title: Akt regulates cell survival and apoptosis at a postmitochondrial level.
abstract: Phosphoinositide 3 kinase/Akt pathway plays an essential role in neuronal survival. However, the cellular mechanisms by which Akt suppresses cell death and protects neurons from apoptosis remain unclear. We previously showed that transient expression of constitutively active Akt inhibits ceramide-induced death of hybrid motor neuron 1 cells. Here we show that stable expression of either constitutively active Akt or Bcl-2 inhibits apoptosis, but only Bcl-2 prevents the release of cytochrome c from mitochondria, suggesting that Akt regulates apoptosis at a postmitochondrial level. Consistent with this, overexpressing active Akt rescues cells from apoptosis without altering expression levels of endogenous Bcl-2, Bcl-x, or Bax. Akt inhibits apoptosis induced by microinjection of cytochrome c and lysates from cells expressing active Akt inhibit cytochrome c induced caspase activation in a cell-free assay while lysates from Bcl-2-expressing cells have no effect. Addition of cytochrome c and dATP to lysates from cells expressing active Akt do not activate caspase-9 or -3 and immunoprecipitated Akt added to control lysates blocks cytochrome c-induced activation of the caspase cascade. Taken together, these data suggest that Akt inhibits activation of caspase-9 and -3 by posttranslational modification of a cytosolic factor downstream of cytochrome c and before activation of caspase-9.
authors.affiliation: Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6084, USA.
authors.forename: H
authors.initials: H
authors.lastname: Zhou
authors.forename: X M
authors.initials: XM
authors.lastname: Li
authors.forename: J
authors.initials: J
authors.lastname: Meinkoth
authors.forename: R N
authors.initials: RN
authors.lastname: Pittman
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002457:Cell Extracts; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002474:Cell-Free System; D003574:Cytochrome c Group / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006822:Hybrid Cells; D008845:Microinjections; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D002457:Cell Extracts; D003574:Cytochrome c Group; D019869:Phosphatidylinositol 3-Kinases; D011065:Poly(ADP-ribose) Polymerases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D013110:Sphingosine; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C494826:BAX protein, human; C494811:BCL2L1 protein, human; C064769:N-acetylsphingosine; C494918:AKT1 protein, human; C505407:CASP3 protein, human; C506433:CASP9 protein, human