Silencing PP2A does not change cleaved PARP level in Cdk4 silencing cells. A cocktail of siRNAs targeting the PP2A catalytic unit was transiently transfected into cells stably expressing shCDK4 and cells were irradiated at 0, 2 and 4 Gy after 48 hours transfection. Protein lysates were then prepared at 48 hours post-irradiation and were immunoblotted with PP2A, cleaved PARP. β-actin was used as a loading control. Protein levels were normalized based on β-actin, and are indicated as fold-induction relative to scrambled siRNA controls.