bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel marine alkaloids from the tunicate Eudistoma sp. are potent regulators of cellular growth and differentiation and affect cAMP‐mediated processes
Authors: Shochet Nava R. , Rudi Amira , Kashman Yoel , Hod Yaacov , El‐Maghrabi M. Raafat , Spector Ilan 
Published: February 2005

AbstractSix novel alkaloids that contain a fused tetracyclic pyrido[2,3,4‐kl]acridine ring system were purified recently from the Red Sea purple tunicate Eudistoma sp. Evaluation of the effects of these alkaloids on cultured neuroblastoma and fibroblast cells revealed that they possess potent growth regulatory properties, and affect cell shape and adhesion. In mouse neuroblastoma cells, the Eudistoma alkaloids inhibited cell proliferation and induced a process of differentiation during which the cels flattened onto the surface, increased considerably in size, and extended long neurites. In hamster fibroblasts the alkaloids slowed down cell multiplication, and caused an exceptional cell flattening or elongation. In a virustransformed derivative of the hamster fibroblasts the alkaloids restored many aspects of normal cell growth and morphology. In addition, several of the alkaloids mimicked the effects of cAMP analogs on two well‐characterized cAMP‐mediated processes involved in hepatic glucose metabolism–inhibition of pyruvate kinase (PK) activity and induction of mRNA for phosphoenolpyruvate carboxykinase (PEPCK). All these effects suggest that the Eudistoma alkaloids may act on the cAMP signaling system. However, a single application of these compounds was sufficient to completely block cell multiplication and to induce and sustain differentiation and “reverse transformation”. Furthermore, these effects were not readily reversible following removal of the drugs. In contrast, a single application of agents that mimic or elevate cAMP induced a transient response that waned with time in culture, and the effects induced by constant elevation of cAMP reverse rapidly following drug removal. We propose that the Eudistoma alkaloids cause growth inhibition, differentiation, and reverse transformation by modifying the activity state of proteins that are involved in the regulation of cell shape and adhesion and serve as a target for the cAMP and/or other second messenger systems. © 1993 Wiley‐Liss, Inc.
Expression of a squamous cell marker, the spr1 gene, is posttranscriptionally down‐regulated by retinol in airway epithelium
Authors: An Gang , Tesfaigzi Johannes , Carlson Don M. , Wu Reen 
Published: February 2005

AbstractVitamin A (retinol) is required for the normal mucociliary differentiation of respiratory epithelium. A depletion of vitamin A promotes squamous cell metaplasia. To understand how vitamin A suppresses squamous cell differentiation, the expression of a squamous cell differentiation marker, the small proline‐rich protein gene (spr1), was studied in cultured monkey tracheobronchial epithelial (TBE) cells. The expression of the spr1 gene was inhibited about 40 fold by retinol. The mRNA levels of the spr1 gene started to decline within 6 h of retinol treatment and reached a minimum level after 7 days. The inhibition by retinol was concentration dependent and did not require concurrent protein synthesis. The inhibition of the spr1 mRNA by retinol was not due to a decrease in the transcription rate of its gene but due to a decrease in its stability, as determined by nuclear run‐on assays and mRNA half‐life measurement, respectively. This result was further supported by a DNA transfection study using a chimeric construct containing the spr1 promoter region and the chloramphenicol acetyltransferase (CAT) reporter gene. The CAT activity in transfected cells was not inhibited by retinol. These results suggest that spr1 gene expression is posttranscriptionally down‐regulated by retinol. © 1993 Wiley‐Liss, Inc.
Oxygen tension regulates neutrophil adhesion to human endothelial cells via an LFA‐1‐dependent mechanism
Authors: Ginis Irene , Mentzer Steven J. , Faller Douglas V. 
Published: February 2005

AbstractExtravasation of leukocytes at the sites of ischemia‐reperfusion is thought to exacerbate the tissue injury. It has been proposed that leukocyte accumulation is a secondary effect of the ischemic damage, mediated by inflammatory cytokines. We have recently demonstrated that physiologically low levels of oxygen tension alone can have a direct effect on the adhesive characteristics of mesenchymal cells for lymphocytes. We now report that decrease of oxygen tension in the environment induces the adhesion of neutrophils to human endothelial cells in culture. Adhesion of human neutrophils to human umbilical vein, bovine aortic, and mouse microvascular endothelial cell monolayers, which had been incubated at pO2 of 50 torr for 3 hours, increased 2.5‐fold, 2‐, and 1.5‐fold, respectively. The effects of decreased oxygen concentration on adhesion were not mediated by a soluble factor elaborated by the hypoxic cells. Low oxygen tension upregulates a saturable, endothelial cell‐associated adhesion mechanism, capable of withstanding centrifugation forces greater than 160g. Hypoxia‐induced adhesion was inhibited by LFA‐1‐specific (CD 11 a/CD18 integrin) antibodies, but not by antibodies directed against the ICAM‐1 ligand for the LFA‐1 receptor. These studies demonstrate that decreases in oxygen tension alone increase the adhesive properties of endothelial cells for leukocytes. In addition, they provide evidence for the existence of a new ligand for the LFA‐1 molecule on edothelial cells which can be affected by hypoxic environments.
Lipophilic impurity of phenol red is a potent cation transport modulator
Authors: Hopp Laszlo , Bunker Clareann H. 
Published: February 2005

AbstractPreviously, we described substantial alterations in the Na+ and K+ homeostasis of human skin fibroblasts following removal of fetal bovine serum (FBS). Herein, we report that FBS removal per se does not cause any cellular ionic changes unless a lipophilic impurity of commercial phenol red preparations is present. This substance accelerates 86Rb+ efflux four to seven times, causes a four to eight time increase in cellular Na+, and a 40–70% reduction in cellular K+ contents. FBS (10%) or albumin (0.8%) appears to bind the impurity thus inhibiting its action. The increased cellular Na+ and decreased K+ contents do not return to baseline within 4 hours following the removal of the phenol red extract. However, albumin completely reverses the cellular cationic changes that develop during a 2 hour exposure of the cells to the free substance. The reversibility of its action by albumin suggests that the substance exerts its effect on or within the cell membrane and not intracellularly. Among seven different cell lines tested the 86Rb+ efflux from, and the Na+‐K+ contents of, COS‐7 and Hs68 cells also responded to unpurified phenol red in a way similar to human fibroblasts. The amount of the phenol red contaminant is manufacturer dependent. As little as 0.5 μM phenol red, from one vendor, was sufficient to elicit response in the 86Rb+ efflux. Given that the impurity is unlikely to be more than a small fraction of phenol red, it seems to be a potent ionic transport modulator. Based on these results, the presence of commercial phenol red in serum‐free growth or test media, including the increasing variety of chemically defined culture media, should be considered as a potential confounding factor in measurements that depend on intracellular Na+‐K+ homeostasis. The findings of such earlier studies may need to be reconsidered if the cells were exposed to unbound phenol red. We recommend that, until the manufacturers further refine their product, phenol red be purified by ether extraction before its use. The evaluation of the potential physiologic or pharmacologic relevance of this potent cation transport modulator awaits its isolation. © 1993 Wiley‐Liss, Inc.
Effect of stretch on growth and collagen synthesis in cultured rat and lamb pulmonary arterial smooth muscle cells
Authors: Kulik Thomas J. , Alvarado Stephen P. 
Published: February 2005

AbstractThere are no studies of the effect of stretch in cultured pulmonary vascular smooth muscle, and some data suggest that a stretch‐mediated increase in connective tissue synthesis in pulmonary arteries is mediated by the endothelium. To investigate whether stretch can serve as a growth stimulus in this smooth muscle, we studied two types of cultured pulmonary arterial smooth muscle cells (a multiply passaged clonal line of rat cells [PAC1], and early passage lamb cells [EPTC]). Cells were grown on a collagen‐coated silicone surface and subjected to repetitive stretch (0.33–0.5 Hz; 10–20% strain). The relative rates of total RNA, DNA, protein, and soluble collagen synthesis were determined using 3H precursors, and c‐fos and collagen mRNAs by Northern blot analysis. Stretch caused no significant change in the rate of RNA synthesis in either PAC1 cells (+9%) or EPTC (—3%). The relative rate of total protein synthesis was decreased by stretch (6% in PAC1 cells and 36% in EPTC [both NS]) as was the rate of collagen synthesis (−24% in EPTC [NS]). In EPTC, the percentage of 3H‐thymidine labeled cells was modestly increased with 24 h stretch (17 ± 5.7%; P ≤.001), but trichloroacetic acid (TCA) precipitated 3H‐thymidine was unaltered by stretch, and the number of cells not significantly changed with stretch. c‐fos mRNA expression was only inconsistently induced by stretch x30 min in EPTC, and not at all in PAC1 cells. Expression of mRNA for α1 (I) and α1 (III) collagen was not changed significantly by 24 h or 48 h of stretch. We conclude that stretch does not serve as a significant growth stimulus in cultured pulmonary vascular smooth muscle cells in this system. These findings do not rule out the possibility that stretch is a growth stimulus for these cells under different conditions, but do suggest that other models will be needed to determine if and how mechanical stimuli affect growth of pulmonary vascular smooth muscle. © 1993 Wiley‐Liss, Inc.
Iron absorption by CaCo 2 cells cultivated in serum‐free medium as in vitro model of the human intestinal epithelial barrier
Authors: Halleux Christine , Schneider Yves‐Jacques 
Published: February 2005

AbstractA cell culture system consisting of confluent monolayer of human enterocyte‐like CaCo 2 cells, cultivated in a serum‐free nutritive medium, on microporous synthetic membranes has been used as an in vitro model of the intestinal epithelial barrier. The uptake of 55ferric citrate, as well as the transepithelial passage from the apical to the basolateral pole, have been studied. CaCo 2 cells accumulate iron in a time‐ and concentration‐dependent process, largely specific from the apical pole. When 55ferric citrate is added at the apical pole, radioiron appears at the basal pole and the clearance rate is ∼four times higher than in the opposite direction; the amounts of 55Fe increase with the concentration in iron citrate and the duration of incubation. At least two concurrent mechanisms could be involved in iron absorption across monolayers of CaCo 2 cells. A first route would correspond to a paracellular passage of the metal from the apical to the basal pole. The second route would involve a selective intake of iron at the apical pole and could require a reduction of ferric iron, prior to the entry. Iron accumulated by the cells would, for a minor part, be stored within ferritin, whereas the major part would be excreted at the basolateral pole, either as low molecular weight material of undetermined chemical composition but from which iron is easily mobilized by apotransferrin or associated with neosynthesized apotransferrin. Vesicular transport and protein synthesis seem to be required. © 1994 Wiley‐Liss, Inc.
Abnormalities of phosphoprotein gene expression in three osteopetrotic rat mutations: Elevated mrna transcripts, protein synthesis, and accumulation in bone of mutant animals
Authors: Shalhoub V. , Bettencourt B. , Jackson M. E. , Mackay C. A. , Glimcher M. J. , Marks S. C. , Stein G. S. , Lian J. B. 
Published: February 2005

AbstractOsteoclast abnormalities that characterize osteopetrosis, a disorder of bone resorption, may derive from aberrant signals from the osteoblast or the bone matrix. In the present studies, both synthesis and the bone matrix content of the major bone phosphoprotein component, osteopontin, were found to be elevated in three osteopetrotic rat mutations (ia, op, and tl). In whole bone, a twofold increase in the content of the characteristic amino acid O‐phosphoserine for osteopontin occurred in op and tl mutant long bone, but a smaller (15%) and more variable increase was observed in ia mutant rat long bone. Extraction of the bone matrix components and partial purification by reverse phase chromatography showed a twofold increase in a phosphoprotein fraction relative to other noncollagenous components. Amino acid analysis and staining characteristics of SDS‐PAGE fractionated proteins indicated this to be osteopontin. Organ cultures of calvarial bone from 4 day ia osteopetrotic mutant and normal rats in the presence of 3H‐proline showed increased synthesis of this 60 kD protein, which was stimulated by vitamin D. Preparation of total cellular RNA from bone of 2‐ and 6‐weekold mutants and normal rats supported increased synthesis of osteopontin as reflected by hybridization with osteopontin cDNA probe, showing significantly higher levels of mRNA transcripts in ia (3–5 fold), tl (1.4–2 fold), and op (6–25 fold) mutant bone compared to normal littermates. The changes in osteopontin mRNA levels in mutant bone were also examined in relation to other growth and phenotype‐expressed genes. The findings of increased accumulation of osteopontin in osteopetrotic bone and increased synthesis by osteoblasts are interesting in light of the previously reported decrease in bone osteocalcin content (Endocrinology, 126:966, 1990), confirmed here by decreased osteocalcin mRNA transcripts. Such aberrations in the composition of skeletal extracellular matrix could be a reflection of or a contributing factor to the osteoclast abnormalities of some of these osteopetrotic disorders. © 1994 Wiley‐Liss, Inc.
Transient mitochondrial transcript level decay in oxidative stressed chondrocytes
Authors: Vincent Françoise , Corral‐Debrinski Marisol , Adolphe Monique 
Published: February 2005

AbstractSteady‐state levels of 12S rRNA and NADH dehydrogenase subunit 4 mRNA (ND4) mitochondrial transcripts were measured on rabbit articular chondrocyte in culture. In pseudosynchronized chondrocytes, changes of mitochondrial RNA levels were observed during the progression of the cells in the cell cycle. Oxidative stress generated by the hypoxanthine‐xanthine oxidase system (HX‐XO) induced a transient decrease in the levels of both ND4 and 12S rRNA. Mitochondrial RNA levels recovered 24 h after the oxidative stress. These RNA level changes were not associated with modifications in the structure or the copy number of the mitochondrial genome. Furthermore, the decrease in the amount of the mitochondrial transcripts observed may be related to a transient inhibition of mitochondrial transcription since the treatment of cells with ethidium bromide (a mitochondrial transcription inhibitor) resulted in the same decrease in 12S rRNA level as HX‐XO treatment alone. © 1994 Wiley‐Liss, Inc.
Epitope mapping and functional studies with three monoclonal antibodies to the C‐KIT receptor tyrosine kinase, YB5.B8, 17F11, and SR‐1
Authors: Ashman Leonie K. , Bühring Hans‐Jörg , Aylett Gabriella W. , Broudy Virginia C. , Müller Claudia 
Published: February 2005

AbstractThree monoclonal antibodies (MAbs) to the human c‐kit receptor tyrosine kinase (P145c‐kit), derived in independent laboratories, have been extensively used in studies of c‐kit expression and the role of its ligand, steel factor (SLF), in hemopoiesis and mast cell differentiation and function. In this study, the relationship between the epitopes they identify, and their effects on SLF binding, receptor internalization, and signal transduction are compared.Epitope mapping studies carried out on the high P145c‐kit‐expressing cell line HEL‐DR showed that SR‐1 identifies an epitope independent of those bound by YB5.B8 and 17F11, while the latter two antibodies bound to distinct but interacting epitopes. SR‐1 potently blocked the binding of SLF to P145c‐kit on these cells and also on cells of the factor‐dependent line MO7e. In contrast, YB5.B8 and 17F11 had minimal effects on ligand binding. Conversely, SLF partially blocked the binding of SR‐1 and YB5.B8 to cells, while binding of 17F11 was actually enhanced by SLF on some target cells. Preincubation of HEL‐DR and MO7e cells with MAbs prior to exposure to SLF revealed that 17F11 itself brought about partial down‐regulation of P145c‐kit and did not inhibit SLF‐mediated down‐regulation. SR‐1 caused minimal down‐regulation and inhibited SLF‐mediated receptor internalization. YB5.B8 had minimal effects on either cell line in this assay. To determine whether the antibodies had any agonist activity, they were compared with SLF for their ability to bring about receptor phosphorylation in intact MO7e cells. All three antibodies induced detectable tyrosine phosphorylation with 17F11 being the most effective, while YB5.B8 was the least effective. Finally, the ability of the antibodies to influence the proliferation of the MO7e cells was examined. As expected, SR‐1 potently inhibited the proliferative response to SLF, while 17F11 weakly inhibited and YB5.B8 had negligible effect. In the absence of SLF both 17F11 and YB5.B8 displayed very weak but reproducible agonist activity. © 1994 Wiley‐Liss, Inc.
Transforming growth factor β1 augments mitogen‐induced prostaglandin synthesis and expression of the TIS10/prostaglandin synthase 2 gene both in swiss 3T3 cells and in murine embryo fibroblasts
Authors: Gilbert Rebecca S. , Reddy Srinivasa T. , Kujubu Dean A. , Xie Weilin , Luner Steven , Herschman Harvey R. 
Published: February 2005

AbstractTransforming growth factor‐beta (TGF‐beta), a potent cytokine, modulates a wide variety of biological responses. Among its actions, TGF‐beta can augment prostaglandin synthesis in several cell types. Although TGF‐beta alone has no effect on prostaglandin production in Swiss 3T3 cells, we find that TGF‐beta augments the ability of tetradecanoyl phorbol acetate (TPA) or serum to stimulate PGE2 production. The TIS10 gene is a primary response gene encoding a second form of prostaglandin synthase (PGS), the rate‐limiting enzyme in the biosynthesis of prostaglandins, thrornboxanes, and prostacyclins from arachidonic acid. TIS10/PGS‐2 expression is induced by mitogens in Swiss 3T3 cells. TGF‐beta also augments mitogen‐induced synthesis and accumulation of TIS10/PGS‐2 protein and induction of TIS10/PGS‐2 message in Swiss 3T3 cells. In contrast, TGF‐beta has little or no effect on the level of PGS‐1 (EC1.14.99.1) message, either alone or in concert with TPA or serum. TGF‐beta concentrations in the range of 0.01–0.10 ng/ml (0.4–4.0 pM) maximally enhance mitogen induction of TIS10/PGS‐2 message. TPA‐induced accumulation of unspliced TIS10/PGS‐2 transcript is augmented by TGF‐beta, suggesting that this cytokine exerts its effect on expression of the TIS10/PGS‐2 gene by transcriptional regulation. TGF‐beta also augments TPA‐induced prostaglandin production, TIS10/PGS‐2 antigen accumulation, and TIS10/PGS‐2 message induction in primary cultures of mouse embryo fibroblasts. Dexamethasone attenuates TGF‐beta enhancement of all these mitogen‐induced responses: PGE2 accumulation, appearance of TIS10/PGS‐2 protein and message, and accumulation of TIS10/PGS‐2 unprocessed transcript. © 1994 wiley‐Liss, Inc.
Amphiregulin‐dependent proliferation of cultured human keratinocytes: Autocrine growth, the effects of exogenous recombinant cytokine, and apparent requirement for heparin‐like glycosaminoglycans
Authors: Piepkorn Michael , Lo Christine , Plowman Greg 
Published: February 2005

AbstractAmphiregulin, a member of the epidermal growth factor family with heparin binding affinity, functions as a natural regulator of keratinocyte growth. Autocrine signaling by amphiregulin and the effects of exogenous recombinant cytokine were studied in serum‐free cultures of human neonatal keratinocytes. A metabolic inhibitor of proteoglycan sulfation was used to assess the role of cellular heparin‐like glycosaminoglycans in amphiregulin‐dependent growth. Keratinocytes plated at >103 cells/cm2 grew in an autocrine manner in the absence of exogenous epidermal growth factor or amphiregulin. Incubation of keratinocytes with an amphiregulin‐blocking antibody indicated that ∼70% of autocrine growth is mediated by endogenous amphiregulin. Proliferation potential in the presence of recombinant human amphiregulin was dose dependent and saturable and above ∼1 ng/ml was comparable to that achieved with similar concentrations of epidermal growth factor. Sodium chlorate, which blocks glycosaminoglycan sulfation, reversibly inhibited epidermal growth factor‐dependent proliferation by 42%, exogenous amphiregulin‐dependent proliferation by 75%, and autocrine growth by 95%; concurrent incubation with 1‐100 μg/ml heparin partially reversed this inhibition. Exogenous heparin in the absence of chlorate, however, nearly completely inhibited growth under autocrine conditions and in the presence of recombinant amphiregulin. Structure‐function studies indicate that the polymerization level, high sulfate group density, and possibly iduronic acid content of heparin‐like moieties correlate with their inhibitory activity. Collectively, these observations indicate that amphiregulin is the major autocrine factor for keratinocytes and demonstrate that exogenous amphiregulin is an effective growth promoting factor with molar potency similar to that of epidermal growth factor. Autocrine and paracrine signaling by amphiregulin may require cellular heparin‐like glycosaminoglycans, presumably as matrix or membrane proteoglycans, whereas soluble glycosaminoglycans inhibit signaling, possibly by competing for cytokine binding. © 1994 wiley‐Liss, Inc.