Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 14, Pages 5953-5958Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0610534104
Keywords
ultraviolet A radiation; photosensitizer; antioxidant; skin cancer
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Funding
- NIEHS NIH HHS [ES06070, R37 ES006070, R01 ES006070] Funding Source: Medline
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An increasingly popular theory ascribes UVA (>320-400 nm) carcinogenicity to the ability of this wavelength to trigger intracellular photosensitization reactions, thereby giving rise to promutagenic oxidative DNA damage. We have tested this theory both at the genomic and nucleotide resolution level in mouse embryonic fibroblasts carrying the lambda phage cll transgene. We have also tested the hypothesis that inclusion of a cellular photosensitizer (riboflavin) can intensify UVA-induced DNA damage and mutagenesis, whereas addition of an antioxidant (vitamin Q can counteract the induced effects. Cleavage assays with formamidopyrimidine DNA glycosylase (Fpg) coupled to alkaline gel electrophoresis and ligation-mediated PCR (LM-PCR) showed that riboflavin treatment (1 mu M) combined with UVA1 (340-400 nm) irradiation (7.68 J/cm(2)) or higher dose UVA1 irradiation alone induced Fpg-sensitive sites (indicative of oxidized and/or ring-opened purines) in the overall genome and in the cll transgene, respectively. Also, the combined treatment with riboflavin and UVA1 irradiation gave rise to single-strand DNA breaks in the genome and in the cll transgene determined by terminal transferase-dependent PCR (TD-PCR). A cotreatment with vitamin C (11 mM) efficiently inhibited the formation of the induced lesions. Mutagenicity analysis showed that riboflavin treatment combined with UVA1 irradiation or high-dose UVA1 irradiation alone significantly increased the relative frequency of cll mutants, both mutation spectra exhibiting significant increases in the relative frequency of G:C -> T:A transversions, the signature mutations of oxidative DNA damage. The induction of cll mutant frequency was effectively reduced consequent to a cotreatment with vitamin C. Our findings support the notion that UVA-induced photosensitization reactions are responsible for oxidative DNA damage leading to mutagenesis.
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