Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0002871 (anemia)
 52,094 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Erythropoietin (Epo)-independent differentiation of erythroid progenitors is a major characteristic of myeloproliferative disorders, including chronic myeloid leukemia. Epo receptor (EpoR) signaling is crucial for normal erythroid development, as evidenced by the properties of Epo(-/-) and EpoR(-/-) mice, which contain a normal number of fetal liver erythroid progenitors but die in utero from a severe anemia attributable to the absence of red cell maturation. Here we show that two constitutively active cytoplasmic protein tyrosine kinases, P210(BCR-ABL) and v-SRC, can functionally replace the EpoR and support full proliferation, differentiation, and maturation of fetal liver erythroid progenitors from EpoR(-/-) mice. These protein tyrosine kinases can also partially complement the myeloid growth factors IL-3, IL-6, and Steel factor, which are normally required in addition to Epo for erythroid development. Additionally, BCR-ABL mutants that lack residues necessary for transformation of fibroblasts or bone marrow cells can fully support normal erythroid development. These results demonstrate that activated tyrosine kinase oncoproteins implicated in tumorigenesis and human leukemia can functionally complement for cytokine receptor signaling pathways to support normal erythropoiesis in EpoR-deficient cells. Moreover, terminal differentiation of erythroid cells requires generic signals provided by activated protein tyrosine kinases and does not require a specific signal unique to a cytokine receptor.
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PMID:BCR-ABL and v-SRC tyrosine kinase oncoproteins support normal erythroid development in erythropoietin receptor-deficient progenitor cells. 1055 95

P210 Bcr-Abl is an activated tyrosine kinase oncogene encoded by the Philadelphia chromosome associated with human chronic myelogenous leukemia (CML). The disease represents a clonal disorder arising in the pluripotent hematopoietic stem cell. During the chronic phase, patients present with a dramatic expansion of myeloid cells and a mild anemia. Retroviral gene transfer and transgenic expression in rodents have demonstrated the ability of Bcr-Abl to induce various types of leukemia. However, study of human CML or rodent models has not determined the direct and immediate effects of Bcr-Abl on hematopoietic cells from those requiring secondary genetic or epigenetic changes selected during the pathogenic process. We utilized tetracycline-regulated expression of Bcr-Abl from a promoter engineered for robust expression in primitive stem cells through multilineage blood cell development in combination with the in vitro differentiation of embryonal stem cells into hematopoietic elements. Our results demonstrate that Bcr-Abl expression alone is sufficient to increase the number of multipotent and myeloid lineage committed progenitors in a dose-dependent manner while suppressing the development of committed erythroid progenitors. These effects are reversible upon extinguishing Bcr-Abl expression. These findings are consistent with Bcr-Abl being the sole genetic change needed for the establishment of the chronic phase of CML and provide a powerful system for the analysis of any genetic change that alters cell growth and lineage choices of the hematopoietic stem cell.
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PMID:Regulated expression of P210 Bcr-Abl during embryonic stem cell differentiation stimulates multipotential progenitor expansion and myeloid cell fate. 1067 27

The first case of B-cell lymphoma of brain in a patient with myelodysplastic syndrome (MDS) was reported. A 68-year-old man was admitted because of anemia, fever, and thrombocytopenia and was diagnosed as having MDS (refractory anemia with excess of blasts) on the basis of the findings of bone marrow aspiration and chromosomal analysis. The patient was followed up without chemotherapy, but a brain tumor appeared after 3 years. Histologic and immunohistologic examinations revealed diffuse large B-cell lymphoma. Mutations of the c-kit proto-oncogene (stem cell factor receptor) and the p53 tumor-suppressor gene were examined in the MDS lesion and malignant lymphoma (ML) by the polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) method followed by direct sequencing. The p53 mutation was not found in either MDS or ML, but a nonsense mutation (Try-557 --> stop) in exon 11 of the c-kit, which might lead to dysfunction of tyrosine kinase activity, was detected in MDS. This is the first report of c-kit mutation in MDS. Epstein-Barr virus (EBV) genome was demonstrated in the nucleus of brain ML cells by in situ hybridization with EBV-encoded RNA-1 probe. Immunohistochemistry showed that the tumor cells expressed latent infection gene products, including EBV nuclear antigen-2 and latent membrane protein-1. This pattern of latent gene expression was Lat III, which is usually found in malignant lymphomas developing in immunocompromised hosts. These findings suggest that a profound pancytopenia in MDS resulted in an immunodeficient condition, after which EBV-positive B-cell lymphoma of brain developed.
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PMID:Epstein-Barr virus associated B-cell lymphoma of brain developing in myelodysplastic syndrome with c-kit mutation (Try-557 -->stop). 1107 41

BCR/ABL, the oncoprotein responsible for chronic myeloid leukemia (CML), transforms hematopoietic cells through both Ras-dependent and -independent mechanisms. Farnesyl protein transferase inhibitors (FTIs) were designed to block mutant Ras signaling, but they also inhibit the growth of transformed cells with wild-type Ras, implying that other farnesylated targets contribute to FTI action. In the current study, the clinical candidate FTI SCH66336 was characterized for its ability to inhibit BCR/ABL transformation. When tested against BCR/ABL-BaF3 cells, a murine cell line that is leukemogenic in mice, SCH66336 potently inhibited soft agar colony formation, slowed proliferation, and sensitized cells to apoptotic stimuli. Quantification of activated guanosine triphosphate (GTP)-bound Ras protein and electrophoretic mobility shift assays for AP-1 DNA binding showed that Ras effector pathways are inhibited by SCH66336. However, SCH66336 was more inhibitory than dominant-negative Ras in assays of soft agar colony formation and cell proliferation, suggesting activity against targets other than Ras. Cell cycle analysis of BCR/ABL-BaF3 cells treated with SCH66336 revealed G2/M blockade, consistent with recent reports that centromeric proteins that regulate the G2/M checkpoint are critical farnesylated targets of FTI action. Mice injected intravenously with BCR/ABL-BaF3 cells developed acute leukemia and died within 4 weeks with massive splenomegaly, elevated white blood cell counts, and anemia. In contrast, nearly all mice treated with SCH66336 survived and have remained disease-free for more than a year. Furthermore, SCH66336 selectively inhibited the hematopoietic colony formation of primary human CML cells. As an oral, nontoxic compound with a mechanism of action distinct from that of ABL tyrosine kinase inhibition, FTI SCH66336 shows promise for the treatment of BCR/ABL-induced leukemia.
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PMID:Activity of the farnesyl protein transferase inhibitor SCH66336 against BCR/ABL-induced murine leukemia and primary cells from patients with chronic myeloid leukemia. 1122 87

The receptor-associated protein tyrosine kinase janus-kinase 2 (JAK2) is essential for normal red cell development and for erythropoietin receptor (EpoR) signaling. JAK2(-/-) embryos are severely deficient in erythropoiesis and die at an early stage of development from fetal anemia. The binding of erythropoietin (Epo) to the EpoR triggers the activation of JAK2, the phosphorylation of the EpoR, and the initiation of the EpoR signaling cascade. In addition to Epo binding to its receptor, signaling pathways downstream of the EpoR can also be stimulated by the BCR-ABL oncoprotein. This study explored whether JAK2 is required for BCR-ABL-mediated stimulation of erythropoiesis. Here, it is shown that JAK2 is constitutively tyrosine phosphorylated in cultured and primary erythroid cells expressing BCR-ABL. However, BCR-ABL effectively supports normal erythroid proliferation, differentiation, and maturation in JAK2-deficient fetal liver cells. Using mutants of BCR-ABL, this study shows that certain signaling pathways activated by BCR-ABL segments distinct from its tyrosine kinase domain are essential for rescue of erythropoiesis in JAK2(-/-) progenitors. The consequences of these multiple signaling pathways for normal erythroid development are discussed.
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PMID:Erythropoiesis in the absence of janus-kinase 2: BCR-ABL induces red cell formation in JAK2(-/-) hematopoietic progenitors. 1169 76

Erythropoietin, in its standard role for the treatment of anemia, is often mechanistically regarded simply as increasing blood oxygen-carrying capacity and hence decreasing tumor hypoxia. In reality, erythropoietin (a member of the cytokine superfamily) is expressed in a multitude of tissues/cell types including erythroid and cancer cells, and the liver and central nervous system. Erythropoietin expression is induced by hypoxia-inducible factor-1, which itself is induced during hypoxia. Whereas it has no endogenous tyrosine kinase activity of its own, erythropoietin, via constitutively associated JAK2, can activate several signaling pathways including STAT5, RAS, and phosphoinositol 3-kinase. An increased understanding of these pathways is already opening up new clinical indications, particularly in terms of oncology and neurology. Current arrays/molecular endpoint studies in clinical trials should identify key components of the particular signaling pathways that will guide further use in the development of both better synergistic therapies as well as new molecular targets.
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PMID:Evidence for erythropoietin as a molecular targeting agent. 1213 9

This minireview is an update of a 1997 review on erythropoietin (EPO) in this journal. EPO is a 30,400-dalton glycoprotein that regulates red cell production. In the human, EPO is produced by peritubular cells in the kidneys of the adult and in hepatocytes in the fetus. Small amounts of extra-renal EPO are produced by the liver in adult human subjects. EPO binds to an erythroid progenitor cell surface receptor that includes a p66 chain, and, when activated, the p66 protein becomes dimerized. EPO receptor activation induces a JAK2 tyrosine kinase, which leads to tyrosine phosphorylation of the EPO receptor and several proteins. EPO receptor binding leads to intracellular activation of the Ras/mitogen-activated kinase pathway, which is involved with cell proliferation, phosphatidylinositol 3-kinase, and STATS 1, 3, 5A, and 5B transcriptional factors. EPO acts primarily to rescue erythroid cells from apoptosis (programmed cell death) to increase their survival. EPO acts synergistically with several growth factors (SCF, GM-CSF, 1L-3, and IGF-1) to cause maturation and proliferation of erythroid progenitor cells (primarily colony-forming unit-E). Oxygen-dependent regulation of EPO gene expression is postulated to be controlled by a hypoxia-inducible transcription factor (HIF-1alpha). Hypoxia-inducible EPO production is controlled by a 50-bp hypoxia-inducible enhancer that is approximately 120 bp 3' to the polyadenylation site. Hypoxia signal transduction pathways involve kinases A and C, phospholipase A(2), and transcription factors ATF-1 and CREB-1. A model has been proposed for adenosine activation of EPO production that involves protein kinases A and C and the phospholipase A(2) pathway. Other effects of EPO include a hematocrit-independent, vasoconstriction-dependent hypertension, increased endothelin production, upregulation of tissue renin, change in vascular tissue prostaglandins production, stimulation of angiogenesis, and stimulation of endothelial and vascular smooth muscle cell proliferation. Recombinant human EPO (rHuEPO) is currently being used to treat patients with anemias associated with chronic renal failure, AIDS patients with anemia due to treatment with zidovudine, nonmyeloid malignancies in patients treated with chemotherapeutic agents, perioperative surgical patients, and autologous blood donation. A novel erythropoiesis-stimulating factor (NESP, darbepoetin) has been synthesized and when compared with rHuEPO, NESP has a higher carbohydrate content (52% vs 40%), a longer plasma half-life, the amino acid sequence differs from that of native human EPO at five positions, and has been reported to maintain hemoglobin levels just as effectively in patients with chronic renal failure as rHuEPO at less frequent dosing. The use of rHuEPO and darbepoetin to enhance athletic performance is officially banned by most sports-governing bodies because the excessive erythrocytosis can lead to increased thrombogenicity and can cause deep vein, coronary, and cerebral thromboses.
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PMID:Erythropoietin: physiology and pharmacology update. 1252 67

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is an essential cascade for mediating normal functions of different cytokines in the development of the hematopoietic and immune systems. Chronic exposure to arsenic has been found to cause immunotoxicity and has been associated with the suppression of hematopoiesis (anemia and leukopenia). Here, we report the novel finding of arsenic-mediated inactivation of the JAK-STAT signaling pathway by its direct interaction with JAK tyrosine kinase. Pretreatment with sodium arsenite strongly inhibited IL-6-inducible STAT3 tyrosine phosphorylation in HepG2 cells and did not affect its serine phosphorylation. As a result, sodium arsenite completely abolished STAT activity-dependent expression of suppressors of cytokine signaling (SOCS). Both cellular and subcelluar experiments showed that the inhibition of JAK-STAT signaling resulted from JAK tyrosine kinase's direct interaction with arsenite, and that arsenic's suppression of JAK tyrosine kinase activity also occurred in the interferon gamma (IFNgamma) pathway. The ligand-independent inhibition by arsenic indicates that JAK was the direct target of arsenic action. Other inflammatory stimulants, stress agents, and metal cadmium failed to induce similar effects on the tyrosine phosphorylation of STAT3 as arsenic does. Our experiments also revealed that arsenic inactivation of the JAK-STAT pathway occurred independent of arsenic activation of MAP kinases. Taken together, our findings indicate that arsenic directly inhibits JAK tyrosine kinase activity and suggest that this direct interference in the JAK-STAT pathway may play a role in arsenic-associated pathogenesis.
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PMID:Arsenic inhibition of the JAK-STAT pathway. 1511 95

In vitro studies have implicated the Lyn tyrosine kinase in erythropoietin signaling. In this study, we show that J2E erythroid cells lacking Lyn have impaired signaling and reduced levels of transcription factors STAT5a, EKLF and GATA-1. Since mice lacking STAT5, EKLF or GATA-1 have red cell abnormalities, this study also examined the erythroid compartment of Lyn(-/-) mice. Significantly, STAT5, EKLF and GATA-1 levels were appreciably lower in Lyn(-/-) erythroblasts, and the phenotype of Lyn(-/-) animals was remarkably similar to GATA-1(low) animals. Although young adult Lyn-deficient mice had normal hematocrits, older mice developed anemia. Grossly enlarged erythroblasts and florid erythrophagocytosis were detected in the bone marrow of mice lacking Lyn. Markedly elevated erythroid progenitors and precursor levels were observed in the spleens, but not bone marrow, of Lyn(-/-) animals indicating that extramedullary erythropoiesis was occurring. These data indicate that Lyn(-/-) mice display extramedullary stress erythropoiesis to compensate for intrinsic and extrinsic erythroid defects.
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PMID:Lyn deficiency reduces GATA-1, EKLF and STAT5, and induces extramedullary stress erythropoiesis. 1551 74

The Fps/Fes tyrosine kinase has been implicated in the regulation of hematopoiesis and inflammation. Mice expressing an activated variant of Fps/Fes (MFps) encoded by a gain-of-function mutant transgenic fps/fes allele (fps(MF)) exhibited hematological phenotypes, which suggested that Fps/Fes can direct hematopoietic lineage output. These mice also displayed marked hypervascularity and multifocal-hemangiomas which implicated this kinase in the regulation of angiogenesis. Here we explored the potential involvement of Fps/Fes in the regulation of hemostasis through effects on blood cells and the vascular endothelium. Hematological parameters of fps(MF) mice were characterized by peripheral blood analysis, histology, and transmission electron microscopy. Hemostasis parameters and platelet functions were assessed by flow cytometry and measurements of activated partial thromboplastin time, prothrombin time, thrombin clot time, platelet aggregation, bleeding times and in vitro fibrinolytic assays. Hematological and morphological analyses showed that fps(MF) mice displayed mild thrombocytopenia, anemia, red cell abnormalities and numerous hemostatic defects, including hypofibrinogenemia, hyper-fibrinolysis, impaired whole blood aggregation and a mild bleeding diathesis. fps(MF) mice displayed a complex array of hemostatic perturbations which are reminiscent of hemostatic disorders such as disseminated intravascular coagulation (DIC) and of hemangioma-associated pathologies such as Kasabach-Merritt phenomenon (KMS). These studies suggest that Fps/Fes influences both angiogenic and hemostatic function through regulatory effects on the endothelium.
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PMID:Hemostatic and hematological abnormalities in gain-of-function fps/fes transgenic mice are associated with the angiogenic phenotype. 1555 33


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