bluuebunny/crossref_metadata_2025_split huggingface dataset:
Delayed and reduced cell replication and diminishing levels of DNA polymerase‐α in regenerating liver of aging mice
Authors: Fry Michael , Silber John , Loeb Lawrence A. , Martin George M. 
Published: February 2005

AbstractKinetics of cell replication was compared in regenerating livers of Mus musculus at ages ranging between 6 and 32 months. Incorporation of [3H]‐thymidine into DNA and autoradiographic analysis showed that the maximal extent of DNA replication following partial hepatectomy became delayed with age. Furthermore, the total fraction of parenchymal and nonparenchymal cells in S phase at different intervals during regeneration diminished as mice aged. The specific activity of DNA polymerase‐α, the putative replicative enzyme, declined progressively during aging. The specific activity of DNA polymerase‐β, the purported repair enzyme, declined to an appreciably lesser extent during the lifespan of the mouse. No evidence was found for the appearance of a specific inhibitor of polymerase‐α in senescent mouse liver. Also, the bulk of the activities of both hepatic DNA polymerase‐α and ‐β remained localized in the cell nucleus throughout the lifetime of the animal and were mainly associated with chromatin.
Inhibition of vascular smooth muscle cell migration by heparin‐like glycosaminoglycans
Authors: Majack Richard A. , Clowes Alexander W. 
Published: February 2005

AbstractPrevious studies have suggested that heparin‐like glycosaminoglycans may be endogenous inhibitors of smooth muscle proliferation in the vessel wall. The purpose of this study was to determine the effects of exogenous glycosaminoglycans on rat vascular (aortic) smooth muscle cell migration following wounding in vitro. Our data indicate that heparin and related molecules (iota carrageenan, dextran sulfate), but not other glycosaminoglycans (hyaluronate, chondroitin, and dermatan sulfates), inhibit smooth muscle cell motility in a cell‐specific, dose‐dependent, and reversible fashion. The effect of heparin was maximal (60% inhibition) at 10 μg/ml; a half‐maximal effect was observed at 1 μg/ml; Heparin did not significantly affect the migration of bovine aortic endothelium or Swiss 3T3 cells. These observations support the concept that heparin‐like glycosaminoglycans may be important regulators of vascular smooth muscle cell function.
Isolation of plasma membrane, Golgi apparatus, and endoplasmic reticulum fractions from single homogenates of mouse liver
Authors: Croze Edward M. , Morré D. James 
Published: February 2005

AbstractProcedures to isolate plasma membrane, Golgi apparatus, and endoplasmic reticulum from a single homogenate of mouse liver are described. Fractions contain low levels of contaminating membranes as determined from morphometry and analyses of marker enzymes. The method requires only 2–3 gm of liver as starting material and yields approximately 0.7, 0.7, and 0.5 mg protein/gm liver, respectively, for endoplasmic reticulum, Golgi apparatus, and plasma membrane. Golgi apparatus fractions show high levels of galactosyltransferase activity and consist of cisternal stacks and associated secretory vesicles and tubules. Endoplasmic reticulum fractions are enriched in both glucose‐6‐phosphatase and nicotinamide adenine dinucleotide phosphate (reduced) (NADPH)‐cytochrome c reductase and contain membrane vesicles with attached ribosomes. K+‐stimulated p‐nitrophenyl phosphatase and (Na+ K+) adenosine triphosphatase activity are enriched in the plasma membrane fraction. This fraction consists of membrane sheets, many with junctional complexes, and bile canaliculi that are representative of the total hepatocyte plasma membrane. The fractionation procedure is designed to utilize small amounts of tissue (e.g., with liver slices), to reduce the total time required for fractionation, and to permit comparisons of constituents of plasma membrane, Golgi apparatus, and endoplasmic reticulum prepared from the same starting homogenates.
Density‐dependent inhibition of growth: Inhibitorydiffusible factors from 3T3‐ and rous sarcoma virus (RSV)‐transformed 3T3 cells
Authors: Harel Louise , Chatelain Gilles , Golde Alice 
Published: February 2005

