Erythroid Differentiation Of Mouse Erythroleukemia Cells Research Articles

Leukemia-related transcription factor TEL accelerates differentiation of Friend erythroleukemia cells.

TEL belongs to a member of the ETS family transcription factors that represses transcription of target genes such as FLI-1. Although TEL is essential for establishing hematopoiesis in neonatal bone marrow, its role in erythroid lineage is not understood. To investigate a role for TEL in erythroid differentiation, we introduced TEL into mouse erythroleukemia (MEL) cells. Overexpressing wild-type-TEL in MEL cells enhanced differentiation induced by hexamethylene bisacetamide or dimethylsulfoxide, as judged by the increased levels of erythroid-specific delta-aminolevulinate synthase and beta-globin mRNAs. TEL bound to a corepressor mSin3A through the helix-loop-helix domain. A TEL mutant lacking this domain still bound to the ETS binding site, but lost its transrepressional effect. This mutant completely blocked erythroid differentiation in MEL cells. Moreover, it showed dominant-negative effects over TEL-mediated transcriptional repression and acceleration of erythroid differentiation. Endogenous TEL mRNA was found to increase during the first 3 days in differentiating MEL cells and drastically decrease thereafter. All these data suggest that TEL might play some role in erythroid cell differentiation.

Chromatin remodeling gene SMARCA5 is dysregulated in primitive hematopoietic cells of acute leukemia

We identified a subset of genes involved in chromatin remodeling whose mRNA expression changes in differentiating mouse erythroleukemia (MEL) cells. We furthermore tested their mRNA expression patterns in normal and malignant CD34+ bone marrow cells. SMARCA5, imitation switch gene homologue, was rapidly silenced during in vitro erythroid differentiation of MEL cells whereas it was up-regulated in CD34+ hematopoietic progenitors of acute myeloid leukemia (AML) patients. Moreover, SMARCA5 mRNA levels decreased in AML CD34+ progenitors after the patients achieved complete hematologic remission. We detected high levels of SMARCA5 mRNA in murine bone marrow and spleen and monitored its expression in these hematopoietic tissues during accelerated hematopoiesis following hemolytic anemia induced by phenylhydrazine. SMARCA5 expression levels decreased after the onset of accelerated erythropoiesis. Our data suggest that both in vitro and in vivo induction of differentiation is followed by down-regulation of SMARCA5 expression. In CD34+ AML progenitors over-expression of SMARCA5 may thus dysregulate the genetic program required for normal differentiation.

Inhibition of erythroid differentiation in MEL cells by UV irradiation. Cell cycle and DNA repair activity

Irradiation with a 3-s pulse of 254 n, UV light has been used to study sensitivity to mutagenic agents of mouse erythroleukemia (MEL) cell cultures in correlation with the cell cycle. A dose of UV irradiation was chosen that had no consequences for cell viability and growth. For this reason phenotypic effects were monitored on the progeny of all cells of the irradiated cultures by scoring those unable to undergo erythroid differentiation upon induction with dimethyl sulfoxide. The very short period of irradiation made it possible to show that MEL cells, synchronized by two sequential blocks of deoxythymidine and one of hydroxyurea (HU), are sensitive to UV irradiation only in a very short period of time at about 60 min after release from HU block. Determinations of deoxythymidine incorporation into DNA show that this time period corresponds only marginally to the initial part of the S phase during which irradiation has no consequences for cell properties. Cells are not sensitive to UV irradiation in G1 and in G2/M unless, immediately after irradiation and for the following 2 h, cultures are treated with 1 mM HU to interfere with DNA repair.Alkaline sucrose gradient analyses show at all tested times that irradiation leads to fragmentation of cell DNA. The data suggest that an immediate increase of deoxythymidine incorporation into DNA following irradiation is not necessary for the efficient repair of damaged DNA. In fact, the percent of cells expressing the erythroid phenotype is normal in the progeny of cells irradiated in G2/M, when TdR incorporation is at a minimum. Repair activities appear then to be mechanistically divided into two phases, (1) recognition labeling of the altered sites and (2) reconstitution of the DNA sequences. The first activity appears to be operative at all phases of the cycle, the second activity is little or not operative in G2/M, possibly delayed to the following G1 period.

Inhibition of mouse GATA-1 function by the glucocorticoid receptor: possible mechanism of steroid inhibition of erythroleukemia cell differentiation.

Treatment of mouse erythroleukemia (MEL) cells with hexamethylene bisacetamide induces a program of erythrodifferentiation, as judged by an increase in the synthesis of globins and other erythroid-specific products. This induction can be inhibited by glucocorticoids, e.g. dexamethasone. All globin and other erythroid-specific genes tested contain GATA response elements (GATA-RE) and can be transactivated by GATA-1, a transcription factor. GATA-1 is highly expressed in erythroid cells, including MEL cells. We noted a glucocorticoid receptor (GR) response element motif near a GATA-RE motif in the promoter region of the mouse beta-major and beta-minor globin genes and about 130 bases away from a GATA-RE in the alpha 1-globin gene promoter and, therefore, investigated the possibility that the dexamethasone-induced inhibition of induced MEL cell differentiation may involve effects of the GR on GATA-1 activity. Evidence obtained from transfection assays and DNA electrophoretic mobility shift assays indicates that the GR binds GATA-1 and interferes with its function before any interaction with DNA, but that the presence of a glucocorticoid response element near a GATA-RE augments the GR effect. The N-terminal 106-amino acid domain of the GR was found to be essential for the effect, possibly by binding to GATA-1. Since GATA-1 is autoregulatory, i.e. it has been shown by others to bind to its own promoter and up-regulate its own transcription, the finding that activated GR can interfere with GATA-1 function may provide an explanation for the inhibition by glucocorticoids of the entire program of erythroid differentiation in MEL cells. That is, by interfering with GATA-1 function, the GR inhibits not only the expression of erythroid structural genes, but may also inhibit the expression of a primary erythroid regulatory gene, GATA-1. It was also shown that the GATA-RE in each of the beta-globin promoters responds to mouse GATA-1 in a functional transfection assay.

Cytoplasmic factors involved in erythroid differentiation in mouse erythroleukemia (MEL) cells

In order to identify and characterize intracellular factors involved in in vitro differentiation of mouse erythroleukemia (MEL) cells, the differentiation process was analyzed by cell and cytoplast fusion. The results suggested that the process is not a single cascade of molecular chain reactions, but a synergistic result of two different inducible intracellular reactions. One reaction is induced following damage to DNA (inhibition of DNA replication) and is not specific to MEL cells. The other reaction, which is specific to MEL cells, is fully induced by typical erythroid inducing agents such as dimethylsulfoxide or hexamethylenebisacetamide even at concentrations suboptimal for the erythroid induction. Based upon these data, we searched for the putative trans-acting differentiation-inducing factors and detected two proteinaceous factors (DIF-I and DIF-II) in the cytosol fraction which apparently correspond to these reactions. When, partially purified, either one of these factors was introduced into undifferentiated MEL cells, it triggered erythroid differentiation, provided that the recipient cells had been potentiated by the induction of the other reaction. In this article, we summarize the basic characteristics of these cytoplasmic factors involved in erythroid differentiation in MEL cells.

Effect of mitochondrial protein synthesis inhibitors on erythroid differentiation of mouse erythroleukemia (Friend) cells.

When mouse erythroleukemia (MEL) cells were incubated in the presence of chloramphenicol (a specific inhibitor for mitochondrial protein synthesis) during the early stage of in vitro erythroid differentiation, the number of induced erythroid cells was greatly reduced. By use of cell fusion between two genetically marked MEL cells, this finding was further investigated. We found that the drug, along with other agents which inhibit mitochondrial protein synthesis, blocked the induction and turnover of the DMSO-inducible intracellular-erythroid-inducing activity (differentiation-inducing factor II) in a manner similar to that of cycloheximide, an inhibitor for nuclear protein synthesis. The inhibitory effect was confirmed by directly assaying differentiation-inducing factor II in the cell extracts. These results strongly suggest that mitochondrial protein synthesis is closely associated with in vitro erythroid differentiation of MEL cells.

Effect of mitochondrial protein synthesis inhibitors on erythroid differentiation of mouse erythroleukemia (Friend) cells.

When mouse erythroleukemia (MEL) cells were incubated in the presence of chloramphenicol (a specific inhibitor for mitochondrial protein synthesis) during the early stage of in vitro erythroid differentiation, the number of induced erythroid cells was greatly reduced. By use of cell fusion between two genetically marked MEL cells, this finding was further investigated. We found that the drug, along with other agents which inhibit mitochondrial protein synthesis, blocked the induction and turnover of the DMSO-inducible intracellular-erythroid-inducing activity (differentiation-inducing factor II) in a manner similar to that of cycloheximide, an inhibitor for nuclear protein synthesis. The inhibitory effect was confirmed by directly assaying differentiation-inducing factor II in the cell extracts. These results strongly suggest that mitochondrial protein synthesis is closely associated with in vitro erythroid differentiation of MEL cells.