title: Auto-ubiquitination of Mdm2 enhances its substrate ubiquitin ligase activity.
abstract: The RING domain E3 ubiquitin ligase Mdm2 is the master regulator of the tumor suppressor p53. It targets p53 for proteasomal degradation, restraining the potent activity of p53 and enabling cell survival and proliferation. Like most E3 ligases, Mdm2 can also ubiquitinate itself. How Mdm2 auto-ubiquitination may influence its substrate ubiquitin ligase activity is undefined. Here we show that auto-ubiquitination of Mdm2 is an activating event. Mdm2 that has been conjugated to polyubiquitin chains, but not to single ubiquitins, exhibits substantially enhanced activity to polyubiquitinate p53. Mechanistically, auto-ubiquitination of Mdm2 facilitates the recruitment of the E2 ubiquitin-conjugating enzyme. This occurs through noncovalent interactions between the ubiquitin chains on Mdm2 and the ubiquitin binding domain on E2s. Mutations that diminish the noncovalent interactions render auto-ubiquitination unable to stimulate Mdm2 substrate E3 activity. These results suggest a model in which polyubiquitin chains on an E3 increase the local concentration of E2 enzymes and permit the processivity of substrate ubiquitination. They also support the notion that autocatalysis may be a prevalent mode for turning on the activity of latent enzymes.
authors.affiliation: Department of Cancer Biology and Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Ruchira S
authors.initials: RS
authors.lastname: Ranaweera
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Yang
mesh_terms: D018797:Cell Cycle Proteins; D005982:Glutathione Transferase / Q000378:metabolism; D057809:HEK293 Cells; D006706:Homeostasis; D006801:Humans; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D018797:Cell Cycle Proteins; C482775:MDM4 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C097308:UBE2D1 protein, human; D044763:Ubiquitin-Conjugating Enzymes; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases; D005982:Glutathione Transferase
keywords: Auto-ubiquitination; Cancer Biology; Mdm2; Ubiquitin; Ubiquitin Ligase; Ubiquitin-conjugating Enzyme (Ubc); Ubiquitination; p53