bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apotransferrin stimulation of thyroid hormone dependent rat pituitary tumor cell growth in serum‐free chemically defined medium: Role of FE(III) chelation
Authors: Eby John E. , Sato Hidetaka , Sirbasku David A. 
Published: February 2005

AbstractTriiodothyronine (T3) dependent growth of GH1 rat pituitary tumor cells in serum‐free defined culture requires apotransferrin (apo Tf) (Sirbasku et al.: Mol. Cell. Endocrinol., 77:C47–C55, 1991). Diferric transferrin (2Fe · Tf) also is necessary as an iron source (Eby et al.: Anal. Biochem., 203:317–325, 1992). Further, T3 dependence is prevented by soluble Fe(III) addition to the medium (Sato et al.: In Vitro Cell. Dev. Biol., 27A:599–602, 1991). While our data suggested that apo Tf caused growth by chelation of Fe(III), direct evidence was required. We used urea polyacrylamide gel electrophoresis along with autoradiography and Western immunoblotting to measure the Fe(III) content of growing GH1 cell cultures and identify the apo Tf, mono‐metal transferrins and 2Fe · Tf present. We found that apo Tf per se did not cause growth but instead chelated inhibitory levels of Fe(III). In fact, apo Tf need not be present at all provided that Fe(III) is reduced to ≤0.6 μM. In addition, other protein and non‐protein Fe(III) chelators were shown to be as effective as apo Tf. Here, we report that pituitary cells are completely inhibited by ≥1.2 μM Fe(III), which are concentrations which might be expected in many culture media and usually are not thought to influence growth. The high sensitivity of pituitary cells to Fe(III) suggests further study to determine what cellular functions are affected and how they interfere with thyroid hormone dependence. © 1993 Wiley‐Liss, Inc.
Density‐dependent inhibitory effect of transforming growth factor‐β on human fibroblasts involves the down‐regulation of platelet‐derived growth factor α‐receptors
Authors: Paulsson Y. , Karlsson C. , Heldin C.‐H. , Westermark B. 
Published: February 2005

AbstractWe have previously found that transforming growth factor‐β1 (TGF‐β1) inhibits the mitogenic activity of platelet‐derived growth factor (PDGF) in cultures of human neonatal fibroblasts in a density‐dependent fashion. In the present investigation we determined the effect of TGF‐β1 on the PDGF α‐receptor, which binds all PDGF isoforms, as well as on the β‐receptor, which binds only PDGF‐BB with high affinity. We found that the inhibitory effect of TGF‐β1 on PDGF‐AA‐induced mitogenesis was density‐dependent; when dense cell cultures were preincubated with TGF‐β1, there was an complete inhibition of 3H‐thymidine incorporation, whereas the effect was less in sparse cultures. A similar density‐dependent effect of TGF‐β1 was seen in PDGF‐BB treated cells, although less pronounced. The binding of 125I‐labeled PDGF‐AA and PDGF‐BB to the α‐receptor was significantly reduced after treatment with TGF‐β1 in dense cultures, whereas the sparse cultures were less affected. A decrease of α‐receptor mRNA was also seen. The levels of β‐receptor protein and mRNA were unaffected. We conclude that the growth inhibitory effect of TGF‐β1 is cell density‐dependent and involves down‐regulation of PDGF α‐receptors. © 1993 Wiley‐Liss, Inc.
Investigation of the ability of several naturally occurring and synthetic polyanions to bind to and potentiate the biological activity of acidic fibroblast growth factor
Authors: Belford David A. , Hendry Ian A. , Parish Christopher R. 
Published: February 2005

AbstractThe ability of several animal, plant, and bacterial derived polyanions (PAs) as well as synthetic PAs to compete with heparin for the binding of acidic fibroblast growth factor (aFGF) was correlated with their ability to potentiate the mitogenic and neurotrophic actions of this factor. Dextran sulphate, K‐carrageenan, pentosan sulphate, polyanethole sulfonate, heparin, and fucoidin competed for the heparin binding site on aFGF at relatively low concentrations (≤50 μg/ml). λ‐carrageenan, ι‐carrageenan, and polyvinyl sulphate exhibited lower affinity for aFGF, whereas hyaluronic acid, dermatan sulphate, chondroitin‐6‐sulphate, chondroitin‐4‐sulphate, and uncharged dextran displayed very low or no demonstrable affinity. Potentiation of the mitogenic action of aFGF for Balb/c 3T3 fibroblasts tended to be in general agreement with the aFGF binding affinity of the PAs. However, polyanethole sulfonate, the carrageenans, polyvinyl sulphate, fucoidin, and pentosan sulphate exerted a mitogenic action on the 3T3 cells that was independent of, and in addition to, the ability of these GAGs to potentiate the action of aFGF. The ability to potentiate the neurotrophic action of aFGF for E8 chick ciliary neurons was a general property of those PA with low or no activity in the mitogen assay. Thus hyaluronic acid, dermatan sulphate, chondroitin‐4‐sulphate, chondroitin‐6‐sulphate, and even uncharged dextran all potentiated aFGF induced neuronal survival. The differential effects of these PA in potentiating the biological activities of aFGF are discussed in relation to their ability to compete for the heparin‐binding site of aFGF. © 1993 Wiley‐Liss, Inc.
Involvement of the conserved acidic amino acid domain of FGF receptor 1 in ligand‐receptor interaction
Authors: Chaudhuri Murari M. , Moscatelli David , Basilico Claudio 
Published: February 2005

AbstractThe fibroblast growth factor receptor 1 (flg) contains eight acidic amino acids between the first and second immunoglobulin domain. This report examines the role of the acidic domain in the interaction of the flg receptor with its ligands. We observed a marked inhibition of binding of bFGF to the receptor when the acidic domain was completely deleted, but mutants with two and four amino acids deleted (flgΔ2 and flgΔ4, respectively) still bound the ligand. After addition of a bifunctional cross‐linking reagent, cross‐linked complexes (between bFGF and receptor) with the expected size were observed in cells expressing mutants lacking two or four acidic residues, but not in cells expressing mutants lacking six or eight acidic residues. Immunoprecipitation with anti‐flg antibody followed by electrophoresis produced a band of 90 Kd in tunicamycin‐treated cells expressing the mutant as well as the wild‐type receptors, indicating that the inhibition of binding was not due to defective expression of the protein. The ability of flgΔ8 to mediate a mitogenic response to FGFs was also greatly reduced when this mutated receptor was expressed in receptor‐negative cells. The effect of replacing the acidic amino acids with lysine residues was also studied. Binding of bFGF to cells transfected with a plasmid encoding a mutated protein with four amino acid substitutions was totally inhibited, but an eight amino acid substitution did not alter ligand binding to the receptor. In this case the mutation with four amino acids substitution caused a drastic impairment of protein expression. Thus the acidic domain of the FGFR‐1 plays an essential role in receptor function, either because it is important for a stable protein configuration or for ligand‐receptor interaction. © 1993 Wiley‐Liss, Inc.
Inhibitors of vacuolar‐type H+‐ATPase suppresses proliferation of cultured cells
Authors: Manabe Tsukasa , Yoshimori Tamotsu , Henomatsu Nobuhiro , Tashiro Yutaka 
Published: February 2005

AbstractWe investigated effects of bafilomycin A1, a specific inhibitor of vacuolar‐type H+‐ATPase (V‐ATPase), and its analogues on proliferation of various cultured cells. The proliferation of the various cell lines was suppressed by adding bafilomycin A1 to the culture medium. This inhibitory effect appeared at a concentration of nanomolar order and was dose dependent. Although the suppression was reversible, the drug exerted not only suppression of the proliferation but also death to some cell lines. Drug concentration required for 50% inhibition of the cell proliferation during 48 h differed markedly depending on cell species and the sensitivity appears to increase by the transformation of the cells. Two derivatives of concanamycin A, an analogue of bafilomycin A1, also inhibited strongly V‐AT‐Pase in vitro and in vivo, and simultaneously cell proliferation. Two concanamycin A derivatives which have lost inhibitory effect on V‐ATPase lost inhibitory effect on cell proliferation as well. These results suggest that V‐ATPase is involved in the machinery maintaining the cell proliferation. © 1993 Wiley‐Liss, Inc.
Polyamine transport regulation by calcium and calmodulin: Role of Ca2+‐ATPase
Authors: Khanp Naim A. , Sezan Alphonse , Quemener Véronique , Moulinoux Jacques‐Ph 
Published: February 2005

