Regulation of FOXO3a/β-catenin/GSK-3β signaling by 3,3′-diindolylmethane contributes to inhibition of cell proliferation and induction of apoptosis in prostate cancer cells

Abstract

Previous studies from our laboratory have shown anti-proliferative and pro-apoptotic effects of 3,3′-diindolylmethane (DIM) through regulation of Akt and androgen receptor (AR) in prostate cancer cells. However, the mechanism by which DIM regulates Akt and AR signaling pathways has not been fully investigated. It has been known that FOXO3a and glycogen synthase kinase-3β(GSK-3β), two targets of activated Akt, interact with β-catenin, regulating cell proliferation and apoptotic cell death. More importantly, FOXO3a, GSK-3β, and β-catenin are all AR coregulators and regulate the activity of AR, mediating the development and progression of prostate cancers. Here, we investigated the molecular effects of B-DIM, a formulated DIM with higher bioavailability, on Akt/FOXO3a/GSK-3β/β- catenin/AR signaling in hormone-sensitive LNCaP and hormoneinsensitive C4-2B prostate cancer cells. We found that B-DIM significantly inhibited the phosphorylation of Akt and FOXO3a and increased the phosphorylation of β-catenin, leading to the inhibition of cell growth and induction of apoptosis. We also found that B-DIM significantly inhibited β-catenin nuclear translocation. By electrophoretic mobility shift and chromatin immunoprecipitation assays, we found that B-DIM inhibited FOXO3a binding to the promoter of AR and promoted FOXO3a binding to the p27KIP1 promoter, resulting in the alteration of AR and p27KIP1 expression, the inhibition of cell proliferation, and the induction of apoptosis in both androgen-sensitive and -insensitive prostate cancer cells. These results suggest that B-DIM-induced cell growth inhibition and apoptosis induction are partly mediated through the regulation of Akt/FOXO3a/GSK-3β/β-catenin/AR signaling. Therefore, B-DIM could be a promising non-toxic agent for possible treatment of hormone-sensitive but most importantly hormone-refractory prostate cancers. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.