Fig. 4. Stabilization of p53 by Mdm2 mutants in stably expressing cells. A, Western blot analysis showing expression levels of Mdm2 mutant protein {Delta}222–437 and 1–440, respectively, in stably transfected clones of U2OS cells. B, Western blot analysis showing endogenous p53 protein levels in the same clones of U2OS cells.