Low Doses Of Ultraviolet Light Research Articles

Chicoric acid provides better ultraviolet protection than the sum of its substrates in purple coneflower plants

Plants live in complex environments and need to cope with various biotic and abiotic stresses. Plant secondary metabolites are not only medicines/supplements for humans but are also important weapons used by plants for defense. Chicoric acid is the main active ingredient and is a major secondary metabolite of purple coneflower (Echinacea purpurea (L.) Moench). A special acyl donor changed serine carboxypeptidase-like acyltransferase catalyzes chicoric acid biosynthesis from caftaric acid and chlorogenic acid. The biological role of chicoric acid in purple coneflower and the significance of its biosynthesis being catalyzed by an acyl donor changed acyltransferase remain unclear. In the present study, correlation analysis and various in vitro experiments were investigated. Chicoric acid contents among different purple coneflower accessions were found to be negatively correlated with latitude, which indicated a possible role in ultraviolet protection. Ultraviolet light induced oxidative stress in purple coneflower leaves and upregulation of chicoric acid biosynthetic genes. However, chicoric acid was consumed by reactive oxygen species to alleviate oxidative stress. Chicoric acid provided ultraviolet protection by acting as a sunscreen and antioxidant agent. Notably, chicoric acid exhibited stronger ultraviolet absorption and antioxidant activity than the sum of its two substrates, which indicated the significance of its biosynthesis by an acyl donor changed acyltransferase. This study also implied that low doses of ultraviolet light might be good elicitors for simulating chicoric acid biosynthesis in purple coneflower.

Deubiquitination of FANCD2 Is Required for DNA Crosslink Repair

SummaryMonoubiquitination of FANCD2 and PCNA promotes DNA repair. It causes chromatin accumulation of FANCD2 and facilitates PCNA's recruitment of translesion polymerases to stalled replication. USP1, a protease that removes monoubiquitin from FANCD2 and PCNA, was thought to reverse the DNA damage response of these substrates. We disrupted USP1 in chicken cells to dissect its role in a stable genetic system. USP1 ablation increases FANCD2 and PCNA monoubiquitination but unexpectedly results in DNA crosslinker sensitivity. This defective DNA repair is associated with constitutively chromatin-bound, monoubiquitinated FANCD2. In contrast, persistent PCNA monoubiquitination has negligible impact on DNA repair or mutagenesis. USP1 was previously shown to autocleave after DNA damage. In DT40, USP1 autocleavage is not stimulated by DNA damage, and expressing a noncleavable mutant in the USP1 knockout strain partially rescues crosslinker sensitivity. We conclude that efficient DNA crosslink repair requires FANCD2 deubiquitination, whereas FANCD2 monoubiquitination is not dependent on USP1 autocleavage.

Sensitivity of oral bacteria to 254 nm ultraviolet light

To explore the sensitivity of bacteria commonly found in root canals to 254 nm ultraviolet (UV) light, either as individual cells or as participants of a bacterial multilayer. The sensitivity of oral bacteria, as individual cells, to UV light was tested by subjecting plates streaked with bacteria to 254 nm UV, at a fluence of 1-20 mJ cm(-2). An experimental model was designed to produce a bacterial multilayer and to study absorption of UV light by bacteria in an outer layer and its effect on the elimination of bacteria in the inner layer. Direct exposure to relatively low doses of UV light (2-7 mJ cm(-2)) effectively eliminated all bacterial strains tested. Furthermore, an Enterococcus faecalis strain, partially resistant to a 24 h exposure to calcium hydroxide, was effectively eliminated within several seconds of exposure to UV light (P < 0.001). UV was absorbed by a multilayer of bacteria. When 4 bacterial cells microm(-2) were present in the light path, the UV light dose had to be increased by a factor of x10 to achieve 100% elimination of the bacteria in an inner layer. The application of UV light to eliminate endodontic pathogens may be possible. Nevertheless, its absorbance by outer layers of bacteria should be considered and the UV light dose adapted accordingly.

Ultraviolet light-induced apoptosis is associated with S-phase in primary human fibroblasts

Transcription-coupled nucleotide excision repair (tcNER)-deficient human fibroblasts are extremely sensitive to the induction of apoptosis in response to low doses of ultraviolet light (UV light), but are less sensitive to the induction of apoptosis following exposure to high doses [J. Invest. Dermatol. 117 (2001) 1162]. This seemingly paradoxical observation led us to re-evaluate the relationship between UV dose and the induction of apoptosis. Here we report that the reduction in the extent of UV-induced apoptosis in tcNER-deficient strains following exposure to elevated doses of UV light does not result from impaired gene expression alone because neither inhibitors of transcription nor inhibitors of translation blocked UV-induced apoptosis. Furthermore, UV-induced apoptosis was greatly reduced by inhibiting S-phase progression with either mimosine or serum withdrawal. Importantly, DNA synthesis following UV-irradiation occurred only at doses that induced apoptosis in these cell lines and the apoptotic cells contained nascent DNA. Moreover, deregulation of G 1- to S-phase transition by expression of human papillomavirus E7 sensitized cells to UV-induced apoptosis. Taken together these results suggest that the induction of apoptosis requires S-phase progression following UV-irradiation.

Immunological responses to ultraviolet light B radiation in Black individuals

Immunological factors are important participants in the pathogenesis of experimental skin tumors. We therefore studied cutaneous immune responses in subjects with either low natural incidence (Black individuals), or a high frequency rate (White individuals) of skin cancer. We performed whole body irradiation with a low dose of ultraviolet light B (UV-B) and evaluated peripheral lymphocytes. UV-B irradiation was associated with small but significant changes in lymphocyte phenotype frequency. In White subjects this consisted of an increased number of CD19 (B cells) and CD 4/29 (inducer of helper T cells); Black subjects had a slight decrease in CD3 (T cells). Natural killer activity, not affected by UV-B in White subjects, increased significantly in Black subjects. UV-B was devoid of immunological effects in vitro for any of the parameters tested. As expected, the low UV-B dose used in this study induced increases of serum vitamin D3 concentrations in White subjects, with lack of response in the Black subjects. We conclude that Black individuals selectively exhibit an increase in Natural Killer activity in response to irradiation with low dose UV-B. This race group-specific immune response to ultraviolet radiation appears to require mediation by the skin. Enhanced Natural Killer activity could underlie at least partly the resistance in Black individuals to the development of photodependent skin cancer.

Interleukin-12 Prevents Ultraviolet B-Induced Local Immunosuppression and Overcomes UVB-Induced Tolerance

Ultraviolet (UV) light abrogates contact hypersensitivity (CHS) responses and induces hapten-specific tolerance. Because Th-1 cells are critically involved in CHS and are induced to develop by the cytokine interleukin (IL)-12, we asked whether IL-12 might overcome UV-induced local immunosuppression. C3H/HeN mice exposed to low doses of UV light over 4 d and hapten sensitized through the irradiated skin area with dinitrofluorobenzene showed profound inhibition of the CHS response, which was completely prevented upon intraperitoneal injection of murine recombinant IL-12 (rIL-12) after the last UV exposure. UV-treated mice resensitized 14 d after the first challenge displayed hapten-specific tolerance, whereas UV-exposed mice injected with rIL-12 before the first sensitization exhibited a vigorous CHS response. Furthermore, mice that were initially sensitized through UV-exposed skin also produced a significant CHS reaction when they received rIL-12 before resensitization. Adoptive transfer of spleen and lymph node cells from UV-irradiated mice treated with rIL-12 had no effect on the CHS response in recipient mice, whereas transfer of cells from UV-treated mice inhibited the immune response. These findings demonstrate that rIL-12 can prevent UV-induced local immunosuppression and overcome UV-induced hapten-specific tolerance.

APPLICATION OF UV-C AND BIO-CONTROL AGENT STRATEGIES TO CONTROL ROT OF FRUIT AND VEGETABLES

Applying low doses of ultraviolet light (254 nm, W-C) reduces the incidence of brown rot of (Monilinia fructicola) peaches, green mold (Penicillium digitatum) of tangerines, and Rhizopus soft rot (Rhizopus stolonifer) of tomatoes and sweetpotatoes resulting from field infection and artificial inoculation. In most studies, applying postharvest fungicide (PF) was better than W-C treatment. In this study, the effectiveness of combining a biocontrol agent, Debaryomyces hansenii (BC), with low UV-C dose for postharvest disease control was investigated. When these commodities were treated with BC 3 days after W-C treatment, the reduction of storage rots was more effective than when UV-C was used alone. For example, the percent brown rot infection of artificially inoculated Elberta peaches 36 hours after inoculation of the nontreated control, peaches treated with UV-C, BC, W-C + BC, and benlate were 100%, 55%, 67%, 12%, and 12%, respectively. The efficacy of W-C + BC was similar to when PF was used alone, indicating that an integration of UV-C treatment and BC can reduce storage rot to the levels of commercial PF treatment.

THE EFFECT OF ULTRAVIOLET LIGHT ON CONTROLLING POSTHARVEST ROTS ON FRUITS

Low doses of ultraviolet light (254nm UV–C) irradiation reduced postharvest rots of pome, stone and citrus fruits. Brown rot (Monilinia fructicola) of `Elberta' and `Loring' peaches was significantly reduced by UV–C. Alternaria rot (Alternaria spp.) and bitter rot (Colletotrichum spp.) the principal storage rots of `Golden Delicious apples showed significant reduction following UV–C treatment. Further application of UV–C was effective in controlling green mold rot (Penicillium digitatum) of `Dancy' Tangerines and `Marsh Seedless' grapefruits, stem end rot (Alternaria citri), as well as sour rot (Geotrichum candidum) of `Dancy' tangerines after irradiation.

High-frequency switching in Dictyostelium

A high-frequency switching system is demonstrated to exist in Dictyostelium discoideum. Switch phenotypes are distinguished by colony morphology and include changes in developmental timing as well as blocks in morphogenesis. The switching system exhibits the following characteristics: (1) a “low” spontaneous frequency of switching (∼10 −2) in the parent strain; (2) stimulation of the basal level of switching roughly fivefold with low doses of ultraviolet light; (3) “high” spontaneous frequencies of switching (as high as 10 −1) in particular variant strains; (4) high spontaneous frequencies of interconvertibility between variant phenotypes; (5) high spontaneous frequencies of reversion to the wild-type phenotype; (6) a set of reproducible switch phenotypes; (7) heritability of switch phenotypes; and (8) a rough correlation between switch phenotype and switching frequency. The extraordinary similarity between the switching systems in D. discoideum and Candida albicans is discussed.

High-frequency switching of colony morphology in Candida albicans.

The pathogenic yeast Candida albicans switches heritably and at high frequency between at least seven general phenotypes identified by colony morphology on agar. Spontaneous conversion from the original smooth to variant phenotypes (star, ring, irregular wrinkle, hat, stipple, and fuzzy) occurs at a combined frequency of 1.4 X 10(-4), but is increased 200 times by a low dose of ultraviolet light that kills less than 10 percent of the cells. After the initial conversion, cells switch spontaneously to other phenotypes at a combined frequency of 2 X 10(-2). Switching is therefore heritable, but also reversible at high frequency. The genetic basis of this newly discovered process and its possible role in Candida pathogenesis are considered.

Decrease in the number of primordial germ cells following injection of the animal pole cytoplasm into the vegetal pole region of Xenopus Eggs

AbstractEffects of the egg cytoplasm on the formation of primordial germ cells (PGCs) were examined through microinjection into the subcortical cytoplasm near the vegetal pole of Xenopus laevis eggs. Injection of vegetal pole cytoplasm and physiological saline did not reduce the number of PGCs. However, the average number of PGCs in tadpoles at stage 46 decreased to about 60% of that in normal controls when the animal pole cytoplasm of fertilized eggs was injected into the intact eggs. Similar effects were observed when the animal pole cytoplasm of fertilized or unfertilized eggs was injected into eggs irradiated with a low dose of ultraviolet light. These facts suggest the possibility that inhibitor(s) of PGC formation exists in the animal pole cytoplasm of both fertilized and unfertilized eggs.

Evidence that DNA excision-repair in xeroderma pigmentosum group A is limited but biologically significant

The loss of pyrimidine dimers in nondividing populations of an excision-repair deficient xeroderma pigmentosum group A strain (XP12BE) was measured throughout long periods (up to 5 months) following exposure to low doses of ultraviolet light (UV, 254 nm) using a UV endonuclease-alkaline sedimentation assay. Excision of about 90% of the dimers induced by 1 J/m 2 occured during the first 50 days. The rate curve has some similarities with that of normal excision-repair proficient cultures that may not be coincidental. Rate curves for both XP12BE and normal cultures are characterized by a fast and slow component, with both rate constants for the XP12BE cultures (0.15 day −1 and 0.025 day −1) a factor of 10 smaller than those observed for the respective components of normal cell cultures. The slow components for both XP12BE and normal cultures extrapolate to about 30% of the initial number of dimers. No further excision was detected throughout an additional 90-day period even though the cultures were capable of excision-repair of other newly-introduced pyrimidine dimers. We conclude that nondividing XP12BE cells in addition to having a slower repair rate, cannot repair some of the UV-induced DNA damage. The repair in XP12BE is shown to have biological significance as detected by a cell-survival assay and dose-fractionation techniques. Nondividing XP12BE cells are more resistant to UV when irradiated chronically than when irradiated acutely with the same total dose.

Ethionine abolishes mutagenesis by 9-aminoacridine (but not by 2-aminopurine) in Salmonella plate tests

Ethionine, the ethyl analogue of methionine, appears to be non-mutagenic in the 'Ames' series of bacterial tester strains (McCann et al., 1975), weakly mutagenic to some fungi (Lewis and Tarrant, 1971; Talmud and Lewis, 1974), and carcinogenic to rats after prolonged feeding (Farber, 1963). More recently, ethionine has been reported to block certain 'SOS' functions in a t i fmu tan t of Escherichia coli following thermal treatments (Weisner and Troll, 1981). Such SOS functions, including prophage induction, filamentous growth and recA +-dependent mutagenesis, are normally switched on in t i fmu tan t s following a temperature shift from 37 ° to 42 ° (Witkin, 1976). Weisner and Troll (1981) found that thermal induction of prophage lambda in a t i f m u t a n t of E. coli did not occur in the presence of 10 mM ethionine. Moreover, the increased mutation response normally observed in t i fcells irradiated with a low dose of ultraviolet light, and then raised to 42 ° (see Witkin, 1976 for details) is abolished by 10 mM ethionine. To determine whether the effects of ethionine on bacterial mutagenesis were restricted to events associated with thermal induction in t i f strains, we initiated a study of the effects of ethionine on chemical mutagenesis in t i f + strains of Salmonella typhimurium. We were particularly interested in possible effects on mutagenesis by 2-aminopurine and 9-aminoacridine, since we have shown that the mutagenic effects of these agents are largely independent of the recA + gene product in S. typhimurium (results to be published elsewhere). In addition, we were interested in the possibility that ethionine might act as an inhibitor of certain DNA methylation reactions, including the methylation of adenine residues which is associated with the product of the E. coli dam ÷ gene and plays an important part in mismatch repair (Marinus, 1973; Glickman et al., 1978). We reasoned that inhibition of a gene product equivalent to the dam + gene product by ethionine in S.

Rapid complementation method for classifying excision repair-defective xeroderma pigmentosum cell strains

A rapid method has been developed that permits demonstration of complementation between different cell strains from ultraviolet-sensitive xeroderma pigmentosum patients. Combining polyethylene glycol-mediated cell fusion with low doses of ultraviolet light to eliminate unfused sensitive cells, the method permits assignment of cell strains to complementation groups by visual inspection, avoiding use of laborious methods involving autoradiography. This method can be augmented by measuring DNA repair synthesis, which shows large quantitative differences between fusions that result in complementation and those that do not.

Postreplication repair in Saccharomyces cerevisiae.

Postreplication events in logarithmically growing excision-defective mutants of Saccharomyces cerevisiae were examined after low doses of ultraviolet light (2 to 4 J/m2). Pulse-labeled deoxyribonucleic acid had interruptions, and when the cells were "chased," the interruptions were no longer detected. Since the loss of interruptions was not associated with an exchange of pyrimidine dimers at a detection level of 10 to 20% of the induced dimers, we concluded that postreplication repair in excision-defective mutants (or leaky mutants) does not involve molecular recombination. Pyrimidine dimers were assayed by utilizing the ultraviolet-endonuclease activity in extracts of Micrococcus luteus and newly developed alkaline sucrose gradient techniques, which yielded chromosomal-size deoxyribonucleic acid after treatment of irradiated cells.

Effect of caffeine on DNA synthesis in irradiated and unirradiated mammalian cells

Caffeine increased the availability of replication origins, and consequently the number of growing points, in the DNA of Chinese hamster V79 and human (HeLa) cells. Caffeine also prevented the inhibition of replicon initiation normally caused by X-radiation and exposure to low doses of ultraviolet light. When caffeine was removed from the medium after irradiation, replicon initiation was inhibited. Caffeine also reversed the inhibition of replicon initiation caused by novobiocin, which is not a DNA-damaging agent. Because caffeine increases the number of growing points, it also partially reversed the inhibition of total DNA synthesis induced by hydroxyurea. It is proposed that caffeine alters the conformation of intracellular chromatin in such a way that the conformation usually induced by DNA-damaging agents is prevented.

Double mutations induced in Escherichia coli by ultraviolet light

Double mutations to azide resistance and to bacteriophage T5 resistance of genes separated by more than 50 kilobases were induced in Escherichia coli WP2s in chemostat cultures by exposure to a single low dose of ultraviolet light. Frequencies of induced double mutations were three orders of magnitude greater than would be predicted by chance. Reversions from azide resistance and phage resistance occurred independently, showing that that the double mutation was not due to pleiotropic effects of a single gene mutation. These results support earlier findings which show that low doses of ultraviolet light induce multiple gene mutations in Bacillus subtilis over a similarly broad range.

Functionally distinct classes of complex phosphorus compounds in lake water1

Complex phosphorus compounds were classified functionally according to the manner by which orthophosphate was released. Filtrable phosphorus compounds in two eutrophic lakes (East and West Twin lakes) and a humic bog (Crazy Eddie Bog) in northeastern Ohio were fractionated by anion‐exchange and gel‐filtration chromatography. Fractions were analyzed for soluble reactive phosphorus and total dissolved phosphorus; absorbance at 400 nm was used as a measure of filtrable “yellow acids.” The eutrophic lakes contained numerous low molecular weight compounds which were resistant to low‐dose ultraviolet irradiation but readily released orthophosphate upon treatment with alkaline phosphatase. Filtrable phosphorus compounds of the humic bog were predominantly high molecular weight, cochromatographed with the yellow acids in each fractionation procedure, and resisted enzyme hydrolysis, but released orthophosphate upon irradiation with low doses of ultraviolet light.

Chromosome damage and DNA repair induced in human fibroblasts by UV and cholesterol oxide.

In human fibroblasts, cholesterol oxide induced a similar degree of chromosome damage (8.6% of metaphases) and DNA repair synthesis (8-10% of cells with lightly-labelled nuclei) as low doses of ultraviolet light (UV), but did not produce single-strand DNA breaks or DNA damage detectable by inhibition of thymidine incorporation. Chromosome aberrations were detected up to 8 weeks after treatment with cholesterol oxide and UV. Combined treatments had almost additive effects on the frequency of chromosome aberrations but not on repair synthesis. Multiple daily doses of UV did not cause more aberrations than a single dose. Attempts to transform two fibroblast strains from normal donors and three derived from melanoma patients using single and combined treatments of UV, cholesterol oxide and hyperthermia (40 degrees) were unsuccessful.

Induction of lambda prophage and of mutations to streptomycin resistance in separate small fractions of a lysogenic derivative of Escherichia coli B/r by very low doses of ultraviolet light

The number of induced mutations to streptomycin resistance is compared at doses of ultraviolet (UV) light between 0.2 and 6.4 J/m2 in a Uvr- (excision-deficient) derivative of E. coli B/r, strain WU, and in its lambda lysogen, strain WU(lambda). At UV doses up to about 1 J/m2, which converts about 5% of the lysogenic population into enfective centers, no difference is observed in the number of mutations to streptomycin resistance produced by the two strains. It is concluded that the capacity to produce UV-induced mutations is not coupled with lysis due to the induction of lambda prophage at low doses of UV radiation. At UV doses above 1 J/m2, the number of mutatants detected in the lysogenic strain decreases appreciably compared to the number detected in the nonlysogen, and is only about 10% as high at UV doses of 3 J/m2 and higher, doses which cause maximal induction of prophage. The results are compatible with the operation of a common "all-or-none" induction signal resulting in expression of UV-inducible functions at high UV doses, but not at low doses.