RT Journal Article
SR Electronic
T1 Genomically Incorporated 5-Fluorouracil that Escapes UNG-Initiated Base Excision Repair Blocks DNA Replication and Activates Homologous Recombination
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 53
OP 62
DO 10.1124/mol.115.100164
VO 89
IS 1
A1 Amelia M. Huehls
A1 Catherine J. Huntoon
A1 Poorval M. Joshi
A1 Carly A. Baehr
A1 Jill M. Wagner
A1 Xiaoxiao Wang
A1 Marietta Y. Lee
A1 Larry M. Karnitz
YR 2016
UL http://molpharm.aspetjournals.org/content/89/1/53.abstract
AB 5-Fluorouracil (5-FU) and its metabolite 5-fluorodeoxyuridine (FdUrd, floxuridine) are chemotherapy agents that are converted to 5-fluorodeoxyuridine monophosphate (FdUMP) and 5-fluorodeoxyuridine triphosphate (FdUTP). FdUMP inhibits thymidylate synthase and causes the accumulation of uracil in the genome, whereas FdUTP is incorporated by DNA polymerases as 5-FU in the genome; however, it remains unclear how either genomically incorporated U or 5-FU contributes to killing. We show that depletion of the uracil DNA glycosylase (UNG) sensitizes tumor cells to FdUrd. Furthermore, we show that UNG depletion does not sensitize cells to the thymidylate synthase inhibitor (raltitrexed), which induces uracil but not 5-FU accumulation, thus indicating that genomically incorporated 5-FU plays a major role in the antineoplastic effects of FdUrd. We also show that 5-FU metabolites do not block the first round of DNA synthesis but instead arrest cells at the G1/S border when cells again attempt replication and activate homologous recombination (HR). This arrest is not due to 5-FU lesions blocking DNA polymerase δ but instead depends, in part, on the thymine DNA glycosylase. Consistent with the activation of HR repair, disruption of HR sensitized cells to FdUrd, especially when UNG was disabled. These results show that 5-FU lesions that escape UNG repair activate HR, which promotes cell survival.