Reactive oxygen species up-regulate p53 and Puma; a possible mechanism for apoptosis during combined treatment with TRAIL and wogonin

Background and purpose: Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptotic death in a variety of cancer cells without marked toxicity to most normal cells. We previously reported that wogonin, a potent anticancer agent from a Chinese herb, up-regulates p53 in prostate cancer cells. In this study, the effects of combinations of TRAIL and wogonin on a human prostate cancer cell line LNCaP, resistant to TRAIL, was evaluated for evidence of synergy in triggering apoptosis. Experimental approach: Western blot assay and the 'comet' assay were used to study the underlying mechanisms of cell death and search for any mechanisms of enhancement of TRAIL-induced apoptosis in the presence of wogonin. Key results: During combined treatment with wogonin and TRAIL, cytotoxicity, poly(ADP-ribose) polymerase cleavage and caspase activation were associated with up-regulation of p53 through DNA damage and reactive oxygen species (ROS) generation. N-acetylcysteine (NAC), an antioxidant, inhibited ROS generation and synergistic interaction between TRAIL and wogonin. Experimental results in human colon cancer HCT116 cells demonstrated that p53-dependent Puma up-regulation played an important role; deficiency in either p53 or Puma prevented wogonin-enhanced TRAIL-induced apoptosis. Conclusions and implications: The present studies suggest that wogonin enhances TRAIL-induced cytotoxicity through up-regulation of p53 and Puma, mediated by ROS.