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Mdm2 and mdmX prevent ASPP1 and ASPP2 from stimulating p53 without targeting p53 for degradation

Daniele Bergamaschi1, Yardena Samuels, Shan Zhong

  • 1Ludwig Institute for Cancer Research, University College London, 91 Riding House Street, London W1W 7BS, UK.

Oncogene
|March 23, 2005
PubMed

Insights

ASPP1 and ASPP2 require p53’s DNA binding and transactivation functions to promote apoptosis. Mdm2 and mdmx inhibit this process by blocking p53

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cellular Signaling

Background:

  • The tumor suppressor protein p53 plays a critical role in preventing cancer by inducing apoptosis or cell cycle arrest in response to cellular stress.
  • ASPP proteins (ASPP1 and ASPP2) are known to interact with p53 and enhance its tumor-suppressive functions, particularly apoptosis.
  • Mdm2 and its homolog mdmx are key negative regulators of p53, primarily by targeting it for proteasomal degradation.

Purpose of the Study:

  • To elucidate the specific roles of p53's DNA binding and transactivation domains in mediating the pro-apoptotic effects stimulated by ASPP1 and ASPP2.
  • To investigate the mechanism by which Mdm2 and mdmx interfere with the ASPP1/ASPP2-mediated stimulation of p53's apoptotic function.
  • To determine if Mdm2 and mdmx inhibit ASPP1/ASPP2's effect on p53 independently of p53 degradation.

Main Methods:

  • Utilized various p53 and Mdm2 mutants to dissect functional requirements.
  • Assessed the impact of ASPP1 and ASPP2 on p53's DNA binding and transactivation activities.
  • Investigated the interaction between Mdm2, mdmx, and p53 in the presence of ASPP1 and ASPP2.
  • Evaluated p53 protein levels and degradation in response to these protein interactions.

Main Results:

  • Both DNA binding and transactivation functions of p53 are essential for ASPP1 and ASPP2 to enhance p53's apoptotic activity.
  • Mdm2 and mdmx inhibit the stimulatory effect of ASPP1 and ASPP2 on p53's apoptosis by binding to p53 and suppressing its transcriptional activity.
  • Crucially, Mdm2 and mdmx can inhibit ASPP1/ASPP2-mediated p53 activation without inducing p53 degradation.

Conclusions:

  • ASPP1 and ASPP2 require intact DNA binding and transactivation domains of p53 to promote apoptosis.
  • Mdm2 and mdmx act as potent inhibitors of p53's tumor-suppressive functions by directly interfering with the ASPP1/ASPP2-mediated apoptotic pathway.
  • This study reveals a novel mechanism of p53 inhibition by Mdm2 and mdmx, highlighting their role in preventing p53-driven apoptosis independent of direct protein degradation.

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