PROTEASE INHIBITORS BLOCK APOPTOSIS AT INTERMEDIATE STAGES - A COMPARED ANALYSIS OF DNA FRAGMENTATION AND APOPTOTIC NUCLEAR MORPHOLOGY

The possible correlation between DNA digestion and changes in nuclear morphology in apoptosis was studied by blocking the apoptotic process at intermediate stages, The apoptogenic action of three drugs: etoposi de, puromycin, tributyltin, was contrasted with protease inhibitors wi th different specificity on U937 cells, The inhibitors interfered with the development of the apoptotic features without shifting cell death to necrosis: treated cells showed abnormal morphologies, which could be recognized as intermediate stages of apoptosis; accordingly, DNA an alysis showed an inhibitor-dependent block of the apoptotic DNA digest ion, The comparison between size of DNA fragments and nuclear morpholo gy suggested the following correlations: loss of normal nuclear shape with the appearence of a greater than or equal to 2 Mb DNA band; ongoi ng chromatin condensation with the progressive DNA digestion up to 50 kb; nuclear fragmentation with DNA laddering, Protease inhibitors in e toposide-treated cells did not allow the formation of 700-300 kb fragm ents, suggesting that they possibly derive from a cell-mediated effect .