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At least 19 recordsLinked to original sources
PubMed1989

Cyclic changes in fluorescence polarization of a membrane probe during the cell cycle of an erythroid precursor cell line.

The membrane lipid bilayer of the K562 cell line undergoes marked changes during cell cycling. These changes can be detected by measuring the fluorescence polarization of the rod-like hydrophobic probe 1,6-diphenyl-1,3,5-hexatriene. Single-cell measurements were performed by flow microfluorometry on synchronized K562 cells. The fluorescence polarization of the probe increased after cell division and was maximal during the S phase. Concomitant with the transition from S to G2 and M phase was a decrease in fluorescence polarization. The data are interpreted as reflecting a minimal membrane lipid fluidity during the S phase and a maximal fluidity during the G2/M-phase of the above erythroid precursor cell line.

Cell Cycle↗
PubMed1989

Folate (pteroylglutamate) uptake in human red blood cells, erythroid precursors and KB cells at high extracellular folate concentrations. Evidence against a role for specific folate-binding and transport proteins.

Membrane-associated folate (pteroylglutamate, PteGlu)-binding proteins (FBPs) play an important role as PteGlu-transport proteins in malignant and normal human cells. Since high extracellular folate (PteGlu) concentrations (EFC) profoundly influenced uptake and toxicity of the anti-PteGlu methotrexate in malignant KB cells, we studied human cells to determine additional mechanisms for PteGlu uptake when the EFC was varied. At low EFC (less than 10 nM), the predominant mechanism for folate uptake in mature erythrocytes was through binding to externally oriented FBPs which were quantitatively insignificant (4-6 orders of magnitude lower) and of no apparent physiological relevance when compared with KB cells. However, the predominant mechanism of PteGlu accumulation at high EFC [10-250 nM] in intact erythrocytes and sealed right-side-out (RSO) ghosts was not FBP-mediated and non-specific. This conclusion was based on the findings that radiolabelled PteGlu uptake: (i) continued even in the presence of a 1000-fold excess of unlabelled PteGlu and was linear and not saturable up to 250 nM; (ii) was two-fold higher at pH 4.5 than 7.5; (iii) was less than 2-fold increased at 37 degrees C compared with 4 degrees C; and (iv) was unaffected after trypsin-mediated proteolysis of greater than 75% FBPs. The [3H]PteGlu and 125I-PteGlu (histamine derivative) accumulated intracellularly through the non-specific PteGlu-uptake mechanism was unaltered biochemically and in a soluble compartment. Raising the EFC 500-fold higher than controls during erythropoiesis in vitro resulted in reversal of the expected anti-(placental folate-receptor)-antiserum-induced megaloblastic changes in orthochromatic normoblasts derived from burst-forming unit-erythroid colonies. Furthermore, at EFC greater than 0.1 microM, KB-cell accumulation of [3H]PteGlu was also predominantly through a mechanism that did not involve specific FBPs. Thus, at high EFC, a major component of PteGlu transport in human cells is not mediated through FBPs and is likely to be a passive diffusion process.

Carrier Proteins↗
PubMed1976

Isolation and in vitro differentiation of human erythroid precursor cells.

There is decreased beta-globin production in beta-thalassemic reticulocytes and nucleated erythroid cells. In this study, we have examined whether unbalanced globin synthesis is expressed at all stages of human erythroid cell maturation. In order to determine the pattern of globin synthesis in early erythroid cells during erythroid cell maturation, an in vitro culture system using human bone marrow erythroid precursor cells has been developed. Early erythroid precursor cells (proerythroblasts and basophilic erythroblasts) have been isolated from nonthalassemic and thalassemic human bone marrows by lysing more mature erythroid cells, using complement and a rabbit antiserum prepared against normal human red cells. In the presence of erythropoietin, differentiation and proliferation of erythroid cells in demonstrable in liquid suspension culture for 24-48 hr, as determined by morphological criteria and by an increase in globin synthesis. The ratio of alpha- to beta-globin chain synthesis in nonthalassemic cells in approximately 1 at all stages of erythroid cell differentiation during culture. In cells from four patients with homozygous beta- thalassemia there is decreased beta-globin synthesis compared to alpha-globin synthesis, both in early erythroid precursor cells and during their maturation in culture. These findings indicate that unbalanced globin chain synthesis is expressed at all stages of red cell maturation in homozygous beta-thalassemia.

Anemia, Sickle Cell↗
PubMed1992

Protein deficiency impairs erythropoiesis in rats by reducing serum erythropoietin concentration and the population size of erythroid precursor cells.

Erythropoietin (EPO), a glycoprotein produced mainly by the kidney, is the major physiological regulator of erythropoiesis. We developed a sensitive and rapid ELISA for measurement of rat serum EPO with two monoclonal antibodies that recognize different epitopes. To understand the mechanism by which erythropoiesis is impaired in rats deficient in dietary protein, we investigated the levels of the immunoreactive EPO (iEPO) in serums and erythroid precursor cells in hemopoietic tissues during protein deprivation. The iEPO level of 32-d-old rats fed a protein-free diet was lowered to one-third that of rats fed 20% casein at 6 h after protein deprivation began. Protein deprivation decreased the number of EPO-responsive cells in spleen. These results indicate that the impairment of erythropoiesis during protein deficiency is caused by the decrease in serum EPO and the subsequent reduction of the population size of erythroid precursor cells in spleen.

Animals↗
PubMed1990

Pteridine modulation of lead inhibition of uroporphyrinogen synthesis in erythroid precursor cells.

The role of nutritional factors on heme synthesis and their influence on the development of anemia in the bone marrow during lead exposure is unclear. Previous reports suggested that pteridines could regulate the formation of uroporphyrinogen, a step midway along the heme synthetic pathway. Studies were undertaken to determine if pteridines could modulate lead inhibition of uroporphyrinogen synthesis in erythroid precursor cells. Pteroylpolyglutamates of various glutamate chain lengths were tested for the ability to protect against lead inhibition of uroporphyrinogen I (URO) synthase prepared from murine erythroleukemia cells (MELC). Pteroylpentaglutamate, the major endogenous polyglutamate form by chain length found to be present in MELC, afforded rapid and specific protection of URO synthase against lead inhibition. MELC are expected to be a useful in vitro model for studying the role of endogenous folates on uroporphyrinogen synthesis and heme formation in erythroid precursor cells following lead exposure.

Animals↗
PubMed1987

Binding and internalization of recombinant human erythropoietin in murine erythroid precursor cells.

Erythropoietin (EPO) biosynthetically labelled with [35S]cysteine was produced from Chinese hamster ovary (CHO) cells containing amplified copies of human EPO cDNA. The glycosylated recombinant [35S]EPO, purified to virtual radiochemical homogeneity, was biologically active. We studied the interaction of this labeled recombinant EPO with erythroid precursor cells from mice made anemic with phenylhydrazine. The [35S]-labeled molecule bound to erythroid precursors in a time- and temperature-dependent manner. The binding was specific for EPO, and neither insulin, transferrin, epidermal growth factor, nor multiplication stimulating activity could compete for EPO binding sites. In the presence of 0.2% sodium azide, which blocks 80% to 90% of internalization, the recombinant molecule bound with an apparent Kd of 750 pmol/L and 100 to 200 binding sites per cell at 37 degrees C. Asialo-EPO was a more effective competitor than sialated EPO for the available binding sites. Thus, the enhanced biological specific activity of asialo-EPO could result from its enhanced binding affinity. We also studied recombinant human EPO labeled with 125I and found that it also bound to the erythroid cells in a saturable and specific manner. After 90 minutes of incubation at 37 degrees C, most of the bound [35S]EPO was internalized, whereas most of the [125I]EPO remained on the cell surface. The reduced internalization of the iodinated molecule could account for the previously reported functional deficit associated with iodination.

Animals↗
PubMed1977

Characterization of an erythroid precursor cell of high proliferative capacity in normal human peripheral blood.

We have found that the peripheral blood of normal humans contains a significant number of committed erythroid stem cells of high proliferative capacity. These erythroid stem cells closely resemble the murine erythroid burst-forming unit (BFU-E) with respect to proliferative capacity, colony morphology, and erythropoietin requirement. BFU-E were isolated from the peripheral blood of normal individuals by Ficoll-Hypaque density gradient centrifugation and cultured in vitro using the plasma culture technique. Macroscopic erythroid colonies of between 100 and 1000 cells were observed after 10-14 days of culture in the presence of either sheep or human erythropoietin at 0.5-4 units/ml. Individual colonies contained between 3 and 20 subcolonies and reached a maximum mean size of approximately 500 cells. Colony number was linearly related to the cell input, suggesting that a single cellular entity was precursor to each colony. The frequency of cells capable of giving rise to an erythroid colony was at least 100 per ml of blood in a number of individuals tested. The ability to assay significant numbers of erythroid precursor cells of high proliferative capacity from normal peripheral blood should facilitate the study of both normal erythropoiesis and of disease states affecting erythropoiesis in which marrow samples are not available on a routine basis.

Blood Cells↗
PubMed1990

Transformation of early erythroid precursor cells (BFU-E) by a recombinant murine retrovirus containing v-erb-B.

Avian erythroblastosis virus (AEV) is a replication-defective retrovirus that transforms erythroid and fibroblast cells in vitro and in vivo. The transforming ability of AEV is due primarily to the oncogene v-erb-B. A recombinant murine retrovirus has been constructed by inserting a chimeric gag-v-erb-B gene into a Moloney murine leukemia virus based vector. This retrovirus was used to examine v-erb-B-induced transformation of murine hematopoietic cells. Infection of murine primary fetal liver, adult bone marrow or adult spleen cells with the recombinant virus generated large hemoglobinized erythroid colonies in the absence of exogenous growth factors. Generation of such colonies usually requires the presence of erythropoietin (Epo) and interleukin-3 (IL-3). These growth-factor independent colonies were shown to be derived from early (BFU-E) and not late (CFU-E) erythroid progenitor cells, and the effect was not attributable to growth factors elicited by the virus-producing cell lines. In order to confirm that the recombinant virus was responsible for this transformation of BFU-E to growth factor independence, bone marrow cells from post 5-fluorouracil treated mice were infected and used to repopulate lethally-irradiated mice. Growth factor-independent BFU-E were obtained in up to 30% of day-13 spleen colonies and it was shown by DNA analysis that cells from these colonies contained integrated provirus. Our results indicate that v-erb-B transforms early erythroid progenitors to growth factor independent growth and subsequent differentiation to erythrocytes -a process that normally requires Epo plus either IL-3 or granulocyte-macrophage colony stimulating factor (GM-CSF).

Alpharetrovirus↗
PubMed1990

Evolution and development of membrane components in erythroid precursor cells in newly-developed two phase culture system.

A selective two phase liquid culture system for human erythroid progenitors was established, utilizing mononuclear cells obtained from human peripheral blood. The culture was performed in the presence of PHA-leukocyte conditioned medium for 7 days as the first phase, and nonphagocytic cells were recultured under hypoxic culture conditions containing iron-saturated transferrin and erythropoietin. During the second phase of the culture, differentiation to orthochromatic erythroblasts was observed on day 4, and to denucleated cells on day 8 with 16.8 +/- 0.7 micrograms/10(6) cells of hemoglobin level, respectively. Flow cytometric analyses revealed that, on day 3, cells became type M-positive, and the expression of ABH increased gradually corresponding to the extent of erythroid maturation. Lewis antigens and P antigens were expressed at day 5. The system is beneficial for studies on human membrane disorders, because the erythroid progenitors in human peripheral blood were utilized and the reasonable number of erythroid cells (0.5-1.5 x 10(7] was obtained with good erythroid maturation, such as denucleated erythrocytes.

Antigens↗
PubMed1987

Identification and characterization of an antigen specific for normal erythroid precursor cells and its application in diagnosis of erythroleukemia.

A monoclonal antibody (designated K:1-6F) generated by hybridization of mouse myeloma cells with spleen cells from mice immunized with the erythroleukemic cell line K562 was found by fluorescence-activated cell sorter analysis, dot-blot assay and electroimmunoblotting to bind to a majority of cells in the K562 and HEL erythroleukemic cell lines, to a subset of cells of the erythroid lineage from normal bone marrow, to a subset of cells in all analysed cases (total 10) of erythroleukemia, and weakly to cells from patients with myeloid leukemia. The antibody did not bind to normal erythrocytes, monocytes, T- and B lymphocytes or granulocytes, as well as a panel of human malignant cell lines of hemopoietic origin (HL60, U937, Daudi, Molt-3, RH-L4 and U266). Biochemical characterization of the antigen defined by the antibody suggests that eht epitope is defined by a carbohydrate structure alone or in combination with proteins. Four molecules with Mr 100 kD, 65 kD, 45 kD and 18 kD respectively were immunoprecipitated from Triton X-100 extract of K562 erythroleukemia cells. Neuraminidase did not affect the binding of the antibody, whereas tunicamycin reduced the K:1-6F expression. The K:1-6F Mab was in normal bone marrow found to be specific for erythroid precursor cells and may therefore be useful in examination of normal and leukemic erythropoiesis.

Animals↗
PubMed1976

Unbalanced globin chain synthesis in erythroid precursor cells of heterozygous alpha-thalassaemia.

Globin biosynthesis was studied in both erythroid precursors and reticulocytes of three individuals with heterozygous alpha-thalassaemia. In contrast to the finding of equal or nearly equal alpha and beta chain synthesis in the marrow of patients with heterozygous beta-thalassaemia previously examined, our studies showed equal degrees of unbalanced globin synthesis in both reticulocytes and nucleated-erythroid cells of alpha-thalassaemia heterozygotes. Greater stability and less susceptibility to proteolysis of the excess beta-chain formed in alpha-thalassaemia may explain our findings.

Anemia, Sickle Cell↗
PubMed1986

Mode of action of erythropoietin and glucocorticoids on the hepatic erythroid precursor cells: role of prostaglandins.

The hypothesis that prostaglandins, and especially PGE2, are the second messengers of erythropoietin (Ep) and that glucocorticoids inhibit Ep action by inhibiting PG synthesis was tested on the erythroid cell line from fetal rat liver. The optimal (10(-9) M) stimulatory concentration of PGE2 did not reproduce, by far, the maximal effect of Ep on the growth of CFUE erythroid colonies. Ep did not increase PGE2 release in liquid culture media of cell suspensions made of the whole erythroid line or enriched (over 85%) in precursor cells. Ep did not modify the turnover rate of arachidonate. Nevertheless, indomethacin partially inhibited Ep effect on CFUE development, and this inhibition was abolished by PGE2. These results suggest that PGE2 potentiates Ep action but is not its second messenger. Spontaneous PGE2 release in liquid culture media brought about concentrations of the order of 10(-9) M, and 10(-7) M dexamethasone completely inhibited this release. Part of (but not all) the anti-Ep effects of glucocorticoids might thus be mediated this way. Dexamethasone effects required previous protein synthesis.

Animals↗
PubMed1977

An assay for serum cytotoxicity against erythroid precursor cells in pure red cell aplasia.

Several reports have indicated that a circulating serum inhibitor (antibody) is involved in the pathogenesis of acquired pure red cell aplasia (PRCA). In the present study, the pathophysiologic significance of this inhibitor was assessed according to the status of erythroid progenitor cells in the bone marrow. So far, direct proof for the antibody acting against erythroid stemcells was lacking. Employing an "in vitro" assay, erythroid colony forming cell (CFU-e) numbers in PRCA marrow were quantified and the cytotoxic effect of PRCA serum on CFU-e was investigated. It was revealed that the CFU-e population size in the marrow of PRCA patients was severely reduced; at the same time the relative number of myeloid colony forming cells was normal. The serum was demonstrated to contain a factor cell which was cytotoxic to CFU-e, in the presence of complement. The results indicate that inhibition of erythropoiesis in PRCA is achieved by a complement dependent plasma factor which eliminates or inactivates CFU-e and which constitutes an effective block at the precursor cell level in the differentiation pathway of the erythroid line. The data present a practical assay for measuring cytotoxic factors affecting erythroid stem cells.

Adult↗
PubMed1987

Expression of the 5'-flanking region of the beta major-globin gene in cultured murine erythroid precursor cells.

The amounts of mouse beta major-globin mRNA and globin gene upstream RNA polymerase III transcripts were compared during the differentiation of purified erythroid colony-forming progenitor cells (CFU-E) in vitro. The accumulation of each RNA was determined relative to the 100% levels in fetal liver erythroid cells. The mRNA level was low in freshly isolated CFU-E and began to accumulate only after a lag period of approximately 2-4 h. It continued to accumulate for approximately 40 h thereafter, at which point it was comparable to that in the fetal liver. In contrast, in three of four CFU-E preparations, the relative level of upstream RNAs was high in freshly isolated CFU-E and reached the maximal level (defined as 100% of the fetal liver level) more rapidly than did the mRNA. The early induction and accelerated accumulation of upstream RNAs in immature erythroid cells suggest some role for these RNAs at an early stage of globin gene activation.

Animals↗
PubMed1988

Maintenance by erythropoietin of viability and maturation of murine erythroid precursor cells.

Erythroblasts isolated from the spleens of mice infected with the anemia-inducing strain of Friend virus (FVA cells)-are erythropoietin (EP)-sensitive cells at the late colony forming unit-erythroid (CFU-E) and cluster forming unit stages of differentiation (Koury et al., J. Cell. Physiol. 121:526-532, 1984). We investigate here the EP requirements of FVA cells in vitro for viability, proliferation, and maturation. By delaying the addition of EP to FVA cell cultures or by withdrawing EP at early times of culture, the subsequent viability, cell numbers, and maturation were diminished. The longer the delay in EP addition or the earlier the EP withdrawal, the more diminished these parameters were when compared to cultures which contained EP throughout the 48 h of differentiation. FVA cells had a period of EP requirement in vitro that lasted for only 24 h or less after the initiation of culture. During these crucial first 24 h, EP induced an increase in the synthesis of all size classes of RNA. Protein synthesis was maintained at a stable level in cells cultured with EP, but it declined in cells cultured without it. In contrast, the synthesis rate of DNA and the content of DNA per cell were not affected by the presence of EP in the culture. However, FVA cells cultured without EP had progressive accumulation of small sized DNA due to breakage of higher molecular weight DNA. The rate of DNA breakdown was sufficient to prevent DNA accumulation and thus it probably plays a role in the abortion of cell proliferation. No such breakage was found in cells cultured with EP. Our results indicate that EP exerts an effect on FVA cells in culture which is reflected in their viability, cell number, and maturation. This effect is not mediated by a stimulation of the rate of DNA synthesis, but is accompanied by stimulation of overall RNA synthesis and maintenance of protein synthesis.

Animals↗
PubMed1979

Particle-induced erythropoietin-independent effects of erythroid precursor cells in murine bone marrow.

A possible regulatory action of phagocytic cells on erythropoiesis was investigated by infusion of inert polystyrene latex particles (LAT). LAT appeared to induce changes in the femoral content of erythroid progenitor cells. These changes were most pronounced in primitive erythroid progenitor cells (BFUe) and appeared to be gradually damped in more differentiated populations (CFUe and erythroblasts). LAT did not influence granulocyte/macrophage progenitor cells (CFUc). The effects of LAT could not be attributed to changes in the systemic erythropoietin (EP) concentration. Administration of dexamethason nullified the effect of low doses of LAT, suggesting that phagocytosis of the particles is essential to the observed effects. Erythroid burst formation was previously found to be dependent on a bone marrow associated activity, termed BFA (burst feeder activity). BFA acts as an in vitro inducer of EP-responsiveness in BFUe. In this study it was found that LAT-induced changes in femoral erythroid progenitor cell content were characteristically preceded by corresponding changes in BFA. It was concluded that BFA-associated cells probably play a role in vivo in the early differentiation of erythroid progenitor cells. The present data are interpreted as direct in vivo evidence supporting a two-step regulatory model operating in erythropoiesis and provide evidence that phagocytic cells are a component of the erythroid haemopoietic inductive micro-environment.

Animals↗
PubMed1986

The fibronectin receptor on mammalian erythroid precursor cells: characterization and developmental regulation.

The plasma membrane of murine erythro-leukemia (MEL) cells contains a 140-kD protein that binds specifically to fibronectin. A 125I-labeled 140-kD protein from surface-labeled uninduced MEL cells was specifically bound by an affinity matrix that contained the 115-kD cell binding fragment of fibronectin, and specifically eluted by a synthetic peptide that has cell attachment-promoting activity. The loss of this protein during erythroid differentiation was correlated with loss of cellular adhesion to fibronectin. Both MEL cells and reticulocytes attached to the same site on fibronectin as do fibroblasts since adhesion of erythroid cells to fibronectin was specifically blocked by a monoclonal antibody directed against the cell-binding fragment of fibronectin and by a synthetic peptide containing the Arg-Gly-Asp-Ser sequence found in the cell-binding fragment of fibronectin. Erythroid cells attached specifically to surfaces coated either with the 115-kD cell-binding fragment of fibronectin or with the synthetic peptide-albumin complex. Thus, the erythroid 140-kD protein exhibits several properties in common with those described for the fibronectin receptor of fibroblasts. We propose that loss or modification of this protein at the cell surface is responsible for the loss of cellular adhesion to fibronectin during erythroid differentiation.

Animals↗