bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of low‐density lipoprotein metabolism by cell density and proliferative state
Authors: Kenagy R. , Bierman E. L. , Schwartz S. 
Published: February 2005

AbstractStimulation of the proliferation of human skin fibroblasts by platelet‐derived growth factor increased the binding and degradation of low‐density lipoproteins at cell densities of 2000–30,000 cells/cm2. Binding and degradation of low‐density lipoprotein was an inverse function of cell density in both proliferating and quiescent cells, indicating that the effect of cell density on the LDL receptor has proliferation‐dependent and proliferation‐independent components. The effect of medium conditioned by confluent fibroblasts on LDL metabolism was tested to determine if the effects of cell density on LDL metabolism might be mediated by cellular secretion products. Fibroblast‐conditioned medium increased LDL metabolism, suggesting secretion products do not mediate these effects of cell density. These data indicate that regulation of the low‐density lipoprotein receptor is not a simple on/off response to growth stimulation, but is responsive to extracellular cues such as cell density.
Possible involvement of cGMP in the control of tyrosine aminotransferase degradation in rat hepatocytes
Authors: Strinden Sarah Taylor , Stellwagen Robert H. 
Published: February 2005

AbstractAddition of theophylline to primary cultures of rat hepatocytes in which tyrosine aminotransferase had been preinduced with dexamethasone caused a further increase in specific activity of the enzyme. This increase was due in part to a reduction in the rate of tyrosine aminotransferase degradation that began about 2 hr after theophylline was added. The level of cGMP also increased with a similar time lag following the addition of theophylline. The concentration of theophylline which produced the above effects (1 mM) did not alter the rate of general protein degradation in hepatocytes. Addition of 8‐bromo‐cGMP (0.5 mM) resulted in an immediate reduction in the rate of tyrosine aminotransferase degradation and in an increase in the activity of the enzyme. Treating hepatocytes with MnCl2 (0.9 mM) caused an elevation of cGMP and a concomitant slowing of tyrosine aminotransferase degradation without changing the level of cAMP significantly. These results suggest an inverse relationship between the level of cGMP and the rate of tyrosine aminotransferase degradation in hepatocytes.
Associations of small nuclear RNAs in human cells
Authors: Smith James H. , Eliceiri George L. 
Published: February 2005

AbstractSeveral observations have been made about the associations of small nuclear RNAs (snRNAs) in human cells. When nuclear RNA was extracted with phenol and chloroform under standard nondenaturing conditions, the proportion of the nuclear snRNA content that cosedimented with high molecular weight RNA was very low. These results do not support the proposal that it is a large percentage of the cellular snRNA content that is involved in relatively stable base‐paired interactions with heterogeneous nuclear RNA at any given time. The various small nuclear ribonucleoprotein particles (snRNPs), in which the snRNAs are found in the cell, appear to differ substantially in their sedimentation rates under conditions of physiological ionic strength. Using anti‐RNP and anti‐Sm antibodies to analyze various subcellular fractions, we found that most, if not all, of the U1 snRNA cellular content is associated with the polypeptide(s) bearing the RNP determinant (in interphase and mitotic cells) and with the polypeptide(s) carrying the Sm determinant (in mitotic cells).
12–0‐tetradecanoylphorbol‐13‐acetatea and concanavalin a enhance glucose uptake in thymocytes by different mechanisms
Authors: Nordenberg Jardena , Stenzel Kurt H. , Novogrodsky Abraham 
Published: February 2005

AbstractThe effects of the tumor promoter 12–0‐tetradecanoylphorbol‐13‐acetate (TPA) and the plant lectin concanavalin A (Con A) on glucose uptake in murine thymocytes were studied. TPA induces a rapid dose‐dependent increase in the uptake of 2‐deoxyglucose and in the transport of 3–0‐methylglucose. Con A also elicits a time‐ and dose‐dependent enhancement of 2‐deoxyglucose uptake. The effect of Con A, however, is less pronounced. The effect of combined treatment of thymocytes with Con A and TPA is not additive. Cytochalasin B completely inhibits the basal, as well as TPA‐ and Con A‐enhanced, 2‐deoxyglucose uptake. Dexamethasone markedly inhibits basal 2‐deoxyglucose uptake, but is less inhibitory to enhanced 2‐deoxyglucose uptake induced by TPA and Con A. The effect of TPA on 2‐deoxyglucose uptake and 3–0‐methylglucose transport is refractory to inhibition by isobutyl methylxanthine, dibutyryl cyclic AMP, and ethyleneglycol tetraacetic acid. These agents markedly inhibit the enhancement of 2‐deoxyglucose (2‐DOG) uptake by Con A. p‐Bromophenacyl bromide, an inhibitor of phospholipase A2, also selectively inhibits Con A enhancement of 2‐DOG uptake. Taken together, the results suggest that Con A and TPA exert their stimulatory effect on glucose uptake by different activating mechanisms, but they may share a final common transport pathway.
Effects of polyamines on cyclic AMP‐mediated stimulation of amino acid transport in isolated rat hepatocytes
Authors: Auberger Patrick , Samson Michel , Cam Ginette Le , Cam Alphonse Le 
Published: February 2005

AbstractThe effects of natural polyamines on cyclic AMP‐mediated stimulation of amino acid transport in isolated rat hepatocytes were analyzed. Despite the fact that polyamines could directly compete with α‐aminoisobutyric acid (AIB) for uptake, preincubation of hepatocytes with polyamines did not significantly alter basal AIB transport. The stimulatory effect of glucagon or cyclic AMP analogs was differently affected by polyamines, since it was reduced in the presence of spermine and, inversely, potentiated by spermidine, putrescine, and cadaverine. Dose‐dependence analysis showed that half maximal and maximal effects occurred with 2–3 and 6–10 mM external concentrations, respectively. None of the polyamine effects could be ascribed to transstimulation or transinhibition of amino acid uptake. The inhibitory effect exerted by spermine correlated its capacity to inhibit [3H]‐leucine incorporation into proteins partially. The potentiating effect of the other polyamines did not result from stabilization of newly synthesized carrier proteins. Instead, the increase in Vmax of the high affinity transport component suggested that more carriers became available, presumably because polyamines facilitated their synthesis by interacting directly with one or several steps controlled by cyclic AMP.Polyamines appear to represent a new class of factors capable of modulating the cyclic AMP‐mediated stimulation of amino acid transport, in hepatocytes.
Growth effect of lithium on mouse mammary epithelial cells in serum‐free collagen gel culture
Authors: Tomooka Yasuhiro , Imagawa Walter , Nandi Satyabrata , Bern Howard A. 
Published: February 2005

AbstractThe effect of lithium on the growth of mammary epithelial cells from adult virgin and midpregnant BALB/c or BALB/cfC3H mice was tested in a serum‐free collagen gel culture system. The serum‐free medium consisted of a 1:1 mixture of Ham's F12 and Dulbecco's Modified Eagle's medium supplemented with insulin, transferrin, cholera toxin, epidermal growth factor (EGF), and bovine serum albumin fraction V (BSA V). A multifold increase in cell number occurred during 10–12 days of culture in this medium. In dose‐response studies in which the concentration of each component of this serum‐free medium was varied in turn, the addition of LiCL (10 mM) enhanced growth at most concentrations of each factor. However, LiCL could not enhance growth in the absence of insulin or BSA V, but could replace EGF. The optimal concentration of LiCl was 5–10 mM; higher concentrations (20–80 mM) were toxic. KCl (1–10 mM) when added to the serum‐free medium slightly stimulated growth; the addition of NaCl to the medium had little effect on growth. LiCl did not enhance the growth of cells from spontaneous mammary tumors of BALB/cfC3H mice.
Myocytes and fibroblasts exhibit functional synergism in mixed cultures of neonatal rat heart cells
Authors: Schroedl Nancy A. , Hartzell Charles R. 
Published: February 2005

AbstractCardiac cells obtained from neonatal rat heart contain a mixed population of cell types that can be enriched in culture in either myocytes or fibroblast‐like cells. A metabolic comparison of mixed heart cell cultures with enriched cultures of the same age‐in‐culture and initial cell density showed that mixed cultures used glucose more rapidly than either enriched myocytes or fibroblasts. Mixed cultures were shown to respond to deprivation of insulin and of serum with decreases in the rate of glucose usage and decreases in the protein content of cells, whereas enriched cultures did not respond in the expected manner to insulin deprivation. Mixed, 11‐day‐old cells also exhibited greater increases in cellular protein and greater resistance to the stress of starvation than enriched cultures. Palmitate usage, however, was similar in all cultures examined. We conclude that mixed cultures may serve as a better model system to study cardiac metabolism and to monitor the effects of drugs and hormones on the neonatal myocardium. In addition, it is clear from our results that myocytes and fibroblastic‐like cells coexist in a metabolically functional synergism.
The presence of a soluble interphotoreceptor retinol‐binding protein (IRBP) in the retinal interphotoreceptor space
Authors: Pfeffer B. , Wiggert B. , Lee L. , Zonnenberg B. , Newsome D. , Chader G. 
Published: February 2005

AbstractA new, gentle technique has been developed for washing of the retinal interphotoreceptor space (IPS) to obtain soluble components of the extracellular matrix (ECM). Using this method, we have determined that the major soluble coustituent of monkey IPS is a 146,000 Mr glycoprotein, which binds [3H]retinol, sediments on sucrose gradients at 7S and has an Rf of 0.42 on native gel electrophoresis. Using size‐exclusion high performance liquid chromatography, the apparent molecular weight of the native protein was calculated to be 250,000 daltons. In contrast to previous studies, no 15,000‐dalton cellular retinol‐binding protein (CRBP) or 33,000‐dalton cellular retinaldehydebinding protein (CRALBP) was observed in the IPS wash, indicating that these proteins are probably not involved in retinol transport between retina and pigment epithelium (PE). In the supernatant fraction of retinal homogenates that contains soluble intracellular proteins as well as extracellular constituents, the 146,000 Mr protein was closely associated with a 93,000 Mr protein that could be separated on SDS‐gel electrophoresis; the 93,000 Mr protein was not found in the IPS wash. The 146,000 Mr interphotoreceptor retinol‐binding protein (IRBP) may function in extracellular retinol transport in the IPS.
Uridine kinase molecular species and uridine uptake in some variants of rat hepatomas
Authors: Fulchignoni‐Lataud Marie‐Claude , Roux Jeanne M. 
Published: February 2005

AbstractIn a family of clonal lines derived from the Reuber H 35 rat hepatoma, four electrophoretically distinct molecular forms of uridine kinase (UK I, II, III, and IV) have been characterized. They are the same as those found in foetal rat liver. Different UK profiles occur in these cell lines, and no strict correlation could be established between the state of differentiation of the cells and the form of UK expressed. A clone of somatic hybrid cells between line p4 (form 1 only) and Fu5‐5 (forms II, III, and IV) that does not express form I indicates that p4 cells may lack a factor controlling the polymerization of form I. This variety of clonal cell lines was used to study the uptake and phosphorylation of labeled uridine. The results suggest a relationship between the UK form present and the rate uridine phosphorylation by the intact cells.
Secretory activity of hamster tracheal explants and isolated tracheal epithelial cells and the effects of cystic fibrosis serum
Authors: Rudick Victoria L. , Wooten Marie W. , Rudick Michael J. 
Published: February 2005

AbstractSerum from cystic fibrosis patients has been shown by scanning electron microscopy to cause release of large quantities of mucus from the cultured tracheal rings of 3–4‐month‐old male Golden Syrian hamsters. In order to study this phenomenon on single cells, an epithelial (HTE) cell culture has been established from the hamster tracheal rings using the cell rescue method of Goldman and Baseman (1980a, In Vitro, 16:313). The cells were demonstrated to be epithelial by histochemical staining and immunofluorescent detection of laminin. Proteins secreted by HTE cells were partially characterized and shown to consist, at least in part, of acidic glycoproteins. The proteins were precipitated by addition of buffered alcian blue (AB) to the cell‐free medium under conditions in which all of a polyanionic protein [3H]‐labeled mucin, was precipitated without carrier. [14C] galactosamine‐labeled AB precipitate was β‐eliminated and, after neutralization and centrifugation, the material in the supernatant was sized by chromatography on a calibrated Bio‐Gel P2 column. The label eluted with a molecular weight close to a disaccharide. HTE cells pulse‐‐labeled for 1.0 hr with [3H] leucine or [14C] galactosamine secreted increasing amounts of labeled glycoprotein during the chase. Sodium dodecylsulfate‐polyacrylamide gel electrophoresis and fluorography of labeled AB precipitates revealed three major bands, two with molecular weights greater than 100 kd. Secretion was stimulated by retinoate (50% increase), but not by retinol. Exposure of HTE cells to whole sera from cystic fibrosis patients resulted in heightened secretion rates as compared to results obtained with normal sera. Heterozygote sera produced secretion rates intermediate between the two extremes.
Human megakaryocytic progenitors (CFU‐M) assayed in methylcellulose: Physical characteristics and requirements for growth
Authors: Kimura Hideo , Burstein Samuel A. , Thorning David , Powell Jerry S. , Harker Laurence A. , Fialkow Philip J. , Adamson John W. 
Published: February 2005

AbstractThe basic culture requirements and several physical characteristics were defined for megakaryocytic colony‐forming cells (CFU‐M) from normal human marrow growing in methylcellulose. Ficoll‐hypaque separated mononuclear cells from human, marrow gave rise to megakaryocytic colonies in the presence of normal human plasma and phytohemagglutinin‐stimulated leukocyte‐conditioned medium (PHA‐LCM). Their identity as megakaryocytic colonies was confirmed by immunofluorescence staining with a monoclonal antibody to human factor VIII antigen and by electron microscopy of individually harvested colonies. Demonstration of the single‐cell origin of the colonies was provided by analysis of the glucose‐6‐phosphate dehydrogenase (G‐6‐PD) enzyme type of individually harvested colonies grown from a G‐6‐PD heterozygote. The colonies grew best in heparinized or citrated plasma as opposed to serum. Detailed studies suggested that platelet‐release products were responsible for this difference. Tritiated thymidine suicide studies showed that the percentage of CFU‐M in DNA synthesis was 23 ± 8% (n = 10). The modal velocity sedimentation rate of CFU‐M was 4.9 ± 0.6 mm/hr (n = 4) while that of concurrently studied granulocyte/macrophage colony‐forming cells (CFU‐GM) was 5.7 ± 0.5 mm/hr. Examination of the PHA‐LCM dose‐response characteristics suggested the presence in the conditioned medium of an inhibitor to megakaryocyte colony growth which was partially removed by chromatography of the medium on Sephadex G‐100. The resulting conditioned medium increased the cloning efficiency for CFU‐M compared with that with crude PHA‐LCM (15.3 ± 7.0 and 8.2 ± 5.3/105 marrow cells, respectively).
A new assay for factors that regulate the synthesis of granulocyte differentiation proteins in vitro
Authors: Evans Warren H. , Wilson Shirley M. , Alvarez Vernon 
Published: February 2005

AbstractMorphological and molecular aspects of granulocyte differentiation can be studied concomitantly using liquid cultures of immature granulocytes in conjunction with a newly developed high‐performance liquid chromatographic (HPLC) assay for differentiation proteins. Immature granulocytes, isolated from guinea pig bone marrow by Ficoll density centrifugation, were placed in liquid cultures and incubated for periods up to 1 week. In the presence of 10% dialyzed, normal guinea pig serum, these cells were almost all converted to mature granulocytes, whereas at serum concentrations below 1% mostly macrophages were formed. Cell multiplication does not appear to be necessary for granulocyte maturation in this culture system. The data also show that morphological maturation in vitro is accompanied by the formation of all the major membrane and secondary granule differentiation proteins detected by the HPLC assay in extracts of mature granulocytes formed in vivo. The techniques described here should facilitate the isolation and purification of the factors in normal serum that control the induction of synthesis of these differentiation markers.
Localisation of Alanine uptake by cultured renal epithelial cells (LLC‐PK1) to the basolateral membrane
Authors: Sepulveda Francisco V. , Pearson Jeremy D. 
Published: February 2005

AbstractAlanine uptake by LLC‐PK1 cells has previously been demonstrated to be almost exclusively sodium dependent. We here confirm that when the cells are grown on an impermeable substratum there is a marked fall in uptake as confluence is reached. By applying an autoradiographic technique to visualize transported alanine, it is clear, however, that even in subconfluent cultures there is marked cellular inhomogeneity with regard to uptake, which takes place predominantly in those cells at the periphery of growing islands and not those at the interior. In contrast, when cells are grown on permeable substrata, a uniform distribution of silver grains is found. In two other types of experiment, we found that when confluent cell monolayers on an impermeable support were treated briefly with a chelating agent or suspended by mechanical treatment, there was a marked increase per cell in sodium‐dependent alanine uptake and in ouabain‐sensitive potassium uptake. We conclude that the apparent fall in alanine uptake as cells reach confluence on an impermeable support is due to masking of transport sites, which are predominantly, if not exclusively, located at the basolateral membrane.
Coordinate regulation of glycolysis by hypoxia in mammalian cells
Authors: Robin Eugene D. , Murphy Brian J. , Theodore James 
Published: February 2005

AbstractThe impact of hypoxic exposure on the activities of all 11 glycolytic enzymes was studied in cell culture into mammalian cells—mouse lung macrophages and L8 rat skeletal muscle cells. During hypoxic exposure, the measured activity of all glycolytic enzymes increased, establishing coordinate regulation. Three nonglycolytic cytoplasmic enzymes showed no change in activity under the same conditions, suggesting a specific mechanism. Hypoxia appears to increase the activities of all glycolytic enzymes whether rate‐limiting or not, presumably increasing adenosine triphosphate availability despite decreased O2 supply.
Aluminum lons stimulate DNA synthesis in quiescent cultures of Swiss 3T3 and 3T6 cells
Authors: Smith Jeffrey Bingham 
Published: February 2005

AbstractMicromolar concentrations of Al3+ are shown to be strongly mitogenic for quiescent cultures of Swiss 3T3 and 3T6 cells. Al3+ caused a striking shift in the dose‐response curve for the effect of fetal bovine serum on 3H‐thymidine incorporation. In the absence of serum the mitogenic effect of aluminum was greatly potentiated by insulin or cholera toxin, but not epidermal growth factor or 12–0‐tetradecanoyl‐phorbol‐13‐acetate. The stimulation of DNA synthesis was maximal by 15–20 μMM Al3+. Al3+ at 100 μMM had no inhibitory effect on DNA synthesis. Al3+ had no significant effect on cellular cyclic adenosine monophosphate in the presence or absence of insulin or an inhibitor of cyclic nucleotide phosphodiesterases.
Uptake of epidermal growth factor into a lysosomal enzyme‐deficient organelle: Correlation with cell's mitogenic response and evidence for ubiquitous existence in fibroblasts
Authors: Miskimins W. Keith , Shimizu Nobuyoshi 
Published: February 2005

AbstractThe internalization process following cell surface receptor binding by epidermal growth factor (EGF) was studied. It was found that EGF is taken up into a dense, membranous organelle. This organelle is deficient in lysosomal enzyme activity and is biochemically dissimilar to the major lysosomal fraction. The uptake of EGF by this organelle was demonstrated in three different cell types representing three different species. Each of these cell types is highly responsive to the mitogenic action of EGF. These results indicate that EGF is endocytosed and delivered to a dense, possibly nonlysosomal, organelle which is ubiquitous in fibroblasts. Furthermore, we demonstrate a close, positive correlation between EGF uptake into this fraction and the ability of cells to respond to the mitogen. A negative relationship between uptake into the subcellular fraction containing lysosomal enzymes and EGF‐stimulated DNA synthesis was observed. Using numerous incubation conditions no exceptions to the correlation between EFG uptake into the lysosomal enzymedeficient fraction and EGF‐induced DNA synthesis were observed. These results suggest a role for this dense organelle in the production of a mitogenic signal.
Oxygen dependence of cellular metabolism: The effect of O2 tension on gluconeogenesis and urea synthesis in isolated rat hepatocytes
Authors: Kashiwagura Tadashi , Wilson David F. , Erecińska Maria 
Published: February 2005

AbstractThe dependencies of gluconeogenesis and urea synthesis on oxygen concentration were measured in suspensions of isolated rat hepatocytes and compared with the O2 dependence of cellular energy supply (reduction of cytochrome c, respiratory rate, mitochondrial [NAD+]/[NADH], lactate production, and [ATP]/[ADP][Pi]). As the oxygen concentration was decreased, production of both glucose and urea declined; the changes were observable at 20 μM oxygen and below, with the apparent Km values for both processes of near 5 μM. The similar dependence of gluconeogenesis and urea synthesis on oxygen concentration indicates that the two pathways have equal access to the cellular ATP supply, i.e., there is no evidence that either pathway is preferentially turned off to spare ATP for the other. The cellular energy state had an oxygen dependence similar to that of glucose and urea synthesis. It is suggested that the behavior of gluconeogenesis and urea production is a reflection of homeostatic regulation of cellular metabolism which is designed to respond to changes in [ATP]/[ADP][Pi].