E4F1 is an atypical ubiquitin ligase that modulates p53 effector functions independently of degradation

Cell. 2006 Nov 17;127(4):775-88. doi: 10.1016/j.cell.2006.09.031.


p53 is regulated by multiple posttranslational modifications, including Hdm2-mediated ubiquitylation that drives its proteasomal degradation. Here, we identify the p53-associated factor E4F1, a ubiquitously expressed zinc-finger protein first identified as a cellular target of the viral oncoprotein E1A, as an atypical ubiquitin E3 ligase for p53 that modulates its effector functions without promoting proteolysis. E4F1 stimulates oligo-ubiquitylation in the hinge region of p53 on lysine residues distinct from those targeted by Hdm2 and previously described to be acetylated by the acetyltransferase PCAF. E4F1 and PCAF mediate mutually exclusive posttranslational modifications of p53. E4F1-dependent Ub-p53 conjugates are associated with chromatin, and their stimulation coincides with the induction of a p53-dependent transcriptional program specifically involved in cell cycle arrest, and not apoptosis. Collectively, our data reveal that E4F1 is a key posttranslational regulator of p53, which modulates its effector functions involved in alternative cell fates: growth arrest or apoptosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylation / radiation effects
  • Active Transport, Cell Nucleus / radiation effects
  • Amino Acid Sequence
  • Apoptosis / radiation effects
  • Cell Cycle Proteins / metabolism
  • Chromatin / metabolism
  • Histone Acetyltransferases / metabolism
  • Humans
  • Lysine / metabolism
  • Molecular Sequence Data
  • Protein Processing, Post-Translational*
  • Protein Structure, Tertiary
  • Protein Transport / radiation effects
  • Proto-Oncogene Proteins c-mdm2 / metabolism
  • Repressor Proteins / chemistry
  • Repressor Proteins / metabolism*
  • Sequence Homology, Amino Acid
  • Thermodynamics
  • Transcription Factors / metabolism
  • Transcription, Genetic / radiation effects
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / metabolism*
  • Ubiquitin-Protein Ligases / metabolism*
  • Ultraviolet Rays
  • p300-CBP Transcription Factors


  • Cell Cycle Proteins
  • Chromatin
  • Repressor Proteins
  • Transcription Factors
  • Tumor Suppressor Protein p53
  • Histone Acetyltransferases
  • p300-CBP Transcription Factors
  • p300-CBP-associated factor
  • E4F1 protein, human
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2
  • Ubiquitin-Protein Ligases
  • Lysine