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Critical role for Daxx in regulating Mdm2

Jun Tang1, Li-Ke Qu, Jianke Zhang

  • 1Abramson Family Cancer Research Institute and Department of Cancer Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.

Nature Cell Biology
|July 18, 2006
PubMed

Insights

Death domain-associated protein (Daxx) stabilizes mouse double minute 2 (Mdm2), a key regulator of the tumor suppressor p53. Disrupting the Mdm2-Daxx interaction is crucial for p53 activation following DNA damage.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • The tumor suppressor p53 regulates apoptosis and cell-cycle arrest in response to cellular stress.
  • Mouse double minute 2 (Mdm2) restrains p53's anti-proliferative functions by promoting its ubiquitination and degradation.
  • The differential regulation of Mdm2's opposing E3 ligase activities (cis- and trans-) remains unclear.

Purpose of the Study:

  • To investigate the role of death domain-associated protein (Daxx) in regulating Mdm2 stability and function.
  • To elucidate the mechanism by which Daxx influences Mdm2's interaction with p53 and its auto-ubiquitination.
  • To understand how the Mdm2-Daxx interaction is modulated during cellular stress, particularly DNA damage.

Main Methods:

  • Investigated the effect of Daxx downregulation and overexpression on Mdm2 protein levels.
  • Assessed the interaction between Daxx, Mdm2, and the deubiquitinase Hausp using co-immunoprecipitation assays.
  • Examined the impact of Daxx on Mdm2's E3 ligase activity towards p53.
  • Analyzed the dissociation of Daxx from Mdm2 upon DNA damage induction.

Main Results:

  • Daxx is essential for Mdm2 stability; Daxx downregulation decreases Mdm2 levels, while Daxx overexpression increases them.
  • Daxx binds to both Mdm2 and Hausp, mediating Hausp's stabilizing effect on Mdm2.
  • Daxx enhances Mdm2's intrinsic E3 ligase activity towards p53.
  • Daxx dissociates from Mdm2 upon DNA damage, correlating with Mdm2 self-degradation.

Conclusions:

  • Daxx modulates Mdm2 function at multiple levels, including stability, interaction with Hausp, and E3 ligase activity.
  • The dissociation of Daxx from Mdm2 during DNA damage is a critical event for p53 activation.
  • Targeting the Mdm2-Daxx interaction represents a potential therapeutic strategy for activating p53 in cancer treatment.

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