Abstract
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.
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Acknowledgements
We thank G. Salvesen for helpful discussions and R. Cornell for manuscript preparation. This work was supported by grants from the NIH (GM 60554-01; N527177), the US Department of Defense BCRP (DAMD 17-96-1-6210), DOE (DE-AC03-7GSF-0098) and the American Heart Association (9920 070Y).
Correspondence and requests for materials should be addressed to J.C.R.
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Matsuyama, S., Llopis, J., Deveraux, Q. et al. Changes in intramitochondrial and cytosolic pH: early events that modulate caspase activation during apoptosis. Nat Cell Biol 2, 318–325 (2000). https://doi.org/10.1038/35014006
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DOI: https://doi.org/10.1038/35014006
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