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Xenopus Cdc7 executes its essential function early in S phase and is counteracted by checkpoint-regulated protein

Wei Theng Poh1, Gaganmeet Singh Chadha, Peter J Gillespie

  • 1Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, UK.

Open Biology
|January 10, 2014
PubMed

Insights

Cdc7 kinase hyperphosphorylates MCM proteins to initiate DNA replication. Protein phosphatase 1 reverses this, and its recruitment by checkpoint kinases inhibits replication initiation, impacting cancer therapy.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • DNA replication initiation requires cyclin-dependent kinase (Cdk) and Cdc7 protein kinases.
  • The precise role of Cdc7 in regulating S phase progression remains less understood compared to Cdk.
  • Understanding Cdc7 function is crucial for dissecting DNA replication control and potential therapeutic strategies.

Purpose of the Study:

  • To investigate the specific role of Cdc7 in regulating DNA replication initiation and progression through S phase.
  • To elucidate the mechanism by which Cdc7 controls replication origins using a specific inhibitor.
  • To explore the interplay between Cdc7, MCM protein phosphorylation, and checkpoint kinases.

Main Methods:

  • Utilized the Cdc7 inhibitor PHA-767491 in Xenopus egg extracts.
  • Analyzed the phosphorylation status of mini-chromosome maintenance (MCM) proteins.
  • Investigated the recruitment of protein phosphatase 1 (PP1) to chromatin.
  • Assessed the impact of checkpoint kinases on MCM dephosphorylation.

Main Results:

  • Cdc7-mediated hyperphosphorylation of MCM proteins is essential for replication initiation but not elongation.
  • Cdc7 phosphorylates MCM proteins at most replication origins early in S phase.
  • Protein phosphatase 1 (PP1) reverses Cdc7-mediated MCM hyperphosphorylation by chromatin recruitment.
  • Checkpoint kinases promote PP1 association with chromatin, inhibiting replication initiation by enhancing MCM dephosphorylation.

Conclusions:

  • Cdc7's primary role is initiating DNA replication through MCM hyperphosphorylation at origins.
  • PP1 acts as a key regulator by reversing Cdc7's effects, with checkpoint kinases modulating this process.
  • This mechanism explains previous discrepancies in Cdc7 regulation and has implications for developing Cdc7 inhibitors as anti-cancer agents.
Keywords:
Cdc7DNA replicationPHA-767491PP1Xenopus

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