title: The role of nucleotide excision repair in protecting embryonic stem cells from genotoxic effects of UV-induced DNA damage.
abstract: In this study the role of nucleotide excision repair (NER) in protecting mouse embryonic stem (ES) cells against the genotoxic effects of UV-photolesions was analysed. Repair of cyclobutane pyrimidine dimers (CPD) in transcribed genes could not be detected whereas the removal of (6-4) photoproducts (6-4PP) was incomplete, already reaching its maximum (30%) 4 h after irradiation. Measurements of repair replication revealed a saturation of NER activity at UV doses >5 J/m2 while at a lower dose (2.5 J/m2) the repair kinetics were similar to those in murine embryonic fibroblasts (MEFs). Cytotoxic and mutagenic effects of photolesions were determined in ES cells differing in NER activity. ERCC1-deficient ES cells were hypermutable (10-fold) compared to wild-type cells, indicating that at physiologically relevant doses ES cells efficiently remove photolesions. The effect of the NER deficiency on cytoxicity was only 2-fold. Exposure to high UV doses (10 J/m2) resulted in a rapid and massive induction of apoptosis. Possibly, to avoid the accumulation of mutated cells, ES cells rely on the induction of a strong apoptotic response with a simultaneous shutting down of NER activity.
authors.affiliation: Department of Radiation Genetics and Chemical Mutagenesis-MGC, Leiden University Medical Center, PO Box 9503, 2300 RA Leiden, The Netherlands.
authors.forename: P P
authors.initials: PP
authors.lastname: Van Sloun
authors.forename: J G
authors.initials: JG
authors.lastname: Jansen
authors.forename: G
authors.initials: G
authors.lastname: Weeda
authors.forename: L H
authors.initials: LH
authors.lastname: Mullenders
authors.forename: A A
authors.initials: AA
authors.lastname: van Zeeland
authors.forename: P H
authors.initials: PH
authors.lastname: Lohman
authors.forename: H
authors.initials: H
authors.lastname: Vrieling
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D002460:Cell Line; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D004720:Endonucleases; D016158:Genes, p53; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D051379:Mice; D009154:Mutation; D011506:Proteins / Q000378:metabolism; D017231:Proto-Oncogene Proteins c-mos / Q000235:genetics; D011740:Pyrimidine Dimers / Q000235:genetics; D013234:Stem Cells / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D004268:DNA-Binding Proteins; D011506:Proteins; D011740:Pyrimidine Dimers; D007041:Hypoxanthine Phosphoribosyltransferase; D017231:Proto-Oncogene Proteins c-mos; D004720:Endonucleases; C499360:Ercc1 protein, mouse