bluuebunny/crossref_metadata_2025_split huggingface dataset:
A membrane‐altered mutant cold‐sensitive for growth
Authors: Ling Victor 
Published: February 2005

AbstractA colchicine‐resistant clone, CHRE5, has been isolated in a single step from a mutagenized culture of Chinese hamster ovary cells. Its resistance correlates with reduced colchicine permeability. At the same time, CHRE5 cells display a pattern of cross‐resistance to unrelated drugs similar to other membrane‐altered drug‐resistant mutants previously described (Ling and Thompson, 1974). However, CHRE5 cells also express a cold‐sensitivity for growth in that at 34° they do not double in number while at 38.5° they grow with a doubling time of about 22 hours. Employing synchronous cultures, the cold sensitive block in CHRE5 cells has been determined to be located prior to S in the G1 phase of the cell cycle. Mutant cells at 33.5° are not able to initiate DNA synthesis, however, cells already synthesizing DNA are able to complete the whole course of S. This cold sensitive block is reversed by shifting cells back to the higher temperature. Additonal clones with the CHRE5 phenotype have been isolated from non‐mutagenized cultures of wild‐type cells. Moreover, partial revertants of CHRE5 with increased ability to grow at 34° have been isolated and found to display increased colchicine sensitivity. These results are consistent with the hypothesis that the two phenotypes observed in CHRE5, namely, an altered plasma membrane (reduced drug permeability) and an altered ability to initiate DNA synthesis are the result of the same mutation.
Antagonistic effects of insulin and cortisol on coordinate control of metabolism and growth in cultured fibroblasts
Authors: Rubin H. 
Published: February 2005

AbstractA variety of metabolic and biosynthetic pathways in chick embryo fibroblasts are stimulated coordinately by many unrelated exogenous agents. Three of the best characterized components of this coordinate response are the uptake of 2‐deoxy‐D‐glucose (2‐dGlc) and of uridine and the incorporation of thymidine into DNA. Insulin stimulates and cortisol inhibits the coordinate response. In cortisol‐treated cultures, as little as 10−3 units/ml of insulin may stimulate thymidine incorporation 4‐fold and 10−1 units/ml may stimulate as much as 40‐fold. The higher concentrations of insulin completely override the inhibitory effect of cortisol. They also cause about a 5‐fold stimulation of the uptake of 2‐dGlc and of uridine and a 2‐fold stimulation of proline incorporation into protein. The uptake rates of 2‐dGlc and uridine double within 30 minutes after addition of insulin to cortisol‐inhibited cultures, but the incorporation of thymidine only begins to increase markedly after a 4‐hour delay. When cortisol is added to cultures in the absence of insulin, the rates of uptake of 2‐dGlc and uridine begin to decrease within two hours, but the incorporation of thymidine remains constant for two hours before beginning to decrease. Deprivation of Mg2+ inhibits the accelerated coordinate response maintained by insulin, but does not further the inhibition induced by cortisol. Results with metabolic inhibitors indicate that the stimulation of 2‐dGlc and uridine uptake by insulin do not require RNA synthesis, and also suggest that they do not require protein synthesis. These and other findings can be explained by a model for coordinate control in which insulin increases and cortisol decreases the availability of Mg2+ for a wide spectrum of regulatory reactions in different metabolic pathways. In this model both hormones affect only the rates of ongoing reactions and do not instruct the cell to carry out specific new reactions unless the cell was predetermined to do so.
PHA stimulation of human lymphocytes during amino acid deprivation. Protein, RNA and DNA synthesis
Authors: Dauphinais Christiane , Waithe William I. 
Published: February 2005

AbstractResting lymphocytes are in the G0 phase of the cell cycle. Upon activation by PHA, they progress into G1 with accompanying increased protein and RNA synthesis, initiate DNA synthesis and divide. We have studied the kinetics of inhibition of macromolecular synthesis during activation in the absence of single amino acids. Three types of kinetics are observed. In the absence of tryptophan or isoleucine, stimulated lymphocytes show a normal increase in protein and RNA synthesis during the first 30 hours of stimulation, initiate DNA synthesis but are subsequently inhibited. In phenylalanine‐deficient medium, no DNA synthesis occurs in spite of a slight increase in protein synthesis. No increase in macromolecular synthesis is observed in medium lacking any one of the other essential amino acids (eg: lysine).Our results indicate that the kinetics of macromolecular synthesis in tryptophan‐deficient medium is the result of a limited reserve of protein‐bound tryptophan which becomes exhausted after 30 hours. On the other hand, delayed inhibition of synthesis in isoleucine‐deficient medium probably reflects an initially low requirement for this amino acid followed by inhibition of the synthesis of isoleucine‐rich proteins involved in some late event of stimulation. Partial deprivation of lysine results in kinetics of protein synthesis similar to that in tryptophan‐ or isoleucine‐deficient media. The results indicate that the kinetics of macromolecular synthesis during activation of lymphocytes in the absence of an essential amino acid is a function of the quantitative requirement for that amino acid, at a given time during stimulation.Upon replacement of lysine, lymphocytes inhibited by lysine deficiency begin RNA and protein synthesis immediately and at a rate faster than that of unstimulated cultures to which PHA is added. They also initiate DNA synthesis earlier and therefore, are closer to the S phase than resting lymphocytes. It is concluded that lymphocytes stimulated in the absence of lysine are activated even though no overall increase in macromolecular synthesis is observed. Furthermore, the kinetics of DNA synthesis following reversal of inhibition by phenylalanine suggests that lymphocytes stimulated during phenylalanine deprivation become arrested at most six hours before S. These results indicate that amino acid deficiencies lead to arrest of activated lymphocytes at various stages of stimulation, depending on how stringent these deficiencies are.
Embryonal carcinoma cells (and their somatic cell hybrids) are resistant to infection by the murine parvovirus MVM, which does infect other teratocarcinoma‐derived cell lines
Authors: Miller Richard A. , Ward David C. , Ruddle Frank H. 
Published: February 2005

AbstractMinute virus of mice (MVM), a non‐defective parvovirus, has been shown to infect cultures of non‐pluripotent differentiated teratocarcinoma‐derived cells, but pluripotent (and “nullipotent”) embryonal carcinoma cells derived from the same teratocarcinoma resist MVN infection. Somatic cell hybrids between an embryonal carcinoma line and Friend erythroblastic leukemia cells are also resistant to MVM, even though Friend cells are susceptible. Among three blastocyst‐derived lines tested, only one, a parietal yolk sac cell line, resists MVM infection. These results suggest that teratocarcinoma cultures may provide useful systems in which to study the cellular factors which mediate susceptibility to this teratogenic and oncolytic virus.
Measurements of contraction latencies to mechanical and electrical stimulation of the protozoan, Spirostomum ambiguum
Authors: Hamilton Thomas C. , Osborn Dustan 
Published: February 2005

AbstractMeasurements made on contraction latencies in Spirostomum suggest that mechanical stimulation causes contractions to be initiated by the release of small amounts of calcium from a store tightly coupled to the contractile apparatus. Contraction to electrical stimulation appears to result from the gross electrophoretic mobilization of large amounts of calcium from a loosely coupled store. Contraction latencies to mechanical stimulation were three milliseconds and were independent of stimulus strength, previous stimulation, and contraction probability. For 0.5‐millisecond biphasic electrical stimulation the contraction latencies varied widely. Latencies to initial contractions were dependent on stimulus strength: from 1.0 milliseconds for a stimulus that caused a 100% probability of contraction to 2.0 milliseconds for a stimulus that caused a 10% probability of contraction. Latencies of contraction to electrical stimulation were also dependent upon previous stimulation, lengthening to over 300 milliseconds after ten minutes of stimulation. Initial contraction latencies were not affected by previous stimulation to the other (electrical or mechanical) stimulus modality. Repeated electrical stimulation also reduced the animal's resting length and slowed the rate of post contraction re‐extension, whereas mechanical stimulation did not have these effects.
Effects of withdrawal of a mitogenic stimulus on progression of fibroblasts into S phase: Differences between serum and purified multiplication‐stimulating activity
Authors: Bolen Joe B. , Smith Gary L. 
Published: February 2005

AbstractMultiplication‐stimulating activity (MSA) for chicken embryo fibroblasts was purified from serum‐free medium conditioned by the growth of a rat liver cell line. A comparison between calf serum and purified MSA was made regarding the regulation of the fibroblast cell cycle. Addition of serum or MSA to stationary, quiescent cells stimulates them to enter the DNA synthetic phase after a characteristic lag period. Exposure to serum for shorter periods of time will irreverisbly commit cells to continue through the cell cycle and initiate DNA replication in the absence of serum. In contrast, the withdrawal of purified MSA from the medium results in an abrupt halt in the progression of cells towards S phase. The results of labeled thymidine incorporation and autoradiographic experiments clearly indicate that the point at which cells become irreversibly committed to enter the DNA synthetic period is at or near the G1‐S boundary.The abrupt decay of the stimulation upon withdrawal of purified MSA provides a unique opportunity to investigate the biochemistry of this discrete phase of the cell cycle.
Specificity of the requirements for magnesium and calcium in the growth and metabolism of chick embryo fibroblasts
Authors: Rubin H. 
Published: February 2005

AbstractThe rate of entry of chick embryo fibroblasts (CEF) into the S‐period of the cell cycle is reduced by lowering the external supply of Mg2+ below 0.2 mM. This slowdown, which is measured by the rate of incorporation of 3H thymidine into DNA, can be largely reversed by doubling or tripling the concentration of Ca2+ in the medium, normally 1.7 mM. The Ca2+‐induced stimulation is shown not to depend on contaminating traces of Mg2+ in the added Ca2+. The increase in cell number in the Ca2+‐stimulated cultures is delayed, possibly due to cell detachment. The effect of Ca2+ on thymidine incorporation can be simulated almost quantitatively by Sr2+. Ba2+ does not produce the effect, nor do any of the other cations tested. As little as 0.2 mM Mg2+ produces a full stimulation of thymidine incorporation in the absence of added Ca2+, and no substitute was found that is effective in the same concentration range. In short term experiments, i.e., 16 hours, even 5.0 mM Ca2+ cannot stimulate thymidine incorporation to the extent achieved with 0.2 mM Mg2+. Large amounts of Ca2+ or Sr2+ can accelerate the uptake of 2‐dGlc in Mg2+‐deprived cultures, but they are much less efficient than Mg2+ in this regard also. It is suggested that Mg2+ is the direct intracellular effector in controlling the diverse reactions of the coordinate response, and that Ca2+ and Sr2+ act indirectly by making Mg2+ available to participate in these reactions.
Effect of calcitonin on the phosphorylation of non‐histones from cultured bone cells
Authors: Bustos Sergio E. , Schuster George S. , Dirksen Thomas R. , McKinney Ralph V. , Lai David Y.‐L. 
Published: February 2005

Abstract32P‐uptake into non‐histones from bone cell cultures was selectively stimulated in the presence of calcitonin. Comparison of the control and experimental radioactivity profiles of non‐histones fractionated by SDS gel electrophoresis showed that, in response to calcitonin stimulation, there was a 2‐ to 3‐fold increase in the specific activity associated with non‐histone proteins in the molecular weight range of 10,000 to 45,000 daltons while that of bands between 50,000 to 200,000 decreased.
Serum stimulation of human fibroblasts: Effect on non‐histones of nuclear ribonucleoprotein and chromatin
Authors: Augenlicht Leonard H. , Lipkin Martin 
Published: February 2005

AbstractIn quiescent human fibroblasts stimulated to proliferate by fresh medium plus 15% serum, no changes were seen in the incorporation of 3H‐tryptophan into the protein of nuclear ribonucleoprotein during the first three hours following re‐feeding. This was in contrast to non‐histone chromosomal proteins where the incorporation increased by 90% within ten minutes. The density of the formaldehyde fixed nuclear ribonucleoprotein in CsCl was 1.43–1.44 g/ml and this also did not change following stimulation. The electrophoretic profile of the proteins of nuclear ribonucleoprotein on SDS gels exhibited a predominant band corresponding to a molecular weight of 44,000 closely trailed by a band at 47,000 and other bands at higher molecular weight. This pattern was not altered by serum stimulation and the same was true for the more complex electrophoretic profile of the chromatin proteins. Following a 10‐minute pulse of 3H‐tryptophan at ten minutes after stimulation, there was a selective increase in the labeling of non‐histone chromosomal protein of molecular weight 59,000; no change was seen in the labeling of any protein of nuclear ribonucleoprotein.
Thrombin potentiates the mitogenic response of cultured fibroblasts to serum and other growth promoting agents
Authors: Zetter Bruce R. , Sun Tung‐Tien , Chen Lan Bo , Buchanan John M. 
Published: February 2005

AbstractThrombin may stimulate the proliferation of resting fibroblasts by itself or by potentiating the mitogenic effects of other growth stimulating agents. When added alone to a dense quiescent culture of chick embryo fibroblasts in either a serum‐free or a low serum medium, thrombin stimulates these cells to proliferation at a rate comparable to that seen with 5% serum. In the case of rabbit corneal fibroblasts neither fibroblast growth factor nor thrombin is particularly effective as a growth stimulant when added alone but exhibited a pronounced synergism on cell proliferation when present together. Established cell lines in the resting state, including 3T3, SV‐3T3, 3T6, BHK‐21 and 3T3 injected with avian sarcoma virus strain B77 (B77‐3T3), are not responsive to thrombin alone. When the serum concentration in the medium equals or exceeds 2%, thrombin potentiates the mitogenic response of 3T3 cells to serum factors. With the exception of 3T3 and SV3T3 cells, the other cell lines show a potentiation of growth when thrombin is added to a low‐serum (0.5%) medium containing epidermal growth factor and prostaglandin F2α. The addition of thrombin to cultures of B77‐3T3 cells growing in the presence of epidermal growth factor and prostaglandin F2α does not increase the initial growth rate of these cells but increases significantly the final cell density of these cultures.
A retarded rate of DNA replication and normal level of DNA repair in Werner's syndrome fibroblasts in culture
Authors: Fujiwara Yoshisada , Higashikawa Toshiaki , Tatsumi Mariko 
Published: February 2005

AbstractWe investigated the cloning efficiency, DNA repair, and the rate of DNA replication in the skin fibroblasts from patients with Werner's syndrome (WS) of an autosomal recessive premature aging disease. Five WS strains exhibited normal levels of sensitivity toward X‐ray and UV killings and repair of X‐ray induced single strand breaks of DNA (rejoining) and UV damage to DNA (unscheduled DNA synthesis). The sedimentation of newly synthesizing DNA in alkaline sucrose gradients demonstrated a characteristic feature that only the elongation rate of DNA chains, estimated by the molecular weight increase, was significantly slower during early passages in WS cells than in normal Hayflick Phase II fibroblasts. In addition, plating efficiencies as well as the replicative potentials of five WS strains were more limited than those of normal cells under the identical culture conditions. It seems therefore that at least in the WS cells tested, the slow rate of DNA replication may be more related to the shortened lifespan and enhanced cell death, as manifestation of premature senescence at the cellular level, than be the DNA repair ability.
Increased messenger RNA from protein synthesis inhibited human fibroblasts
Authors: Maroun L. E. , Miller E. T. 
Published: February 2005

AbstractNumerous reports have demonstrated that specific protein synthesis in response to specific inducers is markedly stimulated by a simultaneous brief exposure to protein synthesis inhibitors such as cycloheximide. This phenomenon is known as “superinduction” and is most often attributed to the accumulation of cytoplasmic messenger RNA during the inhibition period. Messenger RNA, as defined by rapid labeling, oligo (dt)‐cellulose binding, and cell free protein synthesis stimulation was measured in cycloheximide treated human fibroblasts. In spite of a consistent 40% decrease in total polysomal 3H‐uridine labeled RNA, a 1.5‐ to 2‐fold increase in extractable mRNA was observed. These data provide direct evidence that protein synthesis inhibition stimulates the appearance of cytoplasmic mRNA and/or completely blocks its degradation and, are consistent with the hypothesis that mRNA accumulation partly underlies the superinduction phenomena.
Selective lethal effect of thymidine on human and mouse tumor cells
Authors: Lee S. S. , Giovanella B. C. , Stehlin J. S. 
Published: February 2005

AbstractHuman cell lines derived from a melanoma and a colon carcinoma, and cultures of human melanocytes and intestinal epithelial cells, as well as a mouse mesenchymal non‐neoplastic cell line and a malignant subline of the same have been quantitatively studied in tissue culture for their sensitivity to thymidine. All three tumor lines produced solid tumors when injected into nude thymus‐deficient mice. No tumors were obtained by injecting cells of the human normal long‐term cultures or of the non‐neoplastic mouse line.The tumor‐producing lines showed a greater sensitivity to the lethal effects of high concentrations of thymidine than their non‐tumor‐producing counterparts. Less than 23% of the tumor cells survived 72 hours in the presence of 1 mg/ml of thymidine, in contrast to 60% or more of the non‐tumor cells.Colony formation was much more inhibited by thymidine and the differential between normal and tumor cells was even more pronounced. Tumor cells which also were treated for 72 hours with 1 mg/ml of thymidine and then plated in fresh medium formed very few colonies. If the plating efficiency of the untreated controls is considered as 100%, 4.3% or less of the treated tumor cells formed colonies, in contrast to 33% or more of the non‐tumor cells.
Cell surface glycosaminoglycans: Identification and organization in cultured human embryo fibroblasts
Authors: Vogel Kathryn G. , Kelley Robert O. 
Published: February 2005

AbstractA morphologically detectable cell coat, composed of glycoprotein, glycolipid, and glycosaminoglycan, is present on the external surface of most vertebrate cells. We have invetigated the composition and organization of glycosaminoglycans in the cell coat of cultured human embryo fibroblasts by labeling cells with 3H‐glucosamine and Na235SO4 and subsequently treating cultures with specific enzymes. Components released were identified by chromatography and specific enzymatic digestion. In situ incubation with leech hyaluronidase (4 μg/ml) removed only hyaluronic acid from the cell surface whereas testicular hyaluronidase (0.5 mg/ml) removed both hyaluronic acid and chondroitin sulfate. Trypsin (0.1 mg/ml) released a large mass of glycopeptides in addition to hyaluronic acid, chondroitin sulfate, and heparan sulfate. The affinity of the cell coat for the cationic dye, ruthenium red, was reduced by leech hyaluronidase treatment. Sequential enzyme digestions of the cell surface showed that hyaluronic acid could be removed without the concomitant or subsequent release of sulfated glycosaminoglycans, suggesting that the hyaluronic acid is not a structural backbone for glycosaminoglycan complexes of the external cell surface.
Proliferative response of human diploid fibroblasts to intermittent light exposure
Authors: Parshad Ram , Sanford Katherine K. 
Published: February 2005

AbstractThree‐ to four‐hour exposure to fluorescnt light, one to three times weekly, reproducibly enhanced the proliferation rate of human diploid fibroblasts. This enhancement was observed in WI‐38 and a line from whole embryo mince at late population doubling level (PDL) as well as in a line from adult skin at early PDL. Single or multiple exposures of short duration stimulated proliferation, whereas exposures of long duration were cytotoxic. This proliferative response is reversible, and is mediated through the culture medium, Dulbecco Vogt's supplemented with 10% fetal bovine serum. Apparently light produces some mitogenic substance(s) in the culture medium that accumulates in the cells and is toxic or growth‐stimulatory depending on its concentration per cell. Another possibility is that light produces in the medium both cytotoxic and growth‐stimulatory substances.
Renal sugar transport in the winter flounder IV. Effect of CA2+ on sugar transport in teased renal tubules
Authors: Kleinzeller Arnost , Dubyak George R. 
Published: February 2005

AbstractThe electrolyte distribution and sugar uptake by teased renal tubules of winter flounder (Pseudopleuronectes americanus) was studied using incubation media with 1.4 mM Ca2+ (controls) and without Ca2+. The omission of Ca2+: (a) produced some cellular swelling, and increase in cell Na+ and loss of K+; (b) had no effect on the extracellular propylene‐glycol space; (c) increased the uptake of non‐metabolizable methyl‐α‐D‐glucoside by the tissue: whereas in controls the equilibrium tissue/medium ratio (T/M) for the Na+‐independent uptake of the sugar was 0.71 ± 0.03 (SEM, n = 9), in Ca2+‐free media the T/M rose in 1.18 ± 0.06. The increase in sugar uptake seen in absence of Ca2+ was abolished by absence of Na+ (Li+‐media), 0.5 mM ouabain and 0.5 mM phlorizin; (d) produced an increase in the galactose phosphate level without affecting that of free sugar; (e) decreased the active uptake of 2‐deoxy‐D‐galactose by the tubules. These results were analyzed on the basis of available information on the transport characteristics of the sugars at the luminal and antiluminal cell faces. It is suggested that absence of Ca2+ increases the permeability of the intercellular junctions, thus permitting sugars to enter from the external medium into the tubular lumen. Methyl‐α‐D‐glucoside and D‐galactose can then be taken up into the cells by brush‐border localized active processes, whereas 2‐deoxy‐D‐galactose is not reabsorbed at this cellular face. At 1.4 mM Ca2+, the intercellular junction appears to be relatively impermeable to sugars and the transport properties in teased tubules reflect then events predominantly localized at the antiluminal cell face.