3,3′‐Diindolylmethane (DIM) induces apoptosis through p53‐independent pathway in human colon cancer cells.

Abstract

DIM is a major in vivo derivative of the putative anticancer agent indole-3-carbinol, which is present in cruciferous vegetables and has been reported to have anti-carcinogenic properties. Previously we observed that DIM dose-dependently decreased the viable cell numbers and induced apoptosis in HT-29 human colon cancer cells. The present study examined the mechanisms by which DIM induces apoptosis in both HCT116 (wild-type p53) and HT-29 (mutant p53) human colon cancer cells. Cells were cultured with various concentrations of (0 - 30 μmol/L) DIM. DIM substantially decreased the viable cell numbers and induced apoptosis of HCT116 cells in a dose-dependent manner. Western blot analysis of total cell lysates revealed that DIM induced cleavage of caspase-8, -9, -7, and -3, and poly (ADP-ribose) polymerase in both HCT116 and HT-29 cells. In addition, DIM increased the translocation of cytochrome c and Smac/Diablo from the mitochondria to the cytosol in both HCT116 and HT-29 cells. In HCT116 cells, DIM increased truncated Bid levels but did not affect the protein levels of p53, Bcl-2, or Bax. In HT-29 cells, DIM decreased Bcl-2 and increased truncated Bid levels. We have demonstrated that the induction of apoptosis by DIM in colon cancer cells may be mediated through changes in mitochondrial events which are associated with the release of cytochrome c and Smac/Diablo and the activation the caspase pathway through p53-independent pathway.