Chk1 regulates the S phase checkpoint by coupling the physiological turnover and ionizing radiation-induced accelerated proteolysis of Cdc25A.

• Chk1 kinase coordinates cell cycle progression and preserves genome integrity. Here, we show that chemical or genetic ablation of human Chk1 triggered supraphysiological accumulation of the S phase-promoting Cdc25A phosphatase, prevented ionizing radiation (IR)-induced degradation of Cdc25A, and caused radioresistant DNA synthesis (RDS). The basal turnover of Cdc25A operating in unperturbed S phase required Chk1-dependent phosphorylation of serines 123, 178, 278, and 292. IR-induced acceleration of Cdc25A proteolysis correlated with increased phosphate incorporation into these residues generated by a combined action of Chk1 and Chk2 kinases. Finally, phosphorylation of Chk1 by ATM was required to fully accelerate the IR-induced degradation of Cdc25A. Our results provide evidence that the mammalian S phase checkpoint functions via amplification of physiologically operating, Chk1-dependent mechanisms.

Keyword

Cell Cycle/*physiology/radiation effects

Cell Cycle Proteins

DNA Replication/radiation effects

DNA-Binding Proteins

Enzyme Activation

Hela Cells

Humans

Kinetics

Models; Biological

Phosphorylation

Protein Kinases/*metabolism

Protein-Serine-Threonine Kinases/physiology

Radiation; Ionizing

S Phase/radiation effects

Serine/metabolism

Signal Transduction

Tumor Cells; Cultured

Tumor Suppressor Proteins

cdc25 Phosphatase/*physiology/radiation effects

Publication and Content Type

ref (subject category)

art (subject category)