Inhibition of IGF-1 Signaling by Genistein: Modulation of E-Cadherin Expression and Downregulation of β-Catenin Signaling in Hormone Refractory PC-3 Prostate Cancer Cells

Elevated levels of insulin-like growth factor-1 (IGF-1) are associated with an increased risk of several different cancers, including prostate cancer. Inhibition of IGF-1 and the downstream signaling pathways mediated by the activation of the IGF-1 receptor (IGF-1R) may be involved in inhibiting prostate carcinogenesis. We investigated whether genistein downregulated the IGF-1/IGF-1R signaling pathway and inhibited cell growth in hormone refractory PC-3 prostate cancer cells. Genistein treatment caused a significant inhibition of IGF-1-stimulated cell growth. Flow cytometry analysis revealed that genistein significantly decreased the number of IGF-1-stimulated cells in the G0/G1 phase of the cell cycle. In IGF-1-treated cells, genistein effectively inhibited the phosphorylation of IGF-1R and the phosphorylation of its downstream targets, such as Src, Akt, and glycogen synthase kinase-3 beta (GSk-3 beta). IGF-1 treatment decreased the levels of E-cadherin but increased the levels of beta-catenin and cyclin D1. However, genistein treatment greatly attenuated IGF-1-induced beta-catenin signaling that correlated with increasing the levels of E-cadherin and decreasing cyclin D1 levels in PC-3 cells. In addition, genistein inhibited T-cell factor/lymphoid enhancer factor (TCF/LEF)-dependent transcriptional activity. These results showed that genistein effectively Inhibited cell growth in IGF-1-stimulated PC-3 cells, possibly by inhibiting downstream of IGF-1R activation.