title: LINE-1 methylation status of endogenous DNA double-strand breaks.
abstract: DNA methylation and the repair of DNA double-strand breaks (DSBs) are important processes for maintaining genomic integrity. Although DSBs can be produced by numerous agents, they also occur spontaneously as endogenous DSBs (EDSBs). In this study, we evaluated the methylation status of EDSBs to determine if there is a connection between DNA methylation and EDSBs. We utilized interspersed repetitive sequence polymerase chain reaction (PCR), ligation-mediated PCR and combined bisulfite restriction analysis to examine the extent of EDSBs and methylation at long interspersed nuclear element-1 (LINE-1) sequences nearby EDSBs. We tested normal white blood cells and several cell lines derived from epithelial cancers and leukemias. Significant levels of EDSBs were detectable in all cell types. EDSBs were also found in both replicating and non-replicating cells. We found that EDSBs contain higher levels of methylation than the cellular genome. This hypermethylation is replication independent and the methylation was present in the genome at the location prior to the DNA DSB. The differences in methylation levels between EDSBs and the rest of the genome suggests that EDSBs are differentially processed, by production, end-modification, or repair, depending on the DNA methylation status.
authors.affiliation: Center of Excellence in Molecular Genetics of Cancer and Human Diseases, Department of Anatomy, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand.
authors.forename: Wichai
authors.initials: W
authors.lastname: Pornthanakasem
authors.forename: Narisorn
authors.initials: N
authors.lastname: Kongruttanachok
authors.forename: Chutipa
authors.initials: C
authors.lastname: Phuangphairoj
authors.forename: Chotika
authors.initials: C
authors.lastname: Suyarnsestakorn
authors.forename: Taweap
authors.initials: T
authors.lastname: Sanghangthum
authors.forename: Sornjarod
authors.initials: S
authors.lastname: Oonsiri
authors.forename: Wanpen
authors.initials: W
authors.lastname: Ponyeam
authors.forename: Thatchawan
authors.initials: T
authors.lastname: Thanasupawat
authors.forename: Oranart
authors.initials: O
authors.lastname: Matangkasombut
authors.forename: Apiwat
authors.initials: A
authors.lastname: Mutirangura
mesh_terms: D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D019175:DNA Methylation; D004261:DNA Replication; D015894:Genome, Human; D006801:Humans; D020084:Long Interspersed Nucleotide Elements; D016133:Polymerase Chain Reaction / Q000379:methods