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In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity
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In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity

Published on: January 29, 2018

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SUMO-1 modification of Mdm2 prevents its self-ubiquitination and increases Mdm2 ability to ubiquitinate p53

T Buschmann1, S Y Fuchs, C G Lee

  • 1Derald H Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York, New York 10029, USA.

Cell
|July 13, 2000
PubMed

Insights

Mdm2 E3 ubiquitin ligase sumoylation at Lys-446 is crucial for p53 regulation. Reduced Mdm2 sumoylation enhances p53 stability and apoptosis following DNA damage.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Protein Biochemistry

Background:

  • Mdm2 is a key E3 ubiquitin ligase targeting the p53 tumor suppressor.
  • Regulation of Mdm2 activity is critical for controlling p53 levels and function.
  • Post-translational modifications, such as sumoylation, can modulate E3 ligase activity.

Purpose of the Study:

  • To investigate the role of SUMO-1 conjugation (sumoylation) on Mdm2.
  • To determine the functional consequences of Mdm2 sumoylation on its activity towards p53.
  • To explore the impact of DNA damage on Mdm2 sumoylation and p53 stability.

Main Methods:

  • Site-directed mutagenesis to create Mdm2(K446R) mutant.
  • In vitro sumoylation assays of Mdm2.
  • Analysis of Mdm2 self-ubiquitination and p53 ubiquitination.
  • Western blotting to assess protein levels of Mdm2 and p53.
  • Irradiation experiments to induce DNA damage.

Main Results:

  • Mdm2 is sumoylated at Lys-446 within the RING finger domain.
  • Mdm2(K446R) mutant shows increased stability but enhanced p53 degradation.
  • In vitro sumoylation of Mdm2 inhibits self-ubiquitination and boosts p53 ligase activity.
  • Radiation decreases Mdm2 sumoylation, correlating inversely with p53 levels.

Conclusions:

  • Mdm2 E3 ligase activity is dependent on sumoylation for maintaining its intrinsic function.
  • Reduced Mdm2 sumoylation upon DNA damage contributes to p53 stabilization.
  • Sumoylation of Mdm2 represents a novel regulatory mechanism for p53 pathway activation.

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