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Query: UMLS:C0002871 (anemia)
 52,094 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have investigated whether Signal Transducing and Activators of Transcription (STAT) proteins become activated following the binding of erythropoietin (EPO) to immature erythroid cells from the spleens of mice infected with the anemia strain of Friend virus. STAT1 and STAT5 proteins are phosphorylated and translocated to the nucleus in EPO-treated cells. STAT1 and STAT5 DNA binding activities were also activated in an EPO-dependent manner. The presence of these STAT proteins in the DNA binding complex was confirmed by Western blot analysis of the proteins bound to the DNA element in the gel mobility shift assays. This EPO-dependent activation of STAT proteins was maximum within 10 min of exposure of the cells to 10 units of EPO/ml, the concentration of EPO required for maximum STAT activation. The magnitude of the EPO-dependent STAT5 activation appeared to be greater than the EPO-dependent activation of STAT1. The significance of STAT protein activation in EPO signal transduction is discussed.
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PMID:Erythropoietin induces the tyrosine phosphorylation, nuclear translocation, and DNA binding of STAT1 and STAT5 in erythroid cells. 853 96

The purpose of this review is to give an update of the recent progress in research on erythropoietin (Epo), the hormone that regulates red blood cell production. Epo is a glycoprotein with a molecular mass of approx 30 kDa, which circulates in plasma of the human with 165 amino acids with three N-linked and one O-linked acidic oligosaccharide side chains in the molecule. Both the alpha (39% CHO) and beta (24% CHO) forms are available for clinical use, and there does not appear to be any difference in the pharmacokinetics of these two forms of Epo. Radioimmunoassays and enzyme-linked immunoabsorbant (ELISA) assays are available in a kit form. Serum levels of Epo in normal human subjects range between 1 and 27 mmu/ml or approx 5 pmol/l. It seems clear that the cells in the adult mammalian kidney which produce Epo are the interstitial cells in the peritubular capillary bed and the perivenous hepatocytes in the liver. Expression of the human Epo gene sequences that direct expression in the kidney are located 6-14 kilobases 5' to the gene; whereas the sequences that control hepatocyte-specific expression are located within 0.7 KS to the 3'-flanking region and 0.5 KS to the 5'-flanking region. The signal transduction pathways postulated to be involved in the expression of Epo are: kinases A, G and C; both a constitutive factor and a second hypoxia-inducible factor-1 (HIF-1) located in the 5' end of an hypoxia inducible enhancer region of the Epo gene; and reactive oxygen species. The primary target cell in the bone marrow acted on by Epo is the colony-forming unit erythroid (CFU-E) which has the highest number of Epo receptors. It has been postulated that Epo decreases the rate which Epo-dependent progenitor cells undergo programed cell death (apoptosis). There are two major signal transduction pathways activated by the Epo receptor: the JAK2-STAT5 pathway and the ras pathway. Both pathways involve tyrosine phosphorylation. The approved clinical uses of Epo are the anemias associated with end-stage renal disease, cancer chemotherapeutic agents, and patients with HIV infection receiving AZT. Other anemias reported to respond to Epo therapy are anemia of prematurity, rheumatoid arthritis, and myelodysplasia. Other uses of Epo under investigation are in perioperative surgery and preoperative autologous blood donation.
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PMID:Erythropoietin: physiologic and pharmacologic aspects. 940 40

Erythropoietin (EPO) is the major regulator of mammalian erythropoisis, which stimulates the growth and differentiation of hematopoietic cells through interaction with its receptor (EPO-R). Here we use HEL cells (a human erythro-leukemia cell line) as a model to elucidate the pathway of signal transduction in the EPO-induced HEL cells. Our data show that the EPOR (EPO receptor) on the surface of HEL cells interacts with the Janus tyrosine protein kinase (Jak2) to transduce intracellular signals through phosphorylation of cytoplasmic proteins in EPO-treated HEL cells. Both STAT1 and STAT5 in this cell line are tyrosine-phosphorylated and translocated to nucleus following the binding of EPO to HEL cells. Furthermore, the binding of both STAT1 and STAT5 proteins to specific DNA elements (SIE and PIE elements) is revealed in an EPO-dependent manner. Our data demonstrate that the pathway of signal transduction following the binding of EPO to HEL cells is similar to immature erythroid cell from the spleen of mice infected with anemia strain of Friend virus.
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PMID:STAT1 is involved in signal transduction in the EPO induced HEL cells. 966 26

ERYTHROPOIETIN (EPO): Erythropoietin (EPO) is a hormone that promotes the proliferation and differentiation of erythroid progenitor cells and regulates the number of erythrocytes in peripheral blood. EPO is produced mainly by the kidneys, and transcription of the EPO gene is promoted by a reduction in the oxygen concentration in the blood. The existence of EPO was suggested near the end of the 19th century by the discovery that hypoxia increases the production of red blood cells. EPO was identified as a serum factor in the 1950s, and in 1970 Miyake and coworkers succeeded in purifying it by using the urine of patients with aplastic anemia as a starting material. The human EPO gene was cloned in 1985 using a partial amino acid sequence from this purified EPO, and it is well known that recombinant EPO is currently used as a drug to treat anemia associated with chronic renal failure and other illnesses. ACTION OF EPO: When human bone marrow cells are cultured in a semisolid medium containing EPO, they form small erythroblast colonies in five to seven days, and by day 10 large erythroblast colonies appear that resemble fireworks ("burst" colonies). The original cells in the former colonies are called colony forming units-erythroid (CFU-E) or late-stage erythroblast progenitor cells and in the latter colonies they are called burst forming units-erythroid (BFU-E) or early-stage erythroblast progenitor cells. As shown in Figure 1, red blood cells are produced through differentiation from stem cells to BFU-E, CFU-E, and erythroblasts. Although EPO acts on both BFU-E and CFU-E cells, CFU-E cells show greater sensitivity to EPO, and other factors such as stem cell factor (SCF), interleukin (IL)-3, IL-4, and granulocyte macrophage colony-stimulating factor (GM-CSF) must be present together with EPO for BFU-E cell proliferation. In erythroblasts beyond the CFU-E stage, sensitivity to EPO decreases as the cells mature. THE EPO RECEPTOR AND THE CYTOKINE RECEPTOR FAMILY: The EPO receptor gene was cloned by D'Andrea and coworkers in 1989 from murine erythroleukemia cells [1]. It became clear that the EPO receptor belongs to the cytokine receptor family that comprises receptors for the various interleukins, GM-CSF, granulocyte colony-stimulating factor (G-CSF), growth hormone and prolactin. The special characteristic of this family of receptors is that they are switched on (i.e., the receptor is activated) and transduce signals to the interior of the cell by the formation of homo- or hetero-oligomers (dimers or trimers). Moreover, hetero-oligomers of these receptors share a common receptor subunit. As shown in Figure 2, the IL-3, IL-5 and GM-CSF receptors have a common &bgr; subunit, and their ligand specificity is determined by the &agr; subunit. In the same manner, the IL-6, LIF and oncostatin M (OSM) receptors all share gp130, which is the &bgr; subunit of the IL-6 receptor. The IL-2, IL-4 and IL-7 receptors all share the &ggr; subunit of the IL-2 receptor. All the above receptors are activated by the formation of hetero-oligomers, but the G-CSF receptor, EPO receptor, and growth hormone receptor are activated by the formation of homodimers of the same types of molecules [2]. We can see that groups of cytokines such as the interleukins that affect a relatively wide range of cells and have redundant biological activity create this redundancy through the common use of a single receptor subunit. On the other hand, EPO and G-CSF act with high specificity on a relatively limited range of cells, so it was probably unnecessary for their receptors to share one of the subunits. EPO RECEPTOR AND JAK2 KINASE: The signal for cellular proliferation and differentiation into erythroblasts is thought to originate at the EPO receptor. The cytoplasmic domain of the EPO receptor can be divided into two major regions. Roughly half of the cytoplasmic domain, the part lying nearest the plasma membrane, is required for generating the signals for proliferation and differentiation such as the induction of globin synthesis [3, 4]. The remaining half is not required for this signaling, and, conversely, it acts to dampen the signals. It is known that a tyrosine kinase called JAK2 associates with the region near the plasma membrane, undergoes autophosphorylation, and phosphorylates the EPO receptor, and a transcription factor called a STAT [5]. It is thought that JAK2 plays an important role in promoting cellular proliferation. The STAT is activated by the phosphorylation, and it then translocates to the nucleus, recognizes a specific base sequence in the promoter region of its target gene, and initiates transcription. At present, we know that the STAT whose activation is mediated by the EPO receptor is STAT5, and the target genes are CIS [6], which has an SH2 domain (a molecular structure that recognizes a phosphorylated tyrosine) and OSM [7], which is a pleiotropic cytokine. However, activation of STAT5 and activation of the target genes are not unique to the EPO receptor, and they also occur with the IL-2 and IL-3 receptors. Moreover, the JAK2 substrate that is directly linked to cellular proliferation is still unknown. At present, studies are under way to determine the transcription factors specific to EPO and their target genes, as well as the substrates of JAK2. RECEPTOR PHOSPHORYLATION AND CESSATION OF THE SIGNAL: On the other hand, tyrosine phosphorylation of the receptor is necessary at the cytoplasmic tail region far from the plasma membrane, and the signal transduction pathway that originates with this phosphorylated tyrosine and is mediated by proteins with SH2 domains becomes activated. First, a GTP/GDP exchange factor called SOS, which is mediated by Shc and Grb2, migrates to the plasma membrane and converts a ras protein to its GTP form. The activated ras protein then activates the Raf-MAP kinase kinase-MAP kinase cascade, and ultimately initiates the transcription of oncogenes such as c-fos and c-jun. An enzyme called PI3 kinase binds to the tyrosine phosphorylation site of the receptor and a second messenger is born. It is known that this pathway is a requirement for DNA synthesis in certain types of fibroblasts. However, these signal transduction pathways are not unique to the EPO receptor, and they are also activated by most growth factor receptors, so they are not necessarily required for EPO-induced proliferation. Conversely, the tyrosine phosphatase SH-PTP1 (also called HCP) that has an SH2 domain and is specific to blood cells associates with the tyrosine phosphorylation site of the receptor and promotes the dephosphorylation of JAK2. In other words, the role of SH-PTP1 is to stop generation of the signal [8]. Therefore, in mutations lacking this cytoplasmic tail region of the receptor far from the plasma membrane, the receptors do not undergo tyrosine phosphorylation, JAK2 activation continues for a longer period of time, and thus the signal is generated more efficiently. In fact, in one patient with a mild case of familial erythrocytosis a mutation was discovered in which the C-terminus of the EPO receptor was missing 70 amino acids [9]. This was a dominant genetic trait, and the patient's erythroblasts showed an increased sensitivity to EPO. In this family the impairment was not severe enough to be called an illness, and in fact it is said that this patient was proficient enough athletically to compete for a gold medal at the Olympics. More specifically, the reason that athletes undergo training at high altitudes is to boost EPO production because of the lower oxygen partial pressure, and this brings about the desired effect of sustained athletic capability due to a resultant increase in red blood cells. However, the same effect has occurred naturally in this athlete thanks to accelerated receptor capability.
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PMID:Physician Education: The Erythropoietin Receptor and Signal Transduction. 1038 12

Erythropoietin (EPO) is the primary regulator of erythropoiesis, and promotes the survival, proliferation, and differentiation of erythroid progenitor cells. The EPO receptor belongs to the same family of receptors as growth hormone, granulocyte-colony stimulating factor, granulocyte macrophage-colony stimulating factor, and some interleukins. In the erythropoietic process, EPO induces homodimerization of the EPO receptor, which is located on the surface of erythroid progenitor cells. Dimerization activates the receptor-associated Janus kinase 2 via transphosphorylation. Specific tyrosines in the intracellular portion of the receptor are phosphorylated and serve as a docking site for intracellular proteins, including one of the signal transducers and activators of transcription (STAT5). This results in activating various cascades of signal transduction. STAT5 enters the nucleus on phosphorylation, inducing the transcription of erythroid genes. Phosphatases dephosphorylate Janus kinase 2 and downregulate the EPO receptor. Erythropoietin receptor activation seems to exert its effect by inhibiting apoptosis rather than by affecting the commitment of erythroid lineage, although the mechanism by which this occurs is as yet unclear. Anemia in cancer is associated with excessive production of cytokines that inhibit EPO synthesis, thereby interfering with the normal erythropoietic process, which leads to a reduction in red blood cells and the ability to oxygenate tissue.
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PMID:The erythropoietin receptor. 1139 48

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

Erythropoietin (EPO) activates many distinct signal transduction cascades on engagement of its receptor. Deletion of the EPO, EPO receptor (EPO-R), or JAK2 genes in mice results in embryonic lethality due to a fatal anemia. EPO activates signal transducer and activator of transcription 1 (STAT1), STAT3, and STAT5a/b transcription factors in erythroid cell lines. Studies have focused on STAT5 as the primary target of EPO-dependent JAK2 activation. However, STAT5a/b(-/-) mice are viable, displaying a nonfatal anemia during embryogenesis, and delayed differentiation in adult erythropoiesis. Importantly, EPO-R cytoplasmic tyrosines are dispensable for viability in vivo. Interestingly, no cytoplasmic tyrosines are required for phosphorylation of STAT1. This led us to examine whether STAT1-deficient mice have altered erythropoiesis. A shift in erythropoiesis was observed in STAT1(-/-) mice, with reduced bone marrow-derived erythroid colony-forming units (CFU-Es) and a compensatory increase in splenic burst-forming units (BFU-Es) and CFU-Es. Both types of splenic-derived cells displayed EPO hyperresponsiveness. A 1.6-fold reduction in total CFU-Es was observed in STAT1-deficient mice, whereas total BFU-Es were comparable. Flow cytometry of STAT1-deficient erythroid cells revealed a less differentiated phenotype, associated with increased apoptosis of early erythroblasts. STAT1-deficient erythroblasts from phenylhydrazine-primed mice displayed enhanced phosphorylation of STAT5a/b, Erk1/2, and protein kinase B (PKB)/Akt. These results illustrate that STAT1 plays an important role in the regulation of erythropoiesis.
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PMID:A novel role for STAT1 in regulating murine erythropoiesis: deletion of STAT1 results in overall reduction of erythroid progenitors and alters their distribution. 1521 94

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 molecular mechanism of anemia that is hyporesponsive to recombinant human erythropoietin (rHuEPO) in hemodialysis patients without underlying causative factors has not been investigated fully in hematopoietic stem cell system. Circulating CD34+ cells (1 x 10(4)) were isolated from rHuEPO hyporesponsive hemodialysis patients (EPO-H; n = 9), patients who were responsive to rHuEPO (EPO-R; n = 9), and healthy control subjects (n = 9). The patients with known causes of EPO hyporesponsiveness were eliminated from the current study. The cells were cultured in STEM PRO 34 liquid medium, supplemented with rHuEPO, IL-3, stem cell factor, and granulocyte-macrophage colony stimulating factor for 7 d and then transferred to a semisolid methylcellulose culture medium for performing burst forming unit-erythroid (BFU-E) colony assay. Expression of src homology domain 2 (SH2)-containing tyrosine phosphatase-1 (SHP-1), phosphorylated Janus kinase 2 (p-JAK2), and phosphorylated signal transducer and activator of transcription 5 (p-STAT5) was assessed with Western blot analysis. In EPO-H patients, SHP-1 antisense or scrambled S-oligos were included in the culture medium, and its effects were evaluated. The number of circulating CD34+ cells was not statistically different among the three groups, and their proliferation rates were similar for 7 d in culture. However, BFU-E colonies were significantly decreased in EPO-H patients compared with EPO-R and control groups. The mRNA and protein expression of SHP-1 and p-SHP-1 was significantly increased, whereas that of p-STAT5 was reduced in EPO-H patients. The inclusion of SHP-1 antisense S-oligo in culture suppressed SHP-1 protein expression associated with p-STAT5 upregulation, increase in p-STAT5-regulated genes, and partial recovery of BFU-E colonies. In EPO-H hemodialysis patients, the EPO signaling pathway is attenuated as a result of dephosphorylation of STAT5 via upregulation of SHP-1 phosphatase activity, and SHP-1 may be a novel target molecule to sensitize EPO action in these patients.
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PMID:The critical role of SRC homology domain 2-containing tyrosine phosphatase-1 in recombinant human erythropoietin hyporesponsive anemia in chronic hemodialysis patients. 1557 25

An activating point mutation in Janus kinase 2 (JAK2 V617F) was recently identified in myelofibrosis with myeloid metaplasia (MMM). To further elucidate the pathogenic significance, we examined the JAK2 mutation burden, phosphorylation of JAK2 substrates and neutrophil apoptotic resistance. Immunoblotting revealed phosphorylation of signal transducer and activator of transcription-3 (STAT3) in all four JAK2 with high V617F mutant allele burden and seven of eight with intermediate mutant allele burden, but only one of eight with wild-type JAK2 (P<0.001). In contrast, STAT5 phosphorylation was undetectable in patient MMM neutrophils; and phosphorylation of Akt and extracellular signal-regulated kinases (ERKs) failed to correlate with JAK2 mutation status. Apoptosis was lower in MMM neutrophils (median 41% apoptotic cells, n=50) compared to controls (median 66%, n=9) or other myeloproliferative disorder patients (median 53%, n=11; P=0.002). Apoptotic resistance in MMM correlated with anemia (P=0.01) and the JAK2-V617F (P=0.01). Indeed, apoptotic resistance was greatest in MMM neutrophils with high mutant allele burden (median 22% apoptosis, n=5) than with intermediate burden (median 39%, n=23) or wild-type JAK2 (median 47%, n=22; P=0.008). These results suggest that mutant JAK2 contributes to MMM pathogenesis by constitutively phosphorylating STAT3 and diminishing myeloid cell apoptosis.
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PMID:Janus kinase 2 (V617F) mutation status, signal transducer and activator of transcription-3 phosphorylation and impaired neutrophil apoptosis in myelofibrosis with myeloid metaplasia. 1687 Dec 75


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