UV-induced DNA Damage Research Articles

Bombyx mori RPL13 participates in UV-induced DNA damage repair of B. mori nucleopolyhedrovirus through interaction with Bm65.

Ribosomal protein L13 (RPL13) is highly conserved in evolution. At present, the properties and functions of RPL13 have not been characterised in insects. In this study, Bombyx mori RPL13 (BmRPL13) was first found to be specifically recruited to the sites of ultraviolet (UV)-induced DNA damage and contributed to UV damage repair. Escherichia coli expressing BmRPL13 showed better resistance to UV radiation. After knocking down the expression of BmRPL13 in BmN cells, the repair speed of UV-damaged DNA slowed down. The further results showed that BmRPL13 interacted with B. mori nucleopolyhedrovirus (BmNPV) ORF65 (Bm65) protein to locate at the UV-induced DNA damage sites of BmNPV and helped repair UV-damaged viral DNA.

1,25-Dihydroxyvitamin D3 Suppresses UV-Induced Poly(ADP-Ribose) Levels in Primary Human Keratinocytes, as Detected by a Novel Whole-Cell ELISA

Photoprotective properties of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) to reduce UV-induced DNA damage have been established in several studies. UV-induced DNA damage in skin such as single or double strand breaks is known to initiate several cellular mechanisms including activation of poly(ADP-ribose) (pADPr) polymerase-1 (PARP-1). DNA damage from UV also increases extracellular signal-related kinase (ERK) phosphorylation, which further increases PARP activity. PARP-1 functions by using cellular nicotinamide adenine dinucleotide (NAD+) to synthesise pADPr moieties and attach these to target proteins involved in DNA repair. Excessive PARP-1 activation following cellular stress such as UV irradiation may result in excessive levels of cellular pADPr. This can also have deleterious effects on cellular energy levels due to depletion of NAD+ to suboptimal levels. Since our previous work indicated that 1,25(OH)2D3 reduced UV-induced DNA damage in part through increased repair via increased energy availability, the current study investigated the effect of 1,25(OH)2D3 on UV-induced PARP-1 activity using a novel whole-cell enzyme- linked immunosorbent assay (ELISA) which quantified levels of the enzymatic product of PARP-1, pADPr. This whole cell assay used around 5000 cells per replicate measurement, which represents a 200–400-fold decrease in cell requirement compared to current commercial assays that measure in vitro pADPr levels. Using our assay, we observed that UV exposure significantly increased pADPr levels in human keratinocytes, while 1,25(OH)2D3 significantly reduced levels of UV-induced pADPr in primary human keratinocytes to a similar extent as a known PARP-1 inhibitor, 3-aminobenzamide (3AB). Further, both 1,25(OH)2D3 and 3AB as well as a peptide inhibitor of ERK-phosphorylation significantly reduced DNA damage in UV-exposed keratinocytes. The current findings support the proposal that reduction in pADPr levels may be critical for the function of 1,25(OH)2D3 in skin to reduce UV-induced DNA damage.

Evidence for persistent UV-induced DNA damage and altered DNA damage response in xeroderma pigmentosa patient corneas

Xeroderma pigmentosum (XP) is a rare genetic disorder characterized by injury to the ocular surface due to exposure to ultraviolet (UV) radiation. UV-induced damage in the cells leads to the formation of cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine-pyrimidone photoproducts that are repaired by the NER (Nucleotide Excision Repair) pathway. Mutations in the genes coding for NER proteins, as reported in XP patients, would lead to sub-optimal damage repair resulting in clinical signs varying from photo-keratitis to cancerous lesions on the ocular surface. Here, we aimed to provide evidence for the accumulation of DNA damage and activation of DNA repair pathway proteins in the corneal cells of patients with XP. Corneal buttons of patients who underwent penetrating keratoplasty were stained to quantify DNA damage and the presence of activated DNA damage response proteins (DDR) using specific antibodies. Positive staining for pH2A.X and thymidine dimers confirmed the presence of DNA damage in the corneal cells. Positive cells were found in both control corneas and XP samples however, unlike normal tissues, positive cells were found in all cell layers of XP samples indicating that these cells were sensitive to very low levels of UV. pH2A.X-positive cells were significantly more in XP corneas (p < 0.05) indicating the presence of double strand breaks in these tissues. A positive expression of phosphorylated-forms of DDR proteins was noted in XP corneas (unlike controls) such as ataxia telangiectasia mutated/Rad-3 related proteins (ATM/ATR), breast cancer-1 and checkpoint kinases-1 and -2. Nuclear localization of XPA was noted in XP samples which co-localized (calculated using Pearson's correlation) with pATM (0.9 ± 0.007) and pATR (0.6 ± 0.053). The increased presence of these in the nucleus confirms that unresolved DNA damage was accumulating in these cells thereby leading to prolonged activation of the damage response proteins. An increase in pp53 and TUNEL positive cells in the XP corneas indicated cell death likely driven by the p53 pathway. For comparison, cultured normal corneal epithelial cells were exposed to UV-radiation and stained for DDR proteins at 3, 6 and 24 h after irradiation to quantify the time taken by cells with intact DDR pathway to repair damage. These cells, when exposed to UV showed nuclear translocation of DDR proteins at 3 and 6 h which reduced significantly by 24 h confirming that the damaged DNA was being actively repaired leading to cell survival. The persistent presence of the DDR proteins in XP corneas indicates that damage is being actively recognized and DNA replication is stalled, thereby causing accumulation of damaged DNA leading to cell death, which would explain the cancer incidence and cell loss reported in these patients.

Transcriptomic Evidence of Base and Nucleotide Excision Repair Mechanisms in Response to UV-B Radiation in an Arctic Fungus Pseudogymnoascus australis Strain HNDR4

Polar micro-fungi are known to have developed protective mechanisms and responses against the harmful effects of UV radiation. In this study, physiological, cellular, and transcriptomic responses of an Arctic fungal strain of Pseudogymnoascus australis towards UV-B radiation were examined. Fungal isolate was cultured on 0.45μm nylon membranes overlayed on Czapex-Dox agar (CDA) at 15ºC for 10 d in dark condition to reach the mid-log phase. To assess DNA damage and recovery, the isolates were exposed to UV-B radiation (UV dosage of 6.1 kj m-2 d-1) for 130 min, followed by 0, 2 and 6 hr incubation under light condition. Differential gene expression in DNA repair after UV-B treatment at these time points was analysed based on RNA-Seq data output of 40 million reads per sample from an Illumina NovaSeq 6000 system platform. The results revealed that radiation-repair (RAD) genes were upregulated and the photoreactivation (PHR1) gene was downregulated after UV-B exposure in light condition. Downregulation of oxidoreductase activity was observed from the GO enrichment analysis. The KEGG pathway enrichment analysis exhibited upregulation of base excision repair (BER) genes and nucleotide excision repair (NER) genes upon UV-B exposure. This is the fi rst RNASeq transcriptomic study on the DNA repair mechanisms employed by a polar fungus to mitigate UV-induced DNA damage.

Role of autophagy in skin photoaging: A narrative review.

As the largest organ of the human body, the skin serves as the primary barrier against external damage. The continuous increase in human activities and environmental pollution has resulted in the ongoing depletion of the ozone layer. Excessive exposure to ultraviolet (UV) radiation enhances the impact of external factors on the skin, leading to photoaging. Photoaging causes physical and psychological damage to the human body. The prevention and management of photoaging have attracted increased attention in recent years. Despite significant progress in understanding and mitigating UV-induced photoaging, the precise mechanisms through which autophagy contributes to the prevention of photoaging remain unclear. Given the important role of autophagy in repairing UV-induced DNA damage and scavenging oxidized lipids, autophagy is considered a novel strategy for preventing the occurrence of photoaging and other UV light-induced skin diseases. This review aims to elucidate the biochemical and clinical features of photoaging, the relationship of skin photoaging and chronological aging, the mechanisms underlying skin photoaging and autophagy, and the role of autophagy in skin photoaging.

Significance of melanin distribution in the epidermis for the protective effect against UV light

Melanin, the most abundant skin chromophore, is produced by melanocytes and is one of the key components responsible for mediating the skin’s response to ultraviolet radiation (UVR). Because of its antioxidant, radical scavenging, and broadband UV absorbing properties, melanin reduces the penetration of UVR into the nuclei of keratinocytes. Despite its long-established photoprotective role, there is evidence that melanin may also induce oxidative DNA damage in keratinocytes after UV exposure and therefore be involved in the development of melanoma. The present work aimed at evaluating the dependence of UV-induced DNA damage on melanin content and distribution, using reconstructed human epidermis (RHE) models. Tanned and light RHE were irradiated with a 233 nm UV-C LED source at 60 mJ/cm2 and a UV lamp at 3 mJ/cm2. Higher UV-mediated free radicals and DNA damage were detected in tanned RHE with significantly higher melanin content than in light RHE. The melanin distribution in the individual models can explain the lack of photoprotection. Fluorescence lifetime-based analysis and Fontana–Masson staining revealed a non-homogeneous distribution and absence of perinuclear melanin in the tanned RHE compared to the in vivo situation in humans. Extracellularly dispersed epidermal melanin interferes with photoprotection of the keratinocytes.

Cold-induced skin darkening does not protect amphibian larvae from UV-associated DNA damage.

Amphibian declines are sometimes correlated with increasing levels of ultraviolet radiation (UVR).While disease is often implicated in declines, environmental factors such as temperature and UVR play an important role in disease epidemiology. The mutagenic effects of UVR exposure on amphibians are worse at low temperatures. Amphibians from cold environments may be more susceptible to increasing UVR. However, larvae of some species demonstrate cold acclimation, reducing UV-induced DNA damage at low temperatures. Understanding of the mechanisms underpinning this response is lacking. We reared Limnodynastes peronii larvae in cool (15°C) or warm (25°C) waters before acutely exposing them to 1.5 h of high intensity (80 µW cm-2 ) UVBR. We measured the color of larvae and mRNA levels of a DNA repair enzyme. We reared larvae at 25°C in black or white containers to elicit a skin color response, and then measured DNA damage levels in the skin and remaining carcass following UVBR exposure. Cold-acclimated larvae were darker and displayed lower levels of DNA damage than warm-acclimated larvae. There was no difference in CPD-photolyase mRNA levels between cold- and warm-acclimated larvae. Skin darkening in larvae did not reduce their accumulation of DNA damage following UVR exposure. Our results showed that skin darkening does not explain cold-induced reductions in UV-associated DNA damage in L. peronii larvae. Beneficial cold-acclimation is more likely underpinned by increased CPD-photolyase abundance and/or increased photolyase activity at low temperatures.

Unveiling the Spectrum of UV-Induced DNA Damage in Melanoma: Insights From AI-Based Analysis of Environmental Factors, Repair Mechanisms, and Skin Pigment Interactions

Unveiling the Spectrum of UV-Induced DNA Damage in Melanoma: Insights From AI-Based Analysis of Environmental Factors, Repair Mechanisms, and Skin Pigment Interactions

Long-run real-time PCR analysis of repetitive nuclear elements as a novel tool for DNA damage quantification in single cells: an approach validated on mouse oocytes and fibroblasts

Since DNA damage is of great importance in various biological processes, its rate is frequently assessed both in research studies and in medical diagnostics. The most precise methods of quantifying DNA damage are based on real-time PCR. However, in the conventional version, they require a large amount of genetic material and therefore their usefulness is limited to multicellular samples. Here, we present a novel approach to long-run real-time PCR-based DNA-damage quantification (L1-LORD-Q), which consists in amplification of long interspersed nuclear elements (L1) and allows for analysis of single-cell genomes. The L1-LORD-Q was compared with alternative methods of measuring DNA breaks (Bioanalyzer system, γ-H2AX foci staining), which confirmed its accuracy. Furthermore, it was demonstrated that the L1-LORD-Q is sensitive enough to distinguish between different levels of UV-induced DNA damage. The method was validated on mouse oocytes and fibroblasts, but the general idea is universal and can be applied to various types of cells and species.

One More for Light-triggered Conformational Changes in Cryptochromes: CryP from Phaeodactylum tricornutum

Cryptochromes are a ubiquitously occurring class of photoreceptors. Together with photolyases, they form the Photolyase Cryptochrome Superfamily (PCSf) by sharing a common protein architecture and binding mode of the FAD chromophore. Despite these similarities, PCSf members exert different functions. Photolyases repair UV-induced DNA damage by photocatalytically driven electron transfer between FADH¯ and the DNA lesion, whereas cryptochromes are light-dependent signaling molecules and trigger various biological processes by photoconversion of their FAD redox and charge states. Given that most cryptochromes possess a C-terminal extension (CTE) of varying length, the functions of their CTE have not yet been fully elucidated and are hence highly debated. In this study, the role of the CTE was investigated for a novel subclass of the PCSf, the CryP-like cryptochromes, by hydrogen/deuterium exchange and mass-spectrometric analysis. Striking differences in the relative deuterium uptake were observed in different redox states of CryP from the diatom Phaeodactylum tricornutum. Based on these measurements we propose a model for light-triggered conformational changes in CryP-like cryptochromes that differs from other known cryptochrome families like the insect or plant cryptochromes.

Complex coacervate-derived hydrogel with asymmetric and reversible wet bioadhesion for preventing UV light-induced morbidities.

Protecting the skin from UV light irradiation in wet and underwater environments is challenging due to the weak adhesion of existing sunscreen materials but highly desired. Herein we report a polyethyleneimine/thioctic acid/titanium dioxide (PEI/TA/TiO2) coacervate-derived hydrogel with robust, asymmetric, and reversible wet bioadhesion and effective UV-light-shielding ability. The PEI/TA/TiO2 complex coacervate can be easily obtained by mixing a PEI solution and TA/TiO2 powder. The fluid PEI/TA/TiO2 coacervate deposited on wet skin can spread into surface irregularities and subsequently transform into a hydrogel with increased cohesion, thereby establishing interdigitated contact and adhesion between the bottom surface and skin. Meanwhile, the functional groups between the skin and hydrogel can form physical interactions to further enhance bioadhesion, whereas the limited movement of amine and carboxyl groups on the top hydrogel surface leads to low adhesion. Therefore, the coacervate-derived hydrogel exhibits asymmetric adhesiveness on the bottom and top surfaces. Moreover, the PEI/TA/TiO2 hydrogel formed on the skin could be easily removed using a NaHCO3 aqueous solution without inflicting damage. More importantly, the PEI/TA/TiO2 hydrogel can function as an effective sunscreen to block UV light and prevent UV-induced MMP-9 overexpression, inflammation, and DNA damage in animal skin. The advantages of PEI/TA/TiO2 coacervate-derived hydrogels include robust, asymmetric, and reversible wet bioadhesion, effective UV light-shielding ability, excellent biocompatibility, and easy preparation and usage, making them a promising bioadhesive to protect the skin from UV light-associated damage in wet and underwater environments.

Molluscan Genomes Reveal Extensive Differences in Photopigment Evolution Across the Phylum.

In animals, opsins and cryptochromes are major protein families that transduce light signals when bound to light-absorbing chromophores. Opsins are involved in various light-dependent processes, like vision, and have been co-opted for light-independent sensory modalities. Cryptochromes are important photoreceptors in animals, generally regulating circadian rhythm, they belong to a larger protein family with photolyases, which repair UV-induced DNA damage. Mollusks are great animals to explore questions about light sensing as eyes have evolved multiple times across, and within, taxonomic classes. We used molluscan genome assemblies from 80 species to predict protein sequences and examine gene family evolution using phylogenetic approaches. We found extensive opsin family expansion and contraction, particularly in bivalve xenopsins and gastropod Go-opsins, while other opsins, like retinochrome, rarely duplicate. Bivalve and gastropod lineages exhibit fluctuations in opsin repertoire, with cephalopods having the fewest number of opsins and loss of at least 2 major opsin types. Interestingly, opsin expansions are not limited to eyed species, and the highest opsin content was seen in eyeless bivalves. The dynamic nature of opsin evolution is quite contrary to the general lack of diversification in mollusk cryptochromes, though some taxa, including cephalopods and terrestrial gastropods, have reduced repertoires of both protein families. We also found complete loss of opsins and cryptochromes in multiple, but not all, deep-sea species. These results help set the stage for connecting genomic changes, including opsin family expansion and contraction, with differences in environmental, and biological features across Mollusca.

Cross-species investigation into the requirement of XPA for nucleotide excision repair.

After reconstitution of nucleotide excision repair (excision repair) with XPA, RPA, XPC, TFIIH, XPF-ERCC1and XPG, it was concluded that these six factors are the minimal essential components of the excision repair machinery. All six factors are highly conserved across diverse organisms spanning yeast to humans, yet no identifiable homolog of the XPA gene exists in many eukaryotes including green plants. Nevertheless, excision repair is reported to be robust in the XPA-lacking organism, Arabidopsis thaliana, which raises a fundamental question of whether excision repair could occur without XPA in other organisms. Here, we performed a phylogenetic analysis of XPA across all species with annotated genomes and then quantitatively measured excision repair in the absence of XPA using the sensitive whole-genome qXR-Seq method in human cell lines and two model organisms, Caenorhabditis elegans and Drosophila melanogaster. We find that although the absence of XPA results in inefficient excision repair and UV-sensitivity in humans, flies, and worms, excision repair of UV-induced DNA damage is detectable over background. These studies have yielded a significant discovery regarding the evolution of XPA protein and its mechanistic role in nucleotide excision repair.

Inhibiting NOXO1 and CYBA binding to reduce NADPH oxidase I dependent ROS damage in skin explants

NADPH oxidases (NOXs) are newly identified enzymes that generate intracellular reactive oxygen species (ROS) in skin cells. Recent studies demonstrated that NOX1 holoenzyme is expressed in human keratinocytes and melanocytes, which are implicated in skin photo-carcinogenesis due to the high amounts of ROS produced. Holoenzyme activation requires a ternary complex comprised of NOX1, cytochrome B alpha chain (CYBA), and cytoplasmic NADPH Oxidase Organizer 1 (NOXO1) to properly form. By inhibiting this assembly process, an opportunity for reducing the production of catalytic ROS is possible, especially during high ROS conditions that occur under prolonged UV exposure. We designed a series of small molecules and evaluated their inhibitory effects on NOXO2 using in-silico docking methods in the 1WLP crystal structure. We show that the NOX_inh_5 inhibitor was successful in a variety of experiments using primary skin models from various skin tones. NOX_inh_5 proved to be non-cytotoxic while also improving the viability of primary human skin primary cells under UV exposure. Biophysical studies with NOX_inh_5 using an Isothermal calorimetric (ITC) binding and heteronuclear single quantum coherence (HSQC-NMR) exhibited inhibition of complex formation between NOXO2 and CYBA. Authentic human skin explants, treated with and without NOX_inh_5 and UV exposure, decreased p53 stabilization and decreased UV-induced DNA damage as quantified through cyclobutane dimer formation.

A gel-forming α-MSH analog promotes lasting melanogenesis

The α-MSH peptide plays a significant role in the regulation of pigmentation via the melanocortin 1 receptor (MC1R). It increases the DNA repair capacity of melanocytes and reduces the incidence of skin cancers. As such, α-MSH analogs could have the utility for protecting against UV-induced skin DNA damage in susceptible patients. Recently, α-MSH analogs have been approved for the treatment of erythropoietic protoporphyria, hypoactive sexual desire, or pediatric obesity. However, the delivery of these drugs requires inconvenient implants or frequent injections. We recently found that select palmitoylated melanocortin analogs such as afamelanotide and adrenocorticotropin peptides self-assemble to form liquid gels in situ. To explore the utility of these novel analogs, we studied their pharmacological characteristics in vitro and in vivo. Acylated afamelanotide (DDE 313) and ACTH1-24 (DDE314) analogs form liquid gels at 6–20% and have a significantly increased viscosity at >2.5% compared to original analogs. Using the DDE313 analog as a prototype, we showed gel-formation reduces the passage of DDE313 through Centricon filters, and subcutaneous injection of analog gel in rats leads to the sustained presence of the peptide in circulation for >12 days. In addition, DDE313 darkened the skin of frogs for >4 weeks, whereas those injected with an equivalent dose of afamelanotide lost the tanning response within a few days. Because self-assembled gels allow sustained activation of melanocortin receptors, further studies of these analogs may allow the development of effective and convenient tanning therapies to prophylactically protect against UV-induced malignant transformation of skin cells in susceptible patients.

LB1756 The role of cNOS in UV-induced DNA damage and repair

LB1756 The role of cNOS in UV-induced DNA damage and repair

The Over-Irradiation Metabolite Derivative, 24-Hydroxylumister-ol3, Reduces UV-Induced Damage in Skin.

The hormonal form of vitamin D3, 1,25(OH)2D3, reduces UV-induced DNA damage. UV exposure initiates pre-vitamin D3 production in the skin, and continued UV exposure photoisomerizes pre-vitamin D3 to produce "over-irradiation products" such as lumisterol3 (L3). Cytochrome P450 side-chain cleavage enzyme (CYP11A1) in skin catalyzes the conversion of L3 to produce three main derivatives: 24-hydroxy-L3 [24(OH)L3], 22-hydroxy-L3 [22(OH)L3], and 20,22-dihydroxy-L3 [20,22(OH)L3]. The current study investigated the photoprotective properties of the major over-irradiation metabolite, 24(OH)L3, in human primary keratinocytes and human skin explants. The results indicated that treatment immediately after UV with either 24(OH)L3 or 1,25(OH)2D3 reduced UV-induced cyclobutane pyrimidine dimers and oxidative DNA damage, with similar concentration response curves in keratinocytes, although in skin explants, 1,25(OH)2D3 was more potent. The reductions in DNA damage by both compounds were, at least in part, the result of increased DNA repair through increased energy availability via increased glycolysis, as well as increased DNA damage recognition proteins in the nucleotide excision repair pathway. Reductions in UV-induced DNA photolesions by either compound occurred in the presence of lower reactive oxygen species. The results indicated that under in vitro and ex vivo conditions, 24(OH)L3 provided photoprotection against UV damage similar to that of 1,25(OH)2D3.

Nucleotide excision repair in Human cell lines lacking both XPC and CSB proteins.

Nucleotide excision repair removes UV-induced DNA damage through two distinct sub-pathways, global repair and transcription-coupled repair (TCR). Numerous studies have shown that in human and other mammalian cell lines that the XPC protein is required for repair of DNA damage from nontranscribed DNA via global repair and the CSB protein is required for repair of lesions from transcribed DNA via TCR. Therefore, it is generally assumed that abrogating both sub-pathways with an XPC-/-/CSB-/- double mutant would eliminate all nucleotide excision repair. Here we describe the construction of three different XPC-/-/CSB-/- human cell lines that, contrary to expectations, perform TCR. The XPC and CSB genes were mutated in cell lines derived from Xeroderma Pigmentosum patients as well as from normal human fibroblasts and repair was analyzed at the whole genome level using the very sensitive XR-seq method. As predicted, XPC-/- cells exhibited only TCR and CSB-/- cells exhibited only global repair. However, the XPC-/-/CSB-/- double mutant cell lines, although having greatly reduced repair, exhibited TCR. Mutating the CSA gene to generate a triple mutant XPC-/-/CSB-/-/CSA-/- cell line eliminated all residual TCR activity. Together, these findings provide new insights into the mechanistic features of mammalian nucleotide excision repair.

Immune checkpoint VISTA regulates DNA sensing and repair pathways that contribute to type I interferon (IFN-I) production in the skin

Abstract Skin sterile injury by ultraviolet (UV) light stimulates production of type I interferons. While in healthy skin IFN-I response to UV returns to baseline over time, the IFN-I signature persists in photosensitive diseases like lupus. The pathways that downregulate IFN-I production in healthy skin, and fail to do so in lupus skin, are unknown. Previous studies showing that activating VISTA suppresses the IFN-I signature in monocytes suggest a role for this immune checkpoint in the regulation of the IFN-I response. Indeed, we showed that the skin IFN-I signature is elevated in mice globally deficient in VISTA (Vsir−/−), as well as in mice with a conditional deletion of VISTA in keratinocytes. Having confirmed its expression in keratinocytes, we tested if VISTA regulates UV-triggered IFN-I production in the skin. Expression analysis of IFN-I stimulated genes in skin biopsies collected prior to and 3h after a single dose of UVB, revealed ~10-fold higher IFN-I score in Vsir−/− vs. B6 skin after UV. RNAseq studies showed DNA sensors, ZBP1, cGAS, and IFI204 were upregulated, while nucleotide excision repair genes, Polɛ and DNA Ligase1, were suppressed in Vsir−/− skin, both at baseline and 3h after UV. Moreover, Polɛ protein levels were lower in Vsir−/− skin by immunoblot. Relevant to its role in keratinocytes, IFN-k protein levels were higher in VISTA-deficient epidermal keratinocytes ex vivo, accompanied by elevated mRNA levels of ZBP1 and IFI204 before and after UV. Together, this study identifies VISTA as a novel regulator of IFN-I production, by modulating DNA damage repair and sensing. The keratinocyte-intrinsic role of VISTA is therapeutically relevant as lupus keratinocytes express high IFN-k and are direct targets of UV-induced DNA damage. 1R21AR079661 – 01, Hitchcock Foundation, DOD lupus award

Unbalanced Growth, the DNA Replication Cycle and Discovery of Repair Replication.

This article recounts my graduate research at Yale University (1954-1958) on unbalanced growth in Eschericia coli during thymine deprivation or following ultraviolet (UV) irradiation, with early evidence for the repair of UV-induced DNA damage. Follow-up studies in Copenhagen (1958-1960) in the laboratory of Ole Maaløe led to my discovery that the DNA replication cycle can be synchronized by inhibiting protein and RNA syntheses and that an RNA synthesis step is essential for initiation of the cycle, but not for its completion. This work set the stage for my subsequent research at Stanford University, where the repair replication of damaged DNA was documented, to provide compelling evidence for an excision-repair pathway. That universal pathway validates the requirement for the redundant information in the complementary strands of duplex DNA to ensure genomic stability.