MdmX protein is essential for Mdm2 protein-mediated p53 polyubiquitination Journal Article
| Authors: | Wang, X.; Wang, J.; Jiang, X. |
| Article Title: | MdmX protein is essential for Mdm2 protein-mediated p53 polyubiquitination |
| Abstract: | Genetic evidence has implicated both Mdm2 and MdmX as essential in negative regulation of p53. However, the exact role of MdmX in this Mdm2-dependent protein degradation is not well understood. Most, if not all, previous Mdm2 studies used GST-Mdm2 fusion proteins in the in vitro assays. Here, we show that the p53 polyubiquitination activity of GST-Mdm2 is conferred by the GST tag and non-GST-tagged Mdm2 only catalyzes monoubiquitination of p53 even at extremely high concentrations. We further demonstrate that MdmX is a potent activator of Mdm2, facilitating dose-dependent p53 polyubiquitination. This activation process requires the RING domains of both MdmX and Mdm2 proteins. The polyubiquitination activity of Mdm2/MdmX is Mdm2-dependent. UnlikeMdm2or MdmX overexpression alone, co-overexpression of MdmX and Mdm2 consistently triggered p53 degradation in cells. Moreover, cellular polyubiquitination of p53 was only observable in the cytoplasm where both Mdm2 and MdmX are readily detectable. Importantly, RNAi knockdown of MdmX increased levels of endogenous p53 accompanied by reduced p53 polyubiquitination. In conclusion, our work has resolved a major confusion in the field derived from using GST-Mdm2 and demonstrated that MdmX is the cellular activator that converts Mdm2 from a monoubiquitination E3 ligase to a polyubiquitination E3 ligase toward p53. Together, our findings provide a biochemical basis for the requirement of both Mdm2 and MdmX in the dynamic regulation of p53 stability. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc. |
| Keywords: | controlled study; protein expression; human cell; protein domain; proteins; cytology; protein degradation; protein p53; protein mdmx; ubiquitination; hybrid protein; glutathione transferase; cytoplasm; gene silencing; catalysis; fusion proteins; concentration response; dose-dependent; protein mdm2; over-expression; in-vitro assays; chemical activation; e3 ligase; degradation; polyubiquitination; activation process; dynamic regulation; high concentration; potent activators |
| Journal Title: | Journal of Biological Chemistry |
| Volume: | 286 |
| Issue: | 27 |
| ISSN: | 0021-9258 |
| Publisher: | American Society for Biochemistry and Molecular Biology |
| Date Published: | 2011-07-08 |
| Start Page: | 23725 |
| End Page: | 23734 |
| Language: | English |
| DOI: | 10.1074/jbc.M110.213868 |
| PROVIDER: | scopus |
| PMCID: | PMC3129153 |
| PUBMED: | 21572037 |
| DOI/URL: | |
| Notes: | --- - "Export Date: 17 August 2011" - "CODEN: JBCHA" - "Source: Scopus" |
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