title: G2 damage checkpoints: what is the turn-on?
abstract: Cells mount a coordinated response to DNA damage, activating DNA repair pathways and cell-cycle checkpoint pathways to allow time for DNA repair to occur. In human cells, checkpoint responses can be divided into p53-dependent and p53-independent pathways, the latter being predominant in G2 phase of the cell cycle. The p53-independent pathway involves a phosphorylation cascade that activates the Chk1 effector kinase and induces G2 arrest through inhibitory tyrosine phosphorylation of Cdc2. At the top of this cascade are the ATR and ATM kinases. How ATM and ATR recognize DNA damage and activate this checkpoint pathway is only beginning to emerge. Single-stranded DNA, a result of stalled DNA replication or processing of chromosomal lesions, appears to be central to the activation of ATR. The recruitment of replication protein A to single-stranded DNA facilitates the recruitment of several complexes of checkpoint proteins. In this context, ATR is activated and then phosphorylates the C-terminus of Chk1, activating it to enforce a block to mitotic entry.
authors.affiliation: Department of Oncological Sciences, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1130, New York, NY 10029, USA. matthew.oconnell@mssm.edu
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: O'Connell
authors.forename: Karlene A
authors.initials: KA
authors.lastname: Cimprich
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D016195:G2 Phase; D006801:Humans; D008954:Models, Biological; D011494:Protein Kinases / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases