DNA fragmentation induced by a cytoplasmic extract from irradiated cells

Radiat Res. 1998 Sep;150(3):269-74.


Apoptosis is a mode of cell death characterized by distinct morphological features and DNA fragmentation. The program that leads to apoptosis has been considered to be predominantly extranuclear, and a signal transduction pathway to the nucleus exists during apoptosis, while characteristic events occur in the nucleus. As for radiation-induced apoptosis, the signal transduction pathway remains unclear, especially the sites where the primary effect of radiation occurs. In this study, we demonstrate that a cytoplasmic extract prepared from irradiated cells has the ability to cause DNA fragmentation and that caspase-3 is activated in this extract. Normal nuclei of HeLa S3 cells were added to a cytoplasmic extract made from HL60 cells which had been irradiated with 30 Gy of 137Cs gamma rays and were incubated. Agarose gel electrophoresis of the added nuclei showed a characteristic DNA laddering pattern. This reaction was blocked by a caspase-3 inhibitor but not by an ICE inhibitor. These observations suggest that a signal transduction pathway from an unknown target of gamma radiation may exist upstream of caspase-3 during radiation-induced apoptosis.

MeSH terms

  • Caspase 3
  • Caspases*
  • Cell Extracts
  • Cell-Free System
  • Cesium Radioisotopes
  • Cysteine Endopeptidases / drug effects
  • Cysteine Endopeptidases / metabolism*
  • DNA Fragmentation*
  • Enzyme Activation / drug effects
  • Enzyme Activation / radiation effects
  • Enzyme Inhibitors / pharmacology
  • Gamma Rays
  • HL-60 Cells / radiation effects
  • HeLa Cells / radiation effects
  • Humans
  • Oligopeptides / pharmacology
  • Signal Transduction* / radiation effects


  • Cell Extracts
  • Cesium Radioisotopes
  • Enzyme Inhibitors
  • Oligopeptides
  • acetyl-aspartyl-glutamyl-valyl-aspartal
  • L 709049
  • CASP3 protein, human
  • Caspase 3
  • Caspases
  • Cysteine Endopeptidases