Base excision by thymine DNA glycosylase mediates DNA-directed cytotoxicity of 5-fluorouracil

• Published in: PLoS biology 2009-04, Vol.7 (4), p.e91-e1000091
• Main Authors: Kunz, Christophe, Focke, Frauke, Saito, Yusuke, Schuermann, David, Lettieri, Teresa, Selfridge, Jim, Schär, Primo
• Format: Article
• Language: English
• Subjects: Animals; Antimetabolites, Antineoplastic - pharmacology; Antimetabolites, Antineoplastic - therapeutic use; Apoptosis; Binding sites; Biochemistry; Cancer; Cancer therapies; Cell Biology; Cell Cycle - genetics; Cell Death - drug effects; Cell Line, Tumor; Cell-mediated cytotoxicity; Cytotoxicity; Deoxyribonucleic acid; Developmental Biology; DNA; DNA Damage; DNA glycosylases; DNA Glycosylases - metabolism; DNA Repair - drug effects; Experiments; Fluorouracil; Fluorouracil - pharmacology; Fluorouracil - therapeutic use; Genetics and Genomics; Kinases; Metabolites; Mice; Molecular Biology; Neoplasms - drug therapy; Neoplasms - genetics; Physiological aspects; Proteins; Signal Transduction; Thymine DNA Glycosylase - metabolism; Uracil-DNA Glycosidase - metabolism
• ISSN: 1545-7885; 1544-9173; 1545-7885
• DOI: 10.1371/journal.pbio.1000091

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.