AbstractWe recently fractionated, from the culture medium of 3T3 cells, a thermolabile inhibitory diffusible factor (IDFN) with a molecular weight of about 40,000 daltons, which decreased nucleic acids synthesis of stimulated target 3T3 cells. In the present publication the inhibitory activities of IDFN (produced by 3T3 cells) and IDFT (produced by RSV‐transformed 3T3 [3T3 SRA/H] cells) on 3T3 and 3T3 SRA/H cells have been compared. The inhibitory activity of IDFN decreased (by a mean of 57%) when it was tested on transformed instead of 3T3 cells. On the other hand IDFT was able to decrease 14C‐inosine incorporation in target 3T3 cells. However, the inhibitory activity of IDFT decreased (by mean 50%) when tested on 3T3 SRA/H instead of 3T3 cells. Therefore, transformed cells produced an inhibitory factor but were less sensitive than 3T3 cells to its inhibitory activity. The inhibitory activity of IDFT on 3T3 SRA/H cells was only 20% of the inhibitory activity of IDFN on 3T3 cells. This appreciable difference is of particular interest, since it could explain the release of density‐dependent inhibition of growth (DDI) in transformed 3T3 SRA/H cells. Furthermore, it provides more evidence for the hypothesis that, in 3T3 cells, DDI of growth is due to the release of an inhibitory molecule into the medium, and that IDFN is in fact, the inhibitory molecule involved in this phenomenon.
The effects of serine protease inhibitors on morphological differentiation of murine neuroblastoma cells (NB 15)
Authors: Gibson William H. , Burack Shari L. , Picciano Anne 
Published: February 2005

AbstractMorphological differentiation of neuroblastoma cells (NB15) was induced by cAMP effectors in the presence and absence of serine protease inhibitors. In all conditions tested, the percent differentiation was inhibited by protease inhibitors antipain, diisopropylfluorophosphate (DFP), leupeptin, and soybean trypsin inhibitor (SBTI). The level of morphological differentiation obtained in medium containing fetal calf serum was significantly less than the percent differentiation obtained with serum‐free medium alone, so serum‐free medium was the principal method of induction and comparisons were made to control uninduced cultures or cultures induced with the phospho‐diesterase inhibitor R020–1724. Secreted or cell surface caseinolytic protease activity was higher in differentiating cells than in control cultures and was inhibited by the serine protease inhibitors. The effects of the protease inhibitors on growth and differentiation are discussed.
Protein degradation in 3T3 cells and tumorigenic transformed 3T3 cells
Authors: Gronostajski Richard M. , Pardee Arthur B. 
Published: February 2005

AbstractTo study the relation of overall rates of protein degradation in the control of cell growth, we determined if transformation of fibroblasts to tumorigenicity affected their rates of degradation of short‐ and long‐lived proteins. Rates of protein degradation were measured in nontumorigenic mouse Balb/c 3T3 fibroblasts, and in tumorigenic 3T3 cells transformed by different agents. Growing 3T3 cells, and cells transformed with Moloney sarcoma virus (MA‐3T3) or Rous sarcoma virus (RS‐3T3), degraded short‐ and long‐lived proteins at similar rates. Simian virus 40 (SV‐3T3)‐ and benzo(a)pyrene (BP‐3T3)‐transformed cells had slightly lower rates of degradation of both short‐ and long‐lived proteins. Reducing the serum concentration in the culture medium from 10% to 0.5%, immediately caused about a twofold increase in the rate of degradation of long‐lived proteins in 3T3 cells. Transformed lines increased their rates of degradation of long‐lived proteins only by different amounts upon serum deprivation, but none of them to the same extent as did 3T3. Greater differences in the degradation rates of proteins were seen among the transformed cells than between 3T3 cells and some transformed cells. Thus, there was no consistent change in any rate of protein degradation in 3T3 cells due to transformation to tumorigenicity.
Effects of valinomycin on hexose transport and cellular ATP pools in mouse fibroblasts
Authors: Yamanishi Kiyofumi 
Published: February 2005

AbstractThe K+ ionophore valinomycin at concentrations of 1 × 10−8 M and over, stimulated 2‐deoxy‐D‐glucose (2DG) and 3‐O‐methylglucose (3OMG) uptake in Swiss 3T3 fibroblasts. The rate‐limiting step of 2DG uptake was transport rather than phosphorylation, in the control or valinomycin‐treated cells. Kinetic analysis showed that valinomycin increased the Vmax for 2DG uptake without change of the Km. The valinomycin‐stimulated 2DG uptake was insensitive to 10 μg/ml cycloheximide, and extracellular K+ concentrations between 0.1 and 50 mM. On the other hand, valinomycin at the concentration of 1 × 10−8 M and over, induced a rapid decrease in cellular ATP content, followed by stimulation of 2DG uptake and recovery of the ATP content. A similar relationship between the reduction of cellular ATP content and the subsequent stimulation of 2DG uptake was observed when the cells were treated not only with 2,4‐dinitrophenol and iodoacetic acid, but also with other monovalent cation ionophores or inhibitors of oxidative phosphorylation. These results suggest that valinomycin may posttranslationally stimulate hexose transport by increasing the number of functional carriers of hexose or changing their mobility, and the rapid decrease in cellular ATP pools by valinomycin may be a trigger of the stimulation of the hexose transport in Swiss 3T3 fibroblasts.
The purification of an acid‐ and heat‐labile transforming growth factor from an avian sarcoma virus‐ transformed rat cell line
Authors: Yamaoka Kazuko , Hirai Reiko , Tsugita Akira , Mitsui Hiromi 
Published: February 2005

AbstractA new class of transforming growth factor (TGF), with chemical characteristics differing from previously reported TGFs, was isolated and purified from an avian sarcoma virus‐transformed rat cell line, 77N1. Purification steps were simple and consisted of ion‐exchange chromatography on diethylaminoethyl (DEAE)‐Sephacel, ammonium sulfate precipitation, Chromatofocusing, and DEAE‐Sephadex A‐25 chromatography. The purified TGF is a heat‐ and acidlabile protein with a molecular mass of 12,000 daltons and isoelectric point of 5.2–5.4. Because of the acid lability of this TGF, purification was carried out at neutral pH. The TGF induced DNA synthesis in growth‐arrested BALB 3T3 cells and promoted anchorage‐independent growth of nontransformed BALB 3T3 cells in soft agar; the latter activity is specific for the peptide growth factors, called TGFs, but it did not compete with epidermal growth factor (EGF) for binding to the EGF membrane receptors. The TGF activity was not potentiated by EGF. The purified preparation of the TGF stimulated BALB 3T3 cells to grow progressively in soft agar at a dose of 20 ng/ml.
Cyclic AMP‐dependent and ‐independent protein kinases and protein phosphorylation in human promyelocytic leukemia (HL60) cells induced to differentiate by retinoic acid
Authors: Fontana Joseph A. , Emler Carol , Ku Katherine , McClung J. Keith , Butcher Fred R. , Durham John P. 
Published: February 2005

AbstractThe human leukemia cell line HL60 which resembles promyelocytes can be induced to differentiate to cells displaying features of the mature myeloid phenotype by a variety of agents including retinoic acid (RA) and agents that elevate intracellular adenosine 3:5 cyclic monophosphate (cyclic AMP) levels, e.g., 8‐bromo‐cyclic adenosine 3:5 monophosphate (8‐Br‐cyclic AMP), cholera toxin. Since most, if not all the effects of cyclic AMP, are mediated by adenosine 3:5 cyclic monophosphate‐dependent protein kinase (cyclic AMP‐dPK), we investigated the role of cyclic AMP‐dPK and adenosine 3:5 cyclic monophosphate‐independent protein kinase (cyclic AMP‐iPK) in the induced differentiation of HL60 cells. Marked stimulation of cyclic AMP‐dPK and cyclic AMP‐iPK appears to be intimately involved with and specific for HL60 myeloid differentiation as evidenced by: (1) Stimulation of cyclic AMP‐dPK and cyclic AMP‐iPK early during HL60 myeloid differentiation and prior to phenotypic changes. (2) RA and dimethylformamide (DMF), agents that induce differentiation along the myeloid pathway, cause a marked increase in the type I cytosolic cyclic AMP‐dPK and cyclic AMP‐iPK (protamine kinase) while no such increases are noted in cells treated with 12‐0‐tetradecanoyl‐phorbol‐13‐acetate (TPA) which induces differentiation along the monocyte/macrophage pathway. (3) Both native polyacrylamide gel electrophoresis as well as photoaffinity labeling with 8‐azido‐cyclic AMP demonstrate marked increases in type I cyclic AMP‐dPK in the cytosols of cells exposed to agents that induce myeloid differentiation but no increase in TPA‐differentiated cells. (4) The appearance and disappearance of specific cyclic AMP‐dependent and ‐independent protein phosphorylations are associated with the induced myeloid differentiated state.
Hydrocortisone stimulates fibronectin synthesis in cultured fibroblasts
Authors: Lien Yeong‐Hau , Wong Mitchell J. , Golbus Mitchell S. , Stern Robert 
Published: February 2005

AbstractThe effect of hydrocortisone on fibronectin synthesis was investigated in cultured skin fibroblasis. Confluent cells were treated with hydrocortisone (10−7 M to 10−5 M) for 2 days and labeled with [3H]proline for 24 h. Fibronectin levels in both the culture medium and the cell layer were studied by gelatin‐Sepharose affinity chromatography and SDS‐polyacrylamide gel electrophoresis. In control cultures of human fetal skin fibroblasts, fibronectin constituted 8% of the total labeled proteins in the medium. The proportion of fibronectin increased to 13.1% at 10−7 M hydrocortisone, 15.5% at 10−6 M and to 19.4% at 10−5 M. The proportion of fibronectin associated with the cell layer remained at 2‐3% of total [3H]prolne‐labeled proteins and did not increase with hydrocortisone exposure. The stimulating effect of hydrocortisone on medium fibronectin was also demonstrated in cultured human newborn foreskin fibroblasts and in rabbit skin fibroblasts.
Adenosine inhibits cell division and promotes neurite extension in PC12 cells
Authors: Huffaker Tom , Corcoran Teresa , Wagner John A. 
Published: February 2005

AbstractLow concentrations (10–50 μM) of adenosine (EC50 = 17 μM) or chloroadenosine (EC50 = 23 μM) prevent the division of PC12 cells. This inhibition is not mimicked by guanosine, inosine, 3′,5′ dideoxyadenosine, phenylisopropylad‐enosine, or adenylylimidodiphosphate. The growth inhibition is not relieved by addition of uridine or deoxycytidine, nor is it potentiated by homocysteine thiolactone. Inhibition of adenosine uptake does not inhibit adenosine‐de‐pendent growth arrest. PC12 variants that are deficient in adenosine kinase are as sensitive as wild‐type cells to the growth‐inhibitory effects of adenosine. These experiments suggest that adenosine prevents cell division at an adenosine receptor rather than acting after being metabolically altered. The adenosine receptor that inhibits cell division does not appear to be the adenosine receptor that stimulates adenylate cyclase for these reasons: (1) phenylisopropyladenosine, which is a potent agonist of this receptor, does not inhibit cell division; (2) 3′,5′ dideoxyadenosine does not antagonize the effect of adenosine on cell division; and (3) theophylline does not affect growth inhibition by adenosine. Thus, these experiments suggest the existence of a second adenosine receptor that can inhibit cell division.Adenosine also promotes the morphological differentiation of PC12 cells. In the presence of the adenosine deaminase inhibitor, erythro‐9‐(2‐hydroxy‐3‐nonyl)adenosine (EHNA), adencsine causes the formation of short neurites (one‐half to one and one‐half cell diameters in length). Adenosine also increases the rate of neurite formation of both long and short neurites in response to NGF.
Intravesicular pH and iron uptake by immature erythroid cells
Authors: Paterson S. , Armstrong N. J. , Iacopetta B. J. , McArdle H. J. , Morgan E. H. 
Published: February 2005

AbstractThe intravesicular pH of intact rabbit reticulocytes was measured by two methods; one based on the intracellular:extracellular distribution of DMO (5, 5, dimethyl + oxazolidin‐2,4‐dione), methylamine, and chloroquine and the other by quantitative fluorescence microscopy of cell‐bound transferrin. The latter method was also applied to nucleated erythroid cells from the fetal rat liver. A pH value of approximately 5.4 was obtained with both methods and in both types of cells. Treatment of the cells with lysosomotrophic agents, metabolic inhibitors, and ionophores elevated the intravesicular pH and inhibited iron uptake from transferrin. When varying concentrations of NH4Cl were used, a close correlation was observed between the inhibition of iron uptake and elevation of the intravesicular pH. At pH 5.4 iron release from rabbit iron‐bicarbonate transferrin in vitro was much more rapid than from iron‐oxalate transferrin. The bicarbonate complex donates its iron to rabbit reticulocytes approximately twice as quickly as the oxalate complex. It is concluded that the acidic conditions within the vesicles provide the mechanism for iron release from the transferrin molecule after its endocytosis and that the low vesicular pH is dependent on cellular metabolism.
The relationship between purines, pyrimidines, nucleosides, and glutamine for fibroblast cell proliferation
Authors: Engström Wilhelm , Zetterberg Anders 
Published: February 2005

AbstractPrevious studies indicate that glutamine is a critical requirement for cell proliferation in vitro. We recently showed that depletion of glutamine from the cuture medium supporting growing cells significantly reduced the proportion of cells undergoing DNA synthesis. Similarly glutamine depletion significantly reduced the stimulatory response of quiescent cells to 10% serum. This study shows that the inhibitory effects of depletion of glutamine—in either of these two situations—can be overcome by the addition of adenine or adenosine. Adenine was the only nitrogen base and adenosine was the only nucleoside for which this effect was observed. Such effects could, however, also be achieved by addition of the purine metabolites hypoxantine and inosine. Furthermore, it was found that glutamine (or adenine/adenosine) is only required during a limited interval coinciding with the late part of the G1‐phase and the beginning of S‐phase. These data suggest the possibility that glutamine exerts its main regulatory effects on cell proliferation by acting as a precursor for adenine and adenosine.
Initiation of DNA synthesis by human thrombin: Relationships between receptor binding, enzymic activity, and stimulation of 86Rb + influx
Authors: Stiernberg Janet , Carney Darrell H. , Fenton John W. , Lablle Edward F. 
Published: February 2005

AbstractStimulation of amiloride‐sensitive sodium (Na+) influx and the subsequent activation of NA+, K+‐ATPase by serum or growth factors have been implicated as early events leading to initiation of cell proliferation. We recently demonstrated that amiloride inhibits thrombin‐initiated DNA synthesis not by inhibiting an early event occurring during the first 8 hr, but rather by inhibiting some later event 8 to 12 hr after thrombin addition. To further probe the relationship between stimulation of ion influx and initiation of cell proliferation, human α‐thrombin was converted to γ‐thrombin, nitro‐α‐thrombin, and diisopropylphospho (DIP)‐α‐thrombin. These derivatives retain either the capacity to bind cell surface α‐thrombin receptors or thrombin esterase activity, but they do not initiate DNA synthesis. At low concentrations of α‐thrombin or the various thrombin derivatives, only α‐thrombin stimulates 86Rb+ influx, suggesting a correlation between stimulation of influx and the ability of these derivatives to initiate DNA synthesis. Concentrations of a DIP‐α‐thrombin that saturate the α‐thrombin recptors (up to 2 μg/ml) do not stimulate either the early or late influx of 86Rb+, indicating that DIP‐α‐thrombin binding alone is not sufficient to stimulate ion fluxes. High concentrations of either γ‐thrombin or nitro‐α‐thrombin, however, stimulate both early and late 86RB+ uptake but do not initiate DNA synthesis. These results demonstrate that events leading to both the early and late stimulation of 86Rb+ influx by themselves are not sufficient to initiate cell proliferation. Thus, initiation may require a combination of events that can be independently regulated by different transmembrane signals.
Structural determinants of the capacity of heparin to inhibit the proliferation of vascular smooth muscle cells
Authors: Castellot John J. , Karnovsky Morris J. , Beeler David L. , Rosenberg Robert D. 
Published: February 2005

AbstractPrevious work from our laboratory has demonstrated that both anticoagulant and nonanticoagulant heparin species can inhibit the proliferation of vascular smooth muscle cells in vivo and in vitro. In this communication, we report studies on the structure‐function relationships of heparin to its antiproliferative effect on vascular smooth muscle cells. These structure‐function studies were carried out by preparing discrete sizes of heparin fragments and by chemically modifying heparin. The compounds were tested for their ability to inhibit rat and calf aortic smooth muscle cell growth. The minimum fragment size which retains some growth inhibitory activity is a hexasaccharide; maximal antiproliferative activity was obtained with dodecasaccharide and larger fragments. Both O‐sulfation and N‐substitution were found to be important for the growth inhibitory effect. Comparison of the antiproliferative and anticoagulant activities of the different heparin species has allowed us to identify several heparin molecules which have lost their anticoagulant properties, but retain antiproliferative activity.
An antibody that inhibits fibronectin‐independent adhesion of fibroblasts to extracellular matrix material
Authors: Kelleher P. J. , Juliano R. L. 
Published: February 2005

AbstractChinese hamster ovary (CHO) fibroblasts adhere to the extracellular matrix by both fibronectin‐dependent and ‐independent mechanisms (Harper and Juliano, 1981a,b). Previous studies have suggested that a trypsin‐sensitive, 265,000‐dalton membrane glycoprotein (gp265) is involved in the fibronectin‐independent adhesion process. Using a polyclonal antibody against soluble products obtained from trypsin‐treated CHO cells, we have been able to further analyze this involvement. This antibody immunoprecipitates a trypsin‐sensitive 265,000‐dalton protein from detergent‐solubilized cells. Incubation of AdvF11, a variant cell line that does not utilize fibronectin for adhesion, with this antibody blocks their adhesion to extracellular matrix material (ECM). The immunoglobulin fraction will also partially block adhesion of the parental cell line to ECM particularly when the ECM is first treated with an antifibronectin antibody. Taken together these results add support for the involvement of gp265 in fibronectin‐independent adhesion and provide a methodology for further characterization.