bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sex‐dependent effects of 17‐beta‐estradiol on chondrocyte differentiation in culture
Authors: Nasatzky E. , Schwartz Z. , Boyan B. D. , Soskolne W. A. , Ornoy A. 
Published: February 2005

AbstractThis study examined the effects of 17‐beta‐estradiol (E2) on chondrocyte differentiation in vitro. Cells derived from male or female rat costochondral growth zone and resting zone cartilage were used to determine whether the effects of E2 were dependent on the stage of chondrocyte maturation and whether they were sex‐specific. [3H]‐incorporation, cell number, alkaline phosphatase specific activity, and percent collagen production were used as indicators of differentiation. Alakaline phosphatase specific activity in matrix vesicles and plasma membranes isolated from female chondrocyte cultures was measured to determine which membrane fraction was targeted by the hormone. Specificity of the E2 effects was assessed using 17‐alpha‐estradiol. The role of fetal bovine serum and phenol red in the culture medium was also addressed. The results demonstrated that E2 decreases cell number and [3H]‐incorporation in female chondrocytes, indicating that it promotes differentiation of these cells. Alkaline phosphatase specific activity is stimulated in both growth zone and resting zone cells, but the effect is greater in the less mature resting zone chondrocytes. The increase in enzyme activity is targeted to the matrix vesicles in both cell types, but the fold increase is greater in the growth zone cells. In male chondrocytes, there was a decrease in [3H]‐incorporation at high E2 concentrations in resting zone cells at the earliest time point examined (12 hours) and a slight stimulation in alkaline phosphatase activity in growth zone cells at 24 hours. Cells cultured in serum‐free medium exhibited a dose‐dependent inhibition in alkaline phosphatase activity when cultured with E2, even in the presence of phenol red. E2‐stimulation of enzyme activity is seen only in the presence of serum, suggesting that serum factors are also necessary. E2 increased percent collagen production in female cells only; the magnitude of the effect was greatest in the resting zone chondrocyte cultures. The results of this study indicate that the effects of E2 are dependent on time of exposure, presence of serum, and the sex and state of maturation of the chondrocytes. E2‐stimulation of alkaline phosphatase specific activity is targeted to matrix vesicles. © 1993 Wiley‐Liss, Inc.
Effect of amino acid analogs on the development of thermotolerance and on thermotolerant cells
Authors: Laszlo Andrei , Li Gloria C. 
Published: February 2005

AbstractExposure of HA‐1 Chinese hamster fibroblasts to amino acid analogs has been shown to have a heat‐sensitizing effect as well as inducing the heat shock response (Li and Laszlo, 1985a). In this study, we have examined the effect of amino acid analogs on the development of thermotolerance after a brief heat shock or exposure to sodium arsenite and the effect of amino acid analogs on cells that are already thermotolerant. Exposure of HA‐1 cells to amino acid analogs inhibited the development of thermotolerance following a mild heat shock or treatment with sodium arsenite. However, cells that were already thermotolerant were resistant to the sensitizing action of amino acid analogs. The refractoriness of thermotolerant cells to amino acid analog treatment developed in parallel with thermotolerance. The uptake of the arginine analog, canavanine, and its incorporation into proteins was not altered in the thermotolerant cells. Furthermore, another biological consequence of exposure to amino acid analogs, sensitization to ionizing radiation, also was not altered in the thermotolerant cells. The inhibition of the development of thermotolerance by amino acid analogs and the refractoriness of thermotolerant cells to the heat‐sensitizing action of amino acid analogs lend further support the role of heat‐shock proteins in the phenomenon of thermotolerance. © 1993 Wiley‐Liss, Inc.
Stimulation of bone resorption and osteoclast clear zone formation by low pH: A time‐course study
Authors: Murrills Richard J. , Stein Linda S. , Dempster David W. 
Published: February 2005

AbstractThe significance of low pH‐induced stimulation of osteoclastic bone resorption has recently been questioned following the finding that embryonic chick osteoclasts were only weakly stimulated by extremely low pH (6.5) and that the effect was transient, apparently due to cytotoxicity. Although low pH in the range 6.8–7.2 is known to stimulate rat osteoclasts over 24 h, the long‐term effects of low pH on mammalian osteoclasts are not known. We have therefore conducted time‐course studies over 72 h on the effect of pH in the range 6.3–7.3 on bone resorption and cytotoxicity in both rat and chick osteoclasts. In neonatal rat osteoclasts, lowering extracellular pH produced a powerful and significant stimulation of resorption over 24 h. Detailed analysis of the resorption focus revealed that this was due mainly to a higher proportion of active osteoclasts at lower pH. In addition, osteoclasts excavated slightly larger pits at low pH. Stimulation was no longer significant at 72 h, however, due to a pH‐dependent slowing of resorption at acid pH associated 1) with cytotoxicity primarily of nonosteoclastic cells and 2) with an acceleration of bone resorption after 24 h at more alkaline pH. Resorption stimulated by low pH was associated with the formation of actin‐rich “clear zones” within the osteoclast. Chick osteoclasts were less sensitive to low pH than rat osteoclasts but nonetheless showed a consistently higher level of resorption at low pH over 24–72 h. These results suggest that protons play an important regulatory role in neonatal rat osteoclasts, and stimulate the formation of clear zones. The lower sensitivity of the chick osteoclast to acid pH may be due to a species difference or the chick osteoclast's higher basal level of resorption. © 1993 Wiley‐Liss, Inc.
Ruffling and locomotion: Role in cell resistance to growth factor‐induced proliferation
Authors: Heckman C. A. , Oravecz K. I. , Schwab D. , Pontén J. 
Published: February 2005

AbstractIt has long been known that the growth rate of cells in vitro can be retarded by providing substrates of restricted area. Such experiments were performed with adhesive islets, made by depositing metals onto agarose layers through templates of various sizes. Since normal cells are unable to adhere to agarose, they become confined to the metallic surface. Using such haptotactic islets, we have studied the role of membrane ruffling and cell locomotion in the resistance of AG1523 human fibroblasts to growth factor‐induced mitogenesis. Cells plated on small substrates, i.e., 2,150 μm2 in area, initially showed vigorous ruffling, which was suppressed by 8 h after plating but had resumed again by 12 h. In contrast, cells on larger‐size islets showed a rapid decline and stabilization of ruffling activity. When the growth rate was measured for single cells cultured on haptotactic islets, it was found to increase linearly from areas of 4,280 μm2 up to 425,000 μm2. Since the area needed to saturate the growth response was ∼50‐fold larger than the area occupied by a single cell, the growth inhibition was attributed in part to an interference with locomotion. The implication that locomotion provided positive input into growth control mechanisms was subjected to a direct test by evaluating the effect of nine polypeptide growth factors on the motility of serum‐starved cells. All except TGF‐β1 stimulated movement. Finally, the mitogenic effect of growth factors was measured by [3H]thymidine incorporation and found to be proportional to motile activities, as quantitatively assayed. We conclude that locomotion suppression is a factor in AG1523 cell resistance to growth factor‐induced mitogenesis. © 1993 Wiley‐Liss, Inc.
Retinoic acid induces adult muscle cell differentiation mediated by the retinoic acid receptor‐α
Authors: Halevy Orna , Lerman Orna 
Published: February 2005

AbstractRetinoic acid (RA) is known to induce differentiation in many cell systems. This induction is mediated by nuclear RA receptors (RARs), which act as transactivating factors belonging to the superfamily of steroid/thyroid nuclear receptors. In this study, effects of RA were studied in a mouse myogenic C2 cell line and in primary chicken satellite cells, the myogenic precursor cells in adult muscle. Addition of RA decreased the rate of DNA synthesis in a dose‐dependent manner in both cultures. Differentiation was more rapid in cells treated with RA, and these cells exhibited large myotubes after 48 hr of incubation as compared to untreated cells, which were still proliferating. Addition of 10−8 M RA to C2 cells elevated mRNA levels of myogenin, a skeletal muscle‐specific transcription factor. In parallel, activity levels of the muscle‐specific creatine kinase were enhanced in the RA‐treated cells nearly twofold as compared to the untreated cells. RA treatment of both mouse C2 and chicken satellite cells caused rapid induction of the RAR‐α mRNA levels. Maximal mRNA levels were observed after 2 to 5 hr followed by a sharp reduction to nearly zero levels at 9 hr. The RAR‐α mRNA levels augmented in a dose‐dependent manner between concentrations of 10−10 M and 10−8 M RA, whereas higher concentrations caused mRNA levels to decrease. These results indicate that RA induces differentiation in both adult skeletal muscle primary satellite cells and a myogenic cell line. The rapid and specific induction of RAR‐α mRNA in these cells upon exposure to RA may suggest that this receptor is the primary target and a mediator of RA. © 1993 Wiley‐Liss, Inc.
Regulation of fibronectin and laminin binding activity in cultured human lymphoblastic cell lines
Authors: Stoolman L. M. , Wang Tai‐Ling , Situ Rui , Varani J. 
Published: February 2005

AbstractThe current study shows that a clonal derivative of the Jurkat cell line up‐regulates both the avidity and density of the α 6/β1 receptor in response to phorbol 12‐myristate 13‐acetate (PMA). This derivative attaches to fibronectin and, to a lesser degree, laminin constitutively. Adhesion and spreading are dramatically up‐regulated following treatment with PMA. The response on fibronectin peaks within 4 hours, is insensitive to cyclohexaminde, can be blocked by monoclonal antibodies (Mabs) to the β1 and α 5 subunits of the β1 family of integrins, and is not associated with increased expression of the α 5 or β1 epitopes at the cell surface. In contrast, the response on laminin is biphasic. The early phase parallels the response on fibronectin. The second phase peaks after 48–72 hours of treatment with PMA, is sensitive to cycloheximide, can be blocked by Mabs to the β1 and α 6 subunits, and is associated with increased expression of the α 6 epitope. Both the density independent and dependent responses to PMA in Jurkat cells are blocked by the protein kinase inhibitor staurosporine. The HSB‐2, CEM, Molt‐4, and HPB‐ALL T‐lymphoblastic cell lines also up‐regulate attachment to fibronectin and laminin following treatment with PMA. All four lines constitutively attach to fibronectin and show rapid up‐regulation of attachment following treatment with PMA. None of the lines attach to laminin prior to PMA treatment; however, specific adhesion developed after 4–120 hours of treatment. The most mature lines (Jurkat and HPB‐ALL) up‐regulated adhesion on laminin more rapidly than the less phenotypically mature lines (CEM, Molt‐4, and HSB‐2). In summary, clonal derivatives of the Jurkat cell line up‐regulated attachment to laminin through protein kinase dependent increases in α /β1 receptor avidity and density. In addition, the expression of functional receptors for laminin is linked to developmental maturity in a series of T‐lymphoblastic cell lines. © 1993 Wiley‐Liss, Inc.
Intracellular signalling by nucleotide receptors in PC12 pheochromocytoma cells
Authors: Raha Sandeep , De Souza Lynne R. , Reed Juta K. 
Published: February 2005

AbstractThe effect of extracellular ATP was studied in PC12 cells, a neurosecretory line that releases ATP. The addition of micromolar concentrations of ATP to PC12 cells evoked a transient increase in the cytosolic free Ca2+ concentration ([Ca2+]i), as measured with the Ca2+‐dye fura 2. AMP and adenosine were without effect, ruling out the involvement of P1 receptors in mediating this response. The increase in [Ca2+]i was reduced in calcium‐free media and virtually eliminated by the addition of EGTA, suggesting that calcium influx was the primary response initiated by extracellular ATP. Nucleotide triphosphates such as UTP and, to a lesser degree, ITP also evoked an increase in [Ca2+]i while GTP and CTP had little effect. In order to identify the receptor subtype mediating this response, the efficacy of ATP and ATP cogeners was assessed. The rank order potency was ATP > adenosine 5′‐[γ‐thio]triphosphate > ADP > 2‐methylthioadenosine triphosphate (2‐MeSATP) ∼ adenosine 5′‐[β‐thio]diphosphate ≫ adenosine 5′‐[αβ‐methylene] triphosphate, adenosine 5′‐[βγ‐imido]triphosphate. This profile is not characteristic of either the P2X or the conventional P2Y receptors. The Ca2+ response exhibited desensitization to ATP that was dependent on the extracellular metabolism of ATP. UTP was equally effective in desensitizing the response. ATP, UTP, ITP, and to a much lesser extent 2MeSATP increased inositol phosphate production in a dose‐dependent manner, suggesting receptor coupling to phosphatidylinositol‐specific phospholipase C. These data are consistent with the view that PC12 cells express a class of non‐P2Y nucleotide receptors (P2N) that mediate calcium influx and the accumulation of inositol phosphates. © 1993 Wiley‐Liss, Inc.
Nitric oxide and endothelin secretion by brain microvessel endothelial cells: Regulation by cyclic nucleotides
Authors: Durieu‐Trautmann O. , Fédérici C. , Créminon C. , Foignant‐Chaverot N. , Roux F. , Claire M. , Strosberg A. D. , Couraud P. O. 
Published: February 2005

