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Title: Regulation of p53 by catalytically-inactive MDM2 mutants
Author: Nomura, Koji
ISNI:       0000 0004 7655 3373
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2019
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MDM2-MDMX complexes bind to p53, inhibiting the p53 transcriptional activity and targeting p53 for proteasomal degradation. Uncoupling p53 from MDM2 is therefore an attractive strategy to treat cancers that retain wild type p53. Small molecules that inhibit MDM2 binding to p53 release p53 from control by MDM2. While such inhibitors efficiently activate a p53 response, clinical trials have revealed that the therapeutic utility of these compounds is limited by on-target toxicities. I have therefore explored alternative mechanisms to therapeutically target MDM2, based on the hypothesis that inhibition of the MDM2 RING domain would lead to different outcomes than inhibition of the MDM2-p53 interaction. Using our crystal structure of E2 (UbcH5b)-ubiquitin-MDM2RING-MDMXRING complex as a starting point, MDM2 mutants that prevent E2-ubiquitin binding were designed. MDM2 mutants that are unable to interact with E2-ubiquitin complex have lost their E3 ligase activity including the ability to ubiquitinate p53, despite retaining the ability to bind to p53, homo-dimerise and hetero-dimerise with MDMX. As a result, p53 protein accumulates in cells expressing these catalytically-inactive MDM2 mutants. However, the E2-ubiquitin non-binding MDM2 mutants retain the ability to limit p53 transcriptional activity under normal unstressed condition, despite the elevated p53 levels. As a result, cells can proliferate normally, but show a more robust induction of p53 activity in response to stress. These observations suggest that the direct inhibition of E3 activity of MDM2 may be less deleterious to normal cells than inhibition of the MDM2-p53 interaction. To test this, the development of novel in vivo models based on conditional knock-in of one of the MDM2 mutants identified in this study was initiated. Based on preliminary data, mice expressing these mutants are expected to be developmentally normal but less tumour prone due to an increased sensitivity to p53 activation. This study provides mechanistic insight that will help in the development of novel inhibitors that targeting MDM2 while avoiding the on-target toxicities showed in the clinic by currently available MDM2 inhibitors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Q Science (General)