losartan-potassium and Cell-Transformation--Viral

The Friend spleen focus-forming virus has been a valuable tool for understanding the molecular events involved in the multiple stages of leukaemia. As summarized in Figure 3, the primary effect of SFFV, which occurs within days, is to cause a polyclonal proliferation of erythroid precursor cells that can proliferate in the absence of their normal regulator erythropoietin. This is the direct result of the unique envelope glycoprotein encoded by SFFV, which is transported to the cell surface and apparently interacts with the EpoR or another component of the multimeric EpoR complex, resulting in the constitutive activation of the Epo signal transduction pathway. Within this proliferating population of erythroid cells is a rare cell that has undergone several genetic changes due to the integration of the viral genome in specific sites in the mouse DNA. This leads to the activation of a gene encoding the PU.1 transcription factor, whose high expression in erythroid cells may be the cause of the block in differentiation that is characteristic of SFFV-transformed erythroid cells. SFFV integration can also lead to the inactivation of the p53 tumour supressor gene, giving these cells a growth advantage in the mouse. The disease induced by SFFV in mice is very similar to polycythaemia vera in humans (Golde et al, 1981). The major clinical feature of polycythaemia vera is the continuous expansion of the number of mature red blood cells in the presence of low serum Epo levels. Also, BFU-E and CFU-E from these patients can form in the absence of Epo like the analogous cells from SFFV-infected mice (Casadevall et al, 1982). It is possible that haematopoietic cells from individuals suffering from this disease express a protein similar to the envelope glycoprotein of SFFV that can interact with the EpoR and lead to its constitutive activation. Alternatively, these patients may contain a mutant EpoR gene that is constitutively activated like the mutant EpoR described earlier. As we understand more fully how the SFFV envelope protein constitutively activates te EpoR complex, we can begin to design therapies to counteract its action that can then be applied to treating patients with polycythaemia vera or other human diseases associated with uncontrolled erythropoiesis.

Topics: Animals; Cell Transformation, Neoplastic; Cell Transformation, Viral; Defective Viruses; DNA-Binding Proteins; Erythroid Precursor Cells; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Genes, env; Genome, Viral; Helper Viruses; Hyperplasia; Leukemia, Erythroblastic, Acute; Leukemia, Experimental; Mice; Mutagenesis, Insertional; Receptors, Erythropoietin; Retroviridae Infections; Retroviridae Proteins, Oncogenic; Signal Transduction; Spleen Focus-Forming Viruses; Tumor Virus Infections; Viral Envelope Proteins; Virus Replication

Topics: Amino Acid Sequence; Animals; Binding Sites; Cell Membrane; Cell Transformation, Neoplastic; Cell Transformation, Viral; Endoplasmic Reticulum; Erythropoietin; Friend murine leukemia virus; Gene Products, env; Humans; Leukemia, Erythroblastic, Acute; Molecular Sequence Data; Receptors, Erythropoietin; Viral Envelope Proteins

Topics: Animals; Cell Line; Cell Transformation, Neoplastic; Cell Transformation, Viral; Erythropoietin; Friend murine leukemia virus; Humans; Leukemia, Erythroblastic, Acute; Lymphokines; Tissue Inhibitor of Metalloproteinases

Studies are described employing two erythropoietic systems to elucidate regulatory mechanisms that control both normal erythropoiesis and erythroid differentiation of transformed hemopoietic precursors. Evidence is provided suggesting that normal erythroid cell precursors require erythropoietin as a growth factor that regulates the number of precursors capable of differentiating. Murine erythroleukemia cells proliferate without need of erythropoietin; they show a variable, generally low, rate of spontaneous differentiation and a brisk rate of erythropoiesis in response to a variety of chemical agents. Present studies suggest that these chemical inducers initiate a series of events including cell surface related changes, alterations in cell cycle kinetics, and modifications of chromatin and DNA structure which result in the irreversible commitment of these leukemia cells to erythroid differentiation and the synthesis of red-cell-specific products.

Topics: Cell Cycle; Cell Line; Cell Transformation, Neoplastic; Cell Transformation, Viral; Chromatin; Dimethyl Sulfoxide; DNA; Erythropoiesis; Erythropoietin; Globins; Hemoglobins; RNA, Messenger

Infection of mice with Friend spleen focus-forming virus (SFFV) results in a multistage erythroleukemia. In the first stage, the SFFV envelope glycoprotein interacts with the erythropoietin receptor and a short form of the receptor tyrosine kinase sf-Stk, resulting in constitutive activation of signal transducing molecules and the development of erythropoietin (Epo)-independent erythroid hyperplasia and polycythemia. The second stage results from the outgrowth of a rare virus-infected erythroid cell that expresses nonphysiological levels of the myeloid transcription factor PU.1. These cells exhibit a differentiation block and can be grown as murine erythroleukemia (MEL) cell lines. In this study, we examined SFFV MEL cells to determine whether their transformed phenotype was associated with a block in the activation of any Epo signal-transducing molecules. Our studies indicate that Epo- or SFFV-induced activation of STAT1/3 DNA binding activity is blocked in SFFV MEL cells. The block is at the level of tyrosine phosphorylation of STAT1, although Jak2 phosphorylation is not blocked in these cells. In contrast to Epo, alpha interferon can induce STAT1 phosphorylation and DNA binding in SFFV MEL cells. The SFFV-transformed cells were shown to express elevated levels of the hematopoietic phosphatase SHP-1, and treatment of the cells with a phosphatase inhibitor restored STAT1 tyrosine phosphorylation. MEL cells derived from Friend murine leukemia virus (MuLV) or ME26 MuLV-infected mice, which do not express PU.1, express lower levels of SHP-1 and are not blocked in STAT1/3 DNA-binding activity. Our studies suggest that SFFV-infected erythroid cells become transformed when differentiation signals activated by STAT1/3 are blocked due to high SHP-1 levels induced by inappropriate expression of the PU.1 protein.

Topics: Animals; Cell Differentiation; Cell Transformation, Viral; DNA; Erythroblasts; Erythropoietin; Gene Expression Regulation; Intracellular Signaling Peptides and Proteins; Mice; Phosphorylation; Protein Tyrosine Phosphatase, Non-Receptor Type 6; Protein Tyrosine Phosphatases; Proto-Oncogene Proteins; Spleen Focus-Forming Viruses; STAT1 Transcription Factor; Trans-Activators

Selective and regulatable expansion of transduced cells could augment gene therapy for many disorders. The activation of modified growth factor receptors via synthetic chemical inducers of dimerization allows for the coordinated growth of transduced cells. This system can also provide information on specific receptor-mediated signaling without interference from other family members. Although several receptor subunits have been investigated in this context, little is known about the precise molecular events associated with dimerizer-initiated signaling. We have constructed and expressed an AP20187-regulated KDR chimeric receptor in human TF1 cells and analyzed activation of this gene switch using functional, biochemical, and microarray analyses. When deprived of natural ligands, GM-CSF, interleukin-3, or erythropoietin, AP20187 prevented apoptosis of transduced TF1 cells, induced dose-dependent proliferation, and supported long-term growth. In addition, AP20187 stimulation activated the signaling molecules associated with mitogen-activated protein kinase and phosphatidyl-inositol 3-kinase/Akt pathways. Microarray analysis determined that a number of transcripts involved in a variety of cellular processes were differentially expressed. Notably, mRNAs affiliated with heat stress, including Hsp70 and Hsp105, were up-regulated. Functional assays showed that Hsp70 and Hsp105 protected transduced TF1 cells from apoptosis and premature senescence, in part through regulation of Akt. These observations delineate specific roles for kinase insert domain-containing receptor, or KDR, signaling and suggest strategies to endow genetically modified cells with a survival advantage enabling the generation of adequate cell numbers for therapeutic outcomes.

Topics: Apoptosis; Cell Line; Cell Line, Tumor; Cell Proliferation; Cell Transformation, Viral; Dimerization; Dose-Response Relationship, Drug; Down-Regulation; Erythropoietin; Flow Cytometry; Gene Transfer Techniques; Genetic Therapy; Genetic Vectors; Granulocyte-Macrophage Colony-Stimulating Factor; Green Fluorescent Proteins; HeLa Cells; Hematopoietic Stem Cells; HSP110 Heat-Shock Proteins; HSP70 Heat-Shock Proteins; Humans; Immunoblotting; Interleukin-3; Lentivirus; Oligonucleotide Array Sequence Analysis; Phosphorylation; Protein Structure, Tertiary; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; Tacrolimus; Transfection; Up-Regulation; Vascular Endothelial Growth Factor Receptor-2

Members of the mitogen-activated protein kinase (MAPK) family, including Jun amino-terminal kinase (JNK) and extracellular signal-related kinase (ERK), play an important role in the proliferation of erythroid cells in response to erythropoietin (Epo). Erythroid cells infected with the Friend spleen focus-forming virus (SFFV) proliferate in the absence of Epo and show constitutive activation of Epo signal transduction pathways. We previously demonstrated that the ERK pathway was constitutively activated in Friend SFFV-infected erythroid cells, and in this study JNK is also shown to be constitutively activated. Pharmacological inhibitors of both the ERK and JNK pathways stopped the proliferation of primary erythroleukemic cells from Friend SFFV-infected mice, with little induction of apoptosis, and furthermore blocked their ability to form Epo-independent colonies. However, only the JNK inhibitor blocked the proliferation of erythroleukemia cell lines derived from these mice. The JNK inhibitor caused significant apoptosis in these cell lines as well as an increase in the fraction of cells in G(2)/M and undergoing endoreduplication. In contrast, the growth of erythroleukemia cell lines derived from Friend murine leukemia virus (MuLV)-infected mice was inhibited by both the MEK and JNK inhibitors. JNK is important for AP1 activity, and we found that JNK inhibitor treatment reduced AP1 DNA-binding activity in primary erythroleukemic splenocytes from Friend SFFV-infected mice and in erythroleukemia cell lines from Friend MuLV-infected mice but did not alter AP1 DNA binding in erythroleukemia cell lines from Friend SFFV-infected mice. These data suggest that JNK plays an important role in cell proliferation and/or the survival of erythroleukemia cells.

Topics: Animals; Anthracenes; Apoptosis; Calcium-Calmodulin-Dependent Protein Kinases; Cell Line, Transformed; Cell Proliferation; Cell Transformation, Viral; Cells, Cultured; Erythropoietin; Extracellular Signal-Regulated MAP Kinases; Flavonoids; JNK Mitogen-Activated Protein Kinases; Leukemia, Experimental; MAP Kinase Kinase Kinases; Mice; Retroviridae Infections; Signal Transduction; Spleen Focus-Forming Viruses; Transcription Factor AP-1; Tumor Cells, Cultured; Tumor Virus Infections

Progression through the mammalian cell cycle is regulated by cyclins, cyclin- dependent kinases (CDKs), and cyclin-dependent kinase inhibitors (CKIs). The function of these proteins in the irreversible growth arrest associated with terminally differentiated cells is largely unknown. The function of Cip/Kip proteins p21(Cip1) and p27(Kip1) during erythropoietin-induced terminal differentiation of primary erythroblasts isolated from the spleens of mice infected with the anemia-inducing strain of Friend virus was investigated. Both p21(Cip1) and p27(Kip1) proteins were induced during erythroid differentiation, but only p27(Kip1) associated with the principal G(1) CDKs-cdk4, cdk6, and cdk2. The kinetics of binding of p27(Kip1) to CDK complexes was distinct in that p27(Kip1) associated primarily with cdk4 (and, to a lesser extent, cdk6) early in differentiation, followed by subsequent association with cdk2. Binding of p27(Kip1) to cdk4 had no apparent inhibitory effect on cdk4 kinase activity, whereas inhibition of cdk2 kinase activity was associated with p27(Kip1) binding, accumulation of hypo-phosphorylated retinoblastoma protein, and G(1) growth arrest. Inhibition of cdk4 kinase activity late in differentiation resulted from events other than p27(Kip1) binding or loss of cyclin D from the complex. The data demonstrate that p27(Kip1) differentially regulates the activity of cdk4 and cdk2 during terminal erythroid differentiation and suggests a switching mechanism whereby cdk4 functions to sequester p27(Kip1) until a specified time in differentiation when cdk2 kinase activity is targeted by p27(Kip1) to elicit G(1) growth arrest. Further, the data imply that p21(Cip1) may have a function independent of growth arrest during erythroid differentiation. (Blood. 2000;96:2746-2754)

Topics: Animals; CDC2-CDC28 Kinases; Cell Cycle; Cell Cycle Proteins; Cell Transformation, Viral; Cyclin D; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase 6; Cyclin-Dependent Kinase Inhibitor p16; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Cyclin-Dependent Kinases; Cyclins; Erythroid Precursor Cells; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; G1 Phase; Gene Expression Regulation, Developmental; Genes, p16; Humans; Macromolecular Substances; Mice; Mice, Inbred BALB C; Microtubule-Associated Proteins; Phosphorylation; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Recombinant Proteins; Retinoblastoma Protein; T-Lymphocytes; Tumor Cells, Cultured; Tumor Suppressor Proteins

An immortalized cell line representing the primitive erythroid (EryP) lineage was established from in vitro-differentiated progeny (embryoid bodies [EBs]) of embryonic stem (ES) cells using a retroviral insertional mutation, and has been termed EB-PE for embryoid body-derived primitive erythroid. Even though EB-PE cells are immortalized, they show characteristics of normal EryP cells, such as gene expression and growth factor dependency. In addition, EB-PE cells can differentiate further in culture. Investigation of growth factor requirements of EB-PE cells showed that basic fibroblast growth factor (bFGF) and erythropoietin (Epo) play unique roles in EB-PE proliferation and differentiation. While bFGF was a strong mitogen, Epo was required for both proliferation and differentiation. The unique proliferative response to bFGF coincided with upregulation of its receptor, fibroblast growth factor receptor (fgfr-1), and downregulation of erythropoietin receptor (EpoR) gene expression. Studies of primary EryP cells derived from early EBs, when tested in a colony-formation assay, also provided evidence for the mitogenic role of bFGF in concert with Epo.

Topics: Animals; Cell Line; Cell Transformation, Viral; Embryo, Mammalian; Endothelial Growth Factors; Erythroid Precursor Cells; Erythropoietin; Fibroblast Growth Factor 2; Gene Expression; Insulin-Like Growth Factor I; Lymphokines; Mice; Receptor Protein-Tyrosine Kinases; Receptor, Fibroblast Growth Factor, Type 1; Receptors, Erythropoietin; Receptors, Fibroblast Growth Factor; Retroviridae; RNA, Messenger; Stem Cells; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors

Mechanisms of helper virus-induced growth factor-independence were examined in FDC-P1 cells and FDC-P1 cells expressing the erythropoietin receptor (FDER cells). Retroviral mutagenesis of FDC-P1 cells led to factor-independent (FI) colonies from which cell lines could readily be established; whereas control cells exhibited at least 20 to 40-fold lower rates of factor-independence. From 44 independent experiments using either FDC-P1 or FDER cells, 205 autonomous cell lines were obtained. Sixteen colonies displayed a novel ("satellite-inducing") appearance in agar and produced up to 4.1 x 10(5) U/mL granulocyte-macrophage colony-stimulating factor (GM-CSF) (some with altered GM-CSF transcript sizes) and/or interleukin-3 (IL-3). Retroviral mutagenesis of FDER cells increased the repertoire of autocrine growth factors now responsible for stimulating autocrine proliferation: 3% of FI cell lines produced erythropoietin (Epo) (0.5 U/mL). Unexpectedly, in every autonomous FDC-P1 cell line, reverse transcriptase-PCR demonstrated expression of a growth factor normally required for proliferation. Thus, a profound selection for cells able to produce growth factors as the mechanism for achieving autonomous proliferation was documented. The ectopic expression of a receptor lacking a cognate ligand ("orphan") followed by retroviral mutagenesis and selection for autocrine mutants may offer an effective method for identifying new ligands.

Topics: Animals; Autoreceptors; Cell Division; Cell Line, Transformed; Cell Transformation, Viral; Clone Cells; Erythropoietin; Granulocyte-Macrophage Colony-Stimulating Factor; Helper Viruses; Hematopoietic Stem Cells; Interleukin-3; Mice; Moloney murine leukemia virus; Mutagenesis; Polymerase Chain Reaction; Receptors, Growth Factor; Recombinant Proteins

The transcription factor GATA-1 is required for the normal development of erythroid cells. GATA-1 is also expressed in other hemopoietic cells, suggesting that it might be initially activated in a multipotent progenitor. To immortalize GATA-1-expressing progenitors, we generated mice transgenic for a thermosensitive SV40 T gene, driven by the GATA-1 promoter-enhancer. Immortalized marrow cells grow in culture at 32 degrees C but not at 38 degrees C, and are dependent on erythropoietin (Epo) or interleukin 3 (IL-3). Epo dependent cells express hemoglobin, high levels of GATA-1, GATA-2 and NF-E2 p45 mRNAs, and are positive for stem cell antigen 2 (Sca-2) and the early myeloid marker ER-MP12. IL-3 dependent cells can be derived from Epo dependent lines, and are hemoglobin-, Sca-2- and ER-MP12-negative, have low GATA-1 and NF-E2 p45 mRNA levels, and express myeloid markers Mac-1, F4/80 and Gr-1. Brief treatment of Epo dependent cells with myeloid growth factors (plus Epo) leads to the induction of Mac-1, F4/80 and Gr-1, concomitant with the disappearance from most cells of Sca-2, ER-MP12 and GATA-1 driven T antigen nuclear expression. Thus, the immortalized Epo dependent cells have the property of a progenitor capable of differentiation towards either the erythroid or myeloid lineages. These cells initiate transcription of a proportion of GATA-1 RNA molecules at an upstream promoter, previously known to be expressed only in testis cells.

Topics: Animals; Antigens, Polyomavirus Transforming; Base Sequence; Cell Differentiation; Cell Line, Transformed; Cell Transformation, Viral; DNA-Binding Proteins; Erythroid-Specific DNA-Binding Factors; Erythropoietin; GATA1 Transcription Factor; Growth Substances; Hematopoietic Stem Cells; Mice; Mice, Transgenic; Molecular Sequence Data; NF-E2 Transcription Factor; NF-E2 Transcription Factor, p45 Subunit; Promoter Regions, Genetic; Simian virus 40; Temperature; Transcription Factors

We tested the ability of a constitutively activated erythropoietin receptor [EpoR(R129C)] to alter the growth requirements of primary hematopoietic precursors that terminally differentiate in culture. Two recombinant retroviruses expressing EpoR(R129C), spleen focus-forming virus (SFFVc-EpoR) and myeloproliferative sarcoma virus (MPSVcEpoR), were used to infect fetal liver cells that served as a source of hematopoietic progenitors. Methylcellulose cultures were incubated in the absence of any added growth factors or in combination with selected growth factors. EpoR(R129C) completely abrogated the Epo requirement of erythroid colony-forming units to form erythrocytes after 2-5 days in culture and did not interfere with the differentiation program of these cells. In the absence of added growth factors EpoR(R129C) did not enhance erythroid burst-forming unit development. In contrast to experiments in heterologous cell lines, EpoR(R129C) did not render progenitor cells independent of interleukin 3 or granulocyte/macrophage colony-stimulating factor (GM-CSF). However, when progenitors were cultured with added steel factor, but not with interleukin 3 or GM-CSF, EpoR(R129C) augmented the growth and differentiation of erythroid bursts, mixed erythroid/myeloid, and granulocyte/macrophage (GM) colonies. Furthermore, both viruses were capable of expressing EpoR(R129C) in erythroid, mixed erythroid/myeloid, and GM colonies. Thus an aberrantly expressed and constitutively activated EpoR can stimulate proliferation of some GM progenitors. The ability of EpoR(R129C) to abrogate the Epo requirement of primary hematopoietic cells, but not the requirement for other cytokines, is consistent with the induction of erythroblastosis in vivo.

Topics: Animals; Base Sequence; Cell Differentiation; Cell Transformation, Viral; Cells, Cultured; Erythroid Precursor Cells; Erythropoietin; Granulocyte-Macrophage Colony-Stimulating Factor; Granulocytes; Hematopoietic Cell Growth Factors; Hematopoietic Stem Cells; Interleukin-3; Liver; Macrophages; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Receptors, Erythropoietin; Signal Transduction; Stem Cell Factor

The murine allele temperature-sensitive (ts) p53Val-135 encodes a ts p53 protein that behaves as a mutant polypeptide at 37 degrees C and as a wild-type polypeptide at 32 degrees C. This ts allele was introduced into the p53 nonproducer Friend erythroleukemia cell line DP16-1. The DP16-1 cell line was derived from the spleen cells of a mouse infected with the polycythemia strain of Friend virus, and like other erythroleukemia cell lines transformed by this virus, it grows independently of erythropoietin, likely because of expression of the viral gp55 protein which binds to and activates the erythropoietin receptor. When incubated at 32 degrees C, DP16-1 cells expressing ts p53Val-135 protein, arrested in the G0/G1 phase of the cell cycle, rapidly lost viability and expressed hemoglobin, a marker of erythroid differentiation. Erythropoietin had a striking effect on p53Val-135-expressing cells at 32 degrees C by prolonging their survival and diminishing the extent of hemoglobin production. This response to erythropoietin was not accompanied by down-regulation of viral gp55 protein.

Topics: Animals; Cell Cycle; Cell Differentiation; Cell Division; Cell Line, Transformed; Cell Transformation, Viral; Erythropoietin; Friend murine leukemia virus; Hemoglobins; Leukemia, Erythroblastic, Acute; Mice; Mice, Inbred DBA; Mutation; Recombinant Proteins; Spleen; Spleen Focus-Forming Viruses; Tumor Suppressor Protein p53; Viral Envelope Proteins

ME26 virus, which was generated by inserting the coding region of the acute avian leukemia-inducing virus E26 into a murine retrovirus vector, encodes a 135-kDa gag-myb-ets fusion protein. Amphotropic murine leukemia virus pseudotypes of ME26 virus induce a high incidence of erythroleukemia 2 to 4 months after injection into newborn NFS/N mice. Spleen cells from the majority of these mice proliferate to high levels in the presence of the erythroid hormone erythropoietin (Epo) and can easily be established as permanent Epo-dependent cell lines. The cell lines contain multiple copies of ME26 viral DNA and express viral message and protein. An Epo receptor mRNA of normal size can be detected in these cells, and binding studies reveal a single class of lower-affinity Epo receptor with an affinity for Epo that is in the range of that previously reported for erythroid cells. The ME26 virus-induced Epo-dependent cell lines, however, appear more immature than previously described erythroid cell lines and more closely resemble early hematopoietic precursor cells, suggesting that the virus may be activating the Epo receptor in hematopoietic cells that do not normally express it. Consistent with this idea, we are able to infect an interleukin-3-dependent myeloid cell line, FDC-P2, with ME26 virus and convert it to Epo dependence. The ME26 virus-infected FDC-P2 cells, even before growth on Epo, showed a large increase in the amount of Epo receptor mRNA. However, no ME26 viral integrations can be detected adjacent to the Epo receptor gene, indicating that the virus is not activating the Epo receptor gene by promoter/enhancer insertion. Our results are more consistent with the hypothesis that the gag-myb-ets-encoded viral fusion protein, which is known to bind DNA, is directly or indirectly activating the expression of the Epo receptor gene in these cells.

Topics: Animals; Cell Line; Cell Transformation, Viral; Defective Viruses; Erythropoiesis; Erythropoietin; Fluorouracil; Gene Expression Regulation, Viral; Hematopoietic Stem Cells; Interleukin-3; Mice; Receptors, Cell Surface; Receptors, Erythropoietin; Recombinant Fusion Proteins; Retroviridae

c-erbB, encoding the EGF receptor (EGF-R), was originally identified as the cellular homolog of a chicken leukemia oncogene. In humans, EGF-R is distributed widely except in hemopoietic tissues, and its amplification is associated with epidermal and glial malignancies. Here we show that c-erbB is present in normal chicken erythrocytic progenitors and transmits the mitogenic signal induced by TGF alpha. Cells that contain high affinity EGF-R are at approximately the BFU-E stage, and their long-term renewal can be induced by TGF alpha. Upon addition of insulin and erythropoietin, they can be induced to terminally differentiate into red cells. We previously demonstrated that v-erbA blocks differentiation of chicken erythrocytic progenitors but does not abrogate their growth factor dependence for proliferation. These data indicate that proliferation and differentiation are not necessarily coupled in these cells. They also demonstrate a direct role of c-erbB in the control of self-renewal of normal chicken erythrocytic progenitors and could account for the predominant leukemogenic potential of the chicken erbB gene.

Topics: Animals; Bone Marrow Cells; Cell Differentiation; Cell Division; Cell Transformation, Viral; Cells, Cultured; Chickens; ErbB Receptors; Erythroid Precursor Cells; Erythropoietin; Insulin; Oncogene Proteins v-erbA; Oncogenes; Proto-Oncogene Proteins; Receptors, Colony-Stimulating Factor; Retroviridae Proteins, Oncogenic; Transforming Growth Factor alpha

The Friend or Moloney mink cell focus-forming (MCF) virus encodes a recombinant-type envelope glycoprotein, gp70, that is closely related to the membrane glycoprotein, gp55, of Friend spleen focus-forming virus (SFFV). We have shown previously that gp55 has the ability to activate cell growth by binding to the cellular receptor for erythropoietin. Here we show that gp70 encoded by either the Friend or Moloney MCF virus also binds to the erythropoietin receptor and that coexpression of the receptor and gp70 in an interleukin-3 (IL-3)-dependent cell line can activate IL-3-independent growth. Furthermore, when the cDNA for the human IL-2 receptor beta chain, which is related by sequence to the erythropoietin receptor, was introduced into this cell line, it became growth factor independent after infection either with SFFV or with one of the two MCF viruses but not with an ecotropic virus. Based on these observations, we propose a mechanism for the early stage of leukemogenesis induced by the MCF-type murine leukemia viruses.

Topics: Animals; Cell Division; Cell Line; Cell Transformation, Neoplastic; Cell Transformation, Viral; Electrophoresis, Polyacrylamide Gel; Erythropoietin; Friend murine leukemia virus; Humans; Interleukin-3; Leukemia; Mice; Mink Cell Focus-Inducing Viruses; Moloney murine leukemia virus; Receptors, Cell Surface; Receptors, Erythropoietin; Receptors, Interleukin-2; Retroviridae Proteins, Oncogenic; Viral Envelope Proteins

The transforming potential of the c-myc gene is shown here, for the first time, to include murine erythroid cells. Continuously growing cell lines were reproducibly generated by infection of day 13 CBA fetal liver cells with novel recombinant c-myc retroviruses. By cytostaining, most cells resembled early erythroblasts, but certain lines also contained significant numbers of hemoglobinized cells. RNA analysis revealed substantial expression of the genes encoding beta-globin and the erythroid-specific transcription factor GF-1. Although apparently immortal, the lines were not initially transplantable. Thus, constitutive myc expression in early erythroid cells can enhance their self-renewal capacity but is insufficient to fully transform them. The cell lines proliferated without the addition of exogenous factors, but their clonogenicity in semisolid medium was enhanced in the presence of erythropoietin, interleukin 3, and/or leukemia-inhibitory factor. In combination with either interleukin 3 or erythropoietin, leukemia-inhibitory factor also facilitated differentiation of certain lines. These results suggest that leukemia-inhibitory factor may have a previously unsuspected role in the regulation of erythropoiesis and could be considered as a possible therapeutic agent for the clinical management of erythroleukemia.

Topics: Animals; Cell Differentiation; Cell Line; Cell Transformation, Viral; Colony-Forming Units Assay; DNA-Binding Proteins; Erythroblasts; Erythroid Precursor Cells; Erythroid-Specific DNA-Binding Factors; Erythropoiesis; Erythropoietin; Gene Expression Regulation; Genes, myc; Globins; Growth Inhibitors; Interleukin-3; Interleukin-6; Leukemia Inhibitory Factor; Liver; Lymphokines; Mice; Mice, Inbred CBA; Retroviridae; Transcription Factors; Transfection

We have used countercurrent centrifugal elutriation (CCE) to determine the distribution of cells with respect to cell volume and buoyant density for an erythroleukemia cell line (JG6) transformed by the polycythemia strain of Friend virus (FV-P), and to determine the effect of inducing the cells to differentiate with dimethylsulfoxide (DMSO) on this distribution. CCE made it possible to obtain suspensions of modal JG6 populations virtually free of dead cells and uniform with respect to volume and buoyant density. These modal populations were assayed for specific binding of erythropoietin (Epo). Between 500 and 550 Epo receptors per cell were detected. These belonged to a single class having a dissociation constant of 0.36 nM. DMSO induction of differentiation of the JG6 cells had no effect on the number of Epo receptors expressed.

Topics: Cell Differentiation; Cell Line, Transformed; Cell Separation; Cell Transformation, Viral; Centrifugation; Dimethyl Sulfoxide; Erythropoietin; Friend murine leukemia virus; Humans; Iodine Radioisotopes; Leukemia, Erythroblastic, Acute; Receptors, Cell Surface; Receptors, Erythropoietin; Species Specificity; Time Factors

Erythroid cells from mice infected with the polycythemia-inducing strain of Friend spleen focus-forming virus (SFFVP), unlike normal erythroid cells, can proliferate and differentiate in apparent absence of the erythroid hormone erythropoietin (Epo). The unique envelope glycoprotein encoded by SFFV has been shown to be responsible for this biological effect. The recent isolation of an Epo-dependent erythroleukemia cell line, HCD-57, derived from a mouse infected at birth with Friend murine leukemia virus, afforded us the opportunity to study the direct effect of SFFVP on a homogeneous population of factor-dependent cells. The introduction of SFFVP in complex with various helper viruses into these Epo-dependent cells efficiently and reproducibly gave rise to lines which expressed high levels of SFFV and were factor independent. SFFV appears to be unique in its ability to abrogate the factor dependence of Epo-dependent HCD-57 cells, since infection of these cells with retroviruses carrying a variety of different oncogenes had no effect. The induction of Epo independence by SFFV does not appear to involve a classical autocrine mechanism, since there is no evidence that the factor-independent cells synthesize or secrete Epo or depend on it for their growth. However, the SFFV-infected, factor-independent cells had significantly fewer receptors available for binding Epo than their factor-dependent counterparts had, raising the possibility that the induction of factor independence by the virus may be due to the interaction of an SFFV-encoded protein with the Epo receptor.

Topics: Animals; Blotting, Northern; Cell Division; Cell Line; Cell Transformation, Viral; DNA Replication; Erythropoietin; Friend murine leukemia virus; Genes, Viral; Kinetics; Leukemia Virus, Murine; Leukemia, Erythroblastic, Acute; Mice; Nucleic Acid Hybridization; Receptors, Cell Surface; Receptors, Erythropoietin; Spleen Focus-Forming Viruses; Viral Envelope Proteins

We recently developed a new progenitor assay using murine fetal liver cells that provides a source of pluripotent progenitors, bipotent progenitors, and committed macrophage, megakaryocyte, erythroid, and mast cell progenitors. This clonal cell culture system was used to examine the direct effects of Harvey sarcoma virus on murine hemopoietic progenitors. Very large erythroid colonies containing 100,000 to 200,000 cells were seen in the infected group. Only small erythroid colonies were seen in the uninfected control cultures. The cells in the large erythroid colonies from infected cultures expressed the ras gene as demonstrated by immunofluorescence with a monoclonal antibody to p21, the ras gene product. The infected cells were not immortal since they did not yield secondary colonies upon replating. Sequential observation of individual colonies showed that maturation was not blocked by infection with the virus. The size of other colony types, including granulocyte/macrophage, mast cell, and mixed, was unaffected even though some of these colonies expressed the ras gene. Thus, infection with Harvey sarcoma virus appears to give a growth advantage primarily to committed erythroid progenitors.

Topics: Animals; Cell Division; Cell Transformation, Viral; Erythroid Precursor Cells; Erythropoietin; Fetus; Genes, ras; Harvey murine sarcoma virus; Liver; Mice; Mice, Inbred BALB C; Sarcoma Viruses, Murine

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).

Topics: Alpharetrovirus; Animals; Avian Leukosis Virus; Cell Differentiation; Cell Transformation, Viral; Erythroid Precursor Cells; Erythropoietin; Interleukin-3; Mice; Mice, Inbred CBA; Moloney murine leukemia virus; Oncogenes; Recombination, Genetic

Chemical cross-linking of the red blood cell hormone, erythropoietin (Epo), to its receptor on erythroid cells has revealed the presence of two proteins closely associated with Epo, but the relationship between these two proteins is controversial. Using the cross-linking reagents disuccinimidyl suberate and dithiobissuccinimidyl propionate, we show that 125I-Epo can be specifically conjugated in a complex of 224kDa using mouse fetal liver cells, bone marrow cells, and Friend virus-induced splenic erythroblasts as demonstrated by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels under nonreducing conditions. Under reducing conditions, the 224-kDa complex appeared as two Epo conjugates of 136 kDa and 119 kDa, and these bands were also observed to a variable extent in some nonreducing gels. Disulfide linking of the 136-kDa and 119-kDa bands was confirmed by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis run under nonreducing followed by reducing conditions. With increasing time of 125I-Epo binding to Friend virus erythroblasts in the presence of sodium azide to inhibit receptor internalization, the 136-kDa and 119-kDa bands seen under reducing conditions increased markedly in intensity, whereas the 224-kDa band seen under nonreducing conditions declined. These results suggest that the 224-kDa Epo conjugate is inefficiently solubilized under nonreducing conditions following prolonged periods of Epo binding. A single class of saturable, high affinity receptors for Epo on each of the cell types tested is demonstrated. It is concluded that the two disulfide-linked Epo-binding proteins which can be independently cross-linked to Epo form a single ligand binding site.

Topics: Animals; Cell Transformation, Viral; Cross-Linking Reagents; Erythropoietin; Fetus; Friend murine leukemia virus; Gestational Age; Kinetics; Liver; Macromolecular Substances; Mice; Mice, Inbred BALB C; Mice, Inbred Strains; Molecular Weight; Receptors, Cell Surface; Receptors, Erythropoietin; Recombinant Proteins; Spleen

We have used murine splenic erythrolasts infected with the anemia-inducing strain of Friend virus (FVA cells), as an in vitro model to study cytoskeletal elements during erythroid maturation and enucleation. FVA cells are capable of enucleating in suspension culture in vitro, indicating that associations with an extracellular matrix or accessory cells are not required for enucleation to occur. The morphology of FVA cells undergoing enucleation is nearly identical to erythroblasts enucleating in vivo. The nucleus is segregated to one side of the cell and then appears to be pinched off resulting in an extruded nucleus and reticulocyte. The extruded nucleus is surrounded by an intact plasma membrane and has little cytoplasm associated with it. Newly formed reticulocytes have an irregular shape, are vacuolated and contain all cytoplasmic organelles. The spatial distribution of several cytoskeletal proteins was examined during the maturation process. Spectrin was found associated with the plasma membrane of FVA cells at all stages of maturation but was segregated entirely to the incipient reticulocyte during enucleation. Microtubules formed cages around nuclei in immature FVA cells and were found primarily in the incipient reticulocyte in cells undergoing enucleation. Reticulocytes occasionally contained microtubules, but a generalized diffuse distribution of tubulin was more common. Vimentin could not be detected at any time in FVA cell maturation. Filamentous actin (F-actin) had a patchy distribution at the cell surface in the most immature erythroblasts, but F-actin bundles could be detected as the cells matured. F-actin was found concentrated between the extruding nucleus and incipient reticulocyte in enucleating erythroblasts. Newly formed reticulocytes exhibited punctate actin fluorescence whereas extruded nuclei lacked F-actin. Addition of colchicine, vinblastine, or taxol to cultures of FVA cells did not affect enucleation. In contrast, cytochalasin D caused a complete inhibition of enucleation that could be reversed by washing out the cytochalasin D. These results demonstrate that F-actin plays a role in enucleation while the complete absence of microtubules or excessive numbers of polymerized microtubules do not affect enucleation.

Topics: Alkaloids; Animals; Cell Transformation, Viral; Cells, Cultured; Colchicine; Cytochalasin D; Cytoskeleton; Erythroblasts; Erythrocyte Aging; Erythropoietin; Friend murine leukemia virus; Humans; Kinetics; Mice; Microscopy, Electron; Paclitaxel; Recombinant Proteins; Spleen; Vinblastine

Two different strains of Friend spleen focus-forming virus, SFFVP and SFFVA, are known to cause a rapid erythroleukemia. The SFFVP-infected cells can proliferate and differentiate maximally without the addition of the erythroid-specific hormone erythropoietin, whereas the SFFVA-infected cells require erythropoietin for differentiation and for maximum proliferation. We previously reported that a recombinant virus containing sequences from the 3' half of the SFFVP envelope gene and the SFFVP long terminal repeat on an SFFVA background has all of the biological and biochemical characteristics of SFFVP. We are now presenting data on a new recombinant virus to show that only the 3' half of the SFFVP envelope gene is responsible for the differences observed between the two strains.

Topics: Animals; Cell Division; Cell Transformation, Viral; Chromosome Mapping; DNA, Recombinant; Erythropoietin; Leukemia Virus, Murine; Leukemia, Erythroblastic, Acute; Mice; Phenotype; Spleen Focus-Forming Viruses; Viral Envelope Proteins

LSCC HD3 chicken erythroleukemia cells, transformed by a temperature-sensitive avian erythroblastosis virus (tsAEV), secreted into the medium several transforming factors which after separation by Bio-Cel P-60 chromatography, stimulated quiescent (G0) chicken embryo fibroblasts and NIH 3T3 mouse cells to replicate DNA in serum-free medium and to form colonies in soft agar. Most of these factors were also mitogenic for the LSCC HD3 cells themselves when they were rendered phenotypically untransformed by incubation at 42 degrees C to inactivate the ts AEV. The transformed LSCC HD3 cells also secreted a non-mitogenic 40 kDa factor which blocked the erythropoietin-induced differentiation of untransformed LSCC HD3 (at 42 degrees C) and the DMSO-induced differentiation of Friend murine erythroleukemia cells into hemoglobin-synthetizing erythroid cells.

Topics: Alpharetrovirus; Animals; Cell Adhesion; Cell Differentiation; Cell Division; Cell Line; Cell Transformation, Viral; Chickens; Culture Media; Dimethyl Sulfoxide; Erythropoietin; Growth Substances; Leukemia, Erythroblastic, Acute; Mice; Oncogenes

Topics: Animals; Cell Communication; Cell Differentiation; Cell Line; Cell Transformation, Viral; Chromosome Aberrations; Colony-Stimulating Factors; Erythropoiesis; Erythropoietin; Hematopoiesis; Hematopoietic Stem Cells; Leukemia; Lymphokines; Mice; Recombinant Proteins; Transfection

The v-erbB, v-src, v-fps, v-sea, and v-Ha-ras oncogenes induce avian erythroid progenitor cells to self-renew in an erythropoietin-independent manner. These transformed erythroblasts retain both their capacity to differentiate into erythrocytes and their requirement for complex growth media. However, previous studies showed that erythroblasts transformed by v-erbB plus v-erbA (which by itself is not oncogenic) are blocked in differentiation and grow in standard media. Here we show that the introduction of v-erbA into erythroblasts transformed with v-src, v-fps, v-sea, or v-Ha-ras likewise induces a fully transformed phenotype. It also reduces the capacity of ts sea- and ts erbB-transformed erythroblasts to differentiate terminally in an erythropoietin-dependent manner after a temperature shift. Cooperativity involving v-erbA also occurs in vivo since chicks infected with a retroviral construct encoding v-erbA and v-src develop both acute erythroblastosis and sarcomas.

Topics: Alpharetrovirus; Animals; Avian Leukosis Virus; Cell Differentiation; Cell Transformation, Viral; Erythropoiesis; Erythropoietin; Gene Expression Regulation; Oncogenes; Sarcoma, Experimental

A monoclonal antibody to the chicken transferrin receptor (JS-8) blocked temperature-induced and spontaneous differentiation of avian erythroid cells transformed by ts- and wt-retroviral oncogenes. In cells committed to differentiate, JS-8 caused an arrest at the erythroblast or early reticulocyte stage, followed by premature cell death, whereas proliferation of noncommitted erythroid cells or other hematopoietic cells remained unaffected. JS-8 had no effect on transferrin binding or internalization, but blocked subsequent receptor-recycling resulting in reduced iron uptake. Restoration of high intracellular iron levels neutralized the action of JS-8, whereas an inhibitor of porphyrine biosynthesis (4,6-dioxoheptanoic acid) closely mimicked the effect of JS-8. This suggests that erythroid differentiation might involve coordinate synthesis of erythrocyte proteins subject to regulation by hemin or hemoglobin.

Topics: Alpharetrovirus; Animals; Antibodies, Monoclonal; Apoproteins; Biological Transport; Cell Cycle; Cell Differentiation; Cell Transformation, Viral; Chickens; Conalbumin; Erythropoiesis; Erythropoietin; Hemin; Immunologic Techniques; Iron; Iron Chelating Agents; Porphyrins; Receptors, Cell Surface; Receptors, Transferrin; Transferrin

alpha-Difluoromethylornithine (DFMO) and methyl acetylene putrescine (MAP) are inhibitors of the rate limiting enzyme in polyamine synthesis, ornithine decarboxylase. We studied the effects of these compounds on the formation of retrovirus transformed erythroid colonies. DFMO was able to effectively reduce the number of transformed colonies at a concentration of 10(-3) M, whereas MAP achieved total inhibition at 10(-4) M. Putrescine, the product of ornithine decarboxylase, did not alter colony number by itself but it was able to overcome the inhibitory effects of both DFMO and MAP. Addition of DFMO at times after the initiation of culture decreased its effectiveness in reducing transformed colony numbers, while the converse was true for the erythroid stimulant, erythropoietin. We concluded from these data that DFMO and MAP probably diminished colony formation by inhibiting proliferation of the target cells for the retroviruses.

Topics: Animals; Cell Division; Cell Transformation, Viral; Eflornithine; Erythrocytes; Erythropoietin; Hematopoietic Stem Cells; Mice; Ornithine Decarboxylase Inhibitors; Putrescine; Retroviridae

A murine retrovirus (MRSV) containing the src gene of Rous sarcoma virus has been shown to cause an erythroproliferative disease in mice (S. M. Anderson and E. M. Scolnick, J. Virol. 46:594-605, 1983). We now demonstrate that this same virus can transform erythroid progenitor cells in vitro. Infection of fetal liver cells or spleen and bone marrow cells from phenylhydrazine-treated adult mice gave rise to colonies of erythroid cells which grew in methylcellulose under conditions not favorable for the growth of normal erythroid cells. The presence of pp60src in the transformed erythroid cells was demonstrated by an immune complex protein kinase assay. The time course of appearance and subsequent differentiation of erythroid colonies indicated that the target cell for MRSV was a 6- to 8-day burst-forming unit. Differentiation of the erythroid progenitors was not blocked by the presence of pp60src, and the cells retained sensitivity to the hormone erythropoietin. In fact, the transformed cells exhibited increased hormone sensitivity since the number, the size, and the extent of hemoglobinization of the colonies were all increased by the addition of small amounts of erythropoietin. MRSV was not susceptible to restriction by the Fv-2 locus, as MRSV could transform hematopoietic cells from C57BL/6 mice. These results indicate that (i) the erythroid proliferation observed in vivo is caused by a direct effect of MRSV on erythroid progenitors and (ii) the transformed erythroid precursors acquire a growth advantage over uninfected cells without losing the ability to differentiate and respond to physiologic regulators.

Topics: Animals; Bone Marrow; Cell Transformation, Viral; Erythropoiesis; Erythropoietin; Hematopoietic Stem Cells; In Vitro Techniques; Mice; Oncogene Protein pp60(v-src); Oncogenes; Retroviridae; Retroviridae Proteins; Spleen; Time Factors; Tumor Virus Infections

Topics: Animals; Bone Marrow Cells; Cell Differentiation; Cell Division; Cell Transformation, Viral; Erythrocytes; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Hematopoietic Stem Cells; Hormones; Leukemia, Erythroblastic, Acute; Mice; Retroviridae; Spleen

We have shown morphologic and biochemical evidence for erythroid differentiation in the erythropoietin-responsive cell line Rauscher murine erythroleukemia. These cells synthesize adult and presumably embryonic hemoglobin in response to erythropoietin and dimethyl sulfoxide. Clear differences are observed in some clones between different inducers. The molecular basis for these differences, which may relate to differential modes of inducer action, must be clarified. These cells possess a functional beta-adrenergic receptor/adenylyl cyclase complex remarkably similar to that found on erythrocytes of several species. The receptor density is up-regulated specifically by erythropoietin and, as such, is the first description of membrane receptor regulation by this hormone. Thus, we now have the opportunity to investigate the development of the receptor-cyclase complex on the differentiating erythroid cell and to elucidate its role in the complex interplay of erythropoietin and other hormonal effects during erythropoiesis.

Topics: Animals; Cell Differentiation; Cell Transformation, Viral; Cyclic AMP; Erythropoiesis; Erythropoietin; Globins; Isoproterenol; Leukemia, Erythroblastic, Acute; Mice; Rauscher Virus; Receptors, Adrenergic, beta

Murine erythroid precursor cells, stimulated to proliferate in vitro in the absence of added erythropoietin (EP) by the anemia strain of Friend virus (FVA), will subsequently respond to EP by complete erythrocyte differentiation. If not exposed to EP, the erythroid cells divide for about 120 hr in culture, and they maintain the potential for full differentiation in response to EP added at any time during the period from 72 to 120 hr. Between 96 and 120 hr of culture without added EP, the EP-sensitive erythroid precursor cells that have formed discrete erythroid bursts can be isolated in relatively large numbers from such cultures by plucking with a Pasteur pipette. The addition of EP initiates the final stages of erythroid differentiation, including heme synthesis in 70%-80% of these isolated cells. With respect to homogeneity of the precursor cells, quantity of EP-responsive cells obtainable, and uniformity of EP responsiveness, this system is uniquely favorable for biochemical studies of the late differentiation effects of EP. The overall changes in gene expression accompanying EP-induced terminal differentiation were examined by two-dimensional gel electrophoresis of proteins labeled for a short time with radioactive amino acids. Several new proteins are synthesized in these erythroid cells during terminal differentiation, but the number is a very small percentage of the total number of proteins being made. Thus, in this system, the effect of EP is to initiate expression of a small group of genes, including those for globins, spectrin, and other proteins involved in the final stages of erythroid differentiation.

