Pre-processed caspase-9 contained in mitochondria participates in apoptosis.
As shown here, mitochondria purified from different organs (liver, brain, kidney, spleen and heart) contain both pro-caspase-9 and the processed, mature form of caspase-9. Purified liver mitochondria release mature caspase-9 upon induction of permeability transition in vitro. This is accompanied by a discrete increase in the enzymatic cleavage of pro-caspase-9 substrates. We found that SHEP neuroblastoma cells constitutively contain pre-processed caspase-9 in their mitochondria, using a combination of subcellular fractionation and immunofluorescence with an antibody specific for the processed caspase. This is a cell type-specific phenomenon since HeLa cells mitochondria mainly contain pro-caspase-9 and comparatively little processed caspase-9. Upon introduction of apoptosis, mitochondrial pro-caspase-9 translocates to the cytosol and to the nucleus. This phenomenon is inhibited by transfection with Bcl-2. In synthesis, we report the unexpected finding that mitochondria can contain a pre-processed caspase isoform in non-apoptotic cells. Bcl-2-mediated regulation of mitochondrial membrane permeabilization may contribute to apoptosis control by preventing mitochondrial, pre-processed caspase-9 from interacting with its cytosolic activators.
Costantini
P
P
Centre National de la Recherche Scientifique, UMR1599, Institut Gustave Roussy, 39 rue Camille-Desmoulins, F-94805 Villejuif, France.
Bruey
J-M
JM
Castedo
M
M
Métivier
D
D
Loeffler
M
M
Susin
S A
SA
Ravagnan
L
L
Zamzami
N
N
Garrido
C
C
Kroemer
Guido
G
D017209:Apoptosis / Q000502:physiology*; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D009447:Neuroblastoma; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine