Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Ataxia Telangiectasia Mutated Proteins
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Cell Cycle / physiology*
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Cell Cycle / radiation effects
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Cell Cycle Proteins
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Checkpoint Kinase 1
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Checkpoint Kinase 2
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DNA Replication / radiation effects
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DNA-Binding Proteins
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Enzyme Activation
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HeLa Cells
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Humans
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Kinetics
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Models, Biological
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Phosphorylation
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Protein Kinases / metabolism*
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Protein Serine-Threonine Kinases / physiology
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Radiation, Ionizing
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S Phase / radiation effects
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Serine / metabolism
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Signal Transduction
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Tumor Cells, Cultured
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Tumor Suppressor Proteins
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cdc25 Phosphatases / physiology*
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cdc25 Phosphatases / radiation effects
Substances
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Cell Cycle Proteins
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DNA-Binding Proteins
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Tumor Suppressor Proteins
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Serine
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Protein Kinases
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Checkpoint Kinase 2
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ATM protein, human
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Ataxia Telangiectasia Mutated Proteins
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CHEK1 protein, human
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CHEK2 protein, human
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Checkpoint Kinase 1
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Protein Serine-Threonine Kinases
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cdc25 Phosphatases