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The Cul4A-DDB1 E3 ubiquitin ligase complex represses p73 transcriptional activity

M Malatesta1, A Peschiaroli, E M Memmi

  • 1Department of Experimental Medicine and Surgery, University of Rome 'Tor Vergata', Rome, Italy.

Oncogene
|October 23, 2012
PubMed

Insights

The Cullin4A (cul4A)-dependent ligase (CDL4A) complex monoubiquitylates p73, inhibiting its transcriptional activity. This discovery reveals a new regulatory mechanism for p73 and its target genes in processes like cancer.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The Cullin4A (cul4A)-dependent ligase (CDL4A) E3 complex is involved in crucial cellular processes, including cell cycle regulation and DNA damage response.
  • CDL4A functions through both proteolytic and non-proteolytic mechanisms.

Purpose of the Study:

  • To investigate the interaction between the CDL4A complex and the p53 family member p73.
  • To elucidate the functional consequences of this interaction on p73 activity and gene expression.

Main Methods:

  • Co-immunoprecipitation assays to demonstrate p73 binding to DNA-binding protein 1 (DDB1), a subunit of the CDL4A complex.
  • Monoubiquitylation assays to assess the effect of CDL4A on p73.
  • RNA interference (RNAi) and genetic depletion of DDB1 to study p73 target gene expression.
  • Bioinformatic analysis of Cul4A expression in human breast cancer tissues.

Main Results:

  • p73 directly binds to DDB1, facilitating its interaction with the CDL4A complex.
  • The CDL4A complex monoubiquitylates p73 without affecting its protein stability.
  • CDL4A-mediated ubiquitylation negatively regulates p73-dependent transcriptional activity.
  • Depletion of DDB1 leads to increased expression of p73 target genes independently of p53.
  • Elevated Cul4A expression in breast carcinomas correlates with repressed p73 target gene expression.

Conclusions:

  • The CDL4A complex directly regulates p73 through monoubiquitylation.
  • This regulation inhibits p73's transcriptional function, impacting gene expression.
  • These findings provide novel insights into p73 regulation by the CDL4A complex and its implications in diseases like breast cancer.

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