Search PubMed⌕ Search

Biomedical subjects

C Schoch

Publications and source records attributed to C Schoch.

105 records · Page 6Linked to original sources
PubMed1993

Role of the fusion peptide sequence in initial stages of influenza hemagglutinin-induced cell fusion.

The fusion activity of influenza hemagglutinin (HA) and of HA proteins altered in the amino terminus of HA2 (fusion peptide) by site-directed mutagenesis (Gething, M.-J., Doms, R. W., York, D., and White, J. (1986) J. Cell Biol. 102, 11-23) was analyzed following expression in CV-1 cells using SV40-HA recombinant virus vectors. Fusion was monitored by the redistribution of lipid and cytoplasmic dyes between fluorescently labeled erythrocytes and HA-expressing CV-1 cells using spectrofluorometry and fluorescence microscopy. The kinetics of lipid redistribution after lowering the pH showed the same pattern for wild type HA and nonlethal mutants, although there were shifts in the pH threshold. The time for commitment to the fusogenic state and the temperature dependence of the processes leading to HA-mediated fusion were also the same for wild type and nonlethal mutants. However, striking differences were observed between wild type HA and the nonlethal mutants in their ability to induce pH-dependent redistribution from erythrocytes to HA-expressing cells of large molecular weight (M(r) > 10,000) fluorescently labeled dextran molecules. The data indicate that the kinetic processes which are measurable in the time range of seconds are insensitive to the structure of the fusion peptide. Surprisingly, however, the fusion peptide plays an important role in later processes related to pore widening which eventually results in delivery of the nucleocapsid into the cell.

Amino Acid Sequence↗
PubMed1992

A long-lived state for influenza virus-erythrocyte complexes committed to fusion at neutral pH.

The low pH-induced fusion of influenza virus with intact erythrocyte plasma membranes is preceded by a delay time following pH reduction, that is itself pH- and temperature dependent. At 37 degrees C/pH 4.8, lipid mixing between virus and target membranes begins < 2 s after pH reduction, whereas at 4 degrees C/pH 4.8, fusion does not commence until > 10 min after pH reduction. We have found that within this time period at 4 degrees C, a population of virus acquires the capacity to subsequently undergo fusion with high efficiency at elevated temperatures and pH 7.4. Both the kinetics and the extent of this pH 7.4 fusion depend upon the time of pre-incubation at pH 4.8/4 degrees C. Incubation at pH 7.4/4 degrees C, following this pre-incubation does not result in fusion, but the capacity to fuse at pH 7.4/37 degrees C is retained for a time period exceeding 1 h. The longevity of this fusion committed state makes it amenable to biochemical and immunological analysis. We have shown that it is insensitive to dithiothreitol, neuraminidase and trypsin, but is incapacitated by thermolysin or protease K. We conclude that only the HA2 sub-unit of influenza haemagglutinin is a necessary protein component of later stages of the fusion pathway.

Animals↗
PubMed1991

Delay time for influenza virus hemagglutinin-induced membrane fusion depends on hemagglutinin surface density.

We have studied the kinetics of low-pH-induced fusion between erythrocyte membranes and membranes containing influenza virus hemagglutinin by using assays based on the fluorescence dequenching of the lipophilic dye octadecylrhodamine. Stopped-flow mixing and fast data acquisition have been used to monitor the early stages of influenza virus fusion. We have compared this with the kinetics observed for fusion of an NIH 3T3 cell line, transformed with bovine papillomavirus, which constitutively expresses influenza virus hemagglutinin (GP4f cells). Virus and GP4f cells both display a pH-dependent time lag before the onset of fluorescence dequenching, but of an order of magnitude difference, ca. 2 s versus ca. 20 s. We have adopted two strategies to investigate whether the difference in lag time reflects the surface density of acid-activated hemagglutinin, able to undergo productive conformational change. (i) Hemagglutinin expressed on the cell surface requires proteolytic cleavage with trypsin from an inactive HAO form; we have limited the extent of proteolysis. (ii) We have used infection of CV-1 cells with a recombinant simian virus 40 bearing the influenza virus hemagglutinin gene. The surface expression of hemagglutinin is a function of time postinfection. For low-pH-induced fusion of both types of cell with erythrocytes, the lag time decreases with increasing hemagglutinin densities. Our results do not indicate a cooperative phenomenon at the level of the principal rate-determining step. We also show in the instance of virus fusion, that the magnitude of the delay time is a function of the target membrane transbilayer lipid distribution. We conclude that for a given amount of pH-activated hemagglutinin per unit area of membrane, the kinetics of fusion is determined by nonspecific physical properties of the membranes involved.

Animals↗
PubMed1990

Gating kinetics of pH-activated membrane fusion of vesicular stomatitis virus with cells: stopped-flow measurements by dequenching of octadecylrhodamine fluorescence.

