Caspase-independent mitochondrial cell death results from loss of respiration, not cytotoxic protein release.
In apoptosis, mitochondrial outer membrane permeabilization (MOMP) triggers caspase-dependent death. However, cells undergo clonogenic death even if caspases are blocked. One proposed mechanism involved the release of cytotoxic proteins (e.g., AIF and endoG) from mitochondria. To initiate MOMP directly without side effects, we created a tamoxifen-switchable BimS fusion protein. Surprisingly, even after MOMP, caspase-inhibited cells replicated DNA and divided for approximately 48 h before undergoing proliferation arrest. AIF and endoG remained in mitochondria. However, cells gradually lost mitochondrial membrane potential and ATP content, and DNA synthesis slowed to a halt by 72 h. These defects resulted from a partial loss of respiratory function, occurring 4-8 h after MOMP, that was not merely due to dispersion of cytochrome c. In particular, Complex I activity was completely lost, and Complex IV activity was reduced by approximately 70%, whereas Complex II was unaffected. Later, cells exhibited a more profound loss of mitochondrial protein constituents. Thus, under caspase inhibition, MOMP-induced clonogenic death results from a progressive loss of mitochondrial function, rather than the release of cytotoxic proteins from mitochondria.
La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037.
Lydia
L
Lartigue
Yulia
Y
Kushnareva
Youngmo
Y
Seong
Helen
H
Lin
Benjamin
B
Faustin
Donald D
DD
Newmeyer
D000590:Amino Acid Chloromethyl Ketones / Q000378:metabolism; D000818:Animals; D051033:Apoptosis Inducing Factor / Q000378:metabolism*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D020169:Caspases / Q000378:metabolism*; D016923:Cell Death / Q000502:physiology*; D002460:Cell Line; D049109:Cell Proliferation; D019069:Cell Respiration / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism; D006019:Glycolysis / Q000502:physiology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000378:metabolism; D010101:Oxygen Consumption; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014475:Uncoupling Agents / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; D051033:Apoptosis Inducing Factor; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D015853:Cysteine Proteinase Inhibitors; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D014475:Uncoupling Agents; D051028:bcl-2-Associated X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D045304:Cytochromes c; D020169:Caspases; D005947:Glucose