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Cdc25 inhibited in vivo and in vitro by checkpoint kinases Cds1 and Chk1

B Furnari1, A Blasina, M N Boddy

  • 1Departments of Molecular Biology and Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.

Molecular Biology of the Cell
|April 10, 1999
PubMed

Insights

The protein kinase Cds1 and Chk1 inhibit Cdc25, a key regulator of mitosis, by phosphorylating it. This mechanism is crucial for the S-M replication and G2-M damage checkpoints in fission yeast.

Area of Science:

  • Cell cycle regulation
  • DNA replication checkpoints
  • Protein kinase signaling

Background:

  • Cds1 (protein kinase) is activated by the S-M replication checkpoint in fission yeast.
  • Cds1 is known to regulate Wee1 and Mik1, which inhibit the mitotic kinase Cdc2.
  • The precise mechanisms by which Cds1 enforces the S-M checkpoint are still being elucidated.

Purpose of the Study:

  • To investigate the role of Cds1 in regulating Cdc25, the phosphatase that activates Cdc2.
  • To determine if Chk1 also regulates Cdc25.
  • To elucidate the mechanism of Cds1 and Chk1 action on Cdc25.

Main Methods:

  • In vivo assays measuring Cdc25-catalyzed mitosis rates.
  • In vitro assays examining Cds1 and Chk1 inhibition of Cdc25.
  • Site-directed mutagenesis (Cdc25 alanine-99 mutation).

Main Results:

  • Cds1 inhibits Cdc25 activity, contributing to mitotic delay during the S-M replication checkpoint.
  • Chk1 also inhibits Cdc25 activity in vitro.
  • Cds1 and Chk1 phosphorylate Cdc25 on serine-99 in vitro.
  • Mutation of serine-99 in Cdc25 partially impairs both S-M replication and G2-M damage checkpoints in vivo.

Conclusions:

  • Cds1 and Chk1 regulate Cdc25 through similar phosphorylation mechanisms.
  • These kinases play a role in distinct checkpoint pathways (S-M replication and G2-M damage).
  • Phosphorylation of Cdc25 at serine-99 is a key event in checkpoint control.

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