DNA-protein crosslinking in normal human skin fibroblasts exposed to solar ultraviolet wavelengths

UV-induced DNA damage in human keratinocytes: Quantitation and correlation with long-term survival

Ultraviolet (UV) radiation has a major role in the pathogenesis of skin cancer due to its capacity to induce immunosuppression and DNA damage in cells. In this study, we describe the use of a novel extra-long polymerase chain reaction (XL-PCR) assay for detection of UV-inducible DNA lesions in a human keratinocyte line (HaCaT cells). Ultraviolet B (UVB), in doses from 4 to 50 mJ/cm2 resulted in a linear increase in the number of DNA lesions in the genome [range 0.3 +/- 0.2 lesions-3.6 +/- 0.7 lesions (mean +/- SD)/10 kb]. At lower doses of UVB (<10 mJ/cm2), 89 +/- 13% lesions were repaired within 24 h of culture. At higher doses, more lesions remained unrepaired, but the repair efficacy expressed as a proportion of repaired lesions to the total amount of DNA lesions remained constant in the range 0-50 mJ/cm2. Moreover, we demonstrated a correlation between the dose of UV and cell survival. The D37 (dose that reduced clonogenic survival to 37%) of UVB equaled 19 mJ/cm2, corresponding to the introduction of 1.4 lesions/10 kb. In contrast to UVB, UVA1 irradiation neither induced measurable DNA damage nor induced cell death in the doses up to 15 J/cm2. In conclusion, the non-radioactive extra-long (XL)-based real-time (RT)-PCR assay system can be used to quantify the UV-induced DNA damage in intact cells. The DNA lesions detected by this assay are mainly induced by short-waved radiation in the UVB range, and unrepaired DNA lesions cause keratinocyte death or permanent cell-cycle block.

Molecular cloning of the human gene SUVCC3 associated with the formation of DNA-protein crosslinks following exposure to solar UV radiation

DRP 153 cells, which are hypersensitive to solar UV and deficient in the formation of DNA-protein crosslinks (DPC) following irradiation, were transfected with human DNA and a secondary transformant obtained in which a normal DPC response and solar UV sensitivity reestablished. DNA from this secondary transformant was used to construct a genomic DNA library from which a recombinant phage was isolated containing the human gene capable of restoring a normal DPC response and solar UV sensitivity to DRP 153. This gene has been designated SUVCC3 to denote solar UV cross-complementing gene number 3.

Genomic damage and its repair in young and aging brain

A brief review of the available information concerning age-related genomic (DNA) damage and its repair, with special reference to brain tissue, is presented. The usefulness of examining the validity of DNA-damage and repair hypothesis of aging in a postmitotic cell like neuron is emphasized. The limited number of reports that exist on brain seem to overwhelmingly support the accumulation of DNA damage with age. However, results regarding the age-dependent decline in DNA-repair capacity are conflicting and divided. The possible reasons for these discrepancies are discussed in light of the gathering evidence, including some human genetic disorders, to indicate how complex is the DNA-repair system in higher animals. It is suggested that assessment of repair potential of neurons with respect to a specific damage in a specific gene might yield more definitive answers about the DNA-repair process and its role in aging.

Photochemistry of nucleic acids in cells

A survey of the recent aspects of the main photoreactions induced by far-UV radiation in cellular DNA is reported. This mostly includes the formation of cyclobutadipyrimidines, pyrimidine(6-4)pyrimidone photoadducts and related Dewar valence isomers in various eukaryotic and prokaryotic cells, as monitored by using either specific or more general assays. Information is also provided on mechanistic aspects regarding the formation of 5,6-dihydro-5-(alpha-thyminyl) thymine, the so-called "spore photoproduct" within far-UV-irradiated bacterial spores. The second major topic of the review deals with the effects of near-UV radiation and visible light on cellular DNA which are mostly mediated by photosensitizers. The main photoreactions of furocoumarins with DNA, one major class of photosensitizers used in the phototherapy of skin diseases, involve a [2 + 2] cycloaddition to the thymine bases according to an oxygen-independent mechanism. In contrast a second type of photosensitized reaction which appears to play a major role in the genotoxic effects of both near-UV and visible light requires the presence of oxygen. The photodynamic effects which are mediated by either still unidentified endogenous photosensitizers or defined exogenous photosensitizers lead to the formation of a wide spectrum of DNA modifications including base damage, oligonucleotide strand breaks and DNA-protein cross-links.

Effect of vitamin E on cytotoxicity, DNA single strand breaks, chromosomal aberrations, and mutation in Chinese hamster V-79 cells exposed to ultraviolet-B light

The effect of pretreatment with vitamin E on cytotoxicