Biomedical subjects

M Titeux

Publications and source records attributed to M Titeux.

At least 19 recordsLinked to original sources

PubMed2006

Lens cell targetting for gene therapy of prevention of posterior capsule opacification.

Posterior capsule opacification is the main complication of cataract surgery. Using adenovirus-mediated gene transfer, we recently reported that it was feasible to prevent PCO by overexpressing pro-apoptotic molecules such as pro-caspase 3 or Bax in the residual lens epithelial cells post-cataract surgery. However, this approach is feasible only if gene transfer can be restricted to the residual cells responsible for PCO. Initially, we tested an adenovirus (human serotype 5, HAd5), a lentivirus (HIV) and an oncoretrovirus (MLV) vector for the their in vivo transduction efficiency of rabbit lens cells. We found that HAd5 vectors were the most efficient (>90% of the cells could be transduced). Six potential lens-specific promoters were then cloned into HAd5 vectors and assayed for their ability to target expression to a specific population of cells, using in vitro, ex vivo and in vivo rabbit tissues and human lens capsular bags. We found that the LEP503, MIP and Filensin promoters induced strong lens-specific expression of a reporter gene, in human lens cells. Following this ex vivo assay, we showed in a rabbit PCO model that gene transfer could be spatially restricted to the capsular bag by confining the vector with Matrigel. Our combined approach using a lens-specific promoter and a biocompatible gel should render feasible a novel therapeutic strategy for PCO that targets the remaining lens cells.

Adenoviridae↗

PubMed2004

The mouse synemin gene encodes three intermediate filament proteins generated by alternative exon usage and different open reading frames.

We have previously cloned and characterized the human synemin gene, which encodes two intermediate filament proteins (IFPs). We now show that the mouse synemin gene encodes three different synemin isoforms through an alternative splicing mechanism. Two of them, synemin H and M are similar to human alpha and beta synemin, and the third isoform, L synemin, constitutes a new form of IFP. It has a typical rod domain and a short tail (49 residues) with a novel sequence that is produced by a different open reading frame. The synthesis of H/M synemins starts in the embryo, whereas the synemin L isoform is present in adult muscles. The H/M isoforms are bound to desmin or vimentin in the muscle cells of wild-type mice. Using desmin- and vimentin-deficient mice, we have obtained direct evidence that synemin is associated with muscle intermediate filaments in vivo. The organization of the synemin fibril is disrupted in skeletal and cardiac muscle when desmin is absent and in smooth muscle when vimentin is absent. The fact that the three synemin isoforms differ in the sequences of their tail domains as well as in their developmental patterns suggests that they fulfill different functions.

Alternative Splicing↗

PubMed2004

Membrane-bound delta-4 notch ligand reduces the proliferative activity of primitive human hematopoietic CD34+CD38low cells while maintaining their LTC-IC potential.

To examine the role of the Notch ligand Delta-4 on hematopoietic stem cells, human CD34+CD38low cord blood cells were cocultured on S17 cells transduced with transmembrane Delta-4 (mbD4/S17) or an empty vector (C/S17). By the end of a 3-week culture, mbD4/S17 induced a 25-fold reduction in nucleated cell production, as compared to C/S17, by maintaining a higher proportion of cells in G0/G1 phase. A specific retention of a high proportion of CD34+ cells throughout the culture was observed with mbD4/S17, contrary to C/S17. Although mbD4/S17 promoted expansion of cells with the phenotype of committed lymphoid precursors (CD34+CD7+CD45RA+), these cells still retained their myeloid differentiation potential. mbD4/S17 maintained a higher LTC-IC frequency in output CD34+ cells, compared to C/S17, as in the subsets of cells having completed the same number of divisions on mbD4/S17. A Delta4-Fc protein (extracellular part of human Delta4 fused to Fc human IgG1 portion), immobilized on plastic, also reduced cell production and retained the LTC-IC potential. Transplantation of cells grown on mbD4/S17 into NOD/SCID mice showed no significant enhancement of the long-term repopulating ability. Thus, Delta4 appears to inhibit hematopoietic stem cell proliferation, in association with the maintenance of short-term lymphoid and myeloid repopulation capacity.

ADP-ribosyl Cyclase↗

PubMed2002

Successful transduction of human multipotent, lymphoid (T, B, NK) and myeloid, and transplantable CD34+CD38low cord blood cells using a murine oncoretroviral vector.

Hematopoietic stem cells (HSC) are subject to great interest because of their medical importance and their biological properties. Therefore, the possibility of genetically modifying human HSC is a major concern in several inherited pathologies. In this study, we aimed to demonstrate that a murine oncoretroviral vector can transduce multipotential cord blood (CB) stem cells. Sorted CB CD34(+)CD38(low) cells were transduced with a Moloney-based MFG retroviral vector containing the coding sequence of the murine CD2 (mCD2). CD34(+)mCD2(+) cells were sorted by flow cytometry and cultured either in bulk or at one cell per well in culture conditions that allow differentiation along lymphoid (T, B, and NK) and myeloid (M) lineages. Phenotypic analysis of cells generated in culture showed that CD34(+)mCD2(+) cells could give rise to all lymphoid and myeloid progeny, indicating that the MFG/mCD2 vector had transduced progenitors of all tested lineages. Moreover, clonal cultures of 660 CD34(+)mCD2(+) cells showed that approximately 5% of these cells were able to generate both myeloid and lymphoid (B + NK) progenies; for 25% of them, this included the production of lymphoid T cells. We also demonstrate that transduced CD34(+)CD38(low) CB cells with lymphoid and myeloid potentials were capable of engraftment into the bone marrow (BM) of nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice during several months. These results show that MFG retroviral vectors can transduce multipotent (T, B, NK, M) human hematopoietic progenitors with in vivo repopulating activity.

Animals↗

PubMed2001

Human synemin gene generates splice variants encoding two distinct intermediate filament proteins.

Intermediate filament (IF) proteins are constituents of the cytoskeleton, conferring resistance to mechanical stress, and are encoded by a dispersed multigene family. In man we have identified two isoforms (180 and 150 kDa) of the IF protein synemin. Synemin alpha and beta have a very short N-terminal domain of 10 amino acids and a long C-terminal domain consisting of 1243 amino acids for the alpha isoform and 931 amino acids for the beta isoform. An intronic sequence of the synemin beta isoform is used as a coding sequence for synemin alpha. Both mRNA isoforms (6.5 and 7.5 kb) result from alternative splicing of the same gene, which has been assigned to human chromosome 15q26.3. Analyses by Northern and Western blot revealed that isoform beta is the predominant isoform in striated muscles, whereas both isoforms (alpha and beta) are present in almost equal quantities in smooth muscles. Co-transfection and immunolabeling experiments indicate that both synemin isoforms are incorporated with desmin to form heteropolymeric IFs. Furthermore synemin and desmin are found aggregated together in certain pathological situations.

Alternative Splicing↗

PubMed2000

The human immunodeficiency virus type-1 central DNA flap is a crucial determinant for lentiviral vector nuclear import and gene transduction of human hematopoietic stem cells.

Gene transfer in human hematopoietic stem cells (HSCs) has great potential for both gene therapy and the understanding of hematopoiesis. As HSCs have extensive proliferative capacities, stable gene transfer should include genomic integration of the transgene. Lentiviral vectors are now preferred to oncoretroviral vectors especially because they integrate in nondividing cells such as HSCs, thereby avoiding the use of prolonged cytokine stimulation. Human immunodeficiency virus type-1 (HIV-1) has evolved a complex reverse transcription strategy including a central strand displacement event controlled in cis by the central polypurine tract (cPPT) and the central termination sequence (CTS). This creates, at the center of HIV-1 linear DNA molecules, a 99-nucleotide-long plus-strand overlap, the DNA flap, which acts as a cis-determinant of HIV-1 genome nuclear import. The reinsertion of the DNA flap sequence in an HIV-derived lentiviral vector promotes a striking increase of gene transduction efficiency in human CD34(+) hematopoietic cells, and the complementation of the nuclear import defect present in the parental vector accounts for this result. In a short ex vivo protocol, the flap-containing vector allows efficient transduction of the whole hierarchy of human HSCs including both slow-dividing or nondividing HSCs that have multiple lymphoid and myeloid potentials and primitive cells with long-term engraftment ability in nonobese diabetic/severe combined immunodeficiency mice (NOD/SCID).

Adult↗

PubMed2000

In vitro and in vivo evidence for the long-term multilineage (myeloid, B, NK, and T) reconstitution capacity of ex vivo expanded human CD34(+) cord blood cells.

The aim of the present report is to describe clinically relevant culture conditions that support the expansion of primitive hematopoietic progenitors/stem cells, with maintenance of their hematopoietic potential as assessed by in vitro assays and the NOD-SCID in vivo repopulating capacity.CD34(+) cord blood (CB) cells were cultured in serum-free medium containing stem cell factor, Flt3 ligand, megakaryocyte growth and development factor, and granulocyte colony-stimulating factor. After 14 days, the primitive functions of expanded and nonexpanded cells were determined in vitro using clonogenic cell (colony-forming cells, long-term culture initiating cell [LTC-IC], and extended [E]-LTC-IC) and lymphopoiesis assays (NK, B, and T) and in vivo by evaluating long-term engraftment of the bone marrow of NOD-SCID mice. The proliferative potential of these cells also was assessed by determining their telomere length and telomerase activity. Levels of expansion were up to 1,613-fold for total cells, 278-fold for colony-forming unit granulocyte-macrophage, 47-fold for LTC-IC, and 21-fold for E-LTC-IC. Lymphoid B-, NK, and T-progenitors could be detected. When the expanded populations were transplanted into NOD-SCID mice, they were able to generate myeloid progenitors and lymphoid cells for 5 months. These primitive progenitors engrafted the NOD-SCID bone marrow, which contained LTC-IC at the same frequency as that of control transplanted mice, with conservation of their clonogenic capacity. Moreover, human CD34(+)CDl9(-) cells sorted from the engrafted marrow were able to generate CD19(+) B-cells, CD56(+)CD3(-) NK cells, and CD4(+)CD8(+)alphabetaTCR(+) T-cells in specific cultures. Our expansion protocol also maintained the telomere length in CD34(+) cells, due to an 8.8-fold increase in telomerase activity over 2 weeks of culture. These experiments provide strong evidence that expanded CD34(+) CB cells retain their ability to support long-term hematopoiesis, as shown by their engraftment in the NOD-SCID model, and to undergo multilineage differentiation along all myeloid and the B-, NK, and T-lymphoid pathways. The expansion protocol described here appears to maintain the hematopoietic potential of CD34(+) CB cells, which suggests its relevance for clinical applications.

Animals↗

PubMed1999

High-level expression of Mpl in platelets and megakaryocytes is independent of thrombopoietin.

Thrombopoietin (TPO) is a hematopoietic growth factor that regulates megakaryocytopoiesis and platelet production through binding to its receptor, Mpl, encoded by the c-mpl proto-oncogene. Circulating levels of TPO are regulated by receptor-mediated uptake and degradation. To better understand this mode of TPO regulation, we examined whether expression of Mpl was regulated by its ligand. Using RNase protection analysis, we found no differences in the levels of c-mpl transcripts in megakaryocytes (MKs) produced in vitro either in the presence or absence of TPO and in platelets (PLTs) obtained from mice hyperstimulated in vivo by ectopic secretion of TPO. Similarly, Western blot analysis of MKs produced in the presence or absence of TPO showed no difference in Mpl levels. Levels of Mpl, GpIIb, or P-selectin were virtually identical in platelet lysates obtained from normal, TPO knockout and mildly TPO-stimulated mice. In contrast, the expression of Mpl was significantly reduced in PLTs from severely thrombocythemic mice. These results show that TPO does not have a major effect on the transcription or translation of Mpl. However, they do suggest that an excess of circulating TPO can lead to the disappearance of Mpl from PLTs via catabolism.

Animals↗

PubMed1998

Spi-1 transgenic mice develop a clonal erythroleukemia which does not depend on p53 mutation.

Spi-1 transcriptional activation and wild-type p53 extinction are two oncogenic alterations involved in the malignant transformation of erythroblasts during the Friend acute erythroleukemia. To dissect the contribution of these alterations in the deregulation of the differentiation and proliferation of erythroblasts, we generated spi-1 transgenic mice. Analysis of these animals revealed that Spi-1 overexpression was directly involved in the block of proerythroblast differentiation. However, the erythroleukemia that develops in these animals evolved in two steps. During the early step (HS1 step), non tumorigenic proerythroblasts remained strictly dependent upon erythropoietin (Epo) for their survival and proliferation. Later on, Epo-independent and tumorigenic proerythroblasts emerged (HS2 step) suggesting that other oncogenes cooperate with Spi-1 to lead to a fully malignant phenotype. By provirus tagging, we demonstrate that the HS1 step was clonal indicating that a cell selection must occur in vivo. Analysis of the nature of p53 in both the in vivo HS1 and HS2 proerythroblasts and in cultured erythroblastic cell lines showed that--p53 was normal in the HS1 primary tissues but was mutated in the HS1 cultured cell lines--p53 was frequently altered in HS2 primary tissues but was found normal in some mice. These data indicate that (i) the blockage of the erythroblast differentiation by Spi-1 occurs independently of p53 alteration (ii) p53 alteration is not necessary to confer Epo independence and tumorigenicity to spi-1 transgenic proerythroblasts.

Animals↗

PubMed1996

Constitutive expression of Mpl ligand transcripts during thrombocytopenia or thrombocytosis.

Mpl ligand (thrombopoietin [TPO]) is the physiological regulator of platelet production. In mice, mRNA encoding the Mpl ligand (Mpl-L) is predominantly found by Northern blot analysis in the liver and kidney. To investigate the mode of regulation of the Mpl-L gene, we have developed several experimental models of severe thrombocytopenia differing in their kinetics and an opposite model of chronic thrombocytosis. Northern analysis performed at various times after induction of a thrombocytopenic state demonstrates that, whatever the number of circulating platelets, no change in Mpl-L mRNA level occurs in liver and kidney. By ribonuclease protection assays, we analyzed the ratios between mRNAs coding for the wild-type Mpl-L form and various splice variants encoding inactive or nonsecreted Mpl-L proteins. No modification in levels of these various isoforms was detected confirming the data of a previous report. Because the highest level of Mpl-L bioactivity in sera was observed only in mice with drastically reduced numbers of both platelets and megakaryocytes, these results further suggest that not only platelets, but also megakaryocytes, must be involved in the regulation of the level of circulating Mpl-L. In addition, we show that no downregulation of wild-type Mpl-L mRNA and no change in the ratio of Mpl-L mRNA isoforms were detected in mice in which a chronic thrombocytosis was induced. Together, these different models extend and further confirm that the regulation of Mpl-L does not occur at a transcriptional level or by a modulation in the ratios of Mpl-L mRNA isoforms.

Animals↗

PubMed1996

Inhibition of the erythropoietin-induced erythroid differentiation by granulocyte-macrophage colony-stimulating factor in the human UT-7 cell line is not due to a negative regulation of the erythropoietin receptor.

The human pluripotent UT-7 cell line is growth factor-dependent for proliferation and differentiation. We have previously shown that (1) granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (Epo) induce a myeloid and erythroid pattern of differentiation, respectively; (2) GM-CSF acts predominantly over Epo for cell differentiation; (3) GM-CSF induces a rapid downmodulation (4 hours) of Epo receptors (Epo-R) at the mRNA and binding site levels; and (4) in contrast, Epo has no effect on GM-CSF receptor (GM-CSF-R) expression. These results suggested that UT-7 cell commitment or differentiation may be directed by a hierarchical action of growth factors through an early and rapid transmodulation of growth factor receptors. To test this hypothesis, we introduced and expressed the murine Epo-R (muEpo-R) in UT-7 cells using a retroviral strategy. Two retroviral vectors were constructed: one carrying the neomycin resistance gene, and another carrying a mouse Epo-R cDNA devoid of its regulatory untranslated 3' sequence placed under the transcriptional control of the viral long terminal repeat element (LTR) and the neomycin resistance gene. Three UT-7/Epo-R infected clones (12, 6, 10) and one UT-7/neomycin clone (Neo) were selected in medium containing G418. After growth factor deprivation (18 hours), Epo-Rs were expressed at the same level (approximately 6,000 receptors per cell) in all four clones 12, 6, 10, Neo, and in parental UT-7 cells, and exhibited similar affinity (0.1 to 0.2 nmol/L). Cross-linking experiments showed that Epo is associated with three proteins of about 66, 85, and 100 kD in cells of parental UT-7, as well as in cells of clones 10 and 12. An inhibitory antibody directed specifically against the human Epo-R (huEpo-R Ab) abolished almost completely the cross-linking on parental UT-7 cells, but not on cells of clone 12, demonstrating that more than 90% cell surface Epo-Rs were of murine origin. The presence of GM-CSF significantly reduced the number of Epo-Rs expressed on parental UT-7 cells, but not on cells of clones 12, 10, and 6. HuEpo-R Ab inhibited Epo-induced parental UT-7 cell growth, but not that of cells of clone 12, suggesting that the muEpo-R is able to induce human UT-7 cell proliferation. When cells of clone 12 were switched from a medium containing GM-CSF to one with Epo, cell surface glycophorin A (GPA) was induced, as in parental UT-7 cells without inhibition by the huEpo-R Ab, demonstrating that the muEpo-R is also able to transduce a differentiation signal in human cells. However, in cells of clones 12, 6, 10 and Neo, as well as in parental UT-7 cells, the induction of GPA by Epo was inhibited by GM-CSF. This finding demonstrates that, although GM-CSF does not downregulate muEpo-R binding sites on UT-7/muEpo-R infected clones, it still inhibits the effects of Epo on cell differentation. Therefore, hierarchical regulation induced by growth factors for cell commitment or differntiation more likely acts downstream of cell surface receptors at either the signal transduction or transcriptional levels.

Animals↗

PubMed1996

Spi-1/PU.1 transgenic mice develop multistep erythroleukemias.

Insertional mutagenesis of the spi-1 gene is associated with the emergence of malignant proerythroblasts during Friend virus-induced acute erythroleukemia. To determine the role of spi-1/PU.1 in the genesis of leukemia, we generated spi-1 transgenic mice. In one founder line the transgene was overexpressed as an unexpected-size transcript in various mouse tissues. Homozygous transgenic animals gave rise to live-born offspring, but 50% of the animals developed a multistep erythroleukemia within 1.5 to 6 months of birth whereas the remainder survived without evidence of disease. At the onset of the disease, mice became severely anemic. Their hematopoietic tissues were massively invaded with nontumorigenic proerythroblasts that express a high level of Spi-1 protein. These transgenic proerythroblasts are partially blocked in differentiation and strictly dependent on erythropoietin for their proliferation both in vivo and in vitro. A complete but transient regression of the disease was observed after erythrocyte transfusion, suggesting that the constitutive expression of spi-1 is related to the block of the differentiation of erythroid precursors. At relapse, erythropoietin-independent malignant proerythroblasts arose. Growth factor autonomy could be partially explained by the autocrine secretion of erythropoietin; however, other genetic events appear to be necessary to confer the full malignant phenotype. These results reveal that overexpression of spi-1 is essential for malignant erythropoiesis and does not alter other hematopoietic lineages.

Animals↗

PubMed1996

[Mpl ligand (thrombopoietin) and platelet regulation].

After 35 years of research, the physiological regulator of platelet production has been isolated and its gene cloned. This discovery originates from studies performed with the myeloproliferative leukemia virus (MPLV), a murine retrovirus which induces an acute myeloproliferative syndrome in adult mice. MPLV carries in its genome the v-mpl oncogene which corresponds to a truncated form the c-mpl proto-oncogene. c-mpl encodes a cytokine receptor (Mpl-R) belonging to the hematopoietin receptor superfamily. Among the hematopoietic cell lineages, Mpl-R is preferentially expressed on late megakaryocyte progenitors, megakaryocytes and platelets. The ligand for Mpl-R, called Mpl-L or TPO or MGDF or megapoietin, is a glycosylated hormone of 352 amino acids in human which comprises two domains: the N-terminus domain shares 50% similarity with erythropoietin and is responsible for the biological activity; the C-terminus part is required for secretion. Notwithstanding its major action on megakaryocytopoiesis and thrombocytopoiesis, Mpl-L also potentiates the action of other cytokines on several hematopoietic lineages. Mpl-L/TPO/MGDF, the homeostatic regulator of platelet production, might be a useful therapeutical cytokine to treat thrombocytopenia induced in patients by chemotherapy.

Animals↗

PubMed1995

The Mpl receptor is expressed in the megakaryocytic lineage from late progenitors to platelets.

The Mpl receptor (Mpl-R) is a cytokine receptor belonging to the hematopoietin receptor superfamily for which a ligand has been recently characterized. To study the lineage distribution of Mpl-R in normal hematopoietic cells, we developed a monoclonal antibody (designated M1 MoAb) by immunizing mice with a soluble form of the human Mpl-R protein. With few exceptions, Mpl-R was detected by indirect immunofluorescent analysis on all human leukemic hematopoietic cell lines with pluripotential and megakaryocytic phenotypes, but not on other cell lines. By immunoprecipitation and immunoblotting, M1 MoAb recognized a band at 82 to 84 kD corresponding to the expected size of the glycosylated receptor. Among normal hematopoietic cells, M1 MoAb strongly stained megakaryocytes (MK) and Mpl-R was detected on platelets by indirect immunofluorescence staining or immunoblotting. On purified CD34+ cells, less than 2% of the population was stained, but the labeling was weak and just above the threshold of detection. However, dual-labeling with the M1 and antiplatelet glycoprotein MoAbs showed that most Mpl-R+/CD34+ cells coexpressed CD41a, CD61, or CD42a, suggesting that cell surface appearance of Mpl-R and platelet glycoproteins could be coordinated. M1-positive and M1-negative subsets were sorted from purified CD34+ cell populations. Colony assays showed that the absolute number of hematopoietic progenitors was extremely low and no primitive progenitors were present in the CD34+/Mpl-R+ fraction. However, this cell fraction was significantly enriched in low proliferative colony-forming units-MK. When the CD34+/Mpl-R+ fraction was grown in liquid culture containing human aplastic serum and a combination of growth factors, mature MK were seen as early as day 4, whereas the predominant cell population was erythroblasts on day 8. Similar data were also obtained with the CD34+/Mpl-R- fraction with, however, a delay in the time of appearance of both MK and erythroblasts. In conclusion, Mpl-R is a cytokine receptor restricted to the MK cell lineage. Its expression is low on CD34+ cells and these cells mainly correspond to late MK progenitors and transitional cells. These data indicate that the action of the Mpl-R ligand might predominate during the late stages of human MK differentiation.

Amino Acid Sequence↗

PubMed1995

From the v-mpl oncogene to thrombopoietin.

v-mpl is a mouse oncogene that is part of the genome of the myeloproliferative leukemia virus (MPLV). The cellular homolog gene c-mpl encodes an hematopoietic cytokine receptor restricted to the megakaryocytic lineage of differentiation. Using the Mpl receptor protein, cDNAs corresponding to the receptor ligand were isolated in humans, pigs, dogs and mice. In vivo and in vitro, the recombinant molecule has both the thrombopoietin (TPO) and megakaryocyte-colony stimulating factor (MK-CSF) activities. This molecule (Mpl ligand/TPO/MK-CSF) is the humoral physiological regulator of platelet production.

Animals↗

PubMed1995

c-mpl, the thrombopoietin receptor.

v-mpl is a mouse oncogene that is part of the genome of the myeloproliferative leukemia virus (MPLV). The cellular homolog gene c-mpl encodes an hematopoietic cytokine receptor mainly restricted to the megakaryocytic lineage of differentiation. Using the Mpl receptor protein, cDNAs corresponding to the receptor ligand were isolated in humans, pigs, dogs and mice. In vivo and in vitro, the recombinant molecule has both the thrombopoietin (TPO) and megakaryocyte-colony stimulating factor (MK-CSF) activities. This molecule (Mpl ligand/TPO/MK-CSF) seems to be the humoral physiological regulator of platelet production.

Animals↗

PubMed1994

Growth and differentiation of the human megakaryoblastic cell line (ELF-153): a model for early stages of megakaryocytopoiesis.

ELF-153 is a cell line that has been established from a patient with a poorly differentiated acute myeloid leukemia associated with an acute myelofibrosis. A majority of cells had a blast morphology with the phenotype of a myeloid hematopoietic progenitor, ie, CD34+, CD33+, CD13+, HLA-DR+, but CD38-, and the remaining cells (5% to 10%) expressed platelet restricted proteins such as CD41, CD42, CD36, CD61, and von Willebrand factor; some of them were polyploid (up to 32N) and exhibited demarcation membranes and alpha granules. No erythroid or other lineage-specific markers were detected. Proliferation of ELF-153 cells was highly stimulated by interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor and to a lesser extent by stem cell factor and IL-6. In contrast, the cell line did not respond to erythropoietin, leukemia inhibitory factor, IL-7, IL-11, granulocyte colony-stimulating factor, and basic fibroblast growth factor. ELF-153 cells could be separated by flow cytometry into three discrete cell populations (CD34+/CD61-, CD34+/CD61+, and CD34-/CD61+) with different proliferative and endomitotic properties corresponding to distinct stages of the mega karyocyte (MK) differentiation. This MK differentiation, which involved a minority of ELF-153, could be increased in the presence of 5-azacytidine and phorbol ester, but could not be significantly modified by growth factors. By contrast, cytochalasin B dramatically induced polyploidization without differentiation. It is noteworthy that association of 5-azacytidine to cytochalasin B dramatically induced the production of polyploid MK cells. To understand the molecular mechanisms underlying this MK differentiation, the expression of GATA-1 and GATA-2 was investigated in subpopulations of ELF-153. A high level of GATA-1 and GATA-2 mRNA was only present in the CD61+ cells. Therefore, these two transactivating factors may play an important role in the MK differentiation of ELF-153. We conclude that ELF-153 might be an important tool to investigate the mechanisms by which transcription factors control differentiation of MK progenitors.

Acute Disease↗

PubMed1994

cMpl ligand is a humoral regulator of megakaryocytopoiesis.

Megakaryocytopoiesis is the cellular developmental process that leads to platelet production. At least two humoral growth factors may be necessary for megakaryocyte proliferation and maturation. One is a megakaryocyte-colony stimulating factor (MK-CSF) which induces the proliferation and differentiation of megakaryocyte progenitors, and the second, thrombopoietin, is a megakaryocyte maturation factor. Neither of these factors has been fully characterized. The proto-oncogene c-mpl, an orphan member of the haematopoietin receptor family, is specifically involved in megakaryocyte regulation. Here we present evidence that the c-mpl-encoded receptor binds a ligand (c-Mpl ligand) which is a humoral factor implicated in platelet homeostasis. Our results suggest that c-Mpl ligand, thrombopoietin and MK-CSF might be the same molecule.

Animals↗