MDM2 promotes p21waf1/cip1 proteasomal turnover independently of ubiquitylation

EMBO J. 2003 Dec 1;22(23):6365-77. doi: 10.1093/emboj/cdg600.


The CDK inhibitor p21waf1/cip1 is degraded by a ubiquitin-independent proteolytic pathway. Here, we show that MDM2 mediates this degradation process. Overexpression of wild-type or ring finger-deleted, but not nuclear localization signal (NLS)-deleted, MDM2 decreased p21waf1/cip1 levels without ubiquitylating this protein and affecting its mRNA level in p53(-/-) cells. This decrease was reversed by the proteasome inhibitors MG132 and lactacystin, by p19(arf), and by small interfering RNA (siRNA) against MDM2. p21waf1/cip1 bound to MDM2 in vitro and in cells. The p21waf1/cip1-binding-defective mutant of MDM2 was unable to degrade p21waf1/cip1. MDM2 shortened the half-life of both exogenous and endogenous p21waf1/cip1 by 50% and led to the degradation of its lysine-free mutant. Consequently, MDM2 suppressed p21waf1/cip1-induced cell growth arrest of human p53(-/-) and p53(-/-)/Rb(-/-)cells. These results demonstrate that MDM2 directly inhibits p21waf1/cip1 function by reducing p21waf1/cip1 stability in a ubiquitin-independent fashion.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenocarcinoma
  • Animals
  • Cell Division
  • Cell Line
  • Cells, Cultured
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / metabolism*
  • Cysteine Endopeptidases / metabolism*
  • Enzyme Inhibitors / metabolism
  • Gene Expression Regulation
  • Humans
  • Kinetics
  • Male
  • Mice
  • Mice, Knockout
  • Multienzyme Complexes / metabolism*
  • Nuclear Proteins / metabolism
  • Proteasome Endopeptidase Complex
  • Proto-Oncogene Proteins / genetics*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-mdm2
  • RNA, Small Interfering / genetics
  • Recombinant Proteins / metabolism
  • Testicular Neoplasms
  • Transfection
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / deficiency
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Ubiquitin / metabolism


  • CDKN1A protein, human
  • Cdkn1a protein, mouse
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Enzyme Inhibitors
  • Multienzyme Complexes
  • Nuclear Proteins
  • Proto-Oncogene Proteins
  • RNA, Small Interfering
  • Recombinant Proteins
  • Tumor Suppressor Protein p53
  • Ubiquitin
  • MDM2 protein, human
  • Mdm2 protein, mouse
  • Proto-Oncogene Proteins c-mdm2
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex