Mdm-2 and ubiquitin-independent p53 proteasomal degradation regulated by NQO1

Proc Natl Acad Sci U S A. 2002 Oct 1;99(20):13125-30. doi: 10.1073/pnas.202480499. Epub 2002 Sep 13.


The tumor suppressor p53 is a labile protein whose level is known to be regulated by the Mdm-2-ubiquitin-proteasome degradation pathway. We have found another pathway for p53 proteasomal degradation regulated by NAD(P)H quinone oxidoreductase 1 (NQO1). Inhibition of NQO1 activity by dicoumarol induces p53 and p73 proteasomal degradation. A mutant p53 (p53([22,23])), which is resistant to Mdm-2-mediated degradation, was susceptible to dicoumarol-induced degradation. This finding indicates that the NQO1-regulated proteasomal p53 degradation is Mdm-2-independent. The tumor suppressor p14(ARF) and the viral oncogenes SV40 LT and adenovirus E1A that are known to stabilize p53 inhibited dicoumarol-induced p53 degradation. Unlike Mdm-2-mediated degradation, the NQO1-regulated p53 degradation pathway was not associated with accumulation of ubiquitin-conjugated p53. In vitro studies indicate that dicoumarol-induced p53 degradation was ubiquitin-independent and ATP-dependent. Inhibition of NQO1 activity in cells with a temperature-sensitive E1 ubiquitin-activating enzyme induced p53 degradation and inhibited apoptosis at the restrictive temperature without ubiquitination. Mdm-2 failed to induce p53 degradation under these conditions. Our results establish a Mdm-2- and ubiquitin-independent mechanism for proteasomal degradation of p53 that is regulated by NQO1. The lack of NQO1 activity that stabilizes a tumor suppressor such as p53 can explain why humans carrying a polymorphic inactive NQO1 are more susceptible to tumor development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • COS Cells
  • Cell Line
  • Cysteine Endopeptidases / metabolism*
  • DNA-Binding Proteins / metabolism
  • Gene Expression Regulation
  • Genes, Tumor Suppressor
  • Humans
  • Immunoblotting
  • Mice
  • Mice, Inbred BALB C
  • Multienzyme Complexes / metabolism*
  • NAD(P)H Dehydrogenase (Quinone)
  • NADPH Dehydrogenase*
  • Nuclear Proteins / metabolism
  • Plasmids / metabolism
  • Polymorphism, Genetic
  • Proteasome Endopeptidase Complex
  • Protein Binding
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-mdm2
  • Quinone Reductases / chemistry
  • Quinone Reductases / genetics
  • Quinone Reductases / metabolism*
  • Reticulocytes / metabolism
  • Temperature
  • Time Factors
  • Transfection
  • Tumor Cells, Cultured
  • Tumor Protein p73
  • Tumor Suppressor Protein p14ARF / metabolism
  • Tumor Suppressor Protein p53 / metabolism*
  • Tumor Suppressor Proteins
  • Ubiquitin / metabolism*


  • DNA-Binding Proteins
  • Multienzyme Complexes
  • Nuclear Proteins
  • Proto-Oncogene Proteins
  • TP73 protein, human
  • Trp73 protein, mouse
  • Tumor Protein p73
  • Tumor Suppressor Protein p14ARF
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • Ubiquitin
  • NADH dehydrogenase (quinone)
  • NAD(P)H Dehydrogenase (Quinone)
  • Nqo1 protein, mouse
  • Quinone Reductases
  • NADPH Dehydrogenase
  • MDM2 protein, human
  • Mdm2 protein, mouse
  • Proto-Oncogene Proteins c-mdm2
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex