SUMMARY (Parental Award) Biological processes that guard against melanoma are generally successful. Thus, to understand melanoma etiology we must identify the flaws in these mechanisms that lead to tumorigenesis. This proposal will elucidate deficiencies in the cellular mechanisms that combat UV damage and define the tumorigenic consequences of melanocyte pigment production. Our studies will improve mechanistic understanding of melanoma etiology by revealing gaps in the physiological processes that block UV carcinogenesis. We hypothesize that melanoma progression is influenced by melanin production and accelerated by the persistence of unresolved DNA lesions specific to the initiating UV wavelength. To test this hypothesis we will define how full-spectrum (UVA/B) and partitioned solar irradiation (UVA or UVB) influence the onset and progression of melanoma in genetically relevant, Braf- and Nras-mutant mouse models. We will elucidate transcriptional and mutational patterns enriched in tumors driven by each UV spectrum and oncogene, and use this information to define how UV lesions escape repair (Aim 1). Next, we will cross our models to eumelanotic (black), amelanotic (albino) or pheomelanotic (red/yellow) alleles to determine how melanin impacts the formation, progression and immunotherapeutic response of Braf- and Nras-mutant melanomas accelerated by different UV spectra (Aim 2). Knowledge gained from these experiments will aid in the development of melanoma preventatives that progress beyond sunscreens, including interventions that mitigate UV carcinogenesis after an exposure or reduce melanoma risk in individuals with more photosensitive skin types.