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He L, Cohen EB, Edwards APB, Xavier-Ferrucio J, Bugge K, Federman RS, Absher D, Myers RM, Kragelund BB, Krause DS, DiMaio D. Transmembrane Protein Aptamer Induces Cooperative Signaling by the EPO Receptor and the Cytokine Receptor β-Common Subunit. iScience 2019; 17:167-181. [PMID: 31279934 PMCID: PMC6614117 DOI: 10.1016/j.isci.2019.06.027] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 05/10/2019] [Accepted: 06/17/2019] [Indexed: 12/13/2022] Open
Abstract
The erythropoietin receptor (EPOR) plays an essential role in erythropoiesis and other cellular processes by forming distinct signaling complexes composed of EPOR homodimers or hetero-oligomers between the EPOR and another receptor, but the mechanism of heteroreceptor assembly and signaling is poorly understood. We report here a 46-residue, artificial transmembrane protein aptamer, designated ELI-3, that binds and activates the EPOR and induces growth factor independence in murine BaF3 cells expressing the EPOR. ELI-3 requires the transmembrane domain and JAK2-binding sites of the EPOR for activity, but not the cytoplasmic tyrosines that mediate canonical EPOR signaling. Instead, ELI-3-induced proliferation and activation of JAK/STAT signaling requires the transmembrane and cytoplasmic domains of the cytokine receptor β-common subunit (βcR) in addition to the EPOR. Moreover, ELI-3 fails to induce erythroid differentiation of primary human hematopoietic progenitor cells but inhibits nonhematopoietic cell death induced by serum withdrawal.
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Affiliation(s)
- Li He
- Department of Genetics, Yale School of Medicine, P.O. Box 208005, New Haven, CT 06520-8005, USA
| | - Emily B Cohen
- Department of Genetics, Yale School of Medicine, P.O. Box 208005, New Haven, CT 06520-8005, USA
| | - Anne P B Edwards
- Department of Genetics, Yale School of Medicine, P.O. Box 208005, New Haven, CT 06520-8005, USA
| | - Juliana Xavier-Ferrucio
- Department of Laboratory Medicine, Yale School of Medicine, P.O. Box 208073, New Haven, CT 06520-8073, USA
| | - Katrine Bugge
- Structural Biology and NMR Laboratory, The Linderstrøm-Lang Centre for Protein Science and Integrative Structural Biology at University of Copenhagen (ISBUC), Department of Biology, University of Copenhagen, Copenhagen N 2200, Denmark
| | - Ross S Federman
- Department of Immunobiology, Yale School of Medicine, P.O. Box 208011, New Haven, CT 06520-8011, USA
| | - Devin Absher
- HudsonAlpha Institute for Biotechnology, 601 Genome Way, Huntsville, AL 35806, USA
| | - Richard M Myers
- HudsonAlpha Institute for Biotechnology, 601 Genome Way, Huntsville, AL 35806, USA
| | - Birthe B Kragelund
- Structural Biology and NMR Laboratory, The Linderstrøm-Lang Centre for Protein Science and Integrative Structural Biology at University of Copenhagen (ISBUC), Department of Biology, University of Copenhagen, Copenhagen N 2200, Denmark
| | - Diane S Krause
- Department of Laboratory Medicine, Yale School of Medicine, P.O. Box 208073, New Haven, CT 06520-8073, USA; Yale Cancer Center, P.O. Box 208028, New Haven, CT 06520-8028, USA
| | - Daniel DiMaio
- Department of Genetics, Yale School of Medicine, P.O. Box 208005, New Haven, CT 06520-8005, USA; Department of Therapeutic Radiology, Yale School of Medicine, P.O. Box 208040, New Haven, CT 06520-8040, USA; Department of Molecular Biophysics & Biochemistry, P.O. Box 208114, Yale University, New Haven, CT 06520-8114, USA; Yale Cancer Center, P.O. Box 208028, New Haven, CT 06520-8028, USA.
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Desnoyers A, Pavic M, Houle PM, Castilloux JF, Beauregard P, Delisle L, Le Blanc R, Dufresne J, Boisjoly JA, Ethier V. Retrospective Study of High Hemoglobin Levels in 56 Young Adults. J Hematol 2018; 7:43-50. [PMID: 32300411 PMCID: PMC7155863 DOI: 10.14740/jh375w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 02/19/2018] [Indexed: 12/24/2022] Open
Abstract
Background Erythrocytosis is a frequent request for consultation in the hematologic field. The diagnostic approach is well established in the general population but in a young adult, finding the etiology of erythrocytosis can be a real diagnostic challenge. Methods This is an observational retrospective unicentric study made at the Sherbrooke University Hospital Center, over a period of 20 years (1995 - 2015). Every patient aged between 16 and 35 years old with a significant elevation of hemoglobin or hematocrit was included (hemoglobin > 185 g/L and/or hematocrit > 0.52 in men; hemoglobin > 165 g/L and/or hematocrit > 0.48 in women). Results Totally, 426 patients met the inclusion criteria (over a total of 113,453 complete blood counts) but only 56 entered the study for investigations. The majority of patients were of male gender, 43% of the patients were obese, 59% were smokers and 38% used excess alcohol or recreational drugs. Twenty-five patients had the diagnosis of absolute erythrocytosis. Seven patients had the diagnosis of relative erythrocytosis and no cause could be identified in 24 patients. No primary erythrocytosis was found in this cohort. Among the 25 patients with secondary erythrocytosis, hypoxia was the most frequent etiology identified. Less than half of the patients in the cohort had long term follow-up. Search for JAK2 mutation and serum EPO dosage were performed in 17.9% and 23.2% of cases respectively. Seven patients were treated with aspirin and five patients had phlebotomies. Conclusions This retrospective study reveals an actual clinical management that is often discordant with the current recommendations and a frequent lack of follow-up after initial investigations. Harmonization of management of erythrocytosis appears to be highly desirable.
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Affiliation(s)
| | - Michel Pavic
- Sherbrooke University Hospital Center, Sherbrooke, QC, Canada
| | | | | | | | - Line Delisle
- Sherbrooke University Hospital Center, Sherbrooke, QC, Canada
| | | | - Jean Dufresne
- Sherbrooke University Hospital Center, Sherbrooke, QC, Canada
| | | | - Vincent Ethier
- Sherbrooke University Hospital Center, Sherbrooke, QC, Canada
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Carbone CJ, Fuchs SY. Eliminative signaling by Janus kinases: role in the downregulation of associated receptors. J Cell Biochem 2014; 115:8-16. [PMID: 23959845 DOI: 10.1002/jcb.24647] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 07/31/2013] [Indexed: 12/11/2022]
Abstract
Activation of cytokine receptor-associated Janus kinases (JAKs) mediates most, if not all, of the cellular responses to peptide hormones and cytokines. Consequently, JAKs play a paramount role in homeostasis and immunity. Members of this family of tyrosine kinases control the cytokine/hormone-induced alterations in cell gene expression program. This function is largely mediated through an ability to signal toward activation of the signal transducer and activator of transcription proteins (STAT), as well as toward some other pathways. Importantly, JAKs are also instrumental in tightly controlling the expression of associated cytokine and hormone receptors, and, accordingly, in regulating the cell sensitivity to these cytokines and hormones. This review highlights the enzymatic and non-enzymatic mechanisms of this regulation and discusses the importance of the ambidextrous nature of JAK as a key signaling node that integrates the combining functions of forward signaling and eliminative signaling. Attention to the latter aspect of JAK function may contribute to emancipating our approaches to the pharmacological modulation of JAKs.
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Affiliation(s)
- Christopher J Carbone
- Department of Animal Biology and Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, 19104
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Defining an EPOR- regulated transcriptome for primary progenitors, including Tnfr-sf13c as a novel mediator of EPO- dependent erythroblast formation. PLoS One 2012; 7:e38530. [PMID: 22808010 PMCID: PMC3396641 DOI: 10.1371/journal.pone.0038530] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Accepted: 05/07/2012] [Indexed: 01/30/2023] Open
Abstract
Certain concepts concerning EPO/EPOR action modes have been challenged by in vivo studies: Bcl-x levels are elevated in maturing erythroblasts, but not in their progenitors; truncated EPOR alleles that lack a major p85/PI3K recruitment site nonetheless promote polycythemia; and Erk1 disruption unexpectedly bolsters erythropoiesis. To discover novel EPO/EPOR action routes, global transcriptome analyses presently are applied to interrogate EPO/EPOR effects on primary bone marrow-derived CFUe-like progenitors. Overall, 160 EPO/EPOR target transcripts were significantly modulated 2-to 21.8-fold. A unique set of EPO-regulated survival factors included Lyl1, Gas5, Pim3, Pim1, Bim, Trib3 and Serpina 3g. EPO/EPOR-modulated cell cycle mediators included Cdc25a, Btg3, Cyclin-d2, p27-kip1, Cyclin-g2 and CyclinB1-IP-1. EPO regulation of signal transduction factors was also interestingly complex. For example, not only Socs3 plus Socs2 but also Spred2, Spred1 and Eaf1 were EPO-induced as negative-feedback components. Socs2, plus five additional targets, further proved to comprise new EPOR/Jak2/Stat5 response genes (which are important for erythropoiesis during anemia). Among receptors, an atypical TNF-receptor Tnfr-sf13c was up-modulated >5-fold by EPO. Functionally, Tnfr-sf13c ligation proved to both promote proerythroblast survival, and substantially enhance erythroblast formation. The EPOR therefore engages a sophisticated set of transcriptome response circuits, with Tnfr-sf13c deployed as one novel positive regulator of proerythroblast formation.
