title: Mdm-2 and ubiquitin-independent p53 proteasomal degradation regulated by NQO1.
abstract: 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.
authors.affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Gad
authors.initials: G
authors.lastname: Asher
authors.forename: Joseph
authors.initials: J
authors.lastname: Lotem
authors.forename: Leo
authors.initials: L
authors.lastname: Sachs
authors.forename: Chaim
authors.initials: C
authors.lastname: Kahana
authors.forename: Yosef
authors.initials: Y
authors.lastname: Shaul
mesh_terms: D000818:Animals; D017209:Apoptosis; D019556:COS Cells; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D016147:Genes, Tumor Suppressor; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008807:Mice, Inbred BALB C; D009097:Multienzyme Complexes / Q000378:metabolism*; D016660:NAD(P)H Dehydrogenase (Quinone); D009252:NADPH Dehydrogenase; D009687:Nuclear Proteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011110:Polymorphism, Genetic; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D011808:Quinone Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012156:Reticulocytes / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D000072160:Tumor Protein p73; D025803:Tumor Suppressor Protein p14ARF / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C000606460:TP73 protein, human; C000606368:Trp73 protein, mouse; D000072160:Tumor Protein p73; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; C041831:NADH dehydrogenase (quinone); D016660:NAD(P)H Dehydrogenase (Quinone); C491732:Nqo1 protein, mouse; D011808:Quinone Reductases; D009252:NADPH Dehydrogenase; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex