Mutagenic Effects Of Ultraviolet Light Research Articles

104 Loss of Kdm6a and Trp53 drives the development of squamous cell skin cancer in mice

Cutaneous squamous cell carcinoma (cSCC) has among the highest mutation burdens of all cancers, reflecting its association with the mutagenic effects of ultraviolet light. Though mutations in established, cancer-relevant genes like TP53 and NOTCH1 are prevalent in cSCC, they are tolerated in clinically normal skin and are insufficient to cause skin cancer. Whether epigenetic regulators cooperate in the development of squamous cell carcinoma is just starting to be defined. KDM6A encodes a histone H3K27me2/me3 demethylase that is frequently mutated in cSCC and other cancers.

Resistance of airborne fungal propagules to ultraviolet irradiation: Laboratory study

The inuence of ultraviolet (UV) radiation on fungi Aspergillus niger Tiegh. isolate OG168, Paecilomyces puntonii (Vuill.) Nann. isolate OG68, and Penicillium expansum Link isolate PO88 was studied under laboratory conditions. A test system was developed for this study. An aerosol chamber provided a dust-free space of 1.5 m 3 . The source of ultraviolet rays was an UV lamp (DPT 220, 240n320 nm, 15 W). Fungal propagules were injected into the UV exposed chamber space from an external bioaerosol generator. Aerosols from the aerosol chamber after irradiation to UV were sampled into an impinger AGI-30 and measured with the optical aerosol spectrometer LAS-15M (Institute of Physics, Lithuania). The changes in fungi survival caused by exposure to UV radiation were evaluated by determining their relative recovery. The laboratory study indicated that the fungal propagules responded to UV radiation distinctively. P. puntonii propagules were injured without possibility to repair. On the contrary, P. expansum propagules repaired after a long enough exposure to UV radiation, but this ability was limited. The stressed A. niger propagules recovered after the 80 min exposure to UV radiation and the relative recovery reached a plateau. The mutagenic effects of UV light on tested fungi have shown that frequent occurrence of different morphological mutants was detected after the 30 min exposure of conidia. The mean geometrical diameter of fungal propagules exposed to UV irradiation in the aerosol chamber was in the range of 2.5 to 2.8 „m.

A theoretical study of pyrimidine photohydrates and a proposed mechanism for the mutagenic effect of ultraviolet light

Semiempirical AM1, PM3 and all electron MP2 and DFT nonempirical calculations for the normal and rare tautomeric forms of pyrimidine bases and their photohydrates were performed. It is predicted that the trans conformation of the imino form of cytosine photohydrate is more stable than its amino form in the gas phase. The Monte Carlo simulations showed that cytosine amino form is stabilized by a water more than the imino tautomer, while cytosine photohydrate in imino form is more stable than the corresponding amino form. The present results suggest that tautomerism is a possible mechanism of UV-light mutagenic effect.

Interactive Lethal and Mutagenic Effects of Ultraviolet Light and Bleomycin in Yeast: Synergism or Antagonism?

The mutagenic interactions of ultraviolet light and bleomycin in haploid populations of Saccharomyces cerevisiae were analyzed. Survival and mutation frequency as a function of different bleomycin concentrations after one conditioning dose of UV radiation were determined. Furthermore, corresponding interaction functions and sensitization factors were calculated. A synergistic interaction between UV light and bleomycin was shown for both lethal and mutagenic events when the cells were in nutrient broth during the treatments. Conversely, the interaction between UV light and bleomycin was antagonistic when the cells were in deionized water during the treatment. The magnitude of lethal and mutagenic interactions depends on dose, and thus presumably on the number of lesions. The observed interactions between UV light and bleomycin suggest that the mechanism that is most likely involved is the induction of repair systems with different error probabilities during the delay of cell division.

Somatic cell mutation frequency at the HPRT, T-cell antigen receptor and glycophorin A loci in Cockayne syndrome

Skin fibroblasts of patients with Cockayne syndrome (CS) are hypersensitive to the lethal or mutagenic effect of ultraviolet light, which may cause genetic instability. Up to now, however, no systematic study of in vivo somatic cell mutation in CS cells has been reported. This article describes our investigation of the mutation frequencies (Mfs) at three different loci, i.e. hypoxanthine-guanine phosphoribosyl transferase (HPRT), T-cell antigen receptor (TCR) and glycophorin A (GPA), in six patients with CS. Mfs at the HPRT and TCR loci were found to be within the normal range as determined in age-matched controls. In the GPA locus of two patients, there was a slight increase, but it was much smaller than that reported in other DNA repair deficient syndromes. The frequency of spontaneous HPRT mutation in Epstein-Barr virus transformed B-lymphoblastoid cells derived from CS patients was similar to that in cells from normal children. The molecular characterization of the representative HPRT mutant T cell clones from CS patients did not show any structural alterations. These results may explain, at least in part, why CS is not associated with predisposition to cancer.

