Stable expression of wild-type and mutant MDM2. (A) U2OS cells were transduced with lentivirus carrying empty vector (EV), wild-type MDM2 (Wt), or the indicated MDM2 mutant. After selection, the cells were lysed and subjected to western blot analysis of the indicated proteins. (B) U2OS cells expressing empty vector (EV), wild-type MDM2 (Wt), or MDM2 mutants that exhibited defects in the degradation of p53 were subjected to a colony formation assay to analyze cell growth.