Because
tumor necrosis factor (
TNF)-related apoptosis-inducing ligand (TRAIL) selectively kills
tumor cells, it is being tested in
cancer patients. Unfortunately, patients develop resistance to the
cytokine, therefore, agents that can sensitize cells to TRAIL are urgently needed. In this study, we investigated whether dibenzylideneacetone (DBA) can sensitize
cancer cells to TRAIL and potentiates TRAIL-induced apoptosis. As indicated by accumulation of the membrane
phospholipid phosphatidylserine, DNA breaks, intracellular
esterase activity, and activation of
caspase-8, -9, and -3, we concluded that DBA potentiated TRAIL-induced apoptosis in
colon cancer cells. DBA also converted TRAIL resistant-cells to TRAIL-sensitive. When examined for the mechanism, we found that DBA decreased the expression of antiapoptotic
proteins and decoy receptor-2 and increased proapoptotic
proteins. DBA also induced both
death receptor (DR)-5 and DR4. Knockdown of DR5 and DR4 by
small interfering RNA (
SiRNA) reduced the sensitizing effect of DBA on TRAIL-induced apoptosis. In addition, DBA increased the expression of CHOP
proteins. Knockdown of CHOP by
siRNA decreased the induction of DBA-induced DR5 expression and apoptosis. Induction of receptors by DBA, however, was p53-independent, as deletion of p53 had no effect on receptor induction. We observed that DBA-induced induction of DR5 and DR4 was mediated through generation of
reactive oxygen species (ROS), as
N-acetylcysteine blocked the induction of
death receptors and suppression of cell survival
proteins by DBA. Overall, our results show that DBA potentiates TRAIL-induced apoptosis through downregulation of cell survival
proteins and upregulation of
death receptors via activation of ROS and CHOP mediated pathways.