RNA-seq of UV irradiated human epidermal melanocytes from neonatal foreskin, HEMn-DP2.

UVR is the principal risk factor for melanoma development. While the role of UVR in DNA mutagenesis is incontrovertible, it remains controversial what role UVR-induced mutations play in melanoma genesis. To better understand how UVR is contributing to melanoma development, we investigated the non-mutational effect of UVR on the epigenome, specifically DNA methylation. Aberrant DNA methylation changes are a hallmark in melanoma; however, there are few reports on the effects of UVR on DNA methylation. We exposed melanocytes to UVR and cultured them for one-month to detect hertible and stable changes in DNA methylation. We found both hyper and hypo methylated sites after UVR exposure. While many of these changes occured outside of promoters and areas of active gene expression, there were changes in promoter DNA methylation changes that correlated with changes in gene expression. These changes also correlated with those found in melanoma and UVR sensitive sites were prognostic of patient overall survival. Our work shows for the first time UVR induced DNA methylation changes in melanocytes and may be another way in which UVR contributes to melanoma development. Melanocyte cells were UV irradiated with a broad band UVR spectrum ( UVA & UVB) for a total dos of 175 J/m2. Cells were cultured for one month before performing reduced representation bisulfite sequencing (RRBS). Genomic DNA was digested by MspI restriction enzyme, which recgonizes the CCGG sequence, and then subjected to bisulfite converstion. Methylated cytosines within CpG sites are protected from sodium bisulfite conversion and remain unchanged. Unmethylated cyotosines undergo a reaction with sodium bisulfite resulting in a base change from cytosine to uracil. This base change allows for the detection of methylated versus unmethylated CpG sites through high throughput sequencing.