Figure 4

4HPR regulates the β-catenin soluble pool, its transcriptionally active phosphorylated (Ser522) form, GSK3β phosphorylation, cyclin D1 and survivin expression. A). Dose-dependent decrease of β-catenin and phospho-β-catenin (Ser522), and GSK3β- phosphorylation after 4 h of treatment in DU145 cells (left) is associated with reduced levels of the proliferation/survival related genes cyclin D1 and survivin (middle). Loss of β-catenin stability is independent of ROS production as demonstrated by incubating the cells in the presence of the ROS scavenger NAC (right). B). Similar to 4HPR, 4 hours incubation with the specific PI3K/AKT inhibitors wortmannin (Wort, 200 nM) and LY294002 (LY, 10 μM) activate GSK3β and reduce the soluble pool of β-catenin and cyclin D1 levels. C). IGF-I (4 hours at 100 ng/ml), through AKT activation, causes inhibition of its down-stream effector GSK3β, thus leading to β-catenin stabilization, β-catenin (ser522) phosphorylation and cyclin D1 accumulation. 4HPR (5 μM) co-exposure can still antagonize IGF I-induced AKT activity and reduce β-catenin and cyclin D1 levels. The experiments were repeated thrice and similar results were obtained with PC3 cells.