and cortactin was observed in suspended cells. The Fer-mediated effect correlated with multiple membrane protrusions, even on poly-lysine. Together, these observations suggest that Fer may allow a bypass of anchorage-dependency for intracellular signal transduction in hepatocytes.

Stat3 contributes to resistance toward BCR-ABL inhibitors in a bone marrow microenvironment model of drug resistance

Imatinib mesylate is a potent, molecularly targeted therapy against the oncogenic tyrosine kinase BCR-ABL. Although imatinib mesylate has considerable efficacy against chronic myeloid leukemia (CML), advanced-stage CML patients frequently become refractory to this agent. The bone marrow is the predominant microenvironment of CML and is a rich source of both soluble factors and extracellular matrices, which may influence drug response. To address the influence of the bone marrow microenvironment on imatinib mesylate sensitivity, we used an in vitro bone marrow stroma model. Our data show culturing K562 cells, in bone marrow stroma-derived conditioned medium (CM), is sufficient to cause resistance to BCR-ABL inhibitors. Drug resistance correlated with increased pTyrStat3, whereas no increases in pTyrStat5 was noted. Moreover, resistance was associated with increased levels of the Stat3 target genes Bcl-xl, Mcl-1, and survivin. Finally, reducing Stat3 levels with small interfering RNA sensitized K562 cells cultured in CM to imatinib mesylate-induced cell death. Importantly, Stat3 dependency was specific for cells grown in CM, as reducing Stat3 levels in regular growth conditions had no effect on imatinib mesylate sensitivity. Together, these data support a novel mechanism of BCR-ABL-independent imatinib mesylate resistance and provides preclinical rationale for using Stat3-inhibitors to increase the efficacy of imatinib mesylate within the context of the bone marrow microenvironment.

In vitro affinity maturation of human GM-CSF antibodies by targeted CDR-diversification

The mammalian immune system applies somatic hypermutation to select for antibodies with improved dissociation rates in vivo up to an intrinsic limit, previously termed as affinity ceiling. However, for certain therapeutic applications it may be desirable to further improve antibody affinities beyond that limit. In this study the selection of antibodies specific for the pro-inflammatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) from the HuCAL GOLD human antibody library is described. In order to increase affinity and also functional activity, in vitro affinity maturation of a pool of lead Fab candidates was carried out. CDR-L3 and parallel CDR-H2 diversification using trinucleotide consensus cassettes were followed by the combination of optimized CDR-L3 and CDR-H2 leading to a 5000-fold improved affinity finally reaching a K(D) of 400 fM. Cytokine neutralizing potential of MOR04357 was evaluated in a TF-1 proliferation assay. Along with affinity optimization a 2000-fold increase in potency was observed compared to the parental antibody. Due to species cross-reactivity MOR04357 also blocks rat GM-CSF induced proliferation of FDCP-1 cells. Receptor inhibition studies showed that MOR04357 prevents the interaction of GM-CSF with the GM-CSF receptor alpha chain. As a consequence this leads to a blockade in signal transduction as measured by abolished STAT5 phosphorylation in the presence of GM-CSF and antibody. Due to its pro-inflammatory role GM-CSF has been implicated in the pathophysiology of inflammatory diseases like rheumatoid arthritis or asthma. Based on the mode of action described herein MOR04357 shows favourable antibody features as a potential drug candidate.

NF-kappaB in the pathogenesis and treatment of multiple myeloma

PURPOSE OF REVIEW

This review aims to summarize recent advances in the mechanisms through which the activation of the transcription factor NF-kappaB contributes to the pathogenesis of multiple myeloma.

RECENT FINDINGS

This transcription factor regulates expression of numerous genes involved in multiple myeloma pathogenesis, including growth, survival, immortalization, angiogenesis and metastasis. Recently, mutations of NF-kappaB signaling molecules have been identified in multiple myeloma cells. In addition, interactions between multiple myeloma cells and the bone marrow environment play critical roles in NF-kappaB activation as well as in multiple myeloma pathogenesis. Moreover, several drugs that are effective against multiple myeloma, including bortezomib, thalidomide, lenalidomide and arsenic trioxide, have been found to block activation of NF-kappaB. The combination of conventional chemotherapeutic drugs and those that block NF-kappaB activation has now proven to be effective in the treatment of multiple myeloma.

SUMMARY

Recent studies further underscore the critical role of NF-kappaB in multiple myeloma pathogenesis and have provided the rationale for multiple myeloma therapy with NF-kappaB-specific inhibitors combined with conventional chemotherapeutic drugs.

The tyrosine kinase FES is an essential effector of KITD816V proliferation signal

KIT is a tyrosine kinase receptor that is aberrantly activated in several neoplasms. In human pathologies, the most frequent mutation of KIT occurs at codon 816. The resulting KIT mutant protein is activated in the absence of ligand and is resistant to the clinically available inhibitors of KIT. In this report, we provide evidence for an essential function of the cytoplasmic tyrosine kinase FES downstream of KITD816V. FES is phosphorylated on tyrosine residues in cells that carry KITD816V mutation, and this phosphorylation is KIT dependent. Reduction of FES expression using RNA interference results in decreased cell proliferation in human or murine cells harboring KITD816V or the homologous mouse mutation KITD814Y. The reduced cell growth can be rescued using another cytokine (granulocyte-macrophage colony-stimulating factor [GM-CSF]) and is not observed when the closely related fer gene is targeted. Finally, signaling downstream of KITD816V is altered in cells lacking FES expression. This study shows a major function of FES downstream of activated KIT receptor and thereby points to FES as a novel target in KIT-related pathologies.

