Etoposide induces a mixed type of programmed cell death and overcomes the resistance conferred by Bcl-2 in Hep3B hepatoma cells

The Bcl-2 protein is known to exert not only anti-apoptotic but also anti-autophagic activities. Numerous studies have demonstrated that etoposide, which is one of the most widely used cancer chemotherapy agents, induces apoptotic cell death. However, the exact molecular mechanism leading to cell death by etoposide remains to be resolved. This study aimed to dissect the mode of cell death induced by etoposide in Hep3B hepatoma cells. Furthermore, this study was conducted to examine whether etoposide overcomes the resistance conferred by Bcl-2 in Hep3B hepatoma cells. We observed that Hep3B cells treated with etoposide show not only apoptotic but autophagic phenotypes. Autophagy inhibition by 3-methyladenine (3MA) and caspase inhibition by zVAD-fmk effectively decreased autophagic and apoptotic phenotypes, respectively. However, either zVAD-fmk or 3MA only partially prevented cell death. These data indicate that etoposide concomitantly induces autophagic cell death and apoptosis in Hep3B cells. Importantly, etoposide can effectively induce cell death in Bcl-2-overexpressing Hep3B cells. Conversely, staurosporine, which exclusively induces apoptosis in Hep3B cells, did not efficiently induce cell death in Bcl-2-overexpressing Hep3B cells. Staurosporine-treated Hep3B cells also showed an autophagic phenotype. While autophagy is cell death-inducing in Hep3B cells treated with etoposide, it is cytoprotective in Hep3B cells treated with staurosporine. To this end, we observed that etoposide-induced mixed type of programmed cell death is associated with the dissociation of Bcl-2 from Beclin-1. Taken together, etoposide induces a mixed type of programmed cell death and overcomes the resistance conferred by Bcl-2 in Hep3B hepatoma cells.