Stem Cell Factor Receptor Research Articles

Ezrin is a target for oncogenic Kit mutants in murine erythroleukemia

AbstractThe model of erythroleukemia caused by Spi-1/PU.1 transgenesis in mice is a multistage disease. A preleukemic step is characterized by an acute proliferation of proerythroblasts due to the arrest of differentiation provoked by Spi-1/PU.1. Later on, a blastic crisis occurs associated with somatic oncogenic mutations in the stem cell factor (SCF) receptor kit. To gain insights into the mechanisms of the leukemic progression, we performed proteomic profiling analyses of proerythroblasts isolated at the 2 stages of the disease. Our results indicate that the level of ezrin, a membrane cytoskeletal crosslinker, is increased in the leukemic cells. We show that Kit oncogenic forms are responsible for ezrin phosphorylation and that phosphorylation rather than overexpression is essential in the leukemic proerythroblasts. Using expression of dominant-negative forms of ezrin, we show that phosphorylation of ezrin on residue Y353 participates in apoptosis resistance, whereas phosphorylation on residue Y145 promotes proliferation of the leukemic cells in vitro and in vivo. Another recurrent oncogenic form of tyrosine kinases (Flt3) most frequently involved in human myeloid leukemia was also able to phosphorylate ezrin. These findings point to a new role for ezrin as signaling player in the development of leukemia, being a downstream effector of oncogenic tyrosine kinases in leukemic blasts.

Hypoxia-inducible factor (HIF)-1 directly enhances the transcriptional activity of stem cell factor (SCF) in response to hypoxia and epidermal growth factor (EGF)

Stem cell factor (SCF) plays important roles in tumor growth and angiogenesis. However, its regulatory mechanism remains largely undefined. Here, we report that hypoxia upregulated the expression of SCF in MCF-7 breast cancer cells in both messenger RNA and protein levels. When hypoxia-inducible factor (HIF)-1 alpha expression was knocked down by RNA interference, the MCF-7 cell expression of SCF was decreased significantly. Furthermore, the SCF receptor, c-kit phosphorylation was significantly strengthened by the condition culture media from hypoxic MCF-7 and MCF-7-c cells. The survival of A549 cells was more dependent on SCF under hypoxia. Analysis of SCF promoter 5'-flanking region revealed a potential hypoxia-response element (HRE; 5'-GCGTG-3') located at -68 to -64 relative to the transcriptional start site. Chromatin immunoprecipitation assay demonstrated that HIF-1 alpha directly bound to this region under normoxia, and this binding activity was significantly enhanced under hypoxia. Overexpression of HIF-1 alpha significantly upregulated the expression of luciferase reporter gene under control of the SCF promoters in both MCF-7 cells and human embryonic kidney 293 cells, but mutation of the HRE site completely blocked this effect. Epidermal growth factor was also able to enhance the SCF expression under normoxia in MCF-7 cells, which was dependent on HIF-1 alpha. Taken together, our data demonstrated that HIF-1 alpha was a key regulator of SCF expression in breast cancer cells. Hypoxia and epidermal growth factor receptor signal coexisted in the tumor microenvironment and might promote angiogenesis through HIF-1 alpha-mediated upregulation of SCF and other angiogenic factors.

C-kit Is Required for Cardiomyocyte Terminal Differentiation

c-kit, the transmembrane tyrosine kinase receptor for stem cell factor, is required for melanocyte and mast cell development, hematopoiesis, and differentiation of spermatogonial stem cells. We show here that in the heart, c-kit is expressed not only by cardiac stem cells but also by cardiomyocytes, commencing immediately after birth and terminating a few days later, coincident with the onset of cardiomyocyte terminal differentiation. To examine the function of c-kit in cardiomyocyte terminal differentiation, we used compound heterozygous mice carrying the W (null) and W(v) (dominant negative) mutations of c-kit. In vivo, adult W/W(v) cardiomyocytes are phenotypically indistinguishable from their wild-type counterparts. After acute pressure overload adult W/W(v) cardiomyocytes reenter the cell cycle and proliferate, leading to left ventricular growth; furthermore in transgenic mice with cardiomyocyte-restricted overexpression of the dominant negative W(v) mutant, pressure overload causes cardiomyocytes to reenter the cell cycle. In contrast, in wild-type mice left ventricular growth after pressure overload results mainly from cardiomyocyte hypertrophy. Importantly, W/W(v) mice with pressure overload-induced cardiomyocyte hyperplasia had improved left ventricular function and survival. In W/W(v) mice, c-kit dysfunction also resulted in an approximately 14-fold decrease (P<0.01) in the number of c-kit(+)/GATA4(+) cardiac progenitors. These findings identify novel functions for c-kit: promotion of cardiac stem cell differentiation and regulation of cardiomyocyte terminal differentiation.

Acquired Activating NRAS Mutations Associated with Aggressive Systemic Mastocytosis

Over 80% of patients with systemic mastocytosis have an acquired activating mutation (D816V) in the tyrosine kinase domain of the stem cell factor receptor, KIT. Although the majority of patients are classified as indolent, a significant subset of patients with mastocytosis presents with aggressive forms of the disease and have a poor prognosis. This spectrum of clinical manifestations is not explained by a single activating mutation. Recent animal models indicate that activation of the RAS pathway may play an important role in the pathogenesis of mastocytosis.

Detailed conformational dynamics of juxtamembrane region and activation loop in c‐Kit kinase activation process

The stem cell factor receptor (c-Kit) plays critical roles in initiating cell growth and proliferation. Its kinase functional abnormality has been thought to associate with several human cancers. The regulation of c-Kit kinase activity is achieved by phosphorylation on the residues Tyr568 and Tyr570 within juxtamembrane region (JMR) and subsequent structural transition of JMR and activation loop (A-loop). However, the detailed conformational dynamics of JMR and A-loop are far from clear, especially whether their conformational changes are coupled or not during the kinase activation transition. In this investigation, the complete conformational transition pathway was determined using a series of nanosecond conventional molecular dynamics (MD) and targeted molecular dynamics (TMD) simulations in explicit water systems. The results of the MD simulations show that the phosphorylation of residues Tyr568 and Tyr570 within JMR induces the detachment of JMR from the kinase C-lobe and increases the fluctuation in the structure of JMR, thus appearing to initiate the kinase activation process. During the course of the TMD simulation, which characterizes the conformational transition of c-Kit from autoinhibitory to activated state, the JMR undergoes a rapid departure from the allosteric binding site and drifts into solvent, followed by the conformational flip of A-loop from inactive (fold) state to active (extended) state. A change in the orientation of helix alphaC in response to the motion of JMR and A-loop has also been observed. The computational results presented here indicate that the dissociation of JMR from the kinase domain is prerequisite to c-Kit activation, which is consistent with previous experiments.

Progenitors of Interstitial Cells of Cajal in the Postnatal Murine Stomach

Maintaining the integrity of networks of interstitial cells of Cajal (ICC) is essential to preserve orderly contractile activity and neuroregulation in the gastrointestinal tract and to restore these functions after tissue damage or surgeries. Maintenance of ICC requires insulin-dependent or insulin-like growth factor I (IGF-I)-dependent production of membrane-bound stem cell factor (SCF) and may involve regeneration from local progenitors. Our goal was to identify ICC precursors in postnatal murine gastric muscles. We used flow cytometry and immunohistochemistry to examine freshly dissected and cultured muscles for cells expressing CD34, an adhesion molecule expressed by stromal tumors; CD44, which occurs on mesenchymal stem cells; and receptors for SCF (Kit), insulin (Insr), and IGF-I (Igf1r). Slow waves were studied by intracellular recording. In gastric muscles, we identified rare, Kit(low)CD44(+)CD34(+)Insr(+)Igf1r(+) cells resembling common embryonic precursors of ICC and smooth muscle. These putative progenitors were absent from organotypic cultures lacking mature ICC (Kit(+)CD44(+)CD34(-)Insr(-)Igf1r(-)) due to prolonged insulin/IGF-I deprivation but were rescued by IGF-I that also prevented ICC loss. Soluble SCF failed to prevent the loss of mature ICC but dramatically expanded the putative progenitors, which supported robust slow wave activity despite retaining an immature, Kit(+)CD44(+)CD34(+)Insr(+)Igf1r(+) phenotype. Differentiation of these cells into mature, network-forming ICC required IGF-I. Conversely, restoration of ICC networks by IGF-I after prolonged insulin and IGF-I deprivation required the survival of the presumed progenitors. Kit(low)CD44(+)CD34(+)Insr(+)Igf1r(+) cells may be local progenitors for gastric ICC and stromal tumors. Loss of these cells may contribute to gastrointestinal dysmotilities.

Exploring the mast cell enigma: a personal reflection of what remains to be done

Mast cells are traditionally viewed as effector cells of allergic reactions and parasitic diseases, but their importance in host defense against bacteria, in tissue remodelling, their bone marrow and stem cell origin and a central role of the stem cell factor (SCF) as mast cell growth and chemotactic factor has been worked out only in recent years. Despite this, major aspects about the nature of the cells and their role in disease remain unclear. This holds in particular for the identification of mast cell precursors and the role of growth factors that stimulate specific mast cell commitment from stem cells, such as nerve growth factor, neutrotrophin-3 and certain interleukins, alone and during interaction with SCF. Early data suggesting also an involvement of specific transcription factors need to be expanded in this process. Furthermore, although mast cell proliferative disease (mastocytosis) has been shown to be often associated with SCF receptor c-kit mutations, reasons for the development of this disease remain unclear. This holds also for mast cell release mechanisms in many types of mast cell-dependent urticaria. Exciting new insights are emerging regarding the role of mast cells in bacterial infections, in defense against tumors, in wound healing and in the interplay with the nervous system, with hormones, and in the neurohormonal network. The aim of this reflection is to delineate the many known and unknown aspects of mast cells, with a special focus on their development, and to discuss in detail two mast cell-related diseases, namely mastocytosis and urticaria.

Genistein induces radioprotection by hematopoietic stem cell quiescence

Purpose: In this study we addressed whether genistein-induced radioprotection in mice is associated with alterations of the cell cycle of hematopoietic stem and progenitor cells.Materials and methods: C57BL/6J female mice received a single subcutaneous injection of genistein (200 mg/kg) 24 h prior to a lethal dose (7.75 Gy, 60Co) of total body irradiation. Proliferation-associated Ki-67 protein/7-aminoactinomycin-D (Ki67/7AAD) cell cycle staining was used to differentiate between G0, G1, and S/G2/M in bone marrow cell populations negative for expression of mature hematopoietic lineage marker cells but positive for expression of stem cell antigen-1 and tyrosine kinase receptor for stem cell factor (Lin−Sca-1+cKit+, LSK+). Quantitative real-time polymerase chain reaction (qRT-PCR) microarrays were utilized to examine cell cycle specific genes.Results: At 24 h following radiation exposure, a greater percentage of LSK+ in genistein-treated mice accumulated in the G0 phase of the cell cycle, whereas a large percentage of LSK+ bone marrow cells from untreated and vehicle (PEG-400)-treated mice progressed into the G1 and S/G2/M phases. Moreover, the absolute number of marrow total LSK+, long-term LSK+, and short-term LSK+ increased 2.8, 12.1, and 4.2-fold, respectively, at 7 days post-irradiation in genistein-treated vs. untreated irradiated mice. Lin− cells from genistein-treated mice expressed fewer DNA damage responsive and cell cycle checkpoint genes than LSK+ from untreated or vehicle-treated mice.Conclusion: Pretreatment with genistein provides in vivo protection from acute myelotoxicity through extended quiescence followed by reduced senescence of marrow repopulating LSK+.

Reversion of immune tolerance in advanced malignancy: modulation of myeloid-derived suppressor cell development by blockade of stem-cell factor function

Tumor growth induced a significant increase of myeloid-derived suppressor cells (MDSCs) in the tumor-bearing host. In our previous study, we showed that MDSCs induced tumor-specific T-cell tolerance and the development of T regulatory cells (Tregs). Tumor-derived factors have been implicated in the accumulation of MDSCs. We hypothesize that reduction of MDSC accumulation in tumor-bearing hosts, through the blockade of tumor factors, can prevent T-cell anergy and Treg development and thereby improve immune therapy for the treatment of advanced tumors. Several tumor-derived factors were identified by gene array analysis. Among the candidate factors, stem- cell factor (SCF) is expressed by various human and murine carcinomas and was selected for further study. Mice bearing tumor cells with SCF siRNA knockdown exhibited significantly reduced MDSC expansion and restored proliferative responses of tumor-infiltrating T cells. More importantly, blockade of SCF receptor (ckit)-SCF interaction by anti-ckit prevented tumor-specific T-cell anergy, Treg development, and tumor angiogenesis. Furthermore, the prevention of MDSC accumulation in conjunction with immune activation therapy showed synergistic therapeutic effect when treating mice bearing large tumors. This information supports the notion that modulation of MDSC development may be required to achieve effective immune-enhancing therapy for the treatment of advanced tumors.

Motesanib for Thyroid Cancer

Iodine-refractory differentiated thyroid cancer, whether locally recurrent or metastatic, is notoriously resistant to systemic chemotherapy. Differentiated thyroid cancers are characterized by upregulated expression of angiogenesis-stimulating endothelial growth factor (EGF); thus, when initial therapy fails, angiogenesis inhibition might be effective. In a phase I study, motesanib — an oral, multitargeted tyrosine kinase inhibitor of EGF receptors, platelet-derived growth-factor receptors, and KIT stem-cell–factor receptors — demonstrated activity against papillary thyroid cancer (J Clin Oncol 2007; 25:2369). Based on these results, investigators evaluated motesanib’s efficacy against iodine-refractory thyroid cancer in an industry-sponsored phase II trial in …

Targeting microRNA expression to regulate angiogenesis

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression at the post-transcriptional level by either degradation or translational repression of a target mRNA. More than 400 miRNAs have been identified in the human genome, but the relevance of most of them to physiological and pathological processes remains unclear. Although downregulation of the miRNA-processing enzymes Dicer and Drosha is known to impair angiogenesis, only a few specific miRNAs targeting endothelial cell function and angiogenesis have been identified. miR-221 and miR-222 block endothelial cell migration, proliferation and angiogenesis in vitro by targeting the stem cell factor receptor c-Kit and indirectly regulating expression of endothelial nitric oxide synthase. A pro-angiogenic function has been established for the miR-17-92 cluster, which promotes tumor angiogenesis in vivo. Expression of let7-f and miR-27b contributes to in vitro angiogenesis. We review recent studies on the involvement of miRNA in angiogenesis and discuss their implications for miRNA-based therapeutic strategies targeting this process in disease.

Stem Cell Factor in a Rat Model of Serum Nephrotoxic Nephritis

Background: Stem cell factor (SCF) has been implicated in many disease processes characterized by tissue remodelling and fibrosis. The growth factor (SCF) was evaluated in a rat model of nephrotoxic serum nephritis (NTN), characterized by early inflammation followed by later tissue fibrosis. Methods: NTN was induced in male Wistar Kyoto rats using rabbit anti-rat glomerular basement membrane antibodies. Animals were sacrificed at days 7, 15, 30 and 45 (n = 4–10 per group). Rats’ kidneys were immunostained for ED1 as marker of inflammation, CD34, SCF, c-kit, mast cell tryptase and markers of fibrosis; collagens III and IV and α-SMA. Changes in SCF protein and mRNA content were evaluated by Western blotting and Northern blotting, respectively. Results: In the NTN kidney, levels of immunoreactive SCF and SCF receptor (c-kit) were significantly higher in glomerular, tubular and interstitial compartments. Mast cells were barely detectable in NTN and control rat sections. Double immunostaining showed the co-localization of SCF with α-SMA and of the SCF receptor with CD34 and ED1 positive cells. Immunostainable SCF protein in each of the 3 compartments, glomerular, tubular and interstitial, showed a positive linear correlation with serum creatinine, proteinuria, glomerulosclerosis score and interstitial fibrosis scores. Using multivariate analysis, immunostainable tubular SCF was a predictor of glomerular sclerosis and immunostainable glomerular SCF predicted tubular atrophy. Increased SCF immunostain was not a consequence of altered transcription as there was a fall in SCF mRNA determined by Northern blotting. Western blotting of NTN kidney homogenates revealed two bands for SCF, a 43-kDa band which decreased, and a 19-kDa band which increased throughout the study. Conclusion: These results highlight the potential role of SCF and its receptor in the remodelling process of the NTN kidney. Upregulation of SCF may involve a translational mechanism, with the soluble SCF protein KL-S1 (19 kDa) being derived from the transmembrane SCF protein KL-1 (43 kD) by proteolytic cleavage. The immunohistochemical staining of few CD34+ cells in NTN kidneys warrants further evaluation of the nature of these cells in the context of the inflammatory as well as the fibrotic processes.

Stem cell factor/c-kit signaling mediated cardiac stem cell migration via activation of p38 MAPK

It was reported that there are cardiac stem cells (CSCs) in the rat heart, and they could reconstitute well-differentiated myocardium that are formed by blood-carrying new vessels and myocytes. However, how do the CSCs migrate into the peri-infarcted areas after myocardial infarction (MI)? It remains entirely unknown about the signal transduction involved in the migration of CSCs. Rat heart MI was induced by left coronary artery ligation. Both immunohistochemical staining and Western blotting analysis was performed to detect the expression of SCF protein, and RT-PCR was conducted for the expression of SCF mRNA. Cardiac stem cells were isolated from rat hearts, and a cardiac stem cell migration assay was performed using a 48-well chemotaxis chamber system. On day 5 after MI in rats, the expression of stem cell factor (SCF) mRNA and protein was significantly increased in the peri-infarcted area, which was matched with more accumulation of CSCs in the region and improvement of cardiac function, which was blocked by p38 MAPK selective inhibitor SB203580. In in vitro experiments, SCF induced CSC migration in a concentration-dependent manner, and the antibody against SCF receptor (c-kit) blocked the SCF-induced CSC migration. Western blot analysis showed that the phosphorylated p38 MAPK (Phospho-p38 MAPK) was highly increased in the SCF-treated CSCs, and the inhibition of p38 MAPK activity significantly attenuated SCF-induced the migration of CSCs. It demonstrated that SCF/c-kit signaling may mediate the migration of CSCs via activation of p38 MAPK.

Requirement for p85α Regulatory Subunit of Class IA PI3Kinase and Rac2 GTPase in Myeloproliferative Disease Driven by Activation Loop Mutant of KIT.

Oncogenic activation-loop mutants of KIT, the receptor for stem cell factor (SCF), are commonly observed in acute myeloid leukemia (AML) and systemic mastocytosis (SM); however, unlike the KIT juxtamembrane mutants (found in patients with gastrointestinal stromal tumors [GISTs]), the activation-loop mutants are commonly insensitive to inhibition by tyrosine kinase inhibitors. Furthermore, little is known about the signaling pathways that contribute to oncogenic KIT-induced transformation in SM or AML. We demonstrate that expression of KITD814V (KIT activation-loop mutant) in primary hematopoietic stem and progenitor cells induces constitutive KIT autophosphorylation, promotes ligand-independent hyperproliferation, skews myeloid differentiation towards the granulocytic lineage, and promotes promiscuous cooperation with multiple cytokines, including G-CSF, M-CSF and IL-3. KITD814V expressing primary mast cells also demonstrated hyperproliferation in response to SCF, IL-3, IL-4 and IL-10. Biochemical analyses of KITD814V expressing cells revealed constitutively elevated levels of phosphatidylinositol-3-kinase (PI3K) and its downstream substrate, the Rho family GTPase Rac. Genetic disruption of p85a, the regulatory subunit of class IA PI-3Kinase, but not of p85β, or genetic disruption of the hematopoietic cell-specific Rho GTPase, Rac2, normalized KITD814V-induced ligand independent hyperproliferation in vitro. Additionally, deficiency of p85α or Rac2 corrected the promiscuous hyperproliferation observed in response to multiple cytokines in both KITD814V expressing stem/progenitor cells as well as mast cells in vitro. Although p85α is hyperphosphorylated and constitutively bound to KITD814V in bone marrow cells in vitro; its physiologic role in transformation in vivo is not known. To address this, we generated a new mouse model to study KITD814V induced transformation in myeloid cells as opposed to previously described models that primarily result in the generation of phenotypes resembling acute lymphocytic leukemia via this mutation. Our results show that transplantation of KITD814V expressing bone marrow cells from C57/BL6 strain of mice into syngeneic recipients results in a fatal myeloproliferative disease (MPD) characterized by leukocytosis, splenomegaly, disruption of the splenic architecture as well as myeloid cell infiltration in the lung and liver. Importantly, in this model, transplantation of KITD814V expressing p85α deficient bone marrow cells rescued the MPD phenotype, including splenomegaly, peripheral blood leukocytosis and the reduced life span associated with the transplantation of KITD814V expressing wildtype bone marrow cells. Treatment of KITD814V-expressing hematopoietic progenitors with either a Rac inhibitor (NC23766) or rapamycin showed a dose-dependent suppression in KITD814V induced growth. Taken together, our results describe the generation of a new murine transplant model to study KITD814V induced transformation and identify p85a and Rac2 as potential novel therapeutic target for the treatment of KITD814V-bearing diseases including SM and AML.

The Kinase Inhibitors Sunitinib (Sutent®) and Sorafenib (Nexavar®) Differentially Affect Reactivity of NK Cells Against Renal Cell Cancer.

Sunitinib (Sutent®) and Sorafenib (Nexavar®) are multikinase inhibitors licensed for the treatment of patients with advanced renal cell cancer (RCC) because of their direct and indirect anti-tumor and anti-angiogenic effects. Sunitinib and Sorafenib target, among others, vascular endothelial growth factor receptors (VEGFR), platelet-derived growth factor receptors (PDGFR), the stem cell factor receptor (cKIT) and Fms-like tyrosine kinase-3 (Flt3). Beyond that, Sorafenib additionally inhibits c-RAF and B-RAF. NK cells play an important role in the immune surveillance of tumors. Their reactivity is governed by different surface receptors leading to activation of various kinases, phosphatases and transcription factors. Up to now, nothing is known regarding the influence of Sunitinib and Sorafenib on NK cells. Here we report that Sunitinib and Sorafenib differentially affect NK cell cytotoxicity. Analysis of peripheral blood mononuclear cells from 10 independent donors revealed that Sorafenib but not Sunitinib significantly (p<0.05, Mann-Whitney U-test) reduced cell surface CD107a expression (about 50%) on NK cells as a surrogate marker for degranulation in response to tumor targets. In line, pharmacological levels of Sorafenib significantly (p<0.05, Mann-Whitney U-test) diminished cytotoxicity of primary NK cells against the RCC cell lines A498, ACHN and CAKI-2 (from 46% to 14%, from 52% to 22% and from 63% to 42%, respectively) in chromium release assays. Again, no inhibition of cytotoxicity was observed in the presence of pharmacological concentrations of Sunitinib. Since activation of MAP kinases leading to ERK phosphorylation regulates the movement of lytic granula towards target cells, which is responsible for NK cell cytotoxicity we investigated the influence of Sunitinib and Sorafenib on ERK phosphorylation. While Sunitinib had no effect, Sorafenib, alike the specific c-RAF inhibitor ZM336372 or the specific MEK inhibitor PD98059, markedly reduced ERK phosphorylation as determined by Western Blot. Our results indicate that NK cell anti-tumor reactivity is impaired by Sorafenib but not by Sunitinib due to the additional inhibitory effect of Sorafenib on the ERK pathway, which has been demonstrated to dictate NK cell cytotoxicity. We therefore conclude that Sunitinib is exquisitely suitable for combination with immunotherapeutic approaches in RCC patients.

Systemic Mastocytosis with c-KITD816V Mutation Treated with Dasatinib.

Objectives: Systemic mastocytosis (SM) is mainly a clonal disease with a variable clinical outcome. Prognosis is very much related to additional symptoms. If so called c-findings are present, survival is often limited to months. Until recently only Interferon and Cladribine could show some effect on the disease progression. With the introduction of Imatinib some hope grew to treat the disease by acting on c-KIT (CD 117; stem cell factor receptor). However, the substitution of valine for aspartic acid at position 816 in c-KIT (D816V) leads to prolonged mast cell survival and increased proliferation because of constitutive activation of the tyrosine kinase of c-KIT. Between 31% and 100% of patients with SM harbour the c-KIT D816V mutation which is invariably related to Imatinib resistance. Fortunately, the new tyrosinkinase inhibitor Dasatinib (BMS-354825) could show a much higher inhibition of the c-KIT D816V mutated receptor in vitro. Therefore we treated a patient with systemic mastocytosis with associated hematologic clonal non mast cell lineage disease (SM-AHNMD) and c-findings with Dasatinib.Case description: A 69 year old patient was diagnosed 5 years ago with cutaneous mastocytosis. Because of a markedly increased tryptase levels of 130μg/l he was referred to our clinic for further investigation. In a bone marrow biopsy, the classical signs of SM could be found together with a chronic myelomonocytic leukemia (CMML) without any cytogenetic alterations. During 2 years the patient remained clinically stable without any treatment. Subsequently the patient droped weight and got strong lumbar pain. A MRI scan revealed fractures of L2 and L4 without signs for osteoporosis. Additionally, splenomegaly and hepatomegaly have been noticed with enlarged lymph nodes in the retroperitoneal space together with profound thrombocytopenia. Even SM-AHNMD is by definition of the ‘year 2000 Working Conference on Mastocytosis' a distinct entity, the occurring c-findings together with a rapid increase in tryptase levels have been associated with an aggressive disease course. A c-KIT mutation analysis showed a D816V mutation. We decided after approval from the medical council to start the patient on Dasatinib. We started with 50mg daily for 3 days. Because no signs of acute mastcell degranulation we increased the dose to 50mg BID and continued the treatment for 13 weeks. Due to non-hematologic toxicity (fatigue) Dasatinib had to be stopped. Hepatosplenomegaly remained stable, lumbar pain disappeared even after cessation of analgetic therapy and weight increased gradually. However, laboratory follow up (tryptase, soluble interleukin 2 receptor) showed inconsistent results.Conclusion: Our patient with SM-CMML had many signs of systemic aggressive mastocytosis which is a mostly fatal variant of SM. With the introduction of Imatinib, a potent c-kit inhibitor, a novel approach to inhibit mastcell-proliferation was described. However, the most common mutation in CD117 of mastcells (D816V mutation) turned out to be resistant to Imatinib. However, Dasatinib a recently introduced tyrosinkinase inhibitor showed significant efficacy in vitro. A phase II study of Dasatinib in patients with Philadelphia-negative myeloproliferative disorders, including SM has recently been presented by Verstovsek and colleagues showing an overall response rate of 42% in SM. However, these patients were c-KIT mutation negative. This case report shows first evidence of clinical activity of Dasatinib in a patient with systemic aggressive mastocytosis harbouring the c-KIT mutation D816V. Further clinical studies in this patient population are warranted.

Functional Interaction of c-Kit Receptor and Interleukin-3 Receptor.

Hematopoiesis is regulated by a number of growth factors and cytokines, among which stem cell factor (SCF) plays a critical role for normal hematopoiesis. An important feature of SCF is its strong capacity to synergize with the cytokines including interleukin-3(IL-3), granulocyte-marcrophage colony-stimulation factor (GM-CSF) and erythropoietin to regulate proliferation and differentiations of hematopoietic progenitor cells. The mouse hematopoietic progenitor cell line EML contains two populations of lineage negative cells, distinguished by the expression or absence of CD34. The two sub-populations express similar levels of the SCF receptor c-kit, but only the CD34+ population replicates in the presence of SCF alone, while the CD34 negative population replicates in the presence of IL3 but this replication is synergistically stimulated by the addition of SCF. Our previous studies indicated that synergistic proliferation of the mouse hematopoietic progenitor cell line EML induced by SCF in combination with IL-3 was probably mediated by the synergistic increases in tyrosine phosphorylation of c-Kit and β-chain of IL-3 receptor, which is shared with GM-CSF receptor and interleukin-5 receptor. Conversely, the decreased response of c-kit to SCF alone in the CD34 negative population may be a result of the increased expression of IL3 receptor in these cells. Trans-phosphorylation between c-Kit and the β-chain of IL-3 receptor was also observed in EML cells. In studies of the molecular mechanism behind the functional interactions between SCF and IL-3 we found that c-Kit and IL-3 receptor β-chain form a complex in EML cells. Antibody Ab-1 specific against the Ig-like domain 4 in the extracellular region of c-Kit blocked not only cell proliferation induced by SCF but also synergistic proliferation induced by SCF plus IL-3. Consistent with this finding, Ab-1 inhibited phosphorylation of c-Kit induced by SCF or IL-3, and synergistic phosphorylation of c-kit induced by SCF plus IL-3 respectively. SCF and IL-3 in combination synergistically activated the protein kinases Akt and Erks, the downstream mediators of c-Kit and IL-3R. Phosphorylation of Erks is independent on the phosphatidylinositol 3-kinase (PI3-kinase) pathway in EML cells. These data suggested the possibility that the synergistic growth of EML cells induced by SCF in combination with IL-3 was mediated by multiple mechanisms that could include trans- and synergistic phosphorylation of c-Kit and the β-chain of IL-3 receptor, PI3-kinase dependent synergistic phosphorylation of Akt and PI3-kinase independent synergistic phosphorylation of Erks. The trans- and synergistic phosphorylation of c-Kit and β-chain of IL-3 receptor was mediated by physical interaction of two receptors.

Stem cell factor and mesenchymal and neural stem cell transplantation in a rat model of Huntington's disease

Neural and mesenchymal stem cells have been proposed as alternative sources of cells for transplantation into the brain in neurodegenerative disorders. However, the endogenous factors controlling their engraftment within the injured parenchyma remain ill-defined. Here, we demonstrate significant engraftment of undifferentiated exogenous mesenchymal or neural stem cells throughout the lesioned area in a rat model for Huntington's disease, as late as 8 weeks post-transplantation. We show that stem cell factor (SCF), strongly up-regulated within host cells in the damaged striatum, is able to activate the SCF receptor c-kit and its signaling pathway and to promote the migration and proliferation of mesenchymal and neural stem cells in vitro. Furthermore, c-kit receptor blockade alters neural stem cell distribution within the lesioned striatum. Host SCF expression is observed in atypical cells expressing glial fibrillary acidic protein and doublecortin in the lesioned striatum and in migrating doublecortin-positive progenitors. Taken together, these data demonstrate that SCF produced in situ in the lesioned striatum is an important factor in promoting the engraftment of stem cells within the lesioned brain.

A preclinical review of sunitinib, a multitargeted receptor tyrosine kinase inhibitor with anti-angiogenic and antitumour activities

Sunitinib malate is an oral, multitargeted tyrosine kinase inhibitor that targets both angiogenic pathways (i.e., vascular endothelial growth factor receptor and platelet-derived growth factor receptor) and direct pro-oncogenic pathways (e.g., stem-cell factor receptor and FMS-like tyrosine kinase-3). Preclinical studies with this agent have indicated that it exhibits robust inhibitory activity against these targets. Clinical trial results have demonstrated the therapeutic potential of this agent and have implicated sunitinib targets in the pathophysiology of malignancies such as renal cell carcinoma and gastrointestinal stromal tumour. This paper reviews the preclinical data supporting the development of this agent and its translation from benchtop to bedside. It also highlights the importance of the multiple pathways that may be involved in cancer progression and the importance of these pathways in selected malignancies.

The Early Growth Response Factor-1 Is Involved in Stem Cell Factor (SCF)-induced Interleukin 13 Production by Mast Cells, but Is Dispensable for SCF-dependent Mast Cell Growth

The stem cell factor (SCF) plays a central role in the regulation of mast cell function and growth. However, roles of transcription factors involved in these processes remain incompletely defined. The early growth response factor-1 (Egr-1) is a member of the zinc finger transcription factor family. A role for Egr-1 in SCF-induced mast cell activation and growth was investigated in mouse bone marrow-derived mast cells (BMMC). The stimulation of BMMC with SCF induced a strong expression of Egr-1 mRNA. SCF-induced Egr-1 nuclear translocation and DNA binding were demonstrated by electrophoretic mobility shift assay (EMSA) and immunofluorescence assay. SCF-induced IL-13 expression was significantly reduced at both mRNA and protein levels in Egr-1-deficient BMMC. In addition, the synergy between IgE and SCF on IL-13 and IL-4 production was reduced in Egr-1-deficient mast cells. Interestingly, Egr-1 deficiency had little effect on SCF-induced mast cell growth. SCF-induced Egr activation likely requires tyrosine phosphorylation because a tyrosine kinase inhibitor PP2 blocked SCF-induced nuclear protein binding to Egr probe as determined by EMSA. Thus, Egr-1 is required for SCF-induced IL-13 expression, but not mast cell growth. Egr-1 represents a novel mechanism for SCF-induced mast cell activation.