Apaf-1 and caspase-9 are required for cytokine withdrawal-induced apoptosis of mast cells but dispensable for their functional and clonogenic death.
Cytokines promote survival of mast cells by inhibiting apoptotic pathways regulated by the Bcl-2 protein family. We previously showed that lymphocyte apoptosis can proceed via a Bcl-2-inhibitable pathway independent of the canonical initiator caspase, caspase-9, and its adaptor, Apaf-1. Here we report that mast cells lacking caspase-9 or Apaf-1 are refractory to apoptosis after cytotoxic insults but still lose effector function and ability to proliferate. In response to cytokine deprivation or DNA damage, fetal liver-derived mast cells lacking Apaf-1 or caspase-9 failed to undergo apoptosis. Nevertheless, the cytokine-starved cells were not functionally alive, because, unlike those overexpressing Bcl-2, they could not degranulate on Fcepsilon receptor stimulation or resume proliferation on re-addition of cytokine. Furthermore, mast cells lacking Apaf-1 or caspase-9 had no survival advantage over wild-type counterparts in vivo. These results indicate that the Apaf-1/caspase-9-independent apoptotic pathway observed in lymphocytes is ineffective in cytokine-deprived mast cells. However, although Apaf-1 and caspase-9 are essential for mast cell apoptosis, neither is required for the functional or clonogenic death of the cells, which may be due to mitochondrial dysfunction.
Marsden
Vanessa S
VS
The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia.
Kaufmann
Thomas
T
O'reilly
Lorraine A
LA
Adams
Jerry M
JM
Strasser
Andreas
A
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D020169:Caspases / Q000172:deficiency / Q000378:metabolism*; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology; D005333:Fetus / Q000166:cytology / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000378:metabolism*; D008407:Mast Cells / Q000166:cytology / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
C506593:Apaf1 protein, mouse; D053477:Apoptotic Protease-Activating Factor 1; D016207:Cytokines; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases