title: Base excision by thymine DNA glycosylase mediates DNA-directed cytotoxicity of 5-fluorouracil.
abstract: 5-Fluorouracil (5-FU), a chemotherapeutic drug commonly used in cancer treatment, imbalances nucleotide pools, thereby favoring misincorporation of uracil and 5-FU into genomic DNA. The processing of these bases by DNA repair activities was proposed to cause DNA-directed cytotoxicity, but the underlying mechanisms have not been resolved. In this study, we investigated a possible role of thymine DNA glycosylase (TDG), one of four mammalian uracil DNA glycosylases (UDGs), in the cellular response to 5-FU. Using genetic and biochemical tools, we found that inactivation of TDG significantly increases resistance of both mouse and human cancer cells towards 5-FU. We show that excision of DNA-incorporated 5-FU by TDG generates persistent DNA strand breaks, delays S-phase progression, and activates DNA damage signaling, and that the repair of 5-FU-induced DNA strand breaks is more efficient in the absence of TDG. Hence, excision of 5-FU by TDG, but not by other UDGs (UNG2 and SMUG1), prevents efficient downstream processing of the repair intermediate, thereby mediating DNA-directed cytotoxicity. The status of TDG expression in a cancer is therefore likely to determine its response to 5-FU-based chemotherapy.
authors.affiliation: Institute of Biochemistry and Genetics, Department of Biomedicine, University of Basel, Basel, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Kunz
authors.forename: Frauke
authors.initials: F
authors.lastname: Focke
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Saito
authors.forename: David
authors.initials: D
authors.lastname: Schuermann
authors.forename: Teresa
authors.initials: T
authors.lastname: Lettieri
authors.forename: Jim
authors.initials: J
authors.lastname: Selfridge
authors.forename: Primo
authors.initials: P
authors.lastname: Schär
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology* / Q000627:therapeutic use; D002453:Cell Cycle / Q000235:genetics; D016923:Cell Death / Q000187:drug effects*; D045744:Cell Line, Tumor; D004249:DNA Damage; D045647:DNA Glycosylases / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects*; D005472:Fluorouracil / Q000494:pharmacology* / Q000627:therapeutic use; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics; D015398:Signal Transduction; D044502:Thymine DNA Glycosylase / Q000378:metabolism*; D051981:Uracil-DNA Glycosidase / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; C492570:CCNO protein, human; D045647:DNA Glycosylases; C498095:SMUG1 protein, human; D044502:Thymine DNA Glycosylase; D051981:Uracil-DNA Glycosidase; D005472:Fluorouracil