Pyrimidine Dimers (pyrimidine + dimer)

Distribution by Scientific Domains

Kinds of Pyrimidine Dimers

  • cyclobutane pyrimidine dimer

  • Selected Abstracts

    Production and clearance of cyclobutane dipyrimidine dimers in UV-irradiated skin pretreated with 1% pimecrolimus or 0.1% triamcinolone acetonide creams in normal and atopic patients

    Laurence Doelker
    Background:, Ultraviolet (UV)-induced pyrimidine dimers are an early step in skin carcinogenesis, which is accelerated in the setting of long-term immunosuppression with systemic calcineurin inhibitors. It is not known whether topical application of calcineurin inhibitors exposes to a similar risk. Objective:, To assess the formation and clearance of UV-induced dipyrimidine dimers in human epidermis treated with topical pimecrolimus as compared to topical steroid, vehicle and untreated control. Methods:, Pretreated buttock skin of 20 human volunteers with (10) or without (10) atopic dermatitis was exposed to two minimal erythema doses (MED) of simulated solar radiation. DNA was extracted from epidermis 1 and 24 h postirradiation. Pyrimidine dimers were visualized by immuno slot blots and quantified by chemoluminescence image analysis. Results:, One-hour postirradiation, pimecrolimus-treated epidermis contains less DNA damage as compared to untreated control, but there were no statistically significant differences between pimecrolimus, triamcinolone acetonide and vehicle. Dimer levels at 24 h postirradiation showed no significant differences between different treatments. Conclusion:, Treatment with pimecrolimus cream, triamcinolone acetonide cream and vehicle is not associated with increased epidermal DNA damage at 1 and 24 h post-UV exposure. [source]

    The Rad4 homologue YDR314C is essential for strand-specific repair of RNA polymerase I-transcribed rDNA in Saccharomyces cerevisiae

    Ben Den Dulk
    Summary The Saccharomyces cerevisiae protein Rad4 is involved in damage recognition in nucleotide excision repair (NER). In RNA polymerase II-transcribed regions Rad4 is essential for both NER subpathways global genome repair (GGR) and transcription coupled repair (TCR). In ribosomal DNA (rDNA), however, the RNA polymerase I-transcribed strand can be repaired in the absence of Rad4. In Saccharomyces cerevisiae the YDR314C protein shows homology to Rad4. The possible involvement of YDR314C in NER was studied by analysing strand-specific cyclobutane pyrimidine dimer (CPD) removal in both RNA pol I- and RNA pol II-transcribed genes. Here we show that the Rad4-independent repair of rDNA is dependent on YDR314C. Moreover, in Rad4 proficient cells preferential repair of the transcribed strand of RNA pol I-transcribed genes was lost after deletion of YDR314C, demonstrating that Rad4 cannot replace YDR314C. CPD removal from the RNA pol II-transcribed RPB2 gene was unaffected in ydr314c mutants. We conclude that the two homologous proteins Rad4 and YDR314C are both involved in NER and probably have a similar function, but operate at different loci in the genome and are unable to replace each other. [source]

    Decreased Levels of (6,4) Photoproduct Excision Repair in Hybrid Fish of the Genus Xiphophorus,

    David L. Mitchell
    ABSTRACT Selected hybridization in the fish genus Xiphophorus has been used for many years to study the genetics of malignant melanoma. Because DNA damage caused by ultraviolet radiation is implicated in the etiology of sunlight-induced melanoma, the heritability of mechanisms that mitigate DNA damage is a matter of some interest. We examined nucleotide excision repair of the two major types of DNA-damage induced by sunlight; the cyclobutane pyrimidine dimer (CPD) and the pyrimidine (6,4) pyrimidone dimer [(6,4)PD]. In most cases, removal of the (6,4) PD was more rapid than the CPD, and in many cases, the F1 hybrid showed reduced repair efficiency compared with the parental species. These data demonstrate reduced function in multienzyme hybrid systems and provide molecular support for potential reduced fitness in hybrid fish under conditions of environmental stress. [source]

    Characterization of two members of the cryptochrome/photolyase family from Ostreococcus tauri provides insights into the origin and evolution of cryptochromes

    PLANT CELL & ENVIRONMENT, Issue 10 2010
    ABSTRACT Cryptochromes (Crys) are blue light receptors believed to have evolved from the DNA photolyase protein family, implying that light control and light protection share a common ancient origin. In this paper, we report the identification of five genes of the Cry/photolyase family (CPF) in two green algae of the Ostreococcus genus. Phylogenetic analyses were used to confidently assign three of these sequences to cyclobutane pyrimidine dimer (CPD) photolyases, one of them to a DASH-type Cry, and a third CPF gene has high homology with the recently described diatom CPF1 that displays a bifunctional activity. Both purified OtCPF1 and OtCPF2 proteins show non-covalent binding to flavin adenine dinucleotide (FAD), and additionally to 5,10-methenyl-tetrahydrofolate (MTHF) for OtCPF2. Expression analyses revealed that all five CPF members of Ostreococcus tauri are regulated by light. Furthermore, we show that OtCPF1 and OtCPF2 display photolyase activity and that OtCPF1 is able to interact with the CLOCK:BMAL heterodimer, transcription factors regulating circadian clock function in other organisms. Finally, we provide evidence for the involvement of OtCPF1 in the maintenance of the Ostreococcus circadian clock. This work improves our understanding of the evolutionary transition between photolyases and Crys. [source]

    DNA damage and photosynthesis in Antarctic and Arctic Sanionia uncinata (Hedw.) Loeske under ambient and enhanced levels of UV-B radiation

    PLANT CELL & ENVIRONMENT, Issue 12 2002
    D. LUD
    Abstract The response of the bipolar moss Sanionia uncinata (Hedw.) Loeske to ambient and enhanced UV-B radiation was investigated at an Antarctic (Léonie Island, 67°35, S, 68°20, W) and an Arctic (Ny-Alesund, 78°55, N, 11°56, E) site, which differed in ambient UV-B radiation (UV-BR: 280,320 nm) levels. The UV-BR effects on DNA damage and photosynthesis were investigated in two types of outdoor experiments. First of all, sections of turf of S. uncinata were collected in an Arctic and Antarctic field site and exposed outdoors to ambient and enhanced UV-BR for 2 d using UV-B Mini-lamps. During these experiments, chlorophyll a fluorescence, chlorophyll concentration and cyclobutyl pyrimidine dimer (CPD) formation were measured. Secondly, at the Antarctic site, a long-term filter experiment was conducted to study the effect of ambient UV-BR on growth and biomass production. Additionally, sections of moss turf collected at both the Antarctic and the Arctic site were exposed to UV-BR in a growth chamber to study induction and repair of CPDs under controlled conditions. At the Antarctic site, a summer midday maximum of 2·1 W m,2 of UV-BR did not significantly affect effective quantum yield (,F/Fm,) and the ratio of variable to maximal fluorescence (Fv/Fm). The same was found for samples of S. uncinata exposed at the Arctic site, where summer midday maxima of UV-BR were about 50% lower than at the Antarctic site. Exposure to natural UV-BR in summer did not increase CPD values significantly at both sites. Although the photosynthetic activity remained largely unaffected by UV-B enhancement, DNA damage clearly increased as a result of UV-B enhancement at both sites. However, DNA damage induced during the day by UV-B enhancement was repaired overnight at both sites. Results from the long-term filter experiment at the Antarctic site indicated that branching of S. uncinata was reduced by reduction of ambient summer levels of UV-BR, whereas biomass production was not affected. Exposure of specimens collected from both sites to UV-BR in a growth chamber indicated that Antarctic and Arctic S. uncinata did not differ in UV-BR-induced DNA damage. It was concluded that S. uncinata from both the Antarctic and the Arctic site is well adapted to ambient levels of UV-BR. [source]

    Mutation spectrum in UVB-exposed skin epidermis of Xpa -knockout mice: Frequent recovery of triplet mutations

    Hironobu Ikehata
    Abstract Knockout mutations in both alleles of the Xpa gene give rise to a complete deficiency in nucleotide excision repair (NER) in mammalian cells. We used transgenic mice harboring the ,-phage-based lacZ mutational reporter gene to study the effect of Xpa null mutation (Xpa,/,) on damage induction, repair, and mutagenesis in mouse skin epidermis after UVB irradiation. UVB induced equal amounts of cyclobutane pyrimidine dimers (CPDs) and pyrimidine(6-4)pyrimidone photoproducts (64PPs) in mouse skin epidermis of Xpa,/, and wild-type mice. Neither photolesion was removed in the Xpa,/, epidermis by 12 hr after irradiation whereas removal of 64PPs was observed in the epidermis of wild-type mice. Irradiation with 200 and 300 J/m2 UVB increased the lacZ mutant frequency in the epidermis of Xpa,/, mice, but the induced mutant frequencies were not significantly different from those previously determined for wild-type mice. One-hundred lacZ mutants isolated from the UVB-exposed epidermis of Xpa,/, mice were analyzed and compared with mutant sequences previously determined for irradiated wild-type mice. The distribution of the mutations along the lacZ transgene and the preferred dipyrimidine context of the UV-specific mutations were similar in mutants from the Xpa,/, and wild-type mice. The spectra of the mutations in the two genotypes were both highly UV-specific and similar in a dominance of C , T transitions at dipyrimidine sites; however, Xpa,/, mice had a higher frequency than wild-type mice of two-base tandem substitutions, including CC , TT mutations, three-base tandem mutations and double base substitutions that were separated by one unchanged base in a three-base sequence (alternating mutations). These tandem/alternating mutations included a remarkably large number of triplet mutations, a recently reported, novel type of UV-specific mutation, characterized by multiple base substitutions or frameshifts within a three-nucleotide sequence containing a dipyrimidine. We conclude that the triplet mutation is a UV-specific mutation that preferably occurs in NER-deficient genetic backgrounds. Environ. Mol. Mutagen., 2007. © 2006 Wiley-Liss, Inc. [source]

    A model for targeted substitution mutagenesis during SOS replication of double-stranded DNA containing cis-syn cyclobutane thymine dimers

    Helen A. Grebneva
    Abstract A model for ultraviolet mutagenesis is described that is based on the formation of rare tautomeric bases in pyrimidine dimers. It is shown that during SOS synthesis the modified DNA-polymerase inserts canonical bases opposite the dimers; the inserted bases are capable of forming hydrogen bonds with bases in the template DNA. SOS-replication of double-stranded DNA having thymine dimers, with one or both bases in a rare tautomeric conformation, results in targeted transitions, transversions, or one-nucleotide gaps. Structural analysis indicates that one type of dimer containing a single tautomeric base (TT1*, with the "*" indicating a rare tautomeric base and the subscript referring to the particular conformation) can cause A:T , G:C transition or homologous A:T , T:A transversion, while another dimer (TT2*) can cause a one-nucleotide gap. The dimers containing T4* result in A:T , C:G transversion, while TT5* dimers can cause A:T , C:G transversion or homologous A:T , T:A transversion. If both bases in the dimer are in a rare tautomeric form, then tandem mutations or double-nucleotide gaps can be formed. The dimers containing the rare tautomeric forms T1 *,, T2*,, T3*,, T4*,, and T5*, may not result in mutations. The question of whether dimers containing T4*, and T5*, result in mutations requires further investigation. Environ. Mol. Mutagen., 2006. © 2006 Wiley-Liss, Inc. [source]

    Production and clearance of cyclobutane dipyrimidine dimers in UV-irradiated skin pretreated with 1% pimecrolimus or 0.1% triamcinolone acetonide creams in normal and atopic patients

    Laurence Doelker
    Background:, Ultraviolet (UV)-induced pyrimidine dimers are an early step in skin carcinogenesis, which is accelerated in the setting of long-term immunosuppression with systemic calcineurin inhibitors. It is not known whether topical application of calcineurin inhibitors exposes to a similar risk. Objective:, To assess the formation and clearance of UV-induced dipyrimidine dimers in human epidermis treated with topical pimecrolimus as compared to topical steroid, vehicle and untreated control. Methods:, Pretreated buttock skin of 20 human volunteers with (10) or without (10) atopic dermatitis was exposed to two minimal erythema doses (MED) of simulated solar radiation. DNA was extracted from epidermis 1 and 24 h postirradiation. Pyrimidine dimers were visualized by immuno slot blots and quantified by chemoluminescence image analysis. Results:, One-hour postirradiation, pimecrolimus-treated epidermis contains less DNA damage as compared to untreated control, but there were no statistically significant differences between pimecrolimus, triamcinolone acetonide and vehicle. Dimer levels at 24 h postirradiation showed no significant differences between different treatments. Conclusion:, Treatment with pimecrolimus cream, triamcinolone acetonide cream and vehicle is not associated with increased epidermal DNA damage at 1 and 24 h post-UV exposure. [source]

    Accumulation of DNA damage in Antarctic mosses: correlations with ultraviolet-B radiation, temperature and turf water content vary among species

    Abstract The susceptibility of three East Antarctic moss species to UV-B radiation was examined by measuring accumulation of cyclobutane pyrimidine dimers under natural sunlight during the austral summer season of 2002/03. The 2002/03 season was characterized by unusually low springtime ozone depletion and as such our results likely underestimate the DNA damage possible in a more typical UV-B radiation season. Despite this all three species accumulated significant DNA photoproducts. We also found a positive association between photoproduct accumulation and incident UV-B radiation in the two cosmopolitan species, Bryum pseudotriquetrum and Ceratodon purpureus, with more DNA damage in samples collected early in the season compared with later in the summer. For B. pseudotriquetrum, negative associations were also observed between photoproduct accumulation and both turf water content and the 10-day mean air temperature. Photoproduct accumulation in the endemic species Schistidium antarctici was similarly high across the season and no significant association with environmental variables was found. Our results are consistent with the two cosmopolitan species having somewhat higher UV-B-screening capabilities and possibly more efficient mechanisms for repairing DNA damage than the endemic S. antarctici. [source]

    Molecular response of nasal mucosa to therapeutic exposure to broad-band ultraviolet radiation

    David Mitchell
    Abstract Ultraviolet radiation (UVR) phototherapy is a promising new treatment for inflammatory airway diseases. However, the potential carcinogenic risks associated with this treatment are not well understood. UV-specific DNA photoproducts were used as biomarkers to address this issue. Radioimmunoassay was used to quantify cyclobutane pyrimidine dimers (CPDs) and (6,4) photoproducts in DNA purified from two milieus: nasal mucosa samples from subjects exposed to intranasal phototherapy and human airway (EpiAirwayÔ) and human skin (EpiDermÔ) tissue models. Immunohistochemistry was used to detect CPD formation and persistence in human nasal biopsies and human tissue models. In subjects exposed to broadband ultraviolet radiation, DNA damage frequencies were determined prior to as well as immediately after treatment and at increasing times post-treatment. We observed significant levels of DNA damage immediately after treatment and efficient removal of the damage within a few days. No residual damage was observed in human subjects exposed to multiple UVB treatments several weeks after the last treatment. To better understand the molecular response of the nasal epithelium to DNA damage, parallel experiments were conducted in EpiAirway and EpiDerm model systems. Repair rates in these two tissues were very similar and comparable to that observed in human skin. The data suggest that the UV-induced DNA damage response of respiratory epithelia is very similar to that of the human epidermis and that nasal mucosa is able to efficiently repair UVB induced DNA damage. [source]

    Recognition in action: flipping pyrimidine dimers

    David S. Goodsell
    Abstract DNA bases are normally sheltered within a double helix, but enzymes that modify and repair DNA gain access by flipping individual bases out of the double helix. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Induction of Phlorotannins During UV Exposure Mitigates Inhibition of Photosynthesis and DNA Damage in the Kelp Lessonia nigrescens

    Ivan Gómez
    Phlorotannins of brown algae are multifunctional compounds with putative roles in herbivore deterrence, antioxidation and as primary cell wall components. Due to their peripheral localization and absorption at short wavelengths, a photoprotective role is suggested. We examined the induction of phlorotannins by artificial UV radiation in the intertidal kelp Lessonia nigrescens and whether they attenuate the inhibition of photosynthesis and DNA damage, two major detrimental effects of UV. The soluble and cell wall-bound fractions of phlorotannins were quantified in blades collected in summer and winter. Major findings were that (1) the synthesis of phlorotannins (both forms) was induced by UV only in summer; (2) the induction was fast (within 3 days); and (3) there was a positive relationship between of the contents of insoluble phlorotannins and the suppression of photoinhibition and DNA damage, measured as formation of cyclobutane pyrimidine dimers and 6-4 photoproducts. Overall, the photoprotective role of phlorotannins appears to respond to an interplay between the external UV stimulus, seasonal acclimation and intrinsic morpho-functional processes. In summer, when algae are naturally exposed to high UV irradiances, soluble phlorotannins are induced, while their transition to insoluble phlorotannins could be related with the growth requirements, as active blade elongation occurs during this season. [source]

    Temperature Effects on Survival and DNA Repair in Four Freshwater Cladoceran Daphnia Species Exposed to UV Radiation

    Sandra J. Connelly
    The biological responses of four freshwater daphniid species, Daphnia middendorffiana, D. pulicaria, D. pulex and D. parvula, to a single acute dose of ultraviolet B radiation (UVB) were compared. In addition to survival, we compared the induction of DNA damage (i.e. cyclobutane pyrimidine dimers) between species as well as the ability to repair this damage in the presence or absence of photoreactivating light. All four species showed high levels of shielding against DNA damage when compared to damage induced in purified DNA dosimeters at the same time and dose. Significant variation in survival was observed between species depending on temperature and light conditions. Contrary to our expectations, all species showed significantly higher survival and light-dependent DNA damage removal rates at 10°C compared to 20°C, suggesting that the enhanced rate of photoenzymatic repair (PER) at the lower temperature contributed significantly to the recovery of these organisms from UVB. PER was highly effective in promoting survival of three of the four species at 10°C, but at 20°C it was only partially effective in two species, and ineffective in two others. None of the species showed significant dark repair at 20°C and only D. pulicaria showed a significant capacity at 10°C. Two species, D. middendorffiana and D. pulex, showed some short-term survival at 10°C in absence of PER despite their inability to repair any appreciable amount of DNA damage in the dark. All species died rapidly at 20°C in absence of PER, as predicted from complete or near-absence of nucleotide excision repair (NER). Overall, the protective effects of tissue structure and pigmentation were similar in all Daphnia species tested and greatly mitigated the absorption of UVB by DNA and its damaging effects. Surprisingly, the visibly melanotic D. middendorffiana was not better shielded from DNA damage than the three non-melanotic species, and in fact suffered the highest damage rates. Melanin content in this species was not temperature dependent under the experimental growth conditions, and so did not contribute to temperature-dependent responses. It is evident that different species within the same genus have developed diverse biological responses to UVB. Our data strongly suggest that DNA damage is lethal to Daphnia and that photoenzymatic repair is the primary mechanism for removing these lesions. In the absence of light, few species are capable of removing any DNA damage. Surprisingly, the single species in which significant excision repair was detected did so only at reduced temperature. This temperature-dependence of excision repair is striking and may reflect adaptations of certain organisms to stress in a complex and changing environment. [source]

    A Bicyclic Monoterpene Diol and UVB Stimulate BRCA1 Phosphorylation in Human Keratinocytes,

    Matthew T. Canning
    ABSTRACT BRCA1 (breast cancer,associated gene 1) is a tumor suppressor gene that plays a role in DNA repair when phosphorylated. Many DNA-damaging agents including UVC and hydrogen peroxide have been shown to induce phosphorylation of BRCA1. Results of this study now show that both UVB and a bicyclic monoterpene diol (BMT diol) result in phosphorylation of BRCA1. This phosphorylation was maximal 2 h after treatment with either agent and declined to basal levels by 24 h. Inhibitor studies revealed that both UVB and the BMT diol phosphorylate BRCA1 through the FK506-binding protein,FKBP rapamycin-associated binding protein pathway, but the BMT diol also led to phosphorylation of BRCA1 through casein kinase II. This suggests that the signaling pathways for UVB and the BMT diol may diverge. Results of this study also show that the BMT diol stimulates the repair of UVB-induced cyclobutane pyrimidine dimers (CPD). Inhibitors of BMT diol,induced BRCA1 phosphorylation blocked the BMT diol,stimulated repair of CPD. This indicates that the BMT diol induces the phosphorylation of BRCA1, which, in turn, leads to an increase in repair of UVB-induced CPD. Therefore, this BMT diol may be useful for ameliorating the damaging effects of UVB. [source]

    Melanin Offers Protection Against Induction of Cyclobutane Pyrimidine Dimers and 6,4 Photoproducts by UVB in Cultured Human Melanocytes,

    Nico P. M. Smit
    ABSTRACT The goal of this investigation was to correlate the melanin content in human pigmentary cells with the generation of UVB-induced photoproducts and to examine the relationship between the melanin content and the removal of the photoproducts. Cultured melanocytes from light-skinned individuals synthesized less melanin and produced more cyclobutane pyrimidine dimers and 6,4 photoproducts upon UVB exposure than did melanocytes from black skin. Tyrosine-stimulated melanogenesis provided protection against DNA damage in both cell types. In another set of pigmented cell lines a ratio between eumelanin and pheomelanin was determined. The assessment of association between DNA damage induction and the quantity and quality of melanin revealed that eumelanin concentration correlated better with DNA protection than pheomelanin. Skin type,I and skin type,VI melanocytes, congenital nevus (CN)-derived cells and skin type,II melanocytes from a multiple-melanoma patient were grown in media with low or high l -tyrosine concentration. The cells were irradiated with 200 J/m2 UVB, and the levels of the photoproducts were determined immediately and after 6 and 24 h. Once again the induction of the photoproducts was mitigated by increased melanogenesis, and it was inversely correlated with the skin type. No significant differences were found for the removal of photoproducts in the cultures of skin types I and VI and CN cells. No indications of a delay in the removal of photoproducts in the melanocytes from the multiple-melanoma patient were found either. [source]

    Topically Applied Eicosapentaenoic Acid Protects Against Local Immunosuppression Induced by UVB Irradiation, cis -Urocanic Acid and Thymidine Dinucleotides,

    Ralf M. W. Moison
    ABSTRACT UVB-induced immunosuppression, a promoter of photocarcinogenesis, involves the formation of pyrimidine dimers and cis -urocanic acid (cis -UCA), but reactive oxygen species (ROS) also plays an important role. Eicosapentaenoic acid (EPA) can inhibit photocarcinogenesis, but due to its polyunsaturated nature it is susceptible to oxidative damage by ROS. The antioxidant defense system may therefore be challenged upon ultraviolet-B (UVB) irradiation in the presence of EPA. We investigated whether topically applied EPA in mice could protect against local immunosuppression (contact hypersensitivity response to dinitrofluorobenzene) induced by UVB radiation (1.5 J/cm2), or topically applied cis -UCA (150 nmol/cm2) or thymidine dinucleotides (pTpT) (5 nmol/cm2). The influence of EPA on epidermal lipid peroxidation and antioxidant status was also measured. UVB irradiation, cis -UCA and pTpT all caused 70% immunosuppression. Topical pretreatment of mice with EPA partially protected against immunosuppression; the EPA dose needed to accomplish this was 10 nmol/cm2 for UVB irradiation, 100 nmol/cm2 for cis -UCA and 1000 nmol/cm2 for pTpT. Higher EPA doses caused higher UVB-induced lipid peroxidation and lower vitamin C levels. Glutathione only decreased with the highest EPA dose whereas vitamin E was not decreased after UVB irradiation. In conclusion, topically applied EPA protects against UVB-, cis -UCA- and pTpT-induced immunosuppression and maintenance of an adequate antioxidant defense seems to be an important prerequisite for the protective action by EPA. [source]

    UVAI-induced Edema and Pyrimidine Dimers in Murine Skin,

    Ronald D. Ley
    ABSTRACT The induction of edema and pyrimidine dimers in epidermal DNA was determined in the skin of SKH:HR1 mice exposed to graded doses of ultraviolet radiation AI (UVAI; 340,400 nm). Exposure to UVAI induced 1.6 ± 0.08 × 10,6 (mean ± standard error of mean) pyrimidine dimers per 108 Da of DNA per J/m2. Edema in irradiated animals was determined as an increase in skinfold thickness. A dose of 1.8 × 106 J/m2 of UVAI that resulted in a 50% increase in skinfold thickness (SFT50%) would have induced 1.0 × 105 dimers per basal cell genome. A similar increase in SFT induced by full spectrum solar ultraviolet radiation (290,400 nm) would accompany the induction of 11.0 × 105 pyrimidine dimers per basal cell genome. These results support a hypothesis that UVAI-induced pathological changes of the skin are mediated through the formation of nondimer photoproducts. [source]

    Damage to DNA in Bacterioplankton: A Model of Damage by Ultraviolet Radiation and its Repair as Influenced by Vertical Mixing ,

    Yannick Huot
    ABSTRACT A model of UV-induced DNA damage in oceanic bacterioplankton was developed and tested against previously published and novel measurements of cyclobutane pyrimidine dimers (CPD) in surface layers of the ocean. The model describes the effects of solar irradiance, wind-forced mixing of bacterioplankton and optical properties of the water on net DNA damage in the water column. The biological part includes the induction of CPD by UV radiation and repair of this damage through photoreactivation and excision. The modeled damage is compared with measured variability of CPD in the ocean: diel variation in natural bacterioplankton communities at the surface and in vertical profiles under different wind conditions (net damage as influenced by repair and mixing); in situ incubation of natural assemblages of bacterioplankton (damage and repair, no mixing); and in situ incubation of DNA solutions (no repair, no mixing). The model predictions are generally consistent with the measurements, showing similar patterns with depth, time and wind speed. A sensitivity analysis assesses the effect on net DNA damage of varying ozone thickness, colored dissolved organic matter concentration, chlorophyll concentration, wind speed and mixed layer depth. Ozone thickness and mixed layer depth are the most important factors affecting net DNA damage in the mixed layer. From the model, the total amplification factor (TAF; a relative measure of the increase of damage associated with a decrease in ozone thickness) for net DNA damage in the euphotic zone is 1.7, as compared with 2.1,2.2 for irradiance weighted for damage to DNA at the surface. [source]

    Mechanisms of mutation formation with long-wave ultraviolet light (UVA)

    Thomas M. Rünger
    Summary Long-wave ultraviolet (UV) A light is able to damage DNA, to cause mutations, and to induce skin cancer, but the exact mechanisms of UVA-induced mutation formation remain a matter of debate. While pyrimidine dimers are well established to mediate mutation formation with shortwave UVB, other types of DNA damage, such as oxidative base damage, have long been thought to be the premutagenic lesions for UVA mutagenesis. However, pyrimidine dimers can also be generated by UVA, and there are several lines of evidence that these are the most important premutagenic lesions not only for UVB- but also for UVA-induced mutation formation. C,T transition mutations, which are generated by pyrimidine dimers, are called UV-signature mutations. They cannot be interpreted to be solely UVB-induced, as they are induced by UVA as well. Furthermore, there is no consistent evidence for a separate UVA-signature mutation that is only generated with UVA. We hypothesize that a weaker anti-mutagenic cellular response, but not a different type of DNA damage, may be responsible for a higher mutation rate per DNA photoproduct with UVA, as compared with UVB. [source]

    Thalidomide inhibits UVB-induced mouse keratinocyte apoptosis by both TNF-,-dependent and TNF-,-independent pathways

    Kurt Q. Lu
    Background: Thalidomide is an anti-inflammatory pharmacologic agent that has been utilized as a therapy for a number of dermatologic diseases. Its anti-inflammatory properties have been attributed to its ability to antagonize tumor necrosis factor-alfa (TNF-,) production by monocytes. However, its mechanism of action in the skin is not known. Purpose: To test our hypothesis that thalidomide may antagonize TNF-, production in the skin, we used a mouse model for acute ultraviolet-B (UVB) exposure, a known stimulus for inducing this cytokine. Results: A single bolus dose of thalidomide (either 100 or 400 mg/kg) given immediately before UVB exposure (40,120 mJ/cm2) inhibited, in a dose-dependent manner, sunburn cell formation (i.e. keratinocyte (KC) apoptosis as defined by histologic appearance and confirmed by terminal transferase mediated biotinylated dUTP nick end labelling staining) in mouse skin biopsy specimens. However, this agent did not affect the formation of cyclobutane pyrimidine dimers, a measure of UVB-induced DNA damage, which is an early event associated with apoptosis. RNase protection assays confirmed that high (400 mg/kg), but not low (100 mg/kg), doses of thalidomide inhibited the UVB-induced increase in steady-state TNF-, mRNA. Additionally, our in vitro data using neonatal mouse KCs showed that thalidomide prevented UVB-induced cell death (JAM assay). The antiapoptotic effects of thalidomide can be reversed by the addition of exogenous recombinant mouse TNF-, and hence reconstituting UVB-induced programmed cell death. The inhibition of sunburn cell formation by low-dose thalidomide in the absence of TNF-, inhibition suggests that other, unidentified mechanisms of apoptosis inhibition are active. Conclusions: These data suggest that the anti-inflammatory effects of thalidomide can affect UVB injury, and may, in part, explain its action in photosensitivity diseases such as cutaneous lupus erythematosus. [source]

    Repair of cyclobutyl pyrimidine dimers in human skin: variability among normal humans in nucleotide excision and in photorepair

    Betsy M. Sutherland
    Background/Aims: Photoreactivation (PR) of cyclobutyl pyrimidine dimers (CPD) in human skin remains controversial. Recently Whitmore et al. (1) reported negative results of experiments using two photorepair light (PRL) sources on UV-irradiated skin of volunteers. However, their PRL sources induced substantial levels of dimers in skin, suggesting that the additional dimers formed could have obscured PR. We met a similar problem of dimer induction by a PRL source. We designed and validated a PRL source of sufficient intensity to catalyse PR, but that did not induce CPD, and used it to measure photorepair in human skin. Methods and Results: Using a solar simulator filtered with three types of UV-filters, we found significant dimer formation in skin, quantified by number average length analysis using electrophoretic gels of isolated skin DNA. To prevent scattered UV from reaching the skin, we interposed shields between the filters and skin, and showed that the UV-filtered/shielded solar simulator system did not induce damage in isolated DNA or in human skin. We exposed skin of seven healthy human volunteers to 302 nm radiation, then to the improved PRL source (control skin areas were kept in the dark for measurement of excision repair). Conclusions: Using a high intensity PRL source that did not induce dimers in skin, we found that three of seven subjects carried out rapid photorepair of dimers; two carried out moderate or slow dimer photorepair, and three did not show detectable photorepair. Excision repair was similarly variable in these volunteers. Subjects with slower excision repair showed rapid photorepair, whereas those with rapid excision generally showed little or no photoreactivation. [source]

    Effect of photoreactivating light on UV radiation-induced alterations in human skin

    S. E. Whitmore
    Background/Aims: Photoreactivating light (PRL) after ultraviolet radiation (UVR) exposure causes photoreversal of cyclobutane pyrimidine dimers through the activation of photolyase. Although photoreversal has been demonstrated in the ,three kingdoms of life,' its existence in man remains controversial. We sought evidence for photoreversal in man. Methods and Results: Seven subjects were spot-irradiated at two sites with 4 minimal erythema doses (MED) of solar-simulating UVR. Of the two sites, one was then immediately exposed to a PRL source. Epidermal biopsies were taken immediately after exposure. No significant difference in the quantity of pyrimidine dimers was detected comparing the ,UVR only' site to the ,UVR, PRL-exposed' site. Biopsies were repeated 24 h later and no significant difference in p53 protein expression or dendritic cell number was detected. However, the ,UVR, PRL-exposed' site showed a greater reduction in pyrimidine dimer quantity. Conclusions: We found no evidence for a direct effect of PRL causing photoreversal of UVR-induced pyrimidine dimers in man. Our results do, however, suggest that some indirect effect of PRL may enhance pyrimidine dimer repair in the 24-h period following UVR exposure. [source]

    A water soluble extract from Uncaria tomentosa (Cat's Claw) is a potent enhancer of DNA repair in primary organ cultures of human skin

    Thomas Mammone
    Abstract Cat's Claw (Uncaria tomentosa) water extracts, essentially free of oxindole alkaloids, have been shown to possess a broad spectrum of biological activity including DNA repair enhancement and antiinflammatory properties. These two biological mechanisms are key molecular targets to develop treatments that protect skin exposed to ultraviolet light from the sun. Because C-Med-100, a Cat's Claw water extract, is the only documented natural source of components that can up-regulate simultaneously both DNA repair and antiinflammation, its ability to modulate DNA repair in human skin organ cultures was undertaken. For this purpose skin cultures were treated with or without 5 mg/mL C-Med-100, irradiated with 0,100 mJ/cm2 UVB, and microscopically analysed for necrosis as well as the level of pyrimidine dimers using immunofluorescent TT-dimer antibody staining. The data clearly demonstrated that co-incubation with C-Med-100 reduced skin cell death from UV exposure, and this protection was accounted for by a concomitant increase in DNA repair. Based on these results, it was concluded that C-Med-100 was a natural plant extract worthy of further consideration as a sunscreen product. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    UV-B-induced DNA damage and expression of defence genes under UV-B stress: tissue-specific molecular marker analysis in leaves

    PLANT CELL & ENVIRONMENT, Issue 9 2001
    G. Kalbin
    Abstract The aim of this study was to investigate the regulatory effect of ultraviolet-B (UV-B) radiation on a number of key stress response genes found in the epidermis and mesophyll of Pisum sativum L., Argenteum mutant. This mutant was chosen for the ease with which the entire epidermis can be removed from the mesophyll tissue. An additional goal was to explore the potential modifying effect of pre-acclimation of plants to UV-B radiation prior to exposure by UV-B during treatment. Results showed that mRNA accumulation was similar during acute short-term UV-B exposure for chalcone synthase (Chs) and short-chain alcohol dehydrogenase (SadA) in both epidermis and mesophyll. In contrast, the mRNA levels differed considerably between tissues for phenylalanine ammonia lyase, chalcone isomerase and lipid transfer protein. After 24 h incubation in visible light after cessation of UV-B exposure, the regulation of mRNA levels also differed between Chs and SadA, the former showing no expression in the epidermis and the latter none in the mesophyll. Acclimation to low UV-B levels before acute exposures resulted in delayed induction of Chs and SadA. Measurements of UV-B-induced cyclobutane pyrimidine dimers (CPDs) showed a greater formation in epidermis than in mesophyll. In addition, acclimation at low UV-B levels resulted in significantly higher basal levels of CPDs than in non-acclimated plants in both mesophyll and epidermis and also in increased damage in concomitant acute exposures. The lack of correlation between the number of CPDs and levels of transcripts for defence genes, indicates that DNA damage does not control transcription of these genes. [source]

    Repair of UV damage in plants by nucleotide excision repair: Arabidopsis UVH1 DNA repair gene is a homolog of Saccharomyces cerevisiae Rad1

    THE PLANT JOURNAL, Issue 6 2000
    Zongrang Liu
    Summary To analyze plant mechanisms for resistance to UV radiation, mutants of Arabidopsis that are hypersensitive to UV radiation (designated uvh and uvr) have been isolated. UVR2 and UVR3 products were previously identified as photolyases that remove UV-induced pyrimidine dimers in the presence of visible light. Plants also remove dimers in the absence of light by an as yet unidentified dark repair mechanism and uvh1 mutants are defective in this mechanism. The UVH1 locus was mapped to chromosome 5 and the position of the UVH1 gene was further delineated by Agrobacterium -mediated transformation of the uvh1-1 mutant with cosmids from this location. Cosmid NC23 complemented the UV hypersensitive phenotype and restored dimer removal in the uvh1-1 mutant. The cosmid encodes a protein similar to the S. cerevisiae RAD1 and human XPF products, components of an endonuclease that excises dimers by nucleotide excision repair (NER). The uvh1-1 mutation creates a G to A transition in intron 5 of this gene, resulting in a new 3, splice site and introducing an in-frame termination codon. These results provide evidence that the Arabidopsis UVH1/AtRAD1 product is a subunit of a repair endonuclease. The previous discovery in Lilium longiflorum of a homolog of human ERCC1 protein that comprises the second subunit of the repair endonuclease provides additional evidence for the existence of the repair endonuclease in plants. The UVH1 gene is strongly expressed in flower tissue and also in other tissues, suggesting that the repair endonuclease is widely utilized for repair of DNA damage in plant tissues. [source]

    A clinical trial and molecular study of photoadaptation in vitiligo

    C.L. Hexsel
    Summary Background, Photoadaptation to ultraviolet (UV) B phototherapy is due to both pigmentary and nonpigmentary influences. Objectives, To measure photoadaptation in vitiliginous skin and to compare it with normal pigmented skin. Methods, Seventeen patients with Fitzpatrick skin phototypes III,VI with vitiligo received six to nine UVB treatments, two to three times weekly. Minimal erythema dose (MED) testing was done at baseline and after all treatments; the percentage change in MED was analysed as a measure of photoadaptation. The percentage decrease in cyclobutane pyrimidine dimers (CPDs) over 24 h after a single exposure of 1 MED was analysed on vitiliginous and normal skin. Results, The mean ± SD percentage change in MED from before to after treatments was: treated vitiliginous skin 28·5 ± 39·9% (P = 0·015), treated normal skin 35·9 ± 49·9% (P = 0·015), untreated vitiliginous skin 11·9 ± 22·6% (P =0·070), untreated normal skin 25·1 ± 41·3% (P = 0·041). Of these patients, two-thirds had a positive percentage change in MED (photoadaptation). The mean amount of CPDs induced per megabase of DNA immediately after exposure was significantly higher in vitiliginous skin. The mean ± SD percentage decrease in CPDs (rate of repair) in 24 h was 35·7 ± 26·8% in vitiliginous skin (P = 0·027) and 46·2 ± 19·5% in normally pigmented skin (P = 0·001); no difference was noted in the repair in vitiliginous skin compared with normal skin (P = 0·4). Conclusions, Photoadaptation in vitiliginous and normal skin was observed in two-thirds of patients. Vitiliginous skin had significantly more CPDs following UVB exposure; the rate of repair of UVB-induced DNA damage was equivalent to that in normal skin. [source]

    Single nucleotide polymorphisms in the XPG gene: Determination of role in DNA repair and breast cancer risk

    Rajiv Kumar
    Abstract In this study we determined the effect of single nucleotide polymorphisms in the XPG gene on DNA repair and breast cancer susceptibility. Ninety individuals, with previously studied DNA repair rate at 24 hr of 2 types of UV-specific cyclobutane pyrimidines dimers (CPDs) in skin were genotyped for XPG polymorphism at codon 1104 (exon 15 G>C; Asp > His). The repair rate of TT=C dimer was similar in both wild-type GG homozygotes and GC heterozygotes, whereas, for TT=T, dimer repair was non-significantly (Student's t -test, p = 0.34) lower in GC heterozygotes than wild-type GG homozygotes. Genotyping of 220 breast cancer cases and 308 controls for the same single nucleotide polymorphism in exon 15 of the XPG gene exhibited marginally significant increased frequency of the variant allele (,2 3.84, p = 0.05; OR 1.33, 95% CI 1.0,1.8) in cases (C-allele 0.29) compared to controls (C-allele 0.24). Combined heterozygote and variant homozygote genotype frequency was also higher in cases than controls (,2 4.79, p = 0.03; OR 1.50, 95%CI 1.04,2.16). © 2002 Wiley-Liss, Inc. [source]