Ultraviolet Radiation-induced DNA Damage Research Articles

Impact of vitamin D on ultraviolet-induced photoaging and skin diseases

Excessive exposure to ultraviolet (UV) radiation causes premature aging of the skin, known as photoaging. UV radiation induces DNA damage, oxidative stress, inflammatory reactions, and degradation of extracellular matrix (ECM) proteins, contributing to the aged skin phenotype. The skin synthesizes vitamin D upon UVB exposure, which plays a pivotal role in the proper function of multiple body systems. Vitamin D protects skin from photo-damage by repairing cyclobutane pyrimidine dimers, reversing oxidative stress, and reducing chronic inflammation. Moreover, various epidemiological studies have identified vitamin D deficiency as a marker for common dermatological disorders. Improvement of clinical outcomes with vitamin D supplementation further suggests its protective role against skin pathologies. This review comprehensively covers the involvement of vitamin D in combating UV-induced photoaging and various skin disorders, highlighting the significance of maintaining vitamin D adequacy for healthy skin.

Deformation and Trapping of Cell Nucleus Using Micropillar Substrates Possibly Affect UV Radiation Resistance of DNA

DNA damage induced by the ultraviolet (UV) light, which affects adversely on genome stability, causes many kinds of diseases. Thus, a biochemical or biomechanical method in DNA damage protection is well required. In the present study, we investigated the effects of mechanical factors, such as deformation of cell nucleus using polydimethylsiloxane (PDMS)-based microfabricated array of micropillars, on UV radiation resistance of DNA in cultured cells. The epithelial-like cells spread normally in the spaces between micropillars and their nuclei showed remarkable deformation and appeared to be “trapped” mechanically on the array of pillars. We found that the UV radiation-induced DNA damage estimated by the fluorescent intensity of the phospho-histone γ-H2AX, was significantly inhibited with the nucleus deformation on the pillars. The result indicates that the inhibition of UV radiation-induced DNA damages might be resulted from structural change of DNA caused by the mechanical stress of the cell nucleus on the micropillars.

Sustained pigmentation causes DNA damage and invokes translesion polymerase Polκ for repair in melanocytes.

Melanin protects skin cells from ultraviolet radiation-induced DNA damage. However, intermediates of eumelanin are highly reactive quinones that are potentially genotoxic. In this study, we systematically investigate the effect of sustained elevation of melanogenesis and map the consequent cellular repair response of melanocytes. Pigmentation increases γH2AX foci, DNA abasic sites, causes replication stress and invokes translesion polymerase Polκ in primary human melanocytes, as well as mouse melanoma cells. Confirming the causal link, CRISPR-based genetic ablation of tyrosinase results in depigmented cells with low Polκ levels. During pigmentation, Polκ activates replication stress response and keeps a check on uncontrolled proliferation of cells harboring melanin-damaged DNA. The mutational landscape observed in human melanoma could in part explain the error-prone bypass of DNA lesions by Polκ, whose absence would lead to genome instability. Thereby, translesion polymerase Polκ is a critical response of pigmenting melanocytes to combat melanin-induced DNA alterations. Our study illuminates the dark side of melanin and identifies (eu)melanogenesis as a key missing link between tanning response and mutagenesis, mediated via the necessary evil translesion polymerase, Polκ.

Opsin 3 mediates UVA-induced keratinocyte supranuclear melanin cap formation

Solar ultraviolet (UV) radiation-induced DNA damage is a major risk factor for skin cancer development. UV-induced redistribution of melanin near keratinocyte nuclei leads to the formation of a supranuclear cap, which acts as a natural sunscreen and protects DNA by absorbing and scattering UV radiation. However, the mechanism underlying the intracellular movement of melanin in nuclear capping is poorly understood. In this study, we found that OPN3 is an important photoreceptor in human epidermal keratinocytes and is critical for UVA-mediated supranuclear cap formation. OPN3 mediates supranuclear cap formation via the calcium-dependent G protein-coupled receptor signaling pathway and ultimately upregulates Dync1i1 and DCTN1 expression in human epidermal keratinocytes via activating calcium/CaMKII, CREB, and Akt signal transduction. Together, these results clarify the role of OPN3 in regulating melanin cap formation in human epidermal keratinocytes, greatly expanding our understanding of the phototransduction mechanisms involved in physiological function in skin keratinocytes.

099 Aspirin protects against UVB-induced DNA damage through activation of AMP kinase

The anti-inflammatory and chemopreventive activities of aspirin (ASA) may be mediated through its cyclooxygenase (COX) inhibitor function. We have previously shown that ASA can protect against ultraviolet (UV) radiation-induced skin inflammation and DNA damage, but the role of inflammation in UV-induced DNA damage and the mechanism underlying ASA protection are poorly characterized. Using immunodeficient NSG mice and immunocompetent C57BL/6 mice treated with immune cell-depleting antibodies, we found that inflammation was not required for UVB-induced 8-oxoguanine (8-OG) and cyclobutane pyrimidine dimers (CPD) in vivo.

Xeroderma pigmentosum: an updated review.

BackgroundEarly recognition of xeroderma pigmentosum is important to minimize the complications arising from the harmful effects of exposure to ultraviolet radiation. This narrative review aims to familiarize physicians with the clinical features, diagnosis and management of xeroderma pigmentosum.MethodsA search was conducted in December 2021 in PubMed Clinical Queries using the key term “xeroderma pigmentosum”. The search strategy included all clinical trials, observational studies and reviews published within the past 10 years. The information retrieved from the search was used in the compilation of this article.ResultsXeroderma pigmentosum is a condition of abnormal DNA repair of ultraviolet radiation-induced and oxidative DNA damage, which leads to increased skin cancer susceptibility. Approximately 50% of patients with xeroderma pigmentosum have increased photosensitivity and certain types of xeroderma pigmentosum are more prone to ocular disease and progressive neurodegeneration depending on the causative mutation. The diagnosis should be suspected in patients with increased photosensitivity and characteristic cutaneous, ophthalmological and neurological findings. A definite diagnosis can be made by the identification of biallelic mutation in one of the causative genes. Strict and consistent sun avoidance and protection and early detection and treatment of premalignant and malignant skin lesions are the mainstays of management. Treatment options for actinic keratosis include cryotherapy, topical imiquimod, topical 5-fluorouracil, chemical peeling, excision, CO2 laser resurfacing, fractional/pulsed laser therapy, and photodynamic therapy. Cutaneous malignancy can be treated by photodynamic therapy, curettage and electrodesiccation, or surgical excision. Oral isotretinoin, oral niacinamide, topical imiquimod and topical fluorouracil can be used for the prevention of skin malignancy. Treatment options for poikiloderma include chemical peeling, dermabrasion and laser resurfacing. Methylcellulose eyedrops and soft ultraviolet-protective contact lenses may be used to keep the cornea moist and protect against the harmful effects of keratitis sicca. Investigational therapies include the use of T4 endonuclease-V liposome lotion and oral nicotinamide to reduce the rate of actinic keratoses and non-melanoma skin cancers and gene therapy for radical cure of this condition.ConclusionAlthough currently there is no cure for xeroderma pigmentosum, increased awareness and early diagnosis of the condition, followed by rigorous sun avoidance and protection and optimal management, can dramatically improve the quality of life and life expectancy.

Type I Interferons Enhance the Repair of Ultraviolet Radiation-Induced DNA Damage and Regulate Cutaneous Immune Suppression.

Type I interferons (IFNs) are important enhancers of immune responses which are downregulated in human cancers, including skin cancer. Solar ultraviolet (UV) B radiation is a proven environmental carcinogen, and its exposure contributes to the high prevalence of skin cancer. The carcinogenic effects of UV light can be attributed to the formation of cyclobutane pyrimidine dimers (CPD) and errors in the repair and replication of DNA. Treatment with a single dose of UVB (100 mJ/cm2) upregulated IFNα and IFNβ in the skin of C57BL/6 mice. IFNα and IFNβ were predominantly produced by CD11b+ cells. In mice lacking the type I IFN receptor 1 (IFNAR1), the repair of CPD following cutaneous exposure to a single dose of UVB (100 mJ/cm2) was decreased. UVB induced the expression of the DNA repair gene xeroderma pigmentosum A (XPA) in wild-type (WT) mice. In contrast, such treatment in IFNAR1 (IFNAR1-/-) mice downregulated XPA. A local UVB regimen consisting of UVB radiation (150 mJ/cm2) for 4 days followed by sensitization with hapten 2,4, dinitrofluorobenzene (DNFB) resulted in significant suppression of immune responses in both WT and IFNAR1-/- mice. However, there were significantly higher CD4+CD25+Foxp3+ regulatory T-cells in the draining lymph nodes of IFNAR1-/- mice in comparison to WT mice. Overall, our studies reveal a previously unknown action of type I IFNs in the repair of photodamage and the prevention of UVB-induced immune suppression.

PTEN: A novel target for vitamin D in melanoma

Melanoma is the most dangerous form of skin cancer, with poor prognosis in advanced stages. Vitamin D, also produced by ultraviolet radiation, is known for its anti-proliferative properties in some cancers including melanoma. While vitamin D deficiency has been associated with advanced melanoma stage and higher levels of vitamin D have been associated with better outcomes, the role for vitamin D in melanoma remains unclear. Vitamin D synthesis is initiated upon UVB exposure of skin cells and results in formation of the active metabolite 1,25-dihydroxyvitamin D3 (1,25D). We have previously demonstrated that 1,25D plays a role in protection against ultraviolet radiation-induced DNA damage, immune suppression, and skin carcinogenesis. In this study 1,25D significantly reduced cell viability and increased caspase levels in human melanoma cell lines. This effect was not present in cells that lacked both phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a well-known tumour suppressor, and the vitamin D receptor (VDR). PTEN is frequently lost or mutated in melanoma. Incubation of selected melanoma cell lines with 1,25D resulted in significant increases in PTEN levels and downregulation of the AKT pathway and its downstream effectors. This suggests that 1,25D may act to reduce melanoma cell viability by targeting PTEN.

Toll-Like Receptor-4 Antagonist Enhances the Repair of Ultraviolet Radiation-Induced DNA Damage and Augments Anti-Tumor Immune Responses in Mice.

Simple SummaryUltraviolet B (UVB) radiation is largely responsible for the development of skin cancer. When UVB-induced DNA damage in cells is not repaired, it can lead to the initiation of non-melanoma skin cancers. Xeroderma pigmentosum (XP) disease is caused by a defect in the repair of damaged DNA. Toll-like receptor-4 (TLR4) and NLR family pyrin domain containing 3 (NLRP3) belong to the family of innate immune receptors and are highly expressed in skin tumors. In this study, we determined the mechanism through which TLR4 inhibitor TAK-242 regulates inflammation and prevents skin cancer.Ultraviolet (UV) irradiation of the skin is related to the development of skin cancer. UVB also causes DNA damage in the form of cyclobutane pyrimidine dimers (CPDs), which can result in stable mutations. Toll-like receptor 4 (TLR4), a component of innate immunity, plays a key role in cancer. Previous studies from our laboratory have observed that TLR4 deficiency resulted in the repair of UVB-induced DNA damage, inhibition of UVB-induced immune suppression, and carcinogenesis. In this study, we determined the efficacy of TLR4 antagonist TAK-242 in regulation of UVB-induced DNA damage, inflammation, and tumor development. Our results indicate that TAK-242 treatment increased the expression of xeroderma pigmentosum group A (XPA) mRNA, resulting in the repair of UVB-induced CPDs in skin of SKH-1 mice. Treatment with TAK-242 also inhibited the activation of NLR family pyrin domain containing 3 (NLRP3) in UVB-exposed skin of SKH-1 mice. Cutaneous carcinogenesis was significantly reduced in mice treated with TAK-242 in comparison to vehicle-treated mice. The proinflammatory cytokines IL-1β, IL-6, and TNF-α were also found to be significantly greater in vehicle-treated mice than TAK-242-treated mice. Finally, treatment with TAK-242 augmented anti-tumor immune responses in mice. Our data provide further evidence that activation of the TLR4 pathway promotes the development of UV-induced non-melanoma skin cancer mediated at least in part on its negative effects on DNA damage. Moreover, treatment with the TLR4 inhibitor TAK-242 may be effective for prevention of skin cancer.

Systemic photoprotection in 2021.

Systemic photoprotection aims to negate the negative effects of ultraviolet radiation-induced DNA damage. Systemic supplements may be used as a monotherapy or in combination with topical sunscreens. Using the keywords 'carotenoids', 'flavonoids', 'systemic photoprotection', 'polyphenols' and 'polypodium leucotomos extract', we searched the databases MEDLINE and EMBASE to find relevant English-language articles. Few trials have supported the use of any of these supplements as monotherapy, impeding the recommendation of these systemic supplements as an alternative to sunscreen for photoprotection. Nicotinamide has exhibited clinically relevant benefits in reducing nonmelanoma skin cancers in trials and could be recommended as an adjunctive therapy for the most vulnerable indviduals. Further research is required, which needs to be of higher statistical power, using more clinically meaningful outcome measures with comparison to the current gold standard of care (topical photoprotection) to support the use of alternative therapies in clinical practice.

HucMSC exosome-delivered 14-3-3ζ alleviates ultraviolet radiation-induced photodamage via SIRT1 pathway modulation.

Exosomes derived from human umbilical cord mesenchymal stem cells (hucMSC-ex) are nano-sized membrane-bound vesicles that have been reported to facilitate skin regeneration and repair. However, the roles played by hucMSC-ex in ultraviolet (UV) radiation-induced skin photodamage and the underlying mechanisms remain unknown. To investigate the functions of hucMSC-ex in a rat model of acute skin photodamage, immunofluorescence and immunohistochemical staining, quantitative real-time-polymerase chain reaction (qRT-PCR), western blot, and gene silencing assays were performed. We found that the in vivo subcutaneous injection of hucMSC-ex elicited antioxidant and anti-inflammatory effects against UV radiation-induced DNA damage and apoptosis. Further studies showed that the sirtuin 1 (SIRT1) expression level in skin keratinocytes (HaCaT) decreased in a time- and dose-dependent manner under in vitro UV radiation induced-oxidative stress conditions, which could be reversed by treatment with hucMSC-ex. The activation of SIRT1 significantly attenuated UV- and H2O2-induced cytotoxic damage by inhibiting oxidative stress and promoting the activation of autophagy. Our study found that 14-3-3ζ protein, which was delivered by hucMSC-ex, exerted a cytoprotective function via the modulation of a SIRT1-dependent antioxidant pathway. Collectively, our findings indicated that hucMSC-ex might represent a new potential agent for preventing or treating UV radiation-induced skin photodamage and aging.

513 The toll like receptor-4 antagonist, TAK-242, enhances repair of ultraviolet radiation-induced DNA damage and inhibits UVB-induced tumor development in mice

513 The toll like receptor-4 antagonist, TAK-242, enhances repair of ultraviolet radiation-induced DNA damage and inhibits UVB-induced tumor development in mice

Genome-Wide Dynamic Evaluation of the UV-Induced DNA Damage Response.

Genetic screens in Saccharomyces cerevisiae have allowed for the identification of many genes as sensors or effectors of DNA damage, typically by comparing the fitness of genetic mutants in the presence or absence of DNA-damaging treatments. However, these static screens overlook the dynamic nature of DNA damage response pathways, missing time-dependent or transient effects. Here, we examine gene dependencies in the dynamic response to ultraviolet radiation-induced DNA damage by integrating ultra-high-density arrays of 6144 diploid gene deletion mutants with high-frequency time-lapse imaging. We identify 494 ultraviolet radiation response genes which, in addition to recovering molecular pathways and protein complexes previously annotated to DNA damage repair, include components of the CCR4-NOT complex, tRNA wobble modification, autophagy, and, most unexpectedly, 153 nuclear-encoded mitochondrial genes. Notably, mitochondria-deficient strains present time-dependent insensitivity to ultraviolet radiation, posing impaired mitochondrial function as a protective factor in the ultraviolet radiation response.

Ultraviolet Radiation and Melanomagenesis: From Mechanism to Immunotherapy.

Melanoma is the deadliest form of skin cancer, and nearly 90% of melanomas are believed to be caused by ultraviolet radiation (UVR), mainly from sunlight. UVR induces DNA damage, forming products such as cyclobutane pyrimidine dimers (CPD) and 6-4-pyrimidone photoproducts (6-4PP) in a wavelength-dependent manner and causes oxidative DNA damage. These DNA lesions lead to DNA mutations and contribute to the formation of melanoma. In this review, we discuss the protective role of melanocytes against UV-induced DNA damage and how genetic variations, including those in p53 and melanocortin-1 receptor (MC1R), or epigenetic histone modifications in melanocytes result in a tendency toward melanoma. We also provide a summary of prevention and treatment strategies against melanoma, including the most recent immunotherapies. Collectively, this work contributes to the understanding of the molecular pathogenesis of UV-induced melanoma.

Regulation of ultraviolet radiation-induced cutaneous DNA damage by type I interferons

Abstract Type I interferons (IFNs) are cytokines, that are important regulators of immune responses and are downregulated in human cancers, including skin cancer. Solar ultraviolet (UV) radiation is a proven environmental carcinogen, and exposure to solar radiation contributes to the high prevalence of skin cancer. The carcinogenic effects of UV light can be attributed to the formation of cyclobutane pyrimidine dimers (CPD) and errors in repair and replication of DNA. It is believed that type I IFNs reduce cellular proliferation and allow DNA repair in various diseases. Interferon receptor 1 (IFNAR1) is critical for signaling of type I IFNs. We hypothesized that type I IFNs (IFNα/β) will repair UVB induced DNA damage in mice. To test our hypothesis, shaved mice lacking IFNAR1 and wild type mice on a C57BL/6 background were irradiated with single dose of UVB radiation (100 mJ/cm2). Skin samples were examined for CPD by immunofluorescence and ELISA. We found that mice lacking IFNAR1 had more CPD as evident by ELISA and histology. In order to determine the cell type, which produces type I IFNs in skin after UVB exposure, single cell suspensions were prepared from irradiated skin samples and stained for type I IFNs using flow cytometry. We found that type I IFNs were produced by inflammatory monocytes (CD45+CD11b+Ly6C+). We also found that DNA repair gene XPA was downregulated in the mice lacking IFNAR1. In conclusion, our studies show that mice lacking the IFNAR1 had decreased repair of UVB induced CPD in the skin. Our ongoing studies will elucidate whether type I IFNs regulate development of UVB induced skin tumors.

USP7-mediated deubiquitination differentially regulates CSB but not UVSSA upon UV radiation-induced DNA damage

ABSTRACT Cockayne syndrome group B (CSB) protein participates in transcription-coupled nucleotide excision repair. The stability of CSB is known to be regulated by ubiquitin-specific protease 7 (USP7). Yet, whether USP7 acts as a deubiquitinating enzyme for CSB is not clear. Here, we demonstrate that USP7 deubiquitinates CSB to maintain its levels after ultraviolet (UV)-induced DNA damage. While both CSB and UV-stimulated scaffold protein A (UVSSA) exhibit a biphasic decrease and recovery upon UV irradiation, only CSB recovery depends on USP7, which physically interacts with and deubiquitinates CSB. Meanwhile, CSB overexpression stabilizes UVSSA, but decrease UVSSA’s presence in nuclease-releasable/soluble chromatin, and increase the presence of ubiquitinated UVSSA in insoluble chromatin alongside CSB-ubiquitin conjugates. Remarkably, CSB overexpression also decreases CSB association with USP7 and UVSSA in soluble chromatin. UVSSA exists in several ubiquitinated forms, of which mono-ubiquitinated form and other ubiquitinated UVSSA forms are detectable upon 6xHistidine tag-based purification. The ubiquitinated UVSSA forms, however, are not cleavable by USP7 in vitro. Furthermore, USP7 disruption does not affect RNA synthesis but decreases the recovery of RNA synthesis following UV exposure. These results reveal a role of USP7 as a CSB deubiquitinating enzyme for fine-tuning the process of TC-NER in human cells.

Cyclic stretch-induced mechanical stress to the cell nucleus inhibits ultraviolet radiation-induced DNA damage.

Ultraviolet (UV) radiation exerts adverse effects on genome stability, alters the normal state of life, and causes several diseases by inducing DNA damage. Although mechanical stimulation such as stretching has significant effects on the prevention and treatment of diseases, its influence on nuclear morphology and/or intranuclear functions involving resistance to DNA damage remains unknown. Here, we investigated the effects of mechanical stimulation by cyclic stretching on nuclear morphology and resistance of DNA to UV damage in NIH3T3 fibroblasts. Adherent cells on silicone elastic membranes were subjected to ~ 10% cyclic uniaxial stretch at a frequency of 0.5Hz for 12h. As a result, the intracellular actin cytoskeleton and nucleus were found to be elongated and aligned in the direction of zero normal strain (~ 62° with respect to the stretch direction) in an actomyosin tension-dependent manner. The nuclei of the stretched cells were dramatically compressed by the reorganized actin stress fibers located on their apical and both sides, and a significant increase in the intranuclear DNA density was observed. Intercellular tension, as assessed with live cell atomic force microscopy imaging, also increased following exposure to cyclic stretch. The UV radiation-induced DNA damage, estimated from the fluorescence intensity of the phospho-histone γ-H2AX, significantly decreased in these stretched cells. These results indicate that the cyclic stretch-induced morphological changes in the nucleus may improve the UV radiation resistance of cells, probably owing to the intracellular force-induced condensation of chromatin. To our knowledge, this is the first study to demonstrate the inhibition of the UV radiation-induced DNA damage by mechanical stimulation.

Structure and mechanism of pyrimidine-pyrimidone (6-4) photoproduct recognition by the Rad4/XPC nucleotide excision repair complex.

Failure in repairing ultraviolet radiation-induced DNA damage can lead to mutations and cancer. Among UV-lesions, the pyrimidine–pyrimidone (6-4) photoproduct (6-4PP) is removed from the genome much faster than the cyclobutane pyrimidine dimer (CPD), owing to the more efficient recognition of 6-4PP by XPC-RAD23B, a key initiator of global-genome nucleotide excision repair (NER). Here, we report a crystal structure of a Rad4–Rad23 (yeast XPC-Rad23B ortholog) bound to 6-4PP-containing DNA and 4-μs molecular dynamics (MD) simulations examining the initial binding of Rad4 to 6-4PP or CPD. This first structure of Rad4/XPC bound to a physiological substrate with matched DNA sequence shows that Rad4 flips out both 6-4PP-containing nucleotide pairs, forming an ‘open’ conformation. The MD trajectories detail how Rad4/XPC initiates ‘opening’ 6-4PP: Rad4 initially engages BHD2 to bend/untwist DNA from the minor groove, leading to unstacking and extrusion of the 6-4PP:AA nucleotide pairs towards the major groove. The 5′ partner adenine first flips out and is captured by a BHD2/3 groove, while the 3′ adenine extrudes episodically, facilitating ensuing insertion of the BHD3 β-hairpin to open DNA as in the crystal structure. However, CPD resists such Rad4-induced structural distortions. Untwisting/bending from the minor groove may be a common way to interrogate DNA in NER.

Vemurafenib impairs the repair of ultraviolet radiation-induced DNA damage.

Targeted therapy with the BRAF inhibitors vemurafenib and dabrafenib is an effective treatment regimen in patients with advanced melanoma carrying the BRAF V600E mutation. A common side effect is an enhanced rate of nonmelanoma skin cancer (NMSC). BRAF inhibition leads to a paradoxical enhanced MAPK signalling in BRAF wild-type cells, which might in part be responsible for the enhanced NMSC burden. It is known that disturbances of DNA repair result in an increased rate of NMSC. In the present study, it was investigated whether BRAF inhibitors might interfere with the repair of ultraviolet radiation-induced DNA damage in vitro. Epidermal keratinocytes of 11 Caucasian donors were treated with vemurafenib or dabrafenib and, 24 h later, exposed to ultraviolet A. DNA damage and repair capacity were analysed using south-western slot blot detecting cyclobutane pyrimidine dimers. Using PCR and DNA sequencing, RAS mutations and human papilloma virus genes were investigated. RNA expression was determined using a Gene Expression Chip and qRT-PCR. In 36% of keratinocytes, vemurafenib hampers the repair of ultraviolet A-induced DNA damage. No changes in DNA repair were observed with dabrafenib, indicating a possible substance-specific effect of vemurafenib. In none of the keratinocytes, pre-existing RAS mutations or human papilloma virus-associated DNA sequences were detected. The expression of the interferon-related damage resistance signature is decreased upon vemurafenib treatment in 36% of donors. The enhanced rate of NMSC in patients treated with vemurafenib might be partly related to a vemurafenib-driven impaired capacity for DNA repair.

Ultraviolet radiation-induced DNA damage is prognostic for outcome in melanoma.

The melanoma genome is dominated by ultraviolet radiation (UVR)-induced mutations. Their relevance in disease progression is unknown. Here we classify melanomas by mutation signatures and identify ten recurrently mutated UVR signature genes that predict patient survival. We validate these findings in primary human melanomas; in mice we show that this signature is imprinted by short-wavelength UVR and that four exposures to UVR are sufficient to accelerate melanomagenesis.