title: ATR is not required for p53 activation but synergizes with p53 in the replication checkpoint.
abstract: ATR (ataxia telangiectasia and Rad-3-related) is a protein kinase required for survival after DNA damage. A critical role for ATR has been hypothesized to be the regulation of p53 and other cell cycle checkpoints. ATR has been shown to phosphorylate p53 at Ser(15), and this damage-induced phosphorylation is diminished by expression of a catalytically inactive (ATR-kd) mutant. p53 function could not be examined directly in prior studies of ATR, however, because p53 was mutant or because cells expressed the SV40 large T antigen that blocks p53 function. To test the interactions of ATR and p53 directly we generated human U2OS cell lines inducible for either wild-type or kinase-dead ATR that also have an intact p53 pathway. Indeed, ATR-kd expression sensitized these cells to DNA damage and caused a transient decrease in damage-induced serine 15 phosphorylation of p53. However, we found that the effects of ATR-kd expression do not result in blocking the response of p53 to DNA damage. Specifically, prior ATR-kd expression had no effect on DNA damage-induced p53 protein up-regulation, p53-DNA binding, p21 mRNA up-regulation, or G(1) arrest. Instead of promoting survival via p53 regulation, we found that ATR protects cells by delaying the generation of mitotic phosphoproteins and inhibiting premature chromatin condensation after DNA damage or hydroxyurea. Although p53 inhibition (by E6 or MDM2 expression) had little effect on premature chromatin condensation, when combined with ATR-kd expression there was a marked loss of the replication checkpoint. We conclude that ATR and p53 can function independently but that loss of both leads to synergistic disruption of the replication checkpoint.
authors.affiliation: Department of Chemistry, Howard Hughes Medical Institute, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Nghiem
authors.forename: Peter K
authors.initials: PK
authors.lastname: Park
authors.forename: Yong-son
authors.initials: YS
authors.lastname: Kim Ys
authors.forename: Bimal N
authors.initials: BN
authors.lastname: Desai
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Schreiber
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000502:physiology*; D002470:Cell Survival; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D017931:DNA Primers; D004261:DNA Replication; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D012694:Serine / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D017931:DNA Primers; D016159:Tumor Suppressor Protein p53; D012694:Serine; D004247:DNA; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases