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An evolutionarily conserved function of proliferating cell nuclear antigen for Cdt1 degradation by the Cul4-Ddb1

Jian Hu1, Yue Xiong

  • 1Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, 27516-7295, USA.

The Journal of Biological Chemistry
|January 13, 2006
PubMed

Insights

The DNA replication factor Cdt1 is degraded by the Cul4-Ddb1 E3 ligase. Proliferating cell nuclear antigen (PCNA) is crucial for Cdt1 degradation in response to DNA damage, preventing uncontrolled DNA replication.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Cdt1 is a DNA replication licensing factor degraded during S phase and upon DNA damage to prevent re-replication.
  • Constitutive Cdt1 expression is linked to non-small cell lung carcinoma.
  • Cul4-Ddb1-Roc1 is the E3 ubiquitin ligase catalyzing DNA damage-induced Cdt1 degradation in mammals.

Purpose of the Study:

  • To investigate the role of PCNA in Cdt1 degradation.
  • To elucidate the mechanism of Cdt1 regulation by E3 ligases.
  • To understand Cdt1's role in cell cycle control and DNA damage response.

Main Methods:

  • Overexpression of PCNA inhibitory domains in cultured mammalian cells.
  • UV irradiation to induce DNA damage.
  • Co-elution and physical association assays for Cdt1 and PCNA.
  • PCNA silencing in mammalian cells and pcn1 repression in fission yeast.
  • Ddb1 deletion in fission yeast.

Main Results:

  • PCNA inhibitory domains blocked UV-induced Cdt1 degradation.
  • Cdt1 and PCNA physically associate in vivo.
  • PCNA silencing or repression blocked DNA damage-induced Cdt1 degradation.
  • Ddb1 deletion led to Cdt1 accumulation even without DNA damage.

Conclusions:

  • PCNA mediates Cdt1 degradation by the Cul4-Ddb1 ligase in response to DNA damage.
  • The Cul4-Ddb1 ligase ubiquitinates Cdt1 during normal growth and DNA damage.
  • A separate E3 ligase, possibly SCF(Skp2), may handle Cdt1 ubiquitination during normal growth.

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