The Scaffolding Adapter Gab2, via Shp-2, Regulates Kit-evoked Mast Cell Proliferation by Activating the Rac/JNK Pathway

The scaffolding adapter Gab2 mediates cell signaling and responses evoked by various extracellular stimuli including several growth factors. Kit, the receptor for stem cell factor (SCF), plays a critical role in the proliferation and differentiation of a variety of cell types, including mast cells. Kit, via Tyr(567) and Tyr(719), activates Src family kinases (SFK) and PI3K respectively, which converge on the activation of a Rac/JNK pathway required for mast cell proliferation. However, how Kit Tyr(567) signals to Rac/JNK is not well understood. By analyzing Gab2(-/-) mast cells, we find that Gab2 is required for SCF-evoked proliferation, activation of Rac/JNK, and Ras. Upon Kit activation in wild-type mast cells, Gab2 becomes tyrosyl-phosphorylated and associates with Kit and Shp-2. Tyr(567), an SFK binding site in Kit, and SFK activity were required for Gab2 tyrosyl phosphorylation and association with Shp-2. By re-expressing Gab2 or a Gab2 mutant that cannot bind Shp-2 in Gab2(-/-) mast cells or acutely by deleting Shp-2 in mast cells, we found that Gab2 requires Shp-2 for SCF-evoked Rac/JNK, Ras activation, and mast cell proliferation. Lastly, by analyzing mast cells from mice with compound Gab2 and Kit Y719F mutations (i.e., Gab2(-/-): KitY719F/Y719F mice), we find that Gab2, acting in a parallel pathway to PI3K from Kit Tyr(719), regulates mast cell proliferation and development in specific tissues. Our data show that Gab2 via Shp-2 is critical for transmitting signals from Kit Tyr(567) to activate the Rac/JNK pathway controlling mast cell proliferation, which likely contributes to mast cell development in specific tissues.

Endolymphatic hydrops as a cause of audio-vestibular manifestations in relapsing polychondritis

Relapsing polychondritis (RP) is characterized by inflammation and subsequent degeneration of cartilage. We report a 61-year-old woman who had RP with audio-vestibular manifestations. She was also diagnosed as having a myelofibrosis with myeloid metaplasia (MMM). Bilateral endolymphatic hydrops (EH) was confirmed by dominant -SP/AP of the electrocochleogram (ECochG). When thalidomide and prednisolone were prescribed for the treatment of MMM, symptoms of RP -- including the inner ear dysfunction -- were ameliorated. Isosorbide, one of the osmotic diuretics commonly used for the treatment of Meniere's disease (MD) in Japan, was also effective in keeping her free from inner ear dysfunction. This is the first report to confirm the existence of EH in a patient with RP with audio-vestibular manifestations. We suppose that an immunological imbalance due to MMM, in conjunction with a specific immunogenetic background, may have played a role in the pathogenesis of RP and the formation of EH in this patient.

Roles of tyrosine residues 845, 892 and 922 in constitutive activation of murine FLT3 kinase domain mutant

FLT3 tyrosine kinase domain (TKD) mutations are detected in approximately 7% of acute myeloid leukemia patients, and suggested to correlate with poor prognosis and confer resistance to FLT3 inhibitors. To explore activation mechanism of FLT3 TKD mutation, we analysed critical tyrosine residues for the constitutive activation and downstream signaling of the mutant by generating a series of single Tyr --> Phe substitution mutant of all 22 cytoplasmic tyrosine residues of murine FLT3 TKD-mutant (mFLT3Asp838Val). Tyr845Phe, Tyr892Phe and Tyr922Phe substitutions suppressed the phosphorylation of mFLT3Asp838Val itself, the activation of Erk1/2, STAT3 and STAT5, and the factor-independent cell proliferation and survival. In contrast, these three Tyr --> Phe mutations partially suppressed but maintained the ligand-dependent activation and anti-apoptotic activity of wild-type FLT3, suggesting that these tyrosine residues were more critical for the constitutive activation and signaling of mFLT3Asp838Val. These three Tyr --> Phe mutations also inhibited the constitutive activation of other FLT3 mutants bearing internal tandem duplication, Asp838Tyr or Ile839del. The suppression of mFLT3Asp838Val activation and signaling by these substitutions was partially recovered by shifting the culture temperature from 37 to 33 degrees C, or by the introduction of Cdc37 and Hsp90. Taken together, Tyr845, Tyr892 and Tyr922 are the critical residues in mFLT3Asp838Val activation, possibly through stabilizing the active conformation of mFLT3Asp838Val.

GATA Transcription Factors Inhibit Cytokine-dependent Growth and Survival of a Hematopoietic Cell Line through the Inhibition of STAT3 Activity

Although GATA-1 and GATA-2 were shown to be essential for the development of hematopoietic cells by gene targeting experiments, they were also reported to inhibit the growth of hematopoietic cells. Therefore, in this study, we examined the effects of GATA-1 and GATA-2 on cytokine signals. A tamoxifen-inducible form of GATA-1 (GATA-1/ERT) showed a minor inhibitory effect on interleukin-3 (IL-3)-dependent growth of an IL-3-dependent cell line Ba/F3. On the other hand, it drastically inhibited TPO-dependent growth and gp130-mediated growth/survival of Ba/F3. Similarly, an estradiol-inducible form of GATA-2 (GATA-2/ER) disrupted thrombopoietin (TPO)-dependent growth and gp130-mediated growth/survival of Ba/F3. As for this mechanism, we found that both GATA-1 and GATA-2 directly bound to STAT3 both in vitro and in vivo and inhibited its DNA-binding activity in gel shift assays and chromatin immunoprecipitation assays, whereas they hardly affected STAT5 activity. In addition, endogenous GATA-1 was found to interact with STAT3 in normal megakaryocytes, suggesting that GATA-1 may inhibit STAT3 activity in normal hematopoietic cells. Furthermore, we found that GATA-1 suppressed STAT3 activity through its N-zinc finger domain. Together, these results suggest that, besides the roles as transcription factors, GATA family proteins modulate cytokine signals through protein-protein interactions, thereby regulating the growth and survival of hematopoietic cells.

Distinct role for c-kit receptor tyrosine kinase and SgIGSF adhesion molecule in attachment of mast cells to fibroblasts

Binding of stem cell factor (SCF) to c-kit receptor tyrosine kinase (KIT) transduces signals essential for mast cell development via several pathways including activation of phosphatidylinositol 3-kinase (PI3-K). When cultured mast cells (CMCs) are cocultured with fibroblasts expressing membrane-bound SCF, CMCs with normal KIT adhere to fibroblasts and proliferate, whereas CMCs lacking cell surface expression of KIT do neither. Spermatogenic immunoglobulin superfamily (SgIGSF) was identified as another molecule that participates in mast cell adhesion to fibroblasts. Since the IC-2 mast cell line expressed neither KIT nor SgIGSF, the effect of ectopic expression of KIT or SgIGSF on the adhesion of IC-2 cells was examined. Three forms of KIT with the normal ectodomain were used: wild-type (KIT-WT) and two mutant types with a phenylalanine substitution at the tyrosine residue 719 (KIT-Y719F) or 821 (KIT-Y821F). KIT-Y719F does not activate PI3-K, whereas KIT-Y821F does. Firstly, KIT or SgIGSF was expressed singly in IC-2 cells. All three forms of KIT increased the adhesion level of IC-2 cells, whereas SgIGSF did not. Secondly, SgIGSF was coexpressed with one of the three forms of KIT. Coexpression of SgIGSF with KIT-WT or KIT-Y821F increased the adhesion level more markedly than was achieved by KIT-WT or KIT-Y821F alone. The effect was abolished by an antibody that blocks SCF-KIT interaction. In contrast, coexpression of SgIGSF with KIT-Y719F did not increase the adhesion level induced by KIT-Y719F alone. In adhesion of mast cells to fibroblasts, KIT appeared to behave as an adhesion molecule and as an activator of other adhesion molecules through phosphorylating PI3-K.

Notch signals inhibit the development of erythroid/megakaryocytic cells by suppressing GATA-1 activity through the induction of HES1

The effects of Notch signals on the erythroid/megakaryocytic differentiation of hematopoietic cells were examined. Activation of Notch signals by the intracellular Notch1 or an estradiol-inducible form of Notch1/ER suppressed the expression of the erythroid marker glycophorin A in an erythroid/megakaryocytic cell line K562. Although Mock-transfected K562 cells underwent megakaryocytic differentiation in response to 12-O-tetradecanoylphorbol-13-acetate (TPA), estradiol-activated Notch1/ER induced apoptosis during TPA treatment in the transfectant, which was accompanied by the reduced expression of an antiapoptotic molecule Bcl-XL. Even when apoptosis was prevented by the overexpression of Bcl-XL, activated Notch signals still inhibited TPA-induced megakaryocytic differentiation. As for this mechanism, Notch1/recombination signal binding protein J-kappa-induced HES1 but not HES5 was found to inhibit the function of an erythroid/megakaryocytic lineage-specific transcription factor GATA-1. Although HES1 did not affect the DNA binding activity of GATA-1 in gel shift and chromatin immunoprecipitation assays, it directly bound to GATA-1 and dissociated a critical transcriptional cofactor, p300, from GATA-1. Furthermore, overexpressed HES1 inhibited the development of erythroid and megakaryocytic cells in colony assays. Also, the Notch ligand Jagged1 expressed on NIH3T3 cells suppressed the development of erythroid and megakaryocytic cells from cocultured Lin-Sca-1+ hematopoietic stem/progenitor cells. These results suggest that Notch1 inhibits the development of erythroid/megakaryocytic cells by suppressing GATA-1 activity through HES1.

Roles for c-Myc in self-renewal of hematopoietic stem cells

Notch and HOXB4 have been reported to expand hematopoietic stem cells (HSCs) in vitro. However, their critical effector molecules remain undetermined. We found that the expression of c-myc, cyclin D2, cyclin D3, cyclin E, and E2F1 was induced or enhanced during Notch1- or HOXB4-induced self-renewal of murine HSCs. Since c-Myc can act as a primary regulator of G(1)/S transition, we examined whether c-Myc alone can induce self-renewal of HSCs. In culture with stem cell factor, FLT3 ligand, and IL-6, a 4-hydroxytamoxifen-inducible form of c-Myc (Myc/ERT) enabled murine Lin(-)Sca-1(+) HSCs to proliferate with the surface phenotype compatible with HSCs for more than 28 days. c-Myc activated by 4-hydroxytamoxifen augmented telomerase activities and increased the number of CFU-Mix about 2-fold in colony assays. Also, in reconstitution assays, HSCs expanded by c-Myc could reconstitute hematopoiesis for more than 6 months. As for the mechanism of c-myc induction by Notch1, we found that activated forms of Notch1 (NotchIC) and its downstream effector recombination signal-binding protein-J kappa (RBP-VP16) can activate the c-myc promoter through the element between -195 bp and -161 bp by inducing the DNA-binding complex. Together, these results suggest that c-Myc can support self-renewal of HSCs as a downstream mediator of Notch and HOXB4.

Enhanced production of osteopontin in multiple myeloma: clinical and pathogenic implications

In this study, we examined osteopontin (OPN) production in myeloma cells and plasma OPN levels in multiple myeloma (MM) patients. We assessed OPN production in bone marrow cells (BMCs) by immunocytochemistry and enzyme-linked immunosorbent assay (ELISA). We also assessed OPN production in various B-cell malignant cell lines, including three myeloma cell lines by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting. In addition, we measured plasma OPN concentrations by ELISA in 30 MM patients, 21 monoclonal gammopathy of undetermined significance (MGUS) patients and 30 healthy volunteers. As a result, in an immunocytochemical study, abundant OPN was detected in BMCs from overt MM patients, whereas no OPN was detected in BMCs from patients with other haematological diseases, including MGUS. Cultured BMCs from overt MM patients produced more OPN than those from patients with either smouldering MM or MGUS. Myeloma cell lines spontaneously produced OPN. Plasma OPN levels of MM patients were significantly higher than those of MGUS patients and healthy volunteers (P < 0.05). Moreover, they correlated with both progression and bone destruction of the disease (P < 0.05). These suggest that myeloma cells actively produce OPN, which possibly contributes to osteoclastic bone resorption in MM. Plasma OPN levels may be a useful biomarker for assessing bone destruction in MM and distinguishing MM from MGUS or smouldering MM.

Establishment and characterization of unique cell lines derived from pyothorax-associated lymphoma which develops in long-standing pyothorax and is strongly associated with Epstein-Barr virus infection

Malignant lymphoma frequently develops in the pleural cavity of patients with over 20 years' history of pyothorax. The term pyothorax-associated lymphoma (PAL) has been proposed for this type of tumor. We established four novel lymphoma cell lines (OPL-3, -4, -5, and -7) from four patients with PAL. Characteristics of the four cell lines are as follows: B-cell nature with defective expression of B-cell and T-cell surface antigens, monoclonal pattern of Epstein-Barr virus (EBV) infection in lymphoma cells (thus indicating an etiological role of EBV for lymphomagenesis), complicated chromosomal abnormalities with numerous structural and numerical abnormalities, and occasional but distinct genome instability. These abnormalities in cell character might be caused by the specific circumstances of PAL lymphomagenesis, i.e., chronic inflammation. Thus, PAL cell lines could be useful in analysis of molecular mechanisms leading to malignancy in chronic inflammation.

Oncogenic receptor tyrosine kinase in leukemia

Growth, survival and differentiation of hematopoietic cells are regulated by the interaction between hematopoietic growth factors and their receptors. While the defect in this interaction results in an insufficient hematopoiesis, the aberrantly elevated activation leads to the transformation of hematopoietic cells. The constitutive active mutations of receptor tyrosine kinase, such as c-Kit platelet-derived growth factor receptor (PDGFR) or fins-like tyrosine kinase 3 (Flt3), play a major role in the development of hematopoietic neoplasia. The constitutive activation is provoked by several mechanisms, such as making fusion genes by chromosomal translocations, or various mutations involving regulatory regions of the receptor. The chromosomal translocation brings the receptor intracytoplasmic domain juxtaposed to an unrelated molecule which has dimerization or multimerization motif, resulting in the constitutive dimerization of the receptor. The missense, insertion or deletion mutations in the regulatory regions, such as juxtamembrane domain, activation loop and extracellular domain, cause constitutive activation by releasing the respective auto-inhibitory functions of each regulatory region. Constitutive active receptors generate different signals quantitatively and qualitatively from wild type receptor, which mediate the oncogenic phenotype. Given the frequent involvement of constitutive active receptor tyrosine kinase in hematopoietic malignancies, targeted inhibitions of active tyrosine kinase and downstream aberrant signaling are rapidly developing novel therapeutic modality with much promise.

Suppression of myeloid transcription factors and induction of STAT response genes by AML-specific Flt3 mutations

The receptor tyrosine kinase Flt3 is expressed and functionally important in early myeloid progenitor cells and in the majority of acute myeloid leukemia (AML) blasts. Internal tandem duplications (ITDs) in the juxtamembrane domain of the receptor occur in 25% of AML cases. Previously, we have shown that these mutations activate the receptor and induce leukemic transformation. In this study, we performed genome-wide parallel expression analyses of 32Dcl3 cells stably transfected with either wild-type or 3 different ITD isoforms of Flt3. Comparison of microarray expression analyses revealed that 767 of 6586 genes differed in expression between FLT3-WT- and FLT3-ITD-expressing cell lines. The target genes of mutationally activated Flt3 resembled more closely those of the interleukin 3 (IL-3) receptor than those of ligand-activated Flt3. The serine-threonine kinase Pim-2 was up-regulated on the mRNA and the protein level in Flt3-ITD-expressing cells. Further experiments indicated that Pim-2 function was important for clonal growth of 32D cells. Several genes repressed by the mutations were found to be involved in myeloid gene regulation. Pu.1 and C/EBPalpha, both induced by ligand-activation of wild-type Flt3, were suppressed in their expression and function by the Flt3 mutations. In conclusion, internal tandem duplication mutations of Flt3 activate transcriptional programs that partially mimic IL-3 activity. Interestingly, other parts of the transcriptional program involve novel, IL-3-independent pathways that antagonize differentiation-inducing effects of wild-type Flt3. The identification of the transcriptional program induced by ITD mutations should ease the development of specific therapies.

Constitutively activated Rho guanosine triphosphatases regulate the growth and morphology of hairy cell leukemia cells

Hairy cell leukemia (HCL) is a rare type of chronic B-cell leukemia characterized by the hairy morphology of the leukemia cells. All of 5 HCL samples and an HCL-derived cell line, BNBH-I, showed serrated edges and hairlike projections in May-Grünwald Giemsa stain and protruding actin spikes and lamellipodia in phalloidin stain. These structures were hardly detected on B-cell chronic lymphocytic leukemia (B-CLL) and precursor B-cell acute lymphocytic leukemia (B-ALL) cells. Because Rho guanosine triphosphatases (GTPases) regulate the formation of these structures, we examined the expression levels and activation states of Rho GTPases in HCL cells. RhoA, Rac1, and Cdc42 were overexpressed and constitutively activated in HCL samples and BNBH-I cells but not in B-CLL or precursor B-ALL cells. Next we overexpressed dominant-negative (DN)-RhoA, DN-Rac1, and DN-Cdc42 in BNBH-I. As a result, each DN mutant repressed the growth of BNBH-I cells by more than 50% and inhibited actin spike formation, but only DN-Racl suppressed lamellipodia formation. We also found that enforced expression of constitutively active-RhoA, Rac, or Cdc42 in the proB-cell line Ba/F3 was sufficient to induce actin spike formation, whereas none of these molecules produced lamellipodia. These results indicated that constitutively activated Rho GTPases regulate the growth and unique morphology of HCL cells.

Necessity of tyrosine 719 and phosphatidylinositol 3'-kinase-mediated signal pathway in constitutive activation and oncogenic potential of c-kit receptor tyrosine kinase with the Asp814Val mutation

Substitution of valine (Val) for aspartic acid (Asp) at codon 814 constitutively activates murine c-kit receptor tyrosine kinase (KIT), and Asp816Val mutation, corresponding to murine Asp814Val mutation, is found in patients with mastocytosis and acute myelocytic leukemia. However, the signal transduction pathways responsible for oncogenesis by the Asp814Val mutant (KIT(Val814)) are not fully understood. To examine the oncogenic signal transduction of KIT(Val814), we converted 20 tyrosine (Tyr) residues to phenylalanine (Phe) in the cytoplasmic domain of KIT(Val814) or deleted the C-terminal region containing 2 other tyrosine residues (Del). Among various KIT(Val814)- derived mutants, KIT(Val814-Tyr719Phe) and KIT(Val814-Del) severely impaired receptor tyrosine phosphorylation and association with the p85 subunit of phosphatidylinositol 3'-kinase (p85 (PI3-K)). Moreover, KIT(Val814-Tyr719Phe) and KIT(Val814-Del) failed to induce ligand-independent growth in Ba/F3 cells, indicating that Tyr719, the binding site for p85(PI3-K), and the C-terminal region are indispensable for factor-independent growth by KIT(Val814). Although the C-terminal region was also required for ligand-dependent growth by wild-type KIT (KIT(WT)), the Tyr719Phe substitution had negligible effects on ligand-dependent growth by KIT(WT). Furthermore, dominant-negative PI3-K significantly inhibited ligand-independent growth by KIT(Val814). These results demonstrate that Tyr719 is crucial for constitutive activation of KIT(Val814), but not for the ligand-induced activation of KIT(WT), and that the downstream signaling of PI3-K plays an important role in ligand-independent growth and tumorigenicity by KIT(Val814), thereby suggesting that KIT(Val814) is a unique activating mutation that leads to a distinguishable function from the effects of KIT(WT).

Constitutive activation of c-kit by the juxtamembrane but not the catalytic domain mutations is inhibited selectively by tyrosine kinase inhibitors STI571 and AG1296

The c-kit receptor tyrosine kinase (KIT) is constitutively activated by 2 types of naturally occurring mutations, the Val559-->Gly (G559) mutation in the juxtamembrane domain and the Asp814-->Val (V814) mutation in the catalytic domain. We evaluated the effects of the tyrosine kinase inhibitors STI571 and AG1296 on BaF3 cells expressing wild-type KIT (KIT(WT)) or activating mutants of KIT (KIT(G559) and KIT(V814)) in the presence or absence of the KIT ligand, stem cell factor (SCF). Both STI571 and AG1296 inhibited SCF-dependent activation of KIT(WT) and SCF-independent activation of KIT(G559) more efficiently, whereas SCF-independent activation of KIT(V814) was scarcely affected. Furthermore, both inhibitors inhibited SCF-dependent growth of BaF3-KIT(WT) cells and, with higher potencies, SCF-independent growth of BaF3-KIT(G559) cells through the induction of apoptosis. In contrast, the inhibitors had little or no effect on SCF-independent growth of BaF3-KIT(V814) cells or on IL-3-dependent growth of BaF3-Mock cells. These results suggested that both inhibitors may be effective therapeutic agents for oncogenic KIT with the juxtamembrane domain mutation, but not with the catalytic domain mutation, and that the activation mechanism of the catalytic domain mutant KIT is complex and entirely different from that of the wild-type KIT or the juxtamembrane domain mutant KIT.

[Mutations of growth factor receptor Flt3 in acute myeloid leukemia: transformation of myeloid cells by Ras-dependent and Ras-independent mechanisms]

BACKGROUND AND OBJECTIVE

The tyrosine kinase receptor Flt3 mediates important functions in early hematopoietic progenitors. Recently mutations of a growth factor receptor have been identified in about 30 % of patients with acute myeloid leukemia (AML). These mutations are associated with a poor prognosis. In-vitro and animal data show their involvement in leukemic transformation. Experiments analyzing the effects of these mutations on signal transduction and gene expression patterns of myeloid cells allow for the classification of this receptor as an oncogene. Furthermore, they help to define the receptor and its signaling intermediates as therapeutic targets.

METHODS

In order to analyze the signaling properties of mutated FLT3 receptors, we isolated the receptor mRNA from two patients with AML. Wild-type and mutant Flt3 isoforms were expressed in 32D cells that were subsequently analyzed for proliferation, survival, activation of signaling intermediates and gene expression levels. Also, the effects of of Ras-, MAP-Kinase and PI3-Kinase inhibition were analyzed.

RESULTS

The expression of mutated Flt3 (Flt3-ITD) induced factor-independent proliferation and survival in the myeloid progenitor cell line 32D. Flt3-ITD activated Ras- and PI3-kinase-dependent signaling pathways, as well as STAT5 and STAT3. Activation of STAT proteins was followed by the induction of known STAT target genes like SOCS2, SOCS3 and CIS. Inhibition of Ras-dependent signal transduction by a dominant negative Ras construct inhibited some, but not all biological effects of Flt3-ITD. Similar results were obtained by chemical inhibition of the MAP kinases. In contrast, inhibition of PI3 kinase activity inhibited growth factor-independent growth and apoptosis resistance of 32D cells.

CONCLUSIONS

Inhibition of Ras-dependent signaling pathways is not sufficient to abrogate the functional consequences of Flt3-mutations in myeloid cells. Therefore, therapeutic intervention by Ras-Inhibitors may not be sufficient to treat Flt3-driven disease.

Critical roles of c-Kit tyrosine residues 567 and 719 in stem cell factor-induced chemotaxis: contribution of src family kinase and PI3-kinase on calcium mobilization and cell migration

Stem cell factor (SCF) has crucial roles in proliferation, survival, and differentiation of hematopoietic stem cells and mast cells through binding to c-Kit receptor (KIT). Chemotaxis is another unique function of SCF. However, little is known about the intracellular signaling pathway of SCF/KIT-mediated cell migration. To investigate the signaling cascade, we made a series of 22 KIT mutants, in which tyrosine (Y) residue was substituted for phenylalanine (F) in the cytoplasmic domain, and introduced into BAF3 cells or 293T cells. On stimulation with SCF, BAF3 expressing KIT(WT)(WT) showed cell migration and Ca(2+) mobilization. Among 22 YF mutants, Y567F, Y569F, and Y719F showed significantly reduced cell migration and Ca(2+) mobilization compared to WT. In Y567F, Lyn activation on SCF stimulation decreased and C-terminal Src kinase (Csk) suppressed KIT-mediated Ca(2+) influx and cell migration, suggesting that Y567-mediated Src family kinase (SFK) activation leads to Ca(2+) influx and migration. Furthermore, we found that p38 mitogen-activated protein kinase (p38 MAPK) and Erk1/2 were also regulated by Y567/SFK and involved in cell migration, and that p38 MAPK induced Ca(2+) influx, thereby leading to Erk1/2 activation. In Y719F, the binding of phosphatidylinositol 3'-kinase (PI3K) to KIT was lost and KIT-mediated cell migration and Ca(2+) mobilization were suppressed by PI3K chemical inhibitors or dominant-negative PI3K, suggesting the involvement of Y719-mediated PI3K pathway in cell migration. Combination of Csk and the PI3K inhibitor synergistically reduced cell migration, suggesting the cooperation of SFK and PI3K. Taken together, these results indicate that 2 major KIT signaling pathways lead to cell migration, one is Y567-SFK-p38 MAPK-Ca(2+) influx-Erk and the other is Y719-PI3K-Ca(2+) influx.

Functional cooperation among Ras, STAT5, and phosphatidylinositol 3-kinase is required for full oncogenic activities of BCR/ABL in K562 cells

BCR/ABL tyrosine kinase generated from the chromosomal translocation t(9;22) causes chronic myelogenous leukemia and acute lymphoblastic leukemia. To examine the roles of BCR/ABL-activated individual signaling molecules and their cooperation in leukemogenesis, we inducibly expressed a dominant negative (DN) form of Ras, phosphatidylinositol 3-kinase, and STAT5 alone or in combination in p210 BCR/ABL-positive K562 cells. The inducibly expressed DN Ras (N17), STAT5 (694F), and DN phosphatidylinositol 3-kinase (Delta p85) inhibited the growth by 90, 55, and 40%, respectively. During the growth inhibition, the expression of cyclin D2 and cyclin D3 was suppressed by N17, 694F, or Delta p85; that of cyclin E by N17; and that of cyclin A by Delta p85. In addition, N17 induced apoptosis in a small proportion of K562, whereas 694F and Delta p85 were hardly effective. In contrast, coexpression of two DN mutants in any combinations induced severe apoptosis. During these cultures, the expression of Bcl-2 was suppressed by N17, 694F, or Delta p85, and that of Bcl-XL by N17. Furthermore, although K562 was resistant to interferon-alpha- and dexamethasone-induced apoptosis, disruption of one pathway by N17, 694F, or Delta p85 sensitized K562 to these reagents. These results suggested that cooperation among these molecules is required for full leukemogenic activities of BCR/ABL.

Interference between host resistance to Listeria monocytogenes infection and ovalbumin-induced allergic responses in mice

Listeria monocytogenes promotes the induction of the T-helper 1 (Th1) cell response, while ovalbumin (OVA) induces a Th2 cell response and allergic reactions, such as airway hyperreactivity and immunoglobulin E (IgE) production. When mice were immunized with OVA on day 7 after L. monocytogenes infection, eosinophilia in bronchoalveolar lavage and the production of total IgE, OVA-specific IgE, interleukin-4 (IL-4), and IL-5 in the circulation were markedly suppressed. Cytokine responses, including IL-4, IL-5, IL-10, IL-13, and gamma interferon, to OVA were decreased in the spleen cell cultures obtained from OVA-immunized mice that had been infected with L. monocytogenes. Conversely, when OVA-immunized mice were infected with L. monocytogenes, conversion from the nonlethal infection to the lethal infection occurred. Host resistance to L. monocytogenes infection in OVA-immunized mice was enhanced by the administration of anti-IL-10 monoclonal antibody. The present study indicates that striking interference is observed between Th1-inducing L. monocytogenes infection and Th2-driven OVA-induced airway hyperreactivity.

[Relationship between atopic factors and physical symptoms induced by gaseous formaldehyde exposure during an anatomy dissection course]

Formaldehyde (FA) is an occupational and general indoor hazard often affecting the respiratory airways. One of the main causes of multiple chemical sensitivity is gaseous FA, and it has become an important social problem in developed countries. FA concentrations in anatomy dissection classrooms are thought to be higher than under usual circumstances. The number of students developing physical symptoms during the anatomy dissection course in our university has been increasing over recent years. We planned to clarify the causes of such symptoms. Ninety-five medical students were interviewed using a questionnaire about allergic histories, physical symptoms developed during the anatomy dissection course, and symptoms related to chemical sensitivity up to three months after the course had finished. We measured total IgE, specific IgE to FA and specific IgE to house dust mites. Eighty-three percent of students had experienced symptoms, such as burning eyes, nasal discharge, sore throat, general fatigue or skin irritation during the course. Fifty percent of students had a past history of atopic disease. Fifty-eight percent of students tested positive to specific IgE to house dust mites; however, only one student, who did not complain of any symptoms during the course, tested positive to FA-IgE. Students with atopic factors (present histories of atopic diseases and higher total IgE) and/or chemical sensitivity demonstrated worse physical symptoms during the anatomy dissection course than students without such histories. In conclusion, it is suggested that gaseous FA exposure may exacerbate basic allergic symptoms, and moreover that people with chemical sensitivity demonstrated worse symptoms following gaseous FA exposure. Nevertheless, in our study we find no relationship between FA-IgE and the physical symptoms of gaseous FA exposure during or following an anatomy dissection course.

Flt3 mutations from patients with acute myeloid leukemia induce transformation of 32D cells mediated by the Ras and STAT5 pathways

Somatic mutations of the receptor tyrosine kinase Flt3 consisting of internal tandem duplications (ITD) occur in 20% of patients with acute myeloid leukemia. They are associated with a poor prognosis of the disease. In this study, we characterized the oncogenic potential and signaling properties of Flt3 mutations. We constructed chimeric molecules that consisted of the murine Flt3 backbone and a 510-base pair human Flt3 fragment, which contained either 4 different ITD mutants or the wild-type coding sequence. Flt3 isoforms containing ITD mutations (Flt3-ITD) induced factor-independent growth and resistance to radiation-induced apoptosis in 32D cells. Cells containing Flt3-ITD, but not those containing wild-type Flt3 (Flt3-WT), formed colonies in methylcellulose. Injection of 32D/Flt3-ITD induced rapid development of a leukemia-type disease in syngeneic mice. Flt3-ITD mutations exhibited constitutive autophosphorylation of the immature form of the Flt3 receptor. Analysis of the involved signal transduction pathways revealed that Flt3-ITD only slightly activated the MAP kinases Erk1 and 2 and the protein kinase B (Akt) in the absence of ligand and retained ligand-induced activation of these enzymes. However, Flt3-ITD led to strong factor-independent activation of STAT5. The relative importance of the STAT5 and Ras pathways for ITD-induced colony formation was assessed by transfection of dominant negative (dn) forms of these proteins: transfection of dnSTAT5 inhibited colony formation by 50%. Despite its weak constitutive activation by Flt3-ITD, dnRas also strongly inhibited Flt3-ITD-mediated colony formation. Taken together, Flt3-ITD mutations induce factor-independent growth and leukemogenesis of 32D cells that are mediated by the Ras and STAT5 pathways. (Blood. 2000;96:3907-3914)

Roles of endogenous cytokines in liver apoptosis of mice in lethal Listeria monocytogenes infection

Various bacterial pathogens have been identified as mediators of apoptosis. Apoptosis reportedly shows both detrimental and beneficial effects on biological functions. We studied the role of liver apoptosis in lethal Listeria monocytogenes infection and the regulation of apoptosis by endogenous cytokines during infection. Apoptosis was observed in the spleen but not in the liver of infected mice, whereas the induction of liver necrosis was evident by rising levels of serum aminotransferases in these animals. Apoptosis was detected in the liver of L. monocytogenes-infected mice which had been treated with monoclonal antibody (mAb) against tumor necrosis factor-alpha (TNF-alpha) or interleukin-6 (IL-6), or in TNF-alpha(-/-) mice, but not in gamma- interferon (IFN-gamma)(-/-) mice or mice which had been treated with mAb against IL-4 or IL-10. Augmentation of liver apoptosis in mice treated with mAb against TNF-alpha or IL-6 or in TNF-alpha(-/-) mice correlated with the increase in bacterial numbers in the organ, while no augmentation of apoptosis was observed in the liver of IFN-gamma(-/-) mice irrespective of the marked increase in bacterial numbers in the organs, indicating that augmentation of liver apoptosis may not be merely due to the increase in bacterial growth in the organs. These results suggest that TNF-alpha and IL-6 may play an important role in protecting the liver from apoptosis in lethal L. monocytogenes infection.

Interleukin-4 and interleukin-10 are involved in host resistance to Staphylococcus aureus infection through regulation of gamma interferon

Our previous study showed that gamma interferon (IFN-gamma), a T-helper 1 (Th1)-type cytokine, plays a detrimental role in Staphylococcus aureus infection in mice. In this study, the role of Th2-type cytokines such as interleukin-4 (IL-4) and IL-10 in S. aureus infection was investigated. IL-10 mRNA was induced in parallel with IFN-gamma in the spleens and kidneys of mice during S. aureus infection, whereas IL-4 mRNA was induced in the spleens but not in the kidneys of these animals. Spleen cells obtained from S. aureus-infected mice produced lower titers of IFN-gamma and higher titers of IL-4 and IL-10 in response to heat-killed S. aureus than did those from uninfected mice. Administration of anti-IL-4 monoclonal antibody (MAb) or anti-IL-10 MAb inhibited the elimination of S. aureus cells from the kidneys of mice. IFN-gamma mRNA expression was enhanced in the spleens of anti-IL-4 MAb- or anti-IL-10 MAb-treated mice and also in the kidneys of anti-IL-4 MAb-treated animals. Next, we evaluated the role of IFN-gamma in S. aureus infection in IFN-gamma(-/-) mice. An increase in survival rates, a decrease in bacterial numbers in the kidneys, and an amelioration of histologic abnormalities in these organs were observed in IFN-gamma(-/-) mice compared with those in IFN-gamma(+/+) mice. Administration of MAb against IL-4 or IL-10 failed to affect bacterial growth in the spleens and kidneys of IFN-gamma(-/-) mice irrespective of the expression of Th2 response. These results suggest that S. aureus infection induced a Th2 response and that IL-4 and IL-10 might play a protective role through the regulation of IFN-gamma in S. aureus infection.

Altered expression of natural killer cell inhibitory receptors (KIRs) on T cells in bronchoalveolar lavage fluid and peripheral blood of sarcoidosis patients

BACKGROUND AND AIM OF THE WORK

The role for natural killer cell inhibitory receptors (KIRs) on T cells is not fully understood, but signalling through KIRs on T cells may inhibit T cell receptor mediated activation, and KIR expression has been suggested to be one mechanism of controlling T cell mediated immune responses. An aberrant KIR expression on T cells could thus be of importance in autoimmune as well as infectious disorders. Sarcoidosis patients have several immunological impairments that have not been clarified, and we here examined the KIR expression on CD4+ and CD8+ peripheral blood (PBL) and bronchoalveolar lavage (BAL) T cells of sarcoidosis patients and controls.

METHODS

We used three KIR specific monoclonal antibodies, namely DX9 (specific for p70), DX27 (p58) and DX22 (specific for CD94, that belongs to another major group of KIRs) and flow cytometry.

RESULTS

p70 was expressed lower in patient CD8+ PBL (median 2.3%) compared to controls (6.3%) (p < 0.01). In patients, p58 was expressed by less CD8+ BAL lymphocytes (median 1.2%) compared to PBL (6.8%) (p < 0.01) while CD94 was expressed by more CD8+ BAL lymphocytes (median 14.5%) compared to PBL (9.6%) (p < 0.01). Moreover, in CD8+ PBL, CD94 and p58 were expressed significantly lower in patients with an active vs. inactive disease, and in patients with chest radiographic stage I vs. stage II, respectively.

CONCLUSIONS

The significantly altered expression of distinct KIRs on CD8+ T cells in sarcoidosis, especially in patients with signs of an active disease, indicate these cells to be dysregulated and implicate them in the pathogenesis of the disease.

Constitutive activation of FLT3 in acute myeloid leukaemia and its consequences for growth of 32D cells

The receptor tyrosine kinase Flt3 is expressed on leukaemic blasts of most cases with acute myeloid leukaemia (AML). In order to evaluate the presence and significance of constitutive activation of Flt3 for leukaemogenesis, we (1) analysed the expression and activation status of the receptor in AML blasts; and (2) evaluated the functional consequences of constitutively active Flt3 in a myeloid progenitor cell line. Immunoprecipitation studies revealed Flt3 expression in a high proportion of AML cases (27/32) with ligand-dependent Flt3 autophosphorylation in 18, constitutive autophosphorylation in three and no autophosphorylation in six cases. Only one out of three samples with constitutively active Flt3 but 3/18 samples with ligand-dependent autophosphorylated Flt3 contained the recently described internal tandem repeat (ITR) mutations. To test the significance of Flt3 activation in myeloid cell function, we also characterized the biochemical and biological effects of the activating mutation D838V of Flt3 (FLt3D838V) on the factor-dependent myeloid progenitor cell line 32Dcl3: cells transfected with wild-type Flt3 (32D/Flt3) grew FLt3 ligand (FL) dependent, and the receptor was ligand dependently autophosphorylated. In contrast, the receptor was constitutively autophosphorylated in 32D/Flt3D838V cells, which grew independently of FL. We conclude that, in some AML samples, Flt3 is constitutively activated and that this does not correlate with ITR mutations in the juxtamembrane domain. Furthermore, constitutively active Flt3 confers factor independence to the myeloid progenitor cell line 32D. It remains to be determined whether activation of Flt3 is leukaemogenic in vivo and whether strategies aimed at inhibition of Flt3 activation could inhibit leukaemogenesis.