bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mouse embryos contain polypeptide growth factor(s) capable of inducing a reversible neoplastic phenotype in nontransformed cells in culture
Authors: Proper Jacqueline A. , Bjornson Chris L. , Moses Harold L. 
Published: February 2005

AbstractA growth‐factor‐like substance capable of inducing nontransformed mouse AKR‐2B, rat NRK, and EGF‐receptorless mouse NR6 cells to form progressively growing colonies in soft agar was identified in acid/ethanol extracts of 17‐day mouse embryos. This “mouse embryo factor” (MEF) is similar to previously described transforming growth factors in that it is capable of stimulating DNA synthesis and conferring a reversible transformed morphology on nontransformed cells in vitro. Passage of crude embryo extracts over a Bio‐Gel P‐60 column gave a major peak of soft agar growth‐stimulating activity in the 15,000 molecular weight range with a minor peak at about 22,000. This biological activity was sensitive to treatment with either trypsin or dithiothreitol, but was unaffected by heat (56°C for 30 minutes or 100°C for 3 minutes), indicating that the activity is due to a heat‐stable polypeptide(s) with disulfide bonds. Separation of these polypeptide(s) by chromatography on carboxymethyl cellulose revealed two peaks of soft agar growth‐stimulating activity which did not cochromatograph with a peak of epidermal growth factor receptor‐competing activity. The similarities of this mouse embryo‐derived growth factor to previously identified transforming growth factors suggest that both fetal development and neoplastic transformation may be affected by similar mechanisms.
Changes in phenotypic expression in embryonic and adult cells treated with 5‐azacytidine
Authors: Taylor Shirley M. , Jones Peter A. 
Published: February 2005

AbstractWe have previously shown that 5‐azacytidine (5‐Aza‐CR) induced the formation of biochemically differentiated myotubes, adipocytes, and chondrocytes in the mouse embryo cell line, C3H/10T1/2CL8 (10T1/2), and that the induction of the muscle phenotype was cell cycle specific. Here we show that the adipocyte phenotype is also induced maximally in cells treated during early S phase. During this period, the minimum treatment time required for the subsequent formation of myotubes was 5 min and the number of myotubes formed was dependent on treatment time. The incorporation of 14C‐5‐Aza‐CR into DNA during the cell cycle, however, was not enhanced during early S phase, suggesting that incorporation of 5‐Aza‐CR into specific DNA sequences synthesized during early S phase may be required for the expression of the new phenotypes. Single cells, obtained by plating cell suspensions into 16 mm wells at limiting dilution, were treated with 5‐Aza‐CR during S phase. The resulting clones showed a high frequency of phenotypic conversion, indicating that 5‐Aza‐CR did not act via a selective mechanism, and several of the clones were capable of expressing more than one phenotype. The cells required more than 2 division cycles after treatment with the analog for the expression of the muscle phenotype and the capacity to differentiate was retained for long periods of time in the absence of cell division. The adult mouse line, CVP3SC6, differentiated into functional striated muscle cells following treatment with 5‐Aza‐CR. The analog also caused oncogenic transformation in the adult line at the same concentration that was effective at inducing myogenic expression.
Simian virus 40 a gene function: Further characterization and growth of tsA transformed Chinese hamster cells
Authors: Robinson Christine C. , Lehman John M. 
Published: February 2005

AbstractChinese hamster embryo cells transformed with the tsA 58 mutant of Simian virus 40 express the transformed phenotype at the permissive temperature (33°C or 37°C) and a “normal” phenotype at the nonpermissive temperature (40.5°C). Immunofluorescence and immunoprecipitation of T antigens demonstrated that the “T” antigen (100 K) has an increase rate of synthesis and degradation at 40.5°C. However, the cells continue to replicate at the nonpermissive temperature when assayed by flow cytometry and autoradiography. This DNA synthesis was cellular, not viral, and not owing to an increase in DNA repair. When the cell cycle distributions of G1, S, and G2 + M were assayed by the fraction labeled mitoses method, no differences were evident at the permissive and nonpermissive temperature; however, the doubling time was lengthened at 40.5°C, the tsA transformed cells are cycling and dying. However, if the transformed cells are seeded onto monolayers of normal Chinese hamster cells at 40.5°C, the cells are growth arrested when measured by growth assays, flow cytometry, autoradiography, and immunofluorescence for T antigen. Therefore, growth arrest can be obtained in tsA 58 transformed Chinese hamster cells when cocultured with normal Chinese hamster cells.
Synergistic effect of purine derivatives on the toxicity of pyrazofurin and 6‐azauridine towards cultured mammalian cells
Authors: Gupta Radhey S. , Moffat Malcolm R. K. 
Published: February 2005

AbstractA novel synergistic effect of several purine derivatives such as adenine, adenosine, hypoxanthine, and guanine on the toxicity of nucleoside analogs pyrazofurin and 6‐azauridine towards cultured Chinese hamster ovary (CHO) cells has been observed. The presence of the above purine derivatives enhanced the toxicity of pyrazofurin and 6‐azauridine, in a dose dependent manner. The growth inhibitory effects of these nucleoside analogs either alone or in combination with the purine derivatives were reversed by uridine and cytidine, providing evidence that the synergistic effect of the purine derivatives was exerted at the level of pyrimidine nucleotide biosynthesis. Studies with mutant cells lacking various purine phosphorylating enzymes show that phosphorylation of purine derivatives through reactions utilizing phosphoribosylpyrophosate (PRPP) is essential for observing the synergistic response. It is suggested that the above purine derivatives (including adenosine, via conversion to hypoxanthine) exert their synergistic effects by depleting the cellular pool of PRPP by two separate mechanisms (direct utilization and feedback inhibition of its synthesis), which as a result becomes rate limiting in the synthesis of orotidine monophosphate (OMP). The reduced levels of OMP, which is a competing substrate with pyrazofurin‐ and 6‐azauridine‐5'‐monophosphates for binding to the target enzyme OMP decarboxylase, could then account for the inhibition of the enzyme at lower concentrations of these analogs.
The relation between protein accumulation and cell cycle traverse of human NHIK 3025 cells in unbalanced growth
Authors: Rønning Øsytein W. , Seglen Per O. 
Published: February 2005

AbstractHuman NHIK 3025 cells, synchronized by mitotic selection, were given 2 mM thymidine, which inhibited DNA synthesis without reducing the rate of protein accumulation. After removal of the thymidine the cells proceeded towards mitosis and cell division, with an S duration 2 hours shorter than, but a G2 and M duration nearly identical to that of the control cells. If cycloheximide (1.25 m̈M) was present together with thymidine, no net protein accumulation took place during the treatment, and the subsequent duration of S, G2, and M was similar to that of the untreated cells. The shortening of S seen after treatment with thymidine alone would therefore indicate that the rate of DNA synthesis depended on the amount of some preaccumulated protein.The postreplicative period in thymidine‐treated cells was lengthened by cycloheximide treatment although the protein content had already been doubled. This suggests that proteins required for the traverse of this part of the cell cycle might have to be synthesized after completion of DNA replication.Shortly after removal of thymidine, the rate of protein accumulation declined markedly, indicating the existence of some mechanism for negative control of cell mass. In addition, the daughters of thymidine‐treated cells had their cell cycle shortened by 2 hours. As a result, the cells had returned to balanced growth already in the first cell cycle following the induction of unbalanced growth.In conclusion, our experiments suggest that NHIK 3025 cells might require a minimum time in order to traverse the cell cycle, which is independent of cell mass.
A new model system for studying the phosphatidylinositol cycle
Authors: Monaco Marie E. , Lippman Marc E. 
Published: February 2005

AbstractAn early manifestation of the response of WRK‐1 rat mammary tumor cells to vasopressin is an increase in incorporation of (32P)Pi into phospholipids. Incorporation into all classes of phospholipids is stimulated; however, incorporation into phosphatidylinositol (PI) is increased to the greatest degree (3‐ to 10‐fold as compared with 1.3‐ to 2‐fold for the other phosholipids). Furthermore, increased incorporation into PI is accompanied by an increased rate of PI turnover; turnover rates of the other phospholipids are unaffected by vasopressin.
Characterization of neutral amino acid uptake by cultured epithelial cells from pig kidney
Authors: Sepúlveda Francisco V. , Pearson Jeremy D. 
Published: February 2005

AbstractTwo transport systems for neutral amino acids have been characterised in LLC‐PK1 cells. The first, which transport alanine in a sodium‐dependent manner, also mediates alanine exchange and is preferentially inhibited by serine, cysteine, and α‐amino‐n‐butyric acid. This system resembles the ASC system in Ehrlich ascites and some other cell types. There is only a small contribution of other systems to alanine uptake. The second, which transports leucine with no requirement for sodium and mediates leucine exchange, is blocked by 2‐aminonorbornane‐2‐carboxylic acid and hydrophobic amino acids. This system is similar to the L system described in other cell types. LLC‐PK1 cells retain several other features implying renal proximal tubule origin; our results thus suggest that these transport systems may be involved in the reabsorption of neutral amino acids by the nephron in vivo.
The role of vitamin E in cellular energy metabolism in cultured adrenocortical cells
Authors: Hornsby Peter J. 
Published: February 2005

AbstractAC1 cells, a bovine adrenocortical cell clone, are rapidly arrested and killed by 2 mM aminooxyacetate, an inhibitor of transmination reactions. Toxicity of aminooxyacetate to cultured bovine adrenocortical cells was previously linked to a high ratio of capacity for oxidation of glutamine relative to pyruvate and was reversible by adding excess glutamine. The toxic effects of aminooxyacetate were shown in the present study to be completely prevented by the simultaneous addition of low concentrations (<100 nM) of d‐α‐tocopherol (vitamin E) or selenious acid or higher concentration of other tocopherols, antioxidants, and ubiquinones (coenzymes Q6 and Q10). When antioxidant analogs were tested, it was found that structural features of the molecules that increase antioxidant potency increased potency for prevention of aminooxyacetate toxicity. α‐Tocopherol‐supplemented AC1 cells were found to be significantly less sensitive than nonsupplemented cells to growth inhibition by rotenone but not by fluorocitrate or dinitrophenol. Dinitrophenol (100 m̈M) stimulated substrate oxidation fivefold but had relatively slight effects on growth, either with or without α‐tocopherol, indicating that limitation of the maximal activity of the tricarboxylic acid cycle and respiratory chain is probably not responsible for the sensitivity to aminooxyacetate and rotenone in cells not supplemented with α‐tocopherol. Sensitivity to growth inhibition by rotenone and the prevention by ubiquinones of aminooxyacetate toxicity suggest a restriction of electron flow at the NADH‐ubiquinone step. The resultant higher NADH/NAD+ ratio would result in a lowered capacity for metabolism of pyruvate with consequent dependence for tricarboxylic acid cycle function and energy production on 2‐oxoglutarate from glutamine by the transmination pathway. Vitamin E and other antioxidants may restore efficient function of ubiquinone by preventing side reactions involving lipid peroxidation. Selenium may have a similar effect as cofactor for glutathione peroxidase. A high ratio of capacity for oxidation of glutamine relative to pyruvate and accompanying sensitivity to aminooxyacetate may reflect a deficiency of vitamin E and selenium in adrenocortical cells in culture.
Effects of cyclophosphamide on murine bone marrow and splenic megakaryocyte‐CFC, granulocyte‐macrophage‐CFC, and peripheral blood cell levels
Authors: Yeager Andrew M. , Levin Francine C. , Levin Jack 
Published: February 2005

AbstractThe effect of cyclophosphamide (CY) on megakaryocytopoiesis in mice was examined with assays of megakaryocyte colony‐forming cells (Meg‐CFC) in bone marrow and spleen and simultaneous determinations of peripheral blood counts, after a single intraperitoneal dose (200 mg/kg) of CY. Significant rebound thrombocytosis (170% of normal) occurred at day 11 after injection with CY, although only modest preceding thrombocytopenia (70% of normal) was observed. After an initial 3–5‐day period of suppression, total megakaryocyte colony‐forming cells (Meg‐CFC) in both bone marrow and spleen of CY‐treated mice demonstrated rebound increases at 5 and 7 days, respectively, after administration of the drug. Granulocyte‐macrophage colony‐forming cells (GM‐CFC) exhibited alterations which were similar to those of Meg‐CFC, suggesting similar sensitivities of Meg‐CFC and GM‐CFC to CY. The increase in Meg‐CFC in both bone marrow and spleen preceded development of thrombocytosis by 4–6 days. This suggests that increased platelet counts in CY‐treated mice are attributable, at least in part, to alterations in feedback mechanisms which control megakaryocytopoiesis, with resultant stimulation of the megakaryocyte progenitor compartment.
Transport of cystine and cysteine and cell growth in cultured human diploid fibroblasts: Effect of glutamate and homocysteate
Authors: Bannai Shiro , Ishii Tetsuro 
Published: February 2005

AbstractHuman diploid fibroblasts take up cystine in the culture medium and the cystine is immediately reduced to cysteine in the cells. It is found that cysteine thus formed is rapidly released from the cells into the medium and accumulates there. The system transporting cysteine is convincingly similar to the ASC system described by Christensen et al. (1967). Since cysteine in the medium is sensitive to autoxidation and readily changes back to cystine, the uptake of cystine seems crucial to the cells. Inhibitors of cystine uptake, such as glutamate and homocysteate, potently reduce the intracellular and extracellular levels of cysteine. These inhibitors modify the cell growth depending upon the cystine concentration in the medium. They inhibit the growth when cystine concentration is physiological. An excessive concentration of cystine is in itself growth inhibitory, but this inhibitory action is antagonized by glutamate or homocysteate.
Dual pathways for epidermal growth factor processing after receptor‐mediated endocytosis
Authors: Miskimins W. Keith , Shimizu Nobuyoshi 
Published: February 2005

AbstractThe binding, internalization, intracellular translocation, and degradation of epidermal growth factor (EGF) were studied in mouse Swiss/3T3 fibroblasts under two different physiological conditions at 37°C. In serum‐containing medium the maximal level of cell‐bound EGF was maintained for at least 8 h without appreciable degradation in contrast to serum‐free conditions. These phenomena were correlated with a difference in the intracellular site to which the receptor‐bound EGF was delivered as studied using Percoll density gradients. In serum‐containing medium the majority of cell‐bound EGF was initially taken up into a Golgi‐like vesicle of density 1.046, corresponding to the marker galactosyl transferase, and then delivered to a population of vesicles with similar density as lysosomes (ϱ =1.068–1.110). A portion of the EGF became degraded and was released from the cell into the medium while the remainder stayed with the cells, intact, for a long period of time. In serum‐free medium, EGF became associated with a heterogeneous population of vesicles with a mean density of 1.050 which do not correspond to any of the marker enzymes for subcellular organelles for which we have tested (Golgi, endoplasmic reticulum, plasma membrane, lysosomes). It is then transferred to lysosome‐like vesicles (ϱ = 1.068–1.110). We therefore propose that EGF is processed through two separate endocytotic routes which are regulated by the cell depending upon its physiological state.
Effects of GM‐CSF deprivation on precursors of granulocytes and macrophages
Authors: Metcalf D. , Merchav S. 
Published: February 2005

AbstractCulture of C57BL bone marrow cells in the absence of GM‐CSF led to a loss of recoverable granulocyte‐macrophage colony‐forming cells of 2% per hour. The rate of loss of progenitor cells in cultures of CBA fetal liver cells was 5–6% per hour. Surviving colony‐forming cells exhibited a normal responsiveness to GM‐CSF but generated smaller colonies than normal when subsequently stimulated by GM‐CSF. Transfer of washed individual day‐3 granulocyte‐macrophage colony cells to cultures lacking GM‐CSF indicated that most cells were unable to survive or proliferate in the absence of GM‐CSF. Death of transferred cells was rapid and invariable when the cells were from macrophage‐forming colonies. However some cells from 40–70% of granulocyte‐forming colonies were able to undergo one or two divisions in the absence of GM‐CSF. This phenomenon was seen most often with cells from colonies where matching colony cells exhibited a higher‐than‐average proliferative capacity in parallel stimulated cultures. The results indicate the difficulty that will be encoutered in obtaining valid metabolic dta from unstimulated populations of granulocyte‐macrophage precursor cells. The ability of some granulocyte precursor cells to exhibit limited proliferation following GM‐CSF deprivation suggests that significant amounts of GM‐CSF may be bound to or be internalized in some precursor cells and result in cell division in the absence of GM‐CSF from culture medium.
Down regulation and recovery of the epidermal growth factor receptor in serum supplemented versus defined medium
Authors: Kegel Mark , Tupper Joseph T. 
Published: February 2005

AbstractThe down regulation of surface membrane receptors for(125I) epidermal growth factor (EGF) has been evaluated in normal and SV40‐transformed human fibroblasts (WI38) under conditions of serum‐supplemented versus defined growth media. Both normal and transformed WI38 cells down regulate and recover the EGF receptor and these processes do not differ significantly in serum‐supplemented versus defined media. These data are in contrast to a recent study that reported that the HeLa cell does not down regulate the EGF receptor in defined media, whereas it does in serum‐supplemented media.
Isolation by a replica‐plating technique of chinese hamster temperature‐sensitive cell cycle mutants
Authors: Hirschberg Joseph , Marcus Menashe 
Published: February 2005

AbstractIsolation of a wide variety of temperature‐sensitive (ts) cell cycle mutants in mammalian cells has previously proved to be a very difficult task. The various procedures used for the isolation of such mutants included a mutant enrichment step based on exposure of the cells to the restrictive temperatures in order to kill the growing wild‐type cells with agents that kill DNA‐synthesizing cells. Hence, these methods favored the isolation of ts mutants that do not lose viability rapidly at the restrictive temperatures, We have treated cells of the Chinese hamster established cell line E36 with the mutagen ethyl‐methane‐sulfonate (EMS) and used a replicaplating technique that we developed to screen the ts mutants for growth. This technique enabled us to recover all ts mutants for growth including the ts cell cycle mutants. Screening of the ts cell cycle mutants among the ts mutants for growth was performed by the flow microfluorimetry technique and the premature chromosome condensation technique. Our results show that 1.3% of the survivors of the mutagenic treatment are ts mutants for growth. Six of 84 ts mutants analyzed were found to be ts cell cycle mutants. They include ts mutants arrested in phases G1, S, and G2. Many of the ts mutants for growth including the ts cell cycle mutants arrested in S and G2 lose viability very fast when incubated at the restrictive temperature. As a consequence they could not have been isolated by any method that includes a mutant enrichment step based on the exposure of the cells to the restrictive temperature.
Decreased heme content and cessation of cell growth in cultured chick embryo fibroblasts in the presence of horse serum: Stimulation of heme synthesis and cell growth by iron
Authors: Verger Claude , Imbenotte José 
Published: February 2005

AbstractA new spectrofluorometric method for heme quantitation in cultured fibroblasts is described. The method includes: (1) heme extraction by methanol/sulfuric acid, (2) partial purification of heme by a microchromatographic method, and (3) treatment of the purified heme by oxalic acid followed by fluorometric quantitation. Using this method, heme concentration was determined in chick embryo fibroblasts cultured in a medium supplemented with either 7% fetal bovine serum (FBS) or 10% horse serum (HS). In the presence of FBS, cultured cells actively divided and cells contained 34–55 pmol heme/mg protein. In contrast, cultures maintained in HS proliferated at a slower rate and contained 23–25 pmol heme/mg protein. The addition of 40 μM FeSO4 to cultures maintained in the presence of HS stimulated cell proliferation, and the cellular heme concentration increased to 37–51 pmol/ mg protein. These findings suggest that the cessation of growth in the presence of HS may be due to decreased heme content in the cells and that the stimulation of cell growth by iron is mediated by its stimulation of heme synthesis.
Glucocorticoid influence on growth of vascular wall cells in culture
Authors: Longenecker John P. , Kilty Laura A. , Johnson Lorin K. 
Published: February 2005

AbstractPrimary mass cultures and cloned strains of bovine aortic endothelial and smooth muscle cells were investigated with respect to their growth responses to glucocorticoid hormones. The growth of primary endothelial cells was not influenced by glucocorticoid treatment in the absence of fibroblast growth factor (FGF) but was inhibited by about 30% in the presence of FGF; with cloned endothelial cells, glucocorticoids were also growth inhibitory only in the presence of FGF. In contrast, smooth muscle cell growth was inhibited 30%–70% by glucocorticoid treatment in both primary cultures and in the cloned strains in the absence of FCF, and this inhibition was totally abolished by the addition of FGF for both cultures. The corticosteroid influences on cell growth were glucocorticoid specific, concentration dependent, and were observed to be independent of the serum concentration. The results indicate that glucocorticoid hormones have direct and pronounced growth inhibiting effects on aortic smooth muscle cells but only minimal effects on endothelial cells when these components of the vascular wall are analyzed under identical conditions in vitro.