AbstractEndothelin (ET)‐1 was originally characterized as a potent vasoconstrictor peptide secreted by vascular endothelial cells. It possesses a wide range of biological activities within the cardiovascular system and in other organs, including the brain. Also secreted by endothelial cells, nitric oxide (NO), has recently been identified as a relaxing factor, as well as a pleiotropic mediator, second messenger, immune defence molecule, and neurotransmitter. Most of the data concerning the secretion of these two agents in vitro has been collected from studies on macrovascular endothelial cells. Given the remarkable heterogeneity of endothelia in terms of morphology and function, we have analyzed the ability of brain microvessel endothelial cells in vitro to release ET‐1 and NO, which, at the level of the blood‐brain barrier, have perivascular astrocytes as potential targets. The present study was performed with immortalized rat brain microvessel endothelial cells, which display in culture a non transformed phenotype. Our data demonstrate that: (1) these cells release NO when induced by IFNγ and TNFα, (2) they constitutively secrete ET‐1, and (3) cAMP potentiates the cytokine‐induced NO release and exerts a biphasic regulation on ET‐1 secretion: micromolar concentrations of 8‐Br‐cAMP inhibit and higher doses stimulate ET‐1 secretion. This stimulation is blocked by EGTA and the calmodulin antagonist W7, but not by protein kinase C inhibitors, suggesting the involvement of the calmodulin branch of the calcium messenger system. These results suggest that cerebral microvessel endothelial cells may participate in vivo to the regulation of glial activity in the brain through the release of NO and ET‐1. © 1993 Wiley‐Liss, Inc.
Modulation of transforming growth factor‐beta 1 stimulated elastin and collagen production and proliferation in porcine vascular smooth muscle cells and skin fibroblasts by basic fibroblast growth factor, transforming growth factor‐α, and insulin‐like growth factor‐I
Authors: Davidson Jeffrey M. , Zoia Ornella , Liu Ji‐Min 
Published: February 2005

AbstractDuring tissue repair and development, matrix accumulation is modulated as multiple signals impinge on target cells. We have investigated the effects of combinations of the mitogenic cytokines, basic fibroblast growth factor (bFGF), transforming growth factor alpha (TGF‐α), and insulin‐like growth factor‐1 (IGF‐1) with transforming growth factor‐beta 1 (TGF‐β1) with respect to the production of two matrix components, elastin and type I collagen. Using specific enzyme‐linked immunoassays for detection of secreted precursors in both vascular smooth muscle cells and skin fibroblasts from the domestic pig, production of these two fibrous proteins was shown to be strongly stimulated by TGF‐β1. In the smooth muscle cell, both bFGF and TGF‐α were potent antagonists of TGF‐β1‐mediated matrix production, whereas IGF‐1 was only weakly additive with respect to elastin production. Antagonism was also evident to a lesser extent in skin fibroblasts. Reduced responsiveness to TGF‐β1 did not appear to be due to a switch to a proliferative state, since TGF‐β1 itself acted as a mitogen in confluent SMC, and TGF‐α was only a weak mitogen in confluent fibroblast cultures. Although a predominant effect of TGF‐β is matrix accumulation, these findings suggest that this property will be significantly modified by the cytokine context. © 1993 Wiley‐Liss, Inc.
Heparin‐like glycosaminoglycans participate in binding of a human trophoblastic cell line (JAR) to a human uterine epithelial cell line (RL95)
Authors: Rohde Larry H. , Carson Daniel D. 
Published: February 2005

AbstractIn vitro studies in our laboratory have indicated that heparan sulfate proteoglycans (HSPGs) play an important role in murine embryo implantation. In order to investigate the potential function of HSPGs in human implantation, two human cell lines (RL95 and JAR) were used to model uterine epithelium and embryonal trophectoderm, respectively. A heterologous cell‐cell adhesion assay was developed to determine if binding of JAR cells to RL95 cells was heparan sulfate–dependent. Labeled, single cell suspensions of JAR cells attached to confluent monolayers of RL95 cells in a dose‐ and time‐dependent manner. Heparin‐like glycosaminoglycans and JAR cell proteoglycans competitively inhibited JAR cell adhesion to RL95 cells by 50% or more. A panel of chemically modified heparins were used to demonstrate that O‐sulfation and amino group substitution were critical for inhibition of cell‐cell adhesion. Treatment with chlorate, an inhibitor of A ATP‐sulfurylase, resulted in a 56% reduction in cell‐cell binding compared to untreated controls. Heparinase and chondroitinase ABC markedly inhibited JARRL95 binding, while chondroitinase AC had no significant effect. These observations indicated that HSPGs as well as dermatan sulfate–containing proteoglycans participated in cell‐cell binding. Collectively, these results indicate that initial binding interactions between JAR and RL95 cells is mediated by cell surface glycosaminoglycans (GAGs) with heparin‐like properties (i.e., heparan sulfate and dermatan sulfate). These observations are consistent with an important role for HS and heparin‐like GAGs as well as their corresponding binding sites in early stages of human trophoblast‐uterine epithelial cell binding.
Characterization of an unusual mutant of human melanoma cells resistant to anticancer drugs that inhibit topoisomerase II
Authors: Campain Julie A. , Padmanabhan Raji , Hwang Jaulang , Gottesman Michael M. , Pastan Ira 
Published: February 2005

