title: Identification of protein phosphatase 2A as the primary target for microcystin-LR in rat liver homogenates.
abstract: 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.
authors.affiliation: Department of Biology, Abo Akademi University, Turku, Finland.
authors.forename: D M
authors.initials: DM
authors.lastname: Toivola
authors.forename: J E
authors.initials: JE
authors.lastname: Eriksson
authors.forename: D L
authors.initials: DL
authors.lastname: Brautigan
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002458:Cell Fractionation; D002848:Chromatography, DEAE-Cellulose; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D008099:Liver / Q000201:enzymology* / Q000648:ultrastructure; D046911:Macromolecular Substances; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic / Q000378:metabolism / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D054648:Protein Phosphatase 2; D051381:Rats; D017207:Rats, Sprague-Dawley; D014316:Tritium
chemical_list: D046911:Macromolecular Substances; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D014316:Tritium; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C057862:cyanoginosin LR