Changes in intramitochondrial and cytosolic pH: early events that modulate caspase activation during apoptosis.
Mitochondria trigger apoptosis by releasing caspase activators, including cytochrome c (cytC). Here we show, using a pH-sensitive green fluorescent protein (GFP), that mitochondria-dependent apoptotic stimuli (such as Bax, staurosporine and ultraviolet irradiation) induce rapid, Bcl-2-inhibitable mitochondrial alkalinization and cytosol acidification, followed by cytC release, caspase activation and mitochondrial swelling and depolarization. These events are not induced by mitochondria-independent apoptotic stimuli, such as Fas. Activation of cytosolic caspases by cytC in vitro is minimal at neutral pH, but maximal at acidic pH, indicating that mitochondria-induced acidification of the cytosol may be important for caspase activation; this finding is supported by results obtained from cells using protonophores. Cytosol acidification and cytC release are suppressed by oligomycin, a FoF1-ATPase/H +-pump inhibitor, but not by caspase inhibitors. Ectopic expression of Bax in wild-type, but not FoF1/H+-pump-deficient, yeast cells similarly results in mitochondrial matrix alkalinization, cytosol acidification and cell death. These findings indicate that mitochondria-mediated alteration of intracellular pH may be an early event that regulates caspase activation in the mitochondrial pathway for apoptosis.
Matsuyama
S
S
Programme on Apoptosis and Cell Death Regulation, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA.
Llopis
J
J
Deveraux
Q L
QL
Tsien
R Y
RY
Reed
J C
JC
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D003838:Deoxyadenine Nucleotides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D008933:Mitochondrial Swelling / Q000187:drug effects / Q000528:radiation effects; D009154:Mutation; D009840:Oligomycins / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D019311:Staurosporine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000502:physiology
C494826:BAX protein, human; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D003838:Deoxyadenine Nucleotides; D008164:Luminescent Proteins; D009840:Oligomycins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D049452:Green Fluorescent Proteins; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D020169:Caspases; D006180:Proton-Translocating ATPases; D019311:Staurosporine; C026600:2'-deoxyadenosine triphosphate