Caspase-dependent and independent cell death in rat hepatoma 5123tc cells

The objective of this study was to establish whether apoptosis in 5123tc rat hepatoma cells required the caspase-3 dependent pathway. Apoptosis was induced by either growth factor deprivation or treatment with a topoisomerase II inhibitor, VM26, in the absence or presence of caspase inhibitors (DEVD-fmk, z-VAD-fmk and BAF). The results indicated that, although these inhibitors at 10 mu M concentration completely blocked caspase-3 activity, they had no effect on either the rate of cell death or on any other apoptotic features, e.g., chromatin condensation, DNA fragmentation, protein cleavage, suggesting that caspase-3 was not required to mediate nuclear destruction in these hepatoma cells. At higher concentrations, up to 100 mu M, z-VAD-fmk and BAF, but not DEVD-fmk, did block apoptosis, however, they also caused cell swelling and membrane permeabilization, which are the hallmarks of necrotic cell death. Clearly, high concentrations of these inhibitors must have interfered non-specifically with other metabolic pathways, e.g., z-VAD-fmk at a high concentration blocked protein phosphorylation, and caused cell death by a different mechanism.