Formation of UV-induced DNA damage contributing to skin cancer development

Cyclobutane pyrimidine dimers from UVB exposure induce a hypermetabolic state in keratinocytes via mitochondrial oxidative stress

Ultraviolet B radiation (UVB) is an environmental complete carcinogen, which induces and promotes keratinocyte carcinomas, the most common human malignancies. UVB induces the formation of cyclobutane pyrimidine dimers (CPDs). Repairing CPDs through nucleotide excision repair is slow and error-prone in placental mammals. In addition to the mutagenic and malignancy-inducing effects, UVB also elicits poorly understood complex metabolic changes in keratinocytes, possibly through CPDs. To determine the effects of CPDs, CPD-photolyase was overexpressed in keratinocytes using an N1-methyl pseudouridine-containing in vitro-transcribed mRNA. CPD-photolyase, which is normally not present in placental mammals, can efficiently and rapidly repair CPDs to block signaling pathways elicited by CPDs. Keratinocytes surviving UVB irradiation turn hypermetabolic. We show that CPD-evoked mitochondrial reactive oxygen species production, followed by the activation of several energy sensor enzymes, including sirtuins, AMPK, mTORC1, mTORC2, p53, and ATM, is responsible for the compensatory metabolic adaptations in keratinocytes surviving UVB irradiation. Compensatory metabolic changes consist of enhanced glycolytic flux, Szent-Györgyi-Krebs cycle, and terminal oxidation. Furthermore, mitochondrial fusion, mitochondrial biogenesis, and lipophagy characterize compensatory hypermetabolism in UVB-exposed keratinocytes. These properties not only support the survival of keratinocytes, but also contribute to UVB-induced differentiation of keratinocytes. Our results indicate that CPD-dependent signaling acutely maintains skin integrity by supporting cellular energy metabolism.

Natural Exogenous Antioxidant Defense against Changes in Human Skin Fibroblast Proteome Disturbed by UVA Radiation

Daily exposure of the skin to UVA radiation causes oxidative modifications to cellular components and biomolecules. These include proteins involved in the metabolism and cytoprotection of fibroblasts, and their modification can contribute to the disruption of cell function and the development of skin disorders. Therefore, there remains a need for highly active cytoprotective compounds with antioxidant properties. The purpose of this study was to investigate the effect of ascorbic acid on the activity of rutin against UVA-induced changes in the proteome of human fibroblasts. All analyses were carried out on fibroblasts cultured in a three-dimensional system exposed to UVA radiation and incubated with rutin and ascorbic acid. Their proteomic profile was analyzed using nano-HPLC, which revealed 150 proteins whose expression was significantly altered between treatment conditions. UVA radiation led to changes in the expression of 82 proteins. However, some of these changes were mitigated by rutin and ascorbic acid separately (23 and 25 proteins, respectively) and rutin and ascorbic acid together (23 proteins). UVA radiation has led to the upregulation of proteins involved in gene expression, catalytic processes and antioxidant pathways, and downregulation of proteins with binding activity. Nevertheless, rutin and ascorbic acid used separately or together have countered these changes to varying degrees. Moreover, rutin and ascorbic acid stimulated fibroblasts irradiated by UVA to increase the expression of the signalling molecules responsible for the opening of the transmembrane channels. In the context of the results obtained, the observed cytoprotective effect of the cooperation of rutin and ascorbic acid results not only from the overlapping properties of the compounds. The effect of rutin alone is probably inhibited by its limited bioavailability. Therefore, its interaction with ascorbic acid increases membrane penetration and improves the cytoprotective effect on skin fibroblasts.

Apoptosis, the only cell death pathway that can be measured in human diploid dermal fibroblasts following lethal UVB irradiation

Ultraviolet radiation (UVR) is a major environmental genotoxic agent. In skin, it can lead to the formation of mutagenic DNA damage. Several mechanisms are in place to prevent the conversion of these DNA damage into skin cancer-driver mutations. An important mutation prevention mechanism is the programmed cell death, which can safely dispose of the damaged cells. Apoptosis is the most studied and best characterised programmed cell death, but an increasing amount of new cell death pathways are emerging. Using different pharmacological cell death inhibitors and antioxidants, we have evaluated the implication of apoptosis, necroptosis, ferroptosis and parthanatos in UVB-induced cell death in human diploid dermal fibroblasts. Our results show that apoptosis is the only known cell death mechanism induced by UVB irradiation in fibroblasts. We also showed that lethal UVB irradiation induces a PARP-dependent drastic loss of cellular metabolic activity caused by an overused of NAD+.

Calcineurin inhibitor (CNI)-associated skin cancers: New insights on exploring mechanisms by which CNIs downregulate DNA repair machinery

The use of the calcineurin inhibitors (CNI) cyclosporine (CsA) and tacrolimus remains a cornerstone in post-transplantation immunosuppression. Although these immunosuppressive agents have revolutionized the field of transplantation medicine, its increased skin cancer risk poses a major concern. A key contributor to this phenomenon is a reduced capacity to repair DNA damage caused by exposure to ultraviolet (UV) wavelengths of sunlight. CNIs decrease DNA repair by mechanisms that remain to be fully explored. Though CsA is known to decrease the abundance of key DNA repair enzymes, less is known about how tacrolimus yields this effect. CNIs hold the capacity to inhibit both of the main catalytic calcineurin isoforms (CnAα and CnAβ). However, it is unknown which isoform regulates UV-induced DNA repair, which is the focus of this review. It is with hope that this insight spurs investigative efforts that conclusively addresses these gaps in knowledge. Additionally, this research also raises the possibility that newer CNIs can be developed that effectively blunt the immune response while mitigating the incidence of skin cancers with immunosuppression.

UV damage induces G3BP1-dependent stress granule formation that is not driven by mTOR inhibition-mediated translation arrest

Translation arrest is a part of the cellular stress response that decreases energy consumption and enables rapid reprioritisation of gene expression. Often translation arrest leads to condensation of untranslated messenger ribonucleoproteins (mRNPs) into stress granules (SGs). Studies into mechanisms of SG formation and functions are complicated because various types of stress cause formation of SGs with different properties and composition. In this work, we focused on the mechanism of SG formation triggered by UV damage. We demonstrate that UV-induced inhibition of translation does not involve inhibition of the mechanistic target of rapamycin (mTOR) signaling or dissociation of the 48S preinitiation complexes. The general control non-derepressible 2 (GCN2; also known as EIF2AK4) kinase contributes to UV-induced SG formation, which is independent of the phosphorylation of the eukaryotic translation initiation factor 2α. Like many other types of SGs, condensation of UV-induced granules requires the Ras-GTPase-activating protein SH3-domain-binding protein 1 (G3BP1). Our work reveals that, in UV-treated cells, the mechanisms of translation arrest and SG formation may be unlinked, resulting in SGs that do not contain the major type of polysome-free preinitiation complexes that accumulate in the cytoplasm.This article has an associated First Person interview with the first author of the paper.

Haplotypes of (-794(CATT)5-8/-173G>C) MIF gene polymorphisms and its soluble levels in basal cell carcinoma in western Mexican population

Basal cell carcinoma (BCC) is the most common dermatological neoplasms in Caucasian populations. In Mexico, a prevalence of 3.9 per 1000 habitants is estimated. Recently, the macrophage migration inhibitory factor (MIF) has been related to different types of cancer. Therefore, this study aimed to investigate the genetic association of haplotypes of [-794(CATT)5-8/-173G>C]MIF gene polymorphisms and its soluble levels in BCC. A total of 360 individuals were recruited for the study, that is, 180 of the total amounts were patients with BCC histologically confirmed and the remaining 180 individuals were identified as control subjects (CS). Both polymorphisms were genotyped by PCR and PCR-RFLP (restriction fragment length polymorphism), and MIF serum levels were measured by ELISA kit. A borderline difference was found between the 55 genotype and the susceptibility to BCC (5.6% vs 1.7% in BCC and CS, respectively, OR=3.7 and p=0.04). Furthermore, the haplotype 7G showed a significant association with BCC (p=0.02, OR=1.99). Concerning MIF soluble levels, patients with BCC showed a media of 2.1 ng/mL and CS showed 4.4 ng/mL, the comparison between groups was significant (p<0.01). Our findings suggest that the 55 genotype and the haplotype 7G are associated with the susceptibility to BCC; furthermore, a significant difference was found between MIF soluble levels in both study groups.

Focus on UV-Induced DNA Damage and Repair-Disease Relevance and Protective Strategies

The protective ozone layer is continually depleting due to the release of deteriorating environmental pollutants. The diminished ozone layer contributes to excessive exposure of cells to ultraviolet (UV) radiation. This leads to various cellular responses utilized to restore the homeostasis of exposed cells. DNA is the primary chromophore of the cells that absorbs sunlight energy. Exposure of genomic DNA to UV light leads to the formation of multitude of types of damage (depending on wavelength and exposure time) that are removed by effectively working repair pathways. The aim of this review is to summarize current knowledge considering cellular response to UV radiation with special focus on DNA damage and repair and to give a comprehensive insight for new researchers in this field. We also highlight most important future prospects considering application of the progressing knowledge of UV response for the clinical control of diverse pathologies.

How Far Does Energy Migrate in DNA and Cause Damage? Evidence for Long-Range Photodamage to DNA

A new DNA architecture addresses the question, how far energy migrates in DNA and forms cyclobutane pyrimidine dimers (CPDs) as photodamages causing skin cancer. The 3-methoxyxanthone nucleoside allows site-selective photoenergy injection into DNA. The designated CPD site lacks the phosphodiester bond and can be placed in defined distances. The CPD formation links two oligonucleotides together and allows probing by gel electrophoresis. We obtained a sigmoidal distance dependence with R0 of 25±3 Å. Below R0 , short-range energy migration occurs with high CPD yields and shallow distance dependence, characteristic for a coherent process. 5-methyl-C as epigenetic modification on the 3'-side facilitates CPD formation. Above R0 , long-range incoherent energy migration occurs over 30 A-T pairs (105.4 Å). The evidence of long-range CPD formation is fundamental for our understanding of DNA photodamaging. Open access funding enabled and organized by Projekt DEAL.

Jeju Magma-Seawater Inhibits α-MSH-Induced Melanogenesis via CaMKKβ-AMPK Signaling Pathways in B16F10 Melanoma Cells

Melanin protects skin from ultraviolet radiation, toxic drugs, and chemicals. Its synthesis is sophisticatedly regulated by multiple mechanisms, including transcriptional and enzymatic controls. However, uncontrolled excessive production of melanin can cause serious dermatological disorders, such as freckles, melasma, solar lentigo, and cancer. Moreover, melanogenesis disorders are also linked to neurodegenerative diseases. Therefore, there is a huge demand for safer and more potent inhibitors of melanogenesis. In the present study, we report novel inhibitory effects of Jeju magma-seawater (JMS) on melanogenesis induced by α-melanocyte stimulating hormone (α-MSH) in B16F10 melanoma cells. JMS is the abundant underground seawater found in Jeju Island, a volcanic island of Korea. Research into the physiological effects of JMS is rapidly increasing due to its high contents of various minerals that are essential to human health. However, little is known about the effects of JMS on melanogenesis. Here, we demonstrate that JMS safely and effectively inhibits α-MSH-induced melanogenesis via the CaMKKβ (calcium/calmodulin-dependent protein kinase β)-AMPK (5′ adenosine monophosphate-activated protein kinase) signaling pathway. We further demonstrate that AMPK inhibits the signaling pathways of protein kinase A and MAPKs (mitogen-activated protein kinase), which are critical for melanogenesis-related gene expression. Our results highlight the potential of JMS as a novel therapeutic agent for ameliorating skin pigmentation-related disorders.

Protective role of histone deacetylase 4 from ultraviolet radiation-induced DNA lesions

Ultraviolet B (UVB) exposure is a core factor that leads to skin disease or carcinogenesis through the insufficient repair of DNA lesions. UVB-induced DNA lesions are mainly removed by the nucleotide excision repair (NER) mechanism. The expression of histone deacetylase 4 (HDAC4) is altered in the skin upon UVB exposure, indicating its possible implication in UVB-induced DNA lesions repair. Here, we investigated the role of HDAC4 in the NER removal of the main classes of UVB-induced DNA lesions consisting of cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs). We found that UVB irradiation increased HDAC4 expression at both the mRNA and protein levels. HDAC4 interacted with NER factor XPC, which played an important role in effectively removing the UVB-induced DNA lesions. This study provides an understanding of the HDAC4 function in DNA repair, which will allow the development of efficient strategies to protect the skin from UVR-induced diseases.

Formation and Recognition of UV-Induced DNA Damage within Genome Complexity

Ultraviolet (UV) light is a natural genotoxic agent leading to the formation of photolesions endangering the genomic integrity and thereby the survival of living organisms. To prevent the mutagenetic effect of UV, several specific DNA repair mechanisms are mobilized to accurately maintain genome integrity at photodamaged sites within the complexity of genome structures. However, a fundamental gap remains to be filled in the identification and characterization of factors at the nexus of UV-induced DNA damage, DNA repair, and epigenetics. This review brings together the impact of the epigenomic context on the susceptibility of genomic regions to form photodamage and focuses on the mechanisms of photolesions recognition through the different DNA repair pathways.

The Role of Non-Coding RNAs as Prognostic Factor, Predictor of Drug Response or Resistance and Pharmacological Targets, in the Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (CSCC) is the most common keratinocyte-derived skin cancer in the Caucasian population. Exposure to UV radiations (UVRs) represents the main risk carcinogenesis, causing a considerable accumulation of DNA damage in epidermal keratinocytes with an uncontrolled hyperproliferation and tumor development. The limited and rarely durable response of CSCC to the current therapeutic options has led researchers to look for new therapeutic strategies. Recently, the multi-omics approaches have contributed to the identification and prediction of the key role of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), circularRNAs (circRNAs) and long non-coding RNAs (lncRNAs) in the regulation of several cellular processes in different tumor types, including CSCC. ncRNAs can modulate transcriptional and post-transcriptional events by interacting either with each other or with DNA and proteins, such as transcription factors and RNA-binding proteins. In this review, the implication of ncRNAs in tumorigenesis and their potential role as diagnostic biomarkers and therapeutic targets in human CSCC are reported.

Degradation and deactivation of a plasmid-encoded extracellular antibiotic resistance gene during separate and combined exposures to UV254 and radicals

This study investigated the degradation and deactivation of an extracellular ampicillin resistance gene (amp^R) encoded in plasmid pUC19 during exposure to UV₂₅₄, ^•OH (generated by UV_>290/H₂O₂), and combined exposure to UV₂₅₄ and ^•OH (and/or SO₄^•-) using UV₂₅₄/H₂O₂ and UV₂₅₄/S₂O₈^2-. The degradation rates of amp^R measured by quantitative polymerase chain reaction increased with increasing target amplicon length (192-851 bps). The rate constants for the degradation of pUC19 (2686 bps) were calculated as 0.26 cm²/mJ for UV₂₅₄ and 1.5 × 10¹¹ M^-1s^-1 for ^•OH, based on the degradation rates of amp^R amplicons and assuming an equal sensitivity of DNA damage across the entire plasmid. DNA repair-proficient Escherichia coli (E. coli) AB1157 strain (wild-type) and its repair-deficient mutants including AB1886 (uvrA^-), AB2463 (recA^-), AB2480 (uvrA^-, recA^-), and DH5α (recA^-, endA^-) were applied as recipient cells in gene transformation assays. Results suggested that the elimination efficiency of transforming activity during UV₂₅₄ and ^•OH exposure was dependent on the type of DNA repair genes in recipient E. coli strains. Losses of transforming activity were slower than the degradation of pUC19 by a factor of up to ∼5 (for E. coli DH5α), highlighting the importance of DNA repair in recipient cells. The degradation rates of amp^R amplicons were much larger (by a factor of ∼4) in UV₂₅₄/H₂O₂ and UV₂₅₄/S₂O₈^2- than UV₂₅₄ direct photolysis, indicating the significant contribution of ^•OH and SO₄^•- to the gene degradation. Not only UV₂₅₄ and SO₄^•-, but also ^•OH contributed to the degradation of amp^R during UV₂₅₄/S₂O₈^2-, which was attributed to the conversion of SO₄^•- to ^•OH and a 10-fold larger reactivity of ^•OH towards amp^R as compared to SO₄^•-. However, the enhanced gene degradation by radicals did not lead to a faster elimination of gene transforming activity during UV₂₅₄/H₂O₂ and UV₂₅₄/S₂O₈^2-, suggesting that UV₂₅₄- and radical-induced DNA damage were not additive in their contributions to losses of gene transforming activity. Wastewater effluent organic matter (EfOM) accelerated the degradation of amp^R during UV₂₅₄ irradiation by means of reactive species production through indirect photolysis reactions, whereas EfOM mainly acted as a radical scavenger during UV₂₅₄/H₂O₂ and UV₂₅₄/S₂O₈^2- treatments.

The sunless tanning agent dihydroxyacetone induces stress response gene expression and signaling in cultured human keratinocytes and reconstructed epidermis

Sunless (chemical) tanning is widely regarded as a safe alternative to solar UV-induced skin tanning known to be associated with epidermal genotoxic stress, but the cutaneous biology impacted by chemical tanning remains largely unexplored. Chemical tanning is based on the formation of melanin-mimetic cutaneous pigments ('melanoidins') from spontaneous amino-carbonyl ('glycation') reactions between epidermal amino acid/protein components and reactive sugars including the glycolytic ketose dihydroxyacetone (DHA). Here, we have examined the cutaneous effects of acute DHA-exposure on cultured human HaCaT keratinocytes and epidermal reconstructs, profiled by gene expression array analysis and immunodetection. In keratinocytes, DHA-exposure performed at low millimolar concentrations did not impair viability while causing a pronounced cellular stress response as obvious from rapid activation of phospho-protein signal transduction [p-p38, p-Hsp27(S15/S78), p-eIF2α] and gene expression changes (HSPA6, HMOX1, CRYAB, CCL3), not observable upon exposure to the non-ketose, tanning-inactive DHA-control glycerol. Formation of advanced glycation end products (AGEs) from posttranslational protein-adduction was confirmed by quantitative mass spectrometric detection of N-ε-(carboxyethyl)-l-lysine (CEL) and N7-carboxyethyl-l-arginine, and skin cells with CRISPR-Cas9-based elimination of the carbonyl stress response gene GLO1 (encoding glyoxalase 1) displayed hypersensitivity to DHA-cytotoxicity. In human epidermal reconstructs a topical use-relevant DHA-dose regimen elicited a comparable stress response as revealed by gene expression array (HSPA1A, HSPA6, HSPD1, IL6, DDIT3, EGR1) and immunohistochemical analysis (CEL, HO-1, p-Hsp27-S78). In DHA-treated SKH-1 hairless mouse skin IHC-detection revealed epidermal occurrence of CEL- and p-Hsp27-epitopes. For comparison, stress response gene expression array analysis was performed in epidermis exposed to a supra-erythemal dose of solar simulated UV (2 MEDs), identifying genes equally or differentially sensitive to either one of these cutaneous stimuli [DHA ('sunless tanning') versus solar UV ('sun-induced tanning')]. Given the worldwide use of chemical tanners in consumer products, these prototype data documenting a DHA-induced specific cutaneous stress response deserve further molecular exploration in living human skin.

Analysis of mutational signatures in C. elegans: Implications for cancer genome analysis

Genome integrity is constantly challenged by exogenous and endogenous insults, and mutations are associated with inherited disease and cancer. Here we summarize recent studies that utilized C. elegans whole genome next generation sequencing to experimentally determine mutational signatures associated with mutagen exposure, DNA repair deficiency or a combination of both and discuss the implications of these results for the understanding of cancer genome evolution. The experimental analysis of wild-type and DNA repair deficient nematodes propagated under unchallenged conditions over many generations revealed increased mutagenesis in approximately half of all DNA repair deficient strains, its rate, except for DNA mismatch repair, only being moderately increased. The exposure of wild-type and DNA repair defective strains to selected genotoxins, including UV-B and ionizing radiation, alkylating compounds, aristolochic acid, aflatoxin-B1, and cisplatin enabled the systematic analysis of the relative contributions of redundant repair modalities that mend DNA damage. Combining genotoxin exposure with DNA repair deficiency can manifest as altered mutation rates and/or as a change in mutational profiles, and reveals how different DNA alterations induced by one genotoxin are repaired by separate DNA repair pathways, often in a highly redundant way. Cancer genomes provide a snapshot of all mutational events that happened prior to cancer detection and sequencing, necessitating computational models to deduce mutational signatures using mathematical best fit approaches. While computationally deducing signatures from cancer genomes has been tremendously successful in associating some signatures to known mutagenic causes, many inferred signatures lack a clear link to a known mutagenic process. Moreover, analytical signatures might not reflect any distinct mutagenic processes. Nonetheless, combined effects of mutagen exposure and DNA damage-repair deficiency are also present in cancer genomes, but cannot be as easily detected owing to the unknown histories of genotoxic exposures and because biallelic in contrast to monoallelic DNA repair deficiency is rare. The impact of damage-repair interactions also manifests through selective pressure for DNA repair gene inactivation during cancer evolution. Using these considerations, we discuss a theoretical framework that explains why minute mutagenic changes, possibly too small to manifest as change in a signature, can have major effects in oncogenesis. Overall, the experimental analysis of mutational processes underscores that the interpretation of mutational signatures requires considering both the primary DNA lesion and repair status and imply that mutational signatures derived from cancer genomes may be more variable than currently anticipated.

Impact of the Nucleosome Histone Core on the Structure and Dynamics of DNA-Containing Pyrimidine-Pyrimidone (6-4) Photoproduct

The pyrimidine-pyrimidone (6-4) photoproduct (64-PP) is an important photoinduced DNA lesion constituting a mutational signature for melanoma. The structural impact of 64-PP on DNA complexed with histones affects the lesion mutagenicity and repair but remains poorly understood. Here we investigate the conformational dynamics of DNA-containing 64-PP within the nucleosome core particle by atomic-resolution molecular dynamics simulations and multiscale data analysis. We demonstrate that the histone core exerts important mechanical restraints that largely decrease global DNA structural fluctuations. However, the local DNA flexibility at the damaged site is enhanced due to imperfect structural adaptation to restraints imposed by the histone core. If 64-PP faces the histone core and is therefore not directly accessible by the repair protein, the complementary strand facing the solvent is deformed and exhibits higher flexibility than the corresponding strand in a naked, undamaged DNA. This may serve as an initial recognition signal for repair. Our simulations also pinpoint the structural role of proximal residues from the truncated histone tails.

Guanine Radicals Induced in DNA by Low-Energy Photoionization

Guanine (G) radicals are precursors to DNA oxidative damage, correlated with carcinogenesis and aging. During the past few years, we demonstrated clearly an intriguing effect: G radicals can be generated upon direct absorption of UV radiation with energy significantly lower than the G ionization potential. Using nanosecond transient absorption spectroscopy, we studied the primary species, ejected electrons and guanine radicals, which result from photoionization of various DNA systems in aqueous solution.The DNA propensity to undergo electron detachment at low photon energies greatly depends on its secondary structure. Undetected for monomers or unstacked oligomers, this propensity may be 1 order of magnitude higher for G-quadruplexes than for duplexes. The experimental results suggest nonvertical processes, associated with the relaxation of electronic excited states. Theoretical studies are required to validate the mechanism and determine the factors that come into play. Such a mechanism, which may be operative over a broad excitation wavelength range, explains the occurrence of oxidative damage observed upon UVB and UVA irradiation.Quantification of G radical populations and their time evolution questions some widespread views. It appears that G radicals may be generated with the same probability as pyrimidine dimers, which are considered to be the major lesions induced upon absorption of low-energy UV radiation by DNA. As most radical cations undergo deprotonation, the vast majority of the final reaction products is expected to stem from long-lived deprotonated radicals. Consequently, when G radical cations are involved, the widely used oxidation marker 8-oxodG is not representative of the oxidative damage.Beyond the biological consequences, photogeneration of electron holes in G-quadruplexes may inspire applications in nanoelectronics; although four-stranded structures are currently studied as molecular wires, their behavior as photoconductors has not been explored so far.In the present Account, after highlighting some key experimental issues, we first describe the photoionization process, and then, we focus on radicals. We use as show-cases new results obtained for genomic DNA and Oxytricha G-quadruplexes. Generation and reaction dynamics of G radicals in these systems provide a representative picture of the phenomena reported previously for duplexes and G-quadruplexes, respectively.

DNA Damage Induced by Late Spring Sunlight in Antarctica

Sunlight ultraviolet (UV) radiation constitutes an important environmental genotoxic agent that organisms are exposed to, as it can damage DNA directly, generating pyrimidine dimers, and indirectly, generating oxidized bases and single-strand breaks (SSBs). These lesions can lead to mutations, triggering skin and eye disorders, including carcinogenesis and photoaging. Stratospheric ozone layer depletion, particularly in the Antarctic continent, predicts an uncertain scenario of UV incidence on the Earth in the next decades. This research evaluates the DNA damage caused by environmental exposure to late spring sunlight in the Antarctic Peninsula, where the ozone layer hole is more pronounced. These experiments were performed at the Brazilian Comandante Ferraz Antarctic Station, at King's George Island, South Shetlands Islands. For comparison, tropical regions were also analyzed. Samples of plasmid DNA were exposed to sunlight. Cyclobutane pyrimidine dimers (CPDs), oxidized base damage and SSBs were detected using specific enzymes. In addition, an immunological approach was used to detect CPDs. The results reveal high levels of DNA damage induced by exposure under the Antarctic sunlight, inversely correlated with ozone layer thickness, confirming the high impact of ozone layer depletion on the DNA damaging action of sunlight in Antarctica.

Human genes differ by their UV sensitivity estimated through analysis of UV-induced silent mutations in melanoma

We hypothesized that human genes differ by their sensitivity to ultraviolet (UV) exposure. We used somatic mutations detected by genome-wide screens in melanoma and reported in the Catalog Of Somatic Mutations In Cancer. As a measure of UV sensitivity, we used the number of silent mutations generated by C>T transitions in pyrimidine dimers of a given transcript divided by the number of potential sites for this type of mutations in the transcript. We found that human genes varied by UV sensitivity by two orders of magnitude. We noted that the melanoma-associated tumor suppressor gene CDKN2A was among the top five most UV-sensitive genes in the human genome. Melanoma driver genes have a higher UV-sensitivity compared with other genes in the human genome. The difference was more prominent for tumor suppressors compared with oncogene. The results of this study suggest that differential sensitivity of human transcripts to UV light may explain melanoma specificity of some driver genes. Practical significance of the study relates to the fact that differences in UV sensitivity among human genes need to be taken into consideration whereas predicting melanoma-associated genes by the number of somatic mutations detected in a given gene.

XPC as breast cancer susceptibility gene: evidence from genetic profiling, statistical inferences and protein structural analysis

BACKGROUND

Gene polymorphisms that affect nucleotide excision repair (NER) pathway may link with higher susceptibility of breast cancer (BC); however, the significance of these associations may vary conferring to the individual ethnicity. Xeroderma pigmentosum complementation gene (XPC) plays a substantial role in recognizing damaged DNA during NER process.

OBJECTIVE AND METHODS

To estimate the relationship among XPC polymorphisms and breast cancer (BC) risk, we carried out a case-control-association study with 493 BC cases and 387 controls using TETRA-ARMS-PCR. Distributional differences of clinical features, demographic factors and XPC polymorphisms among BC cases and controls were examined by conditional logistic regression model. Kaplan-Meier test was applied to predict survival distributions and protein structure was predicted using computational tools.

RESULTS

Obesity, consanguinity, positive marital status and BC family history were associated (P ≤ 0.01) with higher BC risk. Genotyping revealed significant involvement (P ≤ 0.01) of two XPC polymorphisms rs2228001-A > C (OR = 3.8; CI 1.9-7.6) and rs2733532-C > T (OR = 2.6; CI 1.4-5.03) in BC development, asserting them potential risk factors for increased BC incidence. However, no association (P > 0.05) was detected for overall or progression free survival for both XPC polymorphisms possibly due to shorter follow-up time (45 months). As compared to normal XPC structure, pronounced conformational changes have been observed in the C-terminus of XPC^Q939K, bearing rs2228001-A > C substitution. In XPC^Q939K, two additional α-helices were observed at A292-E297 and Y252-R286, while L623-M630 and L649-L653 helices were converted into loop conformation.

CONCLUSION

In conclusion, both XPC polymorphisms confer significant association with increased BC risk. rs2228001 substitution may change the structural and functional preferences of XPC C-terminus, while rs2733532 may have regulatory role thereby leading to potential BC risk.

Oxidative Stress and Genotoxicity in Melanoma Induction: Impact on Repair Rather Than Formation of DNA Damage?

Keratinocytes and melanocytes, two cutaneous cell types located within the epidermis, are the origin of most skin cancers, namely carcinomas and melanomas. These two types of tumors differ in many ways. First, carcinomas are almost 10 times more frequent than melanomas. In addition, the affected cellular pathways, the mutated genes and the metastatic properties of the tumors are not the same. This review addresses another specificity of melanomas: the role of photo-oxidative stress. UVA efficiently produces reactive oxygen species in melanocytes, which results in more frequent oxidatively generated DNA lesions than in other cell types. The question of the respective contribution of UVB-induced pyrimidine dimers and UVA-mediated oxidatively generated lesions to mutagenesis in melanoma remains open. Recent results based on next-generation sequencing techniques strongly suggest that the mutational signature associated with pyrimidine dimers is overwhelming in melanomas like in skin carcinomas. UVA-induced oxidative stress may yet be indirectly linked to the genotoxic pathways involved in melanoma through its ability to hamper DNA repair activities.

Genoprotective activities of plant natural substances in cancer and chemopreventive strategies in the context of 3P medicine

Severe durable changes may occur to the DNA structure caused by exogenous and endogenous risk factors initiating the process of carcinogenesis. By evidence, a large portion of malignancies have been demonstrated as being preventable. Moreover, the targeted prevention of cancer onset is possible, due to unique properties of plant bioactive compounds. Although genoprotective effects of phytochemicals have been well documented, there is an evident lack of articles which would systematically present the spectrum of anticancer effects by phytochemicals, plant extracts, and plant-derived diet applicable to stratified patient groups at the level of targeted primary (cancer development) and secondary (cancer progression and metastatic disease) prevention. Consequently, clinical implementation of knowledge accumulated in the area is still highly restricted. To stimulate coherent co-development of the dedicated plant bioactive compound investigation on one hand and comprehensive cancer preventive strategies on the other hand, the current paper highlights and deeply analyses relevant evidence available in the area. Key molecular mechanisms are presented to detail genoprotective and anticancer activities of plants and phytochemicals. Clinical implementation is discussed. Based on the presented evidence, advanced chemopreventive strategies in the context of 3P medicine are considered.

Deciphering the Enigma of the Histone H2A.Z-1/H2A.Z-2 Isoforms: Novel Insights and Remaining Questions

The replication independent (RI) histone H2A.Z is one of the more extensively studied variant members of the core histone H2A family, which consists of many replication dependent (RD) members. The protein has been shown to be indispensable for survival, and involved in multiple roles from DNA damage to chromosome segregation, replication, and transcription. However, its functional involvement in gene expression is controversial. Moreover, the variant in several groups of metazoan organisms consists of two main isoforms (H2A.Z-1 and H2A.Z-2) that differ in a few (3–6) amino acids. They comprise the main topic of this review, starting from the events that led to their identification, what is currently known about them, followed by further experimental, structural, and functional insight into their roles. Despite their structural differences, a direct correlation to their functional variability remains enigmatic. As all of this is being elucidated, it appears that a strong functional involvement of isoform variability may be connected to development.

Cytoprotective Effect of Ascorbic Acid and Rutin against Oxidative Changes in the Proteome of Skin Fibroblasts Cultured in a Three-Dimensional System

The combination of ascorbic acid and rutin, commonly used in oral preparations for their antioxidant and anti-inflammatory properties, can also be used to protect skin cells from the effects of UV radiation in sunlight. Here, we tested the potential protective effect of ascorbic acid and rutin used together in UVB-irradiated human skin fibroblasts, and assessed the proteomic profile of these cells, grown in a three-dimensional (3D) system. Proteomic findings revealed a combined effect of ascorbic acid and rutin in UV-irradiated fibroblasts against overexpression of pro-inflammatory signaling proteins and DNA reorganization/expression. These effects were not observed when cells were treated with either compounds alone. The antioxidant effects of ascorbic acid and rutin also prevented protein modifications by lipid peroxidation products. Further, ascorbic acid stimulated rutin-protein adduct formation, which supports intra/extracellular signaling and the Nrf2/ARE antioxidant pathway, contributing to the protective effects against UV-induced oxidative stress. The combined effect of ascorbic acid and rutin suggests that this combination of compounds is potentially effective against skin damage caused by UV radiation.

Bucillamine Inhibits UVB-Induced MAPK Activation and Apoptosis in Human HaCaT Keratinocytes and SKH-1 Hairless Mouse Skin

Ultraviolet B (UVB) radiation is known as a culprit in skin carcinogenesis. We have previously reported that bucillamine (N-[2-mercapto-2-methylpropionyl]-L-cysteine), a cysteine derivative with antioxidant and anti-inflammatory capacity, protects against UVB-induced p53 activation and inflammatory responses in mouse skin. Since MAPK signaling pathways regulate p53 expression and activation, here we determined bucillamine effect on UVB-mediated MAPK activation in vitro using human skin keratinocyte cell line HaCaT and in vivo using SKH-1 hairless mouse skin. A single low dose of UVB (30 mJ cm^-2 ) resulted in increased JNK/MAPK phosphorylation and caspase-3 cleavage in HaCaT cells. However, JNK activation and casaspe-3 cleavage were inhibited by pretreatment of HaCaT cells with physiological doses of bucillamine (25 and 100 µm). Consistent with these results, bucillamine pretreatment in mice (20 mg kg^-1 ) inhibited JNK/MAPK and ERK/MAPK activation in skin epidermal cells at 6-12 and 24 h, respectively, after UVB exposure. Moreover, bucillamine attenuated UVB-induced Ki-67-positive cells and cleaved caspase-3-positive cells in mouse skin. These findings demonstrate that bucillamine inhibits UVB-induced MAPK signaling, cell proliferation and apoptosis. Together with our previous report, we provide evidence that bucillamine has a photoprotective effect against UV exposure.

Ultraviolet radiation and cutaneous melanoma: a historical perspective

In this article, we summarize the research that eventually led to the classification of the full ultraviolet (UV) radiation spectrum as carcinogenic to humans. We recall the pioneering works that led to the formulation of novel hypotheses on the reasons underlying the increasing burden of melanoma in light-skinned populations. It took long before having compelling evidence on the association between UV and melanoma, in particular, the importance of UV exposure during childhood for both the occurrence of melanoma and death. The role of UVA was established only after 2005. If molecular lesions caused by UV radiation are better known, the precise mechanism by which UV exposure drives melanoma occurrence and progression still needs to be elucidated. More research on the UV-melanoma relationships has led to more evidence-based sun-protection recommendations, especially for children, and to effective control of the artificial UV tanning fashion. Since around 1985-1995, the mortality because of melanoma has started to decrease in younger age groups in most light-skinned populations. If sun protection among children remain on top of public health agendas, there is a fairly great chance that melanoma mortality will stabilize and steadily decrease in all light-skinned populations. The introduction of effective therapies against metastatic disease will improve this reversal in mortality trends.

Rhus coriaria L. Fruit Extract Prevents UV-A-Induced Genotoxicity and Oxidative Injury in Human Microvascular Endothelial Cells

Rhus coriaria L. (sumac) is a small plant widely diffused in the Mediterranean region. Its fruit are often consumed as a spice but are also present in traditional medicine of several countries. Recently, interest in this plant has increased and many scientific works reported its beneficial effects including antioxidant and anti-inflammatory properties. Plant extracts can be successfully used against ultraviolet rays, which are able to reach and damage the human skin; however, sumac extracts were never applied to this usage. Thus, in this study, we used a macerated ethanol extract of Rhus coriaria L. dried fruit (mERC) to demonstrate its preventive role against the damage induced by ultraviolet-A rays (UV-A) on microvascular endothelial cells (HMEC-1). In vitro effects of the extract pre-treatment and UV-A exposure were evaluated in detail. The antioxidant capacity was assessed by reactive oxygen species (ROS) formation and cellular antioxidant activity measurement. Genoprotective effects of mERC were investigated as well. Our findings indicate that the extract acts as a cell cycle inhibitor or apoptosis inducer, according to the level of damage. The present work provides new insights into the usage of Rhus coriaria extracts against skin injuries.

A chromatin scaffold for DNA damage recognition: how histone methyltransferases prime nucleosomes for repair of ultraviolet light-induced lesions

The excision of mutagenic DNA adducts by the nucleotide excision repair (NER) pathway is essential for genome stability, which is key to avoiding genetic diseases, premature aging, cancer and neurologic disorders. Due to the need to process an extraordinarily high damage density embedded in the nucleosome landscape of chromatin, NER activity provides a unique functional caliper to understand how histone modifiers modulate DNA damage responses. At least three distinct lysine methyltransferases (KMTs) targeting histones have been shown to facilitate the detection of ultraviolet (UV) light-induced DNA lesions in the difficult to access DNA wrapped around histones in nucleosomes. By methylating core histones, these KMTs generate docking sites for DNA damage recognition factors before the chromatin structure is ultimately relaxed and the offending lesions are effectively excised. In view of their function in priming nucleosomes for DNA repair, mutations of genes coding for these KMTs are expected to cause the accumulation of DNA damage promoting cancer and other chronic diseases. Research on the question of how KMTs modulate DNA repair might pave the way to the development of pharmacologic agents for novel therapeutic strategies.

Human articular cartilage repair: Sources and detection of cytotoxicity and genotoxicity in photo-crosslinkable hydrogel bioscaffolds

Three-dimensional biofabrication using photo-crosslinkable hydrogel bioscaffolds has the potential to revolutionize the need for transplants and implants in joints, with articular cartilage being an early target tissue. However, to successfully translate these approaches to clinical practice, several barriers must be overcome. In particular, the photo-crosslinking process may impact on cell viability and DNA integrity, and consequently on chondrogenic differentiation. In this review, we primarily explore the specific sources of cellular cytotoxicity and genotoxicity inherent to the photo-crosslinking reaction, the methods to analyze cell death, cell metabolism, and DNA damage within the bioscaffolds, and the possible strategies to overcome these detrimental effects.

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.

Light or Dark Pigmentation of Engineered Skin Substitutes Containing Melanocytes Protects Against Ultraviolet Light-Induced DNA Damage In Vivo

Engineered skin substitutes (ESS) containing autologous fibroblasts and keratinocytes provide stable wound closure in patients with large, full-thickness burns, but are limited by hypopigmentation due to absence of added melanocytes. DNA damage caused by ultraviolet radiation (UV) increases risk for skin cancer development. In human skin, melanocytes provide pigmentation that protects skin from UV-induced DNA damage. This study investigated whether inclusion of human melanocytes (hM) affects the response of ESS to UV in vivo. Specifically, pigmentation and formation of cyclobutane pyrimidine dimers (CPDs), the most prevalent UV-induced DNA photoproduct, were analyzed. Three groups of ESS were prepared with fibroblasts and keratinocytes, ± melanocytes, and grafted orthotopically to immunodeficient mice: ESS without melanocytes (ESS-hM), ESS with light skin-derived (Caucasian) melanocytes (ESS+hM-L), and ESS with dark skin-derived (African-American) melanocytes (ESS+hM-D). Pigmentation of ESS+hM-L and ESS+hM-D increased significantly after grafting; pigmentation levels were significantly different among groups. Mean melanocyte densities in ESS+hM-L and ESS+hM-D were similar to each other and to densities in normal human skin. After 8 weeks in vivo, grafts were irradiated with 135 mJ/cm2 UV; non-UV-treated mice served as controls. UV modestly increased pigmentation in the ESS+hM groups. UV significantly increased CPD levels in ESS-hM, and levels in ESS-hM were significantly greater than in ESS+hM-L or ESS+hM-D. The results demonstrate that light or dark melanocytes in ESS decreased UV-induced DNA damage. Therefore, melanocytes in ESS play a photoprotective role. Protection against UV-induced DNA damage is expected to reduce skin cancer risk in patients grafted with ESS containing autologous melanocytes.

Ras-Mediated Activation of NF-κB and DNA Damage Response in Carcinogenesis

Cancer is a multi-step process during which cells acquire mutations that eventually lead to uncontrolled cell growth and division and evasion of programmed cell death. The oncogenes such as Ras and c-Myc may be responsible in all three major stages of cancer i.e., early, intermediate, and late. The NF-κB has been shown to control the expression of genes linked with tumor pathways such as chronic inflammation, tumor cell survival, anti-apoptosis, proliferation, invasion, and angiogenesis. In the last few decades, various biomarker pathways have been identified that play a critical role in carcinogenesis such as Ras, NF-κB and DNA damage.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Biochemical reconstitution of UV-induced mutational processes

We reconstituted two biochemical processes that may contribute to UV-induced mutagenesis in vitro and analysed the mutational profiles in the products. One process is translesion synthesis (TLS) by DNA polymerases (Pol) δ, η and ζ, which creates C>T transitions at pyrimidine dimers by incorporating two dAMPs opposite of the dimers. The other process involves spontaneous deamination of cytosine, producing uracil in pyrimidine dimers, followed by monomerization of the dimers by secondary UV irradiation, and DNA synthesis by Pol δ. The mutational spectrum resulting from deamination without translesion synthesis is similar to a mutational signature found in melanomas, suggesting that cytosine deamination encountered by the replicative polymerase has a prominent role in melanoma development. However, CC>TT dinucleotide substitution, which is also commonly observed in melanomas, was produced almost exclusively by TLS. We propose that both TLS-dependent and deamination-dependent mutational processes are likely involved in UV-induced melanoma development.

Photoprotection of the future: challenges and opportunities

The use of sunscreens is an important and essential component of photoprotection. Since their introduction during the first half of the last century, sunscreens have benefited enormously from major technological advances such as the development of novel UV filters; as a result, their efficacy in preventing UV-induced erythema is unequivocal. More recently, however, new challenges have appeared, which have prompted a robust discussion about the safety of sunscreens. These include topics directly related to photoprotection of human skin such as improved/alternative methods for standardization of assessment of the efficacy of sunscreens, but also many others such as photoprotection beyond UV, concerns about human toxicity and ecological safety, the potential of oral photoprotective measures, consequences of innovative galenic formulations. On a first glance, some of these might raise questions and doubts among dermatologists, physicians and the general public about the use sunscreens as a means of photoprotection. This situation has prompted us to critically review such challenges, but also opportunities, based on existing scientific evidence. We conclude by providing our vision about how such challenges can be met best in the future in an attempt to create the ideal sunscreen, which should provide adequate and balanced protection and be easy and safe to use.

Photoinduced intersystem crossing in DNA oxidative lesions and epigenetic intermediates

The propensity of 5-formyluracil and 5-formylcytosine, i.e. oxidative lesions and epigenetic intermediates, in acting as intrinsic DNA photosensitizers is unraveled by using a combination of molecular modeling, simulation and spectroscopy.

Experimental and theoretical studies on thymine photodimerization mediated by oxidatively generated DNA lesions and epigenetic intermediates

Combined spectroscopic and computational studies reveal that, in spite of their structural similarities, 5-formyluracil and 5-formylcytosine photosensitize cyclobutane thymine dimers through two different types of mechanisms.

7‑MEGA™ 500 regulates the expression of COX‑2, MMP‑3 and type 1 procollagen in UVB‑irradiated human keratinocytes and dermal fibroblasts

AlaskOmega® Omega 7 500, also known as Omega‑7 fatty acid or 7‑MEGA™, is a highly concentrated palmitoleic acid (C16:1). Little is known about how 7‑MEGA regulates skin inflammation and wrinkle formation in cultured skin cells. The present study aimed to investigate the effects of 7‑MEGA on the expression of cyclooxygenase‑2 (COX‑2), matrix metallopeptidase (MMP)‑1/3 and type 1 procollagen, which are markers of skin inflammation and wrinkle formation, in ultraviolet B (UVB)‑irradiated human dermal fibroblasts (HDFs) and keratinocytes (HaCaT). No toxicity was observed upon treatment of HDFs and HaCaT cells with 0.5‑2.5 µl/ml 7‑MEGA. The exposure of HaCaT cells to 10 mJ/cm2 UVB for 6 h resulted in increased protein and/or mRNA expression of COX‑2 and MMP‑3. Treatment of HaCaT cells with 2.5 µl/ml 7‑MEGA suppressed the UVB‑induced expression of COX‑2 and MMP‑3 in these cells. In addition, treatment with 2.5 µl/ml 7‑MEGA attenuated the UVB‑induced expression and phosphorylation levels of c‑Fos and c‑Jun, two components of the activator protein‑1 (AP‑1) transcription factor, in HaCaT cells. Exposure of HDFs to 60 mJ/cm2 UVB for 6 h significantly decreased the expression of type 1 procollagen protein, whereas treatment with 2.5 µl/ml 7‑MEGA partially reversed the effects of UVB on the expression of type 1 procollagen protein. These results demonstrated for the first time that 7‑MEGA regulated the expression of COX‑2, MMP‑3 and type 1 procollagen in UVB‑irradiated skin cells. The present study suggested that 7‑MEGA may serve as a novel agent against UVB‑induced skin inflammation and damage.

Role of the Aryl Hydrocarbon Receptor in Environmentally Induced Skin Aging and Skin Carcinogenesis

The skin is constantly exposed to a variety of environmental threats, including solar electromagnetic radiation, microbes, airborne particulate matter, and chemicals. Acute exposure to these environmental factors results in the activation of different signaling pathways that orchestrate adaptive stress responses to maintain cell and tissue homeostasis. Chronic exposure of skin to these factors, however, may lead to the accumulation of damaged macromolecules and loss of cell and tissue integrity, which, over time, may facilitate aging processes and the development of aging-related malignancies. One transcription factor that is expressed in all cutaneous cells and activated by various environmental stressors, including dioxins, polycyclic aromatic hydrocarbons, and ultraviolet radiation, is the aryl hydrocarbon receptor (AHR). By regulating keratinocyte proliferation and differentiation, epidermal barrier function, melanogenesis, and immunity, a certain degree of AHR activity is critical to maintain skin integrity and to adapt to acute stress situations. In contrast, a chronic activation of cutaneous AHR signaling critically contributes to premature aging and the development of neoplasms by affecting metabolism, extracellular matrix remodeling, inflammation, pigmentation, DNA repair, and apoptosis. This article provides an overview of the detrimental effects associated with sustained AHR activity in chronically stressed skin and pinpoints AHR as a promising target for chemoprevention.

Triplet-Induced Lesion Formation at CpT and TpC Sites in DNA

UV irradiation induces DNA lesions particularly at dipyrimidine sites. Using time-resolved UV pump (250 nm) and mid-IR probe spectroscopy the triplet pathway of cyclobutane pyrimidine dimer (CPD) formation within TpC and CpT sequences was studied. The triplet state is initially localized at the thymine base but decays with 30 ns under formation of a biradical state extending over both bases of the dipyrimidine. Subsequently this state either decays back to the electronic ground state on the 100 ns time scale or forms a cyclobutane pyrimidine dimer lesion (CPD). Stationary IR spectroscopy and triplet sensitization via 2'-methoxyacetophenone (2-M) in the UVA range shows that the lesions are formed with an efficiency of approximately 1.5 %. Deamination converts the cytosine moiety of the CPD lesions on the time scale of 10 hours into uracil which gives CPD(UpT) and CPD(TpU) lesions in which the coding potential of the initial cytosine base is vanished.

Multiple Dorsal Hand Actinic Keratoses and Squamous Cell Carcinomas: A Unique Presentation following Extensive UV Nail Lamp Use

Squamous cell carcinoma (SCC) is the second most common skin cancer worldwide, and exposure to ultraviolet (UV) light is a major cause of SCC. UV nail lamps can be used for drying and hardening acrylic or gel nail polish. We report a case of a 52-year-old Caucasian woman with an 18-year history of UV nail lamp use every 3 weeks and an 18-year history of weekly tanning bed use who presented with over 25 actinic keratoses and two SCC in situ on her dorsal hands. Of note, this patient has never had any previous biopsies, skin cancer or precancers, or skin cancer or precancer treatment at any time in the past and on skin examination had no precancers or cancers elsewhere on her body. We also review the existing research regarding nail lamp use, which overall suggests that the risk of carcinogenesis is low, and discuss ways dermatologists can educate patients regarding proper UV nail lamp use to minimize risks. This patient's extensive UV nail lamp use coupled with UVA exposure from tanning beds may have put her at particular risk and exacerbated the effects of the nail lamp alone.

Impact of ultraviolet radiation on dermal and epidermal DNA damage in a human pigmented bilayered skin substitute

Our laboratory has developed a scaffold-free cell-based method of tissue engineering to produce bilayered tissue-engineered skin substitutes (TESs) from epidermal and dermal cells. However, TES pigmentation is absent or heterogeneous after grafting, due to a suboptimal number of melanocytes in culture. Our objectives were to produce TESs with a sufficient quantity of melanocytes from different pigmentation phototypes (light and dark) to achieve a homogeneous color and to evaluate whether the resulting pigmentation was photoprotective against ultraviolet radiation (UVR)-induced DNA damage in the dermis and the epidermis. TESs were cultured using different concentrations of melanocytes (100, 200, and 1,500 melanocytes/mm² ), and pigmentation was evaluated in vitro and after grafting onto an athymic mouse excisional model. Dermal and epidermal DNA damage was next studied, exposing pigmented TESs to 13 and 32.5 J/cm² UVR in vitro. We observed that melanocyte cell density increased with culture time until reaching a plateau corresponding to the cell distribution of native skin. Pigmentation of melanocyte-containing TESs was similar to donor skin, with visible melanin transfer from melanocytes to keratinocytes. The amount of melanin in TESs was inversely correlated to the UVR-induced formation of cyclobutane pyrimidine dimer in dermal fibroblasts and keratinocytes. Our results indicate that the pigmentation conferred by the addition of melanocytes in TESs protects against UVR-induced DNA damage. Therefore, autologous pigmented TESs could ensure photoprotection after grafting.

In Situ Analysis of DNA-Protein Complex Formation upon Radiation-Induced DNA Damage

The importance of determining at the cellular level the formation of DNA–protein complexes after radiation-induced lesions to DNA is outlined by the evidence that such interactions represent one of the first steps of the cellular response to DNA damage. These complexes are formed through recruitment at the sites of the lesion, of proteins deputed to signal the presence of DNA damage, and of DNA repair factors necessary to remove it. Investigating the formation of such complexes has provided, and will probably continue to, relevant information about molecular mechanisms and spatiotemporal dynamics of the processes that constitute the first barrier of cell defense against genome instability and related diseases. In this review, we will summarize and discuss the use of in situ procedures to detect the formation of DNA-protein complexes after radiation-induced DNA damage. This type of analysis provides important information on the spatial localization and temporal resolution of the formation of such complexes, at the single-cell level, allowing the study of heterogeneous cell populations.