bluuebunny/crossref_metadata_2025_split huggingface dataset:
Depolarization of the membrane potential decreases the ATP‐induced influx of extracellular Ca2+ and the refilling of intracellular Ca2+ stores in rat thyroid FRTL‐5 cells
Authors: Törnquist Kid 
Published: February 2005

AbstractThe aim of the present study was to investigate the effect of membrane depolarization on ATP‐induced changes in intracellular Ca2+ ([Ca2+],) and the refilling of intracellular Ca2+ stores in thyroid follicular FRTL‐5 cells. Depolarizing the cells with 50 mM K+, an amount sufficient to almost totally depolarize the cells as determined by bisoxonol, significantly reduced the ATP‐induced uptake of 45 Ca2+. This effect was not dependent on an enhanced efflux of Ca2+, as no difference in the ATP‐induced efflux of45Ca2+ was obtained between control cells and depolarized cells. The ATP‐induced transient increase in [Ca2+]Į in Fura‐2 loaded cells was not altered by depolarization, whereas the ATP‐induced plateau in [Ca2+]Į was decreased compared with control cells. Furthermore, in cells stimulated with ATP in a Ca2+‐free buffer, readdition of Ca2+ after the termination of the ATP response induced a decreased response in [Ca2+]Į in depolarized cells. Refilling of intracellular Ca2+ stores was investigated by tirst stimulating the cells with noradrenalin (NA). The effect of NA was then terminated with prazosin, and the cells restimulated with ATP. In cells depolarized with high K+ the response to ATP was decreased compared with that seen in control cells. The results thus suggest that both the ATP‐induced influx of extracellular Ca2+ and the refilling of intracellular Ca2+ stores is decreased in depolarized FRTL‐5 cells.
Decreased transforming growth factor‐(β) response and binding in insulin‐independent teratoma‐derived cell lines with increased tumorigenic properties
Authors: Serrero Ginette , Zhou Jian , Mills Dianne , LePak Nancy 
Published: February 2005

AbstractThe mouse C3H teratoma‐derived cell line 1246 is an adipogenic cell line which stringently requires insulin to proliferate and differentiate in defined medium. From this cell line an insulin‐independent cell line celled 1246‐3A was isolated. It was found that, in contrast to 1246 cells, 1246‐3A cells had lost the ability to differentiate and became tumorigenic when injected at a density of 106 cells/mouse into syngeneic host C3H mice. In addition, they produce in their culture medium transforming growth factor (α)‐ and (β)‐like polypeptides which stimulate their proliferation. Highly tumorigenic insulin‐independent cell lines able to give rise to tumor when injected at a density of 104 cells/mouse were isolated by using. an in vitro‐in vivo shuttle technique. The highly tumorigenic cell lines have lost the response to TGF‐(β)1, The binding of TGF‐(β)1, to the nontumorigenic parent cell line or to cells displaying increased tumorigenic properties was investigated. The data presented here indicate that the increased tumorigenicity is accompanied by a progressive decrease of specific binding of TGF‐(β)1, to the cells. However, the decreased number of cell surface TGF‐(β)1, binding sites in the highly tumorigenic cells did not correlate with an increase in the secretion of TGF‐(β) protein by the tumorigenic cells, as all of TGF‐(β) produced by the cells was in a latent form. Affinity cross‐linking experiments indicated that the 1246 cell line displayed several TGF‐(β) cross‐linked molecular species (MW 140, 92, and 70 kDa). Increase of tumorigenicity was accompanied by a marked decrease in the intensity of the cross‐linked bands, particularly of the 92 and 70 kDa species.
The effects of chronic exposure to supraphysiological concentrations of 3,5,3′ triiodo‐L‐thyronine (T3) on cultured GC cells
Authors: Reynolds Anne Marie , Surks Martin I. , Shapiro Lawrence E. 
Published: February 2005

AbstractWe have characterized the effects of supraphysiological concentrations of T3 on GC cells, a cultured cell line in which physiologic concentrations of T3 regulate cell growth, protein content, and growth hormone (GH) production. GC cells were exposed to 3 times (1.0 nM) and 80 times (25.0 nM) the physiologic concentration of T3 (0.3 nM) for either 4 d or for greater than 3 months. Both short and prolonged exposure to supranormal T3 concentrations supported maximal cell growth rate and induced significant increases in total protein (P < 0.025) and GH production (P < 0.01) per celi when compared to measurements in control GC cells. In addition, exposure to 1.0 nM and 25.0 nM T3 for greater than 3 months enhanced the toxicity of heat shock in a manner similar to previously described effects on GC cells due to T3 exposure of shorter duration. Thus, initial responses to raised T3 concentrations in cultured GC cells persisted without alteration when hormone exposure was prolonged for greater than 3 months.
Effects of growth factors, hormones, bacterial lipopolysaccharides, and lipotechoic acids on the clonal growth of normal ureteral epithelial cells in serum‐free culture
Authors: Wille John J. , Park Jong , Elgavish Ada 
Published: February 2005

AbstractIn vitro tissue culture techniques were employed to study the effects of bacterial endotoxins on the growth of normal epithelial cells from the human ureter (NHU). Primary cultures of NHU cells were initiated from explant outgrowth cultures of human ureteral tissue and cultured on collagen gel in F‐12* medium containing 1% fetal calf serum (FCS). Optimal clonal growth of secondary cultures of NHU cells seeded at relatively low seeding cell densities, directly on plastic dishes, was achieved in F‐12* medium containing bovine pituitary extract (0.5% BPE) and 0.05% BSA. Results indicated that insulin in the F‐12* medium could be replaced by three orders of magnitude less IGF‐1. Further clonal growth experiments demonstrated that PGE1 is growth stimulatory and can replace BPE as a growth factor requirement. This finding was in agreement with the fact that BPE growth requirement could be replaced by cholera toxin or dibutyryl cAMP. These results suggested that both BPE and cholera toxin operated by activation of a cAMP‐dependent mitogenic pathway. Seven gram‐negative bacterial lipopolysaccharides (LPS) and three gram‐positive bacterial lipotechoic acids (LT) were tested for their effects on NHU clonal growth. Three out of the five LPS derived from Escherichia coli (strains 055:B5, 0128:B12, and 0127:B8), LPS from Klebsiella pneumoniae, and LPS from Pseudomonas aeruginosa all showed significant growth inhibitory effects at minimally effective doses ranging from 5 to 25 μg/ml. LPS derived from E. coli strain (0111:B4) had no growth effects at the highest concentration tested (100 μg/ml). In contrast, LT derived from Streptococcus pyogenes, S. faecalis, Staphylococcus aureas, and Bacillus subtilis all markedly enhanced clonal growth at concentrations ranging from 1 μg/ml < [LT] < 50 μg/ml. LT from Strep. pyogenes was inhibitory to clonal growth at 100 μg/ml. The growth inhibitory effects of LPS were shown to be sensitive to the presence of hydrocortisone in the growth medium, indicating that LPS effects on growth are mediated via the arachidonic acid cascade. We speculate that these results indicate a link between the susceptibility of uroepithelial tissue to the pathogenic microflora seen in urinary tract diseases and the differential sensitivity of proliferation‐competent uroepithelial cells to growth inhibition by LPS produced by gram‐negative bacteria. However, further studies with uropathogenic serotypes will be necessary to corroborate this possibility. The growth‐stimulating activity of LTs produced by gram‐positive bacteria may be due to their ability to bind to cell‐associated fibronectin and to activate the fibronectin receptor as part of ligand receptor–induced mitogenic transmembrane signalling pathway.
Low‐amplitude, low‐frequency electric field‐stimulated bone cell proliferation may in part be mediated by increased IGF‐II release
Authors: Fitzsimmons Robert J. , Strong Donna D. , Mohan Subburaman , Baylink David J. 
Published: February 2005

AbstractWe have developed an in vitro model incorporating a low‐amplitude (10−7 V/cm), low frequency (f < 100 Hz), capacitively coupled electric field in order to study the mechanism through which an electric field may increase bone cell proliferation. Utilizing this model we have previously shown that electric field‐stimulated bone cell proliferation was dependent on release of mitogen activity into the culture medium from exposed cells. The current studies were intended to characterize this mitogen activity. In these studies we found that electric field‐stimulated human bone cell proliferation was associated with increased IGF‐II mRNA accumulation and IGF‐II secretion suggesting that IGF‐II may in part mediate the increase in bone cell proliferation following electric field exposure.
Density‐dependent regulation of cell surface γ‐glutamyl transpeptidase in cultured glial cells
Authors: Morgenstern Kurt , Hanson‐Painton Olivia , Wang Bao‐Le , De Bault Lawrence 
Published: February 2005

AbstractA decline in cell surface γ‐glutamyl transpeptidase specific activity was previously observed to be concomitant with C6 glial cell proliferation. To elucidate the underlying factor(s) mediating γ‐glutamyl transpeptidase down‐regulation, the effects of C6 cell density and culture conditions on cell surface transpeptidase activity levels were investigated. After 24 h of culture, the transpeptidase specific activities were inversely related to the initial plating densities. The lower‐density cultures showed an induction within 24 h of plating. As the cultures proliferated, the specific transpeptidase activities declined to a common low level at postconfluency. The γ‐glutamyl transpeptidase down‐regulation was unrelated to cell growth rate and was most pronounced during logarithmic proliferation. Induction and down‐regulation of γ‐glutamyl transpeptidase activity at low cell densities were not a result of trypsinization. Supplementation of low‐density cultures with conditioned medium, use of matrix‐coated wells, or periodic replacement of growth media to prevent conditioning had minor effects on the decline of cell surface activity. Kinetic analysis showed that the Michaelis constants and the reaction mechanism were unaltered by cell density, indicating that downregulation was not due to allosteric factors or an alteration in enzyme character. A reduction in the maximal velocity of cell surface transpeptidation at higher cell densities suggested that γ‐glutamyl transpeptidase down‐regulation is related to the concentration of enzyme at the cell surface. Immunocytochemical localization of γ‐glutamyl transpeptidase demonstrated that γ‐glutamyl transpeptidase antigen levels decrease as C6 cell density increases. These results led us to propose that cell‐cell contact stimulates the disappearance of γ‐glutamyl transpeptidase from the surface of cultured C6 glial cells.
Derivatized dextrans mimic heparin as stabilizers, potentiators, and protectors of acidic or basic FGF
Authors: Tardieu Michele , Gamby Chantal , Avramoglou Thierry , Jozefonvicz Jacqueline , Barritault Denis 
Published: February 2005

AbstractAcidic and basic fibroblast growth factors (aFGF and bFGF) belong to a family of structurally related polypeptides characterized by a high affinity for heparin. a and bFGF display mitogenic activity for many cell types. Biological activity is strongly potentiated by heparin which stabilizes their molecular conformation by preventing physicochemical or enzymatic degradation.In our previous study we have shown that a water‐soluble derivatized dextran named DDE, containing 82.2% methyl carboxylic acid groups, 6.1% benzyl‐amide, and 5.6% sulfonate with a specific anticoagulant activity equivalent to heparin of 0.5 IU/mg could potentiate the mitogenic activity of aFGF on CCL39 cells. Optimal concentrations for maximal potentiation of 400 μg/ml and 20 μg/ml were obtained respectively for DDE and heparin. In the present report, we have uncovered the fact that several carboxymethyl benzylamide sulfonate dextrans differing in degree and positioning of the substituent groups can mimic heparin in regard to the protection, stabilization, and potentiating effects with aFGF or bFGF.Our data establishes that the dextran derivatives studied can act as potentiating agents for FGFs. Native dextran (DDA) had no effect. Dextran derivatives can also protect aFGF and bFGF from heat as well as from pH denaturation, and against trypsic and chymotrypsic degradation. The dextran derivative DDI (82% methylcarboxylic acid, 23% benzylamide, 13% sulfonate) was studied in greater detail and exhibited a greater protection for bFGF and a lesser protecting effect for aFGF than heparin. Derivatized dextrans which have very weak anticoagulant activity are of great interest as alternatives to heparin for use as stabilizers, potentiators, protectants, and slow‐release matrices for FGFs in pharmaceutical formulations.
Regulation of prostaglandin H synthase activity in dog urothelial cells
Authors: Zenser Terry V. , Thomas Dori J. , Jacob Ammini K. , Davis Bernard B. 
Published: February 2005

AbstractTPA regulation of prostaglandin H synthase activity in primary and subcultured dog urothelial cells was investigated. Previous studies have demonstrated an early (0–2 hr) increase in PGE2 synthesis mediated by TPA which is dependent upon release of endogenous arachidonic acid by a phospholipase‐mediated pathway. In this study, prostaglandin H synthase activity was assessed directly with microsomes and indirectly after addition of exogenous arachidonic acid at a maximum effective concentration (100 μM) to media. PGE2 synthesis, measured by radioimmunoassay, served as an index of prostaglandin H synthase activity. After a 24‐hr incubation with 0.1 μM TPA or 1.0 μM A23187, arachidonic acid elicited significantly more PGE2, synthesis in agonist‐treated cells than it did in control cells in primary culture. Microsomes from 24‐hr TPA‐treated cells exhibited significantly more prostaglandin H synthase activity than did those from control cells. In addition, the PGE2 content of overnight media was approximately 10‐fold greater in TPA‐treated cells than in control cells. The late (24 hr) response was more sensitive to lower concentrations of TPA than was the earlier (0–2 hr) response. TPA at 0.1 μM was a maximum effective dose for both responses. The 24‐hr response was blocked by cycloheximide and staurosporine, inhibitors of protein synthesis and protein kinase C, respectively. Pretreatment of cells with aspirin, an irreversible inhibitor of prostaglandin H synthase, prior to addition of TPA did not prevent the late TPA‐mediated increase in PGE2 synthesis. Subcultured cells exhibited both an early and a late TPA response. Only the early response was inhibited by aspirin pretreatment. Results suggest that the late response with TPA is caused by de novo synthesis of prostaglandin H synthase. Thus, primary and subcultured dog urothelial cells possess two distinct mechanisms for regulating signal transduction by arachidonic acid metabolism. This study provides a basis for assessing these mechanisms of signal transduction in urothelial cell lines and transformed cells.
Transforming growth factor β1 is a powerful modulator of platelet‐derived growth factor action in vascular smooth muscle cells
Authors: Janat M. Fouad , Liau Gene 
Published: February 2005

AbstractWe have studied the effect of transforming growth factor β1 (TGF‐β1) on vascular smooth muscle cell (SMC) mitogenesis and expression of thrombospondin and other growth related genes. We found that TGF‐β1 treatment of vascular SMC induced a prolonged increase in steady‐state mRNA levels of thrombospondin as well as α1 (lV) collagen. The increase began at approximately 2 h, peaked by 24 h, and remained considerably elevated 48 h after growth factor addition. There was a corresponding increase in thrombospondin protein as well as increased expression of several other secreted polypeptides. The increase in thrombospondin contrasted sharply with that observed for platelet‐derived growth factor (PDGF) which induced a rapid and transient increase in thrombospondin mRNA level. Although TGF‐β1 was able to directly enhance expression of thrombospondin as well as the growth‐related genes c‐fos and c‐myc, and induced c‐fos expression with identical kinetics as PDGF, it was unable to elicit [3H]thymidine incorporation into DNA in three independent smooth muscle cell strains. However, TGF‐β1 was able to strongly increase the mitogenic response of SMC to PDGF. Addition of both TGF‐β1 and PDGF to SMC also caused a synergistic increase in the expression of thrombospondin as well as c‐myc. Interestingly, in one other smooth muscle cell strain, a weak and delayed mitogenic response to TGF‐β1 alone was observed. Our results strongly suggest that induction of throm‐bospondin expression by TGF‐β1 and by PDGF occurs by distinct mechanisms. In addition, that TGF‐β1 can enhance PDGF‐induced mitogenesis may be due to the ability of TGF‐β1 to directly induce the expression of thrombospondin, c‐fos, c‐myc, and the PDGF β‐receptor.
Parathyroid hormone stimulates protein kinase C but not adenylate cyclase in mouse epidermal keratinocytes
Authors: Whitfield James F. , Chakravarthy Balu R. , Durkin Jon P. , Isaacs Richard J. , Jouishomme Hervé , Sikorska Marianna , Williams Ross E. , Rixon Raymond H. 
Published: February 2005

AbstractIntact human parathyroid hormone, hPTH [1–84], and the hPTH [1–34] fragment stimulated membrane‐associated protein kinase C (PKC) activity in immortalized (but still differentiation‐competent) murine BALB/MK‐2 skin keratinocytes. Unexpectedly, the hormone and its fragment did not stimulate adenylate cyclase. The failure of PTH to stimulate adenylate cyclase activity was not due to the lack of a functioning receptor‐cyclase coupling mechanism because the cells were stimulated to synthesize cyclic adenosine monophosphate (cyclic AMP) by the β‐adrenergic drug isoproterenol. Thus, skin keratinocytes seem to have an unconventional PTH receptor that is coupled to a PKC‐activating mechanism but not to adenylate cyclase. These observations suggest that normal and neoplastic skin keratinocytes respond to the PTH‐related peptide that they make and secrete.
Differential expression of asialoglycoprotein receptor subunits in the endocytic compartment during liver regeneration
Authors: Enrich Carlos , Verges Marcel , Evans W. Howard 
Published: February 2005

AbstractAsialoglycoprotein receptors, responsible for the removal of circulating asialogly‐coproteins by the liver, are located in at least two different membrane locations in hepatocytes. Receptors on the cell surface account only for a minor proportion (20–36%), for the majority of receptors in the liver are located intracellularly, mainly in the endocytic membrane networks. An understanding of the basis of receptor distribution and the underlying trafficking of receptors between the hepatocyte's polarised cell surface and the endocytic compartment would be aided if biochemical differences between the receptors in these pools were established. We now show, using three antibodies that recognise the receptor subunits in rat liver (RHL‐1, RHL‐2 and RHL‐3), that the asialoglycoprotein receptors located in the plasma membrane domains and the endocytic compartment differ in oligomeric composition, sialic acid content, and solubility in Triton X‐114 using two‐phase systems. It is well established that the expression of the asialoglycoprotein receptor is down‐regulated in livers regenerating after a partial hepatectomy. We demonstrate that the levels of the receptor subtype that is located mainly in the endocytic compartment (RHL‐1, 42 kDa) was elevated in regenerating liver by agents that regulate cAMP production, whereas the levels of the other receptor subtypes remained unchanged. The asialoglycoprotein receptor subtypes that are present in different subcellular locations are thus regulated independently.
Mitogenic, melanogenic, and cAMP responses of cultured neonatal human melanocytes to commonly used mitogens
Authors: Abdel‐Malek Zalfa , Swope Viki B. , Pallas James , Krug Kimberly , Nordlund James J. 
Published: February 2005

AbstractThe following studies have been undertaken to compare and correlate the effects of 12‐0‐tetradecanoylphorbol acetate (TPA), basic fibroblast growth factor (bFGF), cholera toxin (CT), and isobutyl methylxanthine (IBMX) on neonatal human melanocyte (NHM) proliferation, tyrosinase activity, and cyclic adenosine monophosphate (cAMP) concentration. NHM proliferated at a maximal rate in medium containing 8 nM TPA, 200 ng/ml CT, and 10−4 M IBMX. TPA alone did not result in optimal melanocyte proliferation, and, as previously shown, its mitogenic effect was greatly enhanced by the addition of CT and IBMX individually or concomitantly. Human recombinant (hr) bFGF could replace TPA in the NHM growth medium. Maximal proliferation was achieved using 3 ng/ml hrbFGF, 20 ng/ml CT, and 10−4 M IBMX. The mitogenic effect of 1.2 ng/ml hrbFGF was potentiated in the concomitant but not individual presence of CT and IBMX. TPA alone in the absence of CT and IBMX caused a dose‐dependent stimulation of tyrosinase activity. Maximal tyrosinase activity was obtained in the presence of 0.8 nM TPA, 20 ng/ml CT, and 10−4 M IBMX. Unlike TPA, hrbFGF alone resulted in inhibition of tyrosinase activity. In the presence of hrbFGF, tyrosinase activity was potentiated by CT and IBMX, but not by CT alone. Neither TPA nor hrbFGF alone could increase intracellular cAMP levels. The effects of CT and IBMX on intracellular cAMP concentration were enhanced to a greater extent by TPA than by hrbFGF. Under our experimental conditions, in the presence of hrbFGF, CT but not IBMX resulted in a dose‐dependent increase in cAMP concentration. Further studies on NHM will be aimed at determining the exact role of protein kinase C (PKC) in regulating proliferation and melanogenesis and the mechanism(s) activated by hrbFGF.
Expression, synthesis, and phosphorylation of HSP28 family during development and decay of thermotolerance in CHO plateau‐phase cells
Authors: Lee Yong J. , Hou Zi‐Zheng , Curetty Lindali , Corry Peter M. 
Published: February 2005

AbstractWe investigated a correlation between development of thermotolerance and expression, synthesis, or phosphorylation of HSP28 family in CHO plateau phase cells. After heating at 45.5°C for 10 min, thermotolerance developed rapidly and reached its maximum 12–18 hr after heat shock. This acquired thermal resistance was maintained for 72 hr and then gradually decayed. In parallel, the levels of three 28 kDa heat shock proteins, HSP28a along with its two phosphorylated isoforms (HSP28b, c), increased and reached their maximum 24–48 hr after heat shock. The levels of these polypeptides, except HSP28c, remained elevated for 72 hr and then decreased. The level of HSP28 mRNA increased rapidly and reached its maximum 12 hr after heat shock. However, unlike thermotolerance and the levels of HSP28 family proteins, the level of HSP28 mRNA decreased rapidly within 72 hr. These results demonstrate a correlation between the amount of intracellular HSP28 family proteins and development and decay of thermotolerance.