bluuebunny/crossref_metadata_2025_split huggingface dataset:
Emergence of hamster fibroblast tumors in nude mice—evidence for in vivo selection leading to loss of growth factor requirement
Authors: Pérez‐Rodriguez R. , Chambard J. C. , Van Obberghen‐Schilling E. , Franchi A. , Pouysségur J. 
Published: February 2005

AbstractThe Chinese hamster lung fibroblast cell line (CC139) has high anchorage dependence for growth and has retained the high serum dependence of secondary cultures of adult fibroblasts. This cell line is tumorigenic in nude mice; however, the resulting tumor cells have different properties than those of the cell line injected. The tumor‐derived cells had strongly reduced or even lost both the high anchorage and the high serum dependence of CC139 cells. This finding suggests that an in vivo selection is necessary for CC139 cells to acquire the malignant phenotype. After mutagenesis, which increases the frequency of CC139 colony formation in agarose up to 8‐fold, we selected and analyzed 15 anchorage‐independent colonies. No correlation between the colony‐forming ability in agarose and serum‐growth factor requirement for DNA synthesis was observed. Each of these clones were injected into nude mice and the growth factor dependence of the ensuing tumor cells was compared to that of corresponding injected cells. All of the anchorage‐independent colonies with the exception of one (A71), had acquired in vivo a stable phenotype allowing for partial or total escape of growth factor requirement. A71, the only clone which maintained the same growth factor requirement after two passages in vivo (A71 T1 and A71 T2) had already gained, in vitro, the minimal growth factor “relaxation” compatible with in vivo growth. A71 and A71 T1 tumor cells arrested in G0/G1 can reinitiate DNA synthesis in the presence of mouse plasma, low concentrations of serum, or thrombin. The fact that none of the tumors analyzed (more than 20) were found to have retained the high serum dependence of CC139 cells strongly suggests that the partial loss of serum growth factor requirement acquired in vivo is an essential malignant character for bypassing the hormonal growth restraints imposed by the host upon CC139 cells.
Alterations in calcitonin and parathyroid hormone responsiveness of adenylate cyclase in F9 embryonal carcinoma cells treated with retinoic acid and dibutyryl cyclic AMP
Authors: Evain Danièle , Binet Elisabeth , Anderson Wayne B. 
Published: February 2005

AbstractTeratocarcinoma cells in culture offer an in vitro system for studying certain aspects of embryonic differentiation. To gain some insight into regulatory systems that might be operative during early development, we have characterized the alterations that occur in the hormonal responsiveness of the F9 embryonal carcinoma cell membrane adenylate cyclase with differentiation. Adenylate cyclase of F9 cells is stimulated in the presence of 10 μM GTP by calcitonin, prostaglandin E1, (−) isoproterenol, and epinephrine, while parathyroid hormone is only slightly effective. Of these active hormones, calcitonin is the most potent stimulator of cyclic AMP production.Exposure of F9 cells to retinoic acid induces differentiation to parietal endodermal cells. Basal, GTP‐, and fluoride‐stimulated adenylate cyclase activities show a progressive increase with the retinoic acid‐induced change to the endodermal phenotype. Differentiation to the endodermal cell type markedly alters the adenylate cyclase response to calcitonin and parathyroid hormone; the cyclase of endodermal cells exhibits a low response to calcitonin while parathyroid hormone dramatically enhances cyclic AMP formation.Treatment of the retinoic acid‐generated endodermal cells with dibutyryl cyclic AMP converts these cells to a type exhibiting neural‐like morphology. The adenylate cyclase system of these cells is only stimulated by parathyroid hormone, prostaglandin E1, isoproterenol, and epinephrine. Calcitonin responsiveness has been lost in these cells. These variations in calcitonin and parathyroid hormone responsiveness suggest a possible regulatory role for these hormones during embryonic development. Further more, the results indicate that changes in adenylate cyclase hormonal responsiveness might serve as useful markers during early stages of differentiation.
Effects of serum deprivation on the initiation of DNA synthesis in the second generation in rat 3Y1 cells
Authors: Okuda Atusyuki , Kimura Genki 
Published: February 2005

