bluuebunny/crossref_metadata_2025_split huggingface dataset:
Basolateral distribution of fibronectin matrix assembly sites on vascular endothelial monolayers is regulated by substratum fibronectin
Authors: Kowalczyk Andrew P. , McKeown‐Longo Paula J. 
Published: February 2005

AbstractEndothelial cells exhibit binding sites for the amino terminus of fibronectin that participate in subendothelial fibronectin matrix assembly. These binding sites, termed matrix assembly sites, are localized on the basolateral surface of confluent endothelial monolayers (Kowalczyk et al. Blood, 75:2335, 1990). The present study investigates the role of cell—cell and cell—substratum interactions in the localization of matrix assembly sites to the basal surface of endothelial cells. Cells were cultured in Transwell culture inserts and matrix assembly sites were detected by binding assays using an iodinated 70 Kd amino‐terminal fibronectin fragment. Integrity of intercellular junctions was monitored by measuring protein flux across Transwell filters. Time course experiments demonstrated that matrix assembly site expression on the basolateral cell surface preceded intercellular junction formation. Transfer of confluent monolayers to calcium‐free medium resulted in the loss of junctions and in an increase in 125I‐70 kD binding from the apical medium. The increased 125I‐70 kD binding resulted from increased access of 125I‐70 kD to basolateral matrix assembly sites and not from the relocation of binding sites to the apical membrane. To determine the effect of matrix composition on matrix assembly site expression and localization, cells were seeded onto vitronectin‐ or fibronectin‐coated substrates. Fibronectin increased the expression of matrix assembly sites on the apical surface within 24 hours. By 48 hours, matrix assembly sites were located only on the basolateral surface. Vitronectin had no effect on the expression or localization of matrix assembly sites. These results indicate that the expression and localization of matrix assembly sites on the surface of vascular endothelial cells can be regulated by substratum fibronectin. © 1992 Wiley‐Liss, Inc.
A cryptopromoter is activated in the proliferating cell nuclear antigen gene of growth arrested cells
Authors: Sell Christian , Chang Chung‐Der , Koniecki Janice , Chen Hui‐Min , Baserga Renato 
Published: February 2005

AbstractWe have examined the regulation of the proliferating cell nuclear antigen gene (PCNA) in a hamster fibroblast cell line (tk‐ts 13) which is temperature sensitive for growth. These tk‐ts 13 cells, at the restrictive temperature, are growth arrested in the G1 phase of the cell cycle. The cells were stably transfected with a full length human PCNA gene, and the resulting cell lines (K525 cells) were analyzed. We find that, in growth arrested K525 cells, a cryptopromoter is activated in the transfected human PCNA gene. The cryptopromoter resides in intron 4 which is necessary for proper regulation of the PCNA gene. Removal of this intron leads to increased expression of PCNA in cells which have entered the Go state. An Alu sequence residing in intron 4 is implicated as the promoter element which is active during growth arrest. © 1992 Wiley‐Liss, Inc.
Platelet‐activating factor stimulates phospholipase C activity in human endometrium
Authors: Ahmed A. , Smith S. K. 
Published: February 2005

AbstractHuman preimplantation embryos secrete platelet‐activating factor (PAF), which stimulates prostaglandin E2 synthesis from secretory endometrium. This study investigated the action of PAF on phosphatidylinositol 4,5‐bisphosphate (Ptdlns(4,5)P2)‐specific phospholipase C activity in human endometrium. Slices of normal endometrium were incubated with 5 μCi/ml myo‐[2‐3H] inositol for 3 h at 37°C in 95% O2 and 5% CO2 to label tissue phosphoinositides. Inositol phosphates were extracted using trichloroacetic acid precipitation and diethylether neutralization and production was measured using Dowex 1‐X8 anion‐exchange column chromatography. PAF induced rapid and concentration‐dependent accumulation of inositol phosphates (IP) from secretory endometrium, but had no effect on endometrium removed in the proliferative phase of the menstrual cycle. The IP3 fraction was significantly elevated from a median value of 14.0 c.p.m. mg−1 dry wt [range: 8–41 c.p.m. mg−1 dry wt] to 28.0 c.p.m. mg−1 dry wt [range: 11–87 c.p.m. mg−1 dry wt, P < 0.002] following 1 min exposure of secretory endometrium to PAF‐acether, in the presence of 10 mM LiCl. PAF‐induced hydrolysis of Ptdlns(4,5)P2 was inhibited by the specific PAF receptor antagonist WEB 2086, in a dose‐dependent manner (P < 0.02), indicating that in human endometrium Ptdlns(4,5)P2 hydrolysis is mediated via a PAF receptor. These results indicate that PAF receptor coupling activates endometrial Ptdlns(4,5)P2‐specific phospholipase C only in the secretory phase of the menstrual cycle, suggesting that the PAF response may be under ovarian steroid regulation. It is proposed that the ability of the endometrium to respond to PAF appears to be a feature of the preparation of this tissue for implantation and that the second messengers generated may play a role in cellular processes involved in the maternal recognition of very early human pregnancy. © 1992 Wiley‐Liss, Inc.
IL‐3 stimulated haemopoietic stem cell proliferation: Evidence for G protein independent mitogenic signalling events
Authors: Akinsanya Ayodele A. , Whetton Anthony D. 
Published: February 2005

AbstractInterleukin‐3 stimulates the survival and proliferation of the FDCP‐Mix 1 multipotent stem cell line. We have investigated the possible involvement of a guanyl nucleotide regulatory (G) protein(s) in the IL‐3 stimulated proliferative response. We report here that pertussis toxin (PT) can partially inhibit IL‐3 stimulated DNA synthesis and that this inhibition is bypassed by TPA. The ADP‐ribosylation of the PT substrate G protein in vivo is complete in 2 hours without concomitant inhibition of IL‐3 stimulated hexose transport or Na+/H+ exchange. When loaded into FDCP‐Mix 1 cells fluoroaluminate and GTP‐γ‐S, which can directly activate G proteins, are not capable of mimicking the effects of IL‐3. Evidence is also presented that IL‐3 does not stimulate a membrane‐bound high affinity GTPase activity in the FDCP‐Mix 1 cell line. These data suggest that a PT substrate G protein(s) can influence the IL‐3 signalling cascade in an indirect or permissive manner, but that the IL‐3 receptor does not directly couple to a PT substrate G protein. © 1992 Wiley‐Liss, Inc.
Characterization of metformin transport system in NIH 3T3 cells
Authors: Khan Naim A. , Wiernsperger Nicolas , Quemener Veronique , Havouis René , Moulinoux Jacques P. 
Published: February 2005

AbstractThe biochemical properties of the metformin transport system were studied in NIH 3T3 cells. 14C‐metformin uptake appeared to be a sodium dependent process. Iso‐osmotical replacement of Na+ by choline chloride in the assay medium resulted in a decrease of metformin uptake. Amiloride (200 μM) inhibited the metformin transport by 35% in these cells. Gramicidin, a channel ionophore, was the most effective in inhibiting the metformin transport as compared to valinomycin, a mobile ion carrier, and Ca2+ ionophore (A 23187). Loading of cells with asparagine, ornithine, or polylysine did not influence the uptake process. However, the addition of lysine or arginine significantly stimulated the metformin uptake by NIH 3T3 cells. Similarly, the addition of metformin stimulated the arginine uptake by these cells, suggesting that metformin shares the y+ transport system. Metformin inhibited competitively the uptake of 14C‐spermidine, a molecule of the polyamine family, by NIH 3T3 cells, whereas the latter failed to influence the uptake of the former significantly by these cells. Incubation of NIH 3T3 cells in the presence of difluoromethyl‐ornithine (a suicidal inhibitor of polyamine biosynthesis) stimulated the spermidine, but not the metformin, uptake by these cells. Interestingly, a prolonged incubation of these cells in the presence of metformin failed to down‐regulate the spermidine transport process. The spermidine‐ and methylglyoxal‐bis(guanylhydrazone), MGBG‐transport deficient (3T3MG) cells which do not accumulate exogeneous spermidine or MGBG, took up 14C‐metformin. However, 14C‐metformin uptake by 3T3MG cells was lower than that by normal NIH 3T3 cells. © 1992 Wiley‐Liss, Inc.
Distinct mechanisms of zinc uptake at the apical and basolateral membranes of Caco‐2 cells
Authors: Raffaniello Robert D. , Lee Shih‐Yu , Teichberg Saul , Wapnir Raul A. 
Published: February 2005

