TPO/Mpl Studies in Agnogenic Myeloid Metaplasia
© Hemavathy et al; licensee BioMed Central Ltd. 2005
Received: 17 November 2004
Accepted: 03 February 2005
Published: 03 February 2005
Agnogenic myeloid metaplasia (AMM) is one of the Philadelphia chromosome negative myeloproliferative disorder and is diagnosed by hyperplasia of atypical megakaryocytes, hepatosplenomegaly, extramedullary hematopoiesis and bone marrow fibrosis. Fibrosis is considered to be a secondary consequence of enhanced levels of fibrogenic growth factors such as TGF β1, bFGF and PDGF produced by enhanced numbers of megakaryocytes, while the primary cause is considered to be the enhanced proliferation of a defective stem cell. We have previously reported that thrombopoietin (TPO) is elevated in patients with AMM. Others have reported that Mpl protein is decreased in these patients. Since TPO is essential for the development of megakaryocytes, and Mpl protein is the receptor for TPO, we extended the study of TPO/Mpl to in vitro and in vivo cell culture systems to better understand the mechanism that leads to reduced Mpl protein in AMM patients.
Plasma TPO levels were significantly elevated and Mpl protein levels were significantly reduced in AMM patients in concordance with previous studies. Platelet Mpl transcripts in AMM were however similar to those in controls. We also cloned Mpl cDNA from AMM patients and tested for their ability to make functional proteins in vitro and in the in vivo system of 293 T human embryonic kidney cells. Their expression including the glycosylated forms was similar to those from the controls. We also measured the level of translation initiation factor, eIF4E and found it to be increased in patients with AMM demonstrating that the reduced Mpl protein may not be due to translation defects.
Our studies using the in vitro and in vivo systems further confirm that reduced Mpl protein levels are not due to defects in its transcription/translation. Reduced Mpl protein could be due to its increased internalisation owing to enhanced plasma TPO or in vivo intrinsic defects in patients with AMM.
Agnogenic myeloid metaplasia (AMM), polycythemia vera (PV), essential thrombocythemia (ET) and chronic myelogenous leukemia (CML) are characterized as myeloproliferative disorders (MPDs) arising due to exponential amplification of a haematopoietic stem cell. A typical feature of these disorders is the presence of high number of circulating progenitor cells and their cytokine independent growth in culture. So far, the molecular basis for the disorder has been recognized only for CML and is attributed to the Bcr/Abl or Philadelphia (Ph) chromosome arising due to a translocation event. The aetiology for the other three disorders referred to as Ph negative MPDs is unknown.
AMM, one of the Ph negative MPD is diagnosed by hyperplasia of atypical megakaryocytes, hepatosplenomegaly, extramedullary haematopoiesis and bone marrow fibrosis. Fibrosis is considered to be a secondary consequence of enhanced levels of fibrogenic growth factors such as TGF β1, bFGF and PDGF produced by enhanced numbers of megakaryocytes (MKs), while the primary cause is considered to be the enhanced proliferation of a defective stem cell. What leads to generation of such a defective cell with enhanced proliferation is unknown. We have earlier demonstrated , which has later been confirmed  that thrombopoietin (TPO) is one of the growth factors whose level is enhanced in patients with AMM. TPO is a haematopoietic growth factor that is essential for megakaryocytopoiesis and thrombocytopoiesis . TPO binds to its receptor Mpl (Myeloproliferative leukaemia), gets internalised , and initiates a STAT5 signalling cascade , which results in thrombopoiesis. Studies with TPO knockout mice have shown reduced numbers of platelets and myeloid progenitor cells confirming the role of TPO. Enhanced expression of TPO in mouse by Retroviral/Adenoviral gene transfers and in mice transgenic for TPO, the animals developed extramedullary haematopoiesis and splenomegaly due to MK and granulocytic hyperplasia. The severity of the conditions was related to the expression levels of TPO, resulting in myelofibrosis under very high expression level [6–8]. These results of TPO over expression are similar to the symptoms of AMM and hence indicate that high levels of TPO found in AMM patients could be responsible for the clinical features of AMM. In the mouse knockouts for Mpl receptor, there is about 85% reduction in the number of platelets, MKs and other haematopoietic cell types  and Mpl over expression leads to myeloproliferation . In vitro, Mpl antisense oligonucleotides inhibited megakaryocytopoiesis . These reports augment the role of Mpl in megakaryopoiesis. But in contrast to TPO, Mpl protein level is reduced in AMM patients . This abnormality in the TPO/Mpl pathway may depict the clinical features, but is it the cause for MK hyperplasia and the disease? Studies so far have not been conclusive.
According to Taksin et al.  defects in the TPO/Mpl pathway are unlikely to be primarily responsible for AMM. Autonomously growing MKs in AMM did not have enhanced TPO transcripts and they were not inhibited by TPO antibody. Also no mutations were detected in the Mpl gene in these patients, to account for its reduced protein level. The observation of Li et al.  that Mpl anti-sense oligonucleotide treatment could inhibit the autonomous growth of MKs from ET/PV/AMM in vitro suggests that expression of Mpl is essential for MK autonomy in these disorders. However Moliterno et al. [12, 15] have reported reduced Mpl protein level with glycosylation defects in the platelets of patients with these disorders. Although this could be responsible for the impaired TPO-mediated platelet protein tyrosine phosphorylation seen in PV and AMM patients , it does not confer with MK autonomy/hypersensitivity for growth in vitro. This reduced expression of Mpl in a disorder characterized by MK hyperplasia whose development and differentiation is dependent on this cytokine is paradoxical and needs further investigation.
Hence to better understand the role of TPO/Mpl in AMM, we have extended the study of this growth factor and its receptor gene in these patients. Our studies reveal enhanced plasma TPO level, reduced endogenous level of Mpl protein in the platelets of patients with AMM and absence of any co-relation between TPO level and Mpl expression. We have cloned Mpl cDNA from 15 AMM patients and have found that it has full potential for expression similar to controls both in vitro and in the in vivo heterologous system of 293 T cells. We also assayed for the level of eIF4E, the translation initiation factor that under normal limiting level favours translation of strong mRNAs such as those of house keeping genes and at higher level, enhances the translation of weak mRNAs such as Mpl. AMM patients were found to have elevated eIF4E level.
Mpl Expression is reduced in platelets of patients with AMM
Mpl RNA level is similar in controls and AMM patients
AMM patients have high eIF4E levels
The coding region of Mpl from AMM patients has no mutations
Mpl cDNA was amplified from the platelets of 15 AMM patients along with those from 15 normal controls by RT-PCR, cloned into the Blue Script vector and the recombinant clones sequenced completely. Base changes were detected in some patients and controls as well in the exons 2,3, 4, 6 and 12 but not at the same nucleotide (data not shown). The same changes were however not observed on re-cloning the cDNA of the samples with mutations and sequencing the corresponding genomic region. These base changes were therefore considered to be due to PCR errors and not genuine mutations. Hence Mpl gene abnormalities were not detected in AMM patients.
Mpl from AMM patients is able to transcribe and translate in vitro
About 1 μg of the Mpl cDNA of 15 controls and 15 AMM patients in the pcDNA3 vector were subjected to in vitro transcription/translation employing the rabbit reticulolysates to see if they were capable of translation in vitro. Mpl from AMM patients were able to translate as efficiently as the cDNA from controls revealing their full potential for translation. Also, in the presence of canine microsomal membranes, the translated protein was glycosylated similar to those from the controls.
Mpl from AMM patients is able to transcribe and translate in vivo
AMM is one of the MPDs for which the molecular defect is unknown. A characteristic feature of the disorder is the presence of atypical megakaryocytes in high numbers and their autonomy or hypersensitivity to growth factors in vitro. Since the haematopoietic growth factor TPO that is essential for the development of megakaryocytes is present at high level in AMM patients, it is of interest to study the role of TPO and its receptor in AMM.
We have earlier reported that AMM patients have elevated plasma TPO level and this is not associated with its enhanced transcription in the bone marrow cells [1, 17]. To determine if this enhanced TPO level is due to its receptor abnormalities, we have analysed 12 AMM patients for the presence of Mpl protein in their platelets and found it to be reduced in AMM relative to controls. However, this reduced level was not due to its reduced transcription since Real-Time RT-PCR revealed similar levels of transcripts from AMM patients and controls. To analyse if it could be due to its reduced translation owing to its G-C rich 5' UTR, we estimated the expression of the translation initiation factor eIF4E. The promoter of Mpl displays characteristics of weak mRNA that are not translated very efficiently due to G-C rich 5' UTR . The translation initiation factor eIF4E, that is present at low level under normal conditions favours the translation of strong mRNA at these limiting levels. At higher levels, although the translation of strong mRNA is not increased greatly, the translation of weak mRNAs is highly enhanced and this is usually associated with hyper proliferation of cells as in cancers . Hence we assayed for the expression of eIF4E in AMM to see if reduced Mpl protein level could be due to its reduced translation owing to limiting eIF4E level compared to controls. However eIF4E level was rather significantly higher than in controls as seen in other diseases with hyper cellular proliferation. Although this is not direct evidence, at these levels of eIF4E, normal translation of Mpl can be expected.
Since there was no significant difference in the Mpl RNA level of AMM patients as shown by RT-PCR, we cloned and sequenced Mpl gene from these patients to over-rule any structural defects that could prevent translation. Although base changes were observed for some patients and controls as well, on sequencing the corresponding regions of the genomic DNA, the same base changes were not observed. Hence these were not considered to be genuine mutations. Taksin et al.  also have reported absence of Mpl gene mutations in AMM patients. Hence to date, there are no reports describing Mpl gene mutations in AMM patients although an activating mutation in this gene has been reported by Ding J et al.  in a case of familial ET, a rare hereditary MPD. Moliterno et al.  have recently reported a single base change polymorphism in the Mpl gene of African American patients with MPD that leads to substitution of the 39th amino acid Lysine, with Asparagine in the extra cellular domain of the protein. Patients with this polymorphism exhibited high platelet counts and low platelet Mpl protein. African Americans were however not represented amongst our patients tested. We also performed in vitro transcription/translation with the cloned cDNA from the AMM patients. Similar levels of proteins were formed irrespective of the source of the cDNA, indicating that the cDNA from AMM patients had no structural defects preventing its translation. There was no difference in the extent of glycosylation of the protein either when the reaction was performed in the presence of microsomal membranes capable of post-translational modification in vitro. To further confirm this in vivo, these cDNAs were transfected into 293 T human embryonic kidney cells and the cell lysates analysed by western blots for Mpl expression. Irrespective of the source of the cDNA, similar level of expression of Mpl protein was observed. Two bands were however detected. Since the antibody used can react with both glycosylated and non-glycosylated forms of Mpl, it is likely that the second band corresponds to non-glycosylated form. As the in vivo system is saturated with the over-expressed protein, the system for modification of the protein could be exhausted. Overall, Mpl gene from AMM patients does not seem to have any impaired structural features to prevent its transcription/translation.
Our present study shows elevated TPO level; reduced Mpl platelet protein level; absence of Mpl transcriptional inhibition and absence of any structural defects in Mpl coding region in AMM patients. However, there was no co-relation between TPO level and Mpl expression, similar to the observation of Harrison CN et al.  in ET patients.
Plasma TPO level is regulated by platelet counts and MK mass . TPO binds to its receptor Mpl on platelets/MKs and gets internalised. This receptor mediated endocytosis of TPO leads to its catabolism by the lysozymes, without any recycling of the receptors to the surface . In AMM patients there is initial MK hyperplasia and thrombocytosis that leads to enhanced release of growth factors such as Platelet Derived Growth Factor, bFibroblast Growth Factor and Transforming Growth Factor β1 [25–27]. This may lead to increase in TPO transcription, since these growth factors have been shown to stimulate the transcription of TPO from the bone marrow stromal cells in cultures [28, 29]. Our earlier observation that elevated plasma TPO level is not associated with its enhanced transcription in the bone marrow cells  could be due to the fact that our cultures predominantly consisted of fibroblasts and not stromal cells.
Enhanced expression of TPO and absence of an accompanying increase in Mpl transcription or re-cycling of the internalised receptor may be responsible for persistence of high plasma TPO level in AMM patients. Reduced Mpl level seen in AMM patients may be due to exhaustion of the Mpl pool by binding to the enhanced TPO and its subsequent catabolism. This gains support from an earlier observation in thrombocythemic mice wherein very high and persistent level of TPO due to its induced over expression were found to be associated with reduced platelet Mpl protein without any reduction in Mpl transcription . Also in other MPDs such as ET/PV, high plasma TPO level is associated with low Mpl protein level [16, 31]. In vivo Mpl post-translational defect may also be responsible for impaired Mpl protein forms and levels in these patients as suggested by Moliterno et al. . Cloning and sequencing of TPO 5' UTR from these patients may provide additional valuable information on elevated TPO levels since mutations in 5' UTR of TPO have been associated with elevated TPO levels without any increase in its transcription in patients with thrombocytosis [32, 33].
Our studies with TPO/Mpl show elevated TPO and reduced Mpl level in AMM patients, without any significant co-relation in their expression levels. Mpl cDNAs from AMM patients had full potential for transcription/translation including glycosylation, in vitro and in vivo, similar to those of normal controls. Reduced Mpl protein level may not be due to defects in its transcription/translation but could be due to increased internalisation or intrinsic defects in translation and glycosylation.
Peripheral blood was obtained from patients with AMM after informed consent and peripheral blood was obtained from normal volunteers to serve as controls. Five volumes of peripheral blood was mixed with 1 volume of ACD buffer pH 4.5–5.5 (2.2% W/V Sodium Citrate; 0.8% Citric Acid; 2.2% Glucose; 50 ng/ml PGE-1) and centrifuged at 250 g for 10 minutes. The cell pellet was diluted 5X with Hank's buffer and subjected to Ficoll/Hypaque density gradient centrifugation. The ring of mononuclear cells was washed 2X with Hank's buffer and processed for isolation of genomic DNA using the Wizard Genomic DNA Purification kit from Promega, Madison, WI, following their instructions. The Platelet Rich Plasma (PRP) supernatant was centrifuged at 800 g for 10' to obtain the platelets. The Platelet Poor Plasma (PPP) was stored at -80°C, and the platelet pellet washed 2X with the Citrate buffer, pH 6.2 (0.05 mmol/L Sodium Citrate; 0.1 mol/L NaCl; 0.14 mol/L Glucose). They were then processed for RNA isolation using the Totally RNA isolation kit from Ambion, Texas, following their instructions or were suspended in 1X PBS and lysed with equal amount of 2X Laemelli buffer (0.125 M Tris HCl pH 6.8; 4% SDS; 0.56 M β Mercaptoethanol; 0.02% Bromophenol Blue; 20% Glycerol) for western blot analysis.
TPO level in the blood plasma was estimated using the Human thrombopoietin Quantikine ELISA kit from R & D Systems, Minneapolis, MN. The assay is based on the two-sided sandwich principle. Standards and undiluted PPP samples from 10 normal controls and 20 AMM patients were incubated in micro-titer Plates whose wells are pre-coated with monoclonal TPO antibody. After washing off the unbound substances, the wells were incubated with polyclonal TPO antibody conjugated with HRP enzyme. After subsequent washes to remove any unbound antibody-enzyme, a substrate solution for HRP was added to the wells. The color developed that is proportional to the amount of TPO from plasma bound to the plate was quantitated using the Opsys MR plate reader.
Real-Time RT-PCR was performed to determine the expression of Mpl in platelets of 12 controls and 12 AMM patients, using the Geneamp 5700 SDS Instrument from Applied Bio-systems, Foster City, CA. Reagent for the assay was the Quantitect RT-PCR kit (Qiagen, Valencia, CA). Mpl mRNA in the platelets was reverse transcribed and PCR amplified from 10 ng of total RNA with gene specific primers and a florescent reporter probe that hybridises to the gene in between the two primers. The sequences of the primers were:
MPL FP 5'-AAGTCCTCAGAGAGGACTCCTTTG-3
MPL RP 5'-CAGGCAAGAAGGCTGCAATC-3'
MPL PROBE 5'-FAM CCTCCCAGGCCCAGATGGACTAC-3' BHQ1
The reaction conditions were reverse transcription at 50°C for 30'; 40 cycles of amplification with de-naturation at 94°C for 15", annealing and extension at 60°C for 10".
Sequence Analysis of Mpl
Total RNA extracted from platelets obtained from 15 patients with AMM and 15 normal controls was used to clone the full length Mpl cDNA. First strand cDNA was synthesized using the SuperScript First Strand Synthesis System for RT-PCR from Invitrogen, Carlsbad, CA, following their specifications. About 3 μg of total RNA was mixed with 50 ng of random hexamers, and 1 mM dNTPs in 10 μl reaction volume and incubated at 65°C for 5' and left on ice for 1'. A cocktail mix of RT buffer, MgCl2 and DTT was added to a final concentration of 1X, 5 mM and 10 mM respectively along with 40 Units of RNase OUT Ribonuclease Inhibitor and incubated at 25°C for 2'. 50 Units of SuperScript II Reverse Transcriptase enzyme was added and incubated at 25°C for 10' and 42°C for 50'. The reaction was terminated by heating at 70°C for 15' and chilled on ice. 2 Units of RNase H was added and incubated at 37°C for 20' to remove the RNA from cDNA: RNA hybrids to increase the sensitivity of PCR from cDNA. Mpl was amplified using the Expand High Fidelity PCR kit from Roche, Indianapolis, IN, with gene specific primers containing Eco R 1 (FP) and Xho 1 (RP) Restriction Enzyme sites to enable directional cloning. The Restriction Enzyme sites are indicated in lower case in the Primer sequences given below.
The Products were purified using the Wizard PCR Preps DNA Purification System from Promega, Madison, WI, and digested with the Restriction Enzymes, Eco R 1 and Xho 1. The digested products were then cloned into Blue Script vector. The recombinants were checked by restriction analysis and the selected positive clones were sequenced completely at Northwoods DNA Inc., Becida, MN. Mpl cDNA were re-cloned from samples that had mutations and sequenced completely. The putative mutations were confirmed by sequencing the corresponding region of the Mpl gene from respective samples. For this, the genomic DNA isolated from the peripheral blood samples were PCR amplified with gene specific primers and the PCR products were directly sequenced after purification using the Wizard PCR Preps DNA Purification System from Promega, Madison, WI.
In vitro transcription/translation of Mpl
The Mpl cDNA clones in the Blue Script vector were digested with Eco R 1 and Xho 1 and the released Mpl cDNA was cloned into pcDNA 3 vector to obtain cDNA with 3' translational signals. These constructs were then subjected to in vitro transcription/translation using the TNT Quick Coupled Transcription/Translation Systems from Promega. Madison, WI, in the presence of 35S Methionine from Amersham Biosciences. About 0.5 μg of the constructs were incubated with the TNT Quick-Coupled Master Mix and 35S Methionine in the absence or presence of 2 μl of Canine microsomal membranes provided with the TNT Quick Coupled kit, at 30°C for 2 hours. The reactions were terminated by adding 100 μl of 1X SDS loading buffer (50 mM Tris. HCl pH 6.8; 100 mM DTT; 2% SDS; 0.1% Bromophenol Blue; 10% Glycerol) and stored at -20°C. Appropriately translated and processed products were then separated on a 6% polyacrylamide gel. The gel was dried using Model 583 Gel dryer from BIO-RAD, Hercules, CA. The products of translation were visualized by autoradiography of the dried gel. The bands were quantitated using the Image J program.
293 T human embryonic kidney cells were used for the transient transfection studies with pcDNA3/Mpl constructs of controls and patients used in the in vitro transcription/translation studies. The cells were seeded onto a 6 well plate at a density of 5 × 104 cells/well a day before transfection with DMEM medium containing 10% FBS. On the day of the transfection, the cells were washed with DMEM medium without serum and covered with 800 μl of the same. In an eppendorf tube, 1 μg of the DNA was mixed with 100 μl of serum free DMEM medium and 100 μl of DMEM containing 2 μl of Lipofectamine transfection reagent (Invitrogen, Carlsbad, CA) was added to this DNA. The mixture was incubated for 30' at room temperature and then added to the 800 μl of medium covering the cells. After incubating for 5 hours at 37°C the transfection medium was removed and replaced with DMEM medium with 10% FBS. The cells were harvested 48 hours post-transfection. They were washed twice with 1X PBS and the cells dislodged by gentle re-suspension. The cells were collected and centrifuged at 1000 RPM for 10'. The cell pellets were re-suspended in 100 μl of 1 X PBS each and lysed with 100 μl of 2X Laemelli buffer.
Western Blot Analysis
The Transfection cell lysates/platelet cell lysates in 1X Laemelli buffer were boiled for 5', clarified by centrifugation at 14 000 RPM for 5', loaded onto a 6% SDS PAGE, and transferred onto immobilon nylon membrane. The membrane after transfer was rinsed with 1X PBS and incubated in the blocking solution (5% milk in 1 X PBS; 0.1 % Tween 20) for 1 hr., at room temperature. The membrane was then incubated with 1:10 000 dilutions of Rabbit anti Mpl antibody from Upstate USA Inc. VA, over night at 4°C in the blocking solution. The membrane was then washed 4 X with 1X PBST (1X PBS; 0.1% Tween 20) for 15' each and incubated with 1:5000 dilutions of HRP conjugated anti-rabbit secondary antibodies for 1 hr., at room temperature. Washes with 1X PBST were repeated and the membrane processed for detection using the Western Lightning Chemiluminescence Reagent Kit from Perkin Elmer, Boston, MA, following their recommendations. The bands were quantitated using the Image J program. Similar procedure was followed for the detection of eIF4E protein in the platelets except that a 10% SDS PAGE was used for separation of the proteins. The eIF4E antibody from Transduction Laboratories, CA, was used at 1:1000 dilutions.
This work was supported by a research grant from 'Aplastic Anemia and MDS Foundation' and 'Maimonides Research & Development Foundation'.
- Wang JC, Chen C, Lou LH, Mora M: Blood Thrombopoietin, IL-6 and IL-11 levels in patients with Agnogenic Myeloid Metaplasia. Leukemia. 1997, 11: 1827-1832. 10.1038/sj.leu.2400846.View ArticlePubMedGoogle Scholar
- Elliot MA, Yoon SY, Kao P, Li CY, Tefferi A: Simultaneous measurement of serum Thrombopoietin and expression of megakaryocyte c-Mpl with clinical and laboratory correlates for Myelofibrosis with Myeloid Metaplasia. Eur J Haematol. 2002, 68: 175-179. 10.1034/j.1600-0609.2002.01534.x.View ArticlePubMedGoogle Scholar
- Kaushansky K: Thrombopoietin. N Engl J Med. 1998, 339: 746-754. 10.1056/NEJM199809103391107.View ArticlePubMedGoogle Scholar
- Fielder PJ, Hass P, Nagel M, Stefanich E, Widmer R, Bennett GL, Keller GA, de Sauvage FJ, Eaton D: Human platelets as a model for the binding and degradation of Thrombopoietin. Blood. 1997, 89: 2782-2788.PubMedGoogle Scholar
- Kirito K, Watanabe T, Sawada K, Endo H, Ozawa K, Komatsu N: Thrombopoietin regulates Bcl-xL gene expression through Stat5 and phosphatidylinositol 3-kinase activation pathways. J Biol Chem. 2002, 277: 8329-8337. 10.1074/jbc.M109824200.View ArticlePubMedGoogle Scholar
- Yan XG, Lacey D, Fletcher F, Hartley C, McElroy P, Sun Y, Xia M, Mu S, Saris C, Hill D, Hawley G, McKiece IK: Chronic exposure to retroviral vector encoded MGDF (mpl ligand) induces lineage specific growth and differentiation of megakaryocytes in mice. Blood. 1995, 86: 4025-4033.PubMedGoogle Scholar
- Yan XQ, Lacey D, Hill D, Chen Y, Fletcher F, Hawley RG, McNiece IK: A model of myelofibrosis and osteosclerosis in mice induced by overexpressing thrombopoietin (mpl ligand): reversal of disease by bone marrow transplantation. Blood. 1996, 88: 402-409.PubMedGoogle Scholar
- Zhou W, Toombs CF, Zou T, Guo J, Robinson MO: Transgenic mice overexpressing human c-mpl ligand exhibit chronic thrombocytosis and display enhanced recovery from 5-fluorouracil or antiplatelet serum treatment. Blood. 1997, 89: 1551-1559.PubMedGoogle Scholar
- Gurney AL, Carver-Moore K, de Sauvage FJ, Moore MW: Thrombocytopenia in c-mpl-deficient mice. Science. 1994, 265: 1445-1457.View ArticlePubMedGoogle Scholar
- Cocault L, Bouscary D, Le Bousse-Kerdiles C, Clay D, Picard F, Gisselbrecht S, Souyri M: Ectopic expression of murine TPO receptor (c-mpl) in mice is pathogenic and induces erythroblastic proliferation. Blood. 1996, 88: 1656-1665.PubMedGoogle Scholar
- Methia N, Louache F, Vainchenker W, Wendling F: Oligodeoxynucleotides antisense to the proto-oncogene c-mpl specifically inhibit in vitro megakaryocytopoiesis. Blood. 1993, 82: 1395-1401.PubMedGoogle Scholar
- Moliterno AR, Hankins WD, Spivak JL: Impaired expression of the Thrombopoietin receptor by platelets from patients with Polycythemia Vera. N Engl J Med. 1998, 338: 572-580. 10.1056/NEJM199802263380903.View ArticlePubMedGoogle Scholar
- Taksin AL, Le Couedic JP, Dusanter-Fourt I, Masse A, Giraudler S, Katz A, Wendling F, Vainchenker W, Casadevall N, Debili N: Autonomous megakaryocyte growth in Essential Thrombocythemia and Idiptathic Myelofibrosis is not related to a c-mpl mutation or to an autocrine stimulation by Mpl-L. Blood. 1999, 93: 125-139.PubMedGoogle Scholar
- Li Y, Hetet G, Kiladjian JJ, Gardin C, Grandchamp B, Briere J: Proto-oncogene c-mpl is involved in spontateous megakaryocytopoiesis in myeloproliferative disorders. Br J Haematol. 1996, 92: 60-66. 10.1046/j.1365-2141.1996.00297.x.View ArticlePubMedGoogle Scholar
- Moliterno AR, Spivak JL: Posttranslational processing of the Thrombopoietin receptor is impaired in Polycythemia Vera. Blood. 1999, 94: 2555-2561.PubMedGoogle Scholar
- Moliterno AR, Siebel KE, Sun AY, Hankins WD, Spivak JL: A novel Thrombopoietin signaling defect in Polycythemia Vera platelets. Stem Cells. 1998, 16: 185-192.View ArticlePubMedGoogle Scholar
- Wang JC, Hashmi G: Elevated thrombopoietin levels in patients with myelofibrosis may not be due to enhanced production of thrombopoietin by bone marrow. Leukemia Research. 2003, 27: 13-17. 10.1016/S0145-2126(02)00069-3.View ArticlePubMedGoogle Scholar
- Mignotte V, Vigon I, Boucher de Crevecoeur E, Romeo PH, Lemarchandel V, Chretien S: Structure and transcription of the human c-mpl gene (MPL). Genomics. 1994, 20: 5-12. 10.1006/geno.1994.1120.View ArticlePubMedGoogle Scholar
- De Benedetti A, Harris AL: eIF4E expression in tumors: its possible role in progression of malignancies. Int J Biochem Cell Biol. 1999, 31: 59-72. 10.1016/S1357-2725(98)00132-0.View ArticlePubMedGoogle Scholar
- Ding J, Komatsu H, Wakita A, Kato-Uranishi M, Ito M, Satoh A, Tsuboi K, Nitta M, Miyazaki H, Iida S, Ueda R: Familial essential thrombocythemia associated with a dominant-positive activating mutation of the c-MPL gene, which encodes for the receptor for thrombopoietin. Blood. 2004, 103: 4198-200. 10.1182/blood-2003-10-3471.View ArticlePubMedGoogle Scholar
- Moliterno AR, Williams DM, Gutierrez-Alamillo LI, Salvatori R, Ingersoll RG, Spivak JL: Mpl Baltimore: A thrombopoietin receptor polymorphism associated with thrombocytosis. PNAS. 2004, 101: 11444-11447. 10.1073/pnas.0404241101.PubMed CentralView ArticlePubMedGoogle Scholar
- Harrison CN, Gale RE, Pezella F, Mire-Sluis A, MacHin SJ, Linch DC: Platelet c-mpl expression is dysregulated in patients with essential thrombocythaemia but this is not of diagnostic value. Br J Haematol. 1999, 107: 139-147. 10.1046/j.1365-2141.1999.01667.x.View ArticlePubMedGoogle Scholar
- Nagata Y, Shozaki Y, Nagahisa H, Nagasawa T, Abe T, Todokoro K: Serum thrombopoietin level is not regulated by transcription but by the total counts of both megakaryocytes and platelets during thrombocytopenia and thrombocytosis. Thromb Haemost. 1997, 77: 808-814.PubMedGoogle Scholar
- Jin F, Krzyzanski W: Pharmacokinetic model of target-mediated disposition of thrombopoietin. AAPS PharmSci. 2004, 6: 9-10.1208/ps060109.View ArticleGoogle Scholar
- Martyre MC, Magdelenat H, Bryckaert MC, Laine-Bidron C, Calvo F: Increased intraplatelet levels of platelet-derived growth factor and transforming growth factor-beta in patients with myelofibrosis with myeloid metaplasia. Br J Haematol. 1991, 77: 80-86.View ArticlePubMedGoogle Scholar
- Martyre MC, Le Bousse-Kerdiles MC, Romquin N, Chevillard S, Praloran V, Demory JL, Dupriez B: Elevated levels of basic fibroblast growth factor in megakaryocytes and platelets from patients with idiopathic myelofibrosis. Br J Haematol. 1997, 97: 441-448. 10.1046/j.1365-2141.1997.292671.x.View ArticlePubMedGoogle Scholar
- Le Bousse-Kerdiles MC, Chevillard S, Charpentier A, Romquin N, Clay D, Smadja-Joffe F, Praloran V, Dupriez B, Demory JL, Jasmin C, Martyre MC: Differential expression of transforming growth factor-beta, basic fibroblast growth factor, and their receptors in CD34+ hematopoietic progenitor cells from patients with myelofibrosis and myeloid metaplasia. Blood. 1996, 88: 4534-4546.PubMedGoogle Scholar
- Sakamaki S, Hirayama Y, Matsunaga T, Kuroda H, Kusakabe T, Akiyama T, Konuma Y, Sasaki K, Tsuji N, Okamoto T, Kobune M, Kogawa K, Kato J, Takimoto R, Koyama R, Niitsu Y: Transforming growth factor-beta1 (TGF-beta1) induces thrombopoietin from bone marrow stromal cells, which stimulates the expression of TGF-beta receptor on megakaryocytes and, in turn, renders them susceptible to suppression by TGF-beta itself with high specificity. Blood. 1999, 94: 1961-1970.PubMedGoogle Scholar
- Sungaran R, Chisholm OT, Markovic B, Khachigian LM, Tanaka Y, Chong BH: The role of platelet α-granular proteins in the regulation of thrombopoietin messenger RNA expression in human bone marrow stromal cells. Blood. 2000, 95: 3094-3101.PubMedGoogle Scholar
- Cohen-Solal K, Vitrat N, Titeux M, Vainchenker W, Wendling F: High-Level Expression of Mpl in Platelets and Megakryocytes Is Independent of Thrombopoietin. Blood. 1999, 93: 2859-2866.PubMedGoogle Scholar
- Horikawa Y, Matsumura I, Hashimoto K, Shiraga M, Kosugi S, Tadokoro S, Kato T, Miyazaki H, Tomiyama Y, Kurata Y, Matsuzawa Y, Kanakura Y: Markedly Reduced Expression of Platelet c-mpl Receptor in Essential Thrombocythemia. Blood. 1997, 90: 4031-4038.PubMedGoogle Scholar
- Kondo T, Okabe M, Sanada M, Kurosawa M, Suzuki S, Kobayashi M, Hosokawa M, Asaka M: Familial essential thrombocythemia associated with one-base deletion in the 5'-untranslated region of the thrombopoietin gene. Blood. 1998, 92: 1091-1096.PubMedGoogle Scholar
- Ghilardi N, Wiestner A, Kikuchi M, Ohsaka A, Skoda RC: Hereditary thrombocythaemia in a Japanese family is caused by a novel point mutation in the thrombopoietin gene. Br J Haematol. 1999, 107: 310-316. 10.1046/j.1365-2141.1999.01710.x.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.