title: Ultrarapid caspase-3 dependent apoptosis induction by serine/threonine phosphatase inhibitors.
abstract: The protein phosphatase (PP) inhibitors nodularin and microcystin-LR induced apoptosis with unprecedented rapidity, more than 50% of primary hepatocytes showing extensive surface budding and shrinkage of cytoplasm and nucleoplasm within 2 min. The apoptosis was retarded by the general caspase inhibitor Z-VAD.fmk. To circumvent the inefficient uptake of microcystin and nodularin into nonhepatocytes, toxins were microinjected into 293 cells, Swiss 3T3 fibroblasts, promyelocytic IPC-81 cells, and NRK cells. All cells started to undergo budding typical of apoptosis within 0.5 - 3 min after injection. This was accompanied by cytoplasmic and nuclear shrinkage and externalization of phosphatidylserine. Overexpression of Bcl-2 did not delay apoptosis. Apoptosis induction was slower and Z-VAD.fmk independent in caspase-3 deficient MCF-7 cells. MCF-7 cells stably transfected with caspase-3 showed a more rapid and Z-VAD.fmk dependent apoptotic response to nodularin. Rapid apoptosis induction required inhibition of both PP1 and PP2A, and the apoptosis was preceded by increased phosphorylation of several proteins, including myosin light chain. The protein phosphorylation occurred even in the presence of apoptosis-blocking concentrations of Z-VAD.fmk, indicating that it occurred upstream of caspase activation. It is suggested that phosphatase-inhibiting toxins can induce caspase-3 dependent apoptosis in an ultrarapid manner by altering protein phosphorylation.
authors.affiliation: Cell Biology Research Group, Department of Anatomy and Cell Biology, University of Bergen, Arstadveien 19, N-5009 Bergen, Norway.
authors.forename: K E
authors.initials: KE
authors.lastname: Fladmark
authors.forename: O T
authors.initials: OT
authors.lastname: Brustugun
authors.forename: R
authors.initials: R
authors.lastname: Hovland
authors.forename: R
authors.initials: R
authors.lastname: Boe
authors.forename: B T
authors.initials: BT
authors.lastname: Gjertsen
authors.forename: B
authors.initials: B
authors.lastname: Zhivotovsky
authors.forename: S O
authors.initials: SO
authors.lastname: Døskeland
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D017209:Apoptosis; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D002461:Cell Line, Transformed; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015870:Gene Expression; D006801:Humans; D007424:Intracellular Fluid; D008387:Marine Toxins; D051379:Mice; D052998:Microcystins; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000378:metabolism* / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D011714:Pyrans; D051381:Rats; D017208:Rats, Wistar; D013141:Spiro Compounds; D014407:Tumor Cells, Cultured
chemical_list: D000935:Antifungal Agents; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D052998:Microcystins; D010080:Oxazoles; D010456:Peptides, Cyclic; D019253:Proto-Oncogene Proteins c-bcl-2; D011714:Pyrans; D013141:Spiro Compounds; C063998:nodularin; C053079:tautomycin; D019319:Okadaic Acid; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; C057862:cyanoginosin LR