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.

Caspase-dependent proteolytic cleavage of STAT3alpha in ES cells, in mammary glands undergoing forced involution and in breast cancer cell lines

Background

The STAT (Signal Transducers and Activators of Transcription) transcription factor family mediates cellular responses to a wide range of cytokines. Activated STATs (particularly STAT3) are found in a range of cancers. Further, STAT3 has anti-apoptotic functions in a range of tumour cell lines. After observing a proteolytic cleavage in STAT3α close to a potential apoptotic caspase protease cleavage site we investigated whether STAT3α might be a caspase substrate.

Methods

STAT3α status was investigated in vitro in several cell systems:- HM-1 murine embryonic stem (ES) cells following various interventions; IOUD2 murine ES cells following induction to differentiate along neural or adipocyte lineages; and in a number of breast cancer cell lines. STAT3α status was also analysed in vivo in wild type murine mammary glands undergoing controlled, forced involution.

Results

Immunoblotting for STAT3α in HM-1 ES cell extracts detected amino and carboxy terminal species of approximately 48 kDa and 43 kDa respectively – which could be diminished dose-dependently by cell treatment with the nitric oxide (NO) donor drug sodium nitroprusside (SNP). UV irradiation of HM-1 ES cells triggered the STAT3α cleavage (close to a potential caspase protease cleavage site). Interestingly, the pan-caspase inhibitor z-Val-Ala-DL-Asp-fluoromethylketone (z-VAD-FMK) and the JAK2 tyrosine kinase inhibitor AG490 both inhibited cleavage dose-dependently, and cleavage was significantly lower in a heterozygous JAK2 knockout ES cell clone. STAT3α cleavage also occurred in vivo in normal murine mammary glands undergoing forced involution, coinciding with a pulse of phosphorylation of residue Y705 on full-length STAT3α. Cleavage also occurred during IOUD2 ES cell differentiation (most strikingly along the neural lineage) and in several human breast cancer cell lines, correlating strongly with Y705 phosphorylation.

Conclusion

This study documents a proteolytic cleavage of STAT3α into 48 kDa amino and 43 kDa carboxyl terminal fragments in a range of cell types. STAT3α cleavage occurs close to a potential caspase site, and can be inhibited dose-dependently by SNP, AG490 and z-VAD-FMK. The cleavage seems to be caspase-dependent and requires the phosphorylation of STAT3α at the Y705 residue. This highly regulated STAT3α cleavage may play an important role in modulating STAT3 transcriptional activity.

JAK1 N-terminus binds to conserved Box 1 and Box 2 motifs of cytokine receptor common beta subunit but signal activation requires JAK1 C-terminus

The human interleukin-3 receptor (hIL-3R) consists of a unique alpha subunit (hIL-3Ralpha) and a common beta subunit (betac). Binding of IL-3 to IL-3R activates Janus kinases JAK1 and JAK2. Our previously study showed that JAK2 and JAK1 were constitutively associated with the hIL-3Ralpha and betac subunits, respectively. In this study, we further demonstrate that JAK2 binds to the intracellular domain of hIL-3Ralpha and JAK1 binds to the Box 1 and Box 2 motifs of betac using GST-hIL-3R fusion proteins in pull-down assays. JAK1 mutational analysis revealed that its JH7-3 domains bound directly to the Box 1 and Box 2 motifs of betac. We further examined the role of JAK1 JH7-3 domains in JAK1 and JAK2-mediated signaling using the CDJAKs fusion proteins, which consisted of a CD16 extracellular domain, a CD7 transmembrane domain, and either JAK1 (CDJAK1), JAK2 (CDJAK2), or JAK1-JH7-3 domains (CDJAK1-JH7-3) as intracellular domains. Anti-CD16 antibody crosslinking of wild type fusion proteins CDJAK1 with CDJAK2 could mimic IL-3 signaling, however, the crosslinking of fusion proteins CDJAK1-JH7-3 with CDJAK2 failed to activate downstream proteins. These results suggest that the JAK1-JH7-3 domains are required for betac interaction and abolish wild type JAK1 and JAK2-mediated signaling.

GM-CSF activates the Jak/STAT pathway to rescue polymorphonuclear neutrophils from spontaneous apoptosis in young but not elderly individuals

Polymorphonuclear neutrophils (PMN) are the first cells to be recruited to the site of tissular aggression. They have a short-life span and die by spontaneous apoptosis. However, their life span and functional activities can be extended in vitro by a number of proinflammatory cytokines, including the granulocyte-macrophage colony stimulating factor (GM-CSF). We have reported that the protective effect of GM-CSF did not occur in PMN of elderly subjects. Data reported here showed that this difference was not due to a change in the expression of the GM-CSF receptor in the PMN of elderly individuals compared to young subjects. Furthermore, we showed here that GM-CSF activated the Janus kinase/signal transducer and activator of transcription (Jak/STAT) pathway and this activation appeared to be maintained for an extended period of time (18 h) playing an important role in the GM-CSF induced delayed PMN apoptosis. In marked contrast, GM-CSF had no effects on Jak2 activation in PMN of elderly individuals. We found that an inhibitor of Jak2 activation (AG490) abolished the protective effect of GM-CSF in PMN from young donors, however had no effect in PMN of elderly subjects. GM-CSF induced a transient activation of STAT3 and STAT5 in PMN of young donors but failed to activate to the same extent these signal transducers in PMN of elderly donors. The levels of proCaspase-3 were reduced in PMN of young donors treated with GM-CSF for 18 h but remained unchanged in PMN of elderly subjects treated under the same conditions compared to the untreated PMN. Our data are consistent with the interpretation that, at least in part (1) the protective effect of GM-CSF against apoptosis results from the activation of the Jak/STAT pathway and (2) decreased rescue from apoptosis in PMN of elderly is related to a failure of GM-CSF to activate this pathway in these cells.

