The permeability transition pore signals apoptosis by directing Bax translocation and multimerization.
Mitochondria are key players of apoptosis and can irreversibly commit the cell to death by releasing cytochrome c (Cyt.c) to the cytosol, where caspases 9 and 3 subsequently get activated. Under conditions of oxidative stress, opening of the mitochondrial permeability transition pore (PTP) represents an early trigger and is crucial in causing Cyt.c release. To account for the latter, current models propose that PTP gating would result, as is the case in vitro, in the rupture of the outer mitochondrial membrane caused by mitochondrial matrix swelling. Using live cell imaging and recombinant fluorescent probes based on the green fluorescent protein (GFP) and its mutants, we report that directed repetitive gating of the PTP triggers a delayed Cyt.c efflux, which is not associated with mitochondrial swelling. Instead, subcellular imaging shows that PTP opening signals the redistribution of the cytosolic protein Bax to the mitochondria, where it secondarily forms clusters that appear to be a prerequisite for Cyt.c release. Fluorescence resonance energy transfer imaging further reveals that Bax clustering coincides with the formation of Bax multimers. We conclude that the PTP is not itself a component of the Cyt.c release machinery, but that it acts indirectly by signaling Bax translocation and multimerization.
De Giorgi
FrancesaA
F
European Institute of Chemistry and Biology, and INSERM E.9929, Victor Segalen-Bordeaux 2 University, 33076 Bordeaux cedex, France.
Lartigue
Lydia
L
Bauer
Manuel K A
MK
Schubert
Alexis
A
Grimm
Stefan
S
Hanson
George T
GT
Remington
S James
SJ
Youle
Richard J
RJ
Ichas
François
F
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry; D007425:Intracellular Membranes / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D008954:Models, Biological; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D012235:Rhodamines / Q000737:chemistry; D015398:Signal Transduction; D051028:bcl-2-Associated X Protein
D003574:Cytochrome c Group; D005456:Fluorescent Dyes; D007473:Ion Channels; D046911:Macromolecular Substances; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012235:Rhodamines; D051028:bcl-2-Associated X Protein; C401833:tetramethylrhodamine methyl ester