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Origin licensing and p53 status regulate Cdk2 activity during G(1)

Kathleen R Nevis1, Marila Cordeiro-Stone, Jeanette Gowen Cook

  • 1Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC 27599, USA.

Cell Cycle (Georgetown, Tex.)
|May 15, 2009
PubMed

Insights

Origin licensing, crucial for DNA replication, prevents rereplication. Inhibiting licensing factors Cdc6 or Cdt1 in normal cells causes G1 arrest, while cancer cells undergo apoptosis, revealing cell-type specific responses.

Area of Science:

  • Cell Cycle Regulation
  • DNA Replication Licensing
  • Molecular Biology

Background:

  • DNA replication origins are licensed by prereplication complexes during G1 phase.
  • Regulatory mechanisms prevent new licensing after the G1/S transition to avoid rereplication.
  • Coordination between S phase entry and origin licensing completion is not fully understood.

Purpose of the Study:

  • To investigate the role of origin licensing factors Cdc6 and Cdt1 in cell cycle progression.
  • To elucidate the mechanisms coordinating S phase entry with origin licensing.
  • To compare the effects of licensing inhibition in normal versus cancer cells.

Main Methods:

  • Depletion of essential licensing factors Cdc6 or Cdt1 in normal human fibroblasts.
  • Analysis of cell cycle arrest, cyclin E/Cdk2 activity, and Rb phosphorylation.
  • Comparison of licensing inhibition effects in HeLa and U2OS cancer cell lines.
  • Co-depletion of Cdc6 and p53 in normal cells to assess p53's role.

Main Results:

  • Depletion of Cdc6 or Cdt1 in normal fibroblasts induced G1 arrest, inhibited cyclin E/Cdk2 activity, and caused Rb hypophosphorylation.
  • Inhibition of licensing in cancer cells led to apoptosis, without affecting Cdk2 or Rb phosphorylation.
  • Co-depletion of Cdc6 and p53 in normal cells restored Cdk2 activation and Rb phosphorylation, allowing S phase entry with DNA damage.

Conclusions:

  • Origin licensing is essential for multiple G1 progression events in normal cells.
  • A mechanism preventing premature S phase entry relies on origin licensing and p53.
  • This mechanism functions in normal cells but is impaired in p53-deficient cancer cells.

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