bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced sterol synthesis in concanavalin A‐stimulated lymphocytes: Correlation with phospholipid synthesis and DNA synthesis
Authors: Chen S. Shi‐Hua 
Published: February 2005

AbstractIncorporation of (14C)choline and (3H)myo‐inositol into the total lipid fraction, incorporation of (14C)acetate into the sterol fraction and incorporation of (3H)thymidine into DNA were studied in human lymphocyte cultures. Concanavalin A induced an increase in the incorporation of these labels with the following features: (a) Phospholipid synthesis was increased promptly. The lag time for the increase in sterol synthesis and DNA synthesis were 5 hours and 27 hours respectively; (b) The increase in phospholipid synthesis and sterol synthesis was proportional to ConA concentration initially. Cells treated with a high concentration of ConA showed very low levels of DNA synthesis; (c) The increase in phospholipid synthesis could be abolished immediately by α‐Methyl‐Mannoside. α‐Methyl‐Mannoside blunted but did not abolish the increase in sterol synthesis. α‐Methyl‐Mannoside enhanced DNA synthesis of those cells which had been treated by a high concentration of ConA; and (d) Selective inhibition of sterol synthesis with 25‐hydroxycholesterol did not prevent the increase in phospholipid synthesis, but it blocked the increase in DNA synthesis. Supplement of LDL, HDL or total lipoproteins to lymphocyte cultures was effective in preventing the inhibition of DNA synthesis by 25‐hydroxycholesterol. These results suggest that in lymphocyte activation by ConA phospholipid synthesis, sterol synthesis and DNA synthesis were sequentially increased. The rate of cellular commitment to mitogenesis was proportional to ConA concentrations. High concentrations of ConA arrested the cell growth at a postcommitment point in the G1 phase. Enhanced phospholipid synthesis was a precommitment event. Enhanced sterol synthesis was a postcommitment event and reflected the requirement of an increased cholesterol supply for the passage of cell growth through G1.
Measurement of total, intracellular and surface bound cations in animal cells grown in culture
Authors: Sanui Hisashi , Rubin A. Harry 
Published: February 2005

AbstractA procedure is described in which animal cells grown in culture on a dish are rapidly rinsed in situ with 0.25 M sucrose solutions for subsequent measurement of total, intracellular and rapidly exchangeable Na+, K+, Mg2+ and Ca2+ by atomic absorption spectrophotometry. Repeated rinses with CO2‐free (pH ∼7) 0.25 M sucrose solution produced essentially no loss of cellular protein or cations. One 10‐second rinse with CO2‐saturated (pH 4) 0.25 M sucrose solution removed a rapidly proton exchangeable cellular cation fraction which is interpreted as being externally (membrane) bound. Rinses with physiological electrolyte solutions are shown to produce loss of cellular protein as well as displacement of surface exchangeable cations. Thus, isotonic sucrose solution is more satisfactory than electrolytic media for rinsing cultured cells prior to measurement of cellular cations. The technique employing sucrose rinse media is very rapid and reproducible and permits measurement of total, intracellular or surface bound Na+, K+, Mg2+ and Ca2+ in the same sample.
The chemotactic factors induced movement of calcium and sodium across rabbit neutrophil membranes: Effect of desensitization to cytochalasin B
Authors: Naccache P. H. , Showell H. J. , Becker E. L. , Sha'afi R. I. 
Published: February 2005

AbstractThe preincubation of rabbit neutrophils with the chemotactic factor F‐Met‐Leu‐Phe and the subsequent addition of cytochalasin B has previously been shown to induce a time, concentration and calcium dependent loss of secretory responsiveness in neutrophils. This has been termed desensitization. The results reported here first confirm that lysosomal enzyme release from neutrophils will still occur in the absence of extracellular calcium. In addition, a time dependent decrease in the magnitude of the cytochalasin B induced influxes of 45Ca and 22Na was found upon preincubation with F‐Met‐Leu‐Phe. In the presence of extracellular Ca2+, this decrease in ionic responsiveness reaches a maximum by five minutes preincubation with F‐Met‐Leu‐Phe. In the absence of added extracellular Ca2+ an initial and rapid (<1 minute) loss of ionic responsiveness is followed by partial recovery as the length of the preincubation with the chemotactic factor is increased from one to five minutes. These changes in ionic responses correspond exactly to the changes in secretory behavior of the neutrophils. Desensitization can thus be explained on the same ionic basis as that underlying the secretory response of the neutrophils. In addition, these results provide information about the sequence of events involved in the cytochalasin B and chemotactic factor induced release of lysosomal enzymes in neutrophils.
Electron probe microanalysis of elemental composition of mouse cardiac myocytes during post‐natal maturation
Authors: Dykes Sandra Goles , Cameron Ivan L. , Smith Nancy K. R. 
Published: February 2005

AbstractElemental concentrations in the cytoplasm and nucleus of post‐natal mouse myocytes were measured at 2, 4, 8, 16, 32 days and in adults using electron probe X‐ray microanalysis. Using an analysis of variance test, significant age dependent changes were found in intracellular potassium, sulfur, phosphorus, and chlorine concentations (mg/kg dry weight), while sodium and magnesium concentrations did not show significant changes. The application of t tests following linear regression analyses (age versus concentration for each element) did, however, give a significant slope for cytoplasmic sodium, potassium, sulfur, and phosphorus values. The findings correspond closely with an emission spectroscopy‐titrimetric study of whole heart ventricle of the same developmental period (Hazelwood and Nichols, '70).
The role of Heme in the regulation of the late program of friend cell erythroid differentiation
Authors: Mager Dixie , Bernstein Alan 
Published: February 2005

AbstractThe addition of a chemical inducer, such as dimethylsulfoxide (DMSO), to cultures of mouse Friend erythroleukemic cells results in the induction of a number of late erythroid events, including the accumulation of globin mRNA, the induction of hemoglobin synthesis, the appearance of erythrocyte membrane antigens (EMA), and the cessation of cell division. The experiments presented in this study demonstrate that heme is necessary but not sufficient for the loss of proliferative capacity associated with DMSO‐induced Friend cell differentiation, whereas the accumulation of globin mRNA and EMA can occur in the absence of heme synthesis or heme itself. These conclusions were reached by selectively inhibiting heme synthesis in DMSO‐treated cells in two independent ways: (i) Inducible cells were treated with 3‐amino‐1,2,4‐triazole (AT), a drug which inhibits the induction of heme synthesis in Friend cells in a dose‐dependent manner. Treatment of inducible Friend cells with 1.5% DMSO for five days caused the plating efficiency in methyl cellulose to decrease to 1% of that in untreated cultures. However, treatment of the cells with DMSO plus AT almost totally prevented this decrease in plating efficiency. The addition of exogenous hemin, which alone had no significant effect on plating efficiency, largely reversed the effect of AT in DMSO‐treated cells, reducing the plating efficiency to below 5%. In contrast to the marked effects of AT on the proliferative capacity of differentiating Friend cells, the levels of globin mRNA and EMA were only partially decreased in cells treated with DMSO plus AT, compared to cells treated with DMSO alone. (ii) The relationship between heme synthesis, terminal cell division, and the induction of globin mRNA was investigated further through the use of non‐inducible Friend cell variant clones. One such non‐inducible clone, M18, appears to be a phenotypic analog of inducible cells treated with DMSO plus AT. Clone M18 did not accumulate heme or hemoglobin, as detected by benzidine staining, nor lose its proliferative capacity in response to DMSO. However, globin mRNA was induced by DMSO in this clone. Treatment of clone M18 with DMSO plus hemin overcame the block in hemoglobin accumulation suggesting that M18 has a defect in the induction of heme biosynthesis. In addition, exposure of M18 cells to DMSO plus hemin caused a gradual decrease in plating efficiency which was not due to non‐specific toxicity. Prior incubation of M18 cells in DMSO for three to five days was necessary before hemin caused a rapid loss of proliferative capacity. Thus, these results, in agreement with the AT studies on inducible Friend cells and previous studies on the induction of EMA in clone M18, indicate that there may be both heme‐dependent and heme‐independent events in the program of Friend cell differentiation.
Application of the principles of enzyme kinetics to clonal growth rate assays: An approach for delineating interactions among growth promoting agents
Authors: Lechner John F. , Kaighn M. Edward 
Published: February 2005

