title: Cleavage of claspin by caspase-7 during apoptosis inhibits the Chk1 pathway.
abstract: Claspin is required for the phosphorylation and activation of the Chk1 protein kinase by ATR during DNA replication and in response to DNA damage. This checkpoint pathway plays a critical role in the resistance of cells to genotoxic stress. Here, we show that human Claspin is cleaved by caspase-7 during the initiation of apoptosis. In cells, induction of DNA damage by etoposide at first produced rapid phosphorylation of Chk1 at a site targeted by ATR. Subsequently, etoposide caused activation of caspase-7, cleavage of Claspin, and dephosphorylation of Chk1. In apoptotic cell extracts, Claspin was cleaved by caspase-7 at a single aspartate residue into a large N-terminal fragment and a smaller C-terminal fragment that contain different functional domains. The large N-terminal fragment was heavily phosphorylated in a human cell-free system in response to double-stranded DNA oligonucleotides, and this fragment retained Chk1 binding activity. In contrast, the smaller C-terminal fragment did not bind Chk1, but did associate with DNA and inhibited the DNA-dependent phosphorylation of Chk1 associated with its activation. These results indicate that cleavage of Claspin by caspase-7 inactivates the Chk1 signaling pathway. This mechanism may regulate the balance between cell cycle arrest and induction of apoptosis during the response to genotoxic stress.
authors.affiliation: Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom.
authors.forename: Catriona A L
authors.initials: CA
authors.lastname: Clarke
authors.forename: Lara N
authors.initials: LN
authors.lastname: Bennett
authors.forename: Paul R
authors.initials: PR
authors.lastname: Clarke
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001224:Aspartic Acid / Q000737:chemistry; D001665:Binding Sites; D053179:Caspase 7; D020169:Caspases / Q000737:chemistry / Q000378:metabolism*; D002453:Cell Cycle; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002474:Cell-Free System; D000071877:Checkpoint Kinase 1; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004261:DNA Replication; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D005047:Etoposide / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D019169:Jurkat Cells; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013997:Time Factors; D014981:Xenopus; D029867:Xenopus Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C488158:CLSPN protein, human; D009841:Oligonucleotides; D011500:Protein Synthesis Inhibitors; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D001224:Aspartic Acid; D005047:Etoposide; D004247:DNA; D003513:Cycloheximide; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605875:Chek1 protein, Xenopus; C000605869:Chek1 protein, mouse; C505520:CASP7 protein, human; C505524:Casp7 protein, mouse; D053179:Caspase 7; D020169:Caspases