Complementation of DNA repair in xeroderma pigmentosum group A cell extracts by a protein with affinity for damaged DNA.

Complementation group A of xeroderma pigmentosum (XP) represents one of the most prevalent and serious forms of this cancer-prone disorder. Because of a marked defect in DNA excision repair, cells from individuals with XP-A are hypersensitive to the toxic and mutagenic effects of ultraviolet light and many chemical agents. We report here the isolation of the XP-A DNA repair protein by complementation of cell extracts from a repair-defective human XP-A cell line. XP-A protein purified from calf thymus migrates on denaturing gel electrophoresis as a doublet of 40 and 42 kilodaltons. The XP-A protein binds preferentially to ultraviolet light-irradiated DNA, with a preference for damaged over nondamaged nucleotides of approximately 10(3). This strongly suggests that the XP-A protein plays a direct role in the recognition of and incision at lesions in DNA. We further show that this protein corresponds to the product encoded by a recently isolated gene that can restore excision repair to XP-A cells. Thus, excision repair of plasmid DNA by cell extracts sufficiently resembles genomic repair in cells to reveal accurately the repair defect in an inherited disease. The general approach described here can be extended to the identification and isolation of other human DNA repair proteins.

Altered oncogenes in UV-transformed C3H 10T1/2 mouse cells: identification of mutated H-ras allele(s).

Ultraviolet (UV) light will transform mammalian cells in culture to a phenotype which is characteristic of in vivo neoplasia. The UV-transformed C3H 10T1/2 mouse cell lines, TU-2 and TU-3, were analysed to determine the molecular mechanisms which may account for their phenotype, and to determine the types of mutations induced by UV light. DNA-transfection assays indicated that the transformed phenotype of TU-2 could not be transferred to non-transformed recipient cells. Therefore, studies were initiated to determine the mutagenic effects of UV light with respect to cellular oncogenes. Northern blot analysis indicated that five of the oncogenes analysed (erb-A, erb-B, mos, myb, and N-ras) were not expressed at detectable levels. The steady-state mRNA levels of fos, K-ras, abl, sis, and src oncogenes were similar in the C3H 10T1/2 and TU-2 cells. The mRNA levels of three oncogenes, raf, myc and H-ras, were 1.5-2.0-fold greater in the TU-2 cells compared to C3H 10T1/2. Southern blot analysis of HpaII restriction digested TU-2 DNA indicated that the H-ras oncogene has undergone methylation changes. More extensive analyses of the H-ras locus in TU-2 demonstrated a deletion of the 3' end of the gene, that may involve two separate mutated alleles. This type of damage is consistent with the lesions associated with sister chromatid exchange. While the H-ras locus in the other UV-transformed line, TU-3, showed methylation changes, there were no large genetic mutations detected by Southern blot analysis. These results suggest that UV-irradiation in vitro induces endogenous DNA damage that includes methylation changes and large genomic alterations. Further analysis will be necessary to determine the extent to which each may be involved in cell transformation.

Demonstration of recovery from the potentially mutagenic effects of ultraviolet light by replication-inhibited Chinese hamster V79 cells

The effects of replication-inhibiting conditions on the ability of Chinese hamster (V79) cells to recover from the potentially mutagenic effects of ultraviolet (UV) light were investigated. V79 cells were synchronized by a new technique using a low concentration of hydroxyurea (0.2 mM), which provided a mildly-toxic, non-mutagenic method for producing large quantities of synchronized cells needed for these studies. The protocol developed for this study involved UV-irradiation of synchronized V79 cells which were blocked at the G1/S boundary. Following UV-irradiation, the cells were either allowed to enter S phase immediately or were blocked for increasing periods of time by the addition of more hydroxyurea. The former cells contained the highest frequencies of ouabain-resistant mutants, while cells whose replication was blocked following UV-irradiation showed decreasing mutation frequencies with respect to time. Therefore, V79 cells are able to demonstrate liquid holding recovery from potentially mutagenic UV-lesions. Since the UV-induced mutation frequency was reduced by almost 50% following 6 h of “liquid holding”, the mutagenic lesions seem to be removed at a faster rate than has previously been reported for the removal of pyrimidine dimers from these cells.

Mutation Induction in the Cyanobacterium Gloeocapsa alpicola

The lethal and mutagenic effects of ultraviolet light (u.v.), ethyl methanesulphonate (EMS), methyl methanesulphonate (MMS), N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and mitomycin C on the unicellular cyanobacterium Gloeocapsa alpicola have been investigated. Mitomycin C and EMS did not significantly increase the frequency of streptomycin-resistant mutants above the spontaneous level. MNNG and MMS produced increases of 10 to 30 times the spontaneous frequency. Contrary to previous reports on mutation induction in cyanobacteria, u.v. was the most effective mutagen, increasing the spontaneous mutation frequency 4000-fold. However, since photoreactivating light eliminated most of this mutagenic response it was necessary to rigorously exclude light of wavelengths < 550 nm during post-irradiation growth. Caffeine failed to increase the mutation frequency of u.v.-irradiated cultures, but cells were more sensitive to u.v. killing in the presence of caffeine.

Induced variations in microorganisms. I. The mutagenic effect of ultraviolet light on Rhizobium trifolii.

The mutagenic effect of ultraviolet light on a strain ofRhizobium trifolii T5 was studied. A gradual build-up of radioresistance in the population of the wild cells was observed as a result of cyclic UV irradiation, although there, was no definite indication for a plateau of maximal resistance of the population even after 20 cycles of irradiation. The radio-resistance was built up sooner in a population cycled at a low dose of irradiation (3 sec) than at a high dose (10 sec). The fluctuation test indicated that UV acted as an inducing agent. The frequency of radioresistant cells in a radiation cycled population was about 6.8×10 -6 as against c.4×10 -6 in the nonirradiated population. Five, mutants were examined in detail, in which radioresistance in two was accompanied by resistance to streptomycin also. The mutants did not differ drastically from the wild, strain in their biochemical properties, salt tolerance and clover infectivity. No UV induced auxotrophic mutants were detected.

The influence of analogs of xanthine on the mutagenic effect of ultraviolet light.

Eight compounds can be added to those purine analogs which give synergistic effects with ultraviolet light: 1,3,7,9-tetra-methylxanthine methyl sulfate, 8-chlorocaffeine, ethyltheophylline, 6-dimethylaminopurine, 6-methoxypurine, 8-ethoxycaffeine, 1,3-dimethyl uric acid and 3-methyl uric acid. It appears likely that these are merely representatives of the class of methyl purines, and that other compounds are also active. The synergistic activity varies among the compounds investigated; some give a synergistic effect slightly higher than caffeine, but apparently act by the same mechanism. The height of effect of all of the synergistic purine analogs has been correlated with the stability of the structures determined by inductive effects and steric hindrance. The lack of activity with pyrimidines (l-methyl thymine and 1,3-dimethyluracil) leads to the conclusion that both rings (7,8,9 positions) of the purine molecule are necessary for the synergistic effect.

Mutation and the Repair of Radiation Damage in Bacteria

Early studies of lethal and mutagenic effects of ultraviolet light (UV) in bacteria revealed an unmistakable, but complex, relation between them. The similarity of the action spectra for killing (1) and mutation induction (2), both showing sharp peaks at about 2650 A, suggested absorption by nucleic acids as the initial step in both. The photoreversibility of induced mutations (3, 4) indicated a possible similarity between some premutational UV photoproducts and the photoreversible fraction of the UV damage leading to death. Extensive comparison of dose-effect curves (reviewed in 5), while showing that lethality and mutagenesis usually have similar dose thresholds, made it clear that no simple, universally applicable quantitative relation exists between them. The modifiability of induced mutation frequency by posttreatments not affecting survival (6) reinforced this conclusion. Recent developments in radiation biology prompt the reexamination of mutagenesis as it relates to the production and repair of lethal UV damage. Particularly relevant are the identification of thymine dimer as an important UV photoproduct in the DNA of irradiated bacteria (7); the elucidation of one kind of photoreactivation as an enzymic process (8) involving the monomerization of thymine dimers (9), and the demonstration that the excision of thymine dimers from the DNA is an early step in the dark repair of UV damage in Escherichia coli (10, 11). These insights, as well as recent indications that UV produces dimers of other pyrimidines that may be repaired by similar mechanisms (12), provoke many questions about the possible role of pyrimidine dimers and their repair in the induction of mutations (12, 13). In this discussion, our current knowledge of UV mutagenesis in bacteria will be considered in relation to some of these questions, and the answers will be sought without regard for the historical sequence in which the evidence was obtained. A measure of hindsight may prove of some value in reappraising the bacterial mutation studies of the last decade. An exhaustive review will not be attempted here, and only studies relevant to the particular questions considered will be discussed.

