title: UVA-induced DNA double-strand breaks result from the repair of clustered oxidative DNA damages.
abstract: UVA (320-400 nm) represents the main spectral component of solar UV radiation, induces pre-mutagenic DNA lesions and is classified as Class I carcinogen. Recently, discussion arose whether UVA induces DNA double-strand breaks (dsbs). Only few reports link the induction of dsbs to UVA exposure and the underlying mechanisms are poorly understood. Using the Comet-assay and γH2AX as markers for dsb formation, we demonstrate the dose-dependent dsb induction by UVA in G(1)-synchronized human keratinocytes (HaCaT) and primary human skin fibroblasts. The number of γH2AX foci increases when a UVA dose is applied in fractions (split dose), with a 2-h recovery period between fractions. The presence of the anti-oxidant Naringin reduces dsb formation significantly. Using an FPG-modified Comet-assay as well as warm and cold repair incubation, we show that dsbs arise partially during repair of bi-stranded, oxidative, clustered DNA lesions. We also demonstrate that on stretched chromatin fibres, 8-oxo-G and abasic sites occur in clusters. This suggests a replication-independent formation of UVA-induced dsbs through clustered single-strand breaks via locally generated reactive oxygen species. Since UVA is the main component of solar UV exposure and is used for artificial UV exposure, our results shine new light on the aetiology of skin cancer.
authors.affiliation: Dermatology Center Buxtehude (DZB), Buxtehude, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Greinert
authors.forename: B
authors.initials: B
authors.lastname: Volkmer
authors.forename: S
authors.initials: S
authors.lastname: Henning
authors.forename: E W
authors.initials: EW
authors.lastname: Breitbart
authors.forename: K O
authors.initials: KO
authors.lastname: Greulich
authors.forename: M C
authors.initials: MC
authors.lastname: Cardoso
authors.forename: Alexander
authors.initials: A
authors.lastname: Rapp
mesh_terms: D002478:Cells, Cultured; D002843:Chromatin / Q000737:chemistry / Q000528:radiation effects; D020552:Comet Assay; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004260:DNA Repair; D016166:Free Radical Scavengers / Q000494:pharmacology; D006657:Histones / Q000032:analysis / Q000378:metabolism; D006801:Humans; D010084:Oxidation-Reduction; D010766:Phosphorylation; D017382:Reactive Oxygen Species / Q000378:metabolism; D012867:Skin / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D002843:Chromatin; D016166:Free Radical Scavengers; C468783:H2AX protein, human; D006657:Histones; D017382:Reactive Oxygen Species