AbstractZinc uptake mechanisms at the apical and basolateral membrane borders of caco‐2 cells were examined. This human‐derived cell line possesses many morphological and functional characteritics of absorptive small intestinal cells. By day 14, coniluent and well‐differentiated monolayers were formed when the cells were grown on porous polycarbonate filters. Labelled zinc was placed on the apical or basal side of the monolayer and its uptake by the cells, as well as its transport across the monolayer, were measured. Zinc uptake by the cells from the apical side was found to be a saturable process (Kt = 41 μM; Vmax = 0.3 nmols/cm2/10 min) with a diffusional term at higher concetrations (1.0 sec/cm). Apical uptake was not affected by metabolic inhibitors or potential zinc ligands. Zinc uptake from the basolateral side was concentration dependent (Kd = 1.3 sec/cm) and was partially inhibited (30%) by ouabain and vanadate, suggesting that the (Na‐K)‐ATPase on the basolateral membrane is involved in the serosal uptake of zinc by the cell. Transport of zinc across the monolayers from the apical or basolateral compartment was concentration dependent and was not affected by metabolic inhibitors. Zinc transport from the basolateral side was >2‐fold greater than apical transport. Hence, separate mechanisms can be distinguished with respect to zinc uptake at the apical and basolateral membranes of caco‐2 cells. © 1992 Wiley‐Liss, Inc.
Insulin‐like growth factor‐I (IGF‐i) stimulates protein synthesis and collagen gene expression in monolayer and lattice cultures of fibroblasts
Authors: Gillery Philippe , Leperre Armelle , Maquart François‐Xavier , Borel Jacques‐Paul 
Published: February 2005

AbstractFibroblasts cultivated in three‐dimensional tissue‐like matrices are characterized by a slowed metabolism and a decrease of protein synthesis, unless they are submitted to physical tensions. We checked the effects of insulin like growth factor‐I (IGF‐I), known as a potent stimulator of mitogenesis and protein synthesis for many cell types, in various models of cultures: confluent monolayers, collagen lattices, non‐retracting or retracting fibrin lattices. IGF‐I (1–100 ng · ml−1) had no effect on cell divisions in lattice cultures. It was able to stimulate collagen lattice retraction when the medium was supplemented with low concentrations of serum. IGF‐I at 10 or 100 ng · ml−1 stimulated collagen and non‐collagen syntheses in all culture systems, but stimulation of collagen synthesis only began at the highest concentration (100 ng · ml−1) in retracted lattices. Northern blot and dot‐olot analyses of mRNAs extracted from monolayer cultures of fibroblasts showed that IGF‐I stimulated pro α1(I) collagen synthesis at the pretranslational level. Cycloheximide (7.5 μg · ml−1) completely inhibited pro α1(I) collagen gene expression induced by IGF‐I. These results show that IGF‐I is a potent stimulus for protein synthesis and collagen gene expression in monolayers and tridimensional cultures of fibroblasts, but that it exerts no mitogenic activity in tridimensional lattices. Synergistic associations of IGF‐I with other growth factors will have to be found in order to reverse the quiescent status of fibroblasts in lattices. © 1992 Wiley‐Liss, Inc.
Transforming growth factor‐β1 inhibitory effect of platelet‐derived growth factor‐‐induced signal transduction on human bone marrow fibroblasts: Possible involvement of protein phosphatases
Authors: Fontenay Michaëla , Bryckaert Marijke , Tobelem Gérard 
Published: February 2005

AbstractTransforming growth factor‐β1 (TGF‐β1) is a potent growth inhibitor for many cell types. On fibroblasts, TGF‐β1 has been shown to inhibit human platelet‐derived growth factor (PDGF)‐induced mitogenicity. The mechanism implicated in this growth inhibition is unknown. In this work, we show on human bone marrow fibroblasts that TGF‐β1, which inhibited PDGF‐BB mitogenicity, was able to block PDGF‐BB‐induced early events such as polyphosphoinositide (Ptdlns 4,5‐P2, Ptdlns 4‐P, and Ptdlns) breakdown and Ins 1,4,5‐P3 formation. No significant modification by TGF‐β1 of PDGF‐BB binding (n1 = 200,000 vs. n2 = 195,000 sites per cell with TGF‐β1; Kd1 = Kd2 = 0.5 × 10−9M) and of internalization kinetics was observed. In addition, TGF‐β1 was shown to inhibit PDGF‐BB receptor autophosphorylation either in intact cells or in partially isolated membranes and to partially inhibit PDGF‐R tyrosine kinase activity. Since a dephosphorylation mechanism through protein phosphatases could be implicated, we used okadaic acid, a potent inhibitor of type 1 and 2A serine/threonine phosphatases and showed that okadaic acid restored PDGF‐receptor autophosphorylation on tyrosine residues. Based on these data, we suggest that an alternative regulatory mechanism of PDGF tyrosine phosphorylation seems to involve serine/threonine phosphatase activation. © 1992 Wiley‐Liss, Inc.
Brefeldin A, thapsigargin, and AlF stimulate the accumulation of GRP78 mRNA in a cycloheximide dependent manner, whilst induction by hypoxia is independent of protein synthesis
Authors: Price Brendan D. , Mannheim‐Rodman Laura A. , Calderwood Stuart K. 
Published: February 2005

AbstractThe glucose regulated proteins (GRPs) are major structural components of the endoplasmic reticulum (ER) and are involved in the import, folding, and processing of ER proteins. Expression of the glucose regulated proteins (GRP78 and GRP94) is greatly increased after cells are exposed to stress agents (including A23187 and tunicamycin) which inhibit ER function. Here, we demonstrate that three novel inhibitors of ER function, thapsigargin (which inhibits the ER Ca2+‐ATPase), brefeldin A (an inhibitor of vesicle transport between the ER and Golgi) and AlF−4, (which inhibits trimeric G‐proteins), can increase the expression of both GRP78 and 94. The common characteristic shared by activators of GRP expression is that they disrupt some function of the ER. The increased levels of GRPs may be a response to the accumulation of aberrant proteins in the ER or they may be increased in response to structural/functional damage to the ER. The increased accumulation of GRP78 mRNA after exposure of cells to either thapsigargin, brefeldin A, AlF−4, A23187, or tunicamycin can be blocked by pre‐incubation in cycloheximide. In contrast, accumulation of GRPs after exposure to hypoxia was independent of cycloheximide. In addition, the protein kinase inhibitor genistein blocked the thapsigargin induced accumulation of GRP78 mRNA, whereas the protein phosphatase inhibitor okadaic acid caused increased accumulation of GRP78 mRNA. The data indicates that there are at least 2 mechanisms for induced expression of GRPs, one of which involves a phosphorylation step and requires new protein synthesis (e.g., thapsigargin, A23187) and one which is independent of both these steps (hypoxia). © 1992 Wiley‐Liss, Inc.
β1 integrins isolated from embryonic chicken fibroblasts bind to monomers and polymers of type I collagen
Authors: Potts A. Jeannette , Little Charles D. 
Published: February 2005

AbstractThe avian integrin β1 subfamily consists of multiple α‐β subunit heterodimers. We employed two different physical states of type I collagen, monomers and fibrils, in the isolation and characterization of avian collagen integrins. Affinity chromatography showed that three integrins, tentatively designated α155β1 (band 1), α5aβ1, and α3β1 (band 2), bind fibrillar and monomeric collagen under physiological ionic conditions and require divalent cations for binding activity. Sodium chloride gradients (0–0.5 M) were used to assess the functional ability of the integrins to remain bound to the two forms of type I collagen. The results show that integrins elute from the two forms of collagen with distinct fractionation profiles. One integrin, α155β1, binds fibrillar collagen with relatively higher affinity than the other β1 receptors. This same avian integrin, α155β1, is immunoreactive with an antiserum (Hynes et al., 1989) raised against a peptide that corresponds to the entire α5 cytoplasmic domain, and coincidently, part of the α6 cytoplasmic domain (de Curtis et al., 1991). Cell biological studies employing double immunofluorescence show that integrins recognized by this antiserum co‐localize with extracellular deposits of type I collagen. © 1992 Wiley‐Liss, Inc.
Characterization of a simian virus 40‐transformed human podocyte cell line producing type IV collagen and exhibiting polarized response to atrial natriuretic peptide
Authors: Ardaillou Nicole , Lelongt Brigitte , Turner Neil , Piedagnel Rémi , Baudouin Béatrice , Estrade Simone , Cassingena Roland , Ronco Pierre M. 
Published: February 2005

AbstractBiology of glomerular visceral epithelial cells (“podocytes”) and their role in inflammatory process remain obscure, partly because of the lack of well‐differentiated podocyte cultures. We have established a human cell line by transfecting with a replication‐defective SV40 plasmid (pSVHB1), a primary culture of podocytes derived from an enriched preparation of unencapsulated glomeruli free of tubule and Bowman's capsule contaminants. Podocyte specificity of the primary culture was assessed by a dual immunomorphological and functional approach. The resulting cell line (HGVEC. SV1) was cloned and the clonal cells were adapted to hormonally defined medium supplemented with only 2% newborn bovine serum. Clone A4 has been exhibiting over 35 passages, a combination of markers unique to podocytes, including expression of vimentin, podocalyxin, ectoenzymes (CALLA antigen and mRNA), heparan‐sulfate proteoglycans (molecular mass of core protein = 75 kDa), and production of type IV collagen (α1 and α5 chains) established by immunoprecipitation and Northern blot analysis. Cytokeratin was detected in rare cellular foci and the search of Von Willebrand factor was negative. This clonal cell line has been used to demonstrate: (1) that human podocytes are highly sensitive to atrial natriuretic peptide (ANP) which induced a dose‐dependent increase in cGMP production (x20 at 0.5 μM ANP), and (2) that secretion of ANP‐stimulated cGMP is dramatically polarized as 93% of extracellular cGMP were released in the apical medium when filter‐grown HGVEC. SV1A4 cells were stimulated at their basal pole. © 1992 Wiley‐Liss, Inc.
Interleukin 6 promotes epithelial migration by a fibronectin‐dependent mechanism
Authors: Nishida Teruo , Nakamura Masatsugu , Mishima Hiroshi , Otori Toshifumi 
Published: February 2005

AbstractWe investigated the effect of interleukin 6 (IL‐6) on the migration of rabbit corneal epithelial in vitro and on the attachment of dissociated corneal epithelial cells to a fibronectin matrix. When corneal blocks were cultured with IL‐6 for 24 hours, the length of the path of epithelial migration over exposed corneal stroma increased significantly (p < 0.005 at the concentration of 10 ng/ml) in proportion to the concentrations of IL‐6 (0.1–10.0 ng/ml). The addition of antiserum against fibronectin or of GRGDSP abolished the stimulatory effect of IL‐6 on epithelial migration. When corneal epithelial cells were cultured with various concentrations of IL‐6, suspended, and plated on wells coated with fibronectin (10 μg/ml), the number of cells attached to the wells increased in a dose‐dependent manner. The presence of antibody against fibronectin or of GRGDSP during the attachment assay decreased the number of cells attached to the fibronectin matrix, regardless of the fact that the cells had been cultured with IL‐6 or not. IL‐6 stimulated the attachment of corneal epithelial cells to collagen type IV and to laminin matrices. However, the presence of GRGDSP did not affect the cell attachment to collagen type IV and to laminin. These findings strongly indicate that IL‐6 stimulates epithelial migration in the cornea by a fibronectin‐dependent mechanism, presumably the increased expression of fibronectin receptors. © 1992 Wiley‐Liss, Inc.
Electrogenic Na‐independent HCO3 transport in OK cells
Authors: Pastoriza‐Munoz Enrique , Hsiang Fuling , Graber Mark 
Published: February 2005

AbstractWe have shown previously that OK cells recover from an acid load in a medium nominally CO2‐free by extruding H via a Na/H exchanger and a passive H‐conductive pathway. In this work, the regulation of cell pH (pHi) was studied after additon or withdrawal of CO2/HCO3 (5%CO2, 95 mM HCO3, pH = 8) using the fluoroprobe BCECF. In the presence of Na and amiloride to inhibit Na/H exchange, the recovery of pHi after CO2 entry and CO2 exit were found to depend in part on HCO3 entry and exit, respectively. Efflux of H per se also contributed to restoring pHi after CO2 addition, whereas H influx may have played a smaller role to normalize pHi after CO2 removal. DIDS, 0.5mM, significantly inhibited both recovery phases of pHi. Removal of Na failed to inhibit the recovery of pHi after CO2 addition and removal. Cl removal also failed to inhibit pHi recovery after CO2 removal. Cell depolarization in the presence of Na moderately stimulated the pHi recovery rate after CO2 addition whereas it markedly inhibited the normalization of pHi after CO2 removal. Cell depolarization in the absence of sodium had only a slight effect to increase pHi recovery after CO2 addition but markedly prevented the pHi recovery after CO2 removal. These results indicate that OK cells lack Na or Cl‐dependent HCO3 transport systems. The OK cell possesses a novel stilbene‐sensitive electrogenic HCO3 transport system that is involved in the regulation of cell pH. © 1992 Wiley‐Liss, Inc.