Apoptotic pathways depend on the target enzymatic activity and not on the triggering agent

Molt-4 human leukemia cells were triggered to apoptosis by various agents w ith different mechanisms of action. Staurosporine, a protein kinase C (PKC) inhibitor; camptothecin, a topoisomerase I blocking drug; and tiazofurin, an inhibitor of inosine 5'-phosphate dehydrogenase (IMPDH), were used. Ultr astructural analysis showed morphologic changes characteristic of apoptosis that were very similar for all three agents. Nevertheless, DNA oligonucleo somic fragmentation was not detectable by agarose gel electrophoresis. Howe ver, a genomic DNA cleavage appeared after pulse-field gel electrophoresis (PFGE) in cells treated with these agents for 24 h. Furthermore, in situ ni ck translation (NT) showed a finely spotted nuclear labelling in staurospor ine-treated cells and a compact fluorescence after camptothecin incubation. In tiazofurin-treated cells an intermediate pattern was found. Therefore, apoptotic agents with different mechanisms of action induced the formation of large genomic DNA fragments and very similar ultrastructural changes. Th erefore, both phenomena and the closely related apoptosis progression depen d on target cell machinery and not on the triggering agent.