Search PubMed⌕ Search

Biomedical subjects

S Olsnes

Publications and source records attributed to S Olsnes.

At least 145 records · Page 8Linked to original sources
PubMed1983

Dansylcadaverine eliminates calmodulin stimulation of phosphodiesterase.

Dansylcadaverine, which structurally resembles the calmodulin antagonists W-7 and W-5, prevented the calmodulin dependent stimulation of 3':5'-cyclic nucleotide phosphodiesterase in vitro. Dansylcadaverine and trifluoperazine sensitized cells to Pseudomonas aeruginosa exotoxin A in apparently the same way, exept that 40 times higher concentrations of dansylcadaverine than of trifluoperazine was required.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Entry of Shigella dysenteriae toxin into HeLa cells.

The rate of shigella toxin entry into the cytosol of HeLa S3 cells was estimated from the toxin-induced reduction in protein synthesis. Whereas high toxin concentrations strongly reduced protein synthesis within 30 min, lower concentrations required longer times. The major part of the cell-bound toxin entered only after several hours. Toxin entered cells after incubation at 25 degrees C but not at 20 degrees C, although toxin binding was the same at the two temperatures. Increasing the KCl concentration to 0.2 M protected against toxin. The toxin entry was strongly reduced when the level of ATP in the cells was reduced by incubation with metabolic inhibitors. Lysosomotrophic agents such as NH4Cl and chloroquine had little or no protective effect, but the protonophores carbonyl cyanide p-trifluoromethoxyphenylhydrazone and carbonyl cyanide m-chlorophenylhydrazone and the ionophore monensin protected cells against the toxin. Cells were also protected when the pH was reduced to 6.4. The entry of shigella toxin is discussed in relation to that of other protein toxins with intracellular sites of action.

Bacterial Toxins↗
PubMed1983

Animal toxicity of Shigella dysenteriae cytotoxin: evidence that the neurotoxic, enterotoxic, and cytotoxic activities are due to one toxin.

The lethal effect to rabbits and mice of Shigella dysenteriae toxin and the ability of the toxin to induce fluid accumulation in rabbit ileal loops were studied in relation to the cytotoxic activity. The relative concentrations of the three activities were approximately the same in a crude toxin preparation and in purified, electrophoretically homogenous toxin. The cytotoxic and lethal activities eluted identically from a high pressure liquid chromatography column and migrated at the same rate in polyacrylamide gel electrophoresis under nondenaturing conditions. The cytotoxic, lethal, and enterotoxic activities were inactivated to essentially the same extent upon incubation for few minutes at 80 degrees C and upon treatment with urea. Graded precipitation of Shigella toxin with different amounts of an antiserum to Shigella toxin in each case removed essentially the same fraction of the cytotoxic, the lethal, and the enterotoxic activity. The data indicate that one molecular entity is responsible for the three biologic effects of Shigella toxin studied. After i.v. injection, the LD50 dose was estimated to be 2.2 ng/kg in rabbits and 450 ng/kg in mice.

Animals↗
PubMed1982

Isolation and characterization of viscumin, a toxic lectin from Viscum album L. (mistletoe).

A toxic protein, viscumin, was isolated from extracts of mistletoe by affinity chromatography on acid-treated Sepharose 4B. Viscumin was selectively bound to the column and could be eluted with lactose. It migrated in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate corresponding to Mr = 60,000. In addition, two bands migrating corresponding to Mr = 29,000 and 32,000 were found. After treatment with 2-mercaptoethanol, only 2 bands (Mr = 29,000 and 34,000) were found. Apparently, viscumin consists of two chains which, in some of the molecules, are disulfide-linked. Protection experiments with antiserum against viscumin indicated that the major part of the cytotoxic activity in mistletoe extracts is due to viscumin. Gel filtration experiments on Sephacryl 200 indicated that, at low concentrations, viscumin occurs as a monomer and at higher concentrations as a dimer. Viscumin was found to inhibit protein synthesis in cell-free systems. When the two constituent peptide chains of viscumin were eluted from polyacrylamide gels and tested for ability to inhibit cell-free protein synthesis, this property was found to be associated with the fastest migrating chain, here denoted the A chain. The heavier chain was denoted the B chain. The A chain was found to inhibit protein synthesis by inactivating the ribosomes catalytically. Reconstitution experiments with isolated ribosomal subunits from untreated and A chain-treated ribosomes showed that the 60 S ribosomal subunit was selectively inactivated.

Animals↗
PubMed1982

Action of viscumin, a toxic lectin from mistletoe, on cells in culture.

A toxin from mistletoe, viscumin, inhibited the incorporation of leucine in cells more rapidly than the incorporation of uridine and thymidine, indicating that the toxins act by inhibiting cellular protein synthesis. The presence of galactose, lactose, and melibiose in the medium protected cells against viscumin. The sensitivity to viscumin of different cell lines differed considerably. The cytotoxic properties of viscumin were compared to those of the related toxins abrin, ricin, and modeccin. The profile of the sensitivity of a panel of cell lines to viscumin was dissimilar from those obtained with abrin and modeccin. Cell lines selected for resistance to modeccin and ricin were fully sensitive to viscumin. Ca2+ was required for viscumin to express its toxic effect. In contrast, the Ca2+ ionophore A23187 protected the cells against viscumin. Whereas the sensitivity of cells to viscumin did not vary much between pH 7 and 9, the cells were much less sensitive at pH 6. Also, cells treated with the two metabolic inhibitors, 2-deoxyglucose and NaN3, were insensitive to the toxins. Viscumin taken up by cells in the absence of Ca2+ or at pH 6 was able to intoxicate the cells when Ca2+ was added or when the pH was adjusted to neutrality. In contrast, cells exposed to viscumin in the presence of 2-deoxyglucose and NaN3, which inhibit endocytosis, were not intoxicated when the cells were treated with antiviscumin and then transferred to normal medium. The results indicate that endocytosis is involved in the entry of viscumin.

Animals↗
PubMed1982

Preparation and properties of chimeric toxins prepared from the constituent polypeptides of diphtheria toxin and ricin. Evidence for entry of ricin A-chain via the diphtheria toxin pathway.

A highly toxic conjugate of ricin A-chain and diphtheria toxin fragment B was prepared by disulfide exchange reaction. A similar conjugate between diphtheria toxin fragment A and ricin B-chain was nontoxic. Like native diphtheria toxin, the conjugate ricin A/diphtheria toxin B was much more toxic to Vero than to HeLa cells. Ricin was equally toxic to these cell lines. Lactose, which inhibits ricin binding, did not protect against the conjugate. Cells resistant to ricin, partly due to a reduced number of ricin-binding sites, were fully sensitive to the conjugate, indicating that the conjugate binds to diphtheria toxin receptors. The conjugate was fully toxic to two Vero cell mutants, resistant to diphtheria toxin because the elongation factor 2 could not be ADP-ribosylated by the diphtheria toxin A-fragment. Therefore, the inhibition of protein synthesis by the conjugate must be caused by the ricin A-chain. Ammonium chloride which prevents entry of diphtheria toxin, but not of ricin, also protected against the conjugate. Like diphtheria toxin, the conjugate was most toxic at low pH, whereas ricin is most active at pH above neutrality and inactive at low pH. The results indicate that the conjugate ricin A/diphtheria toxin B binds to diphtheria toxin receptors and inhibits cellular protein synthesis due to the action of ricin A-chain which appears to enter the cell by the diphtheria toxin pathway.

Ammonium Chloride↗
PubMed1982

Entry of the toxic proteins abrin, modeccin, ricin, and diphtheria toxin into cells. I. Requirement for calcium.

