Serum-free mouse embryo cells: growth responses in vitro

Gene amplification during differentiation of mammalian neural stem cells in vitro and in vivo

In development of amphibians and flies, gene amplification is one of mechanisms to increase gene expression. In mammalian cells, gene amplification seems to be restricted to tumorigenesis and acquiring of drug-resistance in cancer cells. Here, we report a complex gene amplification pattern in mouse neural progenitor cells during differentiation with approximately 10% of the genome involved. Half of the amplified mouse chromosome regions overlap with amplified regions previously reported in human neural progenitor cells, indicating conserved mechanisms during differentiation. Using fluorescence in situ hybridization, we verified the amplification in single cells of primary mouse mesencephalon E14 (embryonic stage) neurosphere cells during differentiation. In vivo we confirmed gene amplifications of the TRP53 gene in cryosections from mouse embryos at stage E11.5. Gene amplification is not only a cancer-related mechanism but is also conserved in evolution, occurring during differentiation of mammalian neural stem cells

Ligand-receptor interaction between triterpenoids and the 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) enzyme predicts their toxic effects against tumorigenic r/m HM-SFME-1 cells

The present study deals with in silico prediction and in vitro evaluation of the selective cytotoxic effects of triterpenoids on tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells. Ligand fitting of five different triterpenoids to 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) was analyzed with a molecular modeling method, and glycyrrhetinic acid (GA) was the best-fitted triterpenoid to the ligand binding site in 11βHSD2. Analysis of antiproliferative effects revealed that GA, oleanolic acid, and ursolic acid had selective toxicity against the tumor cells and that GA was the most potent triterpenoid in its selectivity. The toxic activity of the tested triterpenoids against the tumor cells showed good correlations with the partition coefficient (logP) and polar surface area values. Time-lapse microscopy, fluorescence staining, and confocal laser scanning microscopic observation revealed that GA induced morphologic changes typical of apoptosis such as cell shrinkage and blebbing and also disrupted the cytoskeletal proteins. Furthermore, GA exhibited a strong inhibitory effect on 11βHSD2 activity in the tumor cells. Our current results suggest that analysis of the ligand-receptor interaction between triterpenoids and 11βHSD2 can be utilized to predict their antitumor effects and that GA can be used as a possible chemopreventive and therapeutic antitumor agent. To the best of our knowledge, this is the first report on in silico prediction of the toxic effects of triterpenoids on tumor cells by 11βHSD2 inhibition.

Selective toxicity of glycyrrhetinic acid against tumorigenic r/m HM-SFME-1 cells is potentially attributed to downregulation of glutathione

Natural products from plants are expected to play significant roles in creating new, safe and improved chemopreventive and therapeutic antitumor agents. Selectivity is also an important issue in cancer prevention and therapy. The present study was designed to extend our previous study on the c-Ha-ras and c-myc-induced tumor cell-selective antiproliferative effects of a licorice component, glycyrrhetinic acid (GA). An in silico ligand-receptor docking simulation revealed that GA acts as an 11β-hydroxysteroid dehydrogenase type 2 inhibitor. GA disrupted the redox balance in tumor cells through upregulation of reactive oxygen species and downregulation of glutathione (GSH). The GA-induced GSH reduction and cytotoxicity were enhanced by an inhibitor of GSH, l-buthionine-[S,R]-sulfoximine. N-acetyl-l-cysteine, an antioxidant and precursor of GSH, restored the GA-induced GSH reduction and cytotoxicity in tumor cells. Taken together, these data highlighting the downregulation of GSH by GA and the efficacy of GSH in ameliorating GA-mediated cytotoxicity support the notion that GSH is involved in the selective toxicity of GA toward tumor cells.

Glycyrrhetinic acid induces anoikis-like death and cytoskeletal disruption in the central nervous system tumorigenic cells

We analyzed the effects of glycyrrhetinic acid (GA), a licorice compound, on the induction of anoikis-like death and cytoskeletal disruption in the central nervous system (CNS) tumorigenic cells. GA was cytotoxic in time- and dose-dependent manners, and the tumorigenic cells shed floating cells upon the GA treatment and even some of the adherent cells were easily detached from the fibronectin-coated culture dish by gentle shaking and aspiration. Reculture of the detached cells revealed that the longer the duration of GA exposure, the less the number of the proliferatable cells. These results indicate that GA perturbs cell adhesion and induces anoikis-like cell death. Further, GA also induced morphologic changes and disturbed cytoskeletal proteins.

Novel effects of glycyrrhetinic acid on the central nervous system tumorigenic progenitor cells: induction of actin disruption and tumor cell-selective toxicity

Licorice extracts are used worldwide in foods and medicines, and glycyrrhetinic acid (GA) is a licorice component that has been reported to induce various important biological activities. In the present study, we show that GA induces actin disruption and has tumor cell-selective toxic properties, and that its selectivity is superior to those of all the clinically available antitumor agents tested. The cytotoxic activity of GA and the tested antitumor agents showed better correlation with the partition coefficient (log P) values rather than the polar surface area (PSA) values. For selective toxicity against tumor cells, GA was most effective at 10 microM that was the same concentration as the previously reported maximum plasma GA level reached in humans ingesting licorice. These results suggest that GA could be utilized as a promising chemopreventive and therapeutic antitumor agent. The underlying mechanisms involved in the selective toxicity to tumor cells by GA are also preliminarily discussed.

Human lactoferrin stimulates skin keratinocyte function and wound re-epithelialization

BACKGROUND

Human lactoferrin (hLF), a member of the transferrin family, is known for its antimicrobial and anti-inflammatory effects. Recent studies on various nonskin cell lines indicate that hLF may have a stimulatory effect on cell proliferation.

OBJECTIVES

To study the potential role of hLF in wound re-epithelialization.

MATERIALS AND METHODS

The effects of hLF on cell growth, migration, attachment and survival were assessed, with a rice-derived recombinant hLF (holo-rhLF), using proliferation analysis, scratch migration assay, calcein-AM/propidium iodide staining and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) method, respectively. The mechanisms of hLF on cell proliferation and migration were explored using specific pathway inhibitors. The involvement of lactoferrin receptor low-density lipoprotein receptor-related protein 1 (LRP1) was examined with RNA interference technique. An in vivo swine second-degree burn wound model was also used to assess wound re-epithelialization.

RESULTS

Studies revealed that holo-rhLF significantly stimulated keratinocyte proliferation which could be blocked by mitogen-activated protein kinase (MAPK) kinase 1 inhibitor. Holo-rhLF also showed strong promoting effects on keratinocyte migration, which could be blocked by either inhibition of the MAPK, Src and Rho/ROCK pathways, or downregulation of the LRP1 receptor. With cells under starving or 12-O-tetradecanoylphorbol-13-acetate exposure, the addition of holo-rhLF was found greatly to increase cell viability and inhibit cell apoptosis. Additionally, holo-rhLF significantly increased the rate of wound re-epithelialization in swine second-degree burn wounds.

CONCLUSIONS

Our studies demonstrate the direct effects of holo-rhLF on wound re-epithelialization including the enhancement of keratinocyte proliferation and migration as well as the protection of cells from apoptosis. The data strongly indicate its potential therapeutic applications in wound healing.

Selective cytotoxicity of glycyrrhetinic acid against tumorigenic r/m HM-SFME-1 cells: potential involvement of H-Ras downregulation

With the intensive need for the development of more effective and safer agents for chemoprevention and therapy of human cancer, natural products from plants have been expected to play significant roles in creating new and better chemopreventive and therapeutic agents. Selectivity is also an important issue in cancer prevention and therapy. In the present study, normal serum-free mouse embryo (SFME) and tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells were treated with various concentrations of clinically available antitumor agents or glycyrrhetinic acid (GA), and the antiproliferative effects of these compounds were determined by the MTT assay. Western blotting analysis, RT-PCR, fluorescence staining and confocal laser scanning microscopic observation were adopted to analyze H-Ras regulation. GA exhibited the tumor cell-selective toxicity through H-Ras downregulation, and its selectivity was superior to those of all the clinically available antitumor agents examined. For the selective toxicity of tumor cells, GA was most effective at 10 microM. Interestingly, this concentration was the same as the previously reported maximum plasma GA level reached in humans ingesting licorice. These results in the present study suggest that GA with its cytotoxic effects could be utilized as a promising chemopreventive and therapeutic antitumor agent.

Mitogen limitation and bone morphogenetic protein-4 promote neurogenesis in SFME cells, an EGF-dependent neural stem cell line

Serum-free mouse embryo (SFME) cells are an epidermal growth factor (EGF)-dependent established line derived from brains of 16-d-old Balb/c mouse embryos. SFME cells grow indefinitely in serum-free medium without replicative senescence, chromosomal abnormalities, or malignant transformation. SFME cells express nestin, a neural stem cell marker, under serum-free conditions. Exposure to serum or transforming growth factor beta (TGF-beta) leads to a marked increase in differentiation toward the astrocytic lineage with expression of glial fibrillary acidic protein and other astrocyte markers. In this study, we show that treatment of SFME cells with bone morphogenetic protein-4 (BMP-4), another member of the TGF-beta family, led to differentiation toward a neuronal lineage under conditions of low mitogenic stimulation (0.5 ng/mL) by EGF and fibroblast growth factor. Maximum mitogenic stimulation with 50 ng/mL EGF blocked the BMP-4 effect on neuronal differentiation, but did not block TGF-beta-induced expression of markers of the astrocytic lineage. BMP-4 treatment also enhanced the activity of the neuron-specific enolase (NSE) promoter in SFME-NSE-lacZ cells that carry the gene for bacterial beta-galactosidase under the control of the NSE promoter. Extended BMP-4 treatment caused SFME cells to express a neuronal phenotype synthesizing gamma-aminobutyric acid. These results indicate that SFME cells have the capacity to generate both neurons and astrocytes in vitro, which resemble the behavior of EGF-dependent multipotential stem cells in the central nervous system, and establish a relationship between effects of BMP-4 and degree of mitogenic stimulation by other peptide growth factors.

Differentiation of serum-free mouse embryo cells into an astrocytic lineage is associated with the asymmetric production of early neural, neuronal and glial markers

Serum-free mouse embryo (SFME) cells, the astrocyte progenitor cells in the central nervous system (CNS), were exposed to 10 ng/ml leukemia inhibitory factor (LIF) and 10 ng/ml bone morphogenic protein 2 (BMP2) to induce differentiation, and expression of cell-type specific markers. Nestin, a marker of early neural lineage, betaIII-tubulin, a marker of neuronal lineage, oligodendrocyte marker O4 (O4), a marker of oligodendrocytic lineage and glial fibrillary acidic protein (GFAP), a marker of astrocytic lineage, were analyzed. Characteristics of SFME cells, as a CNS progenitor, were identified and a possible mechanism, underlying SFME cell specification into an astrocytic lineage upon differentiation, was investigated. These markers were present, both at the initial proliferative phase and after induction of differentiation. GFAP expression increased strongly upon differentiation, while expression of the other markers changed very little. These results indicate that astrocytic differentiation is associated with the asymmetric production of these markers, rather than through induction of astrocytic markers.

L-NAME inhibits tumor cell progression and pulmonary metastasis of r/m HM-SFME-1 cells by decreasing NO from tumor cells and TNF-alpha from macrophages

Highly metastatic ras/myc-transformed serum-free mouse embryo (r/m HM-SFME-1) cells were injected subcutaneously to mice and the effects of Nomega-nitro-L-arginine methyl ester (L-NAME) on the tumor progression and pulmonary metastasis were investigated. In addition, production of nitric oxide (NO), matrix metalloproteinases (MMPs) and tumor necrosis factor-alpha (TNF-alpha) in the tumor cells and in a mouse macrophage-like cell line, J774.1 cells, was analyzed. The increase in footpad thickness was significantly smaller in the mice which were fed the L-NAME containing water (4.24+/-0.39 mg/day/mouse). The number of the tumor cells metastasized to the lungs was smaller in the L-NAME treated mice, although statistical significance was not found. Co-treatment of r/m HM-SFME-1 cells with interferon-gamma (IFN-gamma; 100 U/ml) and lipopolysaccharide (LPS; 0.5 microg/ml) significantly enhanced NO production, and the presence of L-NAME at 1 mM significantly decreased this response. In r/m HM-SFME-1 cells, MMP-2 was undetectable and MMP-9 was also very little in the basal level, and both MMPs were unaffected by the IFN-gamma and/or LPS treatments, not to mention by the L-NAME treatment. In J774.1 cells, any treatment including LPS appeared to enhance MMP-9 production, however, this upregulation was not inhibited by the additional presence of L-NAME. Production of TNF-alpha by J774.1 cells was markedly enhanced with LPS treatment, and this enhancement was significantly reduced in the presence of L-NAME. These results indicate that the inhibitory effects of L-NAME on the tumor cell progression and pulmonary metastasis could be due to suppression of NO from tumor cells and TNF-alpha from macrophages (Mol Cell Biochem, 2007).

Ras/myc-transformed serum-free mouse embryo cells under simulated inflammatory and infectious conditions increase levels of nitric oxide and matrix metalloproteinase-9 without a direct association between them

Inflammatory and infectious conditions were simulated in cultures of ras/myc-transformed serum-free mouse embryo (ras/myc SFME) cells, using interferon-gamma (IFN-gamma, 100 units/ml) and lipopolysaccharide (LPS, 0.5 microg/ml) co-treatment for 24 h, to investigate their effects on the expression of inducible nitric oxide synthase (iNOS) mRNA and the production of NO. Aminoguanidine (AG, 1 mM; an NOS inhibitor) along with IFN-gamma and LPS, S-nitroso-N-acetyl-DL-penicillamine (SNAP, 100 microM; an NO donor) and/or (+/-)-N-[(E)-4-Ethyl-2-[(Z)-hydroxyimino]-5-nitro-3-hexene-1-yl]-3-pyridine carboxamide (NOR4, 100 microM; an NO donor), were also added to analyze the possible association of NO with matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1). Co-treatment of cells with IFN-gamma and LPS increased iNOS mRNA expression, NO production, MMP-9 mRNA expression, and 105 kDa MMP-9 production. Additional treatment with the NOS inhibitor AG inhibited NO production, but did not down-regulate the expression of MMP-9 mRNA or 105 kDa MMP-9. The NO donors SNAP and NOR4 did not affect the expression of MMP-9 mRNA, 105 kDa MMP-9 or TIMP-1 mRNA. These results suggest that ras/myc SFME cells respond to infectious and inflammatory conditions and can enhance malignancy as cancer cells due to their increased levels of NO and MMP-9 production, but that NO is not directly associated with MMP-9 in these cells.