AbstractThe topoisomerase II inhibitor, VP‐16 (etoposide), is an important component in many chemotherapeutic regimens. To cahracterize resistance to this drug, the human melanoma cell line, FEM‐X, was selected in multiple steps with VP‐16. To prevent the development of typical multidrug resistance, an inhibitor of P‐glycoprotein, the tiapamil analog, RO‐11–2933, was added to the selections. The resultant clone FVP3 is 56‐fold resistant to VP‐16 and cross‐resistant to doxorubicin (Adriamycin) (9‐fold) and VM‐26 (27‐fold). These cells are also two‐ to fourfold resistant to m‐AMSA, daunorubicin, and mitoxantrone. FVP3 is not resistant to the P‐glycoprotein substrate vinblastine, does not express the MDR1 gene at detectable levels, and does not show reduced 3H‐VP‐16 accumulation. Unlike other cell lines that exhibit resistance to inhibitors of topoisomerase II, FVP3 has the same level of topoisomerase II expression and activity as FEM‐X. Using live cells treated with VP‐16, band depeletion assays and KCI/SDS precipitation assays show that topoisomerase II from FVP3 is much less susceptible to drug‐induced cleavable complex formation than is that from FEM‐X. This difference in sensitivity to VP‐16 is also detected using lysates from disrupted cells, but not with isolated nuclei devoid of cytoplasmic and membrane components. In addijtion, the topoisomerase li present in nuclear edtracts from FVP3 is not resistant to the effects of VP‐16 as measured by: (1)inhibition of strand passing activity during decatenation of kinetoplast DNA, (2) drug‐induced linearization of plasmid DNA, and (3) immunodepletion by VP‐16. These results suggest that some component of the cytoplasm or cellular membranes, or a factor depleted from nuclei during their isolation, is responsible for the resistance to VP‐16 in FVP3. © 1993 Wiley‐Liss, Inc.
Two zinc‐dependent steps during G1 to S phase transition
Authors: Chesters John K. , Petrie Linda , Lipson Kenneth E. 
Published: February 2005

AbstractThe influence of zinc (Zn) availability on thymidine kinase mRNA concentration has been investigated in cells in which production of the mRNA was regulated by either truncated thymidine kinase promoters or by the SV40 early promoter. Thymidine kinase mRNA concentrations were decreased by low Zn availability even when the promoter was truncated to 80 bp but not when it was replaced by the SV40 promoter. However, thymidine incorporation by the SV40 cells was still sensitive to lack of Zn, suggesting a second Zn‐sensitive process involved in commitment to S phase. The increase in histone H3 mRNA production prior to S phase was not inhibited by lack of Zn leading to a preferential increase in this mRNA in exponentially growing cells deprived of Zn. © 1993 Wiley‐Liss, Inc.
Synergistic action of calcium‐lonophores and hyperthermia is best interpreted as thermal enhancement of calcium toxicity
Authors: Stege G. J. J. , Wierenga P. K. , Konings A. W. T. , Kampinga H. H. 
Published: February 2005

AbstractIt has been shown that no relation exists between [Ca2+]i and hyperthermic cell killing, although heat‐induced increase of [Ca2+]i can be observed in some cell lines. When ionophores are used, dose‐dependent rises in [Ca2+]i may be found. Beyond a certain threshold of ionophore‐induced increases in [Ca2+]i, cells may be killed. Different threshold levels of [Ca2+]i exist in different cell lines. Hyperthermia can act synergistically with calcium ionophores to potentiate cell killing. Since there is no causal relation between [Ca2+]i and heat toxicity, this synergism can be explained as heat enhanced Ca2+ toxicity. In the current report, it is shown that both ionophore‐induced Ca2+ toxicity (37°C) and its potentiation by heat are dependent on extracellular calcium and related to sustained increases in [Ca2+]i. With ionomycin concentrations up to 15 μM, no increase in [Ca2+]i was seen in cells maintained in medium without Ca2+. Ionomycin effects on intracellular compartments were absent, and the drug seemed to act solely on the level of the plasmamembrane. Also, the synergism of heat and ionomycin appeared to act at the plasmamembrane, because depletion of extracellular calcium completely abolished this synergistic effect. The data presented are also discussed in the light of controversies existing in the literature for the role of calcium in hyperthermic cell killing. © 1993 Wiley‐Liss, Inc.