title: RAD18 signals DNA polymerase IOTA to stalled replication forks in cells entering S-phase with DNA damage.
abstract: Endogenously generated reactive oxygen species and genotoxic carcinogens can covalently modify bases in cellular DNA. If not recognized and removed prior to S-phase of the cell cycle, such modifications can block DNA replication fork progression. If blocked forks are not are not resolved, they result in double strand breaks and cell death. Recent data indicate that the process of translesion DNA synthesis (TLS) is a highly conserved mechanism for bypassing lesions in template DNA. Although not fully understood, in yeast a ubiquitin ligase (RAD18) signals error-prone Y family polymerases to the blocked fork to bypass the damage with potentially mutagenic consequences. Homologs of the yeast proteins are found in higher eukaryotic cells, including human. We are examining the hypothesis that RAD18 acts as a proximal signal to Y-family polymerases to bypass damage, in a manner analogous to yeast but with additional layers of complexity. Here we report that RAD18 accumulates in nuclear foci after UV irradiation only in cells entering S-phase with DNA damage. These foci co-localize with proliferating cell nuclear antigen (PCNA). In addition, a newly described DNA polymerase, pol iota, also forms nuclear foci in a damage- and S-phase dependent manner. These data support our overall hypothesis that RAD18 accumulates at blocked forks and initiates the signal to recruit TLS polymerases.
authors.affiliation: Department of Pharmacology, James Graham Brown Cancer Center, University of Louisville, Louisville, KY 40202, USA.
authors.forename: Shelly
authors.initials: S
authors.lastname: Kakar
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Watson
authors.forename: W Glenn
authors.initials: WG
authors.lastname: McGregor
mesh_terms: D002453:Cell Cycle / Q000528:radiation effects; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D004261:DNA Replication / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005544:Forecasting; D006801:Humans; D008168:Lung / Q000166:cytology / Q000196:embryology; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D016196:S Phase / Q000235:genetics; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D014466:Ultraviolet Rays
chemical_list: D004268:DNA-Binding Proteins; D018809:Proliferating Cell Nuclear Antigen; C485954:RAD18 protein, human; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D004259:DNA-Directed DNA Polymerase