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Updated: May 22, 2025

Purification of Ubiquitinated p53 Proteins from Mammalian Cells
10:55

Purification of Ubiquitinated p53 Proteins from Mammalian Cells

Published on: March 21, 2022

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PP2A adapter protein IER5 induces dephosphorylation and degradation of MDM2, thereby stabilizing p53

Taisei Nakada1, Mayuko Koga1, Hiroto Takeuchi1

  • 1Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan.

Cellular Signalling
|March 13, 2025
PubMed

Insights

The adapter protein IER5 stabilizes the tumor suppressor p53 (protein 53) by inhibiting its ubiquitination. This regulation involves the protein phosphatase PP2A/B55 complex and the MDM2 ligase, maintaining nuclear p53 levels.

Area of Science:

  • Molecular biology
  • Cellular signaling
  • Cancer research

Background:

  • The tumor suppressor p53 plays a critical role in cellular responses to stress.
  • p53 levels are tightly regulated by ubiquitination, primarily mediated by MDM2 (mouse double minute 2 homolog).
  • IER5 (Immediate Early Response 5) is a gene activated by p53 and encodes an adapter protein for protein phosphatase PP2A.

Purpose of the Study:

  • To investigate the role of IER5 in regulating p53 stability and function.
  • To elucidate the mechanism by which IER5 affects p53 ubiquitination.
  • To understand the interplay between IER5, PP2A/B55, and MDM2 in p53 regulation.

Main Methods:

  • Western blotting to assess protein levels and ubiquitination.
  • Immunoprecipitation to study protein-protein interactions.
  • Cellular localization studies (nuclear/cytoplasmic fractionation).
  • Treatment with MDM2 inhibitor Nutlin-3.

Main Results:

  • IER5 inhibits p53 ubiquitination, leading to increased cellular p53 levels.
  • IER5 requires nuclear localization and binding to PP2A/B55 and MDM2 for this function.
  • IER5-PP2A/B55 complex dephosphorylates MDM2 at Ser166.
  • Dephosphorylation of MDM2 by IER5-PP2A/B55 leads to MDM2 ubiquitination and reduced nuclear MDM2 levels.
  • IER5's inhibition of p53 ubiquitination is dependent on MDM2 activity.

Conclusions:

  • IER5 acts as a positive regulator of p53 by preventing its ubiquitination.
  • The IER5-PP2A/B55 complex modulates p53 stability through dephosphorylation of MDM2.
  • This mechanism regulates the nuclear balance between MDM2 and p53, impacting tumor suppression.
Keywords:
IER5MDM2PP2APhosphorylationUbiquitinationp53

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