Akt is activated in response to an apoptotic signal.
Akt is a serine-threonine kinase known to exert antiapoptotic effects through several downstream targets. Akt is cleaved during mitochondrial-mediated apoptosis in a caspase-dependent manner. The reason for this is not clear, however, because Akt has not been demonstrated to be activated in response to mitochondrial apoptotic stimuli. Accordingly, we explored whether the well described mitochondrial apoptotic stimuli staurosporine (STS) and etoposide activate Akt and whether such activation impacts apoptosis. Both STS and etoposide activated Akt in NIH 3T3 cells, maximally at 8 and 2 h, respectively, preceding the onset of apoptosis and poly(ADP-ribose) polymerase cleavage. The overexpression of Akt delayed STS-induced apoptosis with an even more pronounced delay observed with overexpression of constitutively active Akt. Akt activation by proapoptotic stimuli lay upstream of mitochondria, because neither caspase inhibitors nor overexpression of Bcl-2 or Bcl-x(L) could prevent it. Activation depended on phosphatidylinositol 3-kinase activity, however. Conversely, inhibition of phosphatidylinositol 3-kinase with wortmannin sensitized cells to apoptosis initiated by STS. These data demonstrate that mitochondrial apoptotic stimuli also activate Akt and such activation modulates apoptosis in this setting.
Tang
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D
Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8N 1Y2 and Amgen Institute, Toronto, Ontario M5G 2C1, Canada. damut@mcmaster.ca
Okada
H
H
Ruland
J
J
Liu
L
L
Stambolic
V
V
Mak
T W
TW
Ingram
A J
AJ
D016475:3T3 Cells; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D015151:Immunoblotting; D051379:Mice; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D000077191:Wortmannin; D051020:bcl-X Protein
D000730:Androstadienes; D004791:Enzyme Inhibitors; D005047:Etoposide; D019384:Nucleic Acid Synthesis Inhibitors; 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; D019311:Staurosporine; D000077191:Wortmannin; D051020:bcl-X Protein; C494812:Bcl2l1 protein, mouse