Inhibition of MDM2-mediated p53 ubiquitination and degradation by ribosomal protein L5

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Updated: Dec 30, 2025

Purification of Ubiquitinated p53 Proteins from Mammalian Cells
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Purification of Ubiquitinated p53 Proteins from Mammalian Cells

Published on: March 21, 2022

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Mu-Shui Dai1, Hua Lu

  • 1Department of Biochemistry and Molecular Biology, School of Medicine, Oregon Health & Science University, Portland, Oregon 97201, USA.

The Journal of Biological Chemistry
|August 17, 2004
PubMed

Insights

Ribosomal protein L5 activates the tumor suppressor p53 by inhibiting MDM2. This interaction stabilizes p53, enhances its activity, and induces cell cycle arrest, revealing a new p53 regulatory pathway.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Oncology

Background:

  • The oncoprotein MDM2 negatively regulates the tumor suppressor p53.
  • Ribosomal proteins L11 and L23 are known to activate p53 by inhibiting MDM2.
  • The role of ribosomal protein L5 in p53 regulation was previously unclear.

Purpose of the Study:

  • To investigate the role of ribosomal protein L5 in the regulation of p53.
  • To elucidate the mechanism by which L5 affects p53 stability and activity.
  • To identify the molecular complexes involved in L5-mediated p53 activation.

Main Methods:

  • Overexpression studies in H1299 and U2OS cells to assess p53 stabilization and transcriptional activity.
  • Ubiquitination assays to evaluate the effect of L5 on MDM2-mediated p53 ubiquitination.
  • Co-immunoprecipitation experiments to identify protein complexes involving MDM2, L5, and p53.
  • Small interference RNA (siRNA) knockdown to confirm L5's role in actinomycin D-induced p53 activation.

Main Results:

  • Overexpression of L5 stabilized both ectopic and endogenous p53.
  • L5 enhanced p53 transcriptional activity, leading to p53-dependent G1 cell cycle arrest.
  • L5 inhibited MDM2-mediated p53 ubiquitination, similar to L11 and L23.
  • Actinomycin D treatment enhanced L5-MDM2 interaction, and L5 knockdown abrogated actinomycin D-induced p53 stabilization.
  • Two distinct complexes were identified: MDM2-L5-L11-L23 and p53-MDM2-L5-L11-L23.

Conclusions:

  • Ribosomal protein L5 is a novel activator of p53.
  • L5 functions by inhibiting MDM2-mediated p53 ubiquitination, thereby stabilizing p53.
  • The MDM2-L5-L11-L23 complex plays a critical role in p53 activation and tumor suppression.

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