Project description:Exposure to UVB irradiation results in multitude of cellular responses including generation of reactive oxygen species (ROS) and DNA damage and is responsible for non-melanoma skin cancers (NMSCs). Although genetic mutation is well documented, the epi-mutation, the alteration in epigenetics, remains elusive. DNA methylation is a stable and heritable epigenetic change in the control of gene expression. Furthermore, it is unclear how the epigenomic DNA methylome would change during progression of UVB-induced carcinogenesis. In this study, we utilized CpG Methyl-seq to identify a genome-wide DNA CpG methylation, to profile the DNA methylation in ultraviolet B (UVB)-irradiated SKH-1 mouse skin epidermis and non-melanoma skin papillomas at various stages. Agilent mouse SureSelect Methyl-seq Kit was used for enrichment of about 3.3 million CpG sites in the mouse genome. Simultaneously, RNA-seq was performed to examine the corresponding transcriptome alterations. Bioinformatic analysis was utilized to identify differentially methylated and differentially expressed genes. The methylation profiles in mouse epidermis were altered by UVB-irradiation as time progresses. Comparing all epidermis samples at week-15 versus week-25, UVB had great impact on DNA methylome alteration. Examination of the differentially methylated regions (DMRs), most of the DMRs were located in the distal intragenic (>3 kb upstream of TSS or downstream of 3’ UTR) and the promoter regions. Interestingly, at week-25 the methylation profiles between the whole skin versus the tumor samples were different. Ingenuity Pathways Analysis (IPA) identified many cancer related pathways including PTEN, p53, Nrf2 and inflammatory signaling in UVB-irradiation induced carcinogenesis. Cell cycle regulation and cell growth related pathways including State3 signaling and estrogen-mediated S-phase entry were also identified. Additionally, some novel genes involved in skin carcinogenesis that were not previously reported were differentially methylated, including Enf2, Mgst2, Vegfa, and Cdk4. The methylation and expression of these genes were validated by pyrosequencing and qPCR. Taken together, the current study provides novel profiles of methylation and transcriptomic changes at different stages of carcinogenesis in UVB-irradiation induced NMSC and offer potential targets for prevention and treatment of NMSC at different stages of human skin cancer.

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UVB drives different stages of epigenome alterations during progression of skin cancer

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