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J E Eriksson

Publications and source records attributed to J E Eriksson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Solution structure of nodularin. An inhibitor of serine/threonine-specific protein phosphatases.

The three-dimensional solution structure of nodularin was studied by NMR and molecular dynamics simulations. The conformation in water was determined from the distance and dihedral data by distance geometry and refined by iterative relaxation matrix analysis. The cyclic backbone adopts a well defined conformation but the remote parts of the side chains of arginine as well as the amino acid derivative Adda have a large spatial dispersion. For the unusual amino acids the partial charges were calculated and nodularin was subjected to molecular dynamic simulations in water. A good agreement was found between experimental and computational data with hydrogen bonds, solvent accessibility, molecular motion, and conformational exchange. The three-dimensional structure resembles very closely that of microcystin-LR in the chemically equivalent segment. Therefore, it is expected that the binding of both microcystins and nodularins to serine/threonine-specific protein phosphatases is similar on an atomic level.

Enzyme Inhibitors↗
PubMed1995

Involvement of multiple proteases during Fas-mediated apoptosis in T lymphocytes.

The mechanism of Fas antigen-mediated apoptosis is at present unclear. We show here that the 100,000 x g supernatant from cell lysates prepared from anti-Fas-stimulated JUR-KAT T cells, induces chromatin fragmentation in isolated nuclei with concomitant morphological changes typically seen in apoptosis. The formation of this apoptotic nuclei promoting activity (ANPA) in JURKAT T cells after Fas antigen ligation was blocked by the serine protease inhibitors, TPCK and DCI, and by the interleukin 1-beta-converting enzyme inhibitor, VAD-FMK. In addition, chromatin degradation and morphological changes mediated by the ANPA in isolated nuclei were inhibited by TPCK, but not by DCI or VAD-FMK. These results suggest that Fas-mediated apoptosis in T cells involves the activation of a cascade of proteases.

Antigens, Surface↗
PubMed1994

Identification of protein phosphatase 2A as the primary target for microcystin-LR in rat liver homogenates.

The liver-specific toxin microcystin-LR (MC-LR) is a potent inhibitor of type 1 (PP1) and type 2A (PP2A) protein phosphatases. A tritiated form of the toxin, [3H]dihydromicrocystin-LR ([3H]DMC-LR), was used to identify target proteins in cellular fractions prepared from rat liver homogenates. About 80% of the [3H]DMC-LR bound to proteins was in the cytosolic fraction, which contained essentially all of the PP2A. In contrast, much of the PP1 was found in particulate fractions, each with only a few percent of the total protein-bound [3]HDMC-LR. Protein-bound [3H]DMC-LR in the cytosol co-eluted with PP2A, but not with PP-1 from a DEAE-Sepharose column. Native forms of liver cytoplasmic PP2A and PP1 separated by aminohexyl-Sepharose adsorption showed similar sensitivity to inhibition by MC-LR, and bound [3H]DMC-LR proportional to the amount of phosphatase activity. The results indicate that [3H]DMC-LR can bind both PP2A and PP1 in the liver which must be important for microcystin-induced toxicity, but is recovered mainly bound to PP2A in the cytosol.

Animals↗
PubMed1994

Uptake of taurocholic acid and cholic acid in isolated hepatocytes from rainbow trout.

The uptake of the bile acids cholate (CHA) and taurocholate (TCHA) was studied in isolated hepatocytes from rainbow trout (Oncorhynchus mykiss). Both CHA and TCHA were taken up in a concentration- and temperature-dependent manner with optimum temperature at 15 degrees C and a strikingly efficient uptake even at low temperatures (0-5 degrees C). The total uptake was a combination of a saturable [Michaelis-Menten constant (Km) for CHA, 20 microM; Km for TCHA, 19 microM] and a nonsaturable component. The maximal uptake rate of the saturable component was 416 and 805 pmol.mg protein-1.min-1 for CHA and TCHA, respectively. The uptake of both bile acids was shown to be energy dependent, since it was inhibited by the metabolic inhibitors antimycin A, oligomycin and carbonyl cyanide m-chlorophenylhydrazone. The uptake was clearly Na+ independent, since isosmotic replacement of extracellular Na+ by Li+, choline, or K+ did not inhibit the uptake. Furthermore, it seemed to be independent of the presence of extracellular Cl-, since it was not inhibited by replacement of Cl- with sodium gluconate. On the whole, our results show that the hepatocellular uptake of bile acids in rainbow trout is mediated by a Na(+)-independent carrier system, with characteristics resembling the corresponding transport component in mammalian hepatocytes, but with high efficiency even at low temperatures.

Animals↗
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↗