title: Protein phosphatase 2A-linked and -unlinked caspase-dependent pathways for downregulation of Akt kinase triggered by 4-hydroxynonenal.
abstract: We studied the signal pathways for regulation of serine/threonine protein kinase Akt in Jurkat cells that had been treated with 4-hydroxynonenal (HNE) for caspase-dependent apoptosis induction. Treatment of cells with HNE led to a decrease in the level of Akt activity due to the dephosphorylation at Ser473, a major regulatory phosphorylation site. HNE-mediated dephosphorylation of Akt was prevented by a protein phosphatase 2A (PP2A) inhibitor, okadaic acid, and by a caspase-3 inhibitor, DEVD-CHO. HNE treatment resulted in an increase in the total level of PP2A activity, release of active tyrosine-dephosphorylated PP2A from the cytoskeleton and PP2A-Akt association, which were all dependent on caspase-3 activation. These results suggest that the level of PP2A activity is at least in part determined by its tyrosine phosphorylation, which is dually controlled by okadaic acid-sensitive phosphatases and protein-tyrosine kinases. Possibly underlying the mechanism of caspase-mediated activation of PP2A, HNE treatment resulted in downregulation of the activity of Src kinase, as a representative caspase-sensitive kinase to phosphorylate PP2A at tyrosine. In addition, activated caspase-3 partially cleaved Akt at a late stage of the apoptosis. These results indicate the existence of two distinct caspase-dependent signal pathways for downregulation of Akt that works as a mechanism of positive feedback regulation for HNE-triggered apoptotic signals.
authors.affiliation: Department of Immunology, Nagoya University Graduate School of Medicine, Showa-ku, Nagoya, Japan.
authors.forename: W
authors.initials: W
authors.lastname: Liu
authors.forename: A A
authors.initials: AA
authors.lastname: Akhand
authors.forename: K
authors.initials: K
authors.lastname: Takeda
authors.forename: Y
authors.initials: Y
authors.lastname: Kawamoto
authors.forename: M
authors.initials: M
authors.lastname: Itoigawa
authors.forename: M
authors.initials: M
authors.lastname: Kato
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
authors.forename: N
authors.initials: N
authors.lastname: Ishikawa
authors.forename: I
authors.initials: I
authors.lastname: Nakashima
mesh_terms: D000447:Aldehydes / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D025461:Feedback, Physiological / Q000187:drug effects / Q000502:physiology; D006801:Humans; D019169:Jurkat Cells; D019319:Okadaic Acid / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D019061:src-Family Kinases / Q000187:drug effects / Q000378:metabolism
chemical_list: D000447:Aldehydes; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D011518:Proto-Oncogene Proteins; C108637:aspartyl-glutamyl-valyl-aspartal; D019319:Okadaic Acid; D012694:Serine; D019061:src-Family Kinases; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; C027576:4-hydroxy-2-nonenal