The effect of proteasome inhibition by MG-132 on cell cycle progression and radiation-induced cell cycle arrest and apoptosis. Cell cycle distribution of PC-3 prostate cancer cells assessed by flow cytometry after staining with propidium iodide. Cells were pre-incubated with MG-132 (50 μM) for 3 hours, irradiated, and incubated for additional 24 hours in the presence of MG-132. MG-132 prevented cell cycle progression and, consequently, dose-dependent radiation-induced G2/M-arrest. Additionally, MG-132 treatment increased the number of cells in late S-phase.