AbstractThe study was conducted on human leukemia (K 562) cells to characterize the mechanisms implicated in the regulation of the polyamine spermicine (Spd) transport process. The antagonists of calmodulin, trifluoperazine (TFP), W‐7 (N‐[6‐aminohexyl]‐5‐chloro‐1‐naphthelenesulfonamide), or mellitin inhiblted significantly polyamine Spd uptake in these cells. The translocation of calmodulin towards plasma membrane and a concomitant decrease in its contents in cytosol were directly correlated with the time course increases similar to that of Spd uptake, indicating that calmodulin is recruited towards plasma membrane during the Spd transport process. Diminution of free intracellular calcium, (Ca2+)i, by preincubating the cells in BAPTA (bis[2‐amino‐5‐methylphenoxyl]‐ethane‐N,N′,N′,‐tetraacetate) buffer inhibited Spd transport significantly. Addition of lanthanum (LAN), a molecule known to inhibit Ca2 efflux via Ca2+‐ATPase, curtailed Spd uptake by these cells. LAN inhibited Vmax, but not the Km, of Spd uptake, indicating that the former does not directly interact with the polyamine transporter; rather it regulates the transport process, probably via its action on Ca2+‐ATPase. Calmodulin‐stimulated uptake of 45Ca2+ by inside‐out vesicles of K 562 cells, a measure of Ca2+‐ATPase activity. Furthermore, addition of LAN inhibited both basal and calmodulin‐stimulated activity of Ca2+‐ATPase. Thapsigargin (THAP), a molecule known to elevate (Ca2+) i due to its action on the endoplasmic reticulum, increased Spd transport whereas addition of LAN inhibited THAP‐stimulated Spd transport activity. THAP increased free (Ca2+)i in these cells, and a pre‐addition of LAN to these cells curtailed the THAP‐stimulated increases of (Ca2+)i concentrations. Addition of Spd brought about elevations in (Ca2+)i contents. Caffeine also increased (Ca2+)i in these cells; however, it failed to stimulate significantly the Spd uptake process, indicating that (Ca2+)i which is involved in the regulation of polyamine transport pathways does not belong to the calcium‐induced calcium‐release (CICR) pool. Replacement of Ca2+ from the incubation medium (i.e., 0% Ca2+) resulted in higher uptake activity as compared to that in 100% Ca2+ medium, demonstrating that in 100% Ca2+ medium the calcium efflux process is quickly compensated by calcium refilling/influx from the extracellular medium, while in 0% Ca2+ medium there is perpetual efflux of (Ca2+)i which contributes to higher Spd uptake process. The results of this study suggest that an increase in free (Ca2+)i and its release from the cells via Ca2+ ATPase, and concomitant activation of calmodulin, which controls Ca2+‐pump activity, are involved in the regulation of the Spd uptake process in human leukemia cells. © 1993 Wiley‐Liss, Inc.
Endothelial cell hypoxia associated proteins are cell and stress specific
Authors: Graven Krista K. , Zimmerman Leslie H. , Dickson Eric W. , Weinhouse Gerard L. , Farber Harrison W. 
Published: February 2005

AbstractVascular endothelial cells (EC) are one of the initial cells exposed to decreases in blood oxygen tension. Bovine EC respond not only by altering secretion of vasoactive, mitogenic, and thrombogenic substances, but also by developing adaptive mechanisms in order to survive acute and chronic hypoxic exposures. EC exposed to hypoxia in vitro upregulate a unique set of stress proteins of Mr 34, 36, 39, 47, and 56 kD. Previous studies have shown that these proteins are cell associated, upregulated in a time and oxygen‐concentration dependent manner, and are distinct from heat shock (HSPs) and glucose‐regulated proteins (GRPs). To further characterize these hypoxia‐associated proteins (HAPs), we investigated their upregulation in human EC from various vascular beds and compared this to possible HAP upregulation in other cell types. Human aortic, pulmonary artery, and microvascular EC upregulated the same set of proteins in response to hypoxia. In comparison, neither lung fibroblasts, pulmonary artery smooth muscle cells, pulmonary alveolar type II cells, nor renal tubular epithelial cells upregulated proteins of these Mr. Instead, most of these cell types induced synthesis of proteins of Mrs corresponding to either HSPs, GRPs, or both. Further studies demonstrated that exposure of EC to related stresses such as cyanide, 2‐deoxyglucose, hydrogen peroxide, dithiothreitol, and glucose deprivation did not cause upregulation of HAPs. Evaluation of cellular damage during hypoxia using phase‐contrast microscopy, trypan blue exclusion, chromium release, and adherent cell counts showed that EC survived longer with less damage than any of the above cell types. The induction of HAPs, and the lack of induction of HSPs or GRPs, by EC in response to hypoxia may be related to their unique ability to tolerate hypoxia for prolonged periods. © 1993 Wiley‐Liss, Inc.
Phorbol 12‐myristate 13‐acetate stimulates proliferation and ductal morphogenesis and inhibits functional differentiation of normal rat mammary epithelial cells in primary culture
Authors: Wada Tsutomu , Darcy Kathleen M. , Guan Xiaoping , Ip Margot M. 
Published: February 2005

AbstractThe effect of the tumor promoter phorbol 12‐myristate 13‐acetate (PMA) on proliferation and differentiation of normal mammary epithelial cells from 50‐day‐old virgin rats was investigated using a model system that allows for full morphological and functional development of the cells. In this model, mammary epithelial cells are grown within a reconstituted basement membrane in a defined serum‐free medium. PMA at a concentration of 10−6 M effected translocation of protein kinase C from cytosol to membrane. At the same concentration, it stimulated cell proliferation both in the presence and absence of EGF, and this stimulation was observed even when PMA exposure was limited to 15 min at the time of each media change. In contrast to the effect on proliferation, PMA at concentrations of 10−7 and 10−6 M inhibited functional differentiation as assessed by casein accumulation. Phorbol 12,13‐dibutyrate at 10−6 M also stimulated proliferation and inhibited casein accumulation and was more effective than PMA in both cases. In contrast, the nonactive tumor promoter 4‐α PMA had no effect on either proliferation or differentiation. One of the most striking effects of PMA was its ability to stimulate an atypical ductal morphogenesis, as manifested by the formation of intricate web‐like colonies, and to inhibit the development of the well‐differentiated alveolar‐like multilobular colonies. PMA was also shown to completely suppress the growth of the squamous‐like colonies that develop when EGF is absent or deficient. These effects of phorbol esters in mammary epithelial cells to stimulate proliferation, inhibit functional differentiation, and stimulate the development of ductal colonies are consistent with the suggestion that the signal transduction pathways evoked by PMA could act to stimulate the growth of initiated cells or render normal cells more sensitive to carcinogen. © 1994 Wiley‐Liss, Inc.
Calphostin‐C stimulates epidermal growth factor receptor phosphorylation and internalization via light‐dependent mechanism
Authors: Gamou Shinobu , Shimizu Nobuyoshi 
Published: February 2005

AbstractCalphostin‐C with perylenequinone structure is known to bind the regulatory domain of protein kinase C (PKC) and to inhibit kinase activity in vitro in a light‐dependent fashion. We have found that calphostin‐C induces substantial serine and threonine phosphorylation of the epidermal growth factor (EGF) receptor in a light‐dependent fashion in the EGF receptor‐hyperproducing squamous carcinoma cell line NA. Tryptic phospho‐peptide mapping and phospho‐amino acid analysis revealed that calphostin‐C–‐enhanced phosphorylation was on threonine 669, serine 671, serine 1046/1047, and serine 1166. However, caiphostin‐C did not inhibit phosphorylation of the 80 K protein, a cytosolic major substrate of PKC (MARCKS). Staurosporine, a potent PKC inhibitor with affinity for the catalytic domain of PKC, inhibited phosphorylation of the 80 K protein and 12‐O‐tetradecanoyl‐13‐phorbol acetate induction of EGF receptor phosphorylation but did not inhibit the calphostin‐C induction of the EGF receptor phosphorylation. These results suggest that the target of calphostin‐C in vivo is different from that of staurosporine and thus calphostin‐C in vivo does not inhibit PKC. Furthermore, calphostin‐C enhanced the internalization of phosphorylated EGF receptor. Thus, calphostin‐C apparently activates a novel signal transduction pathway which involves phosphorylation and internalization of the EGF receptor via light‐dependent mechanism. © 1994 Wiley‐Liss, Inc.
Stimulation of hepatocyte DNA synthesis by neurotensin
Authors: Hasegawa Kaoru , Kar Siddhartha , Carr Brian I. 
Published: February 2005

AbstractEpidermal growth factor and transforming growth factor alpha stimulated DNA synthesis in primary cultures of adult rat hepatocytes. Neurotensin amplified epidermal growth factor‐stimulated or transforming growth factor alpha‐stimulated DNA synthesis by three‐ to eightfold. Neurotensin by itself did not stimulate DNA synthesis. Amplification of DNA synthesis by neurotensin was observed as low as 10−10 M, and it was increased in a dose‐dependent manner with maximal effects at 10–8 M. These results were obtained when hepatocytes were cultured in Williams' medium E, but not in Leibovitz L‐15 medium, suggesting that a minor component(s) in the medium is required for hepatocytes to fully respond to neurotensin. Neurotensin effect on DNA synthesis was observed not only in normal rat hepatocytes but also in partially hepatectomized rat hepatocytes, although its effect was stronger in normal hepatocytes. Amplified DNA synthesis was inhibited by transforming growth factor β. Secondary mitogens (co‐mitogens) such as insulin, vasopressin, or angiotensin II interacted additively with low concentrations of epidermal growth factor as well as with neurotensin. Neurotensin‐related peptides such as kinetensin or neuromedin‐N, which was released from blood plasma by pepsin digestion, did not have this amplifying effect on DNA synthesis at any concentrations tested. Neurotensin mRNA was found in several organs including brain and intestine, but not liver. These results suggest that neurotensin can be regarded as a new secondary mitogen and that it may be involved in cell proliferation, including regenerating liver as a gastrointestinal hormone and/or a neurotransmitter. © 1994 Wiley‐Liss, Inc.
Consequences of aberrant ornithine decarboxylase regulation in rat hepatoma cells
Authors: Tome Margaret E. , Fiser Steven M. , Gerner Eugene W. 
Published: February 2005

AbstractDH23A cells, an α‐difluoromethylornithine (DFMO)–resistant variant of rat hepatoma tissue culture cells (HTC), contain high levels of very stable ornithine decarboxylase (ODC). In the absence of DFMO, the high ODC activity results in a large accumulation of endogenous putrescine. Concomitant with the putrescine increase is a period of cytostasis and a subsequent loss of viable cells. In contrast, HTC cells with a moderate polyamine content can be maintained in exponential growth. This suggests that a moderate polyamine concentration is necessary for both optimal cell growth and survival. The cytoxicity observed in the DH23A cells is apparently not due to byproducts of polyamine oxidation or alterations in steady state intracellular pH or free [Ca2+]. It is possible to mimic the effects of high levels of stable ODC by treatment of cells with exogenous putrescine in the presence of DFMO. This suggests that overaccumulation of putrescine is the causative agent in the observed cytotoxicity, although the mechanism is unclear. These data support the hypothesis that downregulation of ODC may be necessary to prevent accumulation of cytotoxic concentrations of the polyamines. © 1994 Wiley‐Liss, Inc.
Loss of cytotoxic effect of epidermal growth factor (EGF) on EGF receptor overexpressing cells is associated with attenuation of EGF receptor tyrosine kinase activity
Authors: Gardner David P. , Shimizu Nobuyoshi 
Published: February 2005

AbstractThe biological activity of epidermal growth factor (EGF) is mediated through the intrinsic tyrosine kinase activity of the EGF receptor (EGFR). In numerous cell types, binding of EGF to the EGFR stimulates the tyrosine kinase activity of the receptor eventually leading to cell proliferation. In tumor‐derived cell lines, which overexpress the EGFR, however, growth inhibition is often seen in response to EGF. The mechanism for growth inhibition is unclear. To study the relationship between growth inhibition and EGFR kinase activity, we have used a cell line (PC‐10) derived from a human squamous cell carcinoma that overexpresses EGFR. When exposed to 25 ng/ml EGF at low cell densities (1,300 cells/cm2), PC‐10 cells exhibit cell death. In contrast, if EGF is added to high density cultures, no EGF mediated cell death is seen. When PC‐10 cells were maintained at confluency in the presence of 25 ng/ml EGF for a period of 1 month, they were subsequently found competent to proliferate at low density in the presence of EGF. We designate these cells APC‐10. The APC‐10 cells exhibited a unique response to EGF, and no concentration of EGF tested could produce cell death. By 125I‐EGF binding analysis and [35S]methionine labeling of EGFR, it was found that the total number of EGFR on the cell surface of APC‐10 was not decreased relative to PC‐10. No difference between PC‐10 and APC‐10 was seen in EGF binding affinity to the EGFR. Significantly, EGF stimulated autophosphorylation of the EGFR of APC‐10 was 8–10‐fold lower than that of PC‐10. This reduced kinase activity was also seen in vitro in membrane preparations for EGFR autophosphorylation as well as phosphorylation of an exogenously added substrate. No difference between PC‐10 and APC‐10 in the overall pattern of EGFR phosphorylation in the presence or absence of EGF was detectable. However, the serine and threonine phosphorylation of the EGFR of APC‐10 cells was consistently 2–3‐fold lower than that seen in PC‐10 cells. These results suggest a novel mechanism for EGFR overexpressing cells to survive EGF exposure, one that involves an attenuation of the tyrosine kinase activity of the EGFR in the absence of a change in receptor levels or receptor affinity. © 1994 Wiley‐Liss, Inc.