To identify the initial stages of membrane fusion induced by vesicular stomatitis virus, we performed stopped-flow kinetic measurement with fluorescently labeled virus attached to human erythrocyte ghosts that contained symmetric bilayer distributions of phospholipids. Fusion was monitored spectrofluorometrically using an assay based on mixing of the lipid fluorophore octadecylrhodamine. At 37 degrees C and pH values near the threshold for fusion, a lag phase of 2 s was observed. The lag time decreased steeply as the pH decreased, while the initial rate of fusion showed the reverse functional dependence on pH. The observed rapid fluorescence changes resulted from fusion of virus bound to the target, and the time lags were not due to association-dissociation reactions between virus and target. For a given pH value, the temperature dependence of the lag time was similar to that of the initial rate of fusion. The results were fitted to a multistate model similar to that resulting from ion channel gating kinetics. The model allows testing of hypotheses concerning the role of cooperativity and conformational changes in viral spike glycoprotein-mediated membrane fusion.

Animals↗
PubMed1989

Immunoprint pattern in patients with allergic bronchopulmonary aspergillosis in different stages.

Individual immunoprint patterns of sodium dodecylsulfate-polyacrylamide gel electrophoresis-separated Aspergillus fumigatus (Af) allergens/antigens were evaluated in 28 patients with allergic bronchopulmonary aspergillosis in stages II to V. It could be demonstrated that active disease (stage III) is characterized by a very strong IgE response against a variety of Af components, whereas the IgE antibody pattern in corticosteroid-treated patients who have demonstrated improvement is much weaker. In patients in remission (stage II), it is minimal. In contrast, many patients in stage V without corticosteroid treatment demonstrated a strong reactivity of IgE antibodies, indicating persisting active disease. The pattern of IgG antibodies with individual Af components resembles, in general, that of IgE antibodies; however, discrimination between different stages and between treated patients is much weaker. Our results indicate that a certain relationship between the different stages of allergic bronchopulmonary aspergillosis and Af immunoprint patterns exists.

Allergens↗
PubMed1989

Food intake, body and heart composition, and heart rate in T3 plus atenolol-treated rats.

Thyroid hormones and beta-blockers both affect energy balance and the heart. The interaction of 3,5,3'-triiodothyronine (T3) and the beta-blocker atenolol on some cardiac and energy balance parameters was therefore investigated. Stock-fed male Wistar rats (approximately 400 g) received 5 micrograms (expt 1) or 1.5 micrograms (expt 2) T3.100 g body wt-1.day-1 for 3 wk, with or without atenolol. In expt 3, rats were overfed with a "cafeteria" diet before and during the experiment and otherwise treated as in experiment 2. Compared with stock-fed (expt 1 and 2) or overfed (expt 3) controls, T3 caused an increase in food intake in experiments 1 and 2 but not in experiment 3. There was a large loss of body fat in all experiments, disproportionately greater than the body weight loss. Protein loss was significant only in experiment 1 and negligible in cafeteria rats. Heart rate and weight were increased, although heart composition remained unchanged. Atenolol, in a dose that abolished T3-induced tachycardia, did not modify any of the other T3 effects investigated, including the hypertrophy of the heart. These results indicate that T3-induced tachycardia can be abolished by concomitant treatment with a beta-blocker without altering parameters connected with energy balance, whereas protein loss caused by T3 can be attenuated by lowering the dose of T3 used and can be further blunted by dietary manipulation (cafeteria overfeeding).

Animals↗
PubMed1987

The chromosomal fur gene regulates the extracellular haemolytic activity encoded by certain hly plasmids.

The haemolytic activity encoded by thirteen hly-plasmids of different origin and sources was examined as a function of the Fe3+-concentration in E. coli fur+ and E. coli fur- strains, respectively. In E. coli fur+ the relatively low haemolytic activity of five hly-plasmids isolated in Berne and one isolated in Paris was increased significantly under iron-limiting growth conditions. Contrastingly, in E. coli fur- strains containing the same plasmids, a considerably higher amount of secreted haemolysin was detected. This activity could not be further increased by limiting the extracellular iron concentration. Seven other hly-plasmids expressed similar and non-inducible amounts of secreted haemolysin in both E. coli fur+ and E. coli fur- strains. These results indicate that the extracellular haemolytic activity encoded by certain hly-plasmids was controlled by the chromosomally encoded fur gene.

Animals↗
PubMed1982

A fetal respiratory epithelial cell line for studying some problems of transplacental carcinogenesis in Syrian golden hamsters.

Using repeated cloning and treatment with cis-HPL (200 micrograms/ml), an analogue of a procollagen precursor inhibitory to the growth of collagen-synthesizing cells of mesenchymal origin, clonally premature epithelial cell lines were isolated from fetal SGH lungs cultured on the 15th day of gestation. One of the cell lines, M3E3/C3, which has been extensively studied for biological characterization, developed poorly differentiated carcinomas in injected hamsters after transformation by MNNG. Moreover, when grown on collagen gel, this cell line indicated an obvious potency for in vitro differentiation in response to vitamin A by developing activated Golgi regions, well developed rER and a number of mucus-like granules. Since such a differentiative responses is expected to be definable in the light of respiratory epithelium developing in utero, this cell line may be useful for studying mechanisms of differentiation-dependent sensitivity of fetal organs to transplacental carcinogen exposure.

Animals↗
PubMedDate not supplied

Hemoglobin F in myelodysplastic syndrome.

Reactivation of fetal hemoglobin synthesis in adulthood can be seen in hematological disorders affecting the erythropoietic system. The objective of the present study was to evaluate the incidence and prognostic significance of increased hemoglobin F in patients with myelodysplastic syndrome. Hemoglobin F concentrations and Ggamma/Ggamma + A gamma-globin chain ratios were determined in 26 patients with primary myelodysplastic syndrome. Median age of the patients was 65 years; all FAB subtypes were included. Increased hemoglobin F concentration of up to 20% of total hemoglobin (normal: below 2%) was seen in 16 patients; ten patients had normal values. There was a significant relation between hemoglobin F concentration and the course of disease, e.g., 12 of the 16 patients with elevated hemoglobin F survived at least 1 year after the examination, in contrast to only three of the ten patients with normal hemoglobin F (p < 0.025). All of six patients with hemoglobin F above 5% survived at least 1 year. There was no significant difference in the hemoglobin F concentration between patients with and without cytogenetic anomalies. The Ggamma/Ggamma + A gamma-globin chain ratio was slightly elevated in all patients, with a weak correlation to the degree of hemoglobin F elevation. The values were not of additional prognostic significance. The data of the present study suggest that the hemoglobin F concentration may be a prognostic parameter in myelodysplastic syndrome; increased hemoglobin F concentration may indicate a better prognosis.

Adolescent↗
PubMedDate not supplied

The artificially perfused guinea-pig yolk sac placenta: transfer and uptake of water, glucose and amino acids.

The development of a new technique to investigate maternal-fetal transfer across the near term guinea-pig yolk sac placenta by in-situ perfusion of the yolk sac vessels is described. The maternal-fetal transfer of labeled water, D- and L-glucose, O-methyl-D-glucose (oMDG), D- and L-alanine, D- and L-aspartate, L-lactate and alpha-amino-isobutyric acid (AIBA) was investigated after injection of these substances into the maternal circulation. After 15 min of perfusion at 0.5 ml/min the water clearance was 132 +/- 12 microliters/min (SEM, n = 30). The clearances for D- or L-glucose were less than 1.2 microliters/min. The activity of label in the venous yolk sac perfusate of all other substances was not different from background activity when 14C-label was used. The clearance of 3H-L-alanine approached the clearance value of water. The total uptake (as defined for single-injection double tracer dilution experiments) from the perfusate of D-glucose, oMDG, alanine and aspartate in comparison to L-glucose was also studied. Mean D-glucose uptake was 11.2 +/- 1.9 percent (n = 8), it was significantly reduced to 4.9 +/- 2 percent (n = 5) by cytochalasin B (1 X 10(-4) mmol/l), and by increasing concentrations of D-glucose (1 to 20 mmol/l, n = 4). The uptake of oMDG was 8.8 +/- 1.5 percent (n = 8). L-alanine uptake was 25 +/- 3.4 percent, D-alanine uptake was 8.3 +/- 1.5 percent (n = 12). Both uptake values were decreased significantly by 10 mmol/l L-alanine, but unaffected by [Na+] (less than 15 mequ/l). There was no uptake of AIBA. The uptakes of L-aspartate were 34.9 +/- 3.7 percent and of D-aspartate 40.4 +/- 4.8 percent (n = 11). Both uptake values were significantly and reversibly reduced by 1 mmol/l L-aspartate and D-aspartate, and by low [Na+] (less than 15 mequ/l). It is concluded that water can move by diffusion from maternal circulation into the yolk sac capillaries in considerable amounts whereas the contribution of the yolk sac placenta to fetal nutrition with D-glucose, L-alanine and L-aspartate is negligible. The membranes of yolk sac cells contain specific transport systems for D-glucose, D-/L-alanine and D-/L-aspartate transfer. The function of the vitelline placenta in the near-term guinea-pig is comparable more to the gut than to the chorio-allantoic placenta.

Amino Acids↗