Topics: Animals; Bone Marrow Cells; Cell Differentiation; Cell Separation; Cell Transformation, Viral; Cells, Cultured; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Hematopoietic Stem Cells; Kinetics; Leukemia, Experimental; Mice; Time Factors

Topics: Animals; Cell Line; Cell Transformation, Neoplastic; Cell Transformation, Viral; Dimethyl Sulfoxide; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Helper Viruses; Leukemia, Erythroblastic, Acute; Leukemia, Experimental; Mice; Mice, Inbred BALB C; Spleen

Mouse bone marrow cells infected in vitro with the anemia strain of Friend leukemia virus from large clusters (bursts) of erythroblasts after 5 days in culture in methylcellulose medium. Two types of erythroblast populations can be isolated from bursts of infected cells by manipulation of the culture conditions. One type of erythroblast, which is obtained when erythropoietin (EP) is added to the culture, has proliferated and undergoes differentiation to become an erythrocyte. The second type of erythroblast, which is obtained when no EP is added to the culture, is the product of extensive proliferation, but it fails to undergo the terminal stages of erythroblast differentiation. Comparisons of these two types of erythroblasts demonstrate that specific EP effects include changes in the nucleus, cytoplasm, and membrane of the treated cells. Those events of erythroid differentiation shown to be directed by EP were extrusion of the nucleus from the erythroblast, induction of uroporphyrinogen I synthetase activity, increased iron incorporation into protoporphyrin, synthesis of alpha- and beta-globin polypeptides due largely to increased mRNA production, and synthesis and incorporation of spectrin into the cell membrane. In this system, EP promotes these effects without observable stimulation of progenitor proliferation in addition to that caused by the virus alone. Thus, the role of EP in terminal erythrocyte differentiation is not simply that of an erythroid-specific mitogen.

Topics: Animals; Cell Differentiation; Cell Transformation, Viral; Cells, Cultured; Erythroblasts; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Globins; Heme; Mice; RNA, Messenger; Spectrin; Transcription, Genetic

Transformation in vitro of bone marrow cells by avian erythroblastosis virus (AEV) gives rise to rapidly growing cells of erythroid nature. Target cells of neoplastic transformation by AEV are recruited among the early progenitors of the erythroid lineage, the burst-forming units-erythroid (BFU-E). They express a brain-related antigen at a high level and an immature antigen at a low level. We show that AEV-transformed cells express low levels of the brain antigen and high levels of the immature antigen. Their response to specific factors regulating the erythroid differentiation indicates that they are very sensitive to erythropoietin. Furthermore, cells transformed by a temperature-sensitive mutant of AEV differentiate into hemoglobin-synthesizing cells 4 days after being shifted to the nonpermissive temperature. All these properties are similar to those of late progenitors of the erythroid lineage, the colony-forming units-erythroid (CFU-E). These results indicate that the AEV-transformed cells are blocked in their differentiation at the CFU-E stage.

Topics: Alpharetrovirus; Animals; Antigens, Surface; Bone Marrow; Cell Differentiation; Cell Line; Cell Transformation, Viral; Chickens; Culture Media; Erythropoietin; Hematopoietic Stem Cells; Hemoglobins; Kinetics

Myeloproliferative virus, derived from Moloney sarcoma virus, causes erythroleukemia and myeloid leukemia in adult mice. This virus is also capable of fibroblast transformation in vitro. The virus consists of two separable biological entities which have been cloned. The helper virus component caused no visible changes in adult mice, whereas the defective virus induced both spleen focus formation and a large increase in erythroid precursor cells but retained the sarcoma virus property of transforming fibroblasts in vitro. Thus, myeloproliferative virus is the first murine sarcoma virus which induces erythroleukemia in adult animals.

Topics: Animals; Bone Marrow Cells; Cell Transformation, Viral; Cells, Cultured; Defective Viruses; Erythropoietin; Fibroblasts; Helper Viruses; Leukemia, Erythroblastic, Acute; Leukemia, Experimental; Leukemia, Myeloid; Mice; Mice, Inbred Strains; Rats; Sarcoma Viruses, Murine; Spleen; Virus Cultivation

The transforming capabilities of FVA, RLV and FVP have been examined using an in vitro transformation assay. Treatment of bone marrow cells with FVP in vitro led to the formation of hemoglobinized erythroid bursts even when these cells were cultured in methylcellulose for 5 days without added erythropoietin (Epo). A variety of FVA and RLV preparations also produced erythroid bursts without Epo but these bursts contained significantly less hemoglobin than those induced by FVP. When very low levels of Epo were added to cultures of FVA- and RLV-infected cells, the bursts were hemoglobinized, that is, similar to FVP-induced bursts. The burst-inducing agent in FVA preparations was shown to be a virus and not Epo. Spleen focus-forming virus (SFFV) pseudotypes, derived from FVA or FVP, also produced erythroid bursts in vitro, whereas four helper murine leukemia viruses did not. These studies indicated that the SFFV component was essential for erythroid burst transformation and specified the degree of hemoglobinization in the bursts formed.

Topics: Anemia; Animals; Cell Transformation, Viral; Cells, Cultured; Defective Viruses; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Hot Temperature; Leukemia, Erythroblastic, Acute; Mice; Polycythemia; Rauscher Virus

Topics: Animals; Bone Marrow; Cell Transformation, Viral; Cysteine; Erythropoietin; Female; Friend murine leukemia virus; Hemoglobins; Kinetics; Mice; Spleen; Sulfhydryl Compounds

The role of host hematopoietic stem cells in the formation of tumor colonies in the spleen of (C57BL/6 X DBA/2) F1 mice after grafts of spleen cells from Friend virus (FVP)-infected donors has been investigated. Hematopoietic stem cell compartments of recipient mice were destroyed by Myleran treatment or gamma-ray irradiation. A single injection of Myleran reduced the pluripotent hematopoietic stem cells (CFU) and the erythropoietin responsive cells (ERC) in polycythemic mice to around 1% of that of controls. Repeated injections of erythropoietin (EPO) restored the erythropoietic precursor cell (ERC) population. Pretreatment of polycythemic hosts with Myleran totally suppressed the tumor colony forming ability of grafted Friend virus-infected spleen cells, whereas it had no effect on tumor colonies produced by inoculation of true tumoral Friend cells. After EPO injections in such Myleran-treated recipients, with a consequent appreciable ERC repopulation, splenic colonies again occurred. Similar results were obtained in hosts whose ERC populations were damaged by irradiation. These data strongly suggest that splenic colonies result from the proliferation of the host cells transformed by virus released by Friend virus-infected cells and not from the proliferation of donor tumor cells.

Topics: Animals; Busulfan; Cell Transformation, Viral; Colony-Forming Units Assay; Erythropoiesis; Erythropoietin; Friend murine leukemia virus; Hematopoietic Stem Cells; Leukemia, Experimental; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Neoplasm Transplantation; Spleen; Transplantation, Isogeneic