The KRAB-associated co-repressor KAP-1 is a coiled-coil binding partner, substrate and activator of the c-Fes protein tyrosine kinase

The c-Fes protein tyrosine kinase is implicated in the differentiation of a number of cell types including neuronal, endothelial and myeloid cells. Structurally, Fes consists of a unique N-terminal region, followed by SH2 (Src homology domain 2) and kinase domains. Two coiled-coil (CC) domains (CC1 and CC2) located within the unique N-terminal region are critical regulators of Fes activity in vivo and may function to recruit Fes activators and/or substrates. A yeast two-hybrid screen, utilizing a K-562 cell cDNA library and the Fes CC2 domain as bait, identified an interacting clone encoding the CC domain and B-box motifs (residues 114-357) of the transcriptional co-repressor KRAB-associated protein (KAP)-1. KAP-1(114-357) interacted with full-length Fes in yeast, and the KAP-1 CC domain was sufficient to bind the Fes N-terminal region in Sf-9 cells. Co-expression of Fes with full-length KAP-1 in human 293T cells stimulated Fes autophosphorylation and led to KAP-1 tyrosine phosphorylation. Association of endogenous Fes and KAP-1 was also observed in HL-60 myeloid leukaemia cells. Together, these data identify a novel Fes-KAP-1 interaction, and suggest a dual role for KAP-1 as both a Fes activator and downstream effector.

A specific p47phox -serine phosphorylated by convergent MAPKs mediates neutrophil NADPH oxidase priming at inflammatory sites

Neutrophil NADPH oxidase plays a key role in host defense and in inflammation by releasing large amounts of superoxide and other ROSs. Proinflammatory cytokines such as GM-CSF and TNF-alpha prime ROS production by neutrophils through unknown mechanisms. Here we used peptide sequencing by tandem mass spectrometry to show that GM-CSF and TNF-alpha induce phosphorylation of Ser345 on p47phox, a cytosolic component of NADPH oxidase, in human neutrophils. As Ser345 is located in the MAPK consensus sequence, we tested the effects of MAPK inhibitors. Inhibitors of the ERK1/2 pathway abrogated GM-CSF-induced phosphorylation of Ser345, while p38 MAPK inhibitor abrogated TNF-alpha-induced phosphorylation of Ser345. Transfection of HL-60 cells with a mutated p47phox (S345A) inhibited GM-CSF- and TNF-alpha-induced priming of ROS production. This event was also inhibited in neutrophils by a cell-permeable peptide containing a TAT-p47phox-Ser345 sequence. Furthermore, ROS generation, p47phox-Ser345 phosphorylation, and ERK1/2 and p38 MAPK phosphorylation were increased in synovial neutrophils from rheumatoid arthritis (RA) patients, and TAT-Ser345 peptide inhibited ROS production by these primed neutrophils. This study therefore identifies convergent MAPK pathways on Ser345 that are involved in GM-CSF- and TNF-alpha-induced priming of neutrophils and are activated in RA. Inhibition of the point of convergence of these pathways might serve as a novel antiinflammatory strategy.

Anti-inflammatory effect of interleukin-10 on human neutrophil respiratory burst involves inhibition of GM-CSF-induced p47PHOX phosphorylation through a decrease in ERK1/2 activity

Interleukin-10 (IL-10) exerts its anti-inflammatory properties by down-regulating polymorphonuclear neutrophil (PMN) functions such as reactive oxygen species (ROS) production via NADPH oxidase. The molecular mechanisms underlying this process are unclear. Partial phosphorylation of the NADPH oxidase cytosolic component p47(PHOX) induced by proinflammatory cytokines, such as granulocyte-macrophage colony stimulating factor (GM-CSF) and tumor necrosis factor (TNF)-alpha, is essential for priming ROS production by PMN. The aim of this study was to determine whether IL-10 inhibits GM-CSF- and TNFalpha-induced p47(PHOX) phosphorylation and to investigate the molecular mechanisms involved in this effect. We found that IL-10 selectively inhibited GM-CSF- but not TNFalpha-induced p47PHOX phosphorylation in a concentration-dependent manner. As GM-CSF-induced p47PHOX phosphorylation is mediated by extracellular signal-regulated kinase 1/2 (ERK1/2), we tested the effect of IL-10 on this pathway. We found that IL-10 inhibited GM-CSF-induced ERK1/2 activity in an immunocomplex kinase assay. This inhibitory effect was confirmed by analyzing the phosphorylation status of the endogenous substrate of ERK1/2, p90RSK, in intact PMN. Furthermore, IL-10 decreased ROS production by adherent GM-CSF-treated PMN in keeping with the higher ROS production observed in whole blood from IL-10 knockout mice compared to their wild-type counterparts. Together, these results suggest that IL-10 inhibits GM-CSF-induced priming of ROS production by inhibiting p47PHOX phosphorylation through a decrease in ERK1/2 activity. This IL-10 effect could contribute to the tight regulation of NADPH oxidase activity at the inflammatory site.

Impairment of SHP-1 down-regulation in the lipid rafts of human neutrophils under GM-CSF stimulation contributes to their age-related, altered functions

It has been shown that the functions and the rescue from apoptosis by proinflammatory mediators of polymorphonuclear leukocytes (PMN) tend to diminish with aging. Here, we investigated the role of protein tyrosine phosphatases (PTP), especially Src homology domain-containing protein tyrosine phosphatase-1 (SHP-1), in the age-related, altered PMN functions under granulocyte macrophage-colony stimulating factor (GM-CSF) stimulation. The inhibition of PTP suggested a differential effect of GM-CSF on phosphatase activity in modulating PMN functions with aging. The down-regulation of phosphatase activity of immunopurified SHP-1 from lipid rafts of PMN of young donors was found significantly altered at 1 min of stimulation with aging. In young donors, SHP-1 is displaced from lipid rafts at 1 min of stimulation, whereas in the elderly, SHP-1 is constantly present. We assessed in PMN lipid rafts the phosphorylation of tyrosine and serine residues of SHP-1, which regulates its activity. We observed an alteration in the phosphorylation of tyrosine and serine residues of SHP-1 in PMN of elderly subjects, suggesting that GM-CSF was unable to inhibit SHP-1 activity by serine phosphorylation. GM-CSF activates Lyn rapidly, and we found alterations in its activation and translocation to the lipid rafts with aging. We also demonstrate that SHP-1 in the PMN of elderly is constantly recruited to Lyn, which cannot be relieved by GM-CSF. In contrast, in the young, the resting recruitment could be relieved by GM-CSF. Our results suggest an alteration of the SHP-1 modulation by GM-CSF in lipid rafts of PMN with aging. These alterations could contribute to the decreased GM-CSF effects on PMN.

GM-CSF action in the CNS decreases food intake and body weight

Many proinflammatory cytokines, such as leptin, play key roles in dynamic regulation of energy expenditure and food intake. The present work tested a role for the proinflammatory cytokine GM-CSF. Central but not peripheral administration of GM-CSF to adult rats significantly decreased food intake and body weight for at least 48 hours. Similar results were observed following central administration of GM-CSF in mice. GM-CSF receptor immunoreactivity was found on neurons within the paraventricular and arcuate nuclei of the hypothalamus. GM-CSF-deficient (GM-/-) mice weighed more and had significantly higher total body fat than wild-type (GM+/+) mice. Energy expenditure in GM-/- mice was decreased compared with that in GM+/+ mice. Taken together, these findings demonstrate that GM-CSF signaling in the CNS can regulate energy homeostasis.

Simultaneous activation of JAK1 and JAK2 confers IL-3 independent growth on Ba/F3 pro-B cells

JAK1 and JAK2 are tyrosine kinases involved in the regulation of cell proliferation, differentiation, and survival. These proteins may play a key role in mediating the effects of the cytokine IL-3 on hematopoietic cells. IL-3 induces tyrosine phosphorylation of both JAK1 and JAK2. However, it is not clear whether the activation of JAK1, JAK2, or both is sufficient to confer factor-independent growth in IL-3 dependent cells. To address this issue, fusion proteins CD16/CD7/JAK (CDJAK), comprised of a CD16 extracellular domain, a CD7 transmembrane domain, and a JAK cytoplasmic region (either a wild-type JAK or a dominant negative mutant of JAK) were constructed. We established several Ba/F3 derivatives that stably overexpress the conditionally active forms of either CDJAK1, CDJAK2, or both these fusion proteins. In this study, the autophosphorylation of CDJAK1 or CDJAK2 was induced by crosslinking with anti-CD16 antibody. We demonstrated that, like their wild-type counterparts, CDJAK1 and CDJAK2 were preassociated with the IL-3 receptor beta and alpha subunits, respectively. Furthermore, the simultaneous activation of both CDJAK1 and CDJAK2 fusion proteins, but not either one alone, led to the tyrosine phosphorylation of the IL-3 receptor beta subunit, the activation of downstream signaling molecules, including STAT5, Akt, and MAPK, and the conferring of factor-independent growth to IL-3-dependent Ba/F3 cells. Coexpression of dominant negative mutants CDJAK1KE or CDJAK2KE with wild type CDJAK2 or CDJAK1, respectively, inhibited these activation activities. These results suggest that JAK1 and JAK2 must work cooperatively and not independently and that their actions are dependent on having normal kinase activity to trigger downstream signals leading to IL-3 independent proliferation and survival of Ba/F3 cells.

Spatial and temporal changes in the subcellular localization of the nuclear protein-tyrosine kinase, c-Fes

Tyrosine phosphorylation has emerged as a mechanism to control cellular events in the nucleus. The c-Fes protein-tyrosine kinase is an important regulator of cell growth and differentiation in several cell types, and is found in the nucleus of hematopoietic cells. In this study, we showed nuclear localization of c-Fes in both hematopoietic (K562, TF-1, HEL, U937, and HL-60) and nonhematopoietic cell lines (293T, CaOv3, TfxH, MG-63, HeLa, DU-145) by immunofluorescence and confocal microscopy. c-Fes showed striking changes in subcellular localization at specific stages of mitosis. In interphase cells, the intranuclear distribution of c-Fes was diffuse with occasional bright foci. Some c-Fes was present in the cytosol after breakdown of the nuclear membrane, in prometaphase. At prometaphase and metaphase c-Fes was also associated with the chromosomes, in a punctate pattern that partially overlapped with the centromere. Further comparison with proteins that are known components of the kinetochore suggested that some c-Fes protein was located at the centromeric alpha-satellite DNA, between the kinetochores. At anaphase and telophase, c-Fes was entirely cytoplasmic and no protein was found associated with the chromosomes. The timing of c-Fes' appearance at the centromere coincides with the period of kinetochore assembly. These data suggest that c-Fes is recruited to the kinetochore during mitosis.

Activated Fps/Fes tyrosine kinase regulates erythroid differentiation and survival

OBJECTIVE

A substantial body of evidence implicates the cytoplasmic protein tyrosine kinase Fps/Fes in regulation of myeloid differentiation and survival. In this study we wished to determine if Fps/Fes also plays a role in the regulation of erythropoiesis.

METHODS

Mice tissue-specifically expressing a "gain-of-function" mutant fps/fes transgene (fps(MF)) encoding an activated variant of Fps/Fes (MFps), were used to explore the in vivo biological role of Fps/Fes. Erythropoiesis in these mice was assessed by hematological analysis, lineage marker analysis, bone-marrow colony assays, and biochemical approaches.

RESULTS

fps(MF) mice displayed reductions in peripheral red cell counts. However, there was an accumulation of immature erythroid precursors, which displayed increased survival. Fps/Fes and the related Fer kinase were both detected in early erythroid progenitors/blasts and in mature red cells. Fps/Fes was also activated in response to erythropoietin (EPO) and stem cell factor (SCF), two critical factors in erythroid development. In addition, increased Stat5A/B activation and reduced Erk1/2 phosphorylation was observed in fps(MF) primary erythroid cells in response to EPO or SCF, respectively.

CONCLUSIONS

These data support a role for Fps/Fes in regulating the survival and differentiation of erythroid cells through modulation of Stat5A/B and Erk kinase pathways induced by EPO and SCF. The increased numbers and survival of erythroid progenitors from fps(MF) mice, and their differential responsiveness to SCF and EPO, implicates Fps/Fes in the commitment of multilineage progenitors to the erythroid lineage. The anemic phenotype in fps(MF) mice suggests that downregulation of Fps/Fes activity might be required for terminal erythroid differentiation.

Delayed Neutrophil Apoptosis in Bovine Subclinical Mastitis

Bovine subclinical mastitis can be defined as a moderated inflammatory disease characterized by a persistent accumulation of neutrophils in milk. As GMCSF-mediated delay of neutrophil apoptosis contributes to the accumulation of inflammatory cells at the site of inflammation in many human diseases, we sought to determine whether subclinical mastitis in cows is also associated with a GMCSF-dependent increase in milk-neutrophil survival. We first addressed the hypothesis that GMCSF delays bovine neutrophil apoptosis by activation of the signal transducer and activator of transcription (STAT) family members STAT3 and STAT5, which are critical regulators of the expression of various Bcl-2 family proteins. Granulocyte-macrophage colony-stimulating factor significantly delayed apoptosis of blood neutrophils obtained from healthy cows. In these cells, GMCSF activated STAT5, but not STAT3, and induced an increase in the mRNA of the antiapoptotic Bcl-2 member, Bcl-xL. Granulocyte-macrophage colony-stimulating factor-dependent STAT5 activation and up-regulation of Bcl-xL mRNA were blocked by the Jak inhibitor, AG-490. This inhibition was associated with abrogation of the prosurvival effect of GMCSF, demonstrating a key role for STAT5 in delayed neutrophil apoptosis. We further found that GMCSF expression was increased in milk cells from cows affected with subclinical mastitis. Neutrophils from these cows demonstrated a significant delay of apoptosis as compared with neutrophils obtained from healthy cows and were unresponsive to GMCSF. Active STAT5 complexes were detected in these neutrophils. Finally, in the presence of AG-490, apoptosis was induced and a time-dependent down-regulation of Bcl-xL mRNA was observed in milk neutrophils from mastitis-affected cows. These results indicate that neutrophil survival is enhanced in milk of subclinical mastitis-affected cows and suggest a role for a GMCSF-activated STAT5 signaling pathway in this phenomenon. This pathway could thus represent a target for the control of persistent accumulation of neutrophils in the bovine mammary gland.

Human immunodeficiency virus type 1 infection inhibits granulocyte-macrophage colony-stimulating factor-induced activation of STAT5A in human monocyte-derived macrophages

Human immunodeficiency virus type 1 (HIV-1) infects cells of the monocyte/macrophage lineage. While infection of macrophages by HIV-1 is generally not cytopathic, it does impair macrophage function. In this study, we examined the effect of HIV-1 infection on intracellular signaling in human monocyte-derived macrophages (MDM) stimulated with the growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF is an important growth factor for cells of both the macrophage and granulocyte lineages and enhances effector functions of these cells via the heterodimeric GM-CSF receptor (GM-CSFR). A major pathway which mediates the effects of GM-CSF on macrophages involves activation of the latent transcription factor STAT5A via a Janus kinase 2 (JAK2)-dependent pathway. We demonstrate that GM-CSF-induced activation of STAT5A is inhibited in MDM after infection in vitro with the laboratory-adapted R5 strain of HIV-1, HIV-1(Ba-L), but not after infection with adenovirus. HIV-1 infection of MDM did not decrease the STAT5A or JAK2 mRNA level or STAT5A protein level or result in increased constitutive activation of STAT5A. Surface expression of either the alpha-chain or common beta(c)-chain of GM-CSFR was also unaffected. We conclude that HIV-1 inhibits GM-CSF activation of STAT5A without affecting expression of the known components of the signaling pathway. These data provide further evidence of disruption of cellular signaling pathways after HIV-1 infection, which may contribute to immune dysfunction and HIV-1 pathogenesis.

The fps/fes proto-oncogene regulates hematopoietic lineage output

OBJECTIVE

The fps/fes proto-oncogene is abundantly expressed in myeloid cells, and the Fps/Fes cytoplasmic protein-tyrosine kinase is implicated in signaling downstream from hematopoietic cytokines, including interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin (EPO). Studies using leukemic cell lines have previously suggested that Fps/Fes contributes to granulomonocytic differentiation, and that it might play a more selective role in promoting survival and differentiation along the monocytic pathway. In this study we have used a genetic approach to explore the role of Fps/Fes in hematopoiesis.

METHODS

We used transgenic mice that tissue-specifically express a mutant human fps/fes transgene (fps(MF)) that was engineered to encode Fps/Fes kinase that is activated through N-terminal myristoylation (MFps). Hematopoietic function was assessed using lineage analysis, hematopoietic progenitor cell colony-forming assays, and biochemical approaches.

RESULTS

fps(MF) transgenic mice displayed a skewed hematopoietic output reflected by increased numbers of circulating granulocytic and monocytic cells and a corresponding decrease in lymphoid cells. Bone marrow colony assays of progenitor cells revealed a significant increase in the number of both granulomonocytic and multi-lineage progenitors. A molecular analysis of signaling in mature monocytic cells showed that MFps promoted GM-CSF-induced STAT3, STAT5, and ERK1/2 activation.

CONCLUSIONS

These observations support a role for Fps/Fes in signaling pathways that contribute to lineage determination at the level of multi-lineage hematopoietic progenitors as well as the more committed granulomonocytic progenitors.

Regulation of the class II MHC pathway in primary human monocytes by granulocyte-macrophage colony-stimulating factor

GM-CSF stimulates the growth and differentiation of hematopoietic progenitors and also affects mature cell function. These effects have led to the use of GM-CSF as a vaccine adjuvant with promising results; however, the mechanisms underlying GM-CSF-mediated immune potentiation are incompletely understood. In this study, we investigated the hypothesis that the immune stimulatory role of GM-CSF is in part due to effects on class II MHC Ag presentation. We find that, in primary human monocytes treated for 24-48 h, GM-CSF increases surface class II MHC expression and decreases the relative level of the invariant chain-derived peptide, CLIP, bound to surface class II molecules. GM-CSF also increases expression of the costimulatory molecules CD86 and CD40, but not the differentiation marker CD1a or CD16. Furthermore, GM-CSF-treated monocytes are better stimulators in a mixed leukocyte reaction. Additional analyses of the class II pathway revealed that GM-CSF increases total protein and RNA levels of HLA-DR, DM, and DOalpha. Expression of class II transactivator (CIITA) types I and III, but not IV, transcripts increases in response to GM-CSF. Furthermore, GM-CSF increases the amount of CIITA associated with the DR promoter. Thus, our data argue that the proinflammatory role of GM-CSF is mediated in part through increased expression of key molecules involved in the class II MHC pathway via induction of CIITA.

Fps/Fes and Fer protein-tyrosinekinases play redundant roles in regulating hematopoiesis

OBJECTIVE

The highly related protein-tyrosine kinases Fps (also called Fes) and Fer are sole members of a subfamily of kinases. In this study, knock-in mice harboring kinase-inactivating mutations in both fps and fer alleles were used to assess functional redundancy between Fps and Fer kinases in regulating hematopoiesis.

METHODS

Mice harboring kinase-inactivating mutations in fps and fer alleles were generated previously. Compound homozygous mice were bred that lack both Fps and Fer kinase activities and progeny were analyzed for potential defects in viability and fertility. Potential differences in hematopoiesis were analyzed by lineage analysis of bone marrow cells, peripheral blood counts, and hematopoietic progenitor cell colony-forming assays.

RESULTS

Mice devoid of both Fps and Fer kinase activities were viable and displayed reduced fertility. Circulating levels of neutrophils, erythrocytes, and platelets were elevated in compound mutant mice compared to wild-type controls, suggesting that hematopoiesis is deregulated in the absence of Fps and Fer kinases. Compound mutant mice also showed reduced overall bone marrow cellularity, and lineage analysis revealed elevated CD11b(hi)Ly-6G(lo) myeloid cells, which may reflect increased granulocyte progenitors. Although no differences in the overall number of granulocyte/monocyte colony-forming progenitors were observed, qualitative differences in myeloid colonies from compound mutant mice suggested a role for Fps and Fer kinases in regulating cell-cell adhesion or a skewing in cellularity of colonies.

CONCLUSIONS

Mice lacking both Fps and Fer kinase activities develop normally, show reduced fertility, and display defects in hematopoiesis, thus providing evidence for functional redundancy between Fps and Fer kinases in regulating hematopoiesis.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces antiapoptotic and proapoptotic signals in acute myeloid leukemia

High levels of cytokines are associated with a poor prognosis in acute myeloid leukemia (AML). However, cytokines may induce, on one hand, survival factor expression and cell proliferation and, on the other hand, expression of inhibitory signals such as up-regulation of suppressors of cytokine signaling (SOCS) and induce apoptotic cell death. Because blasts from patients with AML express high procaspase protein levels, we asked whether granulocyte-macrophage colony-stimulating factor (GM-CSF) enhances procaspase protein production in AML cells. In the GM-CSF-responsive OCIM2 AML cell line, GM-CSF induced signal transducer and activator of transcription 5 (Stat 5) phosphorylation, up-regulated cyclin D2, and stimulated cell cycle progression. Concurrently, GM-CSF stimulated expression of SOCS-2 and -3 and of procaspases 2 and 3 and induced caspase 3 activation, poly(ADP[adenosine 5'-diphosphate]-ribose) polymerase (PARP) cleavage, and apoptotic cell death. The Janus kinase (Jak)-Stat inhibitor AG490 abrogated GM-CSF-induced expression of procaspase 3 and activation of caspase 3. Under the same conditions GM-CSF up-regulated production of BAX as well as Bcl-2, Bcl-XL, survivin, and XIAP. GM-CSF also increased procaspase 3 protein levels in OCI/AML3 and Mo7e cells, suggesting that this phenomenon is not restricted to a single leukemia cell line. Our data suggest that GM-CSF exerts a dual effect: it stimulates cell division but contemporaneously up-regulates Jak-Stat-dependent proapoptotic proteins. Up-regulation of procaspase levels in AML is thus a beacon for an ongoing growth-stimulatory signal.

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.

Fes tyrosine kinase promotes survival and terminal granulocyte differentiation of factor-dependent myeloid progenitors (32D) and activates lineage-specific transcription factors

The c-fps/fes proto-oncogene encodes a 92-kDa protein-tyrosine kinase that is involved in myeloid cell development and function. We have recently shown that expression of an activated allele of Fes (Fes(act)) in monocyte precursors resulted in their differentiation into functional macrophages through the activation of lineage-specific transcription factors. We now report that this kinase also plays a role in the survival and terminal differentiation of granulocyte progenitors. The expression of Fes(act) in factor-dependent 32D cells prevented their apoptotic death after interleukin-3 removal, but Fes(act)-expressing cells remained factor-dependent for proliferation. Removal of interleukin-3 from the Fes(act)-expressing cells was followed by granulocytic differentiation in the absence of granulocyte colony-stimulating factor within 4-8 days. The differentiated cells had distinctive granulocyte morphology and there was up-regulation of CD11b, Gr-1, and late differentiation markers such as lactoferrin, suggesting that this kinase induced terminal granulocytic differentiation. Concomitantly, Fes(act) down-regulated the macrophage marker F4/80, suggesting that the biological activity of Fes was coordinated in a lineage-specific manner. Further analysis showed that Fes(act) caused activation of CCAAT/enhancer-binding protein-alpha and STAT3, two transcription factors that are involved in granulocyte differentiation. Our results provide evidence that Fes may be a key component of the granulocyte differentiation machinery, and suggest a potential mechanism by which this kinase may regulate granulocyte-specific gene expression.

Carvedilol modulates in-vitro granulocyte-macrophage colony-stimulating factor-induced interleukin-10 production in U937 cells and human monocytes

Both granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-10 (IL-10) are important mediators regulating inflammatory responses. Inflammatory processes have an important role in atherogenesis. In this paper, the effects of carvedilol on GM-CSF-induced IL-10 production were examined on human monocytic cell line, U937, and purified human monocytes. First, we showed that one-time carvedilol pretreatment at concentrations 0.3-10 microM dose-dependently inhibited GM-CSF-induced IL-10 production in U937 cells. In addition, we found carvedilol to be non-cytotoxic at concentrations equal to or less than 10 microM. However, at concentrations higher than 10 microM, carvedilol induced programmed cell death in U937 cells. The inhibition of GM-CSF-induced IL-10 production by carvedilol was also observed at the expression of mRNA. Furthermore, the inhibition of IL-10 production was demonstrated in GM-CSF-activated purified human peripheral blood monocytes. Finally, long-term carvedilol pretreatment of U937 cells up to 2 months at concentrations of 1.0 microM mildly enhanced the IL-10 production. Our observations that carvedilol modulated GM-CSF-induced IL-10 production may have some implication in understanding the broad-spectrum effects of carvedilol in regulating inflammatory reactions.

Role of PI3-kinase-dependent Bad phosphorylation and altered transcription in cytokine-mediated neutrophil survival

Phosphoinositide 3-kinase (PI3-kinase)-dependent phosphorylation of the proapoptotic Bcl-2 family member Bad has been proposed as an important regulator of apoptotic cell death. To understand the importance of this pathway in nontransformed hematopoietic cells, we have examined the effect of survival cytokines on PI3-kinase activity and Bad expression and phosphorylation status in human neutrophils. Granulocyte macrophage-colony-stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) both reduced the rate of apoptosis in neutrophils cultured in vitro for 20 hours. Coincubation with the PI3-kinase inhibitor LY294002, which in parallel experiments abolished GM-CSF-primed, fMLP-stimulated superoxide anion production and GM-CSF-stimulated PtdIns(3,4,5)P(3) accumulation, inhibited the GM-CSF and TNF-alpha survival effect. In contrast, the MAP kinase kinase (MEK1/2) inhibitor PD98059 and the protein kinase A inhibitor H-89 had only a marginal effect on GM-CSF-mediated neutrophil survival. GM-CSF substantially increased Bad phosphorylation at Ser112 and Ser136 and increased the cytosolic accumulation of Bad. GM-CSF also regulated Bad at a transcription level with a marked decrease in mRNA levels at 4 hours. TNF-alpha caused a biphasic effect on the rate of morphologic apoptosis, which corresponded to an early increase, and a late inhibition, of Bad mRNA levels. LY294002 inhibited GM-CSF- and TNF-alpha-mediated changes in Bad phosphorylation and mRNA levels. These data suggest that the survival effect of GM-CSF and TNF-alpha in neutrophils is caused by a PI3-kinase-dependent phosphorylation and cytosolic translocation of Bad, together with an inhibition of Bad mRNA levels. This has important implications for the regulation of neutrophil apoptosis in vivo.

Differential expression of protein tyrosine kinase genes during microglial activation

Protein tyrosine kinase (PTK) activity is abundant in microglia, but the PTKs that participate in their activation have not been identified. For these studies, we used three paradigms to characterize PTK expression during microglial activation: resting and activated microglia were bulk fractionated from the adult brain, cultured newborn microglia were treated with lipopolysaccharide (LPS) to model the transition from activated toward phagocytic microglia, and PTK expression was examined in activated microglia in situ after facial nerve axotomy. Two PCR-based strategies were used to show that 21 different PTK genes are expressed by rat brain microglia: 5 receptor PTKs, 10 nonreceptor PTKs, and 6 members of the src family. Seven of the 21 PTKs were examined in greater detail. Five PTK mRNAs (fgr, hck, fak, jak-2, and flk-1) increased expression across all three models of activation. We conclude that they represent key components in the cascades that participate in microglial activation. In contrast, expression of fes and fms correlated with stimuli that affect microglial proliferation. Four of the PTKs (hck, fgr, fes, and fms) are believed to be myeloid cell specific and were not expressed by cultured astrocytes. HCK and FAK protein were also not expressed in lysates of immature astrocytes and oligodendrocytes. Because of their putative specificity, these kinases represent potential targets for inhibitors of microglial activation. Because reactive microglia can exacerbate the severity of neurological diseases, the identification of specific kinases that participate in microglial activation represents an important advance toward the development of new therapeutics.

Truncation of c-fes via gene targeting results in embryonic lethality and hyperproliferation of hematopoietic cells

The c-fes protooncogene encodes a nonreceptor tyrosine kinase (Fes) implicated in cytokine receptor signal transduction, granulocyte survival, and myeloid differentiation. To study the role of c-fes during myelopoiesis, we generated embryonic stem (ES) cells with a targeted disruption of the c-fes locus. Targeted mutagenesis deletes the C-terminal SH2 and tyrosine kinase domains of c-fes (referred to as c-fes(Delta c/Delta c)). We demonstrate that the c-fes(Delta c/Delta c) allele results in a truncated Fes protein that retains the N-terminal oligomerization domain, but lacks both the SH2 and the tyrosine kinase domain. In vitro differentiation of c-fes(Delta c/Delta c) ES cells results in hyperproliferation of an early myeloid cell. Generation of c-fes(Delta c/Delta c) mutant chimeric mice causes lethality by E13.5 with embryos exhibiting pleiotropic defects, the most striking being cardiovascular abnormalities. These results establish that c-fes is an important regulator of myeloid cell proliferation and embryonic development.

Tyrosine kinase oncogenes in normal hematopoiesis and hematological disease

Tyrosine kinase oncogenes are formed as a result of mutations that induce constitutive kinase activity. Many of these tyrosine kinase oncogenes that are derived from genes, such as c-Abl, c-Fes, Flt3, c-Fms, c-Kit and PDGFRbeta, that are normally involved in the regulation of hematopoiesis or hematopoietic cell function. Despite differences in structure, normal function, and subcellular location, many of the tyrosine kinase oncogenes signal through the same pathways, and typically enhance proliferation and prolong viability. They represent excellent potential drug targets, and it is likely that additional mutations will be identified in other kinases, their immediate downstream targets, or in proteins regulating their function.

Carboxy-terminal truncated STAT5 is induced by interleukin-2 and GM-CSF in human neutrophils

IL-2 and GM-CSF are potent activators of polymorphonuclear neutrophils (PMN) biologic activity. IL-2 and GM-CSF-mediated activation of STAT proteins was examined in nuclear extracts of human PMN. We found that both cytokines induced STAT5-like DNA-binding complexes that could not be supershifted using C-terminal-specific anti-STAT5 antibodies. Therefore, we performed oligoprecipitation experiments with a STAT5-biotinylated DNA probe (biotin-MGFe) and the precipitated proteins were identified by Western immunoblotting. We found that GM-CSF and IL-2 induced the DNA-binding activity of a C-terminal truncated isoform of STAT5. The truncated STAT5 form was present in the nucleus of PMN but the cytoplasmic extracts contained full-length STAT5, suggesting that PMN proteolytically process full-length STAT5 proteins. Proteolytic experiments demonstrated that PMN express a protease activity capable of producing C-terminal processed STAT5 proteins. In many settings, C-terminal truncation of the STAT5 protein leads to inhibition of STAT5 biological activity. Two known STAT5 regulated genes, encoding pim-1 and OSM proteins, failed to be induced by GM-CSF in PMN. These findings provide new insights to a mechanism by which PMN, a terminally differentiated cell, may regulate gene transcription by alternative proteolytic processing.

Closing in on the biological functions of Fps/Fes and Fer

Fps/Fes and Fer are the only known members of a distinct subfamily of the non-receptor protein-tyrosine kinase family. Recent studies indicate that these kinases have roles in regulating cytoskeletal rearrangements and inside out signalling that accompany receptor ligand, cell matrix and cell cell interactions. Genetic analysis using transgenic mouse models also implicates these kinases in the regulation of inflammation and innate immunity.