Activation of Raf/ERK1/2 MAP kinase pathway is involved in GM-CSF-induced proliferation and survival but not in erythropoietin-induced differentiation of TF-1 cells

RepID depletion enhances TWS119-induced erythropoiesis through chromatin reprogramming and transcription factor recruitment

BACKGROUND

Erythrocytes, derived from hematopoietic stem cells, are essential for oxygen transport, ensuring survival in all vertebrate animals. The process of erythropoiesis is associated with gene expression changes, but many key regulatory factors that govern erythroid differentiation remain to be fully understood.

OBJECTIVE

This study investigates the role of TWS119, a known GSK3β inhibitor, in inducing erythropoiesis in K562 erythroleukemia cells and explores the impact of Replication initiation determinant protein (RepID) depletion on the process.

METHODS

K562 cells were treated with TWS119 and erythropoiesis markers including various erythrocytic phenotypes were assessed. Chromatin-immunoprecipitation analysis was employed to examine the changes in chromatin structure and gene expression regulation. The impact of RepID depletion on TWS119-induced erythropoiesis was also evaluated by analyzing globin promoter euchromatinization and NRF2 binding.

RESULTS

TWS119 treatment led to erythrocytic phenotypes in K562 cells, such as red pellet formation, enucleation, and nucleus condensation, along with the upregulation of erythropoiesis markers. Furthermore, RepID depletion accelerated TWS119-mediated erythropoiesis. Chromatin-immunoprecipitation analysis revealed euchromatinization of the globin promoter and enhanced NRF2 binding in RepID-depleted cells, suggesting a mechanism of gene expression regulation during erythropoiesis.

CONCLUSION

This study demonstrates that TWS119 can induce erythropoiesis in K562 cells, and that RepID depletion enhances this process by modulating chromatin structure and facilitating transcription factor binding. These findings highlight a RepID-dependent mechanism in the regulation of gene expression during erythropoiesis.

The Role of Zinc in GM-CSF-Induced Signaling in Human Polymorphonuclear Leukocytes

SCOPE

Zinc is suggested to be necessary for functional signaling induced by certain growth factors. The granulocyte-macrophage colony-stimulating factor (GM-CSF) is a key factor for differentiation and activation of myeloid cells. This report analyses the impact of different zinc concentrations on GM-CSF-induced signaling in mature polymorphonuclear leukocytes (PMN).

METHODS AND RESULTS

As measured by flow cytometry, zinc increases surface GM-CSF receptor (GM-CSFR) in PMN, whereas monocytes respond with decreased GM-CSFR surface expression. Since total cellular GM-CSFR expression remains unaffected, the observed zinc-induced GM-CSFR surface dynamics may be explained by receptor redistribution. In PMN, zinc enhanced phosphorylation of mitogen-activated protein kinases (MAPK) in a dose-dependent manner as found in western blot. Zinc-induced MAPK phosphorylation is additionally augmented by moderate GM-CSF stimulation.

CONCLUSION

The present study demonstrates the opposing influence of zinc on GM-CSFR surface expression in monocytes and PMN. Zinc and GM-CSF, use in optimized concentrations, augment MAPK signaling, and increase expression of MAPK-induced myeloid cell leukemia-1 (Mcl-1) in PMN. Thus, this study concludes that zinc strengthens growth factor-induced signaling. Hence, the study provides a basis for further in vivo studies, focusing on the therapeutic value of zinc in patients with a disturbed GM-CSF signaling.

PI3k/AKT signaling pathway: Erythropoiesis and beyond

Erythropoiesis is a multi-step process that involves the differentiation of hematopoietic stem cells into mature red blood cells (RBCs). This process is regulated by several signaling pathways, transcription factors and microRNAs (miRNAs). Many studies have shown that dysregulation of this process can lead to hematologic disorders. PI3K/AKT is one of the most important pathways that control many cellular processes including, cell division, autophagy, survival, and differentiation. In this review, we focus on the role of PI3K/AKT pathway in erythropoiesis and discuss the function of some of the most important genes, transcription factors, and miRNAs that regulate different stages of erythropoiesis which play roles in differentiation and maturation of RBCs, prevention of apoptosis, and autophagy induction. Understanding the role of the PI3K pathway in erythropoiesis may provide new insights into diagnosing erythrocyte disorders.

PTEN is indispensable for cells to respond to MAPK inhibitors in myeloid leukemia

Constitutively activated MAPK and AKT signaling pathways are often found in solid tumors and leukemias. PTEN is one of the tumor suppressors that are frequently found deficient in patients with late-stage cancers or leukemias. In this study we demonstrate that a MAPK inhibitor, PD98059, inhibits both AKT and ERK phosphorylation in a human myeloid leukemia cell line (TF-1), but not in PTEN-deficient leukemia cells (TF-1a). Ectopic expression of wild-type PTEN in myeloid leukemia cells restored cytokine responsiveness at physiological concentrations of GM-CSF (<0.02 ng/mL) and significantly improved cell sensitivity to MAPK inhibitor. We also found that Early Growth Response 1 (EGR1) was constitutively over-expressed in cytokine-independent TF-1a cells, and ectopic expression of PTEN down-regulated EGR1 expression and restored dynamics of EGR1 expression in response to GM-CSF stimulation. Data from primary bone marrow cells from mice with Pten deletion further supports that PTEN is indispensible for myeloid leukemia cells in response to MAPK inhibitors. Finally, We demonstrate that the absence of EGR1 expression dynamics in response to GM-CSF stimulation is one of the mechanisms underlying drug resistance to MAPK inhibitors in leukemia cells with PTEN deficiency. Our data suggest a novel mechanism of PTEN in regulating expression of EGR1 in hematopoietic cells in response to cytokine stimulation. In conclusion, this study demonstrates that PTEN is dispensable for myeloid leukemia cells in response to MAPK inhibitors, and PTEN regulates EGR1 expression and contributes to the cytokine sensitivity in leukemia cells.

A Novel Peroxisome Proliferator-activated Receptor (PPAR)γ Agonist 2-Hydroxyethyl 5-chloro-4,5-didehydrojasmonate Exerts Anti-Inflammatory Effects in Colitis

Inflammatory bowel disease (IBD) is a chronic inflammatory disease with increasing incidence and prevalence worldwide. Here we investigated the newly synthesized jasmonate analogue 2-hydroxyethyl 5-chloro-4,5-didehydrojasmonate (J11-Cl) for its anti-inflammatory effects on intestinal inflammation. First, to test whether J11-Cl can activate peroxisome proliferator-activated receptors (PPARs), we performed docking simulations because J11-Cl has a structural similarity with anti-inflammatory 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2), one of the endogenous ligands of PPARγ. J11-Cl bound to the ligand binding domain of PPARγ in the same manner as 15d-PGJ2 and rosiglitazone, and significantly increased transcriptional activity of PPARγ. In animal experiments, colitis was significantly reduced in mice with J11-Cl treatment, determined by analyses of survival rate, body weight changes, clinical symptoms, and histological evaluation. Moreover, J11-Cl decreased production of pro-inflammatory cytokines including IL-6, IL-8, and G-CSF as well as chemokines including chemokine (C-C motif) ligand (CCL)20, chemokine (C-X-C motif) ligand (CXCL)2, CXCL3, and chemokine (C-X3-C motif) ligand 1 (CX3CL1) in colon tissues, and LPS or TNF-α-stimulated macrophages and epithelial cells. In contrast, production of anti-inflammatory cytokines including IL-2 and IL-4 as well as the proliferative factor, GM-CSF, was increased by J11-Cl. Furthermore, inhibition of MAPKs and NF-κB activation by J11-Cl was also observed. J11-Cl reduced intestinal inflammation by increasing the transcriptional activity of PPARγ and modulating inflammatory signaling pathways. Therefore, our study suggests that J11-Cl may serve as a novel therapeutic agent against IBD.

Transcription factor SCL/TAL1 mediates the phosphorylation of MEK/ERK pathway in umbilical cord blood CD34⁺ stem cells during hematopoietic differentiation

Transcription factor stem cell leukemia (SCL), also known as the T-cell acute lymphocytic leukemia 1 (TAL1), plays a key role in the regulation of hematopoiesis, but the molecular mechanisms are not well understood. The aim of the present study is to elucidate the effects of the epidermal growth factor receptor (EGFR) signal pathways underlying the biologic activity of SCL/TAL1 on normal hematopoietic development. Lentiviral vectors with up or down-regulation of SCL/TAL1 were transfected into umbilical cord blood CD34 stem cells. EGFR signaling pathways (including MEK/ERK and Akt/mTOR) and surface hematopoietic markers were analyzed in the process of hematopoietic differentiation. The data revealed that up or down-regulation of SCL/TAL1 gene was accompanied positively by the expressions of p-MEK and p-ERK1/2 protein, but the changes of Akt/mTOR were unobvious. MEK/ERK inhibitor U0126 and SCL/TAL1 down-regulation showed similar inhibitory effects on erythroid, myeloid, and megakaryoid differentiation. However, Akt/mTOR pathway altered insignificantly. MEK/ERK inhibitor U0126 could not affect the expression of SCL/TAL1 mRNA or protein. Taken together, these findings fully illustrated that SCL/TAL1 is located in the up-stream of MEK/ERK pathway and partially regulates hematopoiesis by modulating the phosphorylation level of the key proteins in MEK/ERK pathway.

PI3-kinase and mTOR inhibitors differently modulate the function of the ABCG2 multidrug transporter

The ATP-binding cassette (ABC) transporter ABCG2 plays an important role in tissue detoxification and confers multidrug resistance to cancer cells. Identification of expressional and functional cellular regulators of this multidrug transporter is therefore intensively pursued. The PI3-kinase/Akt signaling axis has been implicated as a key element in regulating various cellular functions, including the expression and plasma membrane localization of ABCG2. Here we demonstrate that besides inhibiting their respective target kinases, the pharmacological PI3-kinase inhibitor LY294002 and the downstream mTOR kinase inhibitor rapamycin also directly inhibit ABCG2 function. In contrast, wortmannin, another commonly used pharmacological inhibitor of PI3-kinase does not interact with the transporter. We suggest that direct functional modulation of ABCG2 should be taken into consideration when pharmacological agents are applied to dissect the specific role of PI3-kinase/Akt/mTOR signaling in cellular functions.

Productive parvovirus B19 infection of primary human erythroid progenitor cells at hypoxia is regulated by STAT5A and MEK signaling but not HIFα

Human parvovirus B19 (B19V) causes a variety of human diseases. Disease outcomes of bone marrow failure in patients with high turnover of red blood cells and immunocompromised conditions, and fetal hydrops in pregnant women are resulted from the targeting and destruction of specifically erythroid progenitors of the human bone marrow by B19V. Although the ex vivo expanded erythroid progenitor cells recently used for studies of B19V infection are highly permissive, they produce progeny viruses inefficiently. In the current study, we aimed to identify the mechanism that underlies productive B19V infection of erythroid progenitor cells cultured in a physiologically relevant environment. Here, we demonstrate an effective reverse genetic system of B19V, and that B19V infection of ex vivo expanded erythroid progenitor cells at 1% O(2) (hypoxia) produces progeny viruses continuously and efficiently at a level of approximately 10 times higher than that seen in the context of normoxia. With regard to mechanism, we show that hypoxia promotes replication of the B19V genome within the nucleus, and that this is independent of the canonical PHD/HIFα pathway, but dependent on STAT5A and MEK/ERK signaling. We further show that simultaneous upregulation of STAT5A signaling and down-regulation of MEK/ERK signaling boosts the level of B19V infection in erythroid progenitor cells under normoxia to that in cells under hypoxia. We conclude that B19V infection of ex vivo expanded erythroid progenitor cells at hypoxia closely mimics native infection of erythroid progenitors in human bone marrow, maintains erythroid progenitors at a stage conducive to efficient production of progeny viruses, and is regulated by the STAT5A and MEK/ERK pathways.

The MAPK ERK1 is a negative regulator of the adult steady-state splenic erythropoiesis

The mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase 1 (ERK1) and ERK2 are among the main signal transduction molecules, but little is known about their isoform-specific functions in vivo. We have examined the role of ERK1 in adult hematopoiesis with ERK1(-/-) mice. Loss of ERK1 resulted in an enhanced splenic erythropoiesis, characterized by an accumulation of erythroid progenitors in the spleen, without any effect on the other lineages or on bone marrow erythropoiesis. This result suggests that the ablation of ERK1 induces a splenic stress erythropoiesis phenotype. However, the mice display no anemia. Deletion of ERK1 did not affect erythropoietin (EPO) serum levels or EPO/EPO receptor signaling and was not compensated by ERK2. Splenic stress erythropoiesis response has been shown to require bone morphogenetic protein 4 (BMP4)-dependent signaling in vivo and to rely on the expansion of a resident specialized population of erythroid progenitors, termed stress erythroid burst-forming units (BFU-Es). A great expansion of stress BFU-Es and increased levels of BMP4 mRNA were found in ERK1(-/-) spleens. The ERK1(-/-) phenotype can be transferred by bone marrow cells. These findings show that ERK1 controls a BMP4-dependent step, regulating the steady state of splenic erythropoiesis.

Pro-inflammatory cytokine-mediated anemia: regarding molecular mechanisms of erythropoiesis

Anemia of cancer and chronic inflammatory diseases is a frequent complication affecting quality of life. For cancer patients it represents a particularly bad prognostic. Low level of erythropoietin is considered as one of the causes of anemia in these pathologies. The deficiency in erythropoietin production results from pro-inflammatory cytokines effect. However, few data is available concerning molecular mechanisms involved in cytokine-mediated anemia. Some recent publications have demonstrated the direct effect of pro-inflammatory cytokines on cell differentiation towards erythroid pathway, without erythropoietin defect. This suggested that pro-inflammatory cytokine-mediated signaling pathways affect erythropoietin activity. They could interfere with erythropoietin-mediated signaling pathways, inducing early apoptosis and perturbing the expression and regulation of specific transcription factors involved in the control of erythroid differentiation. In this review we summarize the effect of tumor necrosis factor (TNF)α, TNF-related apoptosis-inducing ligand (TRAIL), and interferon (IFN)-γ on erythropoiesis with a particular interest for molecular feature.

Post-translational modification of an R2R3-MYB transcription factor by a MAP Kinase during xylem development

Despite the pivotal role played by R2R3-MYB family members in the regulation of plant gene expression, little is known about post-translational regulation of these proteins. In animals, the MYB family member, c-MYB, is post-translationally modified by a mitogen-activated protein kinase (MAPK), p42(mapk). In order to test the hypothesis that R2R3-MYB proteins may be regulated by MAPK activity, interplay between a R2R3-MYB family member expressed in differentiating pine xylem (Pinus taeda MYB4, PtMYB4) and MAPK proteins expressed in the same tissue was examined. One of the MAPK proteins expressed in pine xylem, PtMAPK6, phosphorylated PtMYB4. Recombinant PtMAPK6 phosphorylated PtMYB4 on serine-236, located in the C-terminal activation domain of this transcription factor in a context that is found in other plant MYB proteins. Modification of the PtMAPK6 target serine in PtMYB4 did not appear to alter DNA binding in vitro but did alter the ability of PtMYB4 to promote transcriptional activation in yeast. PtMAPK6 activity was detected in developing xylem cells that had ceased cell division and formed secondary walls. Together, the data support a role for PtMAPK6 during early xylem development and suggest a function for this kinase in regulating gene expression through phosphorylation of PtMYB4.

p38 MAPK signaling mediates IL-17-induced nitric oxide synthase expression in bone marrow cells

The effects of interleukin (IL)-17 on nitric oxide (NO) synthase (NOS) expression, as well as the participation of mitogen-activated protein kinases (MAPKs) in IL-17-mediated effects were examined in murine bone marrow cells. The results demonstrated the ability of IL-17 to upregulate the expression of mRNA for both inducible NOS and constitutive, endothelial NOS isoforms, as well as to enhance the phosphorylation of p38 MAPK. Moreover, both the NOS-inducing effect of IL-17 and the in vitro IL-17-mediated inhibition colony forming unit-erythroid (CFU-E) growth were dependent on p38 MAPK activity. The data demonstrating that the in vivo reducing effect of IL-17 on bone marrow CFU-E was prevented by co-treatment with the NOS inhibitor Nw-nitro-l-arginine methyl ester hydrochloride (L-NAME), implied that this effect is mediated through NOS activation. Besides revealing a link between the IL-17, NO, and haematopoiesis, data presented gave an insight into the mechanisms by which IL-17 exerts its modulatory effects on bone marrow cells.

CREB-dependent gene regulation by prion protein: impact on MMP-9 and beta-dystroglycan

Corruption of the normal function of the cellular prion protein (PrP(C)) by the scrapie isoform (PrP(Sc)) emerges as a critical causal event in Transmissible Spongiform Encaphalopathies (TSE) pathogenesis. However, PrP(C) physiological role remains unclear. By exploiting the properties of the 1C11 neuroectodermal cell line, able to convert into 1C11(5-HT) serotonergic or 1C11(NE) noradrenergic neuronal cells, we assigned a signaling function to PrP(C). Here, we establish that antibody-mediated PrP(C) ligation promotes the recruitment of the cAMP responsive element binding protein (CREB) transcription factor downstream from the MAPK ERK1/2, in 1C11 precursor cells and their 1C11(5-HT) and 1C11(NE) neuronal progenies. Whatever the differentiation state of 1C11 cells, the PrP(C)-dependent CREB activation triggers Egr-1 and c-fos transcription, two immediate early genes that relay CREB's role in cell survival and proliferation as well as in neuronal plasticity. Furthermore, in 1C11-derived neuronal cells, we draw a link between the PrP(C)-CREB coupling and a transcriptional regulation of the metalloproteinase MMP-9 and its inhibitor TIMP-1, which play pivotal roles in neuronal pathophysiology. Finally, the PrP(C)-dependent control on MMP-9 impacts on the processing of the transmembrane protein, beta-dystroglycan. Taken together, our data define molecular mechanisms that likely mirror PrP(C) ubiquitous contribution to cytoprotection and its involvement in neuronal plasticity.

Multiple G-protein-coupling specificity of beta-adrenoceptor in macrophages

Adrenergic signalling of the immune system is one of the important modulator pathways of the inflammatory immune response realized via G protein-mediated pathways. The resulted signal depends on the type of the receptor-coupled G-protein (GPCR) that, according to the classical paradigm in the case of beta-adrenergic receptor (beta-AR), is Gs-type. Recently, alternate and/or multiple G protein coupling specificity of GPCRs have been demonstrated including a switch from Gs to Gi binding. The possibility of a Gs/Gi switch and its role in the immune response of macrophages has not been investigated yet. In this study, we demonstrate that beta-adrenergic stimulation itself is able to induce a transient mitogen-activated protein kinase phosphorylation in murine peritoneal macrophages in a pertussis toxin-sensitive manner, suggesting that the Gs/Gi switch also occurs in the immune system. Although this process is very rapid, it can influence different signalling pathways and can reprogramme effector functions suggesting that sympathetic modulation of the defence mechanism of the innate immune system has an additional, Gs/Gi switch-dependent component.

Reduction of Bcr-Abl function leads to erythroid differentiation of K562 cells via downregulation of ERK

The chimeric bcr-abl gene encodes a constitutively active tyrosine kinase that leads to abnormal transduction of growth and survival signals leading to chronic myeloid leukemia (CML). According to our previous observations, in vitro differentiation of several erythroid cell lines is accompanied by the downregulation of extracellular signal-regulated kinases (ERK)1/2 mitogen-activated protein kinase (MAPK) activities. In this work we investigated whether ERKs have a decisive role in either the erythroid differentiation process or apoptosis of bcr-abl+ K562 cells by means of direct (MEK1/2 inhibitor UO126) and indirect (reduced Bcr-Abl function) inhibition of their activities. We found that both Gleevec and UO126 induced hemoglobin expression. Gleevec treatment reduced the phosphorylation of Bcr-Abl, ERK and STAT-5 for up to 24 h, decreased Bcl-XL levels, and induced caspase-3-dependent apoptosis. In contrast, UO126 treatment resulted in only a transient decrease of ERK activity and did not induce cell death. For studying the effect of reduced Bcr-Abl function on erythroid differentiation at the level of the bcr-abl transcript, we applied the siRNA approach. Stable degradation of bcr-abl mRNA was achieved by using a retroviral vector with enhanced green fluorescent protein (EGFP) reporter. Despite a high (>90%) transduction efficiency we detected only a transient decrease in Bcr-Abl protein and in phosphorylated ERK1/2 levels. This transient change in Bcr-Abl signaling was sufficient to induce hemoglobin expression without significant cell death. These results suggest that by transiently reducing Bcr-Abl function it is possible to overcome the differentiation blockade without evoking apoptosis in CML cells and that reduced ERK activity may have a crucial role in this process.

Dual β-adrenergic modulation in the immune system: Stimulus-dependent effect of isoproterenol on MAPK activation and inflammatory mediator production in macrophages

This is the first study to demonstrate that the interaction between beta-adrenoceptor activation, and the production of inflammatory mediators can be modulated in opposite ways by two inflammatory stimuli, namely, protein kinase C (PKC)-activating phorbol myristyl acetate (PMA) and lipopolysaccharide (LPS). We provided evidence that isoproterenol treatment, when combined with phorbol ester increased the production of tumor necrosis factor-alpha, interleukin-12, and nitric oxide in murine macrophages, as well as in human monocytes and differentiated PLB-985 cells, while in agreement with earlier findings, it decreased inflammatory mediator production in combination with LPS stimulation. The contrasting effect on inflammatory mediator production, shown for the PMA and LPS activated cells was accompanied by parallel changes in activation of ERK1/2 and p38 MAPKs. Thus, isoproterenol significantly increased MAPK activation (phosphorylation) in PMA-treated cells and, conversely, it decreased the activation of extracellular signal regulated kinase 1/2 (ERK1/2) and p38 in LPS-stimulated cells. The opposing effects of isoproterenol on LPS-induced versus PMA-induced mediator production and the concurrent changes in MAPK activation highlight the role of this kinase pathway in macrophage activation and provide new insights regarding the flexible ways through which beta-adrenoceptor stimulation can modulate the inflammatory response in macrophages. Our results challenge the dogma that beta-adrenoceptor signaling is only immunosuppressive, and offer potential opportunities for new therapeutic approaches in the treatment of inflammatory and autoimmune diseases.

A balance between Raf-1 and Fas expression sets the pace of erythroid differentiation

Normal erythropoiesis critically depends on the balance between the renewal of precursor cells and their differentiation. If the renewal phase is shortened, the decrease in the precursor pool results in anemia; conversely, impaired differentiation increases the number of proliferating progenitors and the potential risk of leukemic transformation. Using gene ablation, we have discovered 2 self-sustaining signal transduction loops that antagonize each other and regulate erythroid progenitor proliferation and differentiation, respectively. We identify Raf-1 as the main activator of the MEK/ERK cascade and as the key molecule in maintaining progenitor proliferation. Differentiation, in contrast, is mediated by Fas via the activation of both the ASK1/JNK/p38 module and the caspase cascade. The point of convergence between the 2 cascades is activated ERK, which positively feeds back on the proliferation pathway by maintaining the expression of Raf-1, while inhibiting the expression of Fas and therefore differentiation. In turn, Fas, once expressed, antagonizes proliferation by exerting a negative feedback on ERK activation and Raf-1 expression. Simultaneously, Fas-mediated caspase activation precipitates differentiation. These results identify Raf-1 and Fas as the key molecules whose expression finely tunes erythropoiesis and the extent of ERK activation as the switch that tips the balance between them.

Effects of Intracellular Calcium on Cell Survival and the MAPK Pathway in a Human Hormone-Dependent Leukemia Cell Line (TF-1)

Changes in the cytoplasmic calcium concentration ([Ca(2+)](i)) regulate a wide variety of cellular processes. Here we demonstrate that increased [Ca(2+)](i) was able to induce hormone-independent survival and proliferation, as well as to evoke apoptosis in human myelo-erythroid GM-CSF/IL-3 dependent leukemia cells (TF-1). Cellular responses induced by elevated [Ca(2+)](i) depended on the duration and amplitude of the calcium-signal. Moderate or high, but transient, elevation of [Ca(2+)](i) caused a transient, biphasic activation of ERK1/2 and protected cells from hormone withdrawal-induced apoptosis.(1) In contrast, high and long-lasting elevation of [Ca(2+)](i) led to sustained activation of the ERK1/2 kinases and apoptosis of TF-1 cells. Our data suggest that a time-dependent action of the MAPK pathway works as a decision-point between cell proliferation and apoptosis.

Antiapoptotic effects of erythropoietin in differentiated neuroblastoma SH-SY5Y cells require activation of both the STAT5 and AKT signaling pathways

The hematopoietic cytokine erythropoietin (Epo) prevents neuronal death during ischemic events in the brain and in neurodegenerative diseases, presumably through its antiapoptotic effects. To explore the role of different signaling pathways in Epo-mediated antiapoptotic effects in differentiated human neuroblastoma SH-SY5Y cells, we employed a prolactin receptor (PrlR)/erythropoietin receptor (EpoR) chimera system, in which binding of prolactin (Prl) to the extracellular domain activates EpoR signaling in the cytosol. On induction of apoptosis by staurosporine, Prl supports survival of the SH-SY5Y cells expressing the wild-type PrlR/EpoR chimera. In these cells Prl treatment strongly activates the STAT5, AKT, and MAPK signaling pathways and induces weak activation of the p65 NF-kappaB factor. Selective mutation of the eight tyrosine residues of the EpoR cytoplasmic domain results in impaired or absent activation of either STAT5 (mutation of Tyr(343)) or AKT (mutation of Tyr(479)) or both (mutation of all eight tyrosine residues). Most interestingly, Prl treatment does not prevent apoptosis in cells expressing mutant PrlR/EpoR chimeras in which either the STAT5 or the AKT signaling pathways are not activated. In contrast, ERK 1/2 is fully activated by all mutant PrlR/EpoR chimeras, comparable with the level seen with the wild-type PrlR/EpoR chimera, implying that activation of the MAPK signaling pathway per se is not sufficient for antiapoptotic activity. Therefore, the antiapoptotic effects of Epo in neuronal cells require the combinatorial activation of multiple signaling pathways, including STAT5, AKT, and potentially MAPK as well, in a manner similar to that observed in hematopoietic cells.

Identification of granulocyte-macrophage colony-stimulating factor and lipopolysaccharide-induced signal transduction pathways that synergize to stimulate HIV type 1 production by monocytes from HIV type 1 transgenic mice

HIV-1-infected monocyte/macrophages located in lymph nodes and tissues are highly productive sources of HIV-1 and may function as a persistent reservoir contributing to the rebound viremia observed after highly active antiretroviral therapy is stopped. Mechanisms activating latently infected, primary monocyte/macrophages to produce HIV-1 were investigated using monocytes isolated from a transgenic mouse line carrying a full-length proviral clone of a monocyte-tropic HIV-1 isolate, HIV-1(JR-CSF), regulated by the endogenous long terminal repeat (LTR) (JR-CSF mice). Granulocyte-macrophage colony-stimulating factor (GM-CSF) combined with lipopolysaccharide (LPS) induced infectious HIV-1 production by JR-CSF mouse monocytes over 10-fold and 100-fold higher than that stimulated by GM-CSF or LPS alone, respectively. We examined mechanisms of GM-CSF synergy with LPS and demonstrated that GM-CSF up-regulated the LPS receptor, TLR-4, and also synergized with LPS to activate mitogen-activated protein (MAP) kinase/ERK kinase and the Sp1 transcription factor. Inhibitors of either MAP kinase/ERK kinase or p38 kinase but not PI 3-kinase potently suppressed GM-CSF and LPS-induced HIV-1 production by JR-CSF mouse monocytes. Because Sp1 is activated by both the MAP kinase/ERK kinase and p38 kinase pathways, we postulate that synergistic activation of these pathways by GM-CSF and LPS induced sufficient levels of Sp1 to activate the HIV-1 LTR in a Tat-independent manner and induced HIV-1 production by JR-CSF mouse monocytes. Thus, our study delineated the pathway of HIV-1 LTR activation by GM-CSF and LPS and indicated that JR-CSF transgenic mice may provide a new in vitro and in vivo system for investigating the mechanism by which inflammatory and infectious stimuli activate HIV-1 production from latently infected monocytes.

Establishment and characterization of a new human erythroleukemic cell line, ERY-1

The growth factor-independent erythroleukemic cell line ERY-1 was established from the peripheral blood of a 87-year-old woman with chronic myeloid leukemia (CML) in the acute phase. Immunophenotyping showed that fresh leukemic cells were positive for CD13, CD33, CD36 and CD235a (glycophorin A), a phenotype compatible with that of erythroblastic cells. Cytogenetic and fluorescence in situ hybridization (FISH) analysis demonstrated classical t(9;22)(q34;q11) chromosomic translocation associated with a duplication of the BCR-ABL fusion gene. Other cytogenetic abnormalities were detected in all analyzed mitosis, the most frequent being a trisomy of chromosome 8. The established ERY-1 cell line retains these immunophenotypic and cytogenetic features, and light and electron microscopy confirmed the relatively mature erythroblastic phenotype of the cells. In addition, ERY-1 cell line expressed beta-globin mRNA and a non-phosphorylable form of the erythropoietin receptor, even in presence of erythropoietin. Of note, the proliferation of ERY-1 cells was inhibited by TGFbeta1 or STI-571 (Gleevec), without significant induction of further differentiation. In conclusion, ERY-1 is a new growth factor-independent human erythroleukemic cell line with a relatively mature phenotype that may be useful to study the molecular events involved in erythroblastic differentiation.

HIV-1 Nef promotes survival of TF-1 macrophages by inducing Bcl-XL expression in an extracellular signal-regulated kinase-dependent manner

The Nef protein of human immunodeficiency virus-1 (HIV-1) is essential for the progression from human and simian immunodeficiency virus infection to full-blown AIDS. Recent studies indicate that Nef generates anti-apoptotic signals in HIV-infected T cells, suppressing cell death early in infection to allow productive viral replication. Previous work from our laboratory has shown that Nef also promotes proliferation of myeloid cells through a signal transducer and activator of transcription 3-dependent pathway. Here we demonstrate that Nef suppresses cell death induced by cytokine deprivation in the human macrophage precursor cell line, TF-1. Nef selectively induced up-regulation of Bcl-XL, an anti-apoptotic gene that is also regulated by granulocyte/macrophage-colony stimulating factor in this cell line. Activation of the extracellular signal-regulated kinase (Erk) mitogen-activated protein kinase pathway also correlated with the survival of TF-1/Nef cells. Using the selective mitogen-activated protein kinase kinase inhibitor PD98059, we found that Nef-induced Erk signaling is essential for Bcl-XL up-regulation and cell survival. In contrast, expression of Bcl-XL and TF-1 survival was not affected by dominant-negative signal transducer and activator of transcription 3. These data suggest that Nef produces survival signals in myeloid cells through Erk-mediated Bcl-XL induction, a pathway distinct from Nef survival pathways recently reported in T lymphocytes.

Spred-1 negatively regulates interleukin-3-mediated ERK/mitogen-activated protein (MAP) kinase activation in hematopoietic cells

Sprouty/Spred family proteins have been identified as negative regulators of growth factor-induced ERK/mitogen-activated protein (MAP) kinase activation. However, it has not been clarified whether these proteins regulate cytokine-induced ERK activity. We found that Spred-1 is highly expressed in interleukin-3 (IL-3)-dependent hematopoietic cell lines and bone marrow-derived mast cells. To investigate the roles of Spred-1 in hematopoiesis, we expressed wild-type Spred-1 and a dominant negative form of Spred-1, DeltaC-Spred, in IL-3- and stem cell factor (SCF)-dependent cell lines as well as hematopoietic progenitor cells from mouse bone marrow by retrovirus gene transfer. In IL-3-dependent Ba/F3 cells expressing c-kit, forced expression of Spred-1 resulted in a reduced proliferation rate and ERK activation in response to not only SCF but also IL-3. In contrast, DeltaC-Spred augmented IL-3-induced cell proliferation and ERK activation. Wild-type Spred-1 inhibited colony formation of bone marrow cells in the presence of cytokines, whereas DeltaC-Spred-1 expression enhanced colony formation. Augmentation of ERK activation and proliferation in response to IL-3 was also observed in Spred-1-deficient bone marrow-derived mast cells. These data suggest that Spred-1 negatively regulates hematopoiesis by suppressing not only SCF-induced but also IL-3-induced ERK activation.

Effects of sodium houttuyfonate on phosphorylation of CaMK II, CREB and ERK 1/2 and expression of c-Fos in macrophages

The purpose of this research is to investigate the effects of sodium houttuyfonate on the phosphorylation of CaMK II, CREB and ERK 1/2, and the expression of c-Fos. Macrophages were cultured in vitro with or without sodium houttuyfonate in the culture medium. After cell culture, macrophages were lysed and the lysate of the macrophages was collected for analysis. Western-blotting method was adopted to investigate the phosphorylation or the expression of these signal elements. It was found in this research that the phosphorylation levels of CaMK II and CREB and the expression of c-Fos protein in macrophages were increased by sodium houttuyfonate treatment; however, the phosphorylation level of ERK 1/2 was not affected by the treatment.

The anticancer drug mithramycin A sensitises tumour cells to apoptosis induced by tumour necrosis factor (TNF)

In this report we show that mithramycin considerably increases the direct cytotoxic effect of tumour necrosis factor (TNF) on tumour cells in vitro. Sensitisation to TNF-induced apoptosis was prevented by the broad caspase inhibitor zVAD-fmk, whereas overexpression of Bcl-2 had no effect. Mithramycin also potentiated cell death induced by Fas agonistic antibodies. In contrast, mithramycin reduced the percentage of cells undergoing apoptosis due to factor withdrawal. TNF-induced activation of NF-kappaB (NF-κB)-dependent gene expression was not modulated by mithramycin treatment. Concomitantly with the increased sensitivity, the protein level of the short-spliced cFLIP variant was downregulated. These results indicate that mithramycin enhances TNF-induced cell death in an NF-κB-independent manner, and suggest that the Fas-associated death domain protein plays a crucial role in the TNF-sensitising effect of mithramycin.

Hydroquinone modulates the GM-CSF signaling pathway in TF-1 cells

Human leukemogens, including alkylating chemotherapeutic agents and benzene, enhance granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent proliferation of human CD34+ bone marrow (BM) cells. The extracellular signal-regulated kinase (ERK) pathway plays an important role in GM-CSF-dependent proliferation and also has been implicated in the pathogenesis of acute myelogenous leukemia. Therefore, we investigated the effects of the benzene metabolite, hydroquinone (HQ), on alterations in the GM-CSF signaling pathway in TF-1 erythroleukemia cells and human CD34+ BM cells. HQ treatment in TF-1 cells results in a strong proliferative response that is dependent on ERK activation and GM-CSF production. HQ also induces ERK-dependent AP-1 activation with concomitant increased transcriptional activity of AP-1 reporter gene. However, the kinetics of ERK activation are different between rhGM-CSF and HQ in TF-1 cells: rhGM-CSF results in immediate activation of ERK, whereas HQ activation of ERK is delayed. Further, HQ and rhGM-CSF together produce an immediate increase in ERK phosphorylation, which is sustained for over 48 h. HQ also stimulates colony formation, AP-1 DNA binding and GM-CSF production in human CD34+ BM cells. These results suggest that HQ stimulates proliferation via activation of ERK/AP-1 and is at least partially mediated via the production of GM-CSF.

Opposite effects of inhibitors of mitogen-activated protein kinase pathways on the egr-1 and β-globin expression in erythropoietin-responsive murine erythroleukemia cells

The effect of erythropoietin (Epo) on the expression of mitogen-activated protein kinase (MAPK) target genes egr-1 and c-fos was investigated in Epo-responsive murine erythroblastic cell line ELM-I-1. Epo induced a transient rise in egr-1 mRNA without a similar effect on c-fos expression. The induction of egr-1 correlated with a rapid ERK1/2 phosphorylation and was prevented with MEK1/2 inhibitors PD 98059 and UO126. The p38 inhibitor SB 203580 enhanced ERK1/2 phosphorylation and egr-1 mRNA levels. Longer incubations of ELM-I-1 cells with Epo revealed a second later phase of increase in egr-1 expression which was also prevented by MEK1/2 inhibitors, whereas SB 203580 had a stimulatory effect. In contrast, the beta-globin mRNA production was enhanced in the presence of PD 98059 and UO126 and reduced by SB 203580. The results suggest a regulatory role of egr-1 expression in Epo signal transduction and provide pharmacological evidence for the negative modulation of differentiation-specific gene expression by the ERK1/2 pathway in murine erythroleukemia cells.

TRAIL regulates normal erythroid maturation through an ERK-dependent pathway

In order to investigate the biologic activity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on human erythropoiesis, glycophorin A (GPA)+ erythroid cells were generated in serum-free liquid phase from human cord blood (CB) CD34+ progenitor cells. The surface expression of TRAIL-R1 was weakly detectable in the early-intermediate phase of erythroid differentiation (days 4-6; dim-intermediate GPA expression), whereas a clear-cut expression of TRAIL-R2 was observed through the entire course of erythroid differentiation (up to days 12-14; bright GPA expression). On the other hand, surface TRAIL-R3 and -R4 were not detected at any culture time. Besides inducing a rapid but small increase of apoptotic cell death, which was abrogated by the pan-caspase inhibitor z-VAD-fmk, the addition of recombinant TRAIL at day 6 of culture inhibited the generation of morphologically mature erythroblasts. Among the intracellular pathways investigated, TRAIL significantly stimulated the extracellular signal-regulated kinase 1/2 (ERK1/2) but not the p38/mitogen-activated protein kinase (MAPK) or the c-Jun NH2-terminal kinase (JNK) pathway. Consistently with a key role of ERK1/2 in mediating the negative effects of TRAIL on erythroid maturation, PD98059, a pharmacologic inhibitor of the ERK pathway, but not z-VAD-fmk or SB203580, a pharmacologic inhibitor of p38/MAPK, reverted the antidifferentiative effect of TRAIL on CB-derived erythroblasts.

Opposing effects of PI3 kinase pathway activation on human myeloid and erythroid progenitor cell proliferation and differentiation in vitro

OBJECTIVE

To investigate 1) the effects of lineage-specific cytokines (G-CSF and EPO) combined with ligands for different classes of cytokine receptors (common beta chain, gp130, and tyrosine kinase) on proliferation by human myeloid and erythroid progenitor cells; and 2) the signal transduction pathways associated with combinatorial cytokine actions.

PATIENTS AND METHODS

CFU-GM and BFU-E were cloned in vitro. Secondary colony formation by replated CFU-GM and subcolony formation by BFU-E provided measures of progenitor cell proliferation. Studies were performed in the presence of cytokine combinations with and without signal transduction inhibitors.

RESULTS

Proliferation by CFU-GM and BFU-E was enhanced synergistically when common beta chain receptor cytokines (IL-3 or GM-CSF) were combined with G-CSF or EPO, but not with gp130 receptor cytokines (LIF or IL-6) or tyrosine kinase receptor cytokines (SCF, HGF, Flt-3 ligand, or PDGF). Delayed addition studies with G-CSF+IL-3 and EPO+IL-3 demonstrated that synergy required the presence of both cytokines from the initiation of the culture. The Jak2-specific inhibitor, AG490, abrogated the effect of combining IL-3 with EPO but had no effect on the enhanced CFU-GM proliferation stimulated by IL-3+G-CSF. The PI3 kinase inhibitors LY294002 and wortmannin substituted for G-CSF in combination with IL-3 since proliferation in the presence of LY294002/wortmannin+IL-3 was enhanced to the same extent as in the presence of G-CSF+IL-3. In contrast, LY294002 and wortmannin inhibited proliferation in the presence of EPO and in the presence of EPO+IL-3.

CONCLUSION

1) IL-3 may activate different signal transduction pathways when combined with G-CSF and when combined with EPO; 2) different signal transducing intermediates regulate erythroid and myeloid progenitor cell proliferation; and 3) inhibition of the PI3 kinase pathway suppresses myeloid progenitor cell differentiation and thereby increases proliferation.

Effect of serum deprivation on constitutive production of granulocyte-colony stimulating factor and granulocyte macrophage-colony stimulating factor in lung cancer cells

We previously established 2 lung cancer cell lines, OKa-C-1 and MI-4, which constitutively produce an abundant dose of granulocyte-colony stimulating factor (G-CSF) and granulocyte macrophage-colony stimulating factor (GM-CSF). Many other cases with G-CSF or GM-CSF producing tumors have been reported up to the present. However, the biological properties of the overproduction of G-CSF and GM-CSF by tumor cells have not been well known. Several reports demonstrated the presence of an autocrine growth loop for G-CSF and GM-CSF in nonhematopoietic tumor cells. We showed that exogenous G-CSF and GM-CSF stimulated cell growth in a dose-dependent manner in OKa-C-1 and MI-4 cells. We could detect the presence of G-CSF and GM-CSF receptors in both cell lines by RT-PCR analysis. We have previously shown that inflammatory cytokines, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta enhance the expression of G-CSF and GM-CSF in the cell lines. However, the factors that regulate constitutive production of G-CSF or GM-CSF by tumor cells are still unknown well. In our study, we first reported that serum deprivation stimulated constitutive production of G-CSF and GM-CSF by lung tumor cells through activation of nuclear factor (NF)-kappaB and p44/42 mitogen-activated protein kinase (MAPK) pathway signaling. We suggest that G-CSF and GM-CSF constitutively produced by tumor cells could grow tumor itself and rescue tumor cells from the cytotoxicity of serum deprivation.

Effect of haemopoietic growth factors on cancer cell lines and their role in chemosensitivity

The recombinant growth factors (GFs) erythropoietin (Epo) and granulocyte-macrophage colony stimulating factor (GM-CSF) have important roles in the management of cancer patients. However, the effects of these GFs at a cellular level are not well understood. We examined the effect of GFs alone, and in combination with cytotoxic chemotherapy, in a panel of seven cell lines. Flow cytometric analysis showed varying levels of receptor expression, which correlated with phosphorylated MAPK expression. Additionally, there were also concomitant increases in BCL-2 protein levels in those cells with high levels of MAPK activation. Although culturing cells with Epo or GM-CSF did not alter cell viability by themselves, GF pretreatment in cell lines expressing higher receptor levels resulted in a reduced magnitude of cell kill following exposure to cytotoxic IC50 concentrations of cisplatin. Subsequent co-culture with either the MEK inhibitor U0126 or the GM-CSF antagonist E21R negated this induced resistance to cytotoxic chemotherapy, confirming the importance of the GF receptor as well as MAPK in mediating these effects. These results suggest that the use of GFs during chemotherapy may be detrimental in those cancers expressing higher levels of the specific receptor. Conversely, our results also suggest that GFs are safe to use in chemotherapeutic regimens if the cancer cells do not overexpress the particular receptor.

Inhibition of ERK1/2 and CREB phosphorylation by caspase-dependent mechanism enhances apoptosis in a fibrosarcoma cell line treated with butyrate

We evaluated the role of MAPKs on apoptosis induced by butyrate in cells derived from a human fibrosarcoma (2C4). Culture of 2C4 cells in 5% of fetal bovine serum (FBS) induced ERK1/2 and CREB phosphorylation and delayed apoptosis induced by butyrate. Butyrate inhibited phosphorylation of ERK1/2 and CREB. Furthermore, the use of specific inhibitors PD98059 (MEK) and H89 (PKA), which block ERK1/2 and CREB phosphorylation, accelerated butyrate induced cell death in 2C4 cells. The butyrate effect was shown to be dependent on caspase activation, once caspase inhibitors restored phosphorylation of ERK1/2 and CREB in 2C4 cells. However, the proteolytic effect of caspases was not directly on ERK1/2 and CREB proteins. In conclusion, butyrate induced apoptosis in 2C4 cells is regulated by the levels of ERK1/2 and CREB phosphorylation in a caspase dependent mechanism.

Macrophage-stimulating protein cooperates with erythropoietin to induce colony formation and MAP kinase activation in primary erythroid progenitor cells

We have shown that Fv2, the Friend virus susceptibility 2 locus, encodes a naturally occurring amino-terminally truncated form of the STK receptor tyrosine kinase (Sf-Stk). Sf-Stk appears to interact with the viral glycoprotein gp55 and drive erythropoietin (Epo)-independent expansion of Friend virus-infected erythroblasts. Presumably, Sf-Stk provides signals that cooperate with EpoR signaling to induce the polyclonal expansion of infected cells. In this report, we show that macrophage-stimulating protein (MSP), the ligand for full-length STK, can also cooperate with Epo to enhance burst-forming units-erythroid (BFU-E) formation. To evaluate the signals induced by MSP/STK in primary erythroid progenitor cells, we adapted a method for the expansion of murine bone marrow mononuclear cells. The expanded progenitor cells express STK and respond to MSP in a colony assay. Furthermore, we demonstrate that low doses of MSP and Epo stimulation of the expanded cells cooperate to induce the phosphorylation of MAP kinase. Using the MEK inhibitor PD98059, we show that the activation of ERK is required for the enhanced BFU-E formation in response to MSP. These findings suggest that MSP has the ability to enhance erythroid colony formation in response to Epo, and that this response is dependent on the ability of MSP to induce the MAP kinase pathway.

Calcium induces cell survival and proliferation through the activation of the MAPK pathway in a human hormone-dependent leukemia cell line, TF-1

Survival and proliferation of cells of a human myelo-erythroid CD34+ leukemia cell line (TF-1) depend on the presence of granulocyte-macrophage colony-stimulating factor or interleukin-3. Upon hormone withdrawal these cells stop proliferating and undergo apoptotic process. In this report we demonstrate that a controlled increase in [Ca2+]i induces hormone-independent survival and proliferation of TF-1 cells. We found that moderate elevation of [Ca2+]i by the addition of cyclopiasonic-acid protected TF1 cells from apoptosis. Furthermore, a higher, but transient elevation of [Ca2+]i by ionomycin treatment induced cell proliferation. In both cases caspase-3 activity was reduced, and Bcl-2 was up-regulated. Higher elevation of [Ca2+]i by ionomycin induced MEK-dependent biphasic ERK1/2 activation, sufficient to move the cells from G0/G1 to S/M phases. Meanwhile, activation of ERK1/2, phosphorylation of the Elk-1 transcription factor, and, consequently, a substantial elevation of Egr-1 and c-Fos levels and AP-1 DNA binding were observed. Moderate elevation of [Ca2+]i, on the other hand, caused a delayed monophasic activation of ERK1/2 and Elk-1 that was accompanied with only a small increase of Egr-1 and c-Fos levels and AP-1 DNA binding. The specific MEK-1 kinase inhibitor, PD98059, inhibited all the effects of increasing [Ca2+]i, indicating that the MAPK/ERK pathway activation is essential for TF-1 cell survival and proliferation. Based on these results we suggest that the elevation of the [Ca2+]i may influence the cytokine dependence of hemopoietic progenitors and may contribute to pathological hematopoiesis.

Signal transducer and activator of transcription 5a (STAT5a) is required for eosinophil differentiation of human cord blood-derived CD34+ cells

Signal transducers and activators of transcription (STATs) have been reported to play a critical role in the differentiation of several myeloid cell lines, although the importance of STATs in the differentiation of primary human hematopoietic cells remains to be established. Terminal eosinophil differentiation is induced by interleukin-5 (IL-5), which has also been demonstrated to activate STAT5. We have investigated whether STAT5 plays a critical role during eosinophil differentiation using umbilical cord blood-derived CD34(+) cells. In this ex vivo system, STAT5 expression and activation are high early during differentiation, and STAT5 protein expression is down-regulated during the final stages of eosinophil differentiation. Retroviral transductions were performed to ectopically express wild-type and dominant-negative STAT5a (STAT5aDelta750) in CD34(+) cells. Transduction of cells with STAT5a resulted in enhanced proliferation compared with cells transduced with empty vector alone. Interestingly, ectopic expression of STAT5a also resulted in accelerated differentiation. In contrast, ectopic expression of STAT5aDelta750 resulted in a block in differentiation, whereas proliferation was also severely inhibited. Similar results were obtained with dominant-negative STAT5b. Forced expression of STAT5a enhanced expression of the STAT5 target genes Bcl-2 and p21(WAF/Cip1), suggesting they may be important in STAT5a-mediated eosinophil differentiation. These results demonstrate that STAT5 plays a critical role in eosinophil differentiation of primary human hematopoietic cells.

Phosphatidylinositol-3 kinase inhibitors enhance the anti-leukemia effect of STI571

BCR/ABL fusion tyrosine kinase is responsible for the initiation and maintenance of the Philadelphia chromosome (Ph(1))-positive chronic myelogenous leukemia (CML) and a cohort of acute lymphocytic leukemias (ALL). STI571 (Gleevec), a novel anti-leukemia drug targeting BCR/ABL kinase can induce remissions of the Ph(1)-positive leukemias. STI571 was recently combined with the standard cytostatic drugs to achieve better therapeutic results and to overcome emerging drug resistance mechanisms. We decided to search for a more specific partner compound for STI571. Our previous studies showed that a signaling protein phosphatidylinositol-3 kinase (PI-3k) is essential for the growth of CML cells, but not of normal hematopoietic cells (Blood, 86:726,1995). Therefore the anti- Ph(1)-leukemia effect of the combination of BCR/ABL kinase inhibitor STI571 and PI-3k inhibitor wortmannin (WT) or LY294002 (LY) was tested. We showed that STI571+WT exerted a synergistic effect against the Ph(1)-positive cell lines, but did not affect the growth of Ph(1)-negative cell line. Moreover, the combinations of STI571+WT or STI571+LY were effective in the inhibition of clonogenic growth of CML-chronic phase and CML-blast crisis patient cells, while sparing normal bone marrow cells. Single colony RT-PCR assay showed that colonies arising from the mixture of CML cells and normal bone marrow cells after treatment with STI571+WT were selectively depleted of BCR/ABL-positive cells. Biochemical analysis of the CML cells after the treatment revealed that combination of STI571+WT caused a more pronounced activation of caspase-3 and induced massive apoptosis, in comparison to STI571 and WT alone. In conclusion, combination of STI571+WT or STI571+LY may represent a novel approach against the Ph(1)-positive leukemias.

BCR mediated signal transduction in immature and mature B cells

Ligation of B cell receptors (BCR) on immature B cells may induce apoptosis, while in mature B cells it stimulates cell activation and growth. The signaling pathway regulating the differential functional response, death or survival of the B cell is not fully characterized. We have tested the intracellular signaling requirement of these processes using B cells isolated from the spleen of irradiated auto-reconstituted (transitional immature B cells) and untreated mice (mature B cells), respectively. We compared the BCR induced intracellular [Ca2+] transient, protein tyrosine phosphorylation and ERK phosphorylation, furthermore, the activation of Elk-1 and CREB transcription factors. The BCR induced rise of intracellular [Ca2+] did not significantly differ in the two populations, only a slight difference in the late phase of the response was observed. Immature B cells responded with a maximum tyrosine phosphorylation to a five times lower dose of anti-IgM compared to the mature population. Most importantly, we have found a significant difference in the tyrosine phosphorylation of the Gab family adaptor proteins, Gab1/2. In contrast to mature B cells, crosslinking of BCR on immature B cells did not induce tyrosine phosphorylation of Gab2, thus the Gab2-organized signal amplification complex could not be produced. Furthermore, we detected a significant difference in the kinetics of BCR induced ERK, Elk-1 and CREB phosphorylation. In immature B cells, ERK was transiently phosphorylated, ceasing after 120 min, while in mature cells, ERK phosphorylation was sustained. Elk-1 and CREB activation was also transient in immature B cells, followed the kinetics of ERK phosphorylation. The lack of sustained Erk1/2 activation suppresses the transcription factors necessary for the proliferation signal. Since ERK is regulated by the phosphorylated Gab1/2, these data demonstrate that BCR triggered phosphorylation and signal amplification of Gab1/2 is a critical step in a life or death decision of B cells.