Regulation of wild-type and mutant p53 activity

Stindt, Maren (2012) Regulation of wild-type and mutant p53 activity. PhD thesis, University of Glasgow.

Abstract

The tumour suppressor p53 is extensively regulated by posttranslational modification, including modification by the small Ubiquitin-related modifier SUMO. The data presented here show that MDM2, previously described to promote Ubiquitin, Nedd8 and SUMO-1 modification of p53, can also enhance conjugation of endogenous SUMO-2/3 to p53. SUMOylation activity requires p53-MDM2 binding but does not depend on an intact RING finger. Both p14ARF and L11 can promote SUMO-2/3 conjugation of p53. However, unlike the previously described SUMO-1 conjugation of p53 by an MDM2-p14ARF complex, this activity does not depend on the ability of MDM2 to relocalise to the nucleolus. Strikingly, the SUMO consensus is not conserved in mouse p53, which is therefore not modified by SUMO-2/3. Ultimately, conjugation of SUMO-2/3 to p53 correlates with a reduction of both activation and repression of a subset of p53 target genes and guides the p53 response towards apoptosis rather than cell cycle arrest.
Roughly 30% of all cancers express a p53 protein containing a single amino acid exchange within the DNA binding domain. These mutant p53 proteins not only lose wild-type p53 function, but also gain new oncogenic properties that partially reflect the ability of mutant p53 to interact with and repress the p53-family transcription factors p63 and p73. Like wild-type p53, mutant p53 is also SUMOylated by MDM2, but SUMO-2/3 modification does not affect mutant p53’s ability to interact with p63 and p73. p63 and p73 bind to the DNA binding domain of mutant p53, although these interactions do not require an aggregation domain that has been identified around isoleucine 254 within this region of p53. While the DNA binding domain of p73 is necessary for binding to mutant p53, the core domain of p63 is dispensable for the interaction with mutant p53. The p53-binding protein MDM2 binds TAp73α and ∆Np73α, but does not interact with TAp63α or ∆Np63α. Strikingly, addition of MDM2 to mutant p53-p73 complexes leads to the formation of a trimeric complex with MDM2, while addition of MDM2 to mutant p53-p63 complexes releases p63 from the inhibitory mutant p53 interaction.
Altogether, this study reveals ubiquitination-independent mechanisms, by which MDM2 influences both wild-type and mutant p53 activity.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: p53, MDM2, SUMO, p63, p73
• Subjects: Q Science > QH Natural history > QH301 Biology; R Medicine > RC Internal medicine > RC0254 Neoplasms. Tumors. Oncology (including Cancer)
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Supervisor's Name: Vousden, Prof. Karen H.
• Date of Award: 2012
• Depositing User: Miss Maren H Stindt
• Unique ID: glathesis:2012-3778
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Nov 2012
• Last Modified: 11 Dec 2012 13:34
• URI: https://theses.gla.ac.uk/id/eprint/3778