Interphase and M-phase oral KB carcinoma cells are targetted in staurosporine-induced apoptosis

The effect of staurosporine, an antimicrobial agent and inhibitor of protein kinase C (PKC) on programmed cell death/apoptosis (PCD) was investigated in the human oral cavity epidermoid carcinoma KB cell line. Staurosporine-treated oral KB carcinoma cells exhibited morphological features characteristic of apoptosis such as (a) cell shrinkage and increased nuclear fluorescence (quantitated by image analysis with laser scanning confocal microscopy), (b) nuclear condensation and fragmentation observed under fluorescence microscopy with propidium-iodide-DNA staining and (c) chromatin condensation seen under transmission electron microscopy. Specific terminal deoxynucleotidyl transferase (TdT)-mediated labeling of 3′OH ends of DNA breaks in staurosporine-treated cells confirmed DNA fragmentation. In addition, we show the concomitant existence of M-phase PCD with interphase PCD in staurosporine-treated KB cells. It would appear that staurosporine induces apoptosis regardless of the cell cycle phase and that mitosis and apoptosis are not necessarily mutually exclusive events.