Differentiation Of Friend Cells Research Articles

Sphingosine kinase 1 expression is downregulated during differentiation of Friend cells due to decreased c-MYB

Sphingosine kinase 1 (SPHK1) overexpression in malignant cells has been reported. Mouse Friend cells showed higher SPHK1 but not SPHK2 expression compared with other mouse cell lines. A Sphk1 promoter analysis demonstrated the region between −53bp and the first exon as the minimal promoter. Further promoter truncation revealed the importance of a MYB-binding site. EMSA using this region as the probe demonstrated one band containing c-MYB protein, and its intensity decreased during erythroid differentiation with hexamethylane bisacetamide (HMBA), a potent inducer of erythroid differentiation of Friend cells. ChIP assay also revealed in vivo binding of c-MYB. c-MYB overexpression and siRNA for c-Myb affected SPHK1 expression, confirming the important regulatory role of c-MYB in SPHK1 expression. HMBA reduced c-MYB expression rapidly. Induced differentiation by HMBA caused a marked and rapid reduction of SPHK1 mRNA, protein and enzyme activity leading to the rapid decrease of cellular sphingosine 1-phosphate level. Moreover, terminally differentiated cells did not resume SPHK1 expression. Compared with original Friend cells, stable overexpression of wild-type SPHK1 showed higher cell proliferation, resistance to cell death by serum depletion. Interestingly, HMBA-induced differentiation of these cells was delayed but not completely suppressed. In contrast, SPHK inhibitor and its siRNA inhibited cell growth and enhanced HMBA-induced differentiation significantly, suggesting that SPHK1 delayed HMBA-induced differentiation by its cell proliferation-promoting activity. Effects of pertussis toxin, a G-protein-coupled receptor inhibitor, and S1P receptor antagonist on Friend cell growth and differentiation were negligible, suggesting the importance of the intracellular SPHK1/S1P signaling in Friend cells.

Enhancement of daunomycin toxicity by the differentiation inducer hexamethylene bisacetamide in erythroleukemia cells

Cytotoxic effects of daunomycin were investigated upon differentiation of Friend erythroleukemia cells induced with hexamethylene bisacetamide, a process during which a 20-fold increase in the hemoglobin content occurred. Daunomycin proved to be more toxic to differentiated Friend cells than to their undifferentiated counterparts. No changes in the daunomycin uptake rates of the two cell types were detectable. Externally added catalase and desferrioxamine mesylate protected against the additional cytotoxicity of daunomycin in differentiated cells, pointing to hydrogen peroxide and iron ions as mediators of the toxic effect. Daunomycin-dependent, cyanide-insensitive oxygen consumption of control and induced cells did not differ significantly, and the rate of formation of the daunomycin semiquinone radical electron paramagnetic resonance signal was similar in both cell types, indicating that the difference in toxicity was not due to increased drug activation by plasma membrane enzymes. Differentiated cells had a lowered catalase content; the cellular iron content was shown to increase by 2.8-fold upon cell differentiation, with hemoglobin-bound iron being about 50% of the total. Altogether, the results suggest increased intracellular hydrogen peroxide generation mediated by hemoglobin, combined with a decrease in catalase activity and an increase in accessible iron, as responsible for the higher sensitivity to daunomycin shown by differentiated Friend cells. This represents the first experimental system where the increase in anthracycline cytotoxicity upon cell differentiation can be attributed to redox activation and the formation of reactive oxygen species.

Lipid-dependent nuclear signalling: Morphological and functional features

Enzymes involved in lipid metabolism exist within the nucleus and are responsive to external stimuli. In particular, the kinases which phosphorylate phosphatidylinositol and phosphatidylinositol-4-monophosphate have been demonstrated in nuclei of both undifferentiated and differentiated Friend cells and of quiescent Swiss 3T3 cells as well as of those exposed to insulin-like growth factor I. Besides the lipid kinases, also the phosphoinositidases C (PIC) are active inside the nucleus. In Swiss 3T3 cells the nuclear PIC β1 is activated and its activation by IGF-I temporally precedes the translocation to the nucleus of protein kinase C. In Friend cell nuclei, on the other hand, when erythroid differentiation is induced, the PIC β1 activity is reduced. Another aspect of the nuclear signalling transduction system which appears quite interesting is its actual localization at subcellular level. By using electron microscope immunogold labelling, the nuclear PIC isoforms (the β1 isoform in Swiss 3T3 cells, the β1 and γ1 in Friend cells) are localized mainly in the interchromatin domains. This localization has been further confirmed on in situ matrix preparations of 3T3 cells in which PIC β1 is associated with the inner nuclear matrix but not with the nuclear pore-lamina complex. Colocalization experiments indicate that nuclear PIC β1 is present in sites in which both nuclear phospholipids and PKC can be detected, while the cytoplasmic PIC γ1 can be identified in close association with cytoskeletal filaments identified by anti-actin antibodies. The precise localization of the different PIC isoforms strongly indicates that the signal transduction system operating at the nuclear level may be part of a cross-talk between the cytoplasm and the nucleus controlling either cell proliferation or differentiation.

Calcium ionophore-induced transient down-regulation of c-myb mRNA levels in Friend erythroleukemia cells

The effects of calcium ionophores A23187 and ionomycin on the c-myb and c-myc mRNA levels have been investigated in the Friend erythroleukemia cell line F4-6 using Northern blot analysis. Treatment of the cells with 0.5-4 microM A23187 or 1-4 microM ionomycin induced a concentration-dependent decrease in c-myb mRNA; this decrease was abolished by EGTA. c-myc mRNA levels were only moderately affected. After 12-24 h of calcium ionophore exposure, c-myb mRNA returned to pretreatment levels. No similar decrease in c-myb mRNA was seen with the sodium ionophore monensin (up to 16 microM). The dimethyl sulfoxide-induced suppression of c-myb and also of c-myc mRNA levels was not prevented in Ca(2+)-free medium and thus appeared Ca(2+)-independent. A23187 and ionomycin were capable of inducing beta-globin mRNA synthesis in F4-6 cells. Prolonged calcium ionophore exposure, however, strongly reduced cell viability and resulted only in a slight hemoglobin increase at lower concentrations. These results suggest that a rise in [Ca2+]i may be a signal leading to a transient decrease in c-myb mRNA and the initiation of erythroid differentiation in Friend cells. The transient suppression of c-myb mRNA levels represents a common feature of the action of dimethyl sulfoxide and calcium ionophores.

Positive modulation of hemoglobin, heme, and transferrin receptor synthesis by murine interferon-alpha and -beta in differentiating Friend cells. Pivotal role of heme synthesis.

Administration of highly purified preparations of murine interferon (IFN)-alpha 1, -alpha 4, -alpha 6, or -beta to Friend leukemia cells induced to differentiate by dimethyl sulfoxide leads to a 100% increase of benzidine-positive (B+) cells. Different efficiencies for the two IFN species have been observed; a 10-fold higher dose of IFN-alpha is needed for stimulation of hemoglobin production and inhibition of cell growth as compared with IFN-beta. Both species of IFN induce a substantial increase in heme, hemoglobin, and transferrin receptor levels. In vitro run-on transcription assays indicate that IFN-beta moderately stimulates transcription of the alpha-globin gene but not the transferrin receptor gene. It is postulated that IFN induces the enhancing effect on differentiation via a marked increase of heme synthesis and number of transferrin receptors, which in turn leads to an enhancement of globin chain synthesis. In this regard, the negative feedback reported in a variety of other cell types for the regulation of transferrin receptor expression by heme does not seem to be operative in maturing Friend erythroleukemia cells, which present evidence for a positive mechanism.

Potent and specific inhibition of mammalian histone deacetylase both in vivo and in vitro by trichostatin A.

(R)-Trichostatin A (TSA) is a Streptomyces product which causes the induction of Friend cell differentiation and specific inhibition of the cell cycle of normal rat fibroblasts in the G1 and G2 phases at the very low concentrations. We found that TSA caused an accumulation of acetylated histone species in a variety of mammalian cell lines. Pulse-labeling experiments indicated that TSA markedly prolonged the in vivo half-life of the labile acetyl groups on histones in mouse mammary gland tumor cells, FM3A. The partially purified histone deacetylase from wild-type FM3A cells was effectively inhibited by TSA in a noncompetitive manner with Ki = 3.4 nM. A newly isolated mutant cell line of FM3A resistant to TSA did not show the accumulation of the acetylated histones in the presence of a higher concentration of TSA. The histone deacetylase preparation from the mutant showed decreased sensitivity to TSA (Ki = 31 nM, noncompetitive). These results clearly indicate that TSA is a potent and specific inhibitor of the histone deacetylase and that the in vivo effect of TSA on cell proliferation and differentiation can be attributed to the inhibition of the enzyme.

Differential effects of liposome-entrapped desferrioxamine on proliferation and erythroid differentiation of murine erythroleukemic Friend cells

It is known that iron chelators (such as desferrioxamine) are potent inhibitors of both cell proliferation and erythroid differentiation. We have shown with in vitro studies that in the case of tumor cells desferrioxamine is even more efficient in inhibiting cell proliferation when entrapped in liposomes consisting of egg yolk phosphatidylcholine. At the same time liposome-entrapped desferrioxamine retains only a slight effect on hexamethylenebisacetamide induction of erythroid differentiation and hemoglobin accumulation of murine erythroleukemic Friend cells. Based on these findings, we propose liposome-entrapped desferrioxamine as potential antineoplastic agent as well as a specific chemical for the study of both iron metabolism and distribution in normal and neoplastic cells. In addition, unlike free desferrioxamine, the liposome-entrapped drug could also be used in combination with inducers of differentiation. With respect to this issue, it is possible that liposome-entrapped desferrioxamine, might permit erythroid differentiation of both neoplastic cells as well as normal stem cells.

Tightly bound DNA-protein complexes representing stable attachment sites of large DNA loops to components of the matrix.

This study describes tightly bound DNA-protein complexes in DNA of matrices isolated from Friend erythroleukemia cells. When after radio-iodination of the associated proteins, such DNA is electrophoresed on agarose and the gel is subsequently subjected to autoradiography, the protein components of three or four complexes are visualized. Their two-dimensional electrophoretic analysis revealed that each possesses a simple but specific polypeptide composition, including a set of five non-histone proteins, characteristic for the matrix, and the core histones H3 and H4. Since the polypeptides dissociate from DNA by treatment with SDS, it is suggested that the linkage is not covalent. Reassociation and hybridization analysis of the DNA of the complexes indicated that it is enriched in highly repetitive, satellite sequences. The latter were found to be, to a great extent, similar to sequences localized at the base of large, dehistonized DNA loops obtained by high-salt extraction of isolated nuclei. Further experiments emphasized the complete conservation of this type of attachment throughout erythroid differentiation of Friend cells. It is proposed that the complexes represent attachment sites of basic, 30-100-kbp loop units of DNA.

Interferons and the differentiation of Friend cells.

Annals of the New York Academy of SciencesVolume 567, Issue 1 p. 253-258 Interferons and the Differentiation of Friend Cellsa G. B. ROSSI, Corresponding Author G. B. ROSSI Laboratories of Virology, Istituto Superiore di Sanità Rome, Italyc Address correspondence to Prof. Giovanni B. Rossi, Istituto Superiore di Sanità, Laboratory of Virology, Viale Regina Elena, 299, 00161 Roma, Italy.Search for more papers by this authorR. ALBERTINI, R. ALBERTINI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorA. BATTISTINI, A. BATTISTINI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorE. M. COCCIA, E. M. COCCIA Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorG. ROMEO, G. ROMEO Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorG. FIORUCCI, G. FIORUCCI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorG. MARZIALI, G. MARZIALI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorU. TESTA, U. TESTA Laboratories of Hematology-Oncology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorE. AFFABRIS, E. AFFABRIS Institute of Microbiology University of Messina Messina, ItalySearch for more papers by this author G. B. ROSSI, Corresponding Author G. B. ROSSI Laboratories of Virology, Istituto Superiore di Sanità Rome, Italyc Address correspondence to Prof. Giovanni B. Rossi, Istituto Superiore di Sanità, Laboratory of Virology, Viale Regina Elena, 299, 00161 Roma, Italy.Search for more papers by this authorR. ALBERTINI, R. ALBERTINI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorA. BATTISTINI, A. BATTISTINI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorE. M. COCCIA, E. M. COCCIA Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorG. ROMEO, G. ROMEO Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorG. FIORUCCI, G. FIORUCCI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorG. MARZIALI, G. MARZIALI Laboratories of Virology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorU. TESTA, U. TESTA Laboratories of Hematology-Oncology, Istituto Superiore di Sanità Rome, ItalySearch for more papers by this authorE. AFFABRIS, E. AFFABRIS Institute of Microbiology University of Messina Messina, ItalySearch for more papers by this author First published: August 1989 https://doi.org/10.1111/j.1749-6632.1989.tb16476.xCitations: 1 a This work was supported in part by grants from Consiglio Nazionale delle Ricerche, Rome, Italy: Progetti Finalizzati “Oncologia” N. 8701151.44 and N. 86.02683.44 and from the Associazione Italiana per la Ricerca contra il Cancro, Milan, Italy. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume567, Issue1Viral Oncogenesis and Cell Differentiation: The Contributions of Charlotte FriendAugust 1989Pages 253-258 RelatedInformation

Opposite effects of murine interferons on erythroid differentiation of friend cells

Interferons (IFNs), in addition to inducing an antiviral state in uninfected cells, are able to affect cell physiology, including cell differentiation. In this respect hematopoiesis is certainly the area in which most data have accumulated. In general IFN-α or-β inhibit cell growth of normal progenitors of hematopoietic lineages. In leukemia cell cultures IFNs may either stimulate or inhibit cell growth and differentiation. We report here different biological effects of murine (mu) IFN- α 1, -β and -γ species on the erythroid differentiation of dimethyl sulfoxide (DMSO)-induced Friend leukemia cells. Treatment with mu recombinant IFN-β enhances DMSO-induced FLC differentiation, whereas treatment with IFN- α 1 species as well as with natural and recombinant mu IFN-γ preparations only inhibits it. All these observed effects are neutralized by monoclonal antibodies against IFN-α, -β and -γ species. When mu fibroblast IFN (a mixture of α and β species) was used, the inhibitory effect attributable to IFN-α was partly overshadowed by the simultaneous presence of a majority of IFN-β molecules exerting the opposite effect. This is in agreement with data obtained neutralizing fibroblast IFN preparations with excess amounts of monoclonal antibodies against IFN-β (G. B. Rossi etal., 1988, “The Status of Differentiation Therapy of Cancer,” Raven Press, New York) and with our previous reports indicating that mu fibroblast IFN can either enhance or inhibit DMSO-induced differentiation when administered at low (<500 U/ml) or high (>5000 U/ml) doses, respectively. The inhibitory effect of IFN- α 1 on cell differentiation is not linked to any inhibitory effect on cell growth. Results obtained analyzing the effect of IFN- α 1 and -β on various IFN-resistant FLC clones indicate that different mechanisms underlie the stimulatory effect of IFN-β and the inhibitory effect of IFN- α 1. These results shed light on possibly distinct physiological roles of the various species of IFNs.

Immunofluorescent localization of histone H1 0 in the nuclei of proliferating and differentiating friend cells

By using affinity-purified antibodies to H1 0 and to H1AB the localization of these histones was studied by indirect immunofluorescence in the nuclei of proliferating (EAT and uninduced Friend cells) and of differentiating (induced Friend cells) cell populations. While with H1AB antibodies a bright fluorescence all over the chromatin was obtained, the localization of H1 0 varied depending on the state of the cell population. In the proliferating EAT cells it was localized strictly in the nucleoli. The Friend cell population revealed a heterogeneous picture with two types of H1 0 localization—nucleolar predominating in uninduced cell populations and peripheral predominating in induced cells. A comparison with literature data suggests that H1 0 seems to be associated with chromatin regions containing active genes.

Glycolipids of mouse erythroleukemia cells (Friend cells) and their alteration during differentiation.

Neutral and acidic glycosphingolipids of Friend cells were characterized in 1) undifferentiated Friend cells (745A), 2) differentiated Friend cells induced with dimethyl-sulfoxide, and 3) solid tumors grown in mice after subcutaneous implantation of Friend cells. The structures of the isolated glycosphingolipids were determined by means of compositional analysis, methylation analysis and enzyme treatment. Gangliosides GD1a and N-acetylgalactosaminyl-GD1a, followed by GM1a and GM2, were the main gangliosides in undifferentiated Friend cells. GD1a and N-acetylgalactosaminyl-GD1a accounted for 45 and 25% of the total gangliosides, respectively. On differentiation, ganglioside GM2 decreased significantly, from 10% to a trace amount. In solid tumors, GD1a was the major ganglioside, whereas in contrast to the situation in the cultured cells, N-acetylgalactosaminyl-GD1a was almost completely absent, and ganglioside GM1b, but not GM1a, was detected. In addition, ganglioside GD1 alpha was detected in the solid tumors. Galactosylceramide, glucosylceramide, and lactosylceramide were the main neutral components in both types of cells, while globotetraosylceramide (globoside), IV3-N-acetyl-galactosaminyl globotetraosylceramide (Forssman glycolipid) and gangliotetraosylceramide (GA1) were major in solid tumors grown in vivo.

Cellular-oncogene expression in Friend erythroleukemia cells: relationship to differentiation, commitment and TPA effects.

Induced differentiation of Friend erythroleukemia cells can be continuously and reversibly inhibited by phorbol ester tumor promoters, e.g. 12-O-tetradecanoylphorbol-13-acetate (TPA), for many years, allowing us to study the mechanisms of differentiation and its inhibition by TPA. We previously identified two steps in the differentiation process, which can be inhibited by TPA, before and after commitment to differentiation. Using permanently committed cells and TPA-resistant variants we examined the role of cellular oncogenes in Friend cell differentiation control, and their possible modulation by tumor-promoting phorbol esters. We report here characteristic changes in myc, myb and fos mRNA levels upon induction of differentiation by hexamethylene bisacetamide treatment, and present evidence that c-myb mRNA decline is one feature of Friend cell commitment to differentiation. In addition, using our TPA-sensitive and resistant cell lines, we observed that the hexamethylene bis-acetamide induced pattern of oncogene expression is unperturbed by TPA, regardless of whether the cells are differentiating or not.

Phospholipid asymmetry during erythropoiesis. A study on Friend erythroleukemic cells and mouse reticulocytes

The distribution of phospholipids over the outer and inner layers of the plasma membranes of differentiated Friend erythroleukemic cells (Friend cells) and mouse reticulocytes has been determined. Phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol were found to be distributed symmetrically over both layers, sphingomyelin was found to be enriched in the outer layer (80–85%) and phosphatidylserine appeared to be present mainly in the inner layer (80–90%) of the plasma membranes of differentiated Friend cells. The outer layer of reticulocyte membranes contains 50–60% of the phosphatidylcholine, 20% of the phosphatidylethanolamine, 82–85% of the sphingomyelin and 40–42% of the phosphatidylinositol. All of the phosphatidylserine is present in the inner layer. The results show, that the asymmetric distribution of phospholipids, typical for erythrocyte membranes, is partially apparent already at an early stage of erythropoiesis, the proerythroblast, while the final organization of phospholipid distribution takes place at some stage during enucleation of the enormoblast and release of the reticulocyte into the blood stream.

Transcriptional and translational regulation of ornithine decarboxylase during friend cell differentiation: [formula omitted]. Lab. de Cytologie Expte. (UA256 CNRS), University Rennes 1, F-35042 Rennes cédex, France

Transcriptional and translational regulation of ornithine decarboxylase during friend cell differentiation: [formula omitted]. Lab. de Cytologie Expte. (UA256 CNRS), University Rennes 1, F-35042 Rennes cédex, France

Changes in protein kinase C activity are associated with the differentiation of Friend erythroleukemia cells

We investigated the activity and cellular distribution of protein kinase C during the dimethylsulfoxide (DMSO) and hypoxanthine-induced differentiation of Friend murine erythroleukemia cells. Most of the cellular protein kinase C activity was found in the soluble fraction of unstimulated Friend cells. Within 15 min of the addition of DMSO or hypoxanthine, protein kinase C underwent a dramatic and prolonged reversal of this distribution which was accompanied by a gradual decline in total cellular protein kinase C activity over the ensuing 5 days. The loss of total activity was found to be dose dependent although maximal translocation from soluble to insoluble components occurred at even lower concentrations of the inducers tested. Two clones of Friend cells, selected for their failure to differentiate in response to DMSO, showed alterations in protein kinase C activity and/or distribution following DMSO addition when compared to wild-type Friend cells. These data show that different inducers of Friend cell differentiation have similar effects on cellular protein kinase C, that the protein kinase C changes accompanying this process are immediate but prolonged, and that changes in protein kinase C activity and distribution are associated with Friend cell differentiation.

The influence of amphotericin B on differentiation induced by dimethylsulfoxide and actinomycin D in HL60 and Friend cell lines.

We use murine erythroid Friend cells and human promyelocytic HL60 cells to investigate the influence of a transmembrane signal in triggering myeloid or erythroid cell differentiation. Combined treatments were given with dimethylsulfoxide, actinomycin D and amphotericin B, a substance which resembles a deviant membrane lipid and which seems to influence exclusively membrane activity. Our results suggest that a membrane modification alone is sufficient for in vitro HL60 cell differentiation, whereas both a transmembrane and a nuclear signal are necessary for Friend cell differentiation.

Control of heme synthesis during Friend cell differentiation: role of iron and transferrin.

In many types of cells the synthesis of delta-aminolevulinic acid (ALA) limits the rate of heme formation. However, results from our laboratory with reticulocytes suggest that the rate of iron uptake from transferrin (Tf), rather than ALA synthase activity, limits the rate of heme synthesis in erythroid cells. To determine whether changes occur in iron metabolism and the control of heme synthesis during erythroid cell development Friend erythroleukemia cells induced to erythroid differentiation by dimethylsulfoxide (DMSO) were studied. While added ALA stimulated heme synthesis in uninduced Friend cells (suggesting ALA synthase is limiting) it did not do so in induced cells. Therefore the possibility was investigated that, in induced cells, iron uptake from Tf limits and controls heme synthesis. Several aspects of iron metabolism were investigated using the synthetic iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH). Both induced and uninduced Friend cells take up and utilize Fe for heme synthesis directly from Fe-SIH without the involvement of transferrin and transferrin receptors and to a much greater extent than from saturating levels of Fe-Tf (20 microM). Furthermore, in induced Friend cells 100 microM Fe-SIH stimulated 2-14C-glycine incorporation into heme up to 3.6-fold as compared to the incorporation observed with saturating concentrations of Fe-Tf. In contrast, Fe-SIH, even when added in high concentrations, did not stimulate heme synthesis in uninduced Friend cells but was able to do so as early as 24 to 48 h following induction. In addition, contrary to previous results with rabbit reticulocytes, Fe-SIH also stimulated globin synthesis in induced Friend cells above the level seen with saturating concentrations of transferrin. These results indicate that some step(s) in the pathway of iron from extracellular Tf to protoporphyrin, rather than the activity of ALA synthase, limits and controls the overall rate of heme and possibly hemoglobin synthesis in differentiating Friend erythroleukemia cells.

An intracellular factor that induces erythroid differentiation in mouse erythroleukemia (Friend) cells

We have previously shown that in vitro erythroid differentiation of mouse Friend cells is a result of a synergistic action of two distinctive intracellular reactions. We now have evidence that a factor in the cell free extract is involved in one of the reactions. This factor triggers erythroid differentiation when introduced into undifferentated mouse Friend cells, provided the cells have been briefly exposed to dimethyl sulfoxide. The factor is induced in nonerythroid cells as well following treatment of the cells by agents that affect DNA replication. Cycloheximide inhibited the induction of the factor. The factor, which is in the cytoplasm, was partially purified and proteinaceous. When introduced into the cells the partially purified factor converts 60% to 70% of undifferentiated Friend cells to erythroid cells, at an efficiency almost equivalent to the efficiencies achieved by typical inducing agents. The factor's biochemical characteristics and possible role in erythroid differentiation are also discussed.

Transcriptional and post-transcriptional regulation of c-myc expression during the differentiation of murine erythroleukemia Friend cells.

c-myc RNA rapidly decreases to barely detectable levels in Friend erythroleukemia cells induced to differentiate upon the addition of dimethylsulfoxide. We show here that c-myc gene is down-regulated both at the transcriptional level presumably by a block in the elongation of primary transcripts and at the post-transcriptional level by an increase in the degradation of its mRNA.