bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monoclonal Antibodies Which Alter the Morphology of Cultured Chick Myogenic Cells
Authors: Greve Jeffrey M. , Gottlieb David I. 
Published: December 2004

AbstractTwo monoclonal antibodies that cause changes in the morphology of cultured myogenic cells are described. Antibody JG9 causes myoblasts to round up and causes myotubes to become thin, cable‐like structures with multiple round swellings. Antibody JG22 causes both myoblasts and myotubes to become round refractile cells poorly attached to the substratum. The effects of both antibodies are reversible. Fab fragments of JG22 can cause the morphological change. A tentative identification of the antigen recognized by JG22 is made.
Mitogenicity of Brain Axolemma Membranes and Soluble Factors for Dorsal Root Ganglion Schwann Cells
Authors: Cassel Dan , Wood Patrick M. , Bunge Richard P. , Glaser Luis 
Published: December 2004

AbstractPrevious studies in this laboratory have shown that membranes derived from dorsal root ganglia (DRG) neurites are mitogenic for cultured Schwann cells derived from the same source [Salzer et al (1980): J Cell Biol 84:767–778]. Improved procedures are described for preparing Schwann cells derived from dorsal root ganglia that are highly responsive to various mitogens. Under these conditions, the cells respond not only to the neurite mitogen but also to pituitary extracts, dibutyryl cyclic AMP, and cholera toxin that have been shown previously to be good mitogens for Schwannn cells derived from sciatic nerve [Raff et al (1978): Cell 15:813–822], thus reconciling discrepancies in the response of these different Schwann cell preparations to mitogens. Searching for a source of membranes more suitable for biochemical characterization of the neurite mitogen, we found that bovine brain axolemma, prepared by the method of DeVries et al [(1977): Brain Res 147:339–352] is highly mitogenic for Schwann cells. The milotic index of Schwann cells was increased by the addition of axolemma from 0.5%–2% to 30%–50% during 24‐h incubation with [3H]thymidine. Half maximal effect was obtained at about 0.4 μg axolemma protein per microwell containing 2–4 × 10 3 cells. The axolemma mitogen appears to be an integral membrane protein that remains bound to the membrane under various ionic conditions but can be extracted in a partially active form with deoxycholate. Like the DRG neurite mitogen, the mitogenic activity of axolemma was abolished by trypsin treatment. Unlike the neurite preparation, however, the mitogenic activity of axolemma was only partially inactivated by heat treatment (60%–70% inactivation). A significant difference between the mitogenic activity of axolemma membranes and neurite membranes is the fact that axolemma membranes fail to stimulate Schwann cell proliferation in a defined, serum‐free medium (N‐2), whereas neurites show significant mitogenic activity in this medium. These findings indicate a possible difference between DRG neurites and brain axolemma either in the mitogen itself or surface components responsible for recognition between the membranes and the cells.
Calcium‐Dependent and Calcium‐Independent Adhesive Mechanisms Are Present During Initial Binding Events of Neural Retina Cells
Authors: McClay David R. , Marchase Richard B. 
Published: December 2004

AbstractThe hypothesis that intercellular adhesion can be subdivided into two separable phenomena, an initial recognition event and a subsequent stabilization, is supported by the use of a new cell binding assay that provides a quantitative measure of intercellular binding strengths. Radioactive single cells are brought into contact with cell monolayers at 4°C in sealed compartments. The compartments are inverted and a centrifugal force is then applied tending to dislodge the probe cells from the monolayers. By varying the speed of centrifugation, the force maintaining associations between embryonic chick neural retina cells was determined to be on the order of 10−5 dynes after incubation at 4°C. Brief incubations at 37°C resulted in significant strengthening of the intercellular bond. Using this cell binding assay, neural retina cells were shown to exhibit both a Ca++‐independent and a Ca++‐dependent mechanism in their initial binding to one another.
Effect of phalloidin on liver actin distribution, content, and turnover
Authors: Low Robert B. , Low Elizabeth S. , Chaponnier Christine , Mitchell Janet W. , Gabbiani Giulio 
Published: December 2004

AbstractPhalloidin increases F‐actin microfilament content and actin‐directed immunofluorescence in hepatocytes in vivo and also increases actin polymerization and the stability of F‐actin in vitro. We studied the sensitivity of immunofluorescent staining of actin to an actin depolymerizing factor (ADF) as well as actin content, degree of polymerization, and turnover in livers of in vivo phalloidin‐treated rats. Pretreatment with ADF abolished anti‐actin antibody (AAA) staining of normal liver but did not modify staining of livers from phalloidin‐treated animals. Plani‐metric analyses of SDS‐polyacrylamide gels snowed the percent actin of total protein was increased by approximately 40% and the absolute amount of actin by approximately 43%, ten days after daily phalloidin treatment (50 μg/100 gm body weight). Similar but smaller changes could be seen after one day of treatment. Ultracentrifugational analyses of liver extracts indicated no change in the amount or proportion of G‐actin but a 194% increase in the proportion of F‐actin in ten‐day treated animals, changes also apparent in one day animals. Neither the relative fractional rate of actin synthesis nor its synthesis as a percent of total protein synthesis was altered either at one‐day or ten‐day post‐phalloidin treatment. Dual‐isotope experiments indicated that the rate of actin degradation was decreased selectively in the one‐ to three‐day period ‐following drug treatment. Thus, phalloidin appears to stabilize actin against the depolymerizing actions of ADF, increases the proportion of F‐actin without altering the size of the G‐actin pool, and causes accumulation of actin by decreasing its relative rate of degradation.
Ultrastructural studies on the intracellular fate of 125I‐nerve growth factor in cultured rat sympathetic neurons
Authors: Claude Philippa , Hawrot Edward , Parada Isabel 
Published: December 2004

AbstractPrimary cell cultures of sympathetic neurons from rat were exposed to 125I‐nerve growth factor (NGF) and the fate of the NGF in the cell was followed using electron microscopic autoradiography. The intracellular localization of NGF was determined in the cell bodies and in the proximal neurites of neurons that had been grown in three‐chamber dishes, following 5 or 24 hr of retrograde transport of NGF from the distal portions of the neurites. Label in the proximal neurites was predominantly associated with lysosomes and multivesicular bodies (MVBs), and at 5 hr elongated tubular elements were especially heavily labeled. Most of the label in the cell bodies was concentrated in lysosomes and MVBs. Lysosomes accounted for the largest fraction (45–60%) of the grains in the cell body, with a labeling density (LD = % grains/% area) of 3–5, while MVBs accounted for 5–10% of the grains with an LD of 5–20. We observed no evidence of nuclear labeling after 5 or 24 hr of retrograde transport. Mass cultures of neurons were incubated for 22 hr with NGF in the presence of the lysosomal inhibitors chloroquine (CQ, 0.05 mM) or methylamine (MA, 10 mM). In both agents the lysosomes were swollen with membranous material but still sequestered NGF, especially in CQ where the lysosomes were associated with almost 65% of the grains and had an LD of 6. CQ and MA had different effects on the morphology of the MVBs: in CQ they were few in number and compact while in MA they were numerous and appeared swollen and vacuolated. We observed no evidence for the nuclear accumulation of NGF even in the presence of the lysosomotropic agents.
Involvement of multiple subcellular compartments in intracellular processing of epidermal growth factor
Authors: Miskimins W. Keith , Shimizu Nobuyoshi 
Published: December 2004

AbstractThe intracellular translocation and processing of epidermal growth factor (EOF) in 3T3 cells has been studied utilizing Percoll density gradients. EGF is internalized and rapidly becomes associated with two types of intracellular compartments. The extent to which EGF is delivered to these two compartments is apparently regulated depending upon the cell's physiological condition. In growth medium, an increased proportion of EGF is taken up into a Golgi‐like element. Uptake through this pathway correlates with a decrease in degradation of the ligand. In the absence of scrum and amino acids, an increased proportion of EGF is taken up into a component which has a density of 1.05. Uptake through this pathway correlates with increased degradation of the ligand. The ligand taken up through both pathways is transferred to dense vesicles which comigrate with lysosomes. In the presence of growth medium, however, dense vesicles containing EGF can be shown to be lysosomal enzyme‐deficient upon further fractionation. In addition, in the presence of serum, a portion of the internalized EGF is apparently released from the cells, intact, and then re‐bound. The processes described may be important in the production of a mitogenic response and the ability of cells to self‐regulate their responsiveness to the growth factor.
Ligand/receptor internalization: a spectroscopic analysis and a comparison of ligand binding, cellular response, and internalization by human neutrophils
Authors: Sklar Larry A. , Jesaitis Algirdas J. , Painter Richard G. , Cochrane Charles G. 
Published: December 2004

