DNA FRAGMENTATION INDUCED BY A CYTOPLASMIC EXTRACT FROM IRRADIATED-CELLS

Apoptosis is a mode of cell death characterized by distinct morphologi cal features and DNA fragmentation. The program that leads to apoptosi s has been considered to be predominantly extranuclear, and a signal t ransduction pathway to the nucleus exists during apoptosis, while char acteristic events occur in the nucleus. As for radiation-induced apopt osis, 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 activ ated in this extract. Normal nuclei of HeLa S3 cells were added to a c ytoplasmic extract made from HL60 cells which had been irradiated with 30 Gy of Cs-137 gamma rays and were incubated. Agarose gel electropho resis of the added nuclei showed a characteristic DNA laddering patter n. This reaction was blocked by a caspase-3 inhibitor but not by an IC E inhibitor. These observations suggest that a signal transduction pat hway from an unknown target of gamma radiation may exist upstream of c aspase-3 during radiation-induced apoptosis, (C) 1998 by Radiation Res earch Society.