DNMTs are required for delayed genome instability caused by radiation

Abstract

The ability of ionizing radiation to initiate genomic instability has been harnessed in the clinic where the localized delivery of controlled doses of radiation is used to induce cell death in tumor cells. Though very effective as a therapy, tumor relapse can occur in vivo and its appearance has been attributed to the radio-resistance of cells with stem cell-like features. The molecular mechanisms underlying these phenomena are unclear but there is evidence suggesting an inverse correlation between radiation-induced genomic instability and global hypomethylation. To further investigate the relationship between DNA hypomethylation, radiosensitivity and genomic stability in stem-like cells we have studied mouse embryonic stem cells containing differing levels of DNA methylation due to the presence or absence of DNA methyltransferases. Unexpectedly, we found that global levels of methylation do not determine radiosensitivity. In particular, radiation-induced delayed genomic instability was observed at the Hprt gene locus only in wild-type cells. Furthermore, absence of Dnmt1 resulted in a 10-fold increase in de novo Hprt mutation rate, which was unaltered by radiation. Our data indicate that functional DNMTs are required for radiation-induced genomic instability, and that individual DNMTs play distinct roles in genome stability. We propose that DNMTS may contribute to the acquirement of radio-resistance in stem-like cells.

Keywords: :

• DNA Methylation
• DNA methyltransferase
• embryonic stem cells
• genomic instability
• radiation

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

The intellectual basis to this project was in a large part due to Dr. Mark Plumb, and we dedicate this paper to him. We would like to thank En Li and Taiping Chen for their kind gift of the mESC lines, and Munira Kadhim and Debbie Bowler for cytogenetic training. We are grateful for technical assistance from George Giotopoulos and Rohan Machhar. Finally, most felt thanks go to Yuri Dubrova for continued support, constructive discussions and critical reading of the manuscript. Funding for consumables came from NOTE and from the BBSRC for the PhD studentship to CAA. CT was supported by a Royal Society Dorothy Hodgkin Research Fellowship.

Financial Disclosures

Research was supported by NOTE, CAA was supported by a PhD studentship from BBSRC and CT by a Royal Society Dorothy Hodgkin Research Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.