AbstractThe interaction of mitogenic factors on a single cell type and the comparative activity of a given factor in diverse cell types have been studied byapplying the principles of Michaelis‐Menten kinetics to clonal growth data. Such comparisons are facilitated by derivation of two parameters; K, the mitogen concentration that gives half‐maximal clonal growth and a theoretical maximal growth rate, R. Both parameters are analogous to the Km and VMAX as applied to enzymatic reactions. Use of these parameters permits meaningful comparisons between cells with different growth rates.Using kinetic analysis of dose‐response data, we found that normal human epithelial cells require 200 times more fetal bovine serum protein (FBSP) than a malignant line to multiply at their respective half‐maximal rates. Further, the K of normal cells was reduced to that of the malignant line by the inclusion of growth factors (EGF or FGF, and hydrocortisone) in the medium. On the other hand, even though greater levels of serum were required when growth factors and hydrocortisone were not present, their inclusion did not alter R. Interactions between mitogenic factors were shown to be unidirectional. Although EGF reduced the K, FBSP did not change the K. The same type of analysis revealed that hydrocortisone, which potentiated the mitogenic activity of EGF did not change the K. Kinetic analysis of cell growth should prove useful in studies on the relation between growth and tumor promotion as well as in the evaluation of growth‐inhibiting chemotherapeutic agents.
Rapid changes in poly (A)(+) mRNA content in growth stimulated fibroblasts following perturbations in protein synthesis
Authors: Meister Richard K. , Hulman Sonia E. , Johnson Lee F. 
Published: February 2005

AbstractWe have previously shown that when resting 3T6 cells are serum stimulated in the presence of inhibitors of protein synthesis, poly(A)(+) mRNA content increases extremely rapidly relative to cells stimulated in the absence of drug. Poly(A)(+) mRNA content nearly doubles within two hours, but then remains constant for at least ten hours (Johnson and Meister, '77). In this report we show that continuous exposure to both serum and cycloheximide are required to maintain this elevated mRNA level. Removal of either leads to an equally rapid decrease in poly(A)(+) mRNA content. If cycloheximide is withdrawn at either two or ten hours following serum stimulation in the presence of the drug, allowing the rapid (< 30 minutes) restoration of the rate of protein synthesis, we observe that poly(A)(+) mRNA content decreases within two hours to a level nearly equal to that found in resting cells prior to stimulation. If the drug is withdrawn but the serum stimulus is not, the rapid decrease in poly(A)(+) mRNA content is followed by an increase which is parallel to that which occurs in cultures stimulated in the absence of drug, but displaced from the latter by an interval approximately equal to the length of exposure of the drug. These results show that the mammalian cell is able to decrease as well as increase its content of poly(A)(+) mRNA in response to drug induced perturbations in the rate of protein synthesis. The changes in poly(A)(+) mRNA content occur extremely rapidly and may represent an attempt by the cell to correct the perturbation.
Spontaneous, mutagen‐induced and adenovirus‐induced anchorage independent tumorigenic variants of mouse cells
Authors: Bellett A. J. D. , Younghusband H. B. 
Published: February 2005

AbstractNormal C57 Black mouse embryo cells did not form colonies in agarose, but rare variant (ar+) cells able to grow in agarose were detected. Fluctuation analysis showed that ar+ variants arose by spontaneous mutation in the cultured cells. The frequency of ar+ variants was increased by treating cells with N‐methyl‐N'nitro‐N‐nitrosoguanidine or ethyl methane sulphonate, or by abortive infection by human adenovirus type 5. Induced ar+ cells were fibroblastic; most grew slowly and had slightly reduced saturation density and increased serum requirement, but formed colonies in agarose. Fourteen of twenty ar+ clones induced by Ad5 were T antigen negative and two of these were also negative when tested for viral DNA. Six clones contained a few cells that were T antigen positive when first tested, but were negative when retested later. The ar+ variants were tumorigenic in athymic and in normal syngeneic mice. The results suggest that the ar+ phenotype can arise by spontaneous or chemically‐induced mutation, and can be induced by adenovirus by a process different from classical transformation.
The relationship of ornithine decarboxylase activity to proliferation and differentiation of L6 muscle cells
Authors: Stoscheck Christa M. , Florini James R. , Richman Robert A. 
Published: February 2005

AbstractFour different approaches were used to test a postulated relationship between ornithine decarboxylase (ODC) activity and L6 muscle cell proliferation. In the first approach, the level of ODC activity in myoblasts was compared to that of myotubes. The fusion of proliferating myoblasts to form postmitotic myotubes is a unique property of skeletal muscle differentiation which offers special advantages for this study. If ODC activity reflects proliferation, it should be reduced in myotubes. Four hours after the addition of 10% horse serum (HS), ODC activity in myoblasts was 140 times that in myotubes. The small amount of ODC activity measured in myotube cultures could be attributed to remaining myoblasts. In the second approach, cell density was varied to alter the rate of cell division. Density‐dependent inhibition of myoblast proliferation was closely correlated with a decrease of ODC activity. In the third approach, HS concentration was varied to alter the rate of cell division. Through a tenfold change of HS concentration, ODC activity paralleled cell proliferation. In the fourth approach, 1mM putrescine or spermidine was added with 10% HS to myoblasts. Although these treatments prevented the increase in ODC in response to HS, cell division was unimpaired; it seems likely that the polyamines entered the cell and substituted for endogenous polyamines. Mixing experiments indicated the presence of an inhibitor, tentatively identified as ODC antizyme, in homogenates of polyamine‐treated cells. We conclude that ODC activity closely reflects proliferation in muscle cells, although the presence of extracellular polyamines may disrupt this association.
Isolation and charactrization of a morphologic variant of chinese hamster (CHO) cells
Authors: Sisskin Enid E. , Weinstein I. Bernard 
Published: February 2005

AbstractAn epithelioid clone of Chinese hamster (CHO) cells which is spontaneously transformed was exposed to the mutagen N‐methyl‐N‐Nitro‐N‐Nitrosoguanidine (MNNG), and a fibroblastic variant, clone CHO‐F2, was isolated. This clone is partially reverted in several of the in vitro properties characteristic of transformed cells. When compared to wild type CHO, CHO‐F2 has a longer doubling time, a lower saturation density and less piling up at high cell density, and a higher serum requirement. CHO‐F2 also elaborates less plasminogen activator and has more abundant microtubules and actin cables. On the other hand, both CHO and CHO‐F2 grow in agar suspension (although CHO‐F2 grows with a lower efficiency), both lack detectable LETS protein, and both are tumorigenic in nude mice. Thus, expression of the individual properties frequently associated with transformation and tumorigenicity can be dissociated.The most critical biochemical change in CHO‐F2 appears to bean increase in the intracellular level of cyclic AMP, when compared to CHO, and several growth and morphological properties of CHO‐F2 resemble those induced in wild type CHO exposed to exogenous dibutyryl cyclic AMP. Therole of cyclic AMP in expression of the transformed phenotype and the significance of individual in vitro parameters of transformation with respect to tumorigenicity are discussed.
The suppression of cellular proliferation in SV40‐transformed 3T3 cells by glucocorticoids
Authors: Young Delano V. , Dean Michael C. , Young Delano V. 
Published: February 2005

AbstractGlucocorticosteroids, when added two hours after cell plating to SV40‐transformed, 3T3 mouse fibroblasts in low serum (0.3%v/v), biotin‐supplemented medium, suppress cellular proliferation by 24 hours. While some cell death probably occurs, the growth inhibition is not primarily due to cytotoxicity and cytolysis. This conclusion is supported by the following: (1) both dead and viable cell numbers are suppressed, (2) little cell debris is evident in the medium, and (3) very high concentrations of glucocorticoids do not cause an increase in the dead cell count. Furthermore, this growth suppression, which is specific for glucocorticoids since several non‐glucocorticoid steroids have no inhibitory effect, is not permanent nor irreversible. Removal of the glucocorticoid and replacement with 10% serum restore rapid proliferation.Although higher concentrations (1% and 10%) of serum afford some protection against glucocorticoid inhibition, this protection is not simply a consequence of faster growth rates. SV3T3 cells can be grown in serum‐free medium supplemented with biotin, transferrin, insulin, and epidermal growth factor (EGF). Under these conditions growth rates are comparable to high serum media, yet glucocorticoids are still powerful inhibitors. However, the omission of insulin from serum‐free, glucocorticoid cultures does result in observable cell death and lysis.Flow microfluorometry and autoradiographic studies have determined that glucocorticoid‐inhibited cells are partially blocked in G1. The proportions of S phase and G2 + M cells are greatly reduced with an accompanying accumulation of G1 cells. These results suggest that glucocorticoids regulate a biochemical step(s) in G1 which is critical for DNA initiation.
Cholera toxin and analogues of cyclic AMP stimulate the growth of cultured human mammary epithelial cells
Authors: Taylor‐Papadimitriou Joyce , Purkis Patricia , Fentiman Ian S. 
Published: February 2005

AbstractThe growth of human mammary epithelial cells is stimulated by cholera toxin and analogues of cyclic AMP, while the growth of breast derived fibroblasts is inhibited. These compounds have little effect on DNA synthesis in the absence of other mitogens but show a synergistic effect with serum and/or EGF. The results suggest that high intracellular levels of cyclic AMP in human mammary epithelial cells increase the growth response of the cell to mitogens.
Growth arrest of AKR‐2B cells maintained in the presence of epidermal growth factor or 12‐O‐tetradecanolyhorbol‐13 acetate: Evidence for two separate G1 arrest points
Authors: Moses Harold L. , Proper Jacqueline A. , Volkenant Mary E. , Swartzendruber Douglas E. 
Published: February 2005

AbstractNontransformed mouse embryo derived AKR‐2B cells stop growing in the G1 phase of the cell cycle at saturation density due to depletion of serum growth factors, whereas a chemically transformed derivative line (AKR‐MCA) arrests in G1 at a higher saturation density due to depletion of amino acids and glucose. Stimulation of DNA synthesis is inhibited in the AKR‐2B cells, but not in the AKR‐MCA cells, by two inhibitors of RNA metabolism, α‐amanitin and 5‐fluorouridine (5‐FU). To determine whether the AKR‐MCA cells growth arrest at a uniue point in G1 or whether they arrest in a physiologic state which can also be achieved by the nontransformed cells, AKR‐2B cells were maintained in medium with 10% serum containing the mitogens, epidermal growth factor (EGF) or 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), until they reached saturation density or were arrested at subconfluence by artificial deletion of amino acids from the medium. The AKR‐2B cells maintained in EGF or TPA stopped growing in G1 at a higher saturation density, due to depletion of amino acids. Cells arrested in EGF or TPA or in amino acid deficient medium had a shortened interval between stimulation and the onset of DNA synthesis, and the stimulation of DNA synthesis was not inhibited by α‐amanitin or 5‐FU. The data show that the nontransformed AKR‐2B cells have two different arrest states which may represent two separate and distinct G1 arrest points—a growth factor deficiency arrest point and a nutrient deficiency arrest point. The nutrient deficiency arrested cells were very similar to the G1 arrested transformed AKR‐MCA cells.
Glucocorticoid hormone receptor mediated induction of metallothionein synthesis in HeLa cells
Authors: Karin Michael , Herschman Harvey R. 
Published: February 2005

AbstractHeLa cells grown in chemically defined medium lacking glucocorticoids synthesize metallothioneins, low molecular‐weight heavy‐metal binding proteins. Dexamethasone and hydrocortisone increase the rate of metal‐lothionein synthesis five‐ to ten‐fold. Maximal induction is achieved with 10–8M dexamethasone and 10–7M hydrocortisone. Half‐maximal induction is achieved at 5 ± 10–9M dexamethasone and 5 ± 10–8M hydrocortisone. Although carried for many generations in the absence of any glucocorticoids, HeLa cells (clone S) contain 25,000 specific 3H‐dexamethasone receptors that translocate into the nucleus after one hour of incubation. 3H‐dexamethasone binds to a single class of receptors with an apparent Kd = 18.8 nM. A variety of steroids can be classified into three classes, based on their effect on metallothionein synthesis: (a) full agonists (optimal inducers), (b) intermediate effectors which have either partial agonist or antagonist activities, and (c) inactive steroids. There is a correlation between the effects on metallothionein synthesis of different steroids and their ability to compete with 3H‐dexamethasone binding. We conclude that metallothionein is induced in HeLa cells by a glucocorticoid receptor mediated mechanism.