bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cholinergic desensitization of pepsinogen secretion and calcium mobilization of dispersed guinea pig chief cells
Authors: Cherner Jay A. , Naik Latika , Singh Gurcharn 
Published: February 2005

AbstractWhen dispersed chief cells from guinea pig stomach were first incubated with carbachol, washed, and then reincubated with carbachol in fresh incubation solution, the stimulation of pepsinogen secretion and the rise in intracellular calcium concentration during the second incubation were reduced. Carbachol did not cause residual enzyme secretion, but the same range of concentrations that causes enzyme secretion caused desensitization that was rapid, temperature dependent, and reversible with time. Preincubation with carbachol caused approximately a 65% reduction in enzyme secretion stimulated during a subsequent incubation with this agonist, but the potency of carbachol was unaffected. Prior exposure to carbachol also reduced subsequent stimulation caused by cholecystokinin (CCK‐8), gastrin I, ionophore A23187, or 12‐O‐tetradecanoylphorbol 13‐acetate but did not alter stimulation by any agonist that increases cellular cAMP. Carbachol pretreatment of Fura‐loaded chief cells caused a threefold increase in the EC50 for carbachol‐stimulated [Ca2+]i and approximately a 30% reduction in the maximal rise in [Ca2+]i in response to carbachol or CCK‐8. Inhibition of [N‐methyl‐3H] scopolamine binding by carbachol following carbachol pretreatment indicated that modulation of receptor affinity or number did not account for functional desensitization. These data indicate that carbachol causes heterologous desensitization of pepsinogen secretion stimulated by agonists that mobilize cellular Ca2+ or activate protein kinase C through a postreceptor action and suggest that an attenuated rise in chief cell calcium is one mechanism mediating the desensitization of enzyme secretion.
Thrombin‐induced prostacyclin biosynthesis in human endothelium: Role of guanine nucleotide regulatory proteins in stimulus/coupling responses
Authors: Garcia Joe G. N. , Painter Richard G. , Fenton John W. , English Denis , Callahan Karleen S. 
Published: February 2005

AbstractThe regulation of prostacyclin (PGl2) synthesis by cultured human umbilical vein endothelium (HUVEC) was investigated. HUVEC monolayer generation of PGl2 was monitored by RIA of 6‐keto PGF1α and dose‐dependent increases observed with human α‐and γ‐thrombins, histamine, or arachidonate. Alpha thrombin (10 nM) produced levels of 6‐keto PGF1α approximating responses with 1 μM γ‐thrombin, 5μM arachidonate, or 10 μM histamine. Diisopropyl phosphorofluo‐ridate‐inactivated α‐thrombin did not stimulate PGl2 release, demonstrating that catalytic activity was required for thrombin‐stimulated PGl2 release. Sodium fluoride (NaF), at concentrations known to activate guanine nucleotide regulatory proteins (G proteins), directly stimulated HUVEC PGl2 synthesis in a dose‐dependent and time‐dependent manner (20 mM NaF, 4.4 ± 0.5‐fold increase at 10 min, 11.9 ± 1.5‐fold increase at 30 min). Neither α‐thrombin nor NaF‐stimulated PGl2 release was dependent upon the availability of extracellular Ca+ +. The hypothesis that G proteins are involved in agonist‐stimulated PGl2 synthesis was further supported by studies using digitonin‐permeabilized HUVEC monolayers challenged with another G protein activator, guanosine 5′‐0‐3‐thiotrisphosphate (GTP γ S), which effected significant dose‐dependent increases in PGl2 synthesis compared with control levels of 6‐keto PGFα. In contrast, the G‐protein inhibitor GDP β S, (guanosine 5′‐0‐2‐thiodiphosphate), attenuated α‐thrombin‐mediated prostaglandin generation. Treatment of HUVEC monolayers with pertussis toxin (1 μg/ml) did not inhibit the PGl2 synthesis stimulated by either α‐thrombin, NaF, or histamine but catalyzed the ADP ribosylation of a 40 kDa membrane protein which cross‐reacted with antisera against a synthetic peptide corresponding to an amino acid sequence common to the α‐subunit of other G‐proteins. Preincubation of HUVEC microsomal membranes with α‐thrombin diminished pertussis toxin‐catalyzed ADP ribosylation in a time‐dependent manner. These data suggest that thrombin stimulation of PGl2 synthesis by HUVEC monolayers requires the catalytically functional enzyme and further suggests that the thrombin‐occupied receptor is coupled to phospholipase activities by a pertussis toxin‐insensitive guanine nucleotide regulatory protein in human endothelial cell membranes.
Purification of human blood burst‐forming units‐erythroid and demonstration of the evolution of erythropoietin receptors
Authors: Sawada K. , Krantz S. B. , Dai C‐H. , Koury S. T. , Horn S. T. , Glick A. D. , Civin C. I. 
Published: February 2005

AbstractTo facilitate the direct study of the molecular events that control the development of human burst‐forming units‐erythroid (BFU‐E), we have developed a method to purify BFU‐E from peripheral blood. Using density centrifugation, rosetting with a mixture of neuraminidase‐treated and IgG‐coated sheep erythrocytes, positive panning with anti‐My10 monoclonal antibody, overnight adherence to plastic dishes, negative panning with monoclonal antibodies, and density centrifugation, human blood BFU‐E were purified from 0.04% to 56.6%, a 1,400‐fold purification with a 13% yield. More than 90% of purified BFU‐E were recombinant interleukin‐3 (rlL‐3) dependent, which survived for 48 h with rlL‐3 in the absence of recombinant erythropoietin (rEP), and 80% gave rise to erythroid bursts of more than 500 hemoglobinized cells. rEP dependency was not evident until after 72 h of incubation in vitro. The purified cells (day 1) were incubated with rlL‐3 and rEP in liquid culture for 24 (day 2), 48 (day 3), and 72 (day 4) h and then were transferred into semisolid cultures and incubated until day 15. The size of the erythroid colonies observed in semisolid cultures decreased continuously in association with the incubation time of day 1 purified cells in liquid cultures. The first appearance of colony‐forming units‐erythoid (CFU‐E) that gave rise to colonies of 8 to 49 cells was observed after 72 h of incubation of day 1 cells in the liquid culture. 125I‐rEP was incubated for 5 h at 37°C with purified cells (day 1) or with the cells that had been incubated in liquid culture for an additional 24‐72 h, and the presence of erythropoietin (EP) receptors was investigated using auto‐radiography. Specific binding of 125I‐rEP was detected in 19 ± 7% of the initial day 1 BFU‐E. The percentage of 125I‐rEP‐binding to erythroid progenitor cells and the amount of binding continuously increased as day 1 BFU‐E matured. 125I‐rEP specific binding was observed with all of the erythroid progenitor cells that had been incubated in liquid culture for 72 h. These data demonstrate that primitive BFU‐E have a much lower number of EP receptors than CFU‐E and develop an increased concentration of EP receptors in association with their maturation and loss of proliferative capacity.
Comparison of the ability of basic and acidic fibroblast growth factor to stimulate the proliferation of an established keratinocyte cell line: Modulation of their biological effects by heparin, transforming growth factor β (TGFβ), and epidermal growth factor (EGF)
Authors: Gospodarowicz D. , Plouët J. , Malerstein B. 
Published: February 2005

