Temporal relationship between cytochrome c release and mitochondrial swelling during UV-induced apoptosis in living HeLa cells

J Cell Sci. 2001 Aug;114(Pt 15):2855-62.


During apoptosis, cytochrome c is released from mitochondria to the cytosol to activate a caspase cascade, which commits the cell to the death process. It has been proposed that the release of cytochrome c is caused by a swelling of the mitochondrial matrix triggered by the apoptotic stimuli. To test this theory, we measured directly the dynamic re-distribution of green fluorescence protein (GFP)-tagged cytochrome c and morphological change of mitochondria within living HeLa cells during u.v.-induced apoptosis. We observed that mitochondria did not swell when cytochrome c was released from mitochondria to cytosol during apoptosis. Instead, mitochondria swelled to spherical shapes within 10 minutes of cytochrome c release. This finding strongly suggests that cytochrome c release in apoptosis was not caused by mitochondrial swelling. This conclusion was further supported in two separated experiments using an immunostaining method and carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) treatment. In addition, we found evidence that cytochrome c was also released before mitochondrial swelling in apoptosis induced by other cell death-inducing treatments, including tumor necrosis factor (TNF) and actinomycin D.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Chloromethyl Ketones / pharmacology
  • Apoptosis / physiology*
  • Apoptosis / radiation effects
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone / pharmacology
  • Cysteine Proteinase Inhibitors / pharmacology
  • Cytochrome c Group / metabolism*
  • Fluorescent Antibody Technique
  • Green Fluorescent Proteins
  • HeLa Cells
  • Humans
  • Indicators and Reagents / metabolism
  • Luminescent Proteins / genetics
  • Microscopy, Fluorescence / methods
  • Mitochondria / metabolism
  • Mitochondrial Swelling / drug effects
  • Mitochondrial Swelling / physiology*
  • Ultraviolet Rays
  • Uncoupling Agents / pharmacology


  • Amino Acid Chloromethyl Ketones
  • Cysteine Proteinase Inhibitors
  • Cytochrome c Group
  • Indicators and Reagents
  • Luminescent Proteins
  • Uncoupling Agents
  • benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone
  • Green Fluorescent Proteins
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone