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Pirh2, a ubiquitin E3 ligase, inhibits p73 transcriptional activity by promoting its ubiquitination

Hong Wu1, Rami Abou Zeinab, Elsa R Flores

  • 1Department of Laboratory Medicine and Pathology, 370 Heritage Medical Research Center, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.

Molecular Cancer Research : MCR
|October 14, 2011
PubMed

Insights

Pirh2 protein ubiquinates and downregulates the tumor suppressor p73, impacting its transcriptional activity and cell cycle control. This Pirh2-mediated ubiquitination pathway is crucial for regulating p73

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Biology

Background:

  • p73 is a homolog of p53, a tumor suppressor involved in apoptosis and cell-cycle arrest.
  • p73 plays a role in tumor suppression, as indicated by mouse models.
  • The regulation of p73 function is critical for understanding its role in cancer.

Purpose of the Study:

  • To investigate the interaction between Pirh2 and p73.
  • To elucidate the mechanism by which Pirh2 affects p73 function.
  • To determine the role of Pirh2-mediated ubiquitination in regulating p73 activity.

Main Methods:

  • Co-immunoprecipitation to assess physical interaction between Pirh2 and p73.
  • In vitro and in vivo ubiquitination assays to study p73 modification.
  • RNA interference (siRNA) to deplete Pirh2 levels.
  • Quantitative real-time PCR to measure p73 transcript levels.
  • Reporter assays to assess p73-dependent transcriptional activity.

Main Results:

  • Pirh2 physically interacts with p73 and downregulates its function via E3 ligase activity.
  • Pirh2 promotes p73 ubiquitination both in vitro and in vivo, utilizing various linkage types (K11, K29, K48, K63).
  • Depletion of Pirh2 reduces p73 ubiquitination and restores p73-mediated transcriptional activity and G1 arrest.
  • Pirh2 represses p73 transcriptional activity by directly inhibiting the p73 transcript, independent of p73 protein levels.

Conclusions:

  • Pirh2-mediated ubiquitination of p73 is a key regulatory mechanism controlling p73's tumor suppressive function.
  • This pathway links p73 ubiquitination status to its transcriptional activity and cell cycle regulation.
  • Targeting the Pirh2-p73 interaction could offer therapeutic strategies in cancer treatment.

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