Analysis of erythroid differentiation in Friend cells using noninducible variants

A series of Friend cell variants has been isolated by selecting for resistance to different inducers of Friend cell differentiation. This procedure selects for cells which have lost the capacity to differentiate terminally in the presence of inducer. Fluctuation analysis shows that these variants arise during culture and are not induced by the selective conditions. Moreover, mutagenesis of parental cells increases the frequency of occurrence of DMSO-resistant variants. Our evidence suggests that these resistant variants arise by two mechanisms. Some arise spontaneously at a relatively high rate (5 × 10^?5?5 × 10^?6 per cell per generation), but their phenotypes are not necessarily stable on removal of the selective conditions. Stable variants arise spontaneously at a lower frequency which is consistent with a true mutational origin.Screening of these stable resistant variants shows that they have different phenotypes. Some fail to respond to any inducer; others respond to all inducers tested except the one used for selection, whereas others respond to some but not all inducers. Most of the DMSO-resistant variants are noninducible by DMSO for all aspects of Friend cell differentiation tested (that is, globin mRNA, hemoglobin, spectrin and the ability to undergo terminal differentiation). Two variants, however, are inducible for an early marker of differentiation, the erythrocyte membrane protein spectrin, but not for other markers such as hemoglobin, globin RNA or terminal differentiation. This implies that the regulation of the globin pathway can be uncoupled from that of spectrin.     

Effects of beta adrenergic agents and prostaglandin E1 on erythroid colony (CFU-E) growth and cyclic AMP formation in Friend erythroleukemic cells

The formation of erythroid colonies from bone marrow and spleen cells infected with the polycythemic strain of the Friend virus (FV-P) was characterized in an in vitro methyl cellulose colony-forming system in response to prostaglandin E1 and the beta-2 adrenergic agonist, albuterol. Both drugs markedly inhibited the formation of CFU-E colonies of FV-P-infected bone marrow and spleen in the absence or presence of erythropoietin. The albuterol-mediated inhibition of CFU-E colonies (FV-P-infected) was selectively blocked by butoxamine, a beta-2 antagonist. Adenylate cyclase (AC) activity was also determined in FV-P spleen membrane preparations in response to albuterol and PGE1. Both agents stimulated enzyme activity, and butoxamine blocked the stimulation seen with albuterol. The ability of albuterol and PGE1 to stimulate AC activity in the FV-P-infected cells suggests that the effects of these agents on CFU-E formation may be mediated by specific beta-2 adrenergic and PG receptors through the adenylate cyclase-cyclic AMP system.     

Growth suppression of Friend virus-transformed erythroleukemia cells by p53 protein is accompanied by hemoglobin production and is sensitive to erythropoietin.

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.     

Co-expression of spectrin and fodrin in friend erythroleukemic cells treated with DMSO

Friend erythroleukemic cells can be used as a model of erythroid cell differentiation with the synthesis of the erythrocyte-specific products hemoglobin and spectrin stimulated by agents such as DMSO. In the present study we investigated the expression of both erythroid spectrin and non-erythroid fodrin in uninduced and DMSO-treated Friend cells. We report that both spectrin and fodrin co-exist at low levels in uninduced Friend cells and both are induced by treatment with DMSO. After longer times both spectrin and fodrin appear to undergo rearrangements into submembranous ‘patches’ and ‘caps’. Although both molecules co-localize in most of these cells, they can be independently immunoprecipitated, suggesting that significant amounts of hybrid molecules are not formed.     

Specific binding of 125I-rErythropoietin to Friend polycythemia virus-transformed erythroleukemia cells purified by centrifugal elutriation

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.     

Chromosome analyses and anchorage-independent growth of SV40-induced morphologically transformed epithelial cells from amniotic fluids

Epithelial cells from amniotic fluid cell cultures are morphologically transformed by simian virus 40, 20 to 30 d after infection. The cells of the transformed colonies are highly basophilic, have a high nuclear-to-cytoplasmic ratio, and show a dense growth pattern. The cells are virus producers, and ultimately, after continuous passage, the cell lines reach a crisis situation with no growth. Twelve morphologically transformed cell colonies were isolated from five different individuals for chromosome analyses after approximately 18 population doublings (second bottle passage). For all cell lines diploid cells were observed. Banding of the chromosomes revealed normal morphology of euchromatic and heterochromatic regions. The suggestion is made that chromosome alteration is not necessary, nor a prerequisite, for the morphologically transformed phenotype to be expressed and that the transformation process per se causes chromosomal instability. Tests for colony formation of the 12 cell lines in semisolid medium showed that different transformed colony isolates from the same individual donor of the cells either formed or did not form colonies in agar. The size of the colonies was also consistent within individuals as compared to between individuals. These limited results are suggestive of a dependence upon the genetic constitution of the individual donor of the cells for colony formation in soft agar.     

Erythroid stem cells in Friend-virus infected mice

The erythropoietic stem cell compartment was studied in Friend-virus (polycythemic strain, FV-P) infected DBA/2 and NMRI mice with the CFUE and BFUE technique. Early after infection there was a depression in CFUE number in bone marrow and spleen, followed by an increase of the CFUE concentration, earlier and more pronounced in the spleen than in the marrow. Three days after FV-P infection an erythropoietin (Ep) independent CFUE population started to grow and replaced the normal Ep-dependent population within 8 to 12 days. The shift to Ep independency was not gradual. CFUE colonies of FV-P infected bone marrow cells were two to three times larger than control colonies after three days in vitro incubation. BFUE colonies increased in number during the first days of infection, but were totally lost after more than ten days. After velocity sedimentation of bone marrow cells of FV-P infected animals, however, the BFUE containing fractions showed normal BFUE colony growth and normal Ep sensitivity. In unfractionated bone marrow cell cultures BFUE colony growth could be observed later than ten days post infection when the cultures were refed with medium. It was therefore concluded that the loss of BFUE colony growth after FV-P infection was an in vitro artefact due to inadequate culture conditions.     

Co-expression of differentiation markers in hybrids between friend cells and lymphoid cells and the influence of the cell shape

We have studied the regulation of differentiation within the hemopoietic system by fusing mouse Friend cells (which can be induced to undergo red blood cell differentiation) to various mouse lymphomas and myelomas which express characteristic T and B lymphocyte surface antigens. Our results show that both erythroid and lymphoid differentiation markers can be co-expressed within the same cell. To determine whether this result applies to other differentiation states, we fused suspension Friend cells to three adherent fibroblast cell lines, and isolated both adherent and suspension hybrids. In fact, suspension hybrid clones were inducible for hemoglobin, whereas adherent clones were not. No obvious differences in overall chromosome balance were evident between the adherent and suspension hybrids. A similar correlation between suspension morphology and inducibility of hemoglobin was found in hybrids between suspension Friend cells and an adherent lymphoma line. These results show that different developmental programs can be coexpressed within the same hybrid cell; but the strongly adherent type of morphology is inconsistent with expression of the red blood cell phenotype, both in hybrid cells derived entirely from hemopoietic parental cells and in cells from widely different lineages.     

Chromosome analyses and anchorage-independent growth of SV40-induced morphologically transformed epithelial cells from amniotic fluids

Summary Epithelial cells from amniotic fluid cell cultures are morphologically transformed by simian virus 40, 20 to 30 d after infection. The cells of the transformed colonies are highly basophilic, have a high nuclear-to-cytoplasmic ratio, and show a dense growth pattern. The cells are virus producers, and ultimately, after continuous passage, the cell lines reach a crisis situation with no growth. Twelve morphologically transformed cell colonies were isolated from five different individuals for chromosome analyses after approximately 18 population doublings (second bottle passage). For all cell lines diploid cells were observed. Banding of the chromosomes revealed normal morphology of euchromatic and heterochromatic regions. The suggestion is made that chromosome alteration is not necessary, nor a prerequisite, for the morphologically transformed phenotype to be expressed and that the transformation process per se causes chromosomal instability. Tests for colony formation of the 12 cell lines in semisolid medium showed that different transformed colony isolates from the same individual donor of the cells either formed or did not form colonies in agar. The size of the colonies was also consistent within individuals as compared to between individuals. These limited results are suggestive of a dependence upon the genetic constitution of the individual donor of the cells for colony formation in soft agar. Supported by National Science Foundation Grant PCM77-15876.     

Activation of the Jun N-terminal kinase pathway by friend spleen focus-forming virus and its role in the growth and survival of friend virus-induced erythroleukemia cells

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.     

Spontaneous chromosomal aberrations in Fanconi anaemia,ataxia telangiectasia fibroblast and Bloom's syndrome lymphoblastoid cell lines as detected by conventional cytogenetic analysis and fluorescence in situ hybridisation (FISH) technique

Several primary and transformed human cell lines derived from cancer prone patients are employed routinely for biochemical and DNA repair studies. Since transformation leads to some chromosomal instability a cytogenetic analysis of spontaneous chromosome aberrations in fibroblast cell lines derived from patients with Fanconi anaemia (FA), ataxia telangiectasia (AT), and in lymphoblastoid cell lines derived from patients with Bloom's syndrome (BS), was undertaken. Unstable aberrations were analysed in Giemsa stained preparations and the chromosome painting technique was used for evaluating the frequencies of stable aberrations (translocations). In addition, the frequency of sister-chromatid exchanges (SCEs) was determined in differentially stained metaphases. The SV40-transformed fibroblasts from these cell lines have higher frequencies of unstable aberrations than the primary fibroblasts. In the four lymphoblastoid cell lines derived from BS patients higher frequencies of spontaneously occurring chromosomal aberrations in comparison to normal TK6wt cells were also evident. The frequency of spontaneously occurring chromosome translocations was determined with fluorescence in situ hybridisation (FISH) and using DNA libraries specific for chromosomes 1, 2, 3, 4, 7, 8, 11, 14, 19, 20 and X. The translocation levels were found to be elevated for primary FA fibroblasts and lymphoblastoid cells derived from BS patients in comparison with control cell lines, hetero- and homozygote BS cell lines not differing in this respect. The SV40-transformed cell lines showed very high frequencies of translocations independent of their origin and almost every cell contained at least one translocation. In addition, clonal translocations were found in transformed control TK6wt and AT cell lines for chromosomes 20 and 14, respectively. The spontaneous frequencies of SCEs were similar in transformed fibroblasts derived from normal individuals and AT patients, whereas in SV40-transformed FA cells these were higher (4-fold). Among cell lines derived from BS patients, heterozygote lines behaved like control, whereas in homozygote cell lines very high frequencies of SCEs (about 12-fold) were evident.     

The cellular composition of hemopoietic spleen colonies

The cellular composition of individual hemopoietic spleen colonies has been studied using techniques which tested primarily for cell function rather than cell morphology. Erythroblastic cells were recognized by their capacity to incorporate radioiron, granulocytic cells by their content of peroxidase-positive material, and hemopoietic stem cells by their ability to form spleen colonies in irradiated hosts. It was found that, 14 days after the initiation of spleen colonies, the distribution of these cell types among individual colonies was very heterogeneous, but that most colonies contained detectable numbers of erythroblasts, granulocytes and colony-forming cells. An appreciable proportion of the cells in the colonies could not be identified as any of these three cell types. No strong correlations between numbers of erythroblasts, granulocytes and colony-forming cells in individual colonies were observed, though there was a tendency for colonies containing a high proportion of erythroblasts to contain a low proportion of granulocytes, and for colonies containing a high proportion of granulocytes to contain a higher proportion of colony-forming cells. An analysis of colonies which contained cells bearing radiation-induced chromosomal markers indicated that 83–98% of the dividing cells within 14-day spleen colonies were derived from single precursors.     

Haemopoietic spleen colony growth: a versatile, parsimonious, predictive model

Abstract. Substantial support has been obtained for the stochastic model for stem cell differentiation first proposed by Till, McCulloch & Siminovitch (1964), over 20 years ago. By adding a cell maturation pathway, it is possible to predict (by computer simulation) the total number of cells and consequently the time at which individual colonies appear and disappear.
Only a few uncontroversial assumptions are required to predict that cells, uniform with respect to self-renewal, are capable of producing the high proportions of late disappearing and late appearing colonies observed experimentally in the spleens of irradiated mice that have been injected with normal haemopoietic cells. It is shown that differences in stem cell self-renewal only slightly influence the time of appearance of colonies; whereas changes in the kinetics of the maturing cells, by changing the size of colonies, has a marked effect on the time of appearance and disappearance of colonies and on the average doubling-time of colony-forming cells per colony (but not the doubling-time of individual colonies).
These results (1) seriously question the prevailing view that spleen colonies scored at 8 days measure a separate population (without the capacity for self-renewal), from those scored at 12 days; (2) argue against the existence of multiple sub-populations of stem cells with differing self-renewal and toxicity to cytotoxic agents; (3) help to identify those experiments for which it is obligatory to postulate heterogeneity, and (4) are consistent with self-renewal being regulated by a feedback control of stem cell differentiation, to which only proliferating stem cells can respond and where the stimulus for differentiation decreases at a time when the bone marrow is known to be depleted.     

Viral glycoproteins synthesis in Friend cell lines producing polycythemic (FV-P) and anemic (FV-A) Friend viruses

Two tumor Friend cell lines producing anemia-inducing virus (TF-A line) or polycythemia-inducing virus (TF-P line) were compared for their viral-encoded glycoproteins. The envelope glycoproteins of the two viral populations differ by their electrophoretic mobilities. The gpr^env precursors also differ by their relative mobilities. The TF-P cells contain the typical gp50–52 molecular species, which is coded for by Spleen Focus Forming sequences (SFFV) present in the genome of the polycythemia-inducing virus. The TF-A cells do not contain the gp50–52, but express in small amounts a species with a higher apparent molecular weight. This species which has been named FV-A gp55 could be equivalent to the gp50–52 coded for by the SFFV sequences. Very similar results were obtained with leukemic cells prepared from enlarged spleens of mice infected with the anemic or polycythemic Friend viruses.     

Proteins of Friend leukemia cells. Comparison of hemoglobin-synthesizing and noninduced populations.

Proteins of Friend leukemia cells induced to form large amounts of hemoglobin by dimethylsulfoxide treatment were compared with proteins from noninduced cells by high resolution two-dimensional polyacrylamide gel electrophoresis. Approximately 98% of more than 500 proteins separated by this technique were qualitatively and quantitatively the same in both cell populations. Changes representing more than 50% of the control cell amount were detected in six non-histone chromosomal proteins, two nucleoplasmic proteins, and three cytoplasmic proteins. It is concluded that dimethylsulfoxide induces an extremely specific pattern of erythroid differentiation in these cells, which should be susceptible to detailed analysis. Comparison of protein patterns from Friend leukemia cells and HeLa cells revealed electrophoretic identity of approximately 20% of cytoplasmic proteins and 50% of non-histone chromosomal proteins.     

Interleukin 3-dependent hematopoietic progenitor cell lines

Several biological phenotypes of growth factor-dependent cell lines have been described in recent years, including those with T lymphocyte, neutrophil granulocyte, basophil/mast cell, B lymphocyte, and multipotential stem cell properties. The growth factors for each cell lineage are a subject of intense study. Continuous mouse bone marrow cultures infected with RNA type C viruses (retroviruses) produce nonadherent hematopoietic cells over a longer duration than control cultures. Marrow cultures derived from strains with spontaneously induced ecotropic endogenous retrovirus demonstrate a greater longevity than those from strains with no replicating virus. Cultures infected with murine leukemia virus also generate a greater number, compared with controls, of cloned permanent suspension cell lines dependent for growth on a 41,000-dalton glycoprotein (interleukin 3 [IL 3]). Some are multipotential with capacity for differentiation to erythroid, neutrophil, eosinophil, and basophil/mast cell types. Other cloned IL 3-dependent cell lines are committed to a single pathway. Studies with Friend spleen focus-forming virus indicate that the first effect in the marrow culture is mediated through a subset of adherent hematopoietic stem cells. Bone marrow culture-derived IL 3-dependent cell lines provide a model with which to study the role of viral genes in the control of differentiation and self-renewal capacity of hematopoietic stem cells.     

Expression of a transformation-related protein (p53) in the malignant stage of Friend virus-induced diseases.

Stage 1 (pre-malignant) and stage 2 (malignant) cells derived from mice infected with Friend murine leukemia virus or polycythemia-inducing Friend virus complex were examined and compared for the expression of a transformation-related cellular protein, p53. Stage 2 cells were found to express high levels of p53, whereas stage 1 cells did not express detectable levels of this protein. These results indicate that p53 may be a marker for transformed cells present in the second stage of diseases induced by Friend murine leukemia virus or polycythemia-inducing Friend virus complex.     

Hemoglobin synthesis in cell hybrids formed between teratocarcinoma and friend erythroleukemia cells

Viable hybrid cells have been isolated following fusion of Friend erythroleukemia cells and undifferentiated teratocarcinoma cells. The hybrids formed between near-diploid parental cells resembled Friend cells in their ability to grow in suspension and to synthesize hemoglobin in the presence of the chemical inducers dimethyl sulfoxide (DMSO) and ouabain. Erythropoietin (EPO) was effective in inducing hemoglobin synthesis in some of the hybrid cell lines. The hemoglobins synthesized by the hybrids were of the adult forms, but were quantitatively different from those hemoglobins synthesized by the parental Friend cells, suggesting that the fusion event modulated the expression of the hemoglobin chain genes.