Downregulation of Cdk4 results in impaired phosphorylation of BAD (ser136) and upregulation of protein phosphatase type 2A (PP2A). Cells stably expressing pLKO.1 or shCDK4 were irradiated at 2 Gy. Protein lysates were then prepared at different times (0, 0.5, 1 & 2 hours) post-irradiation and were immunoblotted with anti-Bad(ser136), anti-Mcl-1(ser159/thr163) and anti-Bcl-2(ser70) antibodies, and their counterparts detecting total levels of those proteins. (B) The levels of PP2A and PP2B were further determined by immunoblotting with anti-PP2A and anti-PP2B antibodies. Cells transfected with pLKO.1 were used as control. The β-actin controls for (B) is the same as for (A).