bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alteration of the Cloudman melanoma cell cycle by prostaglandins E1 and E2 determined by using a 5‐bromo‐2′‐deoxyuridine method of DNA analysis
Authors: Abdel‐Malek Zalfa A. , Swope Viki B. , Trinkle Linda S. , Ferroni Elisabeth N. , Boissy Raymond E. , Nordlund James J. 
Published: February 2005

AbstractProstaglandins (PGs) E1 and E2 stimulate tyrosinase activity and suppress the proliferation of Cloudman S91 melanoma cells by altering their progression through the cell cycle. Prostaglandin E1 and PGE2 have prolonged or residual effects on melanoma cells. Cells treated for 5 or 24 hours with 10 μg/ml PGE2 demonstrated decreased proliferation and increased tyrosinase activity for 48 hours after removal of the PGs. The effects of PGs on the cell cycle were investigated by determining total DNA content in cells stained with propidium iodide (Pl) and analyzed by a fluorescence activated cell sorter (FACS). Prostaglandin E1 blocked cells in G2 phase after 5 hours of treatment, corresponding to when inhibition of proliferation was first evident. Similarly, after 9 hours of treatment with PGE2, more cells were in late S, early G2 phase and less in G1 than their control counterparts. Also, melanoma cells were pulse‐labeled with 5‐bromo‐2′‐deoxyuridine (BrdUrd) prior to or at the end of PG treatment and then stained with a fluoresceinated monoclonal antibody to BrdUrd, and with Pl. This allows one to observe how BrdUrd‐labeled S‐phase cells cycle with time. Both PGE1 and PGE2 inhibit proliferation by blocking cells in G2 phase of the cell cycle. The PG‐induced block in G2 may be required by melanoma cells to synthesize mRNA and proteins that are essential for stimulation of tyrosinase activity. Ultrastructurally, only a subpopulation of the cells treated with PGE1 or PGE2 contained more mature melanosomes than control cells.
Uptake of copper by mouse hepatocytes
Authors: McArdle Harry J. , Gross Sharon M. , Danks David M. 
Published: February 2005

AbstractThis study has investigated the uptake of copper by mouse hepatocytes. The cells gave similar results whether they were used right after isolation or maintained overnight on collagen‐coated dishes. Uptake from cells in suspension followed two phases: an initial rapid binding followed by a linear uptake phase. The two phases were not so easily distinguishable in cells grown in culture where uptake was linear over the first hour. The uptake showed saturation but may not have followed simple kinetics. Histidine stimulated uptake in a concentration‐dependent manner, as did some other amino acids, but copper had very little effect on histidine uptake. The process was not dependent on intracellular adenosine triphosphate (ATP), since inhibitors that substantially reduced ATP levels inside the cell did not alter copper uptake. The inhibitors, however, blocked histidine uptake to varying degrees, suggesting that copper and histidine are taken up by different pathways. The uptake was reduced markedly by N‐ethyl maleimide, and preincubation of the cells with “Pronase” resulted in a decrease of uptake. A model for the uptake of copper by hepatocytes that incorporates the data presented in this paper with that produced by earlier workers is suggested.
Superoxide as a signal for increase in intracellular pH
Authors: Shibanuma Motoko , Kuroki Toshio , Nose Kiyoshi 
Published: February 2005

AbstractWe examined the role of superoxide in the increase in intracellular pH (pHi) of human histiocytic leukemia U937 cells treated with 4β‐phorbol‐12,13‐didecanoate (4β‐PDD) or serum. 4β‐PDD or serum induced a rapid increase in pHi, and antioxidants such as superoxide dismutase (SOD), vitamin E, and butylated hydroxyanisole (BHA) were found to inhibit the amiloride‐sensitive increase in pHi induced by 4β‐PDD. SOD inhibited the increase in pHi caused by serum, and essentially the same was found in concanavalin A‐stimulated mouse thymocytes. Also, a superoxide‐generating system, xanthine‐xanthine oxidase (X‐XOD), increased pHi of U937 cells as much as 4β‐PDD or serum. From these findings, it appears that superoxide is the basis for the modulation of pHi.
Concanavalin A‐induced impairment of fibroblast spreading on laminin but not on fibronectin
Authors: Codogno Patrice , Doyennette‐Moyne Marie‐Agnès , Botti Joëlle , Aubery Michèle 
Published: February 2005

AbstractThe effect of concanavalin A (Con A) on the adhesion of 8‐day‐old chick embryo fibroblasts (CEFs) to fibronectin (FN) and laminin (LM) was studied. Con A was shown to inhibit the spreading of CEF on a LM substrate. In contrast, no inhibition of CEF spreading on the FN substrate could be detected when the quantity of FN coated varied from 0.5 to 4 pmoles. The effect induced by Con A was specific, since it was abolished by 100 mM α‐methyl‐mannopyranoside. The inhibition of CEF spreading was only observed when the lectin was added during the 20 min following cell plating. In addition, the effect of Con A on CEF spreading on the LM substrate was shown to be dependent upon its presence at the cell surface, since under conditions which accelerate the uptake of the lectin, the effect on cell spreading is no longer detectable. Furthermore, the number of CEFs attached to LM was not modified by the lectin. The molecular weight of the isolated Con A binding sites revealed glycoproteins ranging from 30,000 to 72,000. On the other hand, these Con A binding sites did not interact with LM‐Sepharose. Only a protein with a molecular weight of 68,000 which did not express affinity for Con A bound tightly to the LM‐Sepharose. These data suggested that cell surface Con A binding sites do not interfere with the initial step of CEF adhesion to LM but play a key role during their spreading on this glycoprotein.
Role of IIb‐IIIa‐like glycoproteins in cell‐substratum adhesion of human melanoma cells
Authors: Knudsen Karen A. , Smith Linda , Smith Sena , Karczewski Jerzy , Tuszynski George P. 
Published: February 2005

AbstractThe platelet fibrinogen receptor, glycoprotein complex IIb‐IIIa, was isolated from human platelets by lectin and monoclonal antibody affinity chromatography and a polyclonal antiserum (anti‐IIb‐IIIa) was generated and used to probe for the presence and function of IIb‐IIIa‐like molecules in two adherent human cell lines. Both C32 melanoma cells and W138 fibroblasts expressed a IIb‐IIIa‐like complex on their surface as indicated by immunoprecipitation of detergent extracts of surface radiolabeled cells. When added to cells plated in medium containing 10% serum, the anti‐IIb‐IIIa antiserum perturbed the adhesion of C32 melanoma cells, but not of W138 fibroblasts. In a serum‐free system, anti‐IIb‐IIIa antibodies inhibited attachment and spreading of C32 cells to fibrinogen, vitronectin, and fibronectin adsorbed to glass. Anti‐IIb‐IIIa had no effect on the attachment and spreading of W138 cells to the extracellular matrix proteins, however. Thus, the IIb‐IIIa‐like complex appears to play a predominant role in cell‐substratum adhesion of C32 cells, but not W138 cells, and may result from the fact that, on a protein basis, the C32 melanoma cells express approximately 3 times more complex on their surface than do W138 fibroblasts. The results suggest that the relative abundance of a particular adhesion receptor on the cell surface may govern its importance to cell‐substratum adhesion.
Differential effect of D‐penicillamine on the cell kinetic parameters of various normal and transformed cellular types
Authors: Friteau L. , Jaffray P. , Ronot X. , Adolphe M. 
Published: February 2005

AbstractThe cell‐growth‐inhibitory and phase‐specific effects of D‐penicillamine on cell‐cycle progression were investigated using cell‐proliferation patterns, quantitative cell‐cycle analysis by flow cytometry, and determination of the mitotic index and binucleate cell fraction of normal (rabbit articular chondrocytes, L 809, rabbit fibroblasts) and transformed (HeLa, L 929) cells. D‐penicillamine treatment resulted in an inhibition of growth within a dose range of 5 × 10−4 M to 7.5 × 10−3 M. Examination of DNA by flow cytometric analysis revealed that rabbit articular chondrocytes were preferentially arrested in the G0/1 phase of the cell cycle, whereas the other cell lines were blocked in the G2 + M phase; the increase in the proportion of cells with G2 + M DNA content was partially due to an enhancement of binucleate cells, resulting in a cytokinesis perturbation for HeLa and L 929 cells. These results showed that D‐penicillamine affects cell proliferation through different events according to cell type.
Multiple mechanisms for the inhibition of rRNA synthesis during HL‐60 leukemia cell differentiation
Authors: Schwartz Edward L. , Nilson Laura 
Published: February 2005

AbstractTreatment of HL‐60 human promyelocytic leukemia cells with inducers of granulocytic differentiation produces a depletion of cellular rRNA, with the anthracycline antibiotics aclacinomycin A (ACM) and marcellomycin (MCM) causing a more rapid loss than dimethylsulfoxide (DMSO). This action is associated with a large reduction in RNA synthesis, which precedes any decreases in protein or DNA synthesis, and is specific for rRNA relative to total polyadenylated RNA synthesis. A 70% reduction in rRNA synthesis occurs within 20 minutes of ACM treatment and by 30 hours of DMSO exposure. Relative to the amount of 28S and 18S rRNA in the cells, there is a nearly complete depletion of the amount of 45S rRNA and other large rRNA precursors in contrast, DMSO treatment produces a more coordinated decrease in 18S and 28S rRNA and rRNA precursors. The anthracycline antibiotics inhibited the synthesis of 5′ proximal and 3′ distal regions of the pre‐rRNA transcript, while actinomycin D had a relatively sparing effect on the transcription of 3′ transcripts. These studies demonstrate that different inducers of HL‐60 differentiation have varying sites of action on rRNA synthesis and/or processing, with depletion of cellular rRNA as a common consequence.
Stimulation of receptor‐mediated low density lipoprotein endocytosis in neuraminidase‐treated cultured bovine aortic endothelial cells
Authors: Sprague Eugene A. , Moser Marianne , Edwards Ellen H. , Schwartz Colin J. 
Published: February 2005

AbstractSialic acids, occupying a terminal position in cell surface glycoconjugates, are major contributors to the net negative charge of the vascular endothelial cell surface. As integral membrane glycoproteins, LDL receptors also bear terminal sialic acid residues. Pretreatment of near‐confluent, cultured bovine aortic endothelial cells (BAEC) with neuraminidase (50 mU/ml, 30 min, 37°C) stimulated a significant increase in receptor‐mediated 125l‐LDL internalization and degradation relative to PBS‐treated control cells. Binding studies at 4°C revealed an increased affinity of LDL receptor sites on neuraminidase‐treated cells compared to control BAEC (6.9 vs. 16.2 nM/106 BAEC) without a change in receptor site number. This enhanced LDL endocytosis in neuraminidase‐treated cells was dependent upon the enzymatic activity of the neuraminidase and the removal of sialic acid from the cell surface. Furthermore, enhanced endocytosis due to enzymatic alteration of the 125l‐LDL molecules was excluded. In contrast to BAEC, neuraminidase pretreatment of LDL receptor‐upregulated cultured normal human fibroblasts resulted in an inhibition of 125l‐LDL binding, internalization, and degradation. Specifically, a significant inhibition in 125l‐LDL internalization was observed at 1 hr after neuraminidase treatment, which was associated with a decrease in the number of cell surface LDL receptor sites. Like BAEC, neuraminidase pretreatment of human umbilical vein endothelial cells resulted in enhanced receptor‐mediated 125l‐LDL endocytosis. These results indicate that sialic acid associated with either adjacent endothelial cell surface molecules or the endothelial LDL receptor itself may modulate LDL receptor‐mediated endocytosis and suggest that this regulatory mechanism may be of particular importance to endothelial cells.
Role of plasma membrane and of cytomatrix in maintenance of intracellular to extracellular ion gradients in chicken erythrocytes
Authors: Cameron I. L. , Hunter K. E. , Smith N. K. R. , Hazlewood C. F. , Ludany A. , Kellermayer M. 
Published: February 2005

AbstractUltrastructural observations in combination with electron probe X‐ray microanalysis on detergent (Brij 58) permeabilized (disruption of the plasma membrane) nucleated chicken erythrocytes support the view that a large fraction of cytoplasmic and nuclear K+ is not freely diffusible and that adsorption of K+ on detergent released mobilizable proteins exists within the cell. The data also suggest that the detergent proteins are normally immobilized by a detergent‐resistant cytoskeleton so that they are not immediately free to diffuse from the cell for several minutes after detergent disruption of the plasma membrane.
A novel function of glutamine in cell culture: Utilization of glutamine for the uptake of cystine in human fibroblasts
Authors: Bannai Shiro , Ishii Tetsuro 
Published: February 2005

