Bax induction activates apoptotic cascade via mitochondrial cytochrome c release and Bax overexpression enhances apoptosis induced by chemotherapeutic agents in DLD-1 colon cancer cells

Cancer cells express different levels of apoptosis-promoting Bax protein. The present study evaluated whether induction of Bax initiates apoptosis and whether Bax overexpression enhances apoptosis induced by several chemotherapeutic agents in DLD-1 colon cancer cells, which originally express a high level of endogenous Bax protein and a low level of Bcl-2 protein. To investigate these two points, parental DLD-1 cells were transfected with the Tet-On Bax induction system (pTef-On and pTRE-Bax plasmids), and stable transduced cells were obtained. Induction of Bax by the Tet-On system initiated cytochrome c release from mitochondria, caspase-3 activation, and apoptosis to some extent in DLD-1 cells. Apoptosis induced by a chemotherapeutic agent, 5-fluorouracil, mitomycin C, paclitaxel, doxorubicin, or cisplatin, was enhanced by Bax overexpression. These findings suggest that Bax-overexpression-based gene therapy combined with chemotherapy would be effective in the treatment of colon cancer.