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Genomically Incorporated 5-Fluorouracil that Escapes UNG-Initiated Base Excision Repair Blocks DNA Replication and Activates Homologous Recombination.

ABSTRACT: 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 ? 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.

SUBMITTER: Huehls AM

PROVIDER: S-EPMC4702102 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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Genomically Incorporated 5-Fluorouracil that Escapes UNG-Initiated Base Excision Repair Blocks DNA Replication and Activates Homologous Recombination.

Huehls Amelia M AM Huntoon Catherine J CJ Joshi Poorval M PM Baehr Carly A CA Wagner Jill M JM Wang Xiaoxiao X Lee Marietta Y MY Karnitz Larry M LM

Molecular pharmacology 20151022 1

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 ...[more]

PMID: 26494862

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Project description:Purpose: The aim of this study is to evaluate the global gene expression induced by OGG1-BER product 8-oxoG in mouse airways. Methods: RNA extracted from individual mouse lungs (experimental group: n=5) were pooled and a total 1 M-NM-<g RNA was used for Next-Generation Sequencing (NGS) analyses on an Illumina HiSeq 1000 sequencing system. Sequence analysis were performed in duplicate. First- and second-strand synthesis, adapter ligation and amplification of the library were performed using the Illumina TruSeq Sample Preparation Kit as recommended by the manufacturer (Illumina). Library quality was evaluated by using an Agilent DNA-1000 chip on an Agilent 2100 Bioanalyzer. Library DNA templates were quantitated by qPCR using known reference starndards. Cluster formation of the library of DNA templates was performed using the TruSeq PE Cluster Kit v3 (Illumina) and the Illumina cBot workstation. Paired-end, 50-base sequencing was performed with a TruSeq SBS kit v3 (Illumina) on the Illumina HiSeq 1000 by protocols defined by the manufacturer. Base call conversion to sequence reads was performed using CASAVA-1.8.2. Sequence data were analyzed with the Bowtie2, Tophat2 and GFOLD programs. Processed data are presented as reads per kilobase transcript per million (RPKM), normalized to the experimental control (RNA from saline-challenged lungs) and reported as fold change (test/control). Results: We mapped an average of 24.76 million sequence reads per sample and identified 23,337 transcripts in total RNA extracted from lungs of Balb/cJ mice as described in Methods. Approximately 10% of the transcripts showed differential expression between the saline-challenged control and 8-oxoguanine-challeged mouse lungs, with a fold change M-bM-^IM-%3.0. We validated the expression changes of 7 selected pro-inflammatory cytokines and chemokines of interest for our studies by qRT-PCR. Hierarchical clustering followed by Protein ANalysis THrough Evolutionary Relationships database (PANTHER) analysis of differentially expressed genes. Results showed overrepresentation of various biological functions (GO terms) including immune system process (GO:0002376; p=5.24e-12) among others. Pathway analysis (PANTHER) indicated that the most overrepresented pathway was inflammation mediated by chemokine and cytokine (P00031, p=<0.01). In addition to gene expression analysis, we confirmed OGG1M-bM-^@M-"8-oxoG-dependent RAS activation in lungs by active RAS pull-down assays, airways neutrophil accumulation by bronchoalveolar lavage fluid (BALF) differential cell counts and airway inflammation by histological examination (H&E staining) of lung sections. Conclusions: This is the first study at the whole-transcriptome level to show induction of innate immune response gene expression in mouse lungs after exposure to OGG1-BER product 8-oxoG. Balb/cJ mice (5 per group) were intranasally challenged with 8-oxoguanine (1 M-BM-5M, 60 M-BM-5l) for 30, 60 and 120 min. Control group mice were intranasally challenged with saline (60 M-BM-5l). RNA from individual mice whithin the same group was pooled and subjected to deep-sequencing analysis in duplicate using NGS on an Illumina HiSeq 1000 sequencing system. After alignment and processing, the resulting RPKM from treatment groups (8-oxoG-challenged) were normalized to the control group (saline-challenged).

Dataset Information

Genomically Incorporated 5-Fluorouracil that Escapes UNG-Initiated Base Excision Repair Blocks DNA Replication and Activates Homologous Recombination.

Publications

Genomically Incorporated 5-Fluorouracil that Escapes UNG-Initiated Base Excision Repair Blocks DNA Replication and Activates Homologous Recombination.

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