Ultraviolet light-induced mutation and deoxyribonucleic acid synthesis in Escherichia coli.

Exposure of a bacterial population to a mutagenic dose of ultraviolet light generally does not establish phenotypically mutant cells immediately. Rather, a period of subeultivation of the irradiated cells is required before newly induced mutants can be detected (Demeree, 1946). It has been postulated (see Witkin, 1956, for a recent discussion) that the delay between irradiation and phenotypic can be accounted for by the time required for three processes: (1) the establishment of a stable, heritable alteration of the genotype, (2) the segregation, if necessary, of the mutant genome from the influence of dominant, nonmutant elements, and (3) the expression of the mutant genotype in an altered phenotype. This hypothetical fractionation of the over-all delay is supported in part by the finding, immediately after irradiation, of an interval of instability with respect to the potentiality for mutation. During this period it is possible to influence the ultimate yield of mutants by appropriate manipulations. This interval is, in some cases, demonstrably distinct from the period of growth still required for the completion of phenotypic (Lieb, 1959). During this labile phase the mutagenic effects of ultraviolet light can be reduced or photoreversed by exposure to white light. Cultivation of the cells in the dark leads to a fixation of the mutagenic effect with loss of susceptibility to photoreversal (Matney, Shankel, and Wyss, 1958; Doudney and Haas, 1959). Witkin (1953, 1956) and Berrie (1953) have shown that the yield of mutants is also depressed by unusually high or low incubation temperatures. The period of temperature sensitivity is relatively short, lasting about one-third of the postirradiation lag phase. Witkin (1956) has clarified the long-known dependence of the mutational process upon postirradiation nutritional supplementation (Demerec, 1946; Demerec and Cahn, 1953). She has shown that efficient mutation induction requires, or at least is associated with, a high rate of protein synthesis immediately following irradiation. This conclusion rests upon the findings that a full complement of amino acids is the essential nutritional element required and that exposure to chloramphenicol, known to be a specific inhibitor of protein synthesis, depresses the yield of mutants. Again, these factors exert. their influence over only a short time period following irradiation. After this time the mutant yield is fixed and no longer susceptible to change by prolongation or cessation of treatment. Haas and Doudney (1957) and Doudney and Haas (1958, 1959) extended Witkin's findings to a better understanding of the kinetics of the amino acid and chloramphenicol effects. In addition they have discovered that certain effects upon the mutation yield are brought about by preand postirradiation incubation in the presence of various purine and pyrimidine nucleosides and their structural analogues. They interpret their findings as suggesting a role for ribonucleic acid (RNA) synthesis in the process of ultravioletinduced mutation. Subsequently, Witkin (1958) has shown that the duration of the period of amino acid dependence and chloramphenicol sensitivity increases linearly with increasing doses of ultraviolet light. A similar extension of the sensitive period may be produced by incubation of the irradiated cells in caffeine. On the basis of the known ability of ultraviolet light to block deoxyribonucleic acid (DNA) synthesis in Escherichia coli strain B/r, the bacterium used, and the fact that caffeine is an inhibitor of nucleic acid synthesis, Witkin reasons that the termination of the period of mutational lability involves nucleic acid and probably DNA synthesis. Thus, synthesis of RNA, protein, and DNA have all three been implicated in the immediate postirradiation events in a fairly specific manner. These events serve, on the one

COCHLIOBOLUS SATIVUS: III. EFFECT OF ULTRAVIOLET RADIATION

The lethal and mutagenic effect of ultraviolet light on two isolates of Cochliobolus sativus was studied. Conidia of a dark-spored strain were considerably more resistant to high doses of radiation than those of a white-spored strain. Ultraviolet radiation increased the frequency of mutation in the fungus. Mutants were recovered that differed from their parents in degree of sporulation, rate of growth, pigmentation, amount of aerial mycelium, topography and consistency of colony, and pathogenicity to wheat seedlings. Tetrads from crosses between weakly and highly pathogenic strains indicated that pathogenicity was not a clearly segregating character.