Apaf-1 and caspase-9 accelerate apoptosis, but do not determine whether factor-deprived or drug-treated cells die.
Apoptosis after growth factor withdrawal or drug treatment is associated with mitochondrial cytochrome c release and activation of Apaf-1 and caspase-9. To determine whether loss of Apaf-1, caspase-2, and caspase-9 prevented death of factor-starved cells, allowing them to proliferate when growth factor was returned, we generated IL-3-dependent myeloid lines from gene-deleted mice. Long after growth factor removal, cells lacking Apaf-1, caspase-9 or both caspase-9 and caspase-2 appeared healthy, retained intact plasma membranes, and did not expose phosphatidylserine. However, release of cytochrome c still occurred, and they failed to form clones when IL-3 was restored. Cells lacking caspase-2 alone had no survival advantage. Therefore, Apaf-1, caspase-2, and caspase-9 are not required for programmed cell death of factor-dependent cells, but merely affect its rate. In contrast, transfection with Bcl-2 provided long-term, clonogenic protection, and could act independently of the apoptosome. Unlike expression of Bcl-2, loss of Apaf-1, caspase-2, or caspase-9 would therefore be unlikely to enhance the survival of cancer cells.
Ekert
Paul G
PG
The Walter and Eliza Hall Institute for Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia. ekert@wehi.edu.au
Read
Stuart H
SH
Silke
John
J
Marsden
Vanessa S
VS
Kaufmann
Hitto
H
Hawkins
Christine J
CJ
Gerl
Robert
R
Kumar
Sharad
S
Vaux
David L
DL
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D020169:Caspases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology*; D045304:Cytochromes c / Q000032:analysis; D005434:Flow Cytometry; D017353:Gene Deletion; D007377:Interleukin-3 / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D014407:Tumor Cells, Cultured
C506593:Apaf1 protein, mouse; D053477:Apoptotic Protease-Activating Factor 1; D007377:Interleukin-3; D011506:Proteins; D045304:Cytochromes c; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases