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J E Eriksson

Publications and source records attributed to J E Eriksson.

16 recordsLinked to original sources
PubMed1992

Cytoskeletal integrity in interphase cells requires protein phosphatase activity.

Phosphorylation by protein kinases has been established as a key factor in the regulation of cytoskeletal structure. However, little is known about the role of protein phosphatases in cytoskeletal regulation. To assess the possible functions of protein phosphatases in this respect, we studied the effects of the phosphatase inhibitors calyculin A, okadaic acid, and dinophysistoxin 1 (35-methylokadaic acid) on BHK-21 fibroblasts. Within minutes of incubation with these inhibitors, changes are seen in the structural organization of intermediate filaments, followed by a loss of microtubules, as assayed by immunofluorescence. These changes in cytoskeletal structure are accompanied by a rapid and selective increase in vimentin phosphorylation on interphase-specific sites, and they are fully reversible after removal of calyculin A. The results indicate that there is a rapid phosphate turnover on cytoskeletal intermediate filaments and further suggest that protein phosphatases are essential for the maintenance and structural integrity of two major cytoskeletal components.

Animals↗
PubMed1992

Intermediate filament dynamics.

The view of intermediate filaments as static cytoskeletal elements is changing. Studies of exogenous intermediate filament proteins, either microinjected or expressed from transfected genes, have demonstrated that a continuous incorporation of subunits into the polymerized filaments is taking place. This incorporation appears to be required for maintaining normal cytoplasmic networks of intermediate filaments. At the post-translational level, phosphorylation is an important factor in regulating dynamic aspects of intermediate filament organization and structure.

Animals↗
PubMed1991

Vimentin is hyperphosphorylated in primary human fibroblasts treated with okadaic acid.

Okadaic acid and dinophysistoxin-1 (35-methylokadaic acid) induced hyperphosphorylation of a 58 kDa protein in primary human fibroblasts, due to inhibition of protein phosphatase 1 and 2A activities. The protein was present in the nuclear and cytosolic fractions. Its pI was 5.3. The hyperphosphorylated protein reacted with monoclonal and polyclonal anti-vimentin antibodies, but not with anti-nucleolin antibody. Phosphorylation of vimentin was stimulated in vitro by dinophysistoxin-1 dose-dependently in the presence of protein phosphatase 2A and protein kinases.

Blotting, Western↗
PubMed1991

Computer modelling of the 3-dimensional structures of the cyanobacterial hepatotoxins microcystin-LR and nodularin.

The 3-dimensional structures of two cyanobacterial hepatotoxins microcystin-LR, a cyclic heptapeptide and nodularin, a cyclic pentapeptide, and the novel amino acid ADDA (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid) were constructed, and optimized using the CHEM-X molecular mechanics program. The peptide rings were planar and of rectangular shape. Optimized ADDA formed a U-shape and a difference in the orientation of ADDA with respect to the peptide ring of the two hepatotoxins was observed.

Computer Simulation↗
PubMed1990

Hepatocyte deformation induced by cyanobacterial toxins reflects inhibition of protein phosphatases.

The cyclic peptide hepatotoxins microcystin-LR, 7-desmethyl-microcystin-RR and nodularin are potent inhibitors of the protein phosphatases type 1 and type 2A. Their potency of inhibition resembles calyculin-A and to a lesser extent okadaic acid. These hepatotoxins increase the overall level of protein phosphorylation in hepatocytes. Evidence is presented to indicate that in hepatocytes the morphological changes and effects on the cytoskeleton are due to phosphatase inhibition. The potency of these compounds in inducing hepatocyte deformation is similar to their potency in inhibiting phosphatase activity. These results suggest that the hepatotoxicity of these peptides is related to inhibition of phosphatases, and further indicate the importance of the protein phosphorylation in maintenance of structural and homeostatic integrity in these cells.

Amino Acid Sequence↗
PubMed1990

Hepatocellular uptake of 3H-dihydromicrocystin-LR, a cyclic peptide toxin.

The cellular uptake of microcystin-LR, a cyclic heptapeptide hepatotoxin from the cyanobacterium Microcystis aeruginosa, was studied by means of a radiolabelled derivative of the toxin. 3H-dihydromicrocystin-LR. The uptake of 3H-dihydromicrocystin-LR was shown to be specific for freshly isolated rat hepatocytes whereas the uptake in the human hepatocarcinoma cell line Hep G2 as well as the mouse fibroblast cell line NIH-3T3, and the human neuroblastoma cell line SH-SY5Y, was negligible. By means of a surface barostat technique it was shown that the membrane penetrating capacity (surface activity) of microcystin-LR was low, indicating that the toxin requires an active uptake mechanism. The hepatocellular uptake of microcystin-LR could be inhibited in the presence of bile acid transport inhibitors such as antamanide (5 microM), sulfobromophthalein (50 microM) and rifampicin (30 microM). The uptake was also reduced in a concentration dependent manner when the hepatocytes were incubated in the presence the bile salts cholate and taurocholate. A complete inhibition of the hepatocellular uptake was achieved by 100 microM of either bile salt. The overall results indicate that the uptake of microcystin-LR is through the multispecific transport system for bile acids. This mechanism of cell entry would explain the previously observed cell specificity and organotropism of microcystin-LR.

Amino Acid Sequence↗
PubMed1990

Synthesis, organotropism and hepatocellular uptake of two tritium-labeled epimers of dihydromicrocystin-LR, a cyanobacterial peptide toxin analog.

Two tritium-labeled epimers of dihydromicrocystin-LR, a derivative of the cyanobacterial peptide hepatotoxin microcystin-LR, were synthesized by reduction with sodium boro[3H]hydride and purified with reversed-phase liquid chromatography. The epimers were hepatotoxic in mice; the i.p. LD50 was 120-135 micrograms/kg. They were concentrated in the liver and to some extent in the intestine and the kidney after an i.v. injection. Freshly isolated rat hepatocytes showed a rapid uptake of both epimers. The cellular uptake of the epimers was almost complete within 5 min at concentrations 1 microM (0.5 microM dihydromicrocystin-LR + 0.5 microM microcystin-LR) and 4 microM (0.5 microM + 3.5 microM). The uptake of the earlier eluting epimer was about three times higher than that of the later eluting epimer.

Animals↗
PubMed1990

Structure of a hepatotoxic pentapeptide from the cyanobacterium Nodularia spumigena.

The structure of a hepatotoxic peptide from the cyanobacterium Nodularia spumigena was determined using 1D and 2D proton nuclear magnetic resonance spectroscopy and fast atom bombardment mass spectrometry. The toxin was a cyclic pentapeptide (mol. wt 824.5) with the structure cyclo-(beta-methylisoAsp-Arg-Adda-isoGlu-N-methylde hydrobutyric acid) (Adda: 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid).

Amino Acid Sequence↗
PubMed1989

Rapid microfilament reorganization induced in isolated rat hepatocytes by microcystin-LR, a cyclic peptide toxin.

The cyclic heptapeptide hepatotoxin microcystin-LR from the cyanobacterium Microcystis aeruginosa induces rapid and characteristic deformation of isolated rat hepatocytes. We investigated the mechanism(s) responsible for cell shape changes (blebbing). Our results show that the onset of blebbing was accompanied neither by alteration in intracellular thiol and Ca2+ homeostasis nor by ATP depletion. The irreversible effects were insensitive to protease and phospholipase inhibitors and also to thiol-reducing agents, excluding the involvement of enhanced proteolysis, phospholipid hydrolysis, and thiol modification in microcystin-induced blebbing. In contrast, the cell shape changes were associated with a remarkable reorganization of microfilaments as visualized both by electron microscopy and by fluorescent staining of actin with rhodamine-conjugated phalloidin. The morphological effects and the microfilament reorganization were specific for microcystin-LR and could not be induced by the microfilament-modifying drugs cytochalasin D or phalloidin. Using inhibition of deoxyribonuclease I as an assay for monomeric actin, we found that the microcystin-induced reorganization of hepatocyte microfilaments was not due to actin polymerization. On the basis of the rapid microfilament reorganization and the specificity of the effects, it is suggested that microcystin-LR constitutes a novel microfilament-perturbing drug with features that are clearly different from those of cytochalasin D and phalloidin.

Actin Cytoskeleton↗
PubMed1989

Structure and toxicity of a peptide hepatotoxin from the cyanobacterium Oscillatoria agardhii.

A peptide hepatotoxin was isolated by reversed phase liquid chromatography from the cyanobacterium Oscillatoria agardhii and characterized structurally and toxicologically. Amino acid analyses, proton nuclear magnetic resonance and fast atom bombardment mass spectrometry showed that the toxin is a cyclic heptapeptide (mol. wt 1023.5) with the structure cyclo-(Ala-Arg-Asp-Arg-Adda-Glu-N-methyldehydroAla) (Adda: 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid). In mice the toxic effects were restricted mainly to the liver where the toxin induced massive hemorrhages and a disruption of the lobular and sinusoidal structure. The i.p. LD50 of the toxin was 250 micrograms/kg. The structural and toxic properties of this peptide are very close to those of microcystins, cyclic peptide toxins produced by the cyanobacterium Microcystis aeruginosa.

Amino Acid Sequence↗
PubMed1988

Rapid analysis of peptide toxins in cyanobacteria.

A quick and easy-to-perform method for routine analysis of cyanobacterial (blue-green algal) peptide toxins is proposed. The toxins are analysed by means of high-performance liquid chromatography using a recently developed internal surface reversed-phase column. The sample clean-up work is minimized and the total analysis time is thus shortened considerably compared to previously described methods.

Chromatography, High Pressure Liquid↗
PubMed1988

Preliminary characterization of a toxin isolated from the cyanobacterium Nodularia spumigena.

A peptide toxin was isolated from the cyanobacterium Nodularia spumigena by high performance liquid chromatography (HPLC). The i.p. LD50 of the toxin was 50 micrograms/kg mouse with death within 1-3 hr. The major effects of the toxin were seen in the liver in the form of extensive haemorrhages. Amino acid analysis showed the presence of equimolar amounts of glutamic acid, beta-methyl-aspartic acid, and arginine. The toxicological and some of the chemical properties of the isolated toxin were similar to those reported for hepatotoxins isolated from the cyanobacterium Microcystis aeruginosa.

Amino Acids↗
PubMed1988

A comparison of toxins isolated from the cyanobacteria Oscillatoria agardhii and Microcystis aeruginosa.

1. A toxin isolated from a strain of Oscillatoria agardhii var. was compared to a peptide toxin isolated from Microcystis aeruginosa. 2. The Oscillatoria toxin possessed similar hepatotoxic properties on mice as the Microcystis toxin but had a higher LD50 than the latter; 320 micrograms/kg compared to 43 micrograms/kg (i.p. mouse), respectively. 3. Ultra-violet and infra-red spectra showed that the Oscillatoria toxin is a peptide which is not identical to the Microcystis toxin. 4. The spectra also indicated some structural similarities in these toxins.

Animals↗
PubMed1987

Cell selective cytotoxicity of a peptide toxin from the cyanobacterium Microcystis aeruginosa.

The effects of a cyclic peptide toxin, isolated from the cyanobacterium Microcystis aeruginosa, on cell morphology and ion transport in human erythrocytes, isolated rat hepatocytes and mouse fibroblasts (3T3) were studied. Neither in erythrocytes nor in fibroblasts did the toxin cause morphological alterations. In hepatocytes the toxin induced marked morphological alterations at a concentration of about 50 nM. In erythrocytes and fibroblasts no effects on ion transport were observed. In hepatocytes the toxin induced a significant increase in both phosphate and potassium efflux at concentrations far below the concentration causing morphological alterations (0.1 and 1 nM, respectively). It is suggested that the cytotoxicity of the toxin is not due to a non-specific interaction with the plasma membrane and that the effects of the toxin in hepatocytes are probably due to an interaction of the toxin with cytoskeletal elements.

Biological Transport↗
PubMed1979

Evaluation of quinidine Lipettes -- a sustained release preparation.

A new sustained release preparation (Lipettes) of quinidine has been evaluated with regard to dissolution, absorption, serum concentration and side-effects. The serum levels of quinidine after single oral doses and after long-term treatment have been compared with the serum levels after administration of some other quinidine preparations on the Swedish market. The side-effects of the sustained release preparations have also been studied. Results indicated that this new sustained release quinidine preparation yields more even serum concentrations of quinidine and seemed to cause less troublesome side-effects than the marketed preparations.

Administration, Oral↗