CHIP interacts with p21 and promotes polyubiquitination and degradation in living cells. A, A549 cells stably expressing WT-CHIP were treated with 10 Gy, incubated for 24 h at which point MG132 was added for 4 h. Lysates were prepared and CHIP was immunoprecipitated and immunoblot analysis performed. B, Reciprocally, p21 was immunoprecipitated from lysate A and blotted for CHIP. C, A549 and D, H460 cells (sh-NT or sh-CHIP-2) were treated as A and ubiquitinated proteins were affinity purified using TUBE (see Methods and Materials) and immunoblotted for p21. 5% input shown in the bottom.