The Akt-regulated forkhead transcription factor FOXO3a controls endothelial cell viability through modulation of the caspase-8 inhibitor FLIP.
FLICE-inhibitory protein (FLIP) is a homolog of caspase-8 that lacks catalytic activity and has been shown to be important in protecting endothelial cells from apoptosis. The serine/threonine kinase Akt/PKB was recently reported to promote FLIP expression in endothelial and tumor cells. Here we examined the role of the forkhead transcription factor FOXO3a, a downstream target of Akt, in controlling FLIP regulation in endothelial cells. FOXO3a nuclear translocation was regulated by Akt in human umbilical vein endothelial cells. Transduction of a nonphosphorylatable, constitutively active mutant of FOXO3a (TM-FOXO3a) led to the down-regulation of FLIP levels. Transduction with TM-FOXO3a also increased caspase-8 activity and promoted apoptosis in endothelial cells. Conversely, transduction of a dominant-negative mutant of FOXO3a up-regulated FLIP levels and protected endothelial cells from apoptosis under serum deprivation conditions. Restoration of intracellular FLIP blocked caspase-8 activation and inhibited apoptosis in TM-FOXO3a-transduced cells. These data suggest that FOXO3a is a downstream target of Akt in endothelial cells that can promote apoptosis via FLIP down-regulation and activation of the extrinsic apoptotic pathway.
Skurk
Carsten
C
Molecular Cardiology/Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Maatz
Henrike
H
Kim
Hyo-Soo
HS
Yang
Jiang
J
Abid
Md Ruhul
MR
Aird
William C
WC
Walsh
Kenneth
K
D021581:Active Transport, Cell Nucleus; D023102:Anoikis; D017209:Apoptosis; D015153:Blotting, Western; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000378:metabolism*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002469:Cell Separation; D002470:Cell Survival; D002478:Cells, Cultured; D053938:DNA Fragmentation; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D015536:Down-Regulation; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D049452:Green Fluorescent Proteins; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012313:RNA / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D015843:Serpins / Q000737:chemistry; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D014471:Umbilical Veins / Q000166:cytology; D015854:Up-Regulation; D014764:Viral Proteins
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D006133:Growth Substances; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D011518:Proto-Oncogene Proteins; D015843:Serpins; D014157:Transcription Factors; D014764:Viral Proteins; D049452:Green Fluorescent Proteins; D012313:RNA; C074641:interleukin-1beta-converting enzyme inhibitor; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D012260:Ribonucleases; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases