Translocation of Bax to mitochondria induces apoptotic cell death in Indole-3-carbinol (I3C) treated breast cancer cells

Epidemiological studies have suggested that the consumption of fruits and v egetables that provide several classes of compounds, including Indole3-carb inol (I3C), may have chemopreventive activity against breast cancer. Severa l in vitro and in vivo animal studies also provide convincing evidence for the anti-tumor activity of I3C, however, the molecular mechanism(s) by whic h I3C exerts its biological effects on breast cancer cells has not been ful ly elucidated. In this study, we investigated the effects of I3C in Her-2/n eu over-expressing MDA-MB-435 breast cancer cells and compared these result s with parental cells transfected with control vector, We focused our inves tigation in elucidating the molecular mechanism(s) by which I3C induces apo ptosis in breast cancer cells. Our data show that I3C inhibits breast cance r cell growth in a dose dependent manner in Her-2/neu overexpressing and in normal Her-2/neu expressing cells. Induction of apoptosis was also observe d in these cell lines when treated with I3C, as measured by poly (ADP-ribos e) polymerase (PARP) and caspase-3 activation. In addition, we found that I 3C up-regulates Bas, downregulates Bcl-2 and, thereby, increased the ratio of Bar to Bcl-2 favoring apoptosis, These results suggest that the alterati on in the expression of these genes may play an important role in mediating the biological effects of I3C. Moreover, we also show the cellular localiz ation of Bar by confocal microscopy, which showed diffuse distribution of B ar throughout the cytoplasmic compartment in breast cancer cells in control culture. However, in 13C treated cells, Bar showed a punctate pattern of d istribution that was localized in the mitochondria, From these results, we conclude that the over-expression and translocation of Bar to mitochondria causes mitochondrial depolarization and activation of caspases, which may b e one of the mechanism(s) by which I3C induces apoptotic processes in I3C t reated breast cancer cells. Overall, our present data provide a novel molec ular mechanism(s) by which 13C elicits its biological effects on both Her-2 /neu over-expressing and with normal Her-2/neu expressing breast cancer cel ls, suggesting that 13C could be an effective agent in inducing apoptosis i n breast cancer cells.