In the absence of Ca2+ cells were not sensitive to the toxic proteins abrin and modeccin and the sensitivity to ricin and diphtheria toxin was reduced. Calcium deprivation had little effect on the binding and endocytosis of abrin, modeccin, and ricin. The binding of diphtheria toxin to cells was, however, reduced, Verapamil and Co2+ inhibited 45Ca2+ uptake and protected cells against abrin and modeccin at low concentrations of Ca2+. At higher Ca2+ concentrations the protection was overcome. La3+ inhibited strongly 45Ca2+ uptake and protected well against all four toxins, even at high Ca2+ concentrations. Fe3+ also afforded protection although it did not inhibit Ca2+ uptake. The Ca2+ ionophore, A23187, which strongly increases the uptake of 45Ca2+, protected cells well against abrin and modeccin, slightly against diphtheria toxin, but not against ricin. Both Ca2+ deprivation and treatment with A23187 protected well against the hybrid toxin abrin A-chain/ricin B-chain. Such treatment afforded little protection against the hybrid ricin A-chain/abrin B-chain. Apparently the protection against abrin is associated with its A-chain. The calmodulin inhibitor, trifluoperazine, protected strongly against modeccin and diphtheria toxin. The data indicate that Ca2+ is involved in the entry mechanism for abrin, modeccin, and ricin, possibly as a Ca2+ flux together with the toxins.

Abrin↗
PubMed1982

Entry of the toxic proteins abrin, modeccin, ricin, and diphtheria toxin into cells. II. Effect of pH, metabolic inhibitors, and ionophores and evidence for toxin penetration from endocytotic vesicles.

The toxicity of abrin, modeccin, and ricin to Vero cells was maximal at neutral and slightly alkaline pH, and it was strongly reduced at pH 6.0 and below. Diphtheria toxin was most toxic at low pH. Binding and endocytosis of abrin, modeccin, and ricin did not vary much within the pH range tested. High concentrations of the carboxylic ionophore Br-X-537A, protected against all four toxins. Combined treatment of cells with an inhibitor of glycolysis and an uncoupler of oxidative phosphorylation strongly inhibited endocytosis of toxins and protected against intoxication. The protective effect of Ca2+ deprivation, of pH 6.0, and of metabolic inhibitors disappeared soon after transfer of the cells to normal medium, whereas the protective effect of Br-X-537A and of trifluoperazine disappeared slowly. The decay rate of the protection by NH4Cl and by the ionophore A23187 differed with the different toxins. Cells exposed to abrin, modeccin, and ricin under protective conditions which did not inhibit endocytosis of the toxins (Ca2+ deprivation, pH 6.0, Br-X-537A), and then treated with antitoxins to inactivate extracellular toxin, were intoxicated when the protection was released. In contrast, cells exposed to toxins while endocytosis was arrested by treatment with metabolic inhibitors were not intoxicated when antitoxins were added and the metabolic inhibitors removed. Modeccin and diphtheria toxin endocytosed in the presence of trifluoperazine and NH4Cl were unable to intoxicate cells. The possibility that endocytosis is a step in the normal entry route of the toxins is discussed.

Abrin↗
PubMed1981

The cytotoxic activity of Shigella toxin. Evidence for catalytic inactivation of the 60 S ribosomal subunit.

The cytotoxic test system for Shigella shigae toxin was improved and used to study the stability of the toxin to various pH values, temperature, and chemicals. Inhibition of protein synthesis is the first demonstrable effect in cells treated with Shigella toxin. This inhibition appears to be at the level of peptide chain elongation. An inhibition effect on cell-free protein synthesis is exhibited by toxin pretreated first with trypsin and then with dithiothreitol and 8 M urea or 1% sodium dodecyl sulfate. Ribosomes treated with toxin or its A1 fragment had lost most of their ability to polymerize [14C]phenylalanine in a poly(U)-dependent cell-free system. Salt-washed ribosomes in simple buffered solutions were inactivated at a rate of at least 40 ribosomes/(min) (A1 fragment). Addition of antitoxin immediately stopped further inactivation, but it did not reactivate the inactivated ribosomes. 60 S ribosomal subunits from toxin-treated ribosomes had a marked reduction in ability to support polyphenylanine synthesis, whereas 40 S subunits from toxin-treated ribosomes retained their activity. Toxin-treated ribosomes retained their ability to incorporate [3H]puromycin into growing peptide chains, indicating that the peptide bond formation is not the function inhibited.

Animals↗
PubMed1981

Subunit structure of Shigella cytotoxin.

Shigella cytotoxin was purified from the culture medium of Shigella shigae 60 R and from the bacterial pellet by an extensive purification scheme involving chromatography on Cibachron Blue F3GA, chitin, and DEAE-cellulose columns, sucrose gradient centrifugation, and finally polyacrylamide gel electrophoresis under nondenaturing conditions. In sodium dodecyl sulfate polyacrylamide gels, purified toxin showed two bands, a heavy one with the molecular weight of 30,500 (A chain), and a broad band migrating near the dye front (B chain). The A chain was easily cleaved by proteases into two fragments, A1 (Mr = 27,500) and A2 (Mr = 3,000). These fragments were linked with a disulfide bridge (nicked toxin). The molecular weight of native toxin was estimated by the method of Ferguson to be 68,000 +/- 4,000. Cross-linking experiments indicated that the native toxin consists of one A chain and six to seven B chains, with each B chain having a molecular weight of congruent to 5,000. The isolated A and B chains were not toxic to cells nor did they bind to cells to a measurable extent. In a cell-free system, the A1 fragment strongly inhibited protein synthesis. The possibility that the B chains form the binding moiety of the toxin is discussed.

Bacterial Toxins↗
PubMed1981

Effects of retinoids and phorbol esters on the sensitivity of different cell lines to the polypeptide toxins modeccin, abrin, ricin and diphtheria toxin.

The effects of retinoic acid and 12-O-tetradecanoylphorbol 13-acetate on the sensitivities of a number of cell lines to the toxins modeccin, abrin, ricin and diphtheria toxin were studied. Retinoic acid and some other retinoids were found to protect a number of the cell lines against the toxins. HeLa cells that were protected bound much more retinoic acid than L-cells that were not protected. The tumour promoter 12-O-tetradecanoylphorbol 13-acetate was found to increase the sensitivity of cells to abrin, ricin and modeccin in the absence as well as in the presence of retinoic acid. Neither retinoic acid nor 12-O-tetradecanoylphorbol 13-acetate affected the extent of binding and pinocytotic uptake of toxins by the cells. Apparently retinoic acid and 12-O-tetradecanoylphorbol 13-acetate interfere with the entry of the toxins through the cell membrane.

Abrin↗
PubMed1981

Chimeric toxins.

Explore the source record for details and available documents.

Animals↗
PubMed1981

Radioimmunoassays of abrin and ricin in blood.

Radioimmunoassays for abrin and ricin are described. There is little cross-reactivity between the two toxins. The procedures described are capable of determining blood concentrations down to 50-100 pg/ml, permitting identification of abrin and ricin poisoning and monitoring of the blood concentrations in cancer patients treated with these agents.

Abrin↗
PubMed1980

In vitro sensitivity of human melanoma xenografts to cytotoxic drugs. Correlation with in vivo chemosensitivity.

Single-cell suspensions prepared from five human melanomas, grown serially as xenografts in athymic nude mice, were exposed in vitro to increasing concentrations of DTIC (Dacarbazine), CCNU (Lomustine), procarbazine, vinblastine, and the cancerostatic lectins abrin and ricin. The in vitro chemosensitivity of the cells, as measured by the drug concentrations required to inhibit colony formation in soft agar by 50%, was correlated with the growth delay of the xenografts in vivo, previously observed after treatment of the animals with maximum tolerable doses of the same drugs. It was found that for each drug the in vitro sensitivity of the different xenografts was strongly correlated with their response in vivo. The results provide evidence that the soft agar test, as carried out here, adequately reflects the relative sensitivity of the xenografts in vivo. The data indicate that human xenografts may be used to develop quantitative in vitro chemosensitivity tests.

Abrin↗