p53-Mediated Oxidative Stress Enhances Indirubin-3'-Monoxime-Induced Apoptosis in HCT116 Colon Cancer Cells by Upregulating Death Receptor 5 and TNF-Related Apoptosis-Inducing Ligand Expression.

Indirubin-3'-monoxime (I3M) exhibits anti-proliferative activity in various cancer cells; however, its anti-cancer mechanism remains incompletely elucidated. This study revealed that I3M promotes the expression of death receptor 5 (DR5) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in HCT116 p53 cells, resulting in caspase-mediated apoptosis. However, this study demonstrated that HCT116 p53 cells were insensitive to I3M-mediated apoptosis, indicating that I3M-induced apoptosis depends on the p53 status of HCT116 cells. Additionally, in HCT116 p53 cells, I3M significantly increased Ras expression, while in HCT116 p53 cells, it reduced Ras expression. Furthermore, I3M remarkably increased the production of reactive oxygen species (ROS), which were reduced in transient knockdown, indicating that I3M-mediated apoptosis was promoted by p53-mediated ROS production. Our results also showed that I3M enhanced transcription factor C/EBP homologous protein (CHOP) expression, resulted in endoplasmic reticulum (ER) stress-mediated DR5 expression, which was upregulated by ROS production in HCT116 p53 cells. Moreover, co-treatment with I3M and TRAIL enhanced DR5 expression, thereby triggering TRAIL-induced apoptosis of HCT116 p53 cells, which was interfered by a DR5-specific blocking chimeric antibody. In summary, I3M potently enhances TRAIL-induced apoptosis by upregulating DR5 expression via p53-mediated ROS production in HCT116 p53 cells. However, HCT116 p53 cells were less sensitive to I3M-mediated apoptosis, suggesting that I3M could be a promising anti-cancer candidate against TRAIL-resistant p53 cancer cells. Additionally, this study also revealed that I3M sensitizes colorectal cancer cells such as HT29 and SW480 to TRAIL-mediated apoptosis.