Mdm-2 and Ubiquitin-Independent p53 Proteasomal Degradation Regulated by NQO1

• Published in: Proceedings of the National Academy of Sciences - PNAS 2002-10, Vol.99 (20), p.13125-13130
• Main Authors: Asher, Gad, Lotem, Joseph, Sachs, Leo, Kahana, Chaim, Shaul, Yosef
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Biological Sciences; Cell Line; Cell lines; COS Cells; Cultured cells; Cysteine Endopeptidases - metabolism; DNA-Binding Proteins - metabolism; Gene Expression Regulation; Genes, Tumor Suppressor; HCT116 cells; Humans; Immunoblotting; Medical research; Mice; Mice, Inbred BALB C; Multienzyme Complexes - metabolism; Mutation; NAD(P)H Dehydrogenase (Quinone); NADPH Dehydrogenase; Nuclear Proteins - metabolism; Oncogenes; Plasmids - metabolism; Polymorphism, Genetic; Proteasome Endopeptidase Complex; Protein Binding; Proteins; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-mdm2; Quinone Reductases - chemistry; Quinone Reductases - genetics; Quinone Reductases - metabolism; Reticulocytes; 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; Tumors; Ubiquitin - metabolism; Ubiquitins
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.202480499

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 p14ARFand 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.