p53 and MAGI-3 protein levels in cells expressing HPV-18 E6 and HPV-33 E6 following proteasome inhibition. Cells were transfected with plasmids expressing p53, MAGI-3, and E6-GFP fusion proteins in the presence and absence of proteasome inhibition with MG132 as indicated. Upper panel: Western blot analysis of p53 and MAGI-3 (anti-V5 tag). Lower panel: Western blot analysis of E6-GFP. Note that addition of MG132 partially restored p53 levels but not MAGI-3 levels.