bluuebunny/crossref_metadata_2025_split huggingface dataset:
Further evidence for an inhibitor of proliferation elaborated by normal human fibroblasts in culture: Partial characterization of the inhibitor
Authors: Strobel‐Stevens Janna D. , Lacey James C. 
Published: February 2005

AbstractWe present evidence that extends our earlier preliminary report on the stimulatory effect of saline washes on confluent cells in culture (Lacey et al., '77). That work suggested that an inhibitory substance was being removed by the washes. The present work suggests that the inhibitor is in the 10,000–30,000 MW range, is reversibly bound, is cationic and is also a protease inhibitor. It is heat stable, but is apparently degraded with time in our experimental systems.
Calcium transport and cellular distribution in quiescent and serum‐stimulated primary cultures of bone cells and skin fibroblasts
Authors: Eilam Y. , Szydel N. 
Published: February 2005

AbstractPrimary cultures of bone cells and skin fibroblasts were examined for their Ca++ content, intracellular distribution and Ca++ fluxes. Kinetic analysis of 45Ca++ efflux curves indicated the presence of three exchangeable Ca++ compartments which turned over at different rates: a “very fast turnover” (S1), a “fast turnover” (S2), and a “slow turnover” Ca++ pool (S3). S1 was taken to represent extracellular membrane‐bound Ca++, S2 represented cytosolic Ca++, and S3 was taken to represent Ca++ sequestered in some intracellular organelles, probably the mitochondria. Bone cells contained about twice the amount of Ca++ as compared with cultured fibroblasts. Most of this extra Ca++ was localized in the “slow turnover” intracellular Ca++ pool (S3). Serum activation caused the following changes in the amount, distribution, and fluxes of Ca++: (1) In both types of cells serum caused an increase in the amount of Ca++ in the “very fast turnover” Ca++ pool, and an increase in the rate constant of 45Ca++ efflux from this pool, indicating a decrease in the strength of Ca++ binding to ligands on cell membranes. (2) In fibroblasts, serum activation also caused a marked decrease in the content of Ca++ in the “slow turnover” Ca++ pool (S3), an increase in the rates of Ca++ efflux from the cells to the medium, and from S3 to S2, as well as a decrease in the rate of influx into S3. (3) In bone cells the amount of Ca++ in S3 remained high in “serum activated” cells, the rate of efflux from S3 to S2 increased, and the rate of influx into S3 also increased. The rate of efflux from the cells to the medium did not change. The results suggest specific properties of bone cells with regard to cell Ca++ presumably connected with their differentiation. Following serum activation we investigated the time course of changes in the amount of exchangeable Ca++ in bone cells and fibroblasts, in parallel with measurements of 3H‐thymidine incorporation and cell numbers. Serum activation caused a rapid decrease in the content of cell Ca++ which was followed by a biphasic increase lasting until cell division.
Inhibition of growth of proline‐requiring Chinese hamster ovary cells (CHO‐K1) resulting from antagonism by a system amino acids
Authors: Curriden Scott , Englesberg Ellis 
Published: February 2005

AbstractCHO‐K1 requires proline for growth. Two proline‐independent revertants were isolated—K1‐J and K1‐6. CHO‐K1 pro− is much more sensitive than the pro+ cell lines to inhibition of growth by addition to the medium of amino acids and amino acid analogues that are transported through the A system. In contrast, pro+ cells are as sensitive as, or in some cases slightly more sensitive than, pro− cells to glycine, basic amino acids, and to amino acids that are mainly transported by the L system. The A system analogue α(methylamino) isobutyric acid (MAIB) in low concentrations reacts competitively with proline to regulate the growth of pro− cells, yielding a Ki for MAIB of 0.56 mM. CHO‐K1 and K1‐6 transport proline at the same initial rate and are equally sensitive to the inhibition of proline transport by alanine. Alanine and MAIB inhibit proline transport strongly and similarly in CHO‐K1. Thus although these compounds inhibit the transport of proline by both cell types to the same extent, pro+ cells are immune to the effect of this starvation since they are able to synthesize their own proline. We also describe a secondary inhibition caused by high A system amino acid concentrations that affects both pro− and pro+ cells.
Collagen gels as a matrix for haemopoiesis
Authors: Lanotte Michael , Schor Seth , Dexter T. Michael 
Published: February 2005

AbstractWe have shown that collagen gel can be used as a culture matrix for the cloning of granulocyte/macrophage progenitor cells (CFU‐C), the production of foci of marrow stromal cells and the maintenance of stem cell proliferation, differentiation and the production of CFU‐C. Since collagen is a physiological matrix and allows the simultaneous growth of a variety of cellular elements, the system should prove useful for examining the role of cell/cell interactions and regulatory molecules involved in haemopoiesis.
Amino acid transport in human lymphocytes: Distinctions in the enhanced uptake with PHA treatment or amino acid deprivation
Authors: Segel George B. , Lichtman Marshall A. 
Published: February 2005

AbstractHuman blood lymphocytes increase their concentrative uptake of amino acids when treated with plant lectins such as phytohemagglutinin or when exposed to an amino acid deficient environment (adaptation). Previous studies of the PHA effect have been conducted principally with α‐aminoisobutyric acid (AIB). We have studied the transport characteristics of naturally occurring amino acids by PHA‐treated lymphocytes. These studies have been conducted in the absence and presence of added carrier amino acid to determine whether an in‐crease in transport after PHA treatment is mediated by the same mechanism that occurs during adaptation to a low amino acid environment.PHA stimulated the uptake of AIB, alanine, and proline 1.5‐ to 2‐fold after 4 hours' exposure. AIB and proline, but not alanine transport, also increased when lymphocytes were in an amino acid‐deficient medium. When lymphocytes were in an amino acid‐deficient medium with PHA, the increase in uptake induced by PHA was superimposed on the increase that occurred in response to an amino acid‐deficient medium. Also, PHA stimulated a delayed increase (16–20 hours) in the transport of leucine, whose uptake does not adapt to an amino acid‐deficient medium. These data suggest that PHA and amino acid deprivation stimulated rate increases in amino acid transport by separate mechanisms.
Effects of dexamethasone and dibutyryl cyclic AMP on polyamine synthesizing enzymes in mouse lymphoma cells
Authors: Russell Diane Handdock , Haddox Mari K. , Gehring Ulrich 
Published: February 2005

AbstractS49.1 Lymphoma cells were arrested in G1 phase of the cell cycle when treated with either 1 μM dexamethasone (Dex) or 0.5 mM N6, O2‐dibutyryl cyclic adenosine 3′ :5′ ‐monophosphate (Bt2cAMP) plus 0.2 mM theophylline. However, the two agents had markedly different effects on aspects of polyamine and cyclic nucleotide metabolism within the arrested cells. Bt2cAMP had an early and pronounced inhibitory effect on ornithine decarboxylase (ODC) activity causing a decrease to 40% of control within 1 h. However, there was no significant inhibition of ODC activity in the Dex‐treated cells until 4 h of exposure, at which time ODC activity was reduced to approximately 60% of the control value. Sadenosyl‐L‐methionine decarboxylase (SAMD) activity was reduced by both agents, Bt2cAMP having the more pronounced inhibitory effect. The activity of SAMD was reduced to 40% of control after 10 h of Dex, whereas Bt2cAMP reduced the activity to approximately 25% of control within 4 h. Intracellular polyamine pools were decreased rapidly in Dex‐treated cells but not in those exposed to Bt2cAMP. Bt2cAMP decreased the amount of type I (PKI) and type II (PKII) cyclic AMP‐dependent protein kinase (cAMP‐PK) activity to 30% of control or less within 2 h. In contrast, Dex had very little effect on either PKI or PKII until 24 h, when cell viability was affected. The specific activity of both PKI and PKII remained significantly decreased in cells exposed to Bt2cAMP for 6 h and then resuspended in fresh medium. The rapid decrease in ODC activity in response to Bt2cAMP and the slow recovery after washout may be due to the marked decreases in total PKI and PKII activities. Dex, which had no effect on PKI and PKII specific activities, only slowly inhibited ODC activity and recovery of enzyme activity was rapid upon resuspension in fresh medium. These data further stress the importance of the maintenance of the cellular protein kinase pools in the regulation of the recovery time to growth inhibition in response to naturally occurring steroids and second messengers.
Hexose transport in normal and SV40‐transformed human endothelial cells in culture
Authors: Corkey Richard F. , Corkey Barbara E. , Gimbrone Michael A. 
Published: February 2005

AbstractThe mechanism of glucose entry into human vascular endothelial cells was studied in monolayer cultures of normal (primary) and virally (SV40) transformed umbilical vein endothelium. Radioisotopic uptake studies with the glucose analogues 2‐deoxy‐D‐glucose, and 3‐O‐methyl‐D‐glucose, and the nonmetabolizable stereoisomer L‐glucose, indicated the presence of a saturable, stereospecific hexose carrier mechanism in both cell types. In other experiments with D‐glucose and 3‐O‐methyl‐D‐glucose, the phenomenon of countertransport was demonstrable. Hexose transport was not affected by KCN, dinitrophenol, or ouabain, but was inhibited by phloretin and phlorizin in a pattern consistent with facilitated diffusion. Kinetic constants were obtained for both 2‐deoxy‐D‐glucose and 3‐O‐methyl‐D‐glucose uptake. Similar Km values (range, 3.3–4.7 mM) were noted with normal and transformed cells, whereas the apparent Vmax was 0.56 nmol/μ1 cytosol/minute for primary cells and 1.7–2.5 nmol/μ cytosol/minute for transformed cells. Under standard culture conditions, as well as following 18 hours of serum deprivation, insulin at concentrations up to 10−5 M did not appear to influence hexose uptake in either cell type. Metabolism of 14C(U)‐D‐glucose to 14CO2 also was not stimulated by insulin. The presence of an insulin‐insensitive, facilitated transport system for glucose in vascular endothelium has relevance for glucose metabolism in this tissue, and potentially for the association of certain vascular diseases (e.g., diabetic microangiopathy, atherosclerosis) with altered glucose homeostasis.
Induction of Macrophage DNA Synthesis by phorbol esters
Authors: Hamilton J. A. , Dientsman S. R. 
Published: February 2005

AbstractTumor‐promoting phorbol esters, such as 12‐0‐tetradecanoyl‐phorbol‐13‐acetate (TPA), stimulate mouse peritoneal exudate macrophages to undergo DNA synthesis without added macrophage growth factor (MGF). Resident peritoneal macrophages do not respond in this manner. Plasminogen activator (PA) levels of both exudate and resident peritoneal macrophages are elevated by TPA. Thus the phorbol esters appear to mimic the action(s) of MGF and may be useful in understanding the events involved in macrophage and precursor cell growth responsiveness.
Calcium spikes in cultured human reticular cells from peritoneal exudates
Authors: Gallin Elaine K. 
Published: February 2005

AbstractIntracellular recordings of cultured human peritoneal exudate cells reveal that cells within the culture exhibit an active depolarizing response to injected currents which can reach positive potentials and resemble slow spikes. The cells exhibiting spikes are similar to the reticular cells described by Stuart and Davidson (1971a,b) in that they are esterase(+), acid phosphatase(+), and internalize colloidal carbon but not opsonized red blood cells. The active depolarizing response is unaffected by either decreasing the external sodium concentration or by adding tetrodotoxin (3 × 10−5 M), whereas increasing the external calcium concentration increases both the spike amplitude and rate of rise, and the addition of cobalt (3 mM) blocks the response. Addition of barium increases the duration and amplitude of the spikes but reduces the afterhyperpolarization. The data indicate that cultued human reticular cells from the peritoneal cavity exhibit a calcium spike.
Effect of serum step‐down on protein metabolism and proliferation kinetics of NHIK 3025 cells
Authors: Rønning Øystein W. , Lindmo Tore , Pettersen Erik O. , Seglen Per O. 
Published: February 2005

AbstractHuman NHIK 3025 cells growing exponentially in 30% or 3% serum had population doubling times of 19.1 and 27.6 hours, respectively. These values were equal to the calculated protein doubling times (17.6 and 26.5 hours, respectively), showing that the cells were in balanced growth at both serum concentrations. Stepdown from 30% to 3% serum reduced the rate of protein synthesis within 1–2 hours, from 5.7% hour to 4.3% hour, while the rate of protein degradation was unchanged (1.7%/hour). In cells synchronized by mitotic selection from an exponentially growing population, the median cell cycle durations in 30% and 3% serum were 17.2 and 23.6 hours, respectively, which were also in good agreement with the protein doubling times. The median G1 durations were 7.1 and 9.6 hours, respectively. Thus the duration of G1 relative to the total cell cycle duration was the same in the two cases. Complete removal of serum for a period of 3 hours resulted in a 3‐hour prolongation of the cell cycle regardless of the time after mitotic selection at which the serum was removed. For synchronized cells, the rate of entry into both the S phase and into the subsequent cell cycle were reduced in 3% serum as compared to 30% serum, the former rate being significantly greater than the latter at both serum concentrations. Our results thus indicate that these cells are continuously dependent upon serum throughout the entire cell cycle.
Variants of 3T3 cells lacking mitogenic response to the tumor promoter tetradecanoyl‐phorbol‐acetate
Authors: Butler‐Gralla Edith , Herschman Harvey R. 
Published: February 2005

AbstractThe potent tumor promoter 12‐O‐tetradecanoyl‐phorbol‐13‐acetate (TPA) can stimulate quiescent, nonproliferating 3T3 cells to reenter the cell cycle and divide. We have previously used a slection technique developed in our laboratory to isolate variant cell lines which no longer divide in response to epidermal growth factor. We have now utilized the same selection procedure to isolate, from 3T3 cells, two variant cell lines, TNR‐2 and TNR‐9, which retain growth control and divide in response to elevated serum or fibroblast growth factor, but which do not respond to TPA. The variants do not incorporate precursors into DNA in response to TPA, demonstrating that the cells do not enter the S phase of the cell cycle. The TPA nonresponsive variant TNR‐2 cannot respond to epidermal growth factor; TNR‐9 responds to this mitogen. TNR‐2 variant cells, which do not respond to EGF, do not bind 125I‐EGF. TPA can modulate 125I‐EGF binding to TNR‐9 cells in a manner similar to its action on parental 3T3 cells. This TPA‐induced alteration of EGF binding indicates that TNR‐9 cells still interact with TPA, despite their inability to mount a mitogenic response.
Neutral amino acid transport during the cell cycle of cultured human lymphocytes
Authors: Glassy Mark C. , Furlong Clement E. 
Published: February 2005

AbstractNeutral amino acid (isoleucine, leucine, and valine) transport was monitored in synchronous populations of WIL‐2 cells, a diploid human lymphoblastoid B cell line. Cells were synchronized by either the double thymidine block technique or by density‐dependent arrest in G1. Cells synchronized by these methods showed up to a 66% decrease in amino acid transport upon progressing from the early S phase through the G2 and M phases with a concomitant increase in transport during the G1 phase. The lowest activities of amino acid transport in synchronized cells were observed during the G2 and M phases.
Studies on a human melanoma cell line: Effect of cell crowding and nutrient depletion on the biophysical and kinetic characteristics of the cells
Authors: Sheridan J. W. , Simmons R. J. 
Published: February 2005

AbstractIn an investigation of the changes that occur in cultured neoplastic cells as they outgrow their supply of nutrient, MM96 human melanoma cells were found to diminish in size and to proliferate more slowly. These changes were accompanied by a moderate increase in the proportion of cells with a G1‐like DNA content. When replated under favorable conditions, many of these cells gradually resumed active proliferation. Continuing adverse culture conditions led to a continued fall in cell size, loss of reproductive viabllity, and finally to rapid cell death. Simultaneous buoyant‐density and velocity‐sedimentation‐fractionation experiments showed that cells from exponential cultures were moderately dense and rapidly sedimenting, cells from postexponential cultures were less dense and much more slowly sedimenting, and dye‐excluding cells from reproductively nonviable, late postexponential cultures were of widely variable though generally high density, and were moderately rapidly sedimenting. Although neither fractionation method resulted in significant enrichment of clonogenic cells, depletion was seen at both extremes of both types of profile. Cells fractionated by velocity were sorted according to DNA content and hence location in the cell cycle. The relationship between sedimentation rate and cell‐cycle location was reflected in the continuous thymidine labeling patterns of the separated cells. Study of these patterns suggested that cycle durations lengthened as crowding increased and nutrient became depleted, and shortened upon reseeding at low density into fresh medium.
Cell population kinetics of the mouse lens epithelium
Authors: Rafferty Nancy S. , Rafferty Keen A. 
Published: February 2005

AbstractThe dividing lens epithelium of 8‐week‐old CF1 mice consists of a monocellular layer of about 31,000 cells and does not include the postmitotic cells of the meridional rows and another postmitotic zone of seven cell positions' width immediately anterior to the rows. The latter two populations contain approximately 3,600 and 9,000 cells, respectively, for a total of 44,000 cells in the entire lens epithelium. Autoradiographic analysis based upon mitotic index and cell cycle times indicates that the epithelium produces 207 new lens fibers a day. Throughout the 20‐day period of study, labeled cells appeared almost entirely as pairs following a single dose of 3H‐thymidine and clusters of labeled nuclei were not seen. Moreover, the number of labeled cells dropped only slowly with time, as did the grain counts. These observations indicate that logarithmic division “cascade” does not occur in the lens.The dividing cell population consists largely of a slowly cycling stem cell group, dividing once about every 17–20 days, and consisting of some 5,000 cells. A subpopulation may exist which undergoes two rapid consecutive divisions before becoming postmitotic, but this is too small to make a significant contribution to lens fiber production. Four days are required to transit the postmitotic zone, and an additional 43 or so are needed to transit the meridional rows and differentiate into anucleate lens fibers. Data from other laboratories indicate that the entire process, from mitosis to final differentiation, requires about 4 months. Hence, most of this time is spent in migration of nondividing cells.
Partial characterization of a mitogenic factor with somatomedin‐like activity produced by culture WI‐38 human fibroblasts
Authors: Atkison Paul R. , Bala R. Marvin 
Published: February 2005

AbstractConditioned serum‐free medium (CSFM) obtained from WI‐38 human fibroblasts was found to contain a mitogenic factor(s) with somatomedin (SM)‐like activity. Treatment of the cells with cycloheximide eliminated the SM‐like activity in CSFM, suggesting that these cells produce and release the activity. Gel filtration revealed that the fibroblast SM‐like activity (FSLA) had a molecular size near 45,000. Isoelectric focusing of this FSLA yielded 2 bands of SM activity with pIs of 4.7 and 6.1, and corresponding molecular sizes of ∼29,000 and 16,500, respectively. The FSLA obtained by gel filtration revealed parallel dose response curves with a basic SM in a SM radioreceptor and radioimmunoassay and stimulated: (1) 35So4 uptake by hypophysectomized rat cartilage; (2) (U‐14C) glucose oxidation is isolated rat adipocytes; and (3) (3H) thymidine uptake and cell division in these same WI‐38 fibroblasts. Out studies indicate that this FSLA and basic SM are similar but not identical.
Aminoimidazole carboxamide ribonucleoside toxicity: A model for study of pyrimidine starvation
Authors: Thomas Cornelius B. , Meade Jean C. , Holmes Edward W. 
Published: February 2005

AbstractAminoimidazole carboxamide ribonucleoside (AIC‐R), a purine precursor, has biphasic effects on the growth of Chinese hamster fibroblasts. At 200 μM AIC‐R cell growth is almost completely arrested, while at 50 and 700 μM AIC‐R cell growth is comparable to that observed in the absence of nucleoside. The growth inhibition produced by AIC‐R is the consequence of inhibition of the orotate phosphoribosyltransferase‐orotidylic decarboxylase (OPRT‐ODC) reactions, as evidenced by a 87% reduction in the intracellular concentrations of UTP and CTP, accumulation of orotate in the medium, and restoration of normal growth by inclusion of 100 μM uridine in the medium. Inhibition of pyrimidine nucleotide synthesis at 200 μM AIC‐R is associated with an 82% reduction in the intracellular concentration of PP‐ribose‐P and a 150% increase in the concentration of purine nucleotides. Restoration of cell growth to a normal rate at 700 μM AIC‐R—a condition under which PP‐ribose‐P remains depressed and purine nucleotide concentrations are also depressed (40% of control)—and absence of toxicity at 50 μM AIC‐R—a condition under which purine nucleotide concentrations are increased by 150% and PP‐ribose‐P concentration is normal—suggest that the inhibition of OPRT‐ODC observed at 200 μM AIC‐R is caused by the combination of the reduction in PP‐ribose‐P and increase in purine nucleotides. These studies provide a better understanding of the control of the OPRT‐ODC reactions in the cell and provide additional insight into the basis of pyrimidine starvation induced by purine nucleosides.
Epstein‐Barr virus in nontumorigenic and tumorigenic nasopharyngeal carcinoma (NPC) somatic cell hybrids
Authors: Staczek John , Steplewski Zenon , Weinmann Roberto , Klein George , Koprowski Hilary 
Published: February 2005

AbstractSomatic cell hybrids between mouse fibroblasts and human cells derived from nasopharyngeal carcinoma (NPC) biopsies or NPC tumors propagated in nude mice were examined for the expression of the Epstein‐Barr nuclear antigen (EBNA), retention of Epstein‐Barr viral (EBV) DNA, and tumorigenicity in nude mice. In all hybrids the expression of EBNA correlated with the detection of EBV‐DNA. After more than 2 years in culture, the hybrids examined retained similar amounts of EBV‐DNA when compared to previously published data. Retention of EBV‐DNA did not correlate with the presence of any particular human chromosome. Use of either rodent cell lines, clone 1D or IT‐22, did not affect the retention nor loss of EBV‐DNA. For tumorigenicity studies, NPC cells were fused with IT‐22 cells and injected into nude mice. Tumor formation did not depend on the presence or absence of EBNA and detectable EBV‐DNA sequences; tumorigenicity in these studies could not be correlated with the presence of any particular human chromosome or the origin of the NPC biopsy.