bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glucocorticoids inhibit the stimulatory effect of epidermal growth factor on the initiation of DNA synthesis
Authors: Otto Angela M. , Natoli Clara , Richmond K.M. Veronica , Iacobelli Stefano , De Asua Luis Jimenez 
Published: February 2005

AbstractConfluent, quiescent Swiss 3T3 cells in culture can be stimulated to initiate DNA synthesis and divide by addition of growth factors to the culture medium. Here we show that hydrocortisone and other steroids which have glucocorticoid activity inhibit the stimulation of these cells by epidermal growth factor (EGF) in contrast to their reported enhancement of stimulation by fibroblast growth factor (FGF). Binding studies using [3H]‐triamcinolone acetonide show that Swiss 3T3 cells contain a single class of glucocortioid receptor of uniform affinity (KD = 2.0 nM), and about 34,000 receptor sites per cell. Those steroids which displace bound [3H]‐triamcinolone acetonide are also effective in inhibiting the stimulation of DNA synthesis by EGF in the presence or absence of insulin, and the concentration of triamcinolone acetonide required for one‐half maximal biological effect is in the same range as the KD. A similar concentration is required for one‐half maximal enhancement of the effect of FGF. These results suggest that both the inhibitory and stimulatory effects of glucocorticoids may be mediated via these receptors, the different effects thus being due to differences in the intracellular events triggered by each growth factor.
The effect of calcium chelation on lymphocyte monovalent cation permeability, transport and concentration
Authors: Quastel Michael R. , Segel George B. , Lichtman Marshall A. 
Published: February 2005

AbstractWe have quantified the effect of EGTA on K exodus and uptake in human blood lymphocytes. When lymphocytes were exposed to a medium containing an EGTA concentration that resulted in an ionized Calcium (Ca) of less than 10 μM, K exodus began to increase. This increase reached nearly threefold that of the control rate in a medium containing sufficient EGTA to reduce the ionized Ca concentration below 0.1 μM. When K exodus was increased, K uptake increased proportionately. This increase in K uptake represented active transport and was associated with an 80% increase in intracellular Na concentration from 15 to 27 mM. The addition of Ca to a medium containing EGTA reversed to normal the increased K exodus and uptake. Histidine, a potent chelator of divalent cations other than Ca, had no effect on K transport. These data indicate that extracellular Ca chelation leads to an increase in lymphocyte membrane permeability and cation leak. This increased leak is associated with an elevation of the cell Na and an increase in transport to a rate equivalent to that of the exodus rate. The compensatory increase in active transport maintains the cell monovalent cation concentration within 10 to 15 mM of unperturbed levels.
Comparison of the control and pathways for degradation of the acetylcholine receptor and average protein in cultured muscle cells
Authors: Libby Peter , Goldberg Alfred L. 
Published: February 2005

AbstractIn the studies reported here, we investigated whether the degradation of the acetylcholine receptor (AChR) in cultured muscle cells involves similar mechanisms as and is controlled in a manner similar to, the catabolism of the bulk of cell protein. We compared these processes after labeling cell protein with radioactive leucine or phenylalanine for 24 hours, or labeling the acetylcholine receptor with (125I)‐bungarotoxin. The apparent average half‐life of cell protein was 38 ± 2 hours and that of the receptor‐toxin complex was 25 ± 1 hours. Incubation in media lacking serum and embryo extract accelerated the degradation of both average protein and the receptor‐toxin complex. Insulin reduced the rate of catabolism of both average protein and the receptor‐toxin complex toward levels seen in the presence of serum. However, although these two degradative processes seem to be controlled similarly, they probably involve different mechanisms. The protease inhibitors leupeptin and chymostatin, which slowed overall proteolysis in nongrowing muscles and hepatocytes, reduced the degradation of the ACh receptor by 2–11‐fold, but had no, or only slight, effects on the catabolism of average protein, even when overall proteolysis was accelerated by omitting serum and embryo extract. Chloroquine, an inhibitor of lysosomal function, also reduced the degradation of AChR, by about 10‐fold, but decreased overall protein breakdown by only 20–30%. Incubation of myotubes at lower temperatures reduced both degradative processes, but affected the breakdown of the receptor to a greater extent. Thus the rate‐limiting steps in these processes have different activation energies. Incubation with 2‐deoxyglucose, an inhibitor of glycolysis, decreased the breakdown of average protein but not that of the receptor‐toxin complex. However, the two degradative processes were sensitive to azide, an inhibitor of oxidative phosphorylation. Although the lysosome is the primary site for AChR degradation and perhaps for degradation of other surface proteins, the breakdown of most proteins in myotubes seems to involve a distinct proteolytic system requiring metabolic energy.
The expression of glial fibrillary acidic protein in a rat cerebellar cell line
Authors: Giotta Gregory J. , Cohn Melvin 
Published: February 2005

AbstractA rat cerebellar cell line, WC5, derived by transformation with Rous sarcoma virus, which is temperature‐sensitive for transformation (ts‐RSV), can be induced to express glial fibrillary acidic protein (GFAP). Immunofluorescence, radioimmune assay, and electron microscopy studies show that GFAP is expressed in WC5 cells grown at the nonpermissive temperature (NPT), but not at the permissive temperature (PT) for transformation. GFAP is first detectable about 3 days after incubating cells at the NPT, and reaches an apparent plateau by the seventh or eighth day. The expression of GFAP is reversible; shifting cells from the NPT to the PT causes a dramatic decrease in GFAP after 96 hr. In order to determine if the expression of GFAP is linked to the temperature‐sensitive transforming activity of the viral src gene product, phenotypic revertants of WC5 were established. By the criteria of morphology and growth in agar, the revertant lines, in contrast to the parent cell line WC5, were shown to exhibit a transformed phenotype at both the NPT and PT. Immunofluorescence studies on several of the revertant cell lines show that they do not express GFAP at either the PT or NPT. These findings suggest that the expression of GFAP in WC5 is linked to the expression of the src gene product. The advantage of using ts‐RSV to derive neural cell lines which exhibit differentiated properties is discussed.
Nutrient transport in a bovine lens epithelial cell line
Authors: Prasad Rajendra , Shopsis Charles , Southern A. Louis , Hochstadt Joy 
Published: February 2005

AbstractA bovine calf lens epithelial cell line (CLE‐1) that synthesizes crystallin has been established in culture and some of its transport properties have been characterized using both cells and membrane vesicles derived from them. The membrane vesicles fractionate with high recovery of plasma membrane markers, showing a 40‐fold purification of 5′‐AMPase and a 20‐fold decrease in the specific activity of the mitochondrial marker enzyme succinic dehydrogenase relative to a cell homogenate. Transport sites demonstrated higher specific activity than has been seen in vesicles from cell lines studied previously. The uptake of α‐amino isobutyric acid (AIB) (an alanine analog) by CLE‐1 cells is stimulated four‐ to fivefold by Na+ and exhibits a Km of 5.4 mM with a Vmax of 50 pmoles/min μg of cell protein. The uptake of leucine was not Na+ stimulatable. The uptake of AIB by the cells was reduced by 43% at confluence. Thus, the cell density dependent behavior of the uptake of the alanine amino acid family in CLE‐1 is similar to that of various fibroblast cells.The Na+ caused a threefold stimulation of AIB uptake in the membrane vesicles, while vesicular uptake of leucine was unaffected by Na+. The uptake of adenine, guanine, uridine, and guanosine was also tested in these vesicles. The substrates were rapidly accumulated, came to a steady state distribution within 1–2 minutes, and were recovered as the unaltered compounds after uptake.
The role of energy in hyperthermia‐induced mammalian cell inactivation: A study of the effects of glucose starvation and an uncoupler of oxidative phosphorylation
Authors: Haveman J. , Hahn G. M. 
Published: February 2005

AbstractWhen cultured Chinese hamster cells were exposed to 43°C hyperthermia, effects due to glucose deprivation and to the presence of the uncoupler of oxidative phosphorylation, carbonylcyanide‐3‐chlorophenylhydrazone, during the 43°C treatment proved to be strongly accelerated compared to the effects at normal temperature (37°C). This strongly indicates that the availability of energy plays an important role in the response of these cells to hyperthermia. One of the reasons cells die after hyperthermia may be a lethal lack of energy. Cells heated before glucose deprivation were able to maintain viability for a longer period during deprivation than cells without the preheat treatment. As the cells might develop thermotolerance after the heat exposure, this suggests that cells in the thermotolerant state use energy in a more economical way.
Properties of a growth factor activity present in crude extracts of rat uterus
Authors: Sirbasku David A. , Leland Frances E. , Benson Robert H. 
Published: February 2005