AbstractWe have compared the kinetics of the responses of neutrophils to the kinetics of ligand‐receptor interaction and internalization, using as a model ligand the fluorcsceinated hexapeptide N‐CHO‐Nle‐Leu‐Phe‐Nle‐Tyr‐Lys‐Fluorescein (Nle, norleucine). Cellular responses, ie, membrane depolarization, enzyme (elastase) secretion, and superoxide anion (O) generation, are all initiated within 10 sec of the exposure of cells to stimulus. In the cases of membrane depolarization and secretion (in cytochalasin B‐treated cells), full responses are elicited by binding which occurs within 15 sec of peptide addition. Ligand binding and internalization have been analyzed over the same time frame with new spectroscopic techniques. The association of ligand and receptor is monitored using an antibody to fluorcscein. The antibody to fluorescein specifically quenches the ligand which is in solution, but receptor‐bound ligand is inaccessible to the antibody. The internalization of the receptor‐bound ligand is monitored by the accessibility of the fluoresceinated peptide to quenching by an external pH change (7.4 → 4.0). Ligand which is either outside or on the cell surface is instantaneously quenched while intracellular peptide (or intracellular fluorescein derived from fluorescein diacetate) is only slowly quenched. No internalization is observed until 1 min after binding begins and internalization proceeds at a rate of up to 5,000 receptors/min/cell following a near optimal stimulatory ligand concentration (∼ 1 nM) while the occupied receptors are being cleared from the surface. A comparison of the kinetics of internalization and the cellular responses suggests that internalization of the ligand is too slow to be involved in the triggering of the cellular responses.
Characterization of growth factors in human cartilage
Authors: Bekoff Marjorie C. , Klagsbrun Michael 
Published: December 2004

AbstractGrowth factor activity has been identified in the chondrocytes and extracellular matrix (ECM) fractions of human costal cartilage. There was about five times more growth factor activity in the ECM than was found to be associated with the chondrocytes. The growth factor activity in chondrocytes was found to be associated with chromatin. Both the chromatin‐associated growth factor (CAGF) activity and extracellular matrix growth factor (EMGF) activity were characterized for molecular weight, charge, and the effect of reduction by sulfhydryl reducing reagents. Biorex cation exchange chromatography showed that both CAGF and EMGF were cationic. CAGF and EMGF have molecular weights between 15,000 and 18,000 as determined by size exclusion chromatography on HPLC TSK 3000 columns equilibrated with guanidine‐HCl and dithiothreitol.
Intracellular processing of 125I‐epidermal growth factor in rat embryo fibroblasts
Authors: Magun Bruce E. , Planck Stephen R. , Wagner Herbert N. 
Published: December 2004

AbstractThe intracellular fate of endocytosed 125I‐epidermal growth factor was examined in Rat‐1 fibroblasts. Cells were pulse‐labeled for 5 min in 125I‐EGF and chased for 3 hr with an excess of unlabeled EGF. At various times after application of the cold chase, cells were harvested and processed for isopycnic gradient centrifugation on Percoll gradients. Within the period of the 125I‐EGF pulse, about 50% of the 125I activity appeared in an organelle containing peak in the gradients. By 20 min after application of the cold chase, 125I activity in the organelle peak began to decrease, and the decrease continued over the next few hours. The 125I activity which exited from its organelle‐associated location appeared to be present in the cytosol and was apparently not confined within organelles. Lysosomotropic amines inhibited the egress of 125I activity from the organelle compartment. The 125I activity from both organelle and nonorganelle compartments reacted as completely as authentic 125I‐EGF with anti‐EGF antibodies and was similar in size to authentic 125I‐EGF. Little or no intracellular low molecular weight 125I‐containing compounds were detected, although they accumulated in the culture medium. Analytical isoelectric focusing revealed that the organelle‐bound form of endocytosed 125I‐EGF was more acidic than authentic 125I‐EGF and, upon exiting from the organelle compartment, was processed to an even more acidic form. It was the second macromolecular form of processed 125I‐EGF that was ultimately degraded to low molecular weight compounds which were then externalized from the cells.
Repair of O6‐methyl‐guanine residues in DNA takes place by a similar mechanism in extracts from hela cells, human liver, and rat liver
Authors: Myrnes Bjørnar , Giercksky Karl Erik , Krokan Hans 
Published: December 2004

AbstractExtracts from HeLa S3 cells, human liver, and rat liver were found to contain an activity that transfers the methyl group from O6‐methyl‐guanine residues in DNA to a cysteine residue of an acceptor protein. The molecular weights of the acceptor proteins in HeLA cells and human liver are 24,000 ± 1,000 and 23,000 ± 1,000. respectively. Assuming that each acceptor molecule is used only once, the average number of acceptor molecules in HeLa cells was calculated to be about 50,000. The extracts also contained 3‐methyl‐adenine‐DNA glycosylase activity and 7‐methyl‐guanine‐DNA glycosylase activity, although the latter activity was not detected in extracts from human liver in our assay system. Thus, the three major alkylation products resulting from the effect of methylating agents, such as N‐methyl‐N‐nitroso urea, can all be repaired in animal cells. Pretreatment of HeLa cells with N‐methyl‐N′‐nitro‐N‐nitrosoguanidinc (0.1 μg/ml) strongly reduced the capacity of HeLa cell extracts to repair O6‐methyl‐guanine residues, while the activity of three DNA‐N‐glycosylases was essentially unaltered. This inactivation was not caused by a direct methylation of the enzyme by the carcinogen. The results demonstrate that the mechanism of repair of O6‐methyl‐guaninc residues, in DNA is strikingly similar in E coli and animal cells, including humans.
Inhibition of heme synthesis in bone marrow cells by succinylacetone: Effect on globin synthesis
Authors: Beru Nega , Sahr Kenneth , Goldwasser Eugene 
Published: December 2004

AbstractThe effects of 4,6‐dioxoheptanoic acid (succinylacetone, SA), an inhibitor of δ‐aminolevulinic acid dehydratase, on total iron uptake, heme synthesis, and globin synthesis were studied in rat marrow cells in culture in order to examine the coordination of heme and globin synthesis. SA inhibited heme synthesis in both control and erythropoietin‐stimulated cells in a dose‐dependent fashion; at 10−3 M, inhibition was complete, whereas at 10−7 M, there was no significant effect. Inhibition of total iron uptake was also dose‐dependent although, at 10−3 M, it was not complete. The inhibition of heme synthesis by SA was partially overcome by addition of 10−4 M porphobilinogen or protoporphyrin IX. SA caused an almost complete suppression of globin formation in both erythropoietin‐stimulated and unstimulated cells as early as five hours after the addition of the inhibitor. When inhibition of heme synthesis was incomplete, globin synthesis was partially inhibited. These results indicate that heme synthesis is required for erythropoietin‐mediated induction of globin synthesis in cultured bone marrow cells.
The uptake of swainsonine, a specific inhibitor of α‐D‐mannosidase, into normal human fibroblasts in culture
Authors: Chotai Kokila , Jennings Christine , Winchester Bryan , Dorling Peter 
Published: December 2004

AbstractSwainsonine, an indolizidine alkaloid, found in plants of the genus Swainsona, has been shown to be a strong inhibitor in vitro of the α‐D‐mannosidase activity in normal human fibroblasts. Therefore, inhibition of α‐D‐mannosidase activity in extracts of harvested cells grown with swainsonine in the medium has been used to follow the association of the alkaloid with normal human fibroblasts in culture. Swainsonine that could not be removed by extensive washing became associated with the cells within 1 min, and it is concluded that the alkaloid is internalized rapidly by the cells. The amount of swainsonine taken up into the cells depended on the length of time in contact and the concentration of swainsonine in the medium, but at 37°C a plateau of internalized swainsonine occurred after 2 hr with extracellular concentrations of swainsonine of 100 μM or greater. At lower concentrations of swainsonine the rate of uptake was found to be temperature‐dependent, increasing greatly at 20°C. The rapidity and temperature sensitivity of the uptake, together with the observation that mannose or mannose‐6‐phosphate did not prevent the association, suggest that swainsonine enters the cells by permeation rather than by endocytosis. When swainsonine is withdrawn from the culture medium, there is a decrease with time of cell‐associated swainsonine. The kinetics of uptake and release of swainsonine and its slightly basic nature make it likely that swainsonine is concentrated initially in the lysosomes. This rapid, but reversible, concentration of swainsonine in lysosomes would be consistent with the observed effects of the toxin in vivo.
Biosynthesis and secretion of fibronectin in human melanoma cells
Authors: Bumol Thomas F. , Reisfeld Ralph A. 
Published: December 2004

AbstractThe biosynthesis and secretion of cellular fibronectin from human melanoma cells have been investigated by pluse‐chase/immunoprecipitation analysis. Melanoma cells synthesize endolglycosidase H (Endo H)‐sensitive glycoprotein precursors of fibronectin glycoproteins which chase to an Endo H‐resistant monomer with an apparent Mr of 240,000 (240 K). This molecule, which has a significantly higher molecular weight than normal plasma or cellular fibronectin, is rapidly secreted by melanoma cells, resulting in the secretion of 80% of newly synthesized fibronectin in 120 min, following a 10‐min biosynthetic pulse. This active secretory process can be inhibited by brief exposure of melanoma cells to sodium monensin (10−7 M), which also results in a modified fibronectin of lower apparent Mr. Monosaccharide‐incorporation studies of melanoma fibronectin reveal that monensin significantly inhibits galactose and fucose incorporation into this glycoprotein, correlating with reported effects of monensin on Golgi apparatus functions. These studies indicate that this tumor‐associated and biosynthetically altered cellular fibronectin is a rapidly secreted major N‐linked glycoprotein of metastatic human melanoma cells.
Interactions between insulin and the cyclic AMP system of Cloudman S91 mouse melanoma cells
Authors: Pawelek John , Emanuel Janet , Kahn Richard , Murray Marilyn , Fleischmann Robert 
Published: December 2004

AbstractInsulin inhibits the proliferation of wild‐type Cloudman S91 mouse melanoma cells. The effects, which are mediated through specific, high‐affinity receptors for insulin, appear to involve interactions with the cAMP system. Our evidence is as follows: (1) Cloudman cells have a cAMP requirement for proliferation and pigmentation. Exposure of cells to insulin results in a lowering of intracellular cAMP levels and inhibition of both cell division and pigment formation. (2) The effects of insulin are reversed by agents which raise cAMP levels, or by the cAMP analogue dibutyryl cAMP. (3) A mutant cell line with a temperature‐dependent requirement for cAMP is most sensitive to the growth inhibitory effects of insulin when its requirements for cAMP are maximal. (4) Mutants selected only for alterations in their response to Insulin frequently have concomitant alterations in their cAMP systems. (5) The melanotropin‐responsive adenylate cyclase system is stimulated following prolonged exposure of cells in culture to insulin. Although we do not know the mechanism(s) for the interactions between the insulin and the cAMP system, our initial findings suggest that protein phosphorylation/dephosphorylation reactions are involved.
Trypanosoma cruzi: The immunological consequences of infection
Authors: Hudson Leslie 
Published: December 2004

AbstractTrypanosoma cruzi, the causative agent of Chagas' disease, infects an estimated 12 million people in Latin America and may induce cardiopathy and megaformation of the oesophagus and colon. During the early, acute stage of the infection, parasite‐induced inflammatory infiltrates may cause transitory disease which terminates with the emergence of an immune response sufficient to reduce the parasite to insignificant levels. Even so, severe disease may develop many years after the original infection. It has been suggested that this might result from an autoimmune process triggered by the parasite and mediated either (1) by the adsorption of parasite antigens to host cells, thus rendering these cells susceptible to the host's own antiparasite immune response, or (2) via cross‐reactive antigens shared by the host and parasite. In common with many parasitic diseases, there is an urgent need for studies on the T‐cell response to T cruzi infection, as this might not only hold the key to the immunopathology but also serve as a means of clearing this lifelong infection which survives by sequestering into an intracellular site.
Graph theoretical characterization and computer generation of certain carcinogenic benzenoid hydrocarbons and identification of bay regions
Authors: Balasubramanian K. , Kaufman Joyce J. , Koski Walter S. , Balaban Alexandru T. 
Published: January 2005

AbstractAn algorithm is developed for generating and characterizing carcinogenic catacondensed benzenoid hydrocarbons. The bay regions in these structures are identified by a technique that we developed at Johns Hopkins. Using the three‐digit code proposed by Balaban, and the concept of ring adjacency matrix expounded here, we generate catacondensed benzenoid hydrocarbons in the computer and identify the number of potentially carcinogenic bay regions in each of them. The results of computer generation agree with the combinatorial enumeration of Harary and Read. All structures containing up to five rings and some with six rings and the number of bay regions in these are presented. Computer results for the structures and bay regions of all seven‐, eight‐, and nine‐membered unbranched catacondensed benzenoid hydrocarbons and the number of bays are available from the authors.