bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ascorbate‐independent proline hydroxylation resulting from viral transformation of balb 3T3 cells and unaffected by dibutyryl camp treatment
Authors: Evans Carla A. , Peterkofsky Beverly 
Published: February 2005

AbstractCollagen synthesis, hydroxylation of proline in collagen, and collagen secretion were studied in the contact‐inhibited mouse fibroblast line, Balb 3T3; the Kirsten virus transformed line, Ki‐3T3; and dibutyryl cAMP (dbcAMP)‐treated Ki‐3T3 cells, during the various phases of the growth cycle. Transformed cells in both logarithmic and stationary phase produced lower levels of collagen than the parent line but 85–90% of the theoretically possible hydroxyproline residues of the collagen were formed even when ascorbic acid was not added to the culture medium. Moreover, the transformed cells showed only about a 20% increase of collagen secretion upon addition of ascorbate. This was in contrast to the ascorbate requirement for maximal proline hydroxylation and the 2–3 fold stimulation of collagen secretion by ascorbate in the parent Balb 3T3 cells. Although dbcAMP treatment caused Ki‐3T3 cells to assume a more normal morphology and increased the relative rate of collagen synthesis to levels similar to that of 3T3, such treatment did not restore an ascorbate requirement for proline hydroxylation or collagen secretion. The specific activity of the enzyme prolyl hydroxylase also was not affected by dbcAMP treatment although collagen synthesis was increased by such treatment. In addition, it was found that ascorbic acid was not effective in activating prolyl hydroxylase derived from Ki‐3T3 or dbcAMP‐treated Ki‐3T3 cell cultures either in logarithmic phase or stationary phase. Ki‐3T3 cultures did not accumulate ascorbic acid in cells or medium nor was ascorbic acid synthesized from the precursor 14C‐glucuronate in cell homogenates. The results suggest that virally transformed Balb 3T3 cells acquire the capacity to synthesize a reducing cofactor for prolyl hydroxylase and that this function may be related to the increased glycolytic metabolism of these cells since neither cellular metabolism nor ascorbate‐in‐dependent hydroxylation was altered by treatment with dbcAMP.
Lysosomal hydrolase secretion by Tetrahymena: A comparison of several intralysosomal enzymes with the isoenzymes released into the medium
Authors: Blum J. J. 
Published: February 2005

AbstractTetrahymena pyriformis were grown in proteose‐peptone medium and then washed and incubated in a dilute salt solution for one hour. The cells were then discarded and the lysosomal hydrolases that had been secreted were subjected to DEAE cellulose column chromatography. At least three iso‐enzymes of acid phosphatase, three of acid protease, and two of β‐N‐acetylhexoseaminidase were found, as well as single peaks of α‐mannosidase, β‐galactosidase, and β‐fucosidase. The latter two activities were not resolved by the DEAE column and could not be separated in a second chromatographic step on CM‐cellulose.Cells were also grown under identical conditions and homogenized in 0.25 M sucrose in order to allow comparison of some of the intracellular lysosomal hydrolases with their secreted counterparts. Two lysosomal populations were resolved by sucrose density gradient sedimentation, a heavy lysosomal fraction, centered at a density of about 1.25 gm/cm3, and a light lysosomal fraction, centered at a density of about 1.16 gm/cm3. These two populations differed in that the light lysosomes did not appear to contain significant amounts of β‐fucosidase, β‐galactosidase, or acid protease, whereas all six of the hydrolase activities studied were present in the heavy lysosomes. The light lysosomal peak occurred in cells grown to transition phase, but was markedly reduced in cells from cultures grown to stationary phase. In addition to these two fractions a third very light particle, containing only α‐mannosidase activity, was detected just inside the gradient.Measurements were made of the effect of heat (10 minutes at 66°) and of a change in pH from 4.5 (standard assay condition) to 6.0 on the three acid phosphatases and two β‐N‐acetylhexoseaminidase isoenzymes resolved by DEAE column chromatography of the secreted hydrolases and on these hydrolyases in the heavy and light lysosomal fractions on the sucrose gradient. Use of the thermostability and pH criteria permitted computation of the expected properties of the intralysosomal acid phosphatase and hexoseaminidase activities if these consisted of the respective isoenzymes in the proportions secreted. It was found that neither the intralysosomal acid phosphatase nor the intralysosomal hexoseaminidase had the properties expected if they consisted of the secreted mixture of the respective isoenzymes, indicating that modification of some of these isoenzymes may have occurred during the 1‐hour starvation period or after secretion.
Derepression and carrier turnover: Evidence for two distinct mechanisms of hexose transport regulation in animal cells
Authors: Christopher C. William , Colby Wendy W. , Ullrey Donna 
Published: February 2005

AbstractHexose uptake by hamster cells was increased five to ten fold by either substituting D‐fructose for glucose or by completely omitting D‐glucose from the culture medium for 24 to 48 hours. Conversely, when cycloheximide was present for 24 hours in media containing glucose, up to 20‐fold decreases in hexose uptake were observed. However, these decreases in uptake activity were only observed over a narrow range of cycloheximide concentrations. After extended exposure to low concentrations of cycloheximide (0.05 to 10 μg/ml), the uptake by the fed cells decreased parallel with inhibition of protein synthesis whereas at high concentrations (>50 μg/ml) uptake was increased. Cells deprived of glucose and maintained in the presence of cycloheximide did not show decreases in uptake activity. In separate experiments the high uptake rates of glucose‐starved cells could be decreased by addition of glucose to the glucose‐free medium. The reversal was complete in 6 to 8 hours. The analog of glucose, 2‐deoxy‐D‐glucose, did not promote the time‐dependent decrease suggesting that the 6‐phosphoester of glucose is not an inhibitor of transport. In addition, when cycloheximide is added at the same time as glucose, there is no decrease in uptake for at least 12 hours. We propose that turnover of components of hexose uptake systems could account for part of the control of hexose transport. Moreover, the results indicate that the turnover mechanism becomes inactive during glucose starvation and must be resynthesized following refeeding of the starved cells with glucose.
Why do tumor cells have a high aerobic glycolysis?
Authors: Racker Efraim 
Published: February 2005

AbstractIn Ehrlich ascites cells and several other tumors, the high aerobic glycolysis is maintained by generation of ADP and Pi by the plasma membrane Na+K+ ATPase. The high ATPase activity is caused by a defective pump that operates at a low efficiency. Studies of the mechanism of action of the Na+K+ ATPase and other pump ATPases suggest several alternative mechanisms that might account for the decreased efficiency. The possibility of involvement of a proteolipid is under investigation.
Studies on intercellular adhesion. I. Adhesion of neural retina cells to isotypic aggregates in serum free medium
Authors: Pessac Bernard , Alliot Françoise , Girard Arlette 
Published: February 2005

AbstractA quantitative assay for intercellular adhesion, which is a modification of the collecting aggregate assay (Roth et al., 1971) is described. The use of mechanically dissociated single cells labeled with 3H‐leucine, and of a gyratory shaker increased considerably the efficiency of cell collection. With chick embryo neural retina, it was shown that isotypic cell adhesion occurs in simple synthetic media and even in sodium chloride solution suggesting that divalent cations do not play a major role in adhesion of these cells. Cell collection in media without serum was not affected by metabolic or protein synthesis inhibitors. However, cell adhesion was temperature‐dependent since no collection occurred at 4°C but was maximal at 38°C.
Electron probe microanalysis of chemical elemental content of single human red cells
Authors: Lechene C. P. , Bronner C. , Kirk R. G. 
Published: February 2005

AbstractSodium, potassium, iron and sulfur contents of single human red cells were measured using electron microprobe microanalysis. Three preparative procedures were compared, and the most reliable technique was found to be spraying of cells onto polished pyrolytic graphite by atomization. Primary standards were prepared by adjusting the intracellular electrolyte content of red cells, eliminating the need to correct for X‐ray absorption. Samples were stable under the electron beam during analysis, and could be stored for long periods of time. Strong correlations were found between the X‐ray intensities of iron and sulfur and between potassium and sodium. X‐ray intensities of potassium and sodium were found to be directly proportional to internal ionic content. Large populations of single cells could be analyzed and the distribution of their elemental content studied.
Serum‐stimulated phosphate uptake and initiation of fibroblast proliferation
Authors: Greenberg Deborah B. , Barsh Gregory S. , Ho Tsung‐Shang , Cunningham Dennis D. 
Published: February 2005

AbstractPrevious studies have shown that initiation of proliferation of density‐inhibited fibroblasts by fresh serum is accompanied by a rapid increase in phosphate uptake. This increase might be a key event in the initiation of DNA synthesis. The present studies examined this possibility.Mouse 3T3, secondary chick embryo, or human diploid foreskin cultures were grown to quiescence in medium containing varying levels of serum. When proliferation of the cultures was initiated by addition of fresh serum, the changes in phosphate uptake were inversely related to the final increases in cell number. Additional experiments showed that the change in phosphate uptake following serum addition was determined by the level of phosphate uptake prior to serum addition.Addition of dexamethasone to quiescent 3T3 cultures caused them to proliferate but did not increase phosphate uptake. Similarly, trypsin or insulin stimulated proliferation of quiescent secondary chick embryo cultures, but caused little or no change in phosphate uptake.Quiescent 3T3 cultures switched to medium containing fresh serum and reduced levels of phosphate showed a decrease in both phosphate uptake and intracellular phosphate pool size. Cell proliferation in these cultures, however, was stimulated to the same degree as cultures switched to medium containing fresh serum and the normal amount of phosphate. In addition, quiescent secondary chick embryo cultures switched to medium containing fresh serum and no phosphate showed a decrease in the intracellular phosphate pool size. Thymidine incorporation and final cell number in these cultures, however, was stimulated to the same or higher degree than in cultures switched to medium containing fresh serum and the normal amount of phosphate. These results demonstrate that the rapid increase in phosphate uptake following addition of fresh serum to quiescent fibroblasts is not a necessary event for the initiation of proliferation.
Growth and biochemical characteristics of a detachment variant of CHO cells
Authors: Atherly Alan G. , Barnhart Benjamin J. , Kraemer Paul M. 
Published: February 2005

AbstractA variant subline of Chinese hamster cells (line CHO) was isolated that had increased resistance to detachment from the substratum. Comparisons between parental and variant cells of the complex carbohydrates liberated during trypsin detachment showed that the variant cells synthesized little or no hyaluronic acid. These cells also had reduced amounts of other complex carbohydrates in the cell periphery. However, parental and variant cells did not differ in morphology, growth control, or cyclic AMP concentration. Profound changes in the physical and chemical nature of the cell periphery, in themselves, evidently are insufficient to cause changes in many aspects of cell behavior.
The relative amounts of the cytoplasmic RNA species in normal, transformed and senescent cultured cell lines
Authors: Johnson Lee F. , Abelson Herbert T. , Penman Sheldon , Green Howard 
Published: February 2005

AbstractWe have examined the relative quantities of 18S and 28S rRNA, 4S RNA and poly (A) + mRNA in the following cultured cells: the mouse fibroblast lines 3T3 and 3T6 in the resting (contact inhibited) and growing (sparse) states, 3T3 clones transformed with SV40 (SV3T3) and with both SV40 and polyoma (SV‐Py 3T3), hamster lung fibroblasts (V79), human cervical carcinoma cells (HeLa), and human diploid fibroblasts at early and late passage. The relative quantities of the RNA species were determined by labeling the cells to equilibrium with 32PO4 and measuring the amount of label in each RNA species.The ratio of mRNA to rRNA varied from 1.1% to 2.7% in the different cell lines, the more rapidly growing cell lines usually giving a higher ratio. In cells experiencing growth limitation either by contact inhibition or due to senescence, the ratio of mRNA to rRNA was about 30% lower than in the corresponding cells in the growing state. In most cell lines the ratio of 4S RNA to 18S rRNA was between 0.8 and 1.2, but in senescent fibroblasts, this ratio increased to greater than 1.7. Senescent fibroblasts also contained much more total RNA per unit of DNA than the same cells at early passage or than 3T6 or 3T3 cells.
The influence of culture conditions on the induction of tyrosine aminotransferase by cyclic nucleotides in rat hepatoma cells
Authors: Stellwagen Robert H. , Kohli Kulwant K. , Sailor Rochelle D. 
Published: February 2005

AbstractThe increase in tyrosine aminotransferase activity which occurs in rat hepatoma tissue culture (HTC) cells in response to cyclic AMP analogs has been shown to be an enzyme induction, similar to the larger response observed in certain other hepatoma cells and in liver. A specific antibody to tyrosine aminotransferase has been used to show that the number of enzyme molecules and the rate of enzyme synthesis are increased by N6,O2′‐dibutyryl cyclic AMP in HTC cells. The effect on tyrosine aminotransferase is also produced by various 8‐substituted derivatives of cyclic AMP and occurs whether or not the enzyme has been preinduced with a glucocorticoid. The response of the enzyme is greater when HTC cells are maintained in monolayer than in suspension cultures. Neither cell growth nor serum is required for the response.
The binding sites of cytochalasin D. II. Their relationship to hexose transport and to cytochalasin B
Authors: Tannenbaum Janet , Tanenbaum Stuart W. , Godman Gabriel C. 
Published: February 2005

AbstractCytochalasin B (CB) was able to compete with tritiated cytochalasin D (3H‐CD) for binding sites in HEp‐2 cells. The pattern of inhibition suggested that CB associates with a low affinity class of CD binding sites. Glucose and maltose did not inhibit binding of 3H‐CD to isolated HEp‐2 plasma membrane. Inhibition of hexose transport by CD was negligible, but CD did not block the potent inhibition of this transport by CB. These results indicate that CD does not bind to the high affinity CB receptor reportedly associated with the hexose transport system, and that this receptor cannot mediate the morphological effects of CD. Both CD and CB induced contraction‐zeoisis in HEp‐2 cells; CB was less potent than CD, and their effects appeared to be additive. It was concluded that the high affinity binding sites for CD and CB are different, but that these congeners share a low affinity site. Both high and low affinity sites for CD appear to mediate its morphological effects; only the low affinity class appears to be involved for CB. Possible identification of the common low affinity binding site as actomyosin (detailed in Tannenbaum et al., 1977) is further discussed.
The diverse effects of 5′‐bromodeoxyuridine on enzyme activities in cultured H35 hepatoma cells
Authors: Gurr James A. , Becker Joyce E. , Potter Van R. 
Published: February 2005

AbstractReuber (H35) hepatoma cells were grown in medium containing 10 −5M bromodeoxyuridine (BrdU), which was incorporated into their DNA. Cell growth rate was unaffected by BrdU for the first two generations, after which it was reduced by about 50%. The effect of BrdU incorporation on the activities of several enzymes with rapid turnover rates was examined to test the hypothesis that the synthesis of such enzymes will be preferentially inhibited by BrdU. Tyrosine amino‐transferase (TAT) activity decreased by 70% within two generations whereas thymidine kinase activity remained at control values. PEP carboxykinase activity was unchanged during the first generation in BrdU‐containing medium but, during the second, its activity increased by at least 30%. Ornithine decarboxylase levels decreased by about 50% only after two generations in the presence of BrdU. There appeared to be no simple relationship between turnover rates and the effect of BrdU on enzyme activity. Incorporation of BrdU was found to inhibit the induction of both TAT and PEP carboxykinase by dexamethasone and to enhance the inhibition of cell growth by this steroid. These results are discussed with respect to possible mechanisms of gene expression and development in both normal and neoplastic cells.
Effects of temperature, metabolic and cytoskeletal inhibitors on the rate of BHK cell adhesion to polystyrene
Authors: Nath Kamalendu , Srere Paul A. 
Published: February 2005

AbstractAdhesion of baby hamster kidney fibroblasts (BHK cells) to a Falcon tissue culture flask was measured under various physiological conditions. While 75–80% of the fibroblasts adhere at temperatures from 19–50°, cellular adhesion decreased dramatically below 19°. Less than 10% of the cells adhere to the substratum even after prolonged incubations at temperatures of 8° or below. This lack of adhesion at low temperatures cannot be overcome by the application of increased gravitational force to the cells.No correlation exists between cellular ATP concentrations or respiration rates and the rate of cell adhesion to the substratum. One millimolar Na F and 1 mM 2,4 dinitrophenol together lower cellular ATP concentration by 95% but adhesion is reduced by only 50%. NaN3 and KCN greatly lower cellular ATP concentrations without a corresponding inhibition of adhesion. Inhibition of cellular respiration by these compounds occurs at lower concentrations than does the inhibition of adhesion. Two micrograms/milliliters of cytochalasin B inhibits adhesion by 90%, 0.1 mM vinblastine sulphate or colchicine by less than 50% and 50 μg/ml colcemid by less than 30%.Fixing the cells with formaldehyde, hardening their membranes with ZnCl2 or treating the cells with toluene, all cause an inhibition in adhesion. Again, application of increased gravitational force cannot overcome these latter inhibitions of BHK cell adhesion to the surface of the flasks.
The adhesion of Chinese hamster cells. I. Effects of temperature, metabolic inhibitors and proteolytic dissection of cell surface macromolecules
Authors: Juliano R. L. , Gagalang E. 
Published: February 2005

AbstractWe have investigated factors controlling the rate of adhesion of suspension culture CHO cells to serum coated glass surfaces. Thus, we have examined (1) the effect of metabolic depletion via KCN treatment; (2) effects of colchicine and cytochalasin‐B, two drugs which are presumptive inhibitors of microtubule and microfilament activities, respectively; (3) effects of temperature on adhesion; (4) the correlation between changes in cell adhesion rate and alterations of lacteroperoxidase labelled cell surface proteins consequent to treatment with proteases.We have found that colchicine is completely without effect on the initial adhesion process in CHO cells, indicating that microtubules are not a determinant of adhesion kinetics. Cytochalasin‐B and depletion of ATP stores by KCN both diminish CHO cell adhesion, but seem to act in different ways. Treatment with cytochalasin‐B results in a dose dependent reduction in the initial slope of adhesion versus time curves, while KCN treatment produces a pronounced lag period during which little cell attachment takes place, followed by a relatively rapid rise to control levels of cell attachment.Analysis of CHO cell adhesion kinetics as a function of temperature reveals that the inhibition produced by low temperature seems similar to that produced by KCN. Thus at elevated (25°C) temperature, CHO cells adhere rapidly, while at 4°C adhesion is completely inhibited. However, at intermediate temperatures (10°C) a pronounced lag period followed by a rapid rise is noted, a result similar to that seen in KCN treated cells.Treatment of CHO cells with low doses (10 μg/ml) of crystalline trypsin results in the loss of several major cell surface proteins, without any appreciable effect on adhesion kinetics. High doses (100–1,000 μg/ml) of trypsin result in the cleavage of other proteins whose loss may be related to a parallel loss in adhesive ability. Some of the CHO cell surface proteins seem resistant to doses of trypsin (1,000 μg/ml) which completely abolish the ability of cells to adhere.Our observations on the effects of inhibitors, temperature, and surface proteolysis on CHO cell adhesion kinetics suggest the involvement of (a) microfilaments, (b) plasma membrane fluidity, and (c) a subclass of the surface proteins as important determinants of the adhesion process.
The inhibition by colchicine of the initiation of DNA synthesis by hepatocytes in regenerating rat liver and by cultivated WI‐38 and C3H10T 1/2 cells
Authors: Roy Walker P. , Boynton Alton L. , Whitfield James F. 
Published: February 2005

AbstractColchicine inhibited the initiation of DNA synthesis by hepatocytes in vivo and by WI‐38 and C3H10T 1/2 cells in vitro. All three cell types were most sensitive to colchicine when it was administered at the time of, or shortly after, proliferative activation (by partial hepatectomy or medium‐serum change). WI‐38 and C3H10T 1/2 cells became less sensitive to colchincine as the time between proliferative activation and addition of the drug was increased. Hepatocytes, on the other hand, showed a second stage of sensitivity immediately before the onset of DNA synthesis. Ongoing DNA synthesis was not inhibited by colchicine in any of the cell types. The two prereplicative stages of colchicine sensitivity in liver were also sensitive to vincristine but not to lumicolchicine, an analogue of colchicine which does not bind to tubulin. The data obtained with these drugs indicates that microtubules may be involved in the prereplicative stages of cell proliferation, but non‐specific binding to other membrane proteins cannot be ruled out. Colchicine (at a dose of 50 μg/100 g of body weight), which when injected 30 minutes after hepatectomy delayed the initiation of DNA synthesis for at least 14 hours, delayed the induction of ornithine decarboxylase (at the beginning of prereplicative development) by only two hours. Thus, the inhibitory action of colchicine on the initiation of DNA synthesis does not appear to be mediated by inhibition of polyamine synthesis.