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Dynamic ligand modulation of EPO receptor pools, and dysregulation by polycythemia-associated EPOR alleles. PLoS One 2012; 7:e29064. [PMID: 22253704 PMCID: PMC3257245 DOI: 10.1371/journal.pone.0029064] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 11/20/2011] [Indexed: 12/13/2022] Open
Abstract
Erythropoietin (EPO) and its cell surface receptor (EPOR) are essential for erythropoiesis; can modulate non-erythroid target tissues; and have been reported to affect the progression of certain cancers. Basic studies of EPOR expression and trafficking, however, have been hindered by low-level EPOR occurrence, and the limited specificity of anti-EPOR antibodies. Consequently, these aspects of EPOR biology are not well defined, nor are actions of polycythemia- associated mutated EPOR alleles. Using novel rabbit monoclonal antibodies to intracellular, PY- activated and extracellular EPOR domains, the following properties of the endogenous hEPOR in erythroid progenitors first are unambiguously defined. 1) High- Mr EPOR forms become obviously expressed only when EPO is limited. 2) EPOR-68K plus -70K species sequentially accumulate, and EPOR-70K comprises an apparent cell surface EPOR population. 3) Brefeldin A, N-glycanase and associated analyses point to EPOR-68K as a core-glycosylated intracellular EPOR pool (of modest size). 4) In contrast to recent reports, EPOR inward trafficking is shown (in UT7epo cells, and primary proerythroblasts) to be sharply ligand-dependent. Beyond this, when C-terminal truncated hEPOR-T mutant alleles as harbored by polycythemia patients are co-expressed with the wild-type EPOR in EPO-dependent erythroid progenitors, several specific events become altered. First, EPOR-T alleles are persistently activated upon EPO- challenge, yet are also subject to apparent turn-over (to low-Mr EPOR products). Furthermore, during exponential cell growth EPOR-T species become both over-represented, and hyper-activated. Interestingly, EPOR-T expression also results in an EPO dose-dependent loss of endogenous wild-type EPOR's (and, therefore, a squelching of EPOR C-terminal- mediated negative feedback effects). New knowledge concerning regulated EPOR expression and trafficking therefore is provided, together with new insight into mechanisms via which mutated EPOR-T polycythemia alleles dysregulate the erythron. Notably, specific new tools also are characterized for studies of EPOR expression, activation, action and metabolism.
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Abstract
PURPOSE OF REVIEW In 1985-1989, erythropoietin (EPO), its receptor (EPOR), and janus kinase 2 were cloned; established to be essential for definitive erythropoiesis; and initially intensely studied. Recently, new impetus, tools, and model systems have emerged to re-examine EPO/EPOR actions, and are addressed in this review. Impetus includes indications that EPO affects significantly more than standard erythroblast survival pathways, the development of novel erythropoiesis-stimulating agents, increasing evidence for EPO/EPOR cytoprotection of ischemically injured tissues, and potential EPO-mediated worsening of tumorigenesis. RECENT FINDINGS New findings are reviewed in four functional contexts: (pro)erythroblast survival mechanisms, new candidate EPO/EPOR effects on erythroid cell development and new EPOR responses, EPOR downmodulation and trafficking, and novel erythropoiesis-stimulating agents. SUMMARY As Current Opinion, this monograph seeks to summarize, and provoke, new EPO/EPOR action concepts. Specific problems addressed include: beyond (and before) BCL-XL, what key survival factors are deployed in early-stage proerythroblasts? Are distinct EPO/EPOR signals transduced in stage-selective fashions? Is erythroblast proliferation also modulated by EPO/EPOR signals? What functions are subserved by new noncanonical EPO/EPOR response factors (e.g. podocalyxin like-1, tribbles 3, reactive oxygen species, and nuclear factor kappa B)? What key regulators mediate EPOR inhibition and trafficking? And for emerging erythropoiesis-stimulating agents, to what extent do activities parallel EPOs (or differ in advantageous, potentially complicating ways, or both)?
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Huang LJ, Shen YM, Bulut GB. Advances in understanding the pathogenesis of primary familial and congenital polycythaemia. Br J Haematol 2010; 148:844-52. [PMID: 20096014 DOI: 10.1111/j.1365-2141.2009.08069.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Primary familial and congenital polycythemia (PFCP) is an autosomal-dominant proliferative disorder characterized by erythrocytosis and hypersensitivity of erythroid progenitors to erythropoietin (Epo). Several lines of evidence suggest a causal role of truncated erythropoietin receptor (EpoR) in this disease. In this review, we discuss PFCP in the context of erythrocytosis and EpoR signalling. We focus on recent studies describing mechanisms underlying Epo-dependent EpoR down-regulation. One mechanism depends on internalization mediated through the p85 regulatory subunit of the Phosphoinositide 3-Kinase, and the other utilizes ubiquitin-based proteasomal degradation. Truncated PFCP EpoRs are not properly down-regulated upon stimulation, underscoring the importance of these mechanisms in the pathogenesis of PFCP.
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Affiliation(s)
- Lily J Huang
- Department of Cell Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9039, USA.
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Ligand-induced EpoR internalization is mediated by JAK2 and p85 and is impaired by mutations responsible for primary familial and congenital polycythemia. Blood 2009; 113:5287-97. [PMID: 19336760 DOI: 10.1182/blood-2008-09-179572] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Epo-induced endocytosis of EpoR plays important roles in the down-regulation of EpoR signaling and is the primary means that regulates circulating Epo concentrations. Here we show that cell-surface EpoR is internalized via clathrin-mediated endocytosis. Both JAK2 kinase activity and EpoR cytoplasmic tyrosines are important for ligand-dependent EpoR internalization. Phosphorylated Y429, Y431, and Y479 in the EpoR cytoplasmic domain bind p85 subunit of PI3 kinase on Epo stimulation and individually are sufficient to mediate Epo-dependent EpoR internalization. Knockdown of p85alpha and p85beta or expression of their dominant-negative forms, but not inhibition of PI3 kinase activity, dramatically impaired EpoR internalization, indicating that p85alpha and p85beta may recruit proteins in the endocytic machinery on Epo stimulation. Furthermore, mutated EpoRs from primary familial and congenital polycythemia (PFCP) patients lacking the 3 important tyrosines do not bind p85 or internalize on stimulation. Addition of residues encompassing Y429 and Y431 to these truncated receptors restored p85beta binding and Epo sensitivity. Our results identify a novel PI3 kinase activity-independent function of p85 in EpoR internalization and support a model that defects of internalization in truncated EpoRs from PFCP patients contribute to Epo hypersensitivity and prolonged signaling.
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Abstract
The approach to a patient with erythrocytosis is greatly simplified by assessing the clonality of the process upfront. In this regard, there has been a dramatic shift toward genetic testing and away from traditional tests, such as measurement of red cell mass. Clonal erythrocytosis is the diagnostic feature of polycythemia vera (PV) and is almost always associated with a JAK2 mutation (JAK2V617F or exon 12). All other scenarios represent non-clonal erythrocytosis, often referred to as secondary erythrocytosis. Serum erythropoietin (Epo) level is usually normal or elevated in secondary erythrocytosis and subnormal in PV. Therefore, in a patient with acquired erythrocytosis, it is reasonable to begin the diagnostic work-up with peripheral blood JAK2 mutation analysis and serum Epo measurement to distinguish PV from secondary erythrocytosis. Conversely, the patient with life-long erythrocytosis is more likely to suffer from congenital polycythemia and should therefore be evaluated for germline mutations that result in enhanced Epo effect (for example, Epo receptor mutations), altered intracellular oxygen sensing (for example, mutations involving the von Hippel-Lindau tumor suppressor gene) or decreased P50 (for example, high-oxygen-affinity hemoglobinopathy). The order of tests in this instance depends on the clinical scenario and serum Epo level.
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Inthal A, Krapf G, Beck D, Joas R, Kauer MO, Orel L, Fuka G, Mann G, Panzer-Grümayer ER. Role of the erythropoietin receptor in ETV6/RUNX1-positive acute lymphoblastic leukemia. Clin Cancer Res 2009; 14:7196-204. [PMID: 19010836 DOI: 10.1158/1078-0432.ccr-07-5051] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE We explored the mechanisms leading to the distinct overexpression of EPOR as well as the effects of EPO signaling on ETV6/RUNX1-positive acute lymphoblastic leukemias. EXPERIMENTAL DESIGN ETV6/RUNX1-expressing model cell lines and leukemic cells were used for real-time PCR of EPOR expression. Proliferation, viability, and apoptosis were analyzed on cells exposed to EPO, prednisone, or inhibitors of EPOR pathways by [3H]thymidine incorporation, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and Annexin V/propidium iodide staining. Western blot analysis was done to detect activation of signaling proteins. Serum EPO levels and sequences of the EPOR (n = 53) as well as hemoglobin levels were taken from children with acute lymphoblastic leukemia enrolled in Austrian protocols. RESULTS We show here that ectopic expression of ETV6/RUNX1 induced EPOR up-regulation. Anemia, however, did not appear to influence EPOR expression on leukemic cells, although children with ETV6/RUNX1-positive leukemias had a lower median hemoglobin than controls. Exposure to EPO increased proliferation and survival of ETV6/RUNX1-positive leukemias in vitro, whereas blocking its binding site did not alter cell survival. The latter was not caused by activating mutations in the EPOR but might be triggered by constitutive activation of phosphatidylinositol 3-kinase/Akt, the major signaling pathway of EPOR in these cells. Moreover, prednisone-induced apoptosis was attenuated in the presence of EPO in this genetic subgroup. CONCLUSIONS Our data suggest that ETV6/RUNX1 leads to EPOR up-regulation and that activation by EPO might be of relevance to the biology of this leukemia subtype. Further studies are, however, needed to assess the clinical implications of its apoptosis-modulating properties.
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Affiliation(s)
- Andrea Inthal
- Children's Cancer Research Institute, St. Anna Kinderkrebsforschung, Vienna, Austria
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Hodges VM, Rainey S, Lappin TR, Maxwell AP. Pathophysiology of anemia and erythrocytosis. Crit Rev Oncol Hematol 2007; 64:139-58. [PMID: 17656101 DOI: 10.1016/j.critrevonc.2007.06.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Revised: 03/02/2007] [Accepted: 06/12/2007] [Indexed: 10/23/2022] Open
Abstract
An increasing understanding of the process of erythropoiesis raises some interesting questions about the pathophysiology, diagnosis and treatment of anemia and erythrocytosis. The mechanisms underlying the development of many of the erythrocytoses, previously characterised as idiopathic, have been elucidated leading to an increased understanding of oxygen homeostasis. Characterisation of anemia and erythrocytosis in relation to serum erythropoietin levels can be a useful addition to clinical diagnostic criteria and provide a rationale for treatment with erythropoiesis stimulating agents (ESAs). Recombinant human erythropoietin as well as other ESAs are now widely used to treat anemias associated with a range of conditions, including chronic kidney disease, chronic inflammatory disorders and cancer. There is also heightened awareness of the potential abuse of ESAs to boost athletic performance in competitive sport. The discovery of erythropoietin receptors outside of the erythropoietic compartment may herald future applications for ESAs in the management of neurological and cardiac diseases. The current controversy concerning optimal hemoglobin levels in chronic kidney disease patients treated with ESAs and the potential negative clinical outcomes of ESA treatment in cancer reinforces the need for cautious evaluation of the pleiotropic effects of ESAs in non-erythroid tissues.
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Affiliation(s)
- Vivien M Hodges
- Haematology Research Group, Centre for Cancer Research and Cell Biology, Queen's University, Belfast, United Kingdom.
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Dunlop EA, Maxwell AP, Lappin TRJ. Impaired Downregulation Following Erythropoietin Receptor Activation in Non-Small Cell Lung Carcinoma. Stem Cells 2007; 25:380-4. [PMID: 17038666 DOI: 10.1634/stemcells.2006-0452] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Recent evidence confirms the presence of erythropoietin receptors on a variety of cancer cells. This has raised concerns about the use of erythropoiesis-stimulating agents in the treatment of cancer-related anemia. Having previously identified expression of functional erythropoietin receptors in a non-small cell lung carcinoma cell line, H838, which activated key signaling pathways in response to erythropoietin stimulation, we now demonstrate impaired downregulation of the erythropoietin receptor in these tumor cells. The erythropoietin receptor is not ubiquitinated following erythropoietin stimulation in this cancer cell line, and there is no turnover of the receptor in either unstimulated or stimulated cells. Compounding this blunted response is impaired SOCS3 induction downstream of erythropoietin stimulation and an extremely delayed SOCS1 response. If this finding in non-small cell lung carcinoma is a widespread phenomenon, then impaired erythropoietin receptor downregulation and degradation in tumor cells has clinical implications for those patients receiving erythropoiesis-stimulating agents for cancer-related anemia.
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Affiliation(s)
- Elaine A Dunlop
- Haematology Research Group, Centre for Cancer Research and Cell Biology, Queen's University, Belfast, United Kingdom.
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Abstract
Erythropoietin (Epo) has long been known to be the principal hematopoietic growth factor that regulates cellular proliferation and differentiation along the erythroid lineage. Recent studies have shown that Epo is a pleiotropic cytokine that is proangiogenic and exerts broad tissue-protective effects in diverse nonhematopoietic organs. Recombinant Epo (rEpo) has been widely used in the clinic to prevent or treat malignancy-associated anemia. A series of clinical trials have documented the efficacy of rEpo in reducing RBC transfusion requirements and improving quality of life in cancer patients, and a recent meta-analysis suggested a positive effect on survival. However, two randomized trials reported negative outcomes with rEpo, as patients in the rEpo arm fared worse than their placebo-treated counterparts with respect to progression-free survival. The expression of Epo receptor (EpoR) in cancer cells has raised the possibility that exogenous rEpo may exert direct effects on tumor cells associated with the potential for stimulation of proliferation, inhibition of apoptosis, or modulation of sensitivity to chemoradiation therapy. The presence of an autocrine-paracrine Epo-EpoR system in tumors and potential effects of Epo on tumor microenvironment and angiogenesis are consistent with a complex biology for Epo-EpoR signaling in cancer that requires further research. This review describes Epo and EpoR biology, focusing on the pleiotropic effects of Epo on nonhematopoietic tissues as well as the expression and function of EpoR in cancer cells.
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Affiliation(s)
- Matthew E Hardee
- Department of Pathology, Duke University Medical Center, Durham, NC 22710, USA
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Menon MP, Fang J, Wojchowski DM. Core erythropoietin receptor signals for late erythroblast development. Blood 2005; 107:2662-72. [PMID: 16332976 PMCID: PMC1895369 DOI: 10.1182/blood-2005-02-0684] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Critical signals for erythroblast formation are transduced by activated, tyrosine-phosphorylated erythropoietin receptor (EpoR) complexes. Nonetheless, steady-state erythropoiesis is supported effectively by EpoR alleles that are deficient in cytoplasmic phosphotyrosine sites. To better define core EpoR action mechanisms, signaling capacities of minimal PY-null (EpoR-HM) and PY343-retaining (EpoR-H) alleles were analyzed for the first time in bone marrow-derived erythroblasts. Jak2 activation via each allele was comparable. Stat5 (and several Stat5-response genes) were induced via EpoR-H but not via EpoR-HM. Stat1 and Stat3 activation was nominal for all EpoR forms. For both EpoR-HM and EpoR-H, Akt and p70S6-kinase activation was decreased multifold, and JNK activation was minimal. ERKs, however, were hyperactivated uniquely via EpoR-HM. In vivo, Epo expression in EpoR-HM mice was elevated, while Epo-induced reticulocyte production was diminished. In vitro, EpoR-HM erythroblast maturation also was attenuated (based on DNA content, forward-angle light scatter, and hemoglobinization). These EpoR-HM-specific defects were corrected not only upon PY343 site restoration in EpoR-H, but also upon MEK1,2 inhibition. Core EpoR PY site-independent signals for erythroblast formation therefore appear to be Stat5, Stat1, Stat3, p70S6-kinase, and JNK independent, but ERK dependent. Wild-type signaling capacities, however, depend further upon signals provided via an EpoR/PY343/Stat5 axis.
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Affiliation(s)
- Madhu P Menon
- Program in Stem Cell Biology, Maine Medical Center Research Institute, 81 Research Dr, Scarborough, ME 04074, USA
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