AbstractWe have shown previously (D.A. Sirbasku, 1978, Proc. Natl. Acad. Sci. U.S.A., 75:3786–3790) that an estrogen‐inducible growth factor activity for rat mammary and rat pituitary tumor cells can be identified in extracts of rat uteri, although at the time of that report only a limited biochemical characterization of the activity was presented. In this report, we have evaluated the growth factor activity for lipid, steroid hormone or protein‐like properties. Uterine growth factor activity was assayed by measure of the increased cell number of the MTW9/PL rat mammary tumor cell line established by this laboratory and described previously (D.A. Sirbasku, 1978, Cancer Res. 38:1154–1165). Studies showed the following characteristics of growth factor activity: destroyed by trypsin treatment; labile when heated at 80°C; partially denatured by 6 M guanidine or 8 M urea treatment or 50% aqueous solutions of organic solvents; inactivated by extremes of pH or overnight treatment with mild acid; not dialyzable at neutral pH; of apparent molecular weight of 70,000 daltons by G‐100 Sephadex chromatography; possessing an isoelectric point of 4.8 to 5.2; not chloroform/methanol extractable; and not in any way identified as either a lipid or a steroid hormone. The data available suggest that the uterine growth factor activity is a protein or polypeptide of apparent high molecular weight, and that this activity does not directly correspond to other known growth factors.
Reverse transformation of vole cells transformed by avian sarcoma virus containing the src gene
Authors: Puck Theodore T. , Erikson Raymond L. , Meek William D. , Nielson Stanley E. 
Published: February 2005

AbstractVole cells transformed by avian sarcoma virus carrying the src gene lose their fibroblastic morphology, the organized cytoskeletal system of the normal fibroblastic cell, the typical fibronectin deposit around the cell membrane, and the ability to shut off multiplication when suspended in liquid medium. All of these transformation characteristics are reversed by treatment with cAMP derivatives. Moreover, the cAMP treatment does not cause loss of activity of the src gene product. These data imply that cAMP exerts its effect at or after the point in the metabolic pathway affected by the src gene product, pp60src. Presumably, the decision to adopt the transformed or the normal state is determined by the degree to which the src gene or cAMP‐mediated kinase activities respectively predominate in the cell. The development of all four transformation characteristics as a result of introduction of the src gene, and their coordinate reversal by cAMP derivatives, supports the previous thesis that in the normal vole or CHO fibroblast all four properties are part of a common regulatory system.
Commitment and proliferation kinetics of human lymphocytes stimulated in vitro: Effects of α‐MM addition and suboptimal dose on concanavalin a response
Authors: Hall David J. , O'Leary James J. , Sand Theodore T. , Rosenberg Andreas 
Published: February 2005

AbstractWe have examined the effect of alpha‐methylmannoside (α‐MM) addition to concanavalin A (con A)‐stimulated peripheral human lymphocytes. With a previously established kinetic model, we have, from the time course of proliferation, extracted the responding clone size, rate of entry of this clone into S phase, and the length of the lag period. We have studied the effect of con A dose and time of addition of α‐MM to optimally stimulated cells on these kinetic parameters. We show that neither a low dose of con A nor an early addition of ‐‐MM to optimally stimulated cells results in a change in the responding clone size. That is, all of the potentially responsive cells appear to become “committed” to enter the cell cycle regardless of the presence of α‐MM early in the culture or in the presence of suboptimal stimulation. However, the rate at which these committed cells enter the first S phase is a function of the dose of con A and time of addition of α‐MM and varies over a wide range. It is the variation in this parameter that accounts for virtually all of the diminished response previously interpreted as a time‐dependent irreversible commitment of mitogen‐stimulated cells. The previous work using only fixed time points for measuring thymidine uptake and the concept of commitment must be reevaluated in light of the kinetic evidence presented.
Hexose sugar transport activity in a mouse fibroblast cell line temperature sensitive for expression of the transformed phenotype
Authors: Karrs Thomas M. , Quinlan Dennis C. 
Published: February 2005

AbstractA temperature‐sensitive mouse fibroblast cell line was used to examine the relationship between hexose sugar uptake rates and the control of cell growth. The cell line used (ts‐H6‐15) is a derivative of SV‐3T3 cells, exhibiting a transformed phenotype at 32°C and a normal phenotype at 39°C. For cells actively growing at either temperature, a marked decrease in the rate of 3‐0‐methyl‐D‐glucose (3‐0‐MeG) transport is observed as cell population density increases. At all cell population densities tested, 3‐0‐MeG transport rates (at a common assay temperature) were greater in H6‐15 cells grown at 32°C than at 39°C, with the enhancement being maximal at the lowest cell densities. The effect of low serum‐arrest on H6‐15 cells revealed that cells growing at 39°C arrest in G1, while cells at 32°C stop more randomly throughout their cycle. Under conditions of low serum‐arrest the rate of 3‐0‐MeG transport remained as high as in actively growing cells at both 32°C and 39°C. However, 2‐deoxyglucose uptake rates were growth state‐dependent at 39°C, indicating perhaps metabolic as well as membrane‐level control of sugar accumulation. These results further demonstrate that rates of hexose sugar transport by themselves are not always absolutely correlated with rates of cell proliferation and, thus, may not be reliable predictors of cell growth potential.
Sensitivity of excision repair in normal human, xeroderma pigmentosum variant and Cockayne's syndrome fibroblasts to inhibition by cytosine arabinoside
Authors: Cleaver James E. 
Published: February 2005

AbstractInhibition of the gap‐filling, polymerizing step of excision repair by 1‐β‐D‐arabinofuranosylcytosine (ara‐C) after irradiation with ultraviolet light in human diploid fibroblasts resulted in the formation of persistent DNA strand breaks in G1, G2, and plateau phase cells, but not in S phase cells. Addition of hydroxyurea to ara‐C resulted in partial inhibition of repair in S phase cells. These observations can be explained either in terms of changing roles in repair for different DNA polymerases throughout the cell cycle or by the presence of a pool of deoxycytidine nucleotides during S phase equivalent to an external source of deoxycytidine at 50 μM concentration. A similar concentration dependence on ara‐C was observed for inhibition of repair in normal human, xeroderma pigmentosum (XP) variant, and Cockayne's syndrome cells. Ara‐C produced a similar number of breaks in normal and Cockayne's syndrome cells but slightly more in XP variant cells. Exonuclease III and S1 nuclease independently both degraded about 50% of the 3H‐thymidine incorporated into repaired regions in the presence of ara‐C. Sequential digestion with both enzymes degraded nearly 90% of the repaired regions. These observations can be explained if excision repair proceeds by displacing the damaged strand so that both the 3H‐labeled patch and the damaged region are still ligated to high molecular weight DNA and compete for the same complementary strand during in vitro incubation with the nucleases. The amount of 3H‐thymidine incorporated in DNA by repair decreased with increasing concentrations of ara‐C and hydroxyurea, suggesting that the incomplete patches became shorter under these conditions. Extrapolation of the digestion kinetics with exonuclease III permits an estimate of the normal patch size of about 100 nucleotides, consistent with previous estimates.
Clonal variation in cultured neuroblastoma cells. I. Isolation and characterization of variants
Authors: Lombardo J. M. , Lanks K. W. 
Published: February 2005

AbstractTwo spontaneously arising variant clones were selected from the N18 neuroblastoma cell line solely on the basis of their flattened morphology and tight adherence to the culture flask. Two other clones having the round loosely adherent morphology typical of the parent line were also selected, and flat variants were shown to arise in them upon prolonged cultivation. The flat variant clones have slower growth rates in culture, lower cloning efficiencies in suspension, and reduced acetylcholinesterase inducibility when compared with either the parent N18 line or the round cell clones. Cells of both morphologic types have high levels of plasminogen activator and are tumorigenic, although the variants have a slower growth rate in vivo, consistent with their slower growth rate in culture. SDS‐polyacrylamide gel electrophoresis of total protein from the two cell types shows that the flat variants have increased amounts of a 200,000 molecular weight polypeptide that has tentatively been identified as the heavy chain of myosin. Round morphological revertants from one of the flat variant clones exhibited growth characteristics typical of the parent N18 line, but their content of myosin heavy chain, although reduced, was not so low as that in the round cell clones originally isolated. The possibility of a causal relationship between flat morphology, reduced suspension cloning efficiency, and increased content of myosin heavy chain is discussed.
The binding and processing of plasminogen by Balb/c 3T3 and SV3T3 cells
Authors: Tobler Jerry , Krieger Monty , Stroud Robert M. 
Published: February 2005

AbstractThe binding and processing of plasminogen by Balb/c 3T3 and SV3T3 cells was studied using 125I‐labeled canine plasminogen. Throughout a 3‐day period, 125I‐plasminogen in the incubation medium bound to the cells and was degraded, first to intermediate‐sized macromolecules that were the same size as the large (74,600‐dalton) and small (25,000‐dalton) chains of active plasmin, and to smaller fragments including 3‐iodo‐L‐tyrosine. Binding to SV3T3 cells was independent of the protease‐dependent morphological change (PDMC)1 characteristic of these and many other transformed cells. The SV3T3, and to a somewhat lesser extent, the 3T3 cells, both accumulated and released into the incubation medium 3‐iodo‐L‐tyrosine, a terminal lysozymal digestion product.The results of a sublethal cell‐surface trypsinization assay suggest that the cell‐associated plasminogen was primarily bound to the surfaces of the 3T3 and SV3T3 cells while the macromolecular degradation products including active plasmin were inside the cells. The rate of 125I plasminogen degradation exhibited by SV3T3 cells was approximately two times greater than that of 3T3 cells, which presumably reflects differences in endocytosis or lysosomal hydrolysis, or both. The rates were unaffected by addition of pancreatic or soybean trypsin inhibitor sufficient to inhibit PDMC.In the incubation medium, plasminogen was activated to plasmin by SV3T3, but not by 3T3 cells. However, 95–100% of plasmin covalently bound to a 47,000‐dalton canine serum component, which could be dissociated from plasmin by hydroxylamine: 95–100% of the plasmin was inactive to reaction with DF32P. Thus the serum component is a plasmin inhibitor. The plasmin‐containing complex in the medium had an apparent molecular weight of 212,000. Under denaturing conditions, the complex dissociated into two covalently modified plasmin‐containing species of 153,000 and 127,000 daltons. In addition to forming a complex with a serum component, the plasmin is cleaved into two small fragments (∼10,000 and 12,000 daltons) by as‐yet uncharacterized serum factors.
The effect of added H1 histone and polylysine on DNA synthesis and cell division of cultured mammalian cells
Authors: Kundahl E. , Richman R. , Flickinger R. A. 
Published: February 2005

AbstractAddition of H1 histone or polylysine (10 μg/ml) to cultured Friend erythroleukemia cells or to two mouse lymphoma cell lines (el‐4 and S‐49) increased levels of cell division in these cultures. There is a stimulation of incorporation of labeled thymidine into DNA in cultures containing H1 histone and polylysine. DNA fiber autoradiographic experiments revealed that replicon size is decreased in the cells cultured with H1 histone and polylysine at later periods of culture.
The effect of reagents that increase membrane fluidity on the activity of 3‐hydroxyl‐3‐methyl glutaryl coenzyme a reductase in the CHO‐K1 cell
Authors: Sinensky Michael , Kleiner Jeffrey 
Published: February 2005

AbstractThe compounds cetyl trimethyl ammonium bromide (CTAB) and ethanol both decrease the order parameter of a spin probe embedded in cholesterol‐lecithin liposomes, but CTAB produces lowering of the order parameter comparable to that produced by ethanol at a 10,000‐fold lower concentration. Treatment of CHO‐K1 cells with CTAB or ethanol at concentrations that produce comparable increases of membrane fluidity produce a 2‐ to 3‐fold increase of microsomal membrane cholesterol to phospholipid ratio and a 2‐ to 3‐fold increase of the activity of the rate‐limiting enzyme of cholesterol biosynthesis, 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase. Cells treated with CTAB or ethanol show a progressively decreasing capacity to accumulate α‐aminoisobutyric acid with increasing drug treatment, but cells pre‐treated with CTAB are relatively resistant to the effects of CTAB on α‐aminoisobutyrate transport. The increase in HMG‐CoA reductase by CTAB or ethanol is not observed when these compounds are added directly to cell extracts but, rather, is only observed after 8 hours of exposure of intact cells to these drugs. Actinomycin D and cycloheximide treatment prevent the increase in enzyme activity, and the increase is also blocked in a regulatory mutant of the CHO‐K1 cell with permanently repressed HMG‐CoA reductase activity.These data are consistent with a homeoviscous adaptation mechanism in the CHO‐K1 cell, in which increased activity of HMG‐CoA reductase, through a process requiring RNA and protein synthesis, compensates for conditions that increase membrane fluidity by increased cellular cholesterol biosynthesis and cholesterol to phospholipid ratio.