bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inhibition of epidermal growth factor/transforming growth factor‐α–stimulated cell growth by a synthetic peptide
Authors: Eppstein Deborah A. , Marsh Y. Vivienne , Schryver Brian B. , Bertics Paul J. 
Published: February 2005

AbstractEstrogen‐stimulated growth of the human mammary adenocarcinoma cell line MCF‐7 is significantly inhibited by monoclonal antibodies to the epidermal growth factor (EGF) receptor that act as antagonists of EGF's mitogenic events by competing for high‐affinity EGF receptor binding sites. These antibodies likewise inhibit the EGF or transforming growth factor‐α (TGF‐α)‐stimulated growth of these MCF‐7 cells. An analogous pattern of specific EGF or TGF‐α growth inhibitory activity was obtained using a synthetic peptide analog encompassing the third disulfide loop region of TGF‐α, but containing additional modifications designed for increased membrane affinity ([Ac‐D‐hArg(Et), Gly32,33]HuTGF‐α(31‐43)NH2). The growth factor antagonism by this synthetic peptide was specific in that it inhibited EGF, TGF‐α, or estrogen‐stimulated growth of MCF‐7 cells but did not inhibit insulin‐like growth factor‐1 (IGF‐1)‐stimulated cell growth. Altogether, these results suggest that a significant portion of the estrogen‐stimulated growth of these MCF‐7 cells is mediated in an autocrine/paracrine manner by release of EGF or TGF‐α‐like growth factors. The TGF‐α peptide likewise inhibited EGF‐ but not fibroblast growth factor (FGF)‐ or platelet‐derived growth factor (PDGF) ‐stimulated growth of NIH‐3T3 cells in completely defined media; but had no effect on growth or DNA synthesis of G0‐arrested cells, nor did it effect growth of NR‐6 cells, which are nonresponsive to EGF. Although this synthetic peptide did not directly compete with EGF for cell surface receptor binding, it exhibited binding to a cell surface component (followed by internalization), which likewise was not competed by EGF. The peptide did not directly inhibit EGF‐stimulated phosphorylation of the EGF receptor, nor did it inhibit phosphorylation of an exogenous substrate, angiotensin II, by activated EGF receptor. The TGF‐α peptide did, however, affect the structure of laminin as manifested by laminin self‐aggregation; this affect on laminin may, in turn, have a modulatory effect on EGF‐mediated cell growth.
Altered responses of regenerating hepatocytes to norepinephrine and transforming growth factor type β
Authors: Houck Keith A. , Michalopoulos George K. 
Published: February 2005

AbstractNorepinephrine (NE), acting through the α1‐adrenergic receptor, modulates the response of rat hepatocytes in primary culture to transforming growth factor type β1(TGFβ) by increasing the amount of TGFβ required for a given degree of inhibition of epidermal growth factor (EGF)‐induced DNA synthesis (Houck et al., J. Cell. Physiol.135:551–555, 1988). This effect was also found in hepatocytes isolated from regenerating livers but was greatly magnified in cells isolated between 12 and 18 hr after two‐thirds partial hepatectomy (PHX). During this period of enhanced sensitivity, NE was equally potent in terms of dose but more efficacious in the regenerating hepatocytes. As it did in control hepatocytes (Cruise et al., Science227:749–751, 1985), the α1‐adrenergic receptor mediated the activity of NE in regenerating hepatocytes. Vasopressin (VP) and angiotensin‐II (AG) also antagonized the effect of TGFβ and showed increased activity in regenerating hepatocytes but at only 50% or less of the maximal effect reached by NE. Regenerating hepatocytes isolated 24–72 hr after PHX exhibited decreased sensitivity to inhibition by TGFβ, with a nadir in 48‐hr‐regenerating cells. These findings suggest that NE may be involved in triggering the early phase of DNA synthesis during liver regeneration, with the subsequent acquisition of innate resistance to TGFβ responsible for continued proliferation at a time when TGFβ mRNA is known to be increasing in the liver (Braun et al., Proc. Natl. Acad. Sci. USA85:1539–1543, 1988). EGF induced increased DNA and protein synthesis in cultures of control hepatocytes; TGFβ inhibited the EGF‐induced DNA synthesis but had no effect on protein synthesis. This may be relevant to the latter stages of liver regeneration, when high levels of TGFβ mRNA are detected in liver and cellular hypertrophy predominates over hyperplasia.
Role of albumin arginyl sites in albumin‐induced reduction of endothelial hydraulic conductivity
Authors: Powers Michael R. , Blumenstock Frank A. , Cooper Jeffrey A. , Malik Asrar B. 
Published: February 2005

AbstractWe determined the effect of albumin on endothelial hydraulic conductivity (Lp) and the contributions of the positively charged arginyl and lysinyl residues of albumin in mediaing the effect. Studies were made using monolayers of cultured sheep pulmonary artery endothelial cells grown to confluence on polycarbonate filters. Water flux was measured as transendothelial hydrostatic pressure was varied from 5 to 20 cm H2 O. Lp was calculated from the slope of the relationship of water flux versus pressure. The Lp of endothelial monolayers perfused with albumin‐free Hanks Balanced Salt Solution (HBSS) was compared to perfusion with HBSS containing either native albumin, or albumin in which the arginyl residues were modified by a condensation reaction with 1,2‐cyclohexanedione (CHD‐albumin), or albumin in which the lysinyl residues were modified by a substitution reaction with succinic anhydride (SC‐albumin). Baseline Lp at 2.5 mg/ml native albumin was 1.6±0.1 × 10−6 cm/s/cm H2O compared to the filter Lp after removing cells of 3.0 ± 0.3 × 10−4 cm/s/cm H2O. Endothelial Lp increased by 60% when albumin concentration was decreased from 2.5 mg/ml to 0.5 mg/ml (P < 0.05), but did not change with an increase in concentration to 10 mg/ml. Albumin‐free buffer and CHD‐albumin increased endothelial Lp by 2.2 ± 0.3‐fold and 1.9 ± 0.3‐fold, respectively (P<0.05). All endothelial Lp values were restored to baseline when the native albumin concentration was returned to 2.5 mg/ml. Excess l‐arginine (2 × 10−3 M) inhibited the effect of native albumin and increased endothelial Lp 1.5 ± 0.02‐fold (P<0.05), but excess l‐lysine (4 × 10−3) in the presence of native albumin had no effect on Lp. None of the perfusates altered the filter Lp value. Neutral dextran (70 kD), in contrast to native albumin, had no effect on endothelial Lp. These results indicate that albumin reduces the hydraulic conductivity of endothelial monolayers in a concentration‐dependent fashion and that the arginyl residues of albumin are required for the response. The effect of albumin may be meditated by a charge interaction of albumin with the endo‐thelium.
Multiple sequential periods of DNA synthesis and quiescence in primary hepatocyte cultures maintained on the DMSO‐EGF on/off protocol
Authors: Chan Krammie , Kost Diane P. , Michalopoulos George 
Published: February 2005

AbstractRepeated periods of DNA synthesis activity (each period consisting of two to three cycles) separated by intervals of quiescence in primary rat hepatocytes can be stimulated by sequential addition and removal of 2% dimethyl sulfoxide (DMSO) in the presence of epidermal growth factor (EGF). Hepatocytes can be kept in nonproliferating cultures for 7 days in media supplemented with 2% DMSO and EGF. If DMSO is removed while EGF is maintained, rat and human hepatocytes enter a 3 to 4 day period of DNA synthesis that declines rapidly by days 4 and 5. If DMSO is reintroduced into cultures at that point, kept on for 3 more days and removed again, hepatocytes reenter into proliferation with another self‐limited response of 3 to 4 days. Similar phenomena can seen with hepatocytes maintained in the presence of 3 mM phenobarbital. These protocols demonstrate that loss of responsiveness to mitogens in primary hepatocyte cultures is not an irreversible process. They also raise the possibility that signals for termination of DNA synthesis in hepatocytes emanate from hepatocytes themselves. These studies also suggest for the first time the possibility of designing in vitro systems that will allow clonal expansion of differential hepatocytes.
Receptor specific for certain nucleotides stimulates inositol phosphate metabolism and Ca2+ fluxes in A431 cells
Authors: Gonzalez Fernando A. , Alfonzo Ramona G. , Toro Jorge R. , Heppel Leon A. 
Published: February 2005

AbstractWe have recently reported that extracellular ATP induces a transient rise in cytosolic free Ca2+([Ca2+]i) in individual human epidermoid carcinoma A431 cells (Gonzalez et al: Journal of Cellular Physiology 135:269–276, 1988). We have now studied nucleotide specificity and desensitization for several early responses. Extracellular ATP (5–100 μM) caused the rapid formation of inositol trisphosphate and later its metabolites, inositol bisphosphate and inositol monophosphate. ATP also induced the efflux of 45Ca2+ from pre‐loaded cells. In addition, an increase in the rate of influx of 45Ca2+ stimulated by extracellular ATP was detected. Based on measurements of 45Ca2+ efflux and influx, desensitization studies, and chlortetracycline fluorimetry, we conclude that ATP mobilizes Ca2+ from internal stores and also stimulates entry across the plasma membrane. These effects were also displayed by UTP and to a lesser extent by ITP, while other nucleoside triphosphates as well as ADP, AMP, and adenosine, were inactive. Furthermore, desensitization of the response to ATP and UTP was seen after prolonged exposure to either nucleotide. This was specific for the nucleotide receptor since a response to bradykinin was not affected by the ATP pretreatment, although pretreatment with phorbol ester inhibited responses to both the nucleotides and bradykinin. Quantitative data on rate of recovery from the desensitized state and the response of desensitized cells to greatly elevated levels of ATP are presented. Extracellular ATP stimulated another early change previously reported for epidermal growth factor, namely, the phosphorylation of an 81‐kDa cytoskeletal protein. The stimulation of these events involves an ATP receptor whose properties differ from other ATP receptors that have been described.
Smooth muscle actin expression during P19 embryonal carcinoma differentiation in cell culture
Authors: Rudnicki Michael A. , Sawtell Nancy M. , Reuhl Kenneth R. , Berg Randy , Craig Jane C. , Jardine Karen , Lessard James L. , McBurney Michael W. 
Published: February 2005

AbstractP19 embryonal carcinoma (EC) cells can be induced in vitro to differentiate into cells resembling those normally formed in the embryo. Among these cell types is one whose morphology is fibroblast‐like. Using indirect immunofluorescence and Western blot analysis with antibodies directed against various isoforms of actin, many of these fibroblast‐like cells were found to express smooth muscle actin isoforms. Northern blot analysis of RNA indicated the presence of a smooth muscle‐specific isoform of myosin heavy‐chain mRNA in immortal lines of these fibroblast‐like cells. These results suggest that these fibroblast‐like cells resemble fetal myofibroblastic or myoepithelial cells, which have a wide distribution during embryonic development.
Effects of interleukin 3 and of granulocyte‐macrophage and macrophage colony stimulating factors on osteoclast differentiation from mouse hemopoietic tissue
Authors: Hattersley G. , Chambers T. J. 
Published: February 2005

AbstractThe effects of granulocyte‐macrophage colony stimulating factor (GM‐CSF), macrophage colony stimulating factor (M‐CSF), and interleukin 3 (IL3) on osteoclast formation were tested by incubation of murine hemopoietic cells on plastic coverslips and bone slices with GM‐CSF, M‐CSF, or IL3, with or without 1,25(OH)2 vitamin D3 (1,25(OH)2D3). Osteoclastic differentiation was detected after incubation by scanning electron microscopical examination of bone slices for evidence of osteoclastic excavations, and by autoradiographic assessment of cells for 1,25(OH)2D3‐calcitonin (CT) binding. The differentiation of CT‐receptor‐positive cells preceded bone resorption, but the number that developed correlated with the extent of bone resorption (r = 0.88). M‐CSF and GM‐CSF substantially reduced bone resorption and CT‐receptor‐positive cell formation. The degree of inhibition of bone resorption could not be attributed to effects on the function of mature cells, since M‐CSF inhibits resorption by such cells only by 50%, and GM‐CSF has no effect. GM‐CSF inhibited the development of mature function (bone resorption) to a greater extent than it inhibited CT‐receptor‐positive cell formation. Since CT‐receptor expression antedated resorptive function, this suggests that GM‐CSF resulted in the formation of reduced numbers of relatively immature osteoclasts. This suggests that it may exert a restraining effect on the maturation of cells undergoing osteoclastic differentiation in response to 1,25(OH)2D3. Conversely, IL3, which also has no effect on mature osteoclasts, by itself induced CT‐receptor expression but not bone resorption; in combination with 1,25(OH)2D3 it induced a threefold increase in bone resorption and CT‐receptor‐positive cells compared with cultures incubated with 1,25(OH)2D3 alone. IL3 did not induce CT‐receptors in peritoneal macrophages, blood mono‐cytes, or J 774 cells. The results suggest that IL3 induces only partial maturation of osteoclasts, which is augmented or completed by additional factors such as 1,25(OH)2D3.
Heat‐induced cytotoxicity in H2O2‐resistant Chinese hamster fibroblasts
Authors: Spitz Douglas R. , Li Gloria C. 
Published: February 2005

AbstractHydrogen‐peroxide‐resistant Chinese hamster fibroblasts, derived from the HA‐1 cell line, were isolated following continuous culturing in the presence of progressively increasing concentrations of hydrogen peroxide. The hydrogen‐peroxide‐resistant phenotype has been stable for over 360 days following removal from H2 O2 stress. These H2 O2‐resisant cell lines demonstrate increased resistance to hyperthermic cell killing, mediated by continuous heating at 43°C but not 45°C. The relationship between mammalian cellular adaptation to oxidative stress mediated by H2 O2 and resistance to 43°C hyperthermia is discussed.
Analysis of the tetrahydrobiopterin synthesizing system during maturation of murine reticulocytes
Authors: Kerler F. , Hüultner L. , Ziegler I. , Katzenmaier G. , Bacher A. 
Published: February 2005

AbstractThe enzymes of tetrahydrobiopterin synthesis have been studied in murine bone marow, in spleen, in erythrocytes, and in reticulocytes. Mice with chemically induced and with genetically conditioned reticulocytosis as found in the lactate dehydrogenase deficient strain (Ldh‐1c/Ldh‐1c) were used for analysis of reticulocytic enzyme activities. The activity of the biopterin synthesizing system is highest in bone marrow even though it amounts to only about 10% as compared with liver. The first enzyme of the biosynthetic pathway, GTP‐cyclohydrolase, virtually disappears during the final maturation step of reticulocytes. In contrast, the activities of 6‐pyruvoyltetrahydropterin synthase and of sepiapterin reductase of erythrocytes are only reduced to about one half of the reticulocyte level. The absence of biopterin in erythrocytes is therefore caused by the loss of the enzyme that initiates the pterin biosynthetic pathway.
Effects of transforming growth factor‐β on long‐term human cord blood monocyte cultures
Authors: Orcel Philippe , Bielakoff Josette , De Vernejoul Marie Christine 
Published: February 2005

AbstractTransforming growth factor‐β (TGF‐β) modulates growth and differentiation in many cel' types and is abundant in bone matrix. We recently showed that human cord blood monocytes cultured in the presence of 1,25(OH)2D3 acquire some features of osteoclast precursors. Since TGF‐β has been shown to influence bone resorption in organ culture, we have studied the effect of TGF‐β (1‐1,000 pg/ml) on cord blood monocyte cultures. These cells were cultured on plastic substrate during 3 weeks in the presence of 20% horse serum and 10−9 M 1,25(OH)2D3 TGF‐β, from a concentration of 10 pg/ml in the culture medium, decreased in a dose dependent manner the formation of multinucleated cells. At a concentration of TGF‐β of 1 ng/ml, the multinucleated cells were reduced to 2.1% ± 0.3%, compared to 19.3% ± 1.5% in control cultures. TGF‐β inhibited in a dose‐dependent manner the proliferation of cord blood monocytes as assessed by 3H‐thymidine incorporation at 7 and 14 days of culture. The fusion index was also decreased by 3 weeks of treatment with TGF‐β Indomethacin did not reverse the inhibitory effects of TGF‐β. The expression of the osteoclastic phenotype was assessed using two different antibodies: 23C6, a monoclonal antibody directed against the vitronectin receptor, which is highly expressed by osteolasts but not by adult monocytes, and an antibody to HLA‐DR, which is not present on osteoclast. TGF‐β decreased the expression of HLA‐DR and increased in a dose‐dependent manner the proportion of 23C6‐labeled cells; these results suggest that TGF‐β could modulate a differentiation effect to the osteoclastic phenotype. However, when cord blood monocytes were cultured on devitalized rat calvariae prelabeled with 45Ca, TGF‐β did not induce any 45Ca release from bone cultured with monocytes, suggesting that full osteoclastic differentiation was not achieved. These results emphasize the complex role of TGF‐β in the local regulation of bone cell differentiation and in bone remodeling.
Cyclical binding, processing, and functional interactions of neutrophils with leukotriene B4
Authors: O'Flaherty Joseph T. , Redman Jimmy F. , Jacobson David P. 
Published: February 2005

AbstractLeukotrene (LT) B4 activates human polymorphonuclear neutrophils. (PMN) by binding to plasmalemmal receptors. It stimulates PMN to raise cytosolic calcium and degranulate. Both responses end within 15–30 sec. However, in < 15 sec, LTB4‐treated PMN lose the ability to respond further to LTB4; decrease the affinity and number of high affinity receptors available for binding LTB4 sequester LTB4 in plasmalemma‐associated sites that are inaccessible to a releasing buffei regi i men; and begin internalizing LTB4. Over the next 90 min, the cells increasingly internalize LTB4 and convert it to less potent metabolites; release the metabolites; recover LTB4 binding sites; and become fully sensitive to LTB4. Contrastingly, during the entire 90 min incubation with LTB4. PMN retained the capacity to bind and respond normally to a second stimulus platelet‐activating factor. We therefore suggest the following model. LTB4 receptors, when ligand‐bound, initiate function but rapidly lose this capacity as they lower their ligand binding affinity and sequester, internalize, or otherwise uncouple from transducing elements. These LTB4 receptor changes contribute to terminating PMN responses and producing a stimulus‐selective state of desensitization. During the desensitization period, PMN progressively process and metabolize LTB4. This removes LTB4 from the environment, thereby allowing PMN to recover functional receptors for and sensitivity to the ligand.
Ultraviolet stimulated melanogenesis by human melanocytes is augmented by di‐acyl glycerol but not TPA
Authors: Friedmann P. S. , Wren F. E. , Matthews J. N. S. 
Published: February 2005

AbstractEpidermal melanocytes (MC) synthesise melanin in response to ultraviolet radiation (UVR). The mechanisms mediating the UV‐induced activation of melano‐genesis are unknown but since UVR induces turnover of membrane phospholipids generating prostaglandins (PGs) and other products, it is possible that one of these might provide the activating signal. We have examined the effects of prostaglandins (PGs) E1, E2, D2, F2α, and di‐acyl glycerol upon the UV‐induced responses of cultured human MC and the Cloudman S91 melanoma cell line. The PGs had little effect on unirradliated cells and did not alter the response to UVR in either human MC or S91 melanoma cells. However, a synthetic analogue of di‐acyl glycerol, 1‐oleyl 2‐acetyl glycerol (OAG), caused a significant (P<0.0001), dose‐related augmentation of melanin content both in human MC (seven‐fold) and S91 cells (three‐fold). UVR caused a significant augmentation of the OAG‐induced melanognesis of both human MC and S91 cells. Since OAG is known to activate protein kinase C, it was possible that the observed modulation of the UVR signal could be via that pathway. Di‐octanoyl glycerol, another di‐acyl glycerol, which activates kinase C, caused a small (70%) increase in melanogenesis in MC which was not altered by UVR. However, 12‐0 tetradecanoyl phorbol 13‐acetate (TPA), a potent activator of protein kinase C, had no significant effect on either basal or UV‐induced melanin synthesis in either cell type. These data suggest that the UV‐induced signal activating melanogenesis could be mediated by di‐acyl glycerol. Furthermore, they imply that the signal is transduced via an alternative, pathway that might be independent of protein kinase C.
Three distinct effects of SV40 T‐antigen gene transfection on cellular differentiation
Authors: Estervig David N. , Minoo Parviz , Tzen Chin‐Yuan , Scott Robert E. 
Published: February 2005

AbstractSV40 large T‐antigen‐induced transformation has been reported to block differentiation, but the mechanism(s) of this effect has not been established. The results presented here show that stable transfection of the SV40 T‐antigen gene, via the pSV3neo plasmid, has at least three distinct effects on 3T3T adipocyte differentiation. Cells first show a decreased ability to undergo predifferentiation growth arrest, which is a prerequisite for in vitro 3T3T adipocyte differentiation. However, if predifferentiation growth arrest is accomplished by use of stringent differentiation‐inducing culture conditions, adipocyte differentiation can occur with high frequency. The pSV3neo‐transfected cell clones also show other modifications of the adipocyte differentiation process, including changes in nonterminal (reversible) and terminal (irreversible) steps of adipocyte differentiation. When compared to nontransfected 3T3T cells, the cell clones containing pSV3neo require markedly reduced growth factor concentrations to restimulate proliferation of nonterminally differentiated adipocytes and the terminal step of differentiation is also blocked. These results suggest that integration of the T‐antigen gene, through pSV3neo transfection, has multiple effects on the cellular mechanisms of differentiation. It does not block the differentiation process per se; rather it appears to make cells highly sensitive to proliferation signals, thereby making differentiation more difficult.