MULTIPLE FORMS OF ENDONUCLEASE ACTIVITY LINKED WITH RADIATION-INDUCEDAPOPTOSIS IN C4-1 CERVICAL-CARCINOMA CELLS

Irradiation of C4-1 cervical carcinoma cells induced apoptosis, as det ermined by their morphology and the presence of oligonucleosomal DNA f ragmentation with the formation of 5'-P and 3'-OH termini. Extracts of nuclear proteins from both control and irradiated cells possessed sim ilar metallodependent endonucleolytic activity which cleaved target pl asmid DNA with the same specificity as that found in apoptotic cells. Fractionation of the nuclear extracts revealed that the predominant en donuclease activity of unirradiated cells was a protein of approximate ly 40 kDa. After irradiation, the predominant activity was found to be associated with a 70 kDa fraction, with a reduction in the 40 kDa for m. The activity of each endonuclease was found to be Ca2+ and Mg2+ dep endent. It is proposed that the changes in molecular weight observed f or these enzymes may be linked to the final step in apoptosis executio n, irreversible chromatin fragmentation, and thus offer a potentially novel target for manipulating the effector pathway of apoptosis in the se cells.