The G(2) DNA damage checkpoint targets both Wee1 and Cdc25

Area of Science:

• Cell cycle regulation
• DNA damage response
• Molecular biology

Background:

• Mitotic entry is governed by Cdc2p kinase activity, modulated by Wee1p kinase and Cdc25p phosphatase.
• The G(2) DNA damage checkpoint in Schizosaccharomyces pombe prevents mitosis entry by maintaining Cdc2p phosphorylation at tyrosine-15 (Y15).
• Chk1p kinase is a key component of this checkpoint pathway, targeting Wee1p and Cdc25p.

Purpose of the Study:

• To elucidate the precise roles of Wee1p and Cdc25p in the Chk1p-mediated G(2) DNA damage checkpoint.
• To determine how Chk1p signaling contributes to cell cycle arrest upon DNA damage.
• To investigate the combined action of Wee1p and Cdc25p in checkpoint control.

Main Methods:

• Investigated G(2) arrest phenotypes in yeast strains with altered wee1(+) and cdc25(+) gene expression.
• Performed in vitro phosphorylation assays of Wee1p and Cdc25p by Chk1p.
• Analyzed Wee1p protein levels during checkpoint activation.

Main Results:

• While Chk1p overexpression causes Wee1p-dependent G(2) arrest, cells lacking wee1(+) remain checkpoint proficient, indicating Wee1p upregulation alone is insufficient.
• Cells regulating mitosis independently of Cdc25p retain an intact G(2) DNA damage checkpoint and sensitivity to Chk1p arrest, showing Cdc25p downregulation is also insufficient.
• Inactivation of both wee1(+) and cdc25(+) abolishes checkpoint control.
• Checkpoint activation leads to a transient increase in Wee1p levels.

Conclusions:

• The G(2) DNA damage checkpoint employs a coordinated mechanism involving both Wee1p upregulation and Cdc25p downregulation.
• This dual signaling provides a robust "double-lock" system to enforce cell cycle arrest, facilitating DNA repair and maintaining genomic stability.