UV damage, repair, and mutagenesis

Beckman Research Institute/City Of Hope, Duarte CA

Investigators

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Abstract

DESCRIPTION (provided by applicant): The incidence of sunlight-associated skin cancers, including melanoma and nonmelanoma tumors, has been on the rise in recent decades. DNA damage induced by the ultraviolet (UV) component of sunlight is thought to be responsible for the induction of mutations and the development of skin cancer in humans. Although the UVB (290-320 nm) fraction of sunlight is clearly involved in the induction of skin tumors, a role of UVA (320-400 nm) in particular in melanoma has been proposed but is less certain. To understand UV carcinogenesis, a more detailed knowledge of the molecular mechanisms of UV damage effects, DNA repair and mutagenesis is necessary. In one of the aims of this proposal, we will address the hypothesis that ultraviolet radiation, in addition to causing genetic mutations, produces changes in the epigenome of irradiated cells. We will determine if UV irradiation produces changes in DNA CpG methylation patterns and/or histone modification patterns in the genome of irradiated cells. Genome-wide approaches analyzing all annotated CpG islands and promoters as well as specific chromosome arms will be used to monitor the induced changes. Microarray analysis and high-throughput sequencing methodology will be applied. Next, we will characterize repair of UV-induced DNA lesions, in particular that of cyclobutane pyrimidine dimers, at a genome-scale level. We will determine if repair is targeted to active promoters of the genome. Our approach will be to use antibodies against CPDs and (6-4) photoproducts in immunoprecipitation experiments. The enriched fractions representing the photoproduct-containing DNA will be compared to the input fraction by using a microarray approach to quantify UV-induced DNA damage and repair genome-wide. We will determine if promoters of active genes are repaired preferentially. We will determine if a molecular link between sunlight exposure and melanoma can be demonstrated. We will try to define a UVA or UVB signature in the BRAF gene and the p16/CDKN2 gene by mapping different UV-induced DNA damage products forming at the nucleotide position(s) most prone to mutation in melanomas. In parallel, we will analyze a series of human melanoma tumor specimens obtained from sun-exposed and sun-protected body sites. Molecular changes in the form of mutations in specific genes, as well as epigenetic changes reflected by DNA CpG methylation patterns will be analyzed.