siRNA knockdown of c-jun and c-fos blocked the G-1 induced inhibition of cell growth, upregulation of p21, and downregulation of cyclin B but showed no effect on G-1–induced phosphorylation of Erk1/2. (A) siRNA specifically reduced c-jun or c-fos expression as determined by real-time RT-PCR analysis. (B) PC-3 cells were treated with 1 μM G-1 for 4 days in the presence of c-jun siRNA, c-fos siRNA, or scramble siRNA as a control. Two reagent controls with ethanol and with G-1 without any siRNA were included. The growth of the cells relative to that of the ethanol control at day 1 was determined. (C) The G-1–treated cells with c-jun siRNA, c-fos siRNA, or the scramble siRNA control were subjected to Western blot analysis to determine levels of phosphorylated Erk1/2, p21, cyclin B1, and β-actin protein. Two reagent controls (ethanol or 1 μM G-1) without any siRNA were included.