Proteasome activator PA28 gamma regulates p53 by enhancing its MDM2-mediated degradation

EMBO J. 2008 Mar 19;27(6):852-64. doi: 10.1038/emboj.2008.25. Epub 2008 Feb 28.


Downregulation of p53 by MDM2-mediated proteasomal degradation makes cells resistant to apoptosis. The MDM2-p53 interaction is well characterized, but the mechanisms that regulate the interaction are not well understood. Here, we show that PA28gamma, a proteasome activator that inhibits apoptosis and promotes cell cycle progression through unknown mechanisms, exerts an effect as a cofactor in the MDM2-p53 interaction. The polymer form of PA28gamma interacts with both MDM2 and p53 proteins and facilitates their physical interaction. This promotes ubiquitination- and MDM2-dependent proteasomal degradation of p53, limiting its accumulation and resulting in inhibited apoptosis after DNA damage. Elimination of endogenous PA28gamma in human cancer cells abrogates MDM2-mediated p53 degradation, increases the activity of p53, and enhances apoptosis. These findings reveal the mechanism by which PA28gamma affects apoptosis and proliferation. Manipulation of the level of PA28gamma, an approach that would regulate the cellular content of p53, may improve the efficacy of current cancer therapies.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Autoantigens / genetics
  • Autoantigens / metabolism
  • Autoantigens / physiology*
  • BALB 3T3 Cells
  • COS Cells
  • Cell Line
  • Chlorocebus aethiops
  • Down-Regulation / physiology*
  • Enzyme Activation
  • HCT116 Cells
  • Humans
  • Mice
  • Mice, Inbred BALB C
  • Mice, Knockout
  • Proteasome Endopeptidase Complex / deficiency
  • Proteasome Endopeptidase Complex / genetics
  • Proteasome Endopeptidase Complex / metabolism*
  • Proteasome Endopeptidase Complex / physiology
  • Protein Binding
  • Proto-Oncogene Proteins c-mdm2 / metabolism
  • Proto-Oncogene Proteins c-mdm2 / physiology*
  • Tumor Suppressor Protein p53 / antagonists & inhibitors*
  • Tumor Suppressor Protein p53 / metabolism*


  • Autoantigens
  • Ki antigen
  • Tumor Suppressor Protein p53
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2
  • Proteasome Endopeptidase Complex