title: Cdc7-Dbf4 and the human S checkpoint response to UVC.
abstract: The S checkpoint response to ultraviolet radiation (UVC) that inhibits replicon initiation is dependent on the ATR and Chk1 kinases. Downstream effectors of this response, however, are not well characterized. Data reported here eliminated Cdc25A degradation and inhibition of Cdk2-cyclin E as intrinsic components of the UVC-induced pathway of inhibition of replicon initiation in human cells. A sublethal dose of UVC (1 J/m(2)), which selectively inhibits replicon initiation by 50%, failed to reduce the amount of Cdc25A protein or decrease Cdk2-cyclin E kinase activity. Cdc25A degradation was observed after irradiation with cytotoxic fluences of UVC, suggesting that severe inhibition of DNA chain elongation and activation of the replication checkpoint might be responsible for the UVC-induced degradation of Cdc25A. Another proposed effector of the S checkpoint is the Cdc7-Dbf4 complex. Dbf4 interacted weakly with Chk1 in vivo but was recognized as a substrate for Chk1-dependent phosphorylation in vitro. FLAG-Dbf4 formed complexes with endogenous Cdc7, and this interaction was stable in UVC-irradiated HeLa cells. Overexpression of FLAG- or Myc-tagged Dbf4 abrogated the S checkpoint response to UVC but not ionizing radiation. These findings implicate a Dbf4-dependent kinase as a possible target of the ATR- and Chk1-dependent S checkpoint response to UVC.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Heffernan
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Keziban
authors.initials: K
authors.lastname: Ünsal-Kaçmaz
authors.affiliation: Growth Control and Cancer Group, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: Alexandra N
authors.initials: AN
authors.lastname: Heinloth
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Simpson
authors.affiliation: Growth Control and Cancer Group, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Paules
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599; Center for Environmental Health and Susceptibility and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Aziz
authors.initials: A
authors.lastname: Sancar
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599; Center for Environmental Health and Susceptibility and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Marila
authors.initials: M
authors.lastname: Cordeiro-Stone
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599; Center for Environmental Health and Susceptibility and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599. Electronic address: wkarlk@med.unc.edu.
authors.forename: William K
authors.initials: WK
authors.lastname: Kaufmann
mesh_terms: D018797:Cell Cycle Proteins / Q000502:physiology* / Q000528:radiation effects; D002460:Cell Line; D002461:Cell Line, Transformed; D004261:DNA Replication / Q000235:genetics / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006367:HeLa Cells; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000502:physiology* / Q000528:radiation effects; D012093:Replicon / Q000235:genetics / Q000528:radiation effects; D016196:S Phase / Q000502:physiology / Q000528:radiation effects*; D015398:Signal Transduction / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D018797:Cell Cycle Proteins; C485678:DBF4 protein, human; C068619:CDC7 protein, human; D017346:Protein Serine-Threonine Kinases