Mitochondria are not required for death receptor-mediated cytosolic acidification during apoptosis.
In addition to cell shrinkage, membrane blebbing, DNA fragmentation and phosphatidylserine exposure, intracellular acidification represents a hallmark of apoptosis. Although the mechanisms underlying cytosolic acidification during apoptosis remained largely elusive, a pivotal role of mitochondria has been proposed. In order to investigate the involvement of mitochondria in cytosolic acidification during apoptosis, we blocked the mitochondrial death pathway by overexpression of Bcl-2 and subsequently activated the death receptor pathway by anti-CD95 or TRAIL or the mitochondrial pathway by staurosporine. We show that Bcl-2 but not caspase inhibition prevented staurosporine-induced intracellular acidification. Thus, intracellular acidification in mitochondrial apoptosis is a Bcl-2-inhibitable, but caspase-independent process. In contrast, Bcl-2 only slightly delayed, but did not prevent intracellular acidification upon triggering of death receptors. The Na(+)/H(+) exchanger NHE1 was partially degraded during apoptosis but only to a small extent and and at a delayed time point when cytosolic acidification was almost completed. We therefore conclude that cytosolic acidification is mitochondrially controlled in response to mitochondria-dependent death stimuli, but requires additional caspase-dependent mechanisms during death receptor-mediated apoptosis.
Waibel
Michaela
M
Department of Internal Medicine I, Eberhard-Karls-University, University of Tübingen, Tübingen, Germany.
Kramer
Stefan
S
Lauber
Kirsten
K
Lupescu
Adrian
A
Manns
Joachim
J
Schulze-Osthoff
Klaus
K
Lang
Florian
F
Wesselborg
Sebastian
S
D000590:Amino Acid Chloromethyl Ketones / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D027682:Cation Transport Proteins / Q000378:metabolism; D024161:Collagen Type XI / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019169:Jurkat Cells; D008928:Mitochondria / Q000378:metabolism*; D053218:Receptors, Death Domain / Q000378:metabolism*; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; C499319:COL11A2 protein, human; D027682:Cation Transport Proteins; D024161:Collagen Type XI; D015853:Cysteine Proteinase Inhibitors; D053218:Receptors, Death Domain; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D045304:Cytochromes c; D020169:Caspases