AbstractTransport and metabolism of glutamine has been investigated in human diploid fibroblasts, IMR‐90. Glutamine was taken up via System ASC (Na+‐dependent amino acid transport system especially reactive with short or polar side chain amino acids). In the routine culture medium the cells contained a large quantity of glutamate; its major source was shown to be glutamine in the medium. Previously we described a transport system that mediates the entrance of cystine in exchange for the exit of glutamate (Bannai, 1986). Since the cystine taken up is reduced to cysteine and the cysteine readily exits to the medium where it is oxidized to cystine, a cystine‐cysteine cycle across the plasma membrane has been postulated. When the cells were cultured in glutamate/glutamine‐free medium, intracellular glutamate decreased, depending on the amount of cystine in the medium; in the absence of cystine, glutamate decreased very slowly. When the cells were cultured in ordinary medium, glutamine in the medium decreased, and glutamate in the medium increased. Both changes were well correlated with cystine concentration in the medium. These results are consistent with the view that the intracellular glutamate, of which the source is glutamine in the medium, is released from the cells into the medium in order to take up cystine and thereby to rotate the cystine‐cysteine cycle. In the routine culture one‐third to one‐half of the total consumption of glautamine seems to be used for the uptake of cystine.
Na+/H+ exchange regulates intracellular pH in a cell clone derived from bovine pigmented ciliary epithelium
Authors: Helbig Horst , Korbmacher Christoph , Stumpff Friederike , Coca‐Prados Miguel , Wiederholt Michael 
Published: February 2005

AbstractThe regulation of intracellular pH (pHi) was monitored in a virus‐transformed cell clone derived from bovine ciliary body exhibiting characteristics of pigmented ciliary epithelium. Data were obtained from confluent monolayers grown on plastic coverslips in nominally bicarbonate‐free media using the pH‐sensitive absorbance of 5‐ (and 6‐) carboxy‐4′,5′‐dimethylfluorescein. Under resting conditions, pHi averaged 6.98 ± 0.01 (SEM; n = 57). When cells were acid loaded by briefly exposing them to Ringer containing NH4+ and the withdrawing the NH4+, pHi spontaneously regained its initial value. In the presence of 1 mM amiloride or in the absence of Na+, this process was blocked, indicating the involvement of an Na+/H+ exchanger in the regulation of pHi after an acid load. Removing Na+ during resting conditions decreased cytoplasmatic pH. This acidification could be slowed by amiloride, which is evidence for reversal of the Na+/H+ countertransport exchanging intracellular Na+ for extracellular protons. Application of 1 mM amiloride during steady state led to a slow acidification. Thus the Na+/H+ exchanger is operative during resting conditions extruding protons, derived from cellular metabolism, or from downhill leakage into the cell. Addition of Na+ to Na+ ‐depleted cells led to an alkalinization, which was senstive to amiloride, with an IC50 of about 20 μM. This alkalinization was attributed to the Na+/H+ exchanger and exhibited saturation kinetics with increasing Na+ concentrations, with an apparent KM of 29.6 mM Na+. It is concluded that Na+/H+ exchange regulates pHi during steady state and after an acid load.
Metabolism of U6 RNA species in nonirradiated and UV‐irradiated mammalian cells
Authors: Choudhury Kanakendu , Choudhury Indrani , Jones Robert W. , Thirunavukkarasu Chellaiah , Eliceiri George L. 
Published: February 2005

AbstractWe observed a series of rapidly labeled U6 RNA bands, which were hybrid selected with U6 DNA, in nonirradiated human cells. The electrophoretic mobility of these bands in denaturing gels was lower than that of the known mature U6 RNA species, and was equivalent to transcripts up to ∼7 nucleotides longer. These multiple U6 RNA species lost their label during a chase without a proportional increase in radioactivity in the known mature U6 RNA, which suggests that a substantial fraction is not processed into the major mature U6 RNA. During a label chase, the multiple U6 RNA bands appeared first in the cytoplasmic fraction and later in nuclei. One of the major rapidly labeled U6 RNA bands had the electrophoretic mobility of an RNA species one nucleotide shorter than the known mature U6 RNA. UV light induced a UV dose‐dependent, preferential disappearance of recently synthesized molecules of the U6 RNA species of higher gel electrophoretic mobility, including the known mature U6 RNA. Since this effect was seen in cells pulse‐labeled immediately before or after irradiation, it suggests that UV radiation induces the specific degradation of the electrophoretically faster moving species of U6 RNA, which are apparently shorter chains. The effect of UV light was RNA species‐specific, was not seen in molecules synthesized long (e.g., 22 hr) before irradiation, and occurred in human and mouse cells.
Effect of reduced protein synthesis on the cell cycle in sea urchin embryos
Authors: Dubé François 
Published: February 2005

AbstractWe have reinvestigated the existence of cyclical fluctuations of protein synthesis and have examined the effects of reducing it in early embryos of the purple sea urchin, Stronglocentrotus purpuratus. The results show that protein synthesis increases linearly during the first 45–60 minutes after fertilization, then transiently decreases during mitosis, and rises again at first cleavage. Reducing protein synthesis of embryos to 35% its normal value only slightly affects the rate of progression through the cell cycle. It is also shown that the observed retardations of the cell cycle, under depressed protein synthesis, are attributable (by 80%) to a lengthening of the premitotic phase but also, to a lesser extent (20%), to a lengthening of the mitotic phase itself. These results suggest that mitotic proteins, in sea urchin embryos, are stable and little affected by an imposed decrease of protein synthesis during their accumulation phase. This analysis supports the view that specific mechanisms, other than decreased protein synthesis, need be turned on only at appropriate times during the cell cycle in order to explain the destruction or deactivation of mitotic proteins. Finally, a one‐dimensional SDS‐PAGE analysis of synthesized proteins, labeled with 35S‐methionine, reveals the presence of a 50‐kDa cyclin showing the expected characteristics of mitotic proteins deduced from our results.
Wheat germ agglutinin inhibits thrombin‐induced rises in cytosolic free calcium and prostacyclin synthesis by human umbilical vein endothelial cells
Authors: Grulich‐Henn Jürgen , Weksler Babette B. , Watanabe Kentaro , Jaffe Eric A. 
Published: February 2005

AbstractTo characterize the endothelial cell surface membrane glycoproteins that mediate thrombin stimulation of PGI2 synthesis by human umbilical vein endothelial cells (HUVEC), HUVEC were stimulated with thrombin in the presence or absence of different lectins. Of the lectins tested, only wheat germ agglutinin (WGA) inhibited thrombin‐induced rises in cytosolic free calcium ([Ca2+]i), measured using Quin 2‐loaded HUVEC and PGI2 production measured by radioimmunoassay. However, WGA by itself had no influence on baseline [Ca2+]i or PGI2 production and did not inhibit histamine‐induced rises in [Ca2+]i. The inhibition of thrombin‐induced rises in [Ca2+]i and PGI2 production by WGA was dose dependent, with half‐maximal inhibition occurring at 2 μg/ml WGA also inhibited thrombin‐induced release of 3H‐arachidonic acid. These effects of WGA were reversed by N‐acetyl‐glucosamine (GlcNAc) and N‐acetyl‐neuraminic acid, which bind specifically to WGA, but not by unrelated sugars. Succinylated WGA (succ‐WGA), a chemically modified derivative of WGA that binds to GlcNAc but, unlike native WGA, not to sialoglycoproteins, did not inhibit thrombin‐induced rises in [Ca2+]i and PGI2 production. These results suggest that thrombin induces rises in [Ca2+]i and PGI2 production by interacting with an endothelial surface membrane sialoglycoprotein.
Actin depolymerization and inhibition of capping induced by pentoxifylline in human lymphocytes and neutrophils
Authors: Rao K. Murali Krishna , Crawford Jeffrey , Currie Mark S. , Cohen Harvey J. 
Published: February 2005

AbstractPentoxifylline is used clinically for the treatment of intermittent claudication. It is believed to exert its effect by altering the rheologic properties of blood. The cytoskeleton plays an important role in the maintenance of cell structure and function. In particular, alterations in the state of actin seem to play an important role in cell motility. Therefore, we examined the effect of pentoxifylline on the actin state in human polymorphonuclear leukocytes (PMN) and mononuclear cells. Pentoxifylline (10 mM final concentration) decreased F‐actin content in both PMN and mononuclear cells. Pentoxifylline also inhibited concanavalin A‐induced capping in PMN and mononuclear cells. Similarly, surface immunoglobulin capping in B lymphocytes was also inhibited. Pretreatment of cells with pertussis toxin did not inhibit pentoxifylline‐induced decrease in F‐actin, suggesting pentoxifylline does not act through pertussis toxin‐sensitive G‐proteins. Dibutyryl cyclic AMP failed to show any significant effect on the F‐actin content in PMN. Therefore, the effect of pentoxifylline cannot be attributed to changes in cyclic AMP levels. Chemotactic peptide‐induced actin polymerization was unaffected in PMN when expressed as percent change in F‐actin. The observations reported here suggest that the rheological effects of pentoxifylline might be due to its effects on the actin state in the cellular elements of the blood. Further studies on the mechanism of action of pentoxifylline on actin state in leukocytes will prove useful in delineating the physiological mechanisms regulating actin state in leukocytes.