title: DNA-PK is involved in repairing a transient surge of DNA breaks induced by deceleration of DNA replication.
abstract: Cells that suffer substantial inhibition of DNA replication halt their cell cycle via a checkpoint response mediated by the PI3 kinases ATM and ATR. It is unclear how cells cope with milder replication insults, which are under the threshold for ATM and ATR activation. A third PI3 kinase, DNA-dependent protein kinase (DNA-PK), is also activated following replication inhibition, but the role DNA-PK might play in response to perturbed replication is unclear, since this kinase does not activate the signaling cascades involved in the S-phase checkpoint. Here we report that mild, transient drug-induced perturbation of DNA replication rapidly induced DNA breaks that promptly disappeared in cells that contained a functional DNA-PK whereas such breaks persisted in cells that were deficient in DNA-PK activity. After the initial transient burst of DNA breaks, cells with a functional DNA-PK did not halt replication and continued to synthesize DNA at a slow pace in the presence of replication inhibitors. In contrast, DNA-PK deficient cells subject to low levels of replication inhibition halted cell cycle progression via an ATR-mediated S-phase checkpoint. The ATM kinase was dispensable for the induction of the initial DNA breaks. These observations suggest that DNA-PK is involved in setting a high threshold for the ATR-Chk1-mediated S-phase checkpoint by promptly repairing DNA breaks that appear immediately following inhibition of DNA replication.
authors.affiliation: Laboratory of Molecular Pharmacology, Center for Cancer Research, NCI, NIH, Bethesda, MD 20892, USA.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Shimura
authors.forename: Melvenia M
authors.initials: MM
authors.lastname: Martin
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Torres
authors.forename: Cory
authors.initials: C
authors.lastname: Gu
authors.forename: Janice M
authors.initials: JM
authors.lastname: Pluth
authors.forename: Maria A
authors.initials: MA
authors.lastname: DeBernardi
authors.forename: Maria A
authors.initials: MA
authors.lastname: DiBernardi
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: McDonald
authors.forename: Mirit I
authors.initials: MI
authors.lastname: Aladjem
mesh_terms: D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000502:physiology*; D004261:DNA Replication / Q000187:drug effects; D051747:DNA-Activated Protein Kinase / Q000737:chemistry / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D021122:Protein Subunits; D016196:S Phase
chemical_list: C468783:H2AX protein, human; D006657:Histones; D021122:Protein Subunits; D016590:Aphidicolin; D051747:DNA-Activated Protein Kinase