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Biomedical subjects

B Westermark

Publications and source records attributed to B Westermark.

At least 199 records · Page 11Linked to original sources
PubMed1982

Novel vesicular extrusions during cell spreading.

During the late stages of cell spreading in vitro, the cells extrude a vesicular material into the medium. This phenomenon was observed in human glia and glioma cells as well as in human diploid fibroblasts MRC-5 and WI-38 cells. This extrusion of vesicular material is inhibited by cytochalasin-B and colcemid suggesting the involvement of microfilaments and microtubules and the active nature of this event. It appears that the cells may be excreting damaged surface components by a mechanism similar to patching, capping and endocytosis.

Cell Line↗
PubMed1982

Interaction of platelet-derived growth factor with its fibroblast receptor. Demonstration of ligand degradation and receptor modulation.

Platelet-derived growth factor (PDGF) has previously been shown to bind to a specific high affinity receptor on human foreskin fibroblasts. The present study was carried out to characterize some of the cellular events resulting from the interaction of the ligand with its receptor. Radiolabeled PDGF was rapidly internalized and degraded after binding to the cells. The degradation was complete and was inhibited by low concentrations of the lysosomotropic agents, chloroquine, ammonium chloride, or methylamine, suggesting that the degradation occurs in the lysosomes. The cellular binding capacity for PDGF decreased after exposure of the cells to PDGF at 37 degrees C. This down regulation of the PDGF receptor was optimal after a 60-min incubation at 37 degrees C and half-maximal at 0.5 nM concentration of PDGF. The binding capacity was restored when the PDGF-containing medium was changed to medium without PDGF; the binding capacity increased from 40 to 80% od the initial value after a 4-h incubation at 37 degrees C. The reappearance on the cell surface of PDGF-binding sites was dependent on protein synthesis and totally blocked by cycloheximide (20 micrograms/ml). Thus, either the receptor has to be resynthesized after internalization or, alternatively, any step in the recycling of "used" receptors is dependent on protein synthesis. Exposure of the cells to PDGF also caused a dose-dependent decrease in the binding capacity for epidermal growth factor which has a distinct receptor on these cells. In contrast, epidermal growth factor did not modulate the PDGF binding capacity, lending no support to the idea that the receptors for epidermal growth factor and PDGF are processed in a common pathway.

Blood Platelets↗
PubMed1982

Effect of epidermal growth factor on membrane motility and cell locomotion in cultures of human clonal glioma cells.

Two clones, designated Cl 2 and Cl 3, were established from the human malignant glioma line U-343 MGa. The astrocytic origin of the cells was proven by the presence in virtually 100% of the cells of the astrocyte marker glial fibrillary acidic protein. The addition of 10 ng epidermal growth factor (EGF) per milliliter to Cl 2 and Cl 3 cells resulted in the rapid appearance of large cell surface ruffles, visualized by scanning electron microscopy. A time course study by phase contrast microscopy showed that the maximal ruffling activity occurred 5 minutes after addition of EGF. Under basic culture conditions (Eagle's MEM, 10% fetal calf serum), Cl 2 and Cl 3 cells were essentially immobile and formed tightly packed, well demarcated colonies. In the presence of 10 ng EGF per milliliter, no defined colonies were formed and the cells seemed to move around freely. The stimulatory effect of EGF on cell migration was confirmed by growing the cells on a deposit of colloidal gold; in the absence of EGF, the cells remained immobile whereas cells grown at 10 ng EGF per ml formed long phagokinetic tracks. The effect of EGF on membrane motility and cell locomotion occurred in the absence of any effect of EGF on growth rate; both clones multiplied at the same rate in the absence as in the presence of EGF. Binding experiments using 125I-labeled EGF demonstrated a single class of high affinity receptors. The number of 180,000 receptors per cell was estimated in both clones. The finding that human glioma cells in culture require EGF for their migration raises the interesting possibility that tumor cells in vivo may respond in a similar fashion, and in that case require a growth factor for migration and for the expression of their infiltrative growth potential. Furthermore, the present findings strengthen the notion that glial cells should be recognized as targets for EGF.

Cell Division↗
PubMed1982

Functional properties of porcine-thyroid follicles in suspension.

Porcine thyroid follicle cells were isolated (about 10(7) cells per gram of tissue) and cultured in small aggregates in agarose-coated culture dishes. The aggregates became arranged into follicle-like structures capable of iodide uptake and organification. In the presence of TSH (0.2 mU/ml), the aggregation of follicles was enhanced, and iodide uptake as well as TSH-stimulated organification of iodide was increased compared with that in the control. In culture, the active iodide metabolism was gradually lost over a 7-day period. This was not due to a disappearance of the TSH-adenylate cyclase system, since cAMP production was retained and stimulated by TSH (half-maximal effect at about 1 mU/ml). Acutely TSH stimulated iodide efflux and iodide organification (half-maximal effect at about 20 microU/ml). The stimulatory effect on organification was transient: within an hour further organification proceeded as in the absence of hormone. The effects on efflux and organification were already maximal at low TSH concentrations, whereas cAMP production was stimulated with up to 50-fold higher TSH levels, i.e. the findings were typical of spare receptors. In the continued presence of epidermal growth factor, a potent mitogen for thyroid cells, the follicles increased in size and contained one single large lumen. Their capability to take up and organify iodide was reduced.

Animals↗
PubMed1982

Hormonally induced changes in the cytoskeleton of human thyroid cells in culture.

Serially cultivated thyroid follicular cells are not active in hormone synthesis but retain a thyrotropin-responsive adenylate cyclase. The exposure of such cells to thyrotropin leads to an increase in the concentration of intracellular cAMP and a drastic change in morphology including a total cytoplasmic arborization. The present communication describes these changes at the cytoskeletal level using a cell line derived from a human functioning thyroid adenoma. Phase contrast microscopy showed that the cytoplasmic arborization was preceded by a total disappearance of stress fibers, visible within 20 min of exposure. Small marginal membrane ruffles could also be seen. These morphological changes could also be induced by the addition of dibutyryl cAMP. The action of both thyrotropin and dibutyryl cAMP was potentiated by theophylline. High voltage electron microscopy of whole mounted cells confirmed the loss of stress fibers (microfilament bundles). In addition, thyrotropin treatment led to an uneven redistribution of the cytoplasmic ground substance and to changes in the organization of the microtrabecular lattice. Stereo images demonstrated numerous minute surface ruffles. The thyrotropin-induced arborization was reversible even in the presence of thyrotropin. After 24 h of treatment, cells had flattened and then contained very straight and condensed microfilament bundles. The results thus demonstrate that thyrotropin induces a disintegration of microfilament bundles in human, partially dedifferentiated, follicular cells and that this effect to all appearances is caused by cAMP, the second messenger in thyrotropin action. The relation of this event in partially dedifferentiated cells to the effect of thyrotropin in the intact thyroid gland is unclear. The fact that several other cultured hormone-responsive cells round up or become arborized in conjunction with an increase in cAMP levels implies that cAMP may be a major factor in the disassembly of microfilament bundles in these cells.

Bucladesine↗
PubMed1981

Establishment of attached and non-attached cell lines from an uncommon human glioma.

A New cell line, U-706, established from an uncommon human glioma (possibly giant-cell glioblastoma) is reported in this communication. The tumor gave rise to two permanent sublines, one attached (U-706M) and one non-attached (U-706S) cell line. The growth characteristics, chromosome banding pattern, electronmicroscopic picture and cell surface characteristics of the two sublines are described.

Brain Neoplasms↗
PubMed1981

Somatomedin B: mitogenic activity derived from contaminant epidermal growth factor.

The mitogenic effect of somatomedin B on human cultured glial cells was neutralized by the addition of antibodies to mouse epidermal growth factor. Somatomedin B contained epidermal growth factor--like activity, competing for binding to the epidermal growth factor receptor. It is concluded that contaminating epidermal growth factor may explain the entire mitogenic activity of somatomedin B.

Cell Division↗
PubMed1981

Growth dependent induction of high affinity gamma-amino-butyric acid transport in cultures of a normal human brain cell line.

Dense, growth inhibited cultures of the human putative glial cell line U-787CG were found to take up gamma-aminobutyric acid (GABA) via a high-affinity transport mechanism (Km = 1.2 microM) not detectable in sparse, rapidly growing cultures. The uptake of GABA was essentially the same in young and old dense cultures indicating that the induction of the high-affinity GABA transport was dependent on cell density and/or growth rate rather than time in culture after trypsinization.

Astrocytes↗
PubMed1981

Platelet-derived growth factor. Isolation by a large-scale procedure and analysis of subunit composition.

Platelet-derived growth factor was purified from fresh platelets by a large-scale procedure not involving the use of SDS (sodium dodecyl sulphate). The product, 0.5 mg of platelet-derived growth factor, obtained from about 3 x 10(13) platelets migrated as a single component in analytical gel electrophoresis in the presence of SDS and showed no inhomogeneity on sedimentation-equilibrium analysis in the ultracentrifuge. It had a high specific activity, 2 ng of platelet-derived growth factor/ml (70pM) being equivalent to 1% (v/v) human serum in an assay for multiplication-stimulating activity. Amino acid analysis revealed that platelet-derived growth factor contains all the common amino acids, except tryptophan, but no hexosamine. The molecular weight of platelet-derived growth factor, as determined by sedimentation-equilibrium analysis, was about 33 000. A similar value was obtained by gel electrophoresis in SDS under non-reducing conditions. In the presence of reducing agents the factor molecule was converted into two distinct components of lower molecular weight (17 000 and 14 000 respectively), as demonstrated by protein staining. The molecular model implicated by these findings is that platelet-derived growth factor consists of two different polypeptides chains, linked by disulphide bridges.

Amino Acids↗
PubMed1981

Specific receptors for platelet-derived growth factor on cells derived from connective tissue and glia.

A cellular receptor for platelet-derived growth factor (PDGF) was demonstrated by incubation of 125I-labeled PDGF with human foreskin fibroblast cultures followed by liberation of cell-bound radioactivity with Triton X-100. The cellular binding of labeled PDGF in the presence of increasing amounts of unlabeled PDGF showed saturation; Scatchard analysis of binding data indicated a single class of receptors having kd = 1 X 10(-9) M. The number of PDGF binding sites was approximately 3 X 10(5)/cell. Labeled PDGF binding reached an apparent equilibrium after 3 hr at 4 degrees C. At 37 degrees C, it passed a maximum after 30 min and then decreased with time due to degradation of the tracer. A large excess of unlabeled PDGF reduced labeled PDGF binding by more than 90% whereas similar doses of epidermal growth factor, fibroblast growth factor, or insulin had no effect. It was concluded that PDGF did not share receptors with these factors. PDGF receptors were found on skin fibroblasts, normal and malignant glial cells, smooth muscle cells, and 3T3 cells but not on epithelial-derived cells, neuroblastoma cells, endothelial cells, or peripheral lymphocytes.l As only the receptor-positive cells--i.e., the connective tissue- and glia-derived cells--are responsive to stimulation with PDGF, these findings imply a functional significance of the PDGF receptor.

Animals↗
PubMed1981

Heterogeneity of Genotypic and phenotypic characteristics of fifteen permanent cell lines derived from human gliomas.

Six new permanent cell lines were established from human gliomas and compared to nine other cell lines from human gliomas. All fifteen lines had individually distinct HLA phenotypes and all but two, which were from a black patient, had type B glucose-6-phosphate-de;hydrogenase isoenzymes. Morphologically, the lines could be classified into four patterns descriptively designated as fibroblastic, fascicular, epithelial, or glial. Four of the lines grew progressively and could be serially transplanted when injected into athymic mice; two others grew initially and then regressed. From none to 100% of cells developed elongated tapering processes and showed reduction in nuclear-cytoplasmic ratio in the presence of 1 mM cyclic AMP and theophylline. Levels of 2'-3' cyclic nucleotide 3'-phosphohydrolase activity ranged from nondetectable to 12.78 +/- 1.49 micromoles 2' AMP formed per hr mgm total protein. None of the lines had detectable S-100 protein, but two had readily demonstrable glial fibrillary acidic protein in indirect immunofluorescence. Fibronectin levels in spent culture supernatants ranged from undetectable levels to 21.4 micrograms/ml/10(5) cells. All but one line shared surface antigens with normal human adult or fetal brain, as detected in absorption analyses with nonhuman primate antiserum raised against glioblastoma multiforme tissue or cell line U-251 MG. Although there were many common properties of the lines, each line had a unique profile of the parameters evaluated. This heterogeneity most likely reflects the individuality of the tumors of origin and individual genotypes and capacity for a range of phenotypic expression of cells.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1981

Interaction of feline sarcoma virus (FeSV) and mycoplasma.

A factor present in the supernatant of an established human glioma cell line U-251 MG strongly suppresses feline sarcoma virus (FeSV) focus forming activity on feline embryo fibroblasts. The factor was identified as mycoplasma arginini. The enriched mycoplasma fraction had no cytpathogenic effect on the glioma cells or on the embryonic feline indicator cells. An antiserum prepared against this strain of mycoplasma abolished the inhibition. The exact mechanism is not known but arginine depletion in the medium seems to be an important factor.

Animals↗
PubMed1980

Surface glycoproteins of normal and neoplastic glia cells in culture.

Two normal and seven malignant human glia lines grown in vitro wer labelled by lactoperoxidase catalysed iodination. The labelled cell surface glycoproteins were isolated by lectin affinity chromatography and compared by SDS gel electrophoresis. The glia and the glioma lines possess a common characteristic glycoprotein pattern. Seven glycoproteins in the molecular weight range between 70,000 and 220,000 daltons and several minor components of low molecular weight could be distinguished. The expression of the glycoproteins was independent of the passage number or the growth conditions although the expression of the different glycoproteins showed quantitative differences for the individual cell lines. The differences found in the tumor lines were either due to an amplification or decrease in the expression of the different glycoproteins and/or their accessibility to the lactoperoxidase-catalysed labelling.

Cell Line↗