DNA damaging drugs-induced down-regulation of Bcl-2 is essential for induction of apoptosis in high-risk HPV-positive HEp-2 and KB cells

DNA damaging chemotherapeutic agents like carboplatin (Carb) and 5-fluorouracil (5-FU), whose effects are mediated through diverse intracellular targets, induce apoptosis in various cancer cells including human papillomavirus (HPV) positive HEp-2 and KB cells. The present work reports the involvement of Bcl-2 in response to the exposure of HEp-2 and KB cells to Carb or 5-FU. We demonstrate that both these drugs are potent inducers of apoptosis. Apoptosis was preceded by decrease in Bcl-2 protein level accompanied by caspase-9 activation and poly(ADP-ribose) polymerase (PARP) cleavage without altering Bax expression. Further analysis revealed down-regulation of Bcl-2 mRNA as well as protein in drugs treated cells. Ectopic expression of Bcl-2 protected cells against drugs mediated DNA damage-induced apoptosis. Overall, data indicates that genotoxic stress leads to down-regulation of Bcl-2 in HEp-2 and KB cells, which plays a decisive role in the outcome of stress in these cells.