AbstractThe bioactivity of both bFGF and aFGF in the BALB/MK‐1 cell line has been compared to that of EGF. Our results indicate that, for that cell type, aFGF was far more potent than bFGF in inducing cell proliferation. In the presence of heparin, aFGF was as potent as EGF. In addition, excess bFGF has an inhibitory effect on the proliferation of MK cells exposed to a saturating concentration of aFGF, therefore acting as a partial agonist of aFGF. Surprisingly, bFGF, although it had low biological activity, was capable of synergizing the effect of EGF. In its presence, culturesexposed to saturating concentration of EGF have a final cell density 3‐to 4‐fold higher than that of counterpart cultures exposed to EGF alone. TGFβ, which in previous studies has been shown to inhibit the growth of keratinocytes, also inhibited the growth of BALB/MK‐1 cells in response to either bFGF or aFGF. These studies suggest a role for FGF in regulating BALB/MK proliferation. aFGF provides positive growth signals which can be negatively modulated by excess bFGF or TGFβ, while bFGF, although a poor mitogen, could act by potentiating the effect of subsaturating concentrations of EGF.
Inhibition of replicon cluster ligation into chromosomal DNA at elevated temperatures
Authors: Warters Raymond L. , Lyons Bradley W. 
Published: February 2005

AbstractThe rate limiting enzymatic step for DNA replication in HeLa cells incubated at 43.5°C v/as the ligation of clusters of replicons into the cell's genome. At 43.5° the reciprocal slope for inhibition of DNA chain (replicon) initiation, or of the ligation of replicon clusters into the genome, was 18 or 7 min, respectively. The failure of replicon clusters to be ligated into chromosomal DNA was not a consequence of the failure of histone proteins to be deposited onto replicating DNA, or of chromatin replicated at 43.5°C to be organized into fully condensed chro‐matin. In addition it was not due to the failure of fully active topoisomerase II to be deposited at a normal frequency along replicating chromatin DNA. The failure of replicon clusters to be ligated into the genome resulted in the persistence of single, but not double, DNA strand breaks in the cell's genome 24 hours after cell heating.
Enhanced glycosyltransferase activity during thermotolerance development in mammalian cells
Authors: Henle Kurt J. , Monson Thomas P. , Stone Angie 
Published: February 2005

AbstractThe cellular heat shock response leads to the enhanced synthesis of a family of heat shock proteins and the development of thermotolerance. In CHO cells, however, heat shock also leads to enhanced synthesis of a 50 kD glycoprotein and elevated activity of N‐acetylgalactosaminyltransferase (GalNAcT). In this study we showed increased GalNAcT activity during thermotolerance expression in all of five mammalian cell lines included in the study. However, there was no simple correlation between cellular heat sensitivity of unheated control cells and basal levels of GalNAcT activity, measured toward the same exogenous acceptor apomucin. Although GalNAcT was elevated in thermotolerant cells, GalNAcT activity itself did not exhibit thermotolerance in terms of reduced sensitivity to heat inactivation. The increase in GalNAcT activity after heating was similar in exponentially growing and plateau‐phase cultures and was inhibited neither by cycloheximide nor actinomycin D. However, the inhibitors by themselves also increased GalNAcT activity in unheated control cells. Chemical inducers of ther‐motolerance (arsenite and diamide) increased GalNAcT activity, but the increase was modest when compared to that following hyperthermia. In addition to GalNAcT, two other glycosyltransferases with specificity for O‐glycans, α1,2‐fuco‐syltransferase and α2,6‐sialyltransferase, also showed increased activity after hyperthermia and during thermotolerance development. Together with previously published data, these results support the hypothesis that heat‐induced activation of O‐glycan‐specific glycosyltransferases plays a physiological role in the cellular heat shock response and in thermotolerance development.
Morphologic changes in human carcinoma cells (A‐431) stimulated by epidermal growth factor: Effect of cholesterol and low‐density lipoproteins on the ruffling response
Authors: Jackowski M. M. , Swift L. L. , Cohen S. , McKanna J. A. 
Published: February 2005

AbstractStimulation of A‐431 carcinoma cells with epidermal growth factor (EGF) causes dramatic morphologic responses including ruffling, rounding, and bulk‐phase pinocytosis. In attempts to explore the mechanisms responsible for changes in plasmalemma topography. we have investigated the effects of exogenous sterols thought to alter membrane fluidity.Light and scanning electron microscopy revealed a time‐ and concentration‐dependent inhibition of ruffling (> 90%) by cholesterol. This effect could be duplicated by preincubation of the cells with comparable levels of low‐density lipoproteins (LDL). EGF‐stimulated bulk‐phase endocytosis also is inhibited by treatment with cholesterol. No alteration of EGF binding, kinase stimulation, or internalization was detected in cells incubated in cholesterol‐enriched medium (175 μg/ml in 0.5% ethanol), nor did cholesterol or LDL have any effect on EGF‐stimulated rounding.Morphometry of electron micrographs from cholesterol‐treated cells revealed a selective depletion of interdigitating lateral surface membrane that normally appears to be recruited to generate apical ruffles. Thus, the sterol inhibition of ruffling may be due to redistribution of plasmalemma rather than to changes in membrane viscosity. Together with previous observations, these data suggest that EGF‐stimulated ruffling and bulk‐phase pinocytosis are related phenomena, whereas EGF‐stimulated cell rounding is an independent process.
Mechanism of human lymphotoxin and tumor necrosis factor induced destruction of cells in vitro: Phospholipase activation and deacylation of specific‐membrane phospholipids
Authors: Knauer Mary Fitzgerald , Longmuir Kenneth J. , Yamamoto Robert S. , Fitzgerald Thomas P. , Granger Gale A. 
Published: February 2005

AbstractThe role of phospholipase (PLase) activation and lipid metabolism in lymphotoxin (LT)‐ and tumor necrosis factor (TNF)‐mediated destruction of murine L929 cells was examined. At the levels of LT and TNF employed, cell destruction began at 4–6 h and was 99% complete by 30 h. Cell membrane phospholipids (PL), labelled in situ at the C2 position with 14C arachidonic acid, were analyzed by two‐dimensional thin‐layer chromatography and quantiated over a 30 h time course after LT or TNF treatment. The ratio of radiolabel incorporation relative to the actual amount of each PL present was determined by inorganic phosphate analysis. Radiolabelled arachidonic acid, eicosanoids, and neutral lipids were released into the medium prior to the onset of cell death (4–6 h) and continued to accumulate linearly throughout the destructive reaction. There was a quantitative relationship between the appearance of radiolabelled metabolites in the media and the loss of radiolabelled cellular PL. Cellular phosphatidylethanola‐mine was the primary PL deacylated by PLase action, showing a 75% reduction in radiolabel. The PLase inhibitors—quinacrine, hydrocortisone, dexamethasone, and indomethacin—were potent inhibitors of LT‐ and TNF‐mediated cell destruction, suggesting that selective deacylation of specific membrane PL by PLase activation is an important step in the events that lead to LT‐ and TNF‐mediated cellular destruction in vitro.
Protein kinase C levels and protein phosphorylation associated with inhibition of proliferation in a murine macrophage tumor
Authors: Goode Nigel T. , Hart Ian R. 
Published: February 2005

AbstractTreatment of M5076 tumor cells with the phorbol esters 12‐O‐tetradecanoyl‐phorbol 13‐acetate (TPA) and phorbol 12, 13 dibutyrate (PdBu) inhibited cellular proliferation, whereas 1,2‐dioctanoyl‐glycerol (DiC8) and 1‐oleoyl2‐acetyl‐glycerol (OAG) did not affect cell growth. Inhibition of cellular proliferation in this cell line appears to be a consequence of protein kinase C (PKC) down‐regulation since phorbol esters, but not a single application of diacylglycerols (DGs) down‐regulated cellular PKC levels. By repeated application of DGs, PKC down‐regulation was achieved and correlated with inhibition of proliferation. Phorbol ester‐induced PKC down‐regulation was reversible, upon removal of the phorbol ester, and the reappearance of PKC was associated with resumption of proliferation. The mitogenic responsiveness of these cells to added serum depended upon cellular PKC levels. Phorbol esters also caused the phosphorylation of two proteins which were not phosphorylated in response to DG treatment. Inhibition of growth of M5076 cells appears to be associated with phosphorylation of two novel proteins and/or PKC down‐regulation.
Epidermal G1‐chalone and transforming growth factor‐β are two different endogenous inhibitors of epidermal cell proliferation
Authors: Richter K. Hartmut , Schnapke Ruben , Clauss Matthias , Fürstenberger Gerhard , Hinz Detlef , Marks Friedrich 
Published: February 2005

AbstractEpidermal G1‐chalone and transforming growth factor‐β (TGFβ), two endogenous inhibitors of epidermal cell proliferation, were compared with regard to several effects on epidermis in vivo and in vitro. Both factors inhibited DNA labeling in a rat tongue epithelial cell line, with similar kinetics and half‐maximal effects at approximately 1 pg/ml (enriched chalone) and 1 ng/ml (TGFβ). For primary neonatal mouse keratinocytes, (TGFβ) was found to be a rather strong inhibitor of cell proliferation, whereas chalone showed only a weak effect on cells grown in medium containing 1.2 mM Ca2+ and no effect at all in the presence of 0.06 mM Ca2+. Vice versa, upon i.p. injection, only chalone was able to inhibit mouse epidermal DNA synthesis in vivo, whereas TGFβ had no effect at all. A moderate increase of transglutaminase activity in neonatal primary mouse keratinocytes was induced by both factors at concentrations of about 300 pg TGFβ/ml and 10 pg chalone fraction/ml. Chalone did not compete with [125]TGFβ for specific binding sites on primary murine keratinocytes. A polyclonal "chalone antiserum" did not interact with TGFβ, and a neutralizing TGFβ antibody that inhibited the effect of TGFβ on cell proliferation could not block the inhibitory effect of chalone on RTE2 cells. In contrast to TGFβ, epidermal G1‐chalone did not induce proliferation of NIH‐3T3 cells. These results indicate that epidermal G1‐chalone and TGFβ are two different inhibitors of epidermal cell proliferation.
Fibroblast growth factor‐dependent mitogenic signal transduction pathway in chemically transformed mouse fibroblasts is similar to but distinct from that initiated by phorbol esters
Authors: Buchou T. , Měster J. 
Published: February 2005

AbstractTreatment of the quiescent, chemically transformed Balb/c mouse 3T3 cells (BP‐A31) with fibroblast growth factor (FGF) leads to reinitiation of the cell division cycle in a large proportion of the cells. The characteristics of the mitogenic action of FGF closely resemble those of phorbol esters (activators of protein kinases type C) and differ from those of insulin (mediated by insulin‐like growth factor 1 receptors). In particular, the effects of FGF as well as of phorbol‐2‐myristate‐13‐acetate (PMA), unlike the effects of insulin, are prevented by a low concentration (7.5 nM) of staurosporin (an efficient inhibitor of protein kinase C) as well as by 3‐isobutyl‐1‐methyl xanthin (IBMX). Both FGF and PMA are good inducers of the accumulation of c‐fos and c‐jun mRNAs, whereas insulin has little effect. However, FGF was fully active (both as a mitogen and as inducer of c‐fos mRNA accumulation) also in cells where the protein kinase C‐mediated pathway had been downregulated by a long exposure to phorbol dibutyrate. We propose that the mitogenic effect of FGF does not require activation of protein kinase C, but that the subsequent events in the transduction pathways initiated by FGF and PMA, respectively, are (in part) coincident.
Coordinate reciprocal trends in glycolytic and mitochondrial transcript accumulations during the in vitro differentiation of human myoblasts
Authors: Webster Keith A. , Gunning Peter , Hardeman Edna , Wallace Douglas C. , Kedes Larry 
Published: February 2005

AbstractChanges in the mRNA levels during mammalian myogenesis were compared for seven polypeptides of mitochondrial respiration (the mitochondrial DNA‐encoded cytochrome oxidase subunit III, ATP synthase subunit 6, NADH dehydrogenase subunits 1 and 2, and 16S ribosomal RNA; the nuclear encoded ATP synthase β subunit and the adenine nucleotide translocase) and three polypeptides of glycolysis (glyceraldehyde‐3‐phosphate dehydrogenase, pyruvate kinase, and triose‐phosphate isomerase). Progressive changes during the conversion from myoblasts to myotubes were monitored under both atmospheric oxygen (nor‐moxic) and hypoxic environments. Northern analyses revealed coordinate, biphasic, and reciprocal expression of the respiratory and glycolytic mRNAs during myogenesis. In normoxic cells the mitochondrial respiratory enzymes were highest in myoblasts, declined 3‐ to 5‐fold during commitment and exit from the cell cycle, and increased progressively as the myotubes matured. By contrast, the glycolytic enzyme mRNAs rose 3‐ to 6‐fold on commitment and then progressively declined. When partially differentiated myotubes were switched to hypoxic conditions, the glycolytic enzyme mRNAs increased and the respiratory mRNAs declined. Hence, the developmental regulation of muscle bioenergetic metabolism appears to be regulated at the pretranslational level and is modulated by oxygen tension.
Intracellular processing of residualizing labels in different cell types in vitro
Authors: Lucas Karen L. , Baynes John W. , Thorpe Suzanne R. 
Published: February 2005

AbstractIn previous autoradiographic studies on the sites of catabolism of rat serum albumin (RSA) in the rat, fibroblasts in skin and muscle were shown to accumulate degradation product from RSA labeled with the residualizing label dilactitol‐125I‐tyramine (125I‐DLT) (Strobel et al., 1986 J. Biol. Chem., 261:7989—7994). Residualizing labels remain at the cellular site of degradation of the carrier protein because of their size, hydrophilicity, and resistance to lysosomal hydrolases. This study was designed to evaluate whether fibroblasts might retain labeled degradation products more efficiently than other cell types. The uptake of 125I‐DLT‐RSA and release of its degradation products and of a second non‐biodegradable probe, fluorescein isothiocyanate (FITC)‐dextran, were studied in fibroblasts, endothelial cells, and macrophages, all cell types previously implicated in the catabolism of albumin in vivo. The rates of uptake of labeled protein and dextran were comparable in all cell types and consistent with fluid phase endocytosis. The rate of release of both intact protein (30—35% of total radioactivity released) and radioactively labeled degradation products followed similar kinetics and had half‐lives ranging from 26 to 37 hr. The rate of release of FITC‐dextran was slower than that of radioactivity, with a half‐life of 42—125 hr. Thus, although there were differences between the rates of release of the fluorescent and radioactive materials in vitro, there were no significant differences in the disposition of protein‐derived catabolites among these three cell types.
Osmotic and motional properties of intracellular water as influenced by osmotic swelling and shrinkage of Xenopus Oocytes
Authors: Cameron Ivan L. , Merta Phillip , Fullerton Gary D. 
Published: February 2005

AbstractExperiments were done on fully grown Xenopus oocytes to determine the extent and the properties of cellular water of hydration. The studies involved the osmotic shrinking and swelling of the oocytes under known osmotic pressure as well as proton NMR spectral, titration, and free induction decay analyses. Studies were done both on whole oocytes and on subcellular fractions. The results show that little if any of the oocyte water in situ has the motional or osmotic properties expected of pure "bulk" water. Four distinct water of hydration compartments were found and defined on the basis of distinct hydrogen bounding mechanisms. Some of the water in yolk platelets was found not to be in fast exchange with other water compartments. Osmotic shrinkage of oocytes caused an adaptive decrease in the bound water of hydration compartments. This osmotically induced decrease is attributed to decreased surface area available for the hydrogen bounding of water molecules on cellular proteins.