Figure 2. Endogenous p53β is accumulated upon inhibition of the proteasome by MG132 and Mdm2 can promote degradation of p53β. (A) SK-N-AS cells were transfected with either non-specific siRNA (siNS), siRNAs against p53β (siβ), exon 7 of p53 (siE7) or mock transfected as indicated. Actin was used as a loading control. (B) SK-N-AS cells were transfected with increasing amount of expression vector encoding wild-type Mdm2 or mutant Mdm2 C464A, devoid of ubiquitin-ligase activity. Actin was used as a loading control.