bluuebunny/crossref_metadata_2025_split huggingface dataset:
Serum‐independent regulation of initiation of DNA synthesis relating to temperature‐sensitive defect in rat 3Y1tsD123 fibroblasts and its compensation by simian virus 40
Authors: Zaitsu Hirokazu , Kimura Genki 
Published: February 2005

AbstractRandomly proliferating 3Y1stD123 cells are arrested in G1 phase within 24 h after a shift up to 39.8°C (temperature arrest), yet the density‐arrested cells (prepared at 33.8°C) enter S phase at 39.8°C with serum stimulation, with or without preexposure to 39.8°C for 24 h (Zaitsu and Kimura 1984a). When the density‐arrested 3Y1tsD123 cells were preexposed to 39.8°C for 96 h, they lost the ability to enter S phase at 39.8°C by serum stimulation and required a longer lag time to enter S phase at 33.8°C by serum stimulation than did the cells not preexposed to 39.8°C. Simian virus 40 induced cellular DNA synthesis at 39.8°C in the density‐arrested 3Y1tsD123 preexposed to 39.8°C for 96 h. In the absence of serum after a shift down to 33.8°C, the temperature‐arrested 3Y1stD123 cells entered S phase and then divided once. We postulate from these results that (1) that ts defect in 3Y1tsD123 is involved in a serum‐independent process. Once this process is accomplished, its accomplishment is invalidated slowly with preexposure to 39.8°C. This and the serum‐dependent processes occur in parallel but not necessarily simultaneously. The accomplishment of both (all) processes is required for the initiation of S phase. The density‐arrested 3Y1tsD123 cells have accomplished the serum‐independent process related to the ts defect, but have not accomplished serum‐dependent processes. In case of the temperature‐arrested 3Y1tsD123 cells, the reverse holds true. The lag time for entry into S phase depends on the preparedness for the initiation of DNA synthesis (on the extent of accomplishment of each of all processes required for entry into S phase). (2) To induce cellular DNA synthesis, simian virus 40 stimulates directly the serum‐independent process. However, we do not rule out the possibility that simian virus 40 stimulates serum‐dependent processes simultaneously.
Oxonol dyes as monitors of membrane potential: The effect of viruses and toxins on the plasma membrane potential of animal cells in monolayer culture and in suspension
Authors: Bashford C. Lindsay , Alder Glenn M. , Gray Michael A. , Micklem Kingsley J. , Taylor C. Christopher , Turek Paul J. , Pasternak Charles A. 
Published: February 2005

AbstractOptical indicators of the cationic, cyanine and anionic oxonol classes were used to evaluate the plasma membrane potential of animal cells in suspension and in monolayer culture. The optical signals were calibrated by using diffusion potential either of K+ (in the presence of valinomycin) or of H+ (in the presence of carbonyl cyanide p‐trifluoromethoxyphenylhydrazone; FCCP); both classes of dye gave similar values of plasma membrane potential, in the range −40 to −90 mV for different cell types. Addition of haemolytic Sendai virus or Staphylococcus aureus α‐toxin depolarizes cells and causes them to leak monovalent cations; these effects are antagonized by extracellular Ca2+. Cells infected with vesicular stomatitis or Semliki Forest virus become depolarized during an infectious cycle; infection with other viruses was without affect on plasma membrane potential.
1α, 25‐Dihydroxyvitamin D3 specific regulation of growth, morphology, and fibronectin in a human osteosarcoma cell line
Authors: Franceschi Renny T. , James Wilbur M. , Zerlauth Gerold 
Published: February 2005

AbstractThe ability of the hormonally active vitamin D metabolite, lα,25‐dihydroxyvitamin D3, to affect cell growth, morphology and fibronectin production has been examined using the MG‐63 human osteosarcoma cell line. Hormone treatment reduced cell growth rate, saturation density and [3H]thymidine incorporation. Inhibition was specific for lα,25‐dihydroxyvitamin D3 relative to other vitamin D metabolites (lα,25‐dihydroxyvitamin D3 > 25‐dihydroxyvitamin D3 > 24R,25‐dihydroxyvitamin D3D3), antagonized by high concentrations of serum and readily reversed by removal of lα,25‐dihydroxyvitamin D3 from the culture medium. Hormone treatment also increased cell associated alkaline phosphatase activity up to twofold and altered morphology such that treated cells were more spread out on the culture dish and contained more cytoplasmic processes. Significantly, lα,25‐dihydroxyvitamin D3 increased cellular and medium concentrations of fibronectin, a glycoprotein known to be involved in cellular adhesiveness. MG‐63 cells contain a specific lα,25‐dihydroxyvitamin D3 receptor which may mediate these responses.
Characterization of mouse lymphoma cells with altered nucleoside transport
Authors: Cohen Amos , Leung Changyee , Thompson Ellen 
Published: February 2005

AbstractA mutant clone (NT‐1) of a T‐cell lymphoma was selected for its ability to grow in HAT medium (hypoxanthine, aminopterin and thymidine) in the presence of the nucleoside transport inhibitor P‐nitrobenzyl‐6‐mercaptoinosine (NBMI). NT‐1 cells contain half the number of NBMI binding sites present on the parental S49 cells and are partially able to transport nucleosides in the presence of the transport inhibitor (NBMI). These observations suggest that the mutant cells are heterozygous for nucleoside transport proteins and contain two types of transport proteins: the first protein can both bind and is inhibited by NBMI similar to the wild type phenotype, and the second is an altered protein. The altered transport protein apparently lost its NBMI binding sites without a parallel loss of nucleoside transport ability suggesting that the nucleoside transported sites are separate from the binding sites of the transport inhibitor.
The influence of cell population density and serum on the (Na+K)‐ATPase of 3T3 cells
Authors: McCaldin Brian , Tenang Effendi M. 
Published: February 2005

AbstractThe (Na+K)‐ATPase of 3T3 cells has been measured as a function of culture density and the type of serum in which the cells were grown. When 3T3 cells were grown in medium containing 10% newborn calf serum their (Na+K)‐ATPase activity increased as the culture density increased and the cells became quiescent at densities of about 17.5 × 104 cells/cm2. When these cells are subcultured into medium containing 10% foetal bovine serum the activity of the enzyme decreases as the culture density increases and the cells attain final densities of about 5 × 104 cells/cm2.
Differential expression of two linked selection genes (HSVI‐tk and Eco.gpt) in transformed teratocarcinoma and in L cells
Authors: Lasserre C. , Thillet J. , Besnard C. , Bucchini D. , Pictet R. , Jami J. 
Published: February 2005

AbstractUpon transfection of (TK−)F9 teratocarcinoma stem‐cells and (TK−)L fibroblasts with a plasmid carrying two selection genes, Eco.gpt and HSVI‐tk, selection for gpt gene yielded ten times fewer colonies than selection for tk. Only the transformed clones selected for gpt had measurable xanthine guanine phosphoribosyltransferase (XGPRT) activity (Jami et al., 1983). Eco.gpt coding for XGPRT was under the control of simian virus 40 (SV40) early genes' regulating sequences (SV‐gpt). In the present study, it was verified that the low efficiency of gpt selection in mouse cells was not due to the eucaryotic controlling sequences added to the bacterial gene. The transformed clones selected for tk that had no XGPRT activity possessed at least one uninterrupted copy of the composite SV‐gpt gene and as many copies of the transforming plasmid as the cells selected for gpt expression. In a further test, the gpt gene was placed under the control of tk‐regulating sequences and inserted with the tk gene in the same vector. Under these conditions, expression of XGPRT in the transformed clones selected for tk was improved, even though relative selection for gpt remained low.
Similar action of platelet‐derived growth factor and epidermal growth factor in the prereplicative phase of human fibroblasts suggests a common intracellular pathway
Authors: Westermark Bengt , Heldin Carl‐Henrik 
Published: February 2005

AbstractWe have investigated the effects of platelet‐derived growth factor (PDGF) and epidermal growth factor (EGF) in the prereplicative phase of human foreskin fibroblasts cultured under defined conditions in serum‐free MCDB 105 medium. Specific antisera against PDGF and EGF were used to inhibit the stimulation after certain incubation times. It was found that PDGF or EGF had to be present during the major part of the G0G1 phase (> 8 h) in order to cause any appreciable commitment to DNA synthesis; half maximal stimulations were obtained after 9 h and 11 h of incubat ons with PDGF and EGF, respectively. When tested during a suboptimal period of time (6 h), neither an increase in concentration of PDGF or EGF, nor the addition of both growth factors simulataneously caused any appreciable stimulation of DNA synthesis. However, a suboptimal pulse of PDGF, followed by a suboptimal pulse of EGF, or vice versa, led to commitment to DNA synthesis. This finding indicates that PDGF and EGF, at least in part, induce similar intracellular events that transmit the mitogenic signal.
Development of heart cells in culture: Studies using an affinity purified antibody to a myosin light chain
Authors: Klein Irwin , Daood Monica , Whiteside Theresa 
Published: February 2005

AbstractCultured neonatal rat heart cells can be used to study the factors that regulate cardiac contractility and myocyte development in vitro. An antibody to the 26,000 dalton light chain of myosin (MLC1), has been produced and purified on a Sepharose 4B affinity column prepared with rat heart myosin. When primary cultures of myocytes are studied by indirect immunofluorescence using the antibody a predictable pattern of myofibrillar structure is observed to develop over 72h. This myosin cytoskeleton is highly organized and the myosin fibrils exhibit cross striations. The antibody does not stain non‐muscle heart cells and there is no evidence for myocyte division in culture. The qualitative immunofluorescent pattern of myosin organization in the same in both spontaneously beating and in non‐contracting cells.
Biotin and choline replace the growth requirement of Madin‐Darby canine kidney cells for high‐density lipoproteins
Authors: Cohen David C. , Gospodarowicz Denis 
Published: February 2005

AbstractMDCK cells maintained on extracellular matrix (ECM)‐coated dishes and exposed to Dulbecco's modified Eagle's medium (DME) supplemented with transferrin and either high‐density lipoproteins (HDLs) or phosphatidyl choline (PC) liposomes have a growth rate and final cell density similar to those of cultures exposed to serum‐supplemented DME. When MDCK cells are exposed to a medium consisting of a mixture (1:1) of DME and F12 medium (D/F), the addition of transferrin (10 μg/ml) alone supports cell growth and the presence of HDLs or PC liposomes is no longer required. MDCK cells exposed to D/F medium supplemented with transferrin can be passaged for more than 50 generations in total absence of serum. The F12 components that support growth in the absence of HDLs or PC liposomes are biotin (which is absent in DME) and choline (which is present in insufficient concentration in DME). Supplementation of DME with transferrin, biotin (3.6 ng/ml), and choline (10 μg/ml) allows optimal growth of MDCK cells and permits serial propagation through more than 50 generations. The growth requirement of MDCK cells for HDLs or PC liposomes can therefore be replaced by adequate concentrations of biotin and choline. The widely observed fact that a combination of DME/F12 medium is more effective than DME alone in supporting cell growth may be due in part to the lack of biotin and suboptimal choline concentration in DME.
Temperature effects upon the time course of contraction and reextension in Stentor coeruleus
Authors: Nielsen Lis Engdahl , Rotne Jens 
Published: February 2005

AbstractA double‐flash microphotographic technique has been used to follow the variation with temperature of the following kinetic parameters related to the contraction and reextension of the ciliate Stentor coeruleus, namely the rate of contraction, the initiation time before contraction, the rate of reextension and the initiation time before reextension, all described by first order kinetics. Activation enthalpies, entropies and free energies related to the above mentioned parameters were calculated from the variation of the rate constants with temperature. The enthalpies and entropies appear to be of minor interest compared to the free energies. For the contraction and the initiation of contraction the ΔG‡ values obtained were 14 and 15 kcal/mole, respectively, while the reextension and the initiation of reextension both were represented by a value of ΔG‡ about 19 kcal/mole. These results are compared to activation parameters for different motile systems and for the formation and breakdown of ATP‐myosin complexes. A model for the contraction and reextension processes is proposed in accordance with the results measured.
Transcription of ribosomal RNA is differentially controlled in resting and growing BALB/c 3T3 cells
Authors: Perrone‐Bizzozero Nora , Iapalucci‐Espinoza Silvia , Medrano Estela E. , Franze‐Fernández María T. 
Published: February 2005

AbstractShortly after serum‐deprived BALB/c 3T3 fibroblasts are stimulated to grow in medium containing 10% calf serum, the RNA polymerase I activity in permeabilized cells shows a two‐fold increase over the values observed in either serum‐deprived or density‐inhibited resting cells. Inhibition of protein synthesis by pactamycin or cycloheximide specifically reduces the enhanced RNA polymerase I activity in serum‐stimulated cultures without affecting the values in resting cells. On the other hand, inhibition of rRNA processing by the nucleoside analogs 5‐fluoruridine and toyocamycin decreases the rate of 45S rRNA transcription in serum‐stimulated cells but has no effect on the values found in resting cultures. These data suggest that the regulation of rRNA transcription occurs by two different mechanisms, depending on the growth state of the cell. One mechanism, in serum‐stimulated cells, is dependent on a continuous protein synthesis and a correct 45S rRNA processing; the other, in resting cells, is independent of these two parameters.
An analysis of multiple mechanisms of adenosine toxicity in baby hamster kidney cells
Authors: Archer Sherry , Juranka Peter F. , Ho Jeok H. , Chan Voon‐Loong 
Published: February 2005

AbstractAnalysis of the response of baby hamster kidney cells to adenosine in the presence of the adenosine deaminase inhibitor erythro‐9‐(2‐hydroxy‐3‐nonyl) adenine has revealed two distinct mechanisms of toxicity. The first is apparent at low concentrations of adenosine (< 5 μM) and is dependent upon the presence of a functional adenosine kinase. The initial toxicity is abolished by uridine, is unrelated to the inhibition of ribonucleotide reductase, and is accompanied by a decrease in the size of the pyrimidine nucleotide pool. Toxicity at higher concentrations of adenosine is adenosine kinase independent and is potentiated by homocysteine thiolactone. An elevation in the intracellular level of S‐adenosylhomocysteine, which was observed following treatment with higher concentrations of adenosine (> 10 μM), is believed to mediate toxicity at these levels. Interestingly, BHK cells were resistant to intermediate levels of adenosine. The mechanism of resistance is currently unknown, but appears unrelated to a lack of inhibition of aenosine deaminase. It is proposed that substrate inhibition of adenosine kinase may be a determinant of this property.
Characterization of neutrophil alkaline phosphatase‐inducing factor (NAP‐IF)
Authors: Sato Noriharu , Asano Shigetaka , Mori Mayumi , Ueyama Yoshito , Sugano Kentaro , Ohsawa Nakaaki , Takaku Fumimaro 
Published: February 2005

AbstractA factor, termed neutrophil alkaline phosphatase‐inducing factor (NAP‐IF), that has the capacity to increase the NAP activity of granulocytes was characterized by using two samples: cystic fluid (CF) and conditioned medium of a tumor cell line (T3M5). The molecular weight of NAP‐IF was shown to be between 13,000 and 45,000, and its isoelectric point was between 5.5 and 6.2. It was sensitive to heat and proteolytic enzymes, but was resistant to DNase and RNase, suggesting that NAP‐IF is an acidic protein or glycoprotein. These characteristics of NAP‐IF seem to be similar to those of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) that is also present in the CF. NAP‐IF rich fractions obtained by isoelectric focusing from CF were also found to be rich in a subclass of GM‐CSF: granulocyte‐CSF (G‐CSF). Furthermore, a high correlation was noted between the activities of G‐CSF and NAP‐IF (γ = 0.798, P < 0.005). These results suggest that the two activities, i.e., G‐CSF and NAP‐IF, may be attributable to an identical macromolecule.
Investigation of adenylate energy charge, phosphorylation potential, and ATP concentration in cells stressed with starvation and heat
Authors: Calderwood Stuart K. , Bump Edward A. , Stevenson Mary Ann , Van Kersen Ine , Hahn George M. 
Published: February 2005

AbstractWe have attempted to determine the appropriate parameter of energy status assoiciated with the survival of CHO fibroblasts under starvation conditions. Survival correlated well with adenylate energy charge (EC) but not so well with the phosphorylation potential or ATP concentration. Starved cells exhibited the capacity to resist (transiently) decreases in both EC and survival. A fall in EC was associated with decreased survival. Using this correlation, we subsequently investigated whether killing after thermal stress occurred by a mechanism analogous to starvation, perhaps due to inhibition of energy yielding pathways. This hypothesis proved to be false; over 99% of cells were killed before a decrease was observed in any of the parameters of energy status. Cells were, however, sensitized to heat under nutritionally deprived conditions, a finding which may be significant for tumor treatment by heat in vivo.
F.9 Embryonal carcinoma cell calcitonin autocrine system: Correlation between immunoreactive calcitonin secretion and calcitonin receptor number
Authors: Binet Elisabeth , Laurent Pascale , Evain‐Brion Daniele 
Published: February 2005

AbstractMouse teratocarcinoma cells in culture offer an in vitro system to study the initial steps of embryogenesis. It has been suggested that, at such early stages, cell functions are regulated by an autocrine process in which embryonic cells produce factors that in turn act on themselves. F.9 cells possess specific membrane receptors for calcitonin (CT) (120 fmol/mg of protein, Ka, = 3.5 × 108 M−1). These cells produce CT detected by heterologous radioimmunossay in serum‐free culture‐conditioned medium (75 pg/107 cells/12 h). When F.9 cells are incubated in serum‐free medium, CT binding and secretion concomitantly drop by 50% within the first 2 h, then increase progressively to an upper plateau after the sixth hour. Preincubation with 10−6 M CT leads to disappearance of CT receptors and CT secretion in the culture medium up to 6 h. Avoiding accumulation of CT in the medium by a continuous flow rate for 6 h leads to a progressive decrease of CT receptors. In addition, retinoic acid treatment of cells induces a parallel progressive decrease of CT receptor number and of total CT synthesis. These results suggest a reciprocal regulation of CT receptors and CT secretion, or a close relationship between their regulations.
Altered degradation of epidermal growth factor in a diphtheria toxin‐resistant clone of KB cells
Authors: Haigler Harry T. , Wiley H. Steven , Moehring Joan M. , Moehring Thomas J. 
Published: February 2005

AbstractWe have investigated the cellular fate of epidermal growth factor (EGF) in KB cells and a variant, KB‐R2A, that was isolated based on its resistance to diphtheria toxin and subsequently was shown to be resistant to infection by RNA viruses (Moehring and Moehring, 1972, Infect. Immunity. 6:487–492). Both cell lines bind 125I‐EGF and internalize the cell‐bound hormone at the same rate. However, when the degradation of internalized 125I‐EGF was measured by the release of low molecular weight (mw) hydrolysis products into the medium, the toxin‐resistant KB‐R2A cells degraded the hormone at a drastically reduced rate; 50% and 3% of the cell‐bound 125I‐EGF was degraded and released by 80 min in the KB and KB‐R2A cells, respectively. To investigate the fate of cell‐associated EGF prior to release into the medium, the radioactivity in extracts of cells labeled with 125I‐EGF was fractionated by native gel electrophoresis. In KB cells three peaks of radioactivity other than native 125I‐EGF were resolved. Time course and subcellular fractionation studies showed that the first processed product appeared while the hormone was located in the endocytic vesicles and the appearance of the other two peaks correlated with the arrival of the hormone in the lysosomal compartment. KB‐R2A cells also produced the first intermediate but they produced only very low amounts of the other two peaks. These studies show that endocytic vesicles in both cell lines contain enzymes capable of processing EGF prior to the arrival of the hormone in the lysosomes and show that the KB‐R2A cells have a lesion that prevents the complete degradation of the hormone. We propose that the KB‐R2A cell line has a defective mechanism for the intracellular processing of a number of ligands that are internalized by the process of receptor‐mediated endocytosis and that this defect is located beyond the initial endocytic step.
cAMP‐induced phenotypic reversion of adhesion, aggregation, and endocytosis in adhesion‐defective CHO cell variants
Authors: Cheung E. , Juliano R. L. 
Published: February 2005

AbstractADvF11 cells are a CHO adhesion variant which, unlike wild type (WT) cells, are not able to adhere to fibronectin (Fn) coated substrata or to be aggregated by Fn‐beads. However, ADvF11 cells bind Fn‐beads to the same extent as WT cells, thus suggesting that the defect(s) associated with ADvF11 cells are distal to the initial receptor‐ligand binding event (Cheung and Juliano, Exp. Cell Res. 152:127, 1984). In this communication we report that cAMP analogs such as dibutyryl‐cAMP (dbcAMP) and 8‐bromo‐cAMP are able to correct defect(s) associated with ADvF11 cells enabling them to adhere to Fn‐coated dishes and to aggregate in the presence of Fn‐beads. However, only approximately 40% of ADvF11 cells were found to be responsive to dbcAMP suggesting heterogeneity in the cell population with respect to dbcAMP sensitivity. Further analysis of this partial response led us to isolate a subclone of ADvF11 cells, F11CA11, which is highly responsive to dbcAMP treatment. Induction of Fn‐mediated cell adhesion and aggregation in F11CA11 by dbcAMP is both time and dose dependent. Optimal responses were obtained after overnight incubation in alpha‐MEM containing, 1% fetal calf serum, 4% bovine serum albumin, 0.5 mM dbcAMP and 0.2 mM methyl‐isobutyl‐xanthine (MIX), a phosphodiesterase inhibitor. Under these conditions, 70–80% of F11CA11 cells were found to be adherent, compared to 5–7% of untreated F11CA11 cells and 95–100% of WT cells. Aggregation of dbcAMP‐MIX treated F11CA11 cells induced by Fn‐beads also approached that of WT cells. In addition, treatment with dbcAMP‐MIX markedly increased the ability of F11CA11 cells to internalize Fn‐beads. The maintenance of the adherent phenotype required the constant presence of dbcAMP‐MIX. Removal of dbcAMP‐MIX from the incubation medium resulted in return to the original nonadhesive phenotype. Thus, elevation of cAMP levels can dramatically modify the behavior of F11CA11 cells with respect to fibronectin mediated adhesion, aggregation and endocytosis, in effect causing a phenotypic reversion of all three parameters to wild type status. This suggests that the mechanisms for adhesion, aggregation and endocytosis may each involve regulation by cyclic AMP‐protein kinase systems.