bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of extreme amino acid starvation on the protein synthetic machinery of CHO cells
Authors: Stanners C. P. , Wightman T. M. , Harkins J. L. 
Published: February 2005

AbstractWhen CHO cells are incubated under conditions of extreme amino acid starvation, effected by withdrawal of an amino acid from the medium together with genetic or chemical interference with the activity of the corresponding aminoacyl‐tRNA synthetase, there is a rapid and profound decline in the functional capacity of the protein synthetic machinery. The effect was observed for all amino acids tested including leucine, asparagine, histidine, methionine and glutamine. This decline in protein synthetic potential appears to be due to a progressive permanent inactivation of the specific aminoacyl‐tRNA synthetase concerned, as shown by a decline in the amount of cellular, specific aminoacyl‐tRNA and a decline in the cell‐free enzyme activity, measured after reversal of the starvation conditions. When cells are left for more than several hours under these starvation conditions, they shrink in size, lose viability and eventually disintegrate, with anomalous rapidity. We suggest that the progressive loss of protein synthetic capacity of the cells is the prime cause of these subsequent events.If the starvation conditions are reversed before cell death, regeneration of the protein synthetic potential occurs rapidly but requires protein synthesis itself, implying the existence of strong control mechanisms for cellular aminoacyl‐tRNA synthetase activities.
Co‐cultivation of tumorigenic mouse melanoma cells with cells of a non‐tumorigenic subclone inhibits plasminogen activator expression by the melanoma cells
Authors: Kyner David , Christman Judith , Acs George , Silagi Selma , Newcomb Elizabeth W. , Silverstein Samuel C. 
Published: February 2005

AbstractClone B5 59 mouse melanoma cells are highly tumorigenic and produce plasminogen activator. Cells of clone C3471, a line obtained by continued growth of B559 cells in medium containing 5‐bromodeoxyuridine (1 μg/ml), have no plasminogen activator and are non‐tumorigenic. When B559 cells are co‐cultivated with C3471 cells, the ability of B559 cells to activate plasminogen is suppressed. Under these conditions cell fusion occurs. Lack of expression of plasminogen activators is not a consequence of cell fusion, inhibition of cell division or release of soluble inhibitors of either plasminogen activators or plasmin. No inhibitors of plasminogen activators could be demonstrated in association with subcellular fractions of C3471 cells or with the C‐type viral particles released from C3471 cells. Close contact between cells of the two lines is shown to be essential for suppression of plasminogen activation.
Significance of the cell cycle in commitment of murine erythroleukemia cells to erythroid differentiation
Authors: Geller Ruth , Levenson Robert , Housman David 
Published: February 2005

AbstractThe relationship between differentiation of murine erythroleukemia cells (MEL) induced by DMSO and the cell division cycle has been analyzed. We demonstrate that incubation in the presence of DMSO increases the length of the G1 phase of the cell cycle. A method of synchronization of MEL cells by unit gravity sedimentation has been developed and characterized. Using this method, a series of synchronized cell populations covering the entire cell division cycle can be generated simultaneously. Cells synchronized by this technique were challenged with DMSO and analyzed for kinetics of commitment to the differentiation program. Our results indicate that populations of cells in G1 or G2 at the time of addition of inducer give rise to a greater proportion of committed cells than an unfractionated population, while cells in S phase result in a lower percentage of committed cells than the unfractionated population when cultured in DMSO.
The development of lysosomal apparatus I. Lysosomal enzyme activities in the liver of mice at perinatal stages and those of their mothers
Authors: Mazzei Héctor R. , Bertini Francisco 
Published: February 2005

AbstractThe enzymatic activity of five acid hydrolases: acid phosphatase, arylsulfatase A, deoxyribonuclease, β‐glucuronidase, and cathepsin D, was assayed in fetal (fifteenth and eighteenth days of pregnancy) and neonatal (Days 0, 5, 10, and 15 post‐partum) mouse liver. With the exception of cathepsin D, the activity increased around birth to levels varying according to the enzyme. Histochemical observations of other authors appear to justify, at least in part, the present results, which indicate that late days of fetal development and early neonatal life may constitute a transitional stage to full lysosomal enzyme functionality of the adult organThe livers of the mothers were also assayed for the same enzymes. Each activity showed a peculiar pattern which was, in turn, different from that found in the liver of the litter for the same enzyme, probably as a cause of the metabolic requirement of the glandThe hypothesis that the lysosomes are heterogeneous in their enzyme composition is suggested by the variety of enzymatic patterns found in the liver of the litters and their mothers.
Ontogeny of human neutrophil granulocyte alkaline phosphatase
Authors: Kelemen Endre , Gulya Ernö , Vass Katalin 
Published: February 2005

AbstractHuman embryonic neutrophils (N) in the liver (from 8.5 mm crown‐rump length) are alkaline phosphatase (AP) negative during the first trimester of pregnancy. Early bone marrow granulocytes (from eleventh to sixteenth weeks of gestation) behave similarly. Only a small percentage of slightly AP positive cells could be found. Occasional cells with strong NAP reaction appear in the second trimester. NAP positivity greatly increases in the third trimester and term‐babies have a somewhat higher than normal NAP activity in circulating blood. Unlike NAP reaction, naphthol‐AS‐D‐chloroacetate esterase and peroxidase reactions are positive even in the earliest (AP negative) neutrophils.
Regulation of megakaryocytes in W/Wv mice
Authors: Ebbe Shirley , Phalen Eizabeth 
Published: February 2005

AbstractW/Wv mice were injected with antiplatelet serum to produce thrombocytopenia or with platelet transfusions to induce thrombocytosis. The responses of their platelets and megakaryocytes were followed to determine if proliferative abnormalities of the megakaryocytic system would be detected.W/Wv mice responded normally to the stimulation from thrombocytopenia with rebound thrombocytosis, macromegakaryocytosis, and macrothrombocytosis. The megakaryocytes of these mice became smaller than normal in response to post‐thrombocytopenic rebound thrombocytosis but not to transfusion‐induced thrombocytosis. Thus, endogenous thrombocytosis appeared to be a more potent suppressor of megakaryocyte growth than exogenous.These results failed to reveal an effective abnormality of the thrombocytopoietic regulatory system of W/Wv mice in spite of their intrinsically reduced numbers of megakaryocytes and the well known defect of stem cell proliferation. Thrombocytopoietic regulation appeared, therefore, to occur mainly at the committed, rather then pluripotential, stem cell level, and normal responses of the platelet system were observed in spite of severe abnormalities at the pluri‐potential stem cell level.
Control of glycolysis and the pentose phosphate shunt in transformed 3T3 cultures rendered permeable by ATP
Authors: Makan Nizar R. , Heppel Leon A. 
Published: February 2005

AbstractExogenous ATP has been shown earlier to activate a permeability change in transformed 3T3 cultures leading to massive efflux of the acidsoluble pools. This leads to reduction of the basal rate of glycolysis to a very low level so that glycolysis becomes almost totally dependent on the addition to the medium of glucose, inorganic phosphate and ADP in order to restore the rate to that of untreated cells. No such depression of glycolysis is observed in untreated transformed cells or in ATP‐treated normal 3T3 cells. In such permeabilized cultures, phosphorylated intermediates such as glucose‐6‐phosphate and fructose‐1,6‐diphosphate can serve as effective substrates for lactic acid formation. ATP treatment of cultured cells also allows molecules as big as NADP to enter the cells and participate in the pentose phosphate shunt pathway. This ability to temporarily and differentially render transformed cells permeable allows a review of several aspects of cellular metabolism and biosynthesis in the intact cell where the cellular organization is maintained. Furthermore, it deserves serious consideration as a means to achieve differential cytotoxicity of transformed cells by chemotherapeutic agents which, on their own, are indiscriminate in their action.
Characterization of a guanine‐sensitive mutant defective in adenylo‐succinate synthetase activity
Authors: Tu Alice S. , Patterson David 
Published: February 2005

AbstractA contingent auxotrophic mutant of CHO‐Kl cell is described. This mutant grow in minimal medium. Its growth is inhibited by the exogenous addition of guanine at levels which do not affect the wild type parent. Adenine reverses the guanine effect. This mutant does not complement ade−H (defective in adenylosuccinate synthetase) and has been denoted as ade−HG because of its guanine sensitivity. Some partial revertants of ade−H are found to be also sensitive to guanine, suggesting a close relationship between the ade−H locus and the guanine sensitivity. Studies of 14C‐hypoxanthine incorporation into nucleotides indicated that ade−HG has some adenylosuccinate synthetase activity whether it is pre‐exposed to guanine or not. Early de novo purine synthesis in ade−HG, however, is greatly inhibited when pre‐exposed to guanine. This inhibition of purine synthesis by guanine is reversible and its recovery is facilitated by adenine.
The isolation of a low molecular weight serum factor which enhances the viability of sv3t3 cells
Authors: Young Delano V. , Nakano Eileen T. , Wiggins Douglas S. , McElaney Mary A. 
Published: February 2005

AbstractA serum factor which enhances the growth/viability of SV40 transformed 3T3 mouse fibroblasts, but not untransformed 3T3 cells in tissue culture has been partially purified from calf serum. The purification, which involves acidification to pH 2, chromatography on Sephadex G‐100 at pH 2 followed by either Sephadex G‐25 or BioGel P‐2, results in material exhibiting two ninhydrin positive spots on thin layer chromatography and five to six dansylatable bands on SDS gels. This substance, termed Peak III or Serum Factor III, has been found in every serum examined thus far (including calf, rat, mouse, goat, lamb, rabbit, pig, horse, and chicken) and appears to be a low molecular weight, heat‐insensitive molecule. Attempts to characterize it by chemical analyses and specific enzymatic inactivation have been either negative or inconclusive.Its biological mode of action is presently obscure. While it does not affect DNA synthesis, it does greatly increase the viability of SV3T3 cultures growing in low serum (0.15–0.30% calf serum) medium and, when added to “stationary phase” cells, restores healthy proliferation. This and evidence reported by others suggest that Peak III may affect SV3T3 cells in either overcoming a potentially lethal block in G1 or in passage through G2/M.
Transport and accumulation of purine bases by Crithidia fasciculata
Authors: Kidder G. W. , Dewey Virginia C. , Nolan Linda L. 
Published: February 2005

AbstractThe capacity for the rapid transport of purine bases by Crithidia fasciculata is found only in cells starved for purines. Cells grown in complete medium transport poorly. Rapid transport capability appears and then disappears during growth of purine‐depleted cultures. This rapid transport appears to occur by a process of mediated diffusion. Two mechanisms are involved, one of low velocity and high affinity, the other of high velocity and low affinity. Accumulation of the bases within the cell occurs by their rapid conversion to ribonucleotides by phosphoribosyltransferases.
The modulation of the induction of ornithine decarboxylase by spermine, spermidine and diamines
Authors: Heller John S. , Chen Kuang Yu , Kyriakidis Dimitri A. , Fong Wang F. , Canellakis E. S. 
Published: February 2005

AbstractExtremely low concentrations of putrescine, spermidine and spermine added to the extracellular medium of cultures of mammalian cells inhibit the induction of ornithine decarboxylase activity despite 100‐ to 1,000‐fold greater intracellular polyamine concentrations. The diamines, 1,2‐diaminoethane, 1,3‐diaminopropane, 1,5‐diaminopentane, 1,7‐diaminoheptane, 1,10‐diaminodecane, 1,12‐diaminododecane also inhibit ornithine decarboxylase at all concentrations tested (greater than 10−6 M). In contrast, 10−6 M to 10 −3 M 1,8‐diaminooctane, the alkyl analog of spermidine, enhances ornithine decarboxylase activity.The concentraton of putrescine required to inhibit the activity of ornithine decarboxylase by 50% is a characteristic of each cell line; however, it varies by as much as 1,000‐fold among the five cell lines we have tested (L1210 leukemic, H35 hepatoma, N18 neuroblastoma, W256 carcinosarcoma and 3T3 fibroblasts).The antizyme to ornithine decarboxylase can be induced in all these cells by high (di)(poly)amine concentrations.Based on these and other experiments we suggest a working hypothesis: that the polyamines regulate ornithine decarboxylase activity through two different sites that may be interrelated; a sensitive membrane‐mediated site that responds to minute fluctuations of extracellular polyamine levels and a coarse site which may be intracellular or membrane associated that responds to larger fluctuations of intracellular polyamine levels. The consequences of such a control mechanism operating within the whole organism are discussed.
Platelet derived growth factor(s) for a hormone‐responsive rat mammary tumor cell line
Authors: Eastment Caroline T. , Sirbasku David A. 
Published: February 2005

AbstractMammary tumor cell growth factor(s) has been identified in extracts of platelets from both male and female rats, as well as in extracts prepared from pooled outdated human platelets. When assayed by the growth promotion of MTW9/PL rat mammary tumor cells in culture, platelet extracts alone were able to support growth 50–75% as well as whole serum. The mitogenic activity from crude human platelet lysates was shown to be trypsin sensitive, relatively stable to extremes of pH, labile to heat treatment at 70°, non‐dialysable, ammonium sulfate precipitable, not removed by 56° charcoal treatment, and of apparent molecular weight of 30,000 to 50,000 daltons as estimated by G‐100 Sephadex chromatography. The platelet derived mammary growth factor activity was not replaced or potentiated by thrombin or known hormones and growth factors such as prolactin, insulin, 17‐β‐estradiol, progesterone, hydrocortisone, L‐thyroxine, and mouse epidermal growth factor. The experimental report demonstrates that platelets are a rich source growth factor activity for rat epithelial mammary tumor cells, and that the activity appears to be a polypeptide(s) different from other mitogenic activities known to influence growth of mammary tissue.
Ribonucleotide reductase from wild type and hydroxyurea‐resistant chinese hamster ovary cells
Authors: Lewis William H. , Wright Jim A. 
Published: February 2005

AbstractThe kinetic properties of partially purified ribonucleotide reductase from Chinese hamster ovary cells have been investigated. Double reciprocal plots of velocity against substrate concentration were found to be linear for three the substrates tested, and yielded apparent Km values of 0.12 mM for CDP, 0.14 mM for ADP and 0.026 mM for GDP. Hydroxyurea, a potent inhibitor of ribonucleotide reduction, was tested against varying concentrations of ribonucleotide substrates and inhibited the enzyme activity in an uncompetitive fasion. Intercept replots were linear and exhibited Ki values for hydroxyurea of 0.08 mM for CDP reduction, 0.13 mM for ADP reduction and 0.07 mM for GDP reduction. Guanazole, another inhibitor of ribonucleotide reductase, interacted with the enzyme in a similar manner to hydroxyurea showing an uncompetitive pattern of inhibition with CDP reduction and yielding a Ki value of 0.57 mM.Partially purified ribonucleotide reductase from hydroxyurea‐resistant cells was compared to enzyme activity from wild type cells. Significant differences were observed in the hydroxyurea Ki values with the three ribonucleotide substrates that were tested. Also, CDP reductase activity from the drug‐resistant cells yielded a significantly higher Ki value for guanazole inhibition than the wild type activity. The properties of partially purified ribonucleotide reductase from a somatic cell hybrid constructed from wild type and hydroxyurea‐resistant cells was also examined. The Ki value for hydroxyurea inhibition of CDP reductase was intermediate between the Ki values of the parental lines and indicated a codominant expression of hydroxyurea‐resistance at the enzyme level. The most logical explanation for these results is that the mutant cells contain a structurally altered ribonucleotide reductase whose activity is less sensitive to inhibition by hydroxyurea or guanazole.
Studies on the nature of protease‐induced growth stimulation in normal and transformed BHK cells
Authors: Kiehn Don , Brown McKay 
Published: February 2005

AbstractIn the presence of growth‐limiting serum concentrations trypsin displays mitogenic activity on actively‐growing but not quiescent BHK cells. These results suggest that BHK cells arrested in G1 (G0) are not sensitive to protease‐induced growth stimulation. Previous work strongly suggested that the trypsin active‐site is not directly involved in its mitogenic activity on BHK cells. Additional studies on denatured trypsin fragments further indicate that the molecular conformation and size of native trypsin may not be absolutely required for mitogenic activity.Cellular multiplication induced by the addition of fresh serum to quiescent BHK cultures is not inhibited by high concentrations of soybean trypsin inhibitor. Similar to our previous findings with trypsin, it has been further observed that plasmin is not sufficient to initiate the growth of BHK cells in soft agar. Trypsin also fails to enhance the growth of a thermosensitive polyoma‐transformed BHK line in soft agar at the restrictive temperature. Finally, the growth of transformed BHK cells in soft agar does not display a requirement for plasminogen and is not inhibited by soybean trypsin inhibitor. These studies argue against the involvement of plasmin or other exogenous trypsin‐like enzymes in the growth and transformation of BHK cells.
Regulation of cell‐cycle initiation in yeast by nutrients and protein synthesis
Authors: Shilo B. , Simchen G. , Pardee A. B. 
Published: February 2005

AbstractArrested Saccharomyces cerevisiae cells initiate the cell cycle in an asynchronous mode. The asynchronous manner of cycle initiation generates variability in cell‐cycle times of individual cells. Limiting concentrations of adenine, methionine or histidine regulate the rate of cycle initiation in auxotrophs. A sigmoidal curve of rate vs. concentration is obtained for each of the three substances. Moreover, the three curves have similar Hill coefficients of 2.4, suggesting that a common intermediate requiring adenine, methionine and histidine regulates cell‐cycle initiation in yeast.Low concentrations of cycloheximide reduce the rate of cycle initiation of arrested cells that are released from the block in a similar way as limiting nutrients. It thus appears that the common intermediate that requires the limiting nutrients depends upon protein synthesis. The rate of cycle initiation is more sensitive to cycloheximide or nutrient limitation than is protein synthesis. It is also affected by limiting nutrients to a much greater extent than is the overall rate of protein accumulation (i.e., net protein synthesis). Hence the mechanism that controls cycle initiation does not depend on the overall synthesis or accumulation of proteins in the cell. It may depend on synthesis of particular proteins whose production or function requires the limiting nutrients.The high sensitivity of cycle initiation to a decrease in the rate of protein synthesis could explain the ability of yeast cells to complete the cycle and arrest at stationary phase upon depletion of medium components. The cells cannot initiate the cycle although their protein synthesis capacity remains sufficiently high to allow traversal of the rest of the cell cycle.
Responsiveness to insulin is a dominant characteristic in somatic cell hybrids
Authors: Straus Daniel S. , Williamson Robert A. 
Published: February 2005

AbstractThe mouse melanoma cell line PG19 has been found to be unresponsive to the growth‐stimulatory action of insulin, although it responds well to other growth factors present in serum. Insulin stimulates DNA synthesis in mouse embryo fibroblasts, and responsiveness to insulin has been found to be a dominant characteristic in mouse fibroblast x PG19 hybrids. To examine the possibility that the unresponsiveness to insulin of the melanoma cells is attributable to a lack of insulin receptors, we have measured the binding of 125I‐labeled insulin to the fibroblasts, melanoma cells, and fibroblast x melanoma hybrids. Insulin binds to the surface of the melanoma cells; however, the binding affinity appears to be lower than that observed for binding to diploid fibroblasts. In addition, the dissociation of insulin from the melanoma cells is not accelerated by excess unbound insulin, a kinetic effect observed in the dissociation of insulin from the fibroblasts and fibroblast x melanoma hybrids. This suggests that the class of insulin receptors characterized by this effect is absent on the PG19 cells, and present on the fibroblasts and fibroblast x PG19 hybrids.
Presence of spectrin in untreated friend erythroleukemic cells. Its accumulation upon treatment of the cells with dimethyl sulfoxide
Authors: Rossi Giovanni B. , Aducci Patrizia , Gambari Roberto , Minetti Maurizio , Vernole Patrizia 
Published: February 2005

AbstractFriend leukemia cells (FLC) are nucleated erythroid precursors, and are markedly stimulated towards more advanced stages of differentiation by treatment with dimethyl sulfoxide (DMSO). The presence of spectrin, an erythrocyte membrane protein, has been investigated in untreated and in DMSO‐treated FLC by indirect immunofluorescence and by analysis in SDS‐polyacrylamide gel electrophoresis of low‐ionic‐strength cell extracts immuno‐precipitated with a monospecific anti‐spectrin serum.Spectrin is detectable in significant amounts in the “inducible” clones prior to DMSO stimulation, and accumulates 4‐ to 5‐fold upon addition of this compound to the cultures. Spectrin accumulation occurs rather early (24 hours after cell seeding) and reaches its peak on the third day, to decline thereafter. Semiquantitative determinations of spectrin amounts present in DMSO‐stimulated 745A and A°1 cells on the third day after treatment were 2.4 × 105 and 3.0 × 105 molecules/cell, respectively.Spectrin is also detectable in very low amounts in an “uninducible” line of FLC, and is not accumulated upon DMSO treatment thereof, whereas treatment with hemin does cause a significant increase of spectrin‐positive cells.These data indicate that spectrin is a convenient “early” marker for in vitro studies of erythropoiesis.