Low-level bisphenol A increases production of glial fibrillary acidic protein in differentiating astrocyte progenitor cells through excessive STAT3 and Smad1 activation

The effects of bisphenol A (BPA) on the differentiation of serum-free mouse embryo (SFME) cells, the astrocyte progenitor cells in the central nervous system, were examined. SFME cells were exposed to 10 ng/ml leukemia inhibitory factor (LIF) and 10ng/ml bone morphogenetic protein 2 (BMP2) to increase glial fibrillary acidic protein (GFAP) expression and induce cell differentiation. Various concentrations of BPA (0.1 pg/ml-1 microg/ml) were then added to determine their effects on the cell differentiation. SFME cells were effectively differentiated by LIF and BMP2 in completely serum-free cultures. Cell proliferation following cell differentiation was not significantly affected by low-level BPA. However, GFAP expression was significantly increased in SFME cells in the presence of 1-100 pg/ml BPA. These increases were due to excessive activation of signal transducer and activator of transcription 3 (STAT3) and mothers against decapentaplegic homolog 1 (Smad1) by the low-level BPA.

Increased synthesis of GFAP by TCDD in differentiation-disrupted SFME cells

The effects of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) on gene expression and synthesis of glial fibrillary acidic protein (GFAP) in differentiation-disrupted serum-free mouse embryo (SFME) cells were examined. SFME cells were exposed to fetal calf serum (FCS) and dimethyl sulfoxide (DMSO) to induce differentiation and increase GFAP synthesis. Disruption of differentiation was caused by low-level toluene, significantly inhibiting GFAP synthesis. TCDD at 0.01, 0.1 and 1 pg/ml in the presence of low-level toluene increased GFAP synthesis in the SFME cells, while expression of GFAP mRNA showed no significant change. The TCDD-treated SFME cells detached from the culture substratum, indicating an apparent change in cell adhesion. These results suggest that low-level TCDD further disrupts differentiation of SFME cells in the presence of low-level toluene by upregulating GFAP synthesis and by altering the ability in cell adhesion and that GFAP synthesis is not disrupted at transcription but at translation.

Selective cloning of cell surface proteins involved in organ development: epithelial glycoprotein is involved in normal epithelial differentiation

Coordinating the activities of neighboring cells during development in multicellular organisms requires complex cellular interactions involving secreted, cell surface, and extracellular matrix components. Although most cloning efforts have concentrated on secreted molecules, recent work has emphasized the importance of membrane-bound molecules during development. To identify developmental genes, we raised antibodies to normal embryonic pancreatic epithelial cell surface proteins. These antibodies were characterized and used to clone the genes coding for the proteins by a panning strategy. Using this approach, we cloned the rat homologue of the mouse epithelial glycoprotein (EGP). Our immunohistochemistry data, describing the expression of EGP during rat development, as well as our in vitro data, looking at the effect of the anti-EGP antibody and the extracellular domain of EGP on embryonic pancreatic epithelial cell number and volume, strongly suggest a role for EGP during pancreatic development.

Bone morphogenetic proteins inhibit proliferation, induce reversible differentiation and prevent cell death in astrocyte lineage cells

Bone Morphogenetic Proteins (BMPs) induce the differentiation of Serum-free Mouse Embryo (SFME) cells into astrocytes (D'Alessandro et al., 1994) as demonstrated by change in morphology, increase in Glial Fibrillary Acidic Protein (GFAP) content and classification as both type 1 and 2 astrocytes. Further analyses showed that in the presence of BMP, cells which had differentiated into astrocytes were inhibited from proliferation. Moreover, removal of BMP resulted in a resumption of proliferation accompanied by a loss of GFAP expression over time, indicating that under these in vitro conditions the differentiation was reversible. Since EGF is absolutely required for the survival of SFME cells, we examined the effect of its removal in the presence of BMP. Cell survival was > 80% in the presence of BMP-2, 7 or 2/7 and < 10% in the presence of TGF-beta 1. These data demonstrate that BMPs have effects on the proliferation, differentiation and survival of cells in the astrocyte lineage.

Bone morphogenetic proteins induce differentiation in astrocyte lineage cells

Serum-free mouse embryo (SFME) cells express Glial Fibrillary Acidic Protein (GFAP), a specific marker of the astrocyte lineage, when treated with either Transforming Growth Factor Beta (TGF-beta) or calf serum. We examined the effects of the related Bone Morphogenetic Proteins (BMPs) which are expressed in the developing murine nervous system. Treatment with the heterodimers BMP-2/6 and 2/7 followed by the homodimers BMP-2, 4, 5, 6, and 7 induced higher levels of GFAP in these cells than either TGF-beta 1 or activin when tested at the same concentration. The BMP-induced cells resembled classically described astrocytes and were characterized by antibody markers as type 1 and type 2. In addition, these astrocytes also showed increased levels of the cell adhesion molecules CD44 and neural cell adhesion molecule (N-CAM), both known to be expressed by this cell type. These data clearly demonstrate that the BMPs function as differentiation factors as well as regulators of adhesion molecule expression for cells of the astrocyte lineage and suggest a key role in glial development in the nervous system.

Regulation of glial fibrillary acidic protein in serum-free mouse embryo (SFME) cells by leukemia inhibitory factor and related peptides

The serum-free mouse embryo (SFME) cell line, derived in serum-free medium from 16-day-old mouse embryos, exhibits unique properties. SFME cells grow indefinitely in culture without senescence, require epidermal growth factor (EGF) or fibroblast growth factor (FGF) for survival and are growth-inhibited by serum. The cell line expresses glial fibrillary acidic protein (GFAP) in response to transforming growth factor beta or serum and cells with similar properties can be isolated directly from brain. Culture of SFME cells with leukemia inhibitory factor (LIF), a peptide implicated in neural tissue development, also resulted in expression of GFAP. Other peptides that share signal transduction mechanisms with LIF--ciliary neurotropic factor, oncostatin M and interleukin-6--also caused expression of GFAP in these cells. These effects were inhibited by concentrations of EGF or FGF that promoted rapid cell growth.

Expression of a TGF beta regulated, brain-specific mRNA in serum-free mouse embryo (SFME) cells

The serum-free mouse embryo (SFME) cell line was isolated from 16-day-old Balb/c mouse embryos in medium in which the usual serum supplement to the culture medium was replaced by purified growth factors and other components. SFME is an unusual line that does not undergo senescence in vitro, maintains an apparently normal karyotype, and is growth inhibited by serum. Transforming growth factor beta (TGF beta) or calf serum induces expression of the astrocyte marker glial fibrillary acidic protein (GFAP) in these cells, and similar cells can be isolated directly from brain. By differential screening of a cDNA library derived from SFME cells, a calf serum- and TGF beta-regulated 8.5 kb mRNA was identified in SFME cells and the cDNA partially sequenced. This mRNA was detected only in RNA preparations from brain among a number of tissues examined, and may provide an additional marker of TGF beta-regulated differentiation in these cells.

A free-radical hypothesis for the instability and evolution of genotype and phenotype in vitro

It has been known for several decades that cultured murine cells undergo a defined series of changes, i.e., an in vitro evolution, which includes crisis, spontaneous transformation ('immortalization'), aneuploidy, and spontaneous neoplastic transformation. These changes have been shown to be caused by the in vitro environment rather than an inherent instability of the murine phenotype or genotype. Serum amine oxidases were recently identified as a predominant cause of crisis. These enzymes generate hydrogen peroxide from polyamine substrates that enter the extracellular milieu. This finding implicates free-radical toxicity as the underlying cause of in vitro evolution. We propose an oxyradical hypothesis to explain each of the stages of in vitro evolution and discuss its significance for cytotechnology and long-term cultivation of mammalian cell types.

Apoptosis of serum-free C2.8 mouse embryo hepatocytic cells caused by hepatocyte growth factor deprivation

C2.8 mouse embryo hepatocytic cells, acutely required exogenous hepatocyte growth factor (HGF) to survive and proliferate in serum-free Dulbecco's modified Eagle's medium supplemented with insulin, transferrin and Na-selenite. Greater than 90% of cultured C2.8 cells died within 48 hours from plating in the absence of HGF. Conversely, HGF prolonged maintenance of life and stimulated cell proliferation. Removal of HGF from the medium of cultures that had grown to confluency, also resulted in a rapid decreased cell survival. In the last circumstance, light microscopic observations revealed, with high frequency, morphological features characteristic of apoptosis. DNA within the affected cells underwent rapid fragmentation, revealed as a ladder of DNA fragments in multiples of about 200 base pairs. HGF prevented loss of cell viability, morphological damages and retarded DNA fragmentation in confluent C2.8 cells. Cycloheximide delayed cell death caused by HGF deprivation.

Non-transformed, but not ras/myc-transformed, serum-free mouse embryo cells recover from growth suppression by azatyrosine

The anti-proliferative effect of azatyrosine, a newly discovered antibiotic from Streptomyces, was examined in Balb/c-originated serum-free mouse embryo (SFME) cells and transformed ras/myc SFME cells which have activated human c-Ha-ras genes. Azatyrosine suppressed their growth in a concentration-dependent manner. Growth suppression in both cells was detectable within 2 days after culture with 250 micrograms/ml azatyrosine. Non-transformed SFME cells, however, regained rapid growth after 6 days even in the presence of azatyrosine, whereas ras/myc SFME cells did not recover from the suppression. Despite the growth inhibition of ras/myc SFME cells, expression of human ras in the cells was not inhibited by azatyrosine. Meanwhile, SFME cells have the ability to express glial fibrillary acidic protein (GFAP). This expression is induced by serum-supplemented medium, though the serum inhibits the growth of SFME cells. Azatyrosine did not induce GFAP in ras/myc SFME cells, but inhibited growth. Furthermore, azatyrosine did not induce GFAP in SFME cells, and had no effect upon the expression of GFAP induced by serum in these cells. These results suggest that azatyrosine inhibited the growth of ras/myc SFME cells through a mechanism independent of those involved in growth inhibition and induction of GFAP expression by serum in SFME cells.

Death of serum-free mouse embryo cells caused by transforming growth factor beta 1 and effects of nutritional factors

Transforming growth factor beta 1 (1 ng/ml) caused death of serum-free mouse embryo cells cultured in a medium consisting of a 1:1 mixture of Dulbecco's Modified Eagle's medium and Ham's F12 medium supplemented with fibronectin, insulin, transferrin, epidermal growth factor, and high density lipoprotein. Cell death occurred in the presence of polyunsaturated fatty acids including linoleic acid in the absence of selenium. The death could be reversed by adding alpha-tocopherol to the culture indicating a mechanism involving fatty acid peroxidation. Butylated hydroxytoluene was a poor suppressor of cell death in contrast to alpha-tocopherol. High density lipoprotein and fatty acid-free albumin also suppressed cell death at the level of 20 micrograms/ml and 1 mg/ml, respectively. Transforming growth factor beta 1 also caused a low rate of cell growth after heat treatment of the cells at 45 degrees C.

Culture of cells from zebrafish (Brachydanio rerio) embryo and adult tissues

The zebrafish is a popular model for studies of vertebrate development and toxicology. However, in vitro approaches with this organism have not been fully exploited because cell culture systems have been unavailable. We developed methods for the culture of cells from blastula-stage diploid and haploid zebrafish embryos, as well as cells from the caudal and pelvic fin, gill, liver, and viscera of adult fish. The haploid embryo-derived cells differentiated in culture to a pigmented phenotype and expressed, upon exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin, a protein that was immunologically and functionally similar to rainbow trout cytochrome P450IA1. Zebrafish cultures were grown in a complex basal nutrient medium supplemented with insulin, trout embryo extract, and low concentrations of trout and fetal bovine serum; they could not be maintained in conventional culture medium containing a high concentration of mammalian serum. Using calcium phosphate-mediated transfection, a plasmid constructed for use in mammalian cells was introduced into zebrafish embryo cell cultures and expressed in a stable manner. These results indicated that the transfection procedures utilized in mammalian systems can also be applied to zebrafish cell cultures, providing a means for in vitro alteration of the genotype and phenotype of the cells.

Karyotypic stability of serum-free mouse embryo (SFME) cells

Mouse embryo cultures derived in serum-containing medium undergo growth crisis or senescence after fewer than 20 population doublings, followed by the emergence of genetically altered, polyploid 'immortalized' cells capable of growing indefinitely. Serum-free mouse embryo (SFME) cells, derived in medium in which serum is replaced with growth factors and other supplements, do not exhibit growth crisis or gross chromosomal aberrations when cultured for well over 100 population doublings and display other unique properties. We examined culture conditions and physiological factors affecting karyotypic stability in long term cultures of SFME cells derived from several mouse strains. Cloning SFME cells consistently isolated colonies with altered karyotype, even when the clones were derived from parent cultures with no karyotypic alterations. After 140-200 population doublings in vitro, the percentage of SFME cells showing hyperdiploidy or structural chromosomal abnormalities increased, although the modal chromosome number remained diploid. SFME cells transformed with molecularly cloned oncogenes did not show alterations in karyotype beyond that expected from the clonal origins of these cells, indicating that malignant transformation of SFME cells does not result in general karyotypic instability.

Death of serum-free mouse embryo cells caused by epidermal growth factor deprivation

Serum-free mouse embryo (SFME) cells, derived in medium in which serum is replaced with growth factors and other supplements, are proastroblasts that are acutely dependent on epidermal growth factor (EGF) for survival. Ultrastructurally, an early change found in SFME cells deprived of EGF was a loss of polysomes which sedimentation analysis confirmed to be a shift from polysomes to monosomes. The ribosomal shift was not accompanied by decreased steady-state level of cytoplasmic actin mRNA examined as an indicator of cellular mRNA level. With time the cells became small and severely degenerate and exhibited nuclear morphology characteristic of apoptosis. Genomic DNA isolated from cultures undergoing EGF deprivation-dependent cell death exhibited a pattern of fragmentation resulting from endonuclease activation characteristic of cells undergoing apoptosis or programmed cell death. Flow cytometric analysis indicated that cultures in the absence of EGF contained almost exclusively G1-phase cells. Some of the phenomena associated with EGF deprivation of SFME cells are similar to those observed upon NGF deprivation of nerve cells in culture, suggesting that these neuroectodermal-derived cell types share common mechanisms of proliferative control involving peptide growth factor-dependent survival.

Correlation of the inability to sustain growth in defined serum-free medium with the suppression of tumorigenicity in Wilms' nephroblastoma

We report the investigation of the growth properties of tumorigenic and reverted nontumorigenic Wilms' nephroblastoma cells when cultured in serum-free medium. Wilms' tumor, a pediatric nephroblastoma, has been associated with deletions encompassing the p13 band of chromosome 11 and an independent loss of heterozygosity at 11p15. Weissman et al. (Science 236:175-180, 1987) transferred a human der(11) chromosome into the G401.6TG.6 Wilms' tumor cell line via the microcell-mediated chromosome transfer technique. The resulting microcell hybrids were nontumorigenic when assayed in nude mice; however these cells retained all of the in vitro growth and morphological characteristics of the tumorigenic parental cells in 10% fetal calf serum (FCS). Segregation of the der(11) chromosome from the nontumorigenic microcell hybrid cells resulted in the reappearance of the tumorigenic phenotype in vivo. In vitro culture of these cell lines in serum-free medium supplemented with 0.1% bovine serum albumin (BSA) and 10 ng/ml Na2O3Se resulted in sustained growth of both the tumorigenic parent and the tumorigenic segregant while the nontumorigenic microcell hybrids were unable to divide. The separate addition of either 10 ng/ml of epidermal growth factor (EGF) or 5 micrograms/ml of insulin did not alter this effect. However, the addition of 5 micrograms/ml of transferrin stimulated the nontumorigenic microcell hybrid cells to grow at a rate comparable to the tumorigenic cells. In addition, conditioned serum-free medium from the tumorigenic parental or tumorigenic segregant cell lines was able to stimulate the growth of the nontumorigenic microcell hybrid cells, whereas the reciprocal experiment had no effect on the growth of the tumorigenic cells. These data suggest that the inability of the microcell hybrid cells to grow in serum-free conditions is correlated with their genetic nontumorigenic phenotype and that a specific growth factor, transferrin, can bypass or alter this negative growth regulatory pathway(s) in vitro.

Serum inhibition of proliferation of serum-free mouse embryo cells

Serum-free mouse embryo (SFME) cells, derived in medium supplemented with insulin, transferrin, high density lipoprotein, epidermal growth factor, and fibronectin, do not undergo crisis, maintain a predominantly diploid karyotype with no detectable chromosomal abnormalities for well over 100 population doublings in vitro, and are growth inhibited by concentrations of serum that are growth-stimulatory for most cell lines in culture. Serum inhibition of SFME cell proliferation was reversible and was not prevented by addition of the supplements of the serum-free medium, even when added repeatedly during the culture period. The serum effect on SFME cell proliferation could be detected after incubation in serum-containing medium for as little as 8 h. SFME cells in serum-containing medium were arrested in the G1 phase of the cell cycle with a greatly reduced rate of incorporation of precursors into DNA and thymidine kinase activity, while a reduction in rate of incorporation of amino acids into protein was not observed. SFME cultures maintained for extended periods in serum-containing medium underwent a crisis-like period followed by the appearance of variant cells capable of growing in serum-supplemented medium. These cells exhibited abnormal karyotype and were resistant to several inhibitors of proliferation active on the parent SFME cell type.

Serial passage of embryonic human astrocytes in serum-free, hormone-supplemented medium

We applied serum-free cell culture methods that allow extended proliferation of mouse astrocyte precursor cells to the multipassage culture of embryonic human brain cells. Cells were cultured in nutrient medium supplemented with insulin, transferrin, epidermal growth factor, fibroblast growth factor, heparin, high-density lipoprotein, and fibronectin. Cultures were maintained for a maximum of 70 population doublings before proliferation ceased. The cells synthesized glial fibrillary acidic protein, an astrocyte marker, and expression of this protein was increased by incubation of the cells with transforming growth factor beta or serum. These results identify extracellular factors important for proliferation and differentiation of embryonic human astrocytes and provide a controlled system for multipassage culture.

Serum and transforming growth factor beta regulate glial fibrillary acidic protein in serum-free-derived mouse embryo cells

Serum-free mouse embryo (SFME) cells, derived in medium in which serum is replaced with growth factors and other supplements, display distinctive properties: (i) SFME cells do not lose proliferative potential or show gross chromosomal aberration upon extended culture, (ii) these cells depend on epidermal growth factor for survival; and (iii) SFME cell proliferation is reversibly inhibited by serum. Treatment of SFME cells with serum or transforming growth factor beta led to the appearance of glial fibrillary acidic protein, a specific marker for astrocytes. The appearance of glial fibrillary acidic protein in cultures was reversed upon removal of transforming growth factor beta or serum. Cells with properties similar to SFME cells were also isolated from adult mouse brain. These results suggest a role for transforming growth factor beta in astrocyte differentiation in developing organisms and in response to injury and identify the cell type that has the unusual properties of SFME cells.

Transforming growth factor beta regulates cystatin C in serum-free mouse embryo (SFME) cells

Differential screening of a cDNA library derived from mRNA of TGF beta-treated serum-free mouse embryo (astrocyte precursor) cells isolated a strongly TGF beta-regulated mRNA that codes for cystatin C, a cysteine protease inhibitor. Increase in cystatin C mRNA level was observed within four hours after treatment with picomolar concentrations of TGF beta. The increase was reversible upon removal of TGF beta and was not prevented by cycloheximide. These results suggest that cystatin C expression may represent a developmentally regulated differentiated function of astrocytes, and also suggest that cystatin C expression may be involved in the response of brain cells to platelet release of TGF beta after trauma or injury.

ras and neu oncogenes reverse serum inhibition and epidermal growth factor dependence of serum-free mouse embryo cells

Serum-free mouse embryo cells, cultured in basal nutrient medium supplemented with insulin, transferrin, epidermal growth factor, fibronectin, and high-density lipoprotein, do not exhibit growth crisis, lack detectable chromosomal aberrations, are nontumorigenic in vivo, are dependent on epidermal growth factor for survival, and are growth inhibited by serum or platelet-free plasma. These cells after transfection with the human Ha-ras or rat neu oncogenes no longer required epidermal growth factor for survival, were tumorigenic in vivo, and also proliferated in serum-containing medium. Autocrine activity capable of replacing epidermal growth factor was detected in conditioned medium from ras-transformed cultures, but little such activity was detected in medium from neu-transformed cultures. In addition, the capability of ras or neu-transformed cells to grow in serum-containing medium could not be mimicked in untransformed cells by the addition of growth factors or conditioned medium from transformed cells. These results suggest that the known structural similarity of the neu gene product to the EGF receptor is also reflected in a functional similarity by which the mutationally activated neu protein can replace the ligand-activated EGF receptor. These results also suggest that the ability of ras- and neu-transformed cells to escape the effect of the inhibitory serum activity is a nonautocrine property distinct from the acquisition of EGF autonomy.

Glucocorticoid and thyroid hormones inhibit proliferation of serum-free mouse embryo (SFME) cells

Mouse embryo cells derived in a serum-free medium formulation (SFME cells) do not exhibit growth crisis or chromosomal abnormalities and are nontumorigenic in vivo; these cells are also reversibly growth inhibited by serum or platelet-free plasma (Loo et al.; Science, 236:200-202, 1987). A portion of the inhibitory activity of serum could be extracted by charcoal, a procedure that removes steroid and thyroid hormones. Both L-3,5,3'-triiodothyronine (T3) and hydrocortisone inhibited growth of SFME cells in a reversible manner. The inhibitory activity of serum also was partially removed by treatment with anion exchange resin in a procedure designed to deplete serum of thyroid hormone. However, the effect of serum on untransformed SFME cells could not be prevented by addition of the antiglucocorticoid RU38486, and ras-transformed clones of SFME cells, which are capable of growing in serum-containing medium, retained inhibitory responses to glucocorticoid and, with some clonal variability, to T3. These results suggest that glucocorticoid or thyroid hormones may contribute to the inhibitory activity of serum on SFME cells, but additional factors are also involved.

Death of serum-free mouse embryo cells caused by epidermal growth factor deprivation is prevented by cycloheximide, 12-O-tetradecanoylphorbol-13-acetate, or vanadate

Serum-free mouse embryo cells cultured in medium supplemented with insulin, transferrin, high-density lipoprotein, and fibronectin are dependent on epidermal growth factor for survival. Cycloheximide or actinomycin D prevented cell death caused by growth factor deprivation, suggesting that cell death required the synthesis of RNA and protein, a phenomenon similar to that reported for neuronal cell death in the absence of nerve growth factor. Orthovanadate, an inhibitor of phosphotyrosine phosphatases, and 12-O-tetradecanoylphorbol-13-acetate, an activator of protein kinase C, also prevented serum-free mouse embryo cell death in the absence of epidermal growth factor.