1,1-Bis(3′-indolyl)-1-(p-methoxyphenyl)methane activates Nur77-independent proapoptotic responses in colon cancer cells

1,1-Bis(3′-indolyl)-1-(p-methoxyphenyl)methane (DIM-C-pPhOCH ₃) is a methylene-substituted diindolylmethane (C-DIM) analog that activates the orphan receptor nerve growth factor-induced-Bα (NGFI-Bα, Nur77). RNA interference studies with small inhibitory RNA for Nur77 demonstrate that DIM-C-pPhOCH₃ induces Nur77-dependent and -independent apoptosis, and this study has focused on delineating the Nur77-independent proapoptotic pathways induced by the C-DIM analog. DIM-C-pPhOCH₃ induced caspase-dependent apoptosis in RKO colon cancer cells through decreased mitochondrial membrane potential which is accompanied by increased mitochondrial bax/bcl-2 ratios and release of cytochrome c into the cytosol. DIM-C-pPhOCH₃ also induced phosphatidylinositol-3-kinase- dependent activation of early growth response gene-1 which, in turn, induced expression of the proapoptotic nonsteroidal anti-inflammatory drug-activated gene-1 (NAG1) in RKO and SW480 colon cancer cells. Moreover, DIM-C-pPhOCH ₃ also induced NAG-1 expression in colon tumors in athymic nude mice bearing RKO cells as xenografts. DIM-C-pPhOCH₃ also activated the extrinsic apoptosis pathway through increased phosphorylation of c-jun N-terminal kinase which, in turn, activated C/EBP homologous transcription factor (CHOP) and death receptor 5 (DR5). Thus, the effectiveness of DIM-C-pPhOCH₃ as a tumor growth inhibitor is through activation of Nur77-dependent and -independent pathways.