AbstractRat 3Y1 cells arrested at early S by hydroxyurea traversed the remainder of S and G2 and completed mitosis after removal of the drug, irrespective of the absence of serum from the culture medium. When cells were deprived of serum for a period between early S and mitosis after removal of hydroxyurea, the cells delayed entry into S in the presence of serium in the second generation for the time length approximately equal to that of serum deprivation. When mitotic cells, which had been continously exposed to serum after removal of hydroxyurea, were deprived of serum for the next 24 hours and then were reexposed to serum, the cells delayed entry into S for more than 24 hours (more than the time length of serum deprivation). On the other hand, the cells already deprived of serum between early S and G2 in the first generation were less delayed in entry into S after postmitotic 24‐hour serum deprivation than were the cells exposed to serum between early S and G2 in the first generation. These results suggest that serum‐dependent events continue to occur in the first generation for on‐time entry into S in the next generation, and that these premitotic events (the potential for entry into S) decay if serum is absent for a long period of time after mitosis.
Selective isolation of stable and unstable dedifferentiated variants from a rat hepatoma cell line
Authors: Moore Emma E. , Weiss Mary C. 
Published: February 2005

AbstractThis paper describes the selective isolation of dedifferentiated variants from a well‐differentiated rat hepatoma cell line (Fao). The well‐differentiated cells express the gluconeogenic enzymes, FDPase and PEPCK, and so can grow in a glucose‐free medium. By using glucose‐free medium in conjunction with the BudR‐visible light suicide technique it was possible to isolate two different classes of dedifferentiated variants from a mutagenized population of Fao cells. The variants of the first class resemble those previously described in that they display (1) an altered cellular morphology, (2) a pleiotrophic loss of all (or most) of the hepatic functions routinely analyzed in this laboratory, and (3) an extremely low reversion frequency (⩽ 10−8). The variants of the second class are characterized by an unstable phenotype and uncoordinated expression of the hepatic functions. Unstable variants can give rise to stable dedifferentiated variants, suggesting that the unstable variants may actually represent an intermediate in a two‐step dedifferentiation process.
Modulation of cell competence for induction of differentiation in myeloid leukemic cells
Authors: Symonds Geoff , Sachs Leo 
Published: February 2005

AbstractIt is shown that the competence of differentiation‐defective clones of mouse myeloid leukemic cells (MGI−D− clones) to be induced for some differentiation‐associated properties can be modulated. For certain inducers this was effected by changing the type of serum and for another inducer by removing serum from the culture medium. All the clones which could not be induced to differentiate by the differentiation‐inducing from of the normal macrophage and granulocyte inducing proteins MGI (MGI‐2), lipopolysaccharide (LPS), or dexamethasone (Dex) in serum‐free medium or in medium with horse, calf, rabbit, or sheep serum (nonpermissive serum) could be induced, by all three inducers, for the differentiation‐associated properties of lysozyme and Fc and/or C3 rosettes in syngeneic or allogeneic mouse serum or rat serum (permissive serum). The competence for induction of differentiation was altered merely by washing the cells and changing the type of serum, and addition of nonpermissive serum blocked the induction in permissive serum. This increased competence was associated with an increase in the ability for cap formation by concanavalin A. Removal of serum allowed some MGI−D− clones to be induced for lysozyme, Fc, and C3 rosettes by insulin. However, neither the changes in type of serum nor the removal of serum modulated in these clones the inducing effect of the tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate. In contrast to the MGI−D− clones, changing the serum type or removing the serum did not modulate inducibility by MGI‐2, LPS, Dex, or insulin in other clones of myeloid leukemic cells that could be induced by MGI‐2 to differentiate either partly (MGI+D− clones) or completely (MGI+D+ clones) in horse or calf serum. The results indicate that by the appropriate modulation all MGI−D− clones tested could be induced for some differentiation‐associated properties; that there are factor(s) present in permissive sera which allow MGI−D− clones to be induced by MGI‐2, LPS, and Dex; that there are other factor(s) in nonpermissive sera which block this induction; and that in serum‐free medium cells of the appropriate clone can become susceptible to induction of these properties by insulin.
Isolation of hamster intestinal epithelial cells using hypoosmotic media and PVP
Authors: Carter Julia H. , Carter H. , Nussbaum J. , Eichholz Alexander 
Published: February 2005

AbstractVibration of hamster small intestinal segments in hypotonic media containing PVP is a rapid method for obtaining quantitative yields of viable intestinal epithelial cells. This preparation of epithelial cells offers a unique system for the study of epithelial cell function in vitro. The method for cell separation combines hypoosmotic swelling of cells, which separates them at the desmosomes, with mechanical agitation which releases the cells from the lamina propria. No chemical agents known to affect cell proteins and cell surfaces are employed in this procedure. Only a short time is elapsed between in vivo and in vitro conditions, i.e., a preparation time of approximately 75 minutes.Although the technique yields a pure population of epithelial cells, the cells are of different morphologies, are removed from different areas of the crypts and villi, and therefore presumably have different functions. Examination of the intestinal tissue remaining after several vibration intervals by light and scanning electron microscopy indicates that the sequences of release of cells is removal of: (1) cells from the villus based, (2) cells from the lower one‐half to two‐thirds of the villi, (3) cells from the villus tips (and some crypts), and (4) cells from the crypts. When pools of a + b cells are compared to pools of c + d cells, it is found that villus cells can be characterized by: (1) processes, such as monosaccharide absorption, associated with the brush border, and (2) synthesis of components (e. g., glycoproteins) of the brush border. Surprisingly, disaccharide hydrolytic activity is found in cells which transport monosaccharides poorly. The subpopulations of cells synthesize proteins equally.
Activation of transglutaminase during cell cycle in CHO cells
Authors: Scott Karen F. Frasier , Russell Diane Haddock 
Published: February 2005

AbstractTransglutaminase (TGase) activity was measured during cell cycle progression in Chinese hamster ovary (CHO) cells synchronized by release of quiescent cultures and in CHO cells synchronized by mitotic shake off. In cells released from quiescent cultures, a greater than 2‐fold increase in TGase activity occurred within 3 h of stimulation, followed by a rapid decline and a second and third peak of activity at 6 and 9 h after stimulation. The increase in TGase activity was not inhibited at any time measured by the administration of cycloheximide. Further, there was a significant increase in TGase activity detectable at 1, 5, and 6 h in CHO cells exposed to actinomycin D at time zero. TGase activity in CHO cells was not increased by the addition of either dibutyryl cAMP or 8‐bromo‐cAMP whereas ornithine decarboxylase (ODC) activity was increased at all times measured by the administration of cAMP analogs. These data suggest that TGase and ODC are regulated by separate hormonal pathways during cell cycle progression. In addition, ODC is induced in CHO cells by a transcriptional mechanism whereas TGase appears to be activated. In order to determine if the biphasic increase in TGase exhibited in G1 of cell cycle was the result of two populations of cells progressing through G1, we assessed TGase activity in CHO cells synchronized by mitotic shake off, which produces a greater than 95% cell synchrony. Again, there were two major peaks of TGase activity at 3 and 5 h, respectively. However, there was a marked difference in the expression of TGase within the first 2 h after release from mitosis. During this period, there was a marked and significant decrease in TGase activity within 1 h to a value about 35% of the time zero value. Another G1‐specific marker, ODC, also exhibited a marked decline in activity within the first hour, followed by a single peak of expression between 4 and 5 h in these cells. Both enzymes have high activity during G2 phase of cell cycle as previously reported for ODC. Both enzymes are rapidly decreased after release from mitosis. The peak expression of both TGase and ODC suggest they catalyze important enzymatic events required for cell cycle progression.
Modulation of synthesis of specific proteins in endothelial cells by copper, cadmium, and disulfiram: An early response to an angiogenic inducer of cell migration
Authors: Hannan G. N. , McAuslan B. R. 
Published: February 2005

AbstractCopper, cadmium, and disulfiram (an ionophore for copper) modulate the synthesis of several polypeptides in two clonal lines of bovine aortal endothelial cells. After treatment of type 1 endothelial cells with 10−3 M CuSO4 or 10−5 M CdCl2 four cell‐associated polypeptides (Mr = 28,000, 32,000, 73,000, and 83,000 daltons) were induced. In contrast, in Type 2 endothelial cells, which have cultural characteristics distinct from Type 1, only one new cell‐associated protein (Mr = 32,000 and 40,000 daltons) was induced.Other differences are revealed by analyses of proteins secreted into the growth medium. In particular low levels of only CuSO4 (10−6 M) enhanced the synthesis in Type 2 cells of a protein (Mr = 220,000 daltons) identified as fibronectin. Since only copper ions induced fibronectin, we propose that the mechanism of induction of fibronectin synthesis, in contrast to the induction of cell−associated polypeptides, does not involve a sulphydryl−containing receptor molecule. It is suggested that the specific enhancement of fibronectin synthesis by copper ions may be a controlling event in the stimulation by copper ions of endothelial cell migration and angiogenesis.
Effect of insulin on folic‐acid transport in cultured fibroblasts
Authors: Eilam Y. , Ariel M. , Grossowicz N. 
Published: February 2005

AbstractUptake of folic acid was measured in secondary cultures of skin fibroblasts from fetal rats. The cultures were made quiescent by 24 hours preincubation in medium containing 1% serum and subsequent 3 hours preincubation in phosphate buffered saline. The uptake of 3H‐folic acid was linear with time during 15 seconds and reached a plateau level at 2–3 minutes. There was no further increase in the intracellular radioactivity until the end of the experiments at 10 minutes. The uptake of folic acid in fibroblasts was not concentrative and proceeded until equilibration with the extracellular concentration. Intracellular metabolic conversion of folic acid was not significant during the time of the experiments (up to 10 minutes). Insulin caused a two‐fold increase in the initial rate of folate uptake as determined from the 15 second uptake values. The dose response curves for the insulin effect showed that 85% of the maximal effect was exerted by 1 m̈M insulin. A lag period of 7–10 minutes was observed after the addition of insulin and before the effect on folic acid uptake was manifested. Thereafter the effect increased with the time of preincubation with insulin. The concentration dependence of folate uptake yielded non homogeneous curves. At low concentrations of substrate, saturable components were observed while at high concentration (above 5 × 10−6 M) a linear component was observed. Insulin increased the slope of the linear component and the Vmax of the saturable component while the Km remained unaltered.
Effect of glycosaminoglycans on fibronectin‐mediated cell attachment
Authors: Klebe Robert J. , Mock Penny J. 
Published: February 2005

AbstractIn this study, the role of glycosaminoglycans in fibronectin‐mediated cell attachment to collagen has been investigated. While it has been established that fibronectin possesses binding sites for several glycosaminoglycans, it was found that only dextran sulfate and macromolecular heparin could decrease the initial rate of cell attachment to collagen. Low molecular weight heparin was inactive. This study suggests that the glycosaminoglycan binding site of fibronectin plays a role in the mechanism of cell attachment.
Immunological characterization of metallothioneins in mouse LMTK cells and in a variant resistant to cadmium
Authors: Maiti Indu , Mbikay Majambu , Marengo Claude , Thirion Jean‐Paul 
Published: February 2005

AbstractA cadmium‐resistant variant isolated from mouse fibroblast LMTK cells can grow in the presence of 40 μM Cd2+. This variant retained its properties in the absence of selecting agent. Induction of metallothionein was measured in cell extracts by radioimmunoassay. The maximum amount of metallothioneins in the cells was reached after 36 hours. The cadmium resistant variant produced two times more metallothionein than the wild‐type when exposed to 10–20 μM Cd2+. By Ouchterlony double diffusion, the metallothioneins from cultured cells formed a line of parital identity with the mouse liver serotype and a line of complete identity with one of the two mouse kidney serotypes. These observations raise the possibility of a tissue‐specific expression of metallothionein genes.
Commitment and proliferation kinetics of human lymphocytes stimulated in vitro: Effects of colchicine on mitogen response
Authors: Hall David J. , O'leary James J. , Rosenberg Andreas 
Published: February 2005

AbstractWe have examined the effects of colchicine on concanavalin A (Con A)‐ and phytohemagglutinin (PHA)‐stimulated human peripheral blood lymphocytes and from the time course of proliferation have extracted the relative size of the responding cell population, the rate of entry of this population into S‐phase, and the length of the lag period. Additions of colchicine at any time did not appear to influence the size of the responding population nor did it greatly affect the duration of the lag period. Only the rate at which the cell population enters initial S‐phase is a function of the time of previous exposure to colchicine. Colchicine does not appear to inhibit the commitment of stimulated lymphocytes to enter the cell cycle. Rather, it merely serves to decrease the biochemical processes responsible for fixing a maximal rate of entry into S‐phase.
Regulation of amino acid transport in L6 muscle cells: I. Stimulation of transport system a by amino acid deprivation
Authors: Logan William J. , Klip Amira , Gagalang Enriqueta 
Published: February 2005

AbstractThe regulation of amino acid transport in L6 muscle cells by amino acid deprivation was investigated. Proline uptake was Na+‐dependent, saturable and concentrative, and was predominantly through system A. Proline uptake was inhibited by alanine, α‐amino isobutyric acid (AIB), and by α‐methylamino isobutyric acid, but not by lysine or valine. At 25°C, Km of proline uptake was 0.5 mM. Amino acid‐deprivation resulted in a progressive increase in the rate of proline uptake, reaching up to 6‐fold stimulation after 6 hours. The basal and stimulated transport were equally Na+‐dependent, and both were inhibited by competition with the same amino acids. Kinetic analysis showed that Km decreased by a factor of 2.4 and Vmax increased 1.9‐fold in deprived cells. Amino acid‐deprivation did not stimulate amino acid uptake through systems other than system A. This suggests that the higher Km in proline‐supplemented cells is not due to release of intracellular amino acids into unstirred layers surrounding the cells. The presence of amino acids which are substrates of system A (including AIB) during proline‐deprivation, prevented stimulation of proline uptake, whereas those transported by systems Ly+ or L exclusively were ineffective. The stimulation of the transport‐rate in deprived cells could be reversed by subsequent exposure to proline or other substrates of system A. L6 cells, deprived of proline for 6 hours, retained the stimulation of transport after detachment from the monolayers with trypsin. Uptake rates were comparable in suspended and attached cells in monolayer culture. Thus, amino acid‐depreivation of L6 cells results in an adaptive increase in proline uptake, which is not due to unstirred layers but appears to be mediated by other mechanisms of selective transport regulation.
The use of fluorescent dyes to measure membrane potentials: A critique
Authors: Johnstone R. M. , Laris P. C. , Eddy A. A. 
Published: February 2005

AbstractUnder controlled conditions, fluorescent cyanine dyes can be used to mesure membrane potentials of cell suspensions. Similar changes in membrane potential can be followed both with fluorescent dyes and electrophysiological probes in response to changes in the ion composition of the medium. Recent reports that attempt to abrogate the use of the cyanine dyes in measurements of the membrane potential are misleading.
Evidence that myosin light chain phosphorylation regulates contraction in the body wall muscles of the sea cucumber
Authors: Kerrick W. G. L. , Bolles L. L. 
Published: February 2005

AbstractThe Ca2+ activation mechanism of the longitudinal body wall muscles of Parastichopus californicus (sea cucumber) was studied using skinned muscle fiber bundles. Reversible phosphorylation of the myosin light chains correlated with Ca2+‐activated tension and relaxation. Pretreatment of the skinned fibers with ATPγS and high Ca2+ (10‐5M) resulted in irreversible thiophosphorylation of the myosin light chains and activation of a Ca2+ insensitive tension. In contrast, pretreatment with low Ca2+ (10‐8M) and ATPγS results in no thiophosphorylation of the myosin light chains or irreversible activation of tension. These results are consistent with a Ca2+‐sensitive myosin light chain kinase/phosphatase system being responsible for the activation of the muscle. Other agents known to have an effect upon the Ca2+‐activated tension in skinned vertebrate smooth muscle fibers (trifluoperazine, catalytic subunit of the cyclic AMP‐dependent protein kinase, and calmodulin) did not have an effect on myosin light chain phosphorylation or Ca2+‐activated tension. These results suggest a different type of myosin light chain kinase than is found in vertebrate smooth muscle is responsible for the activation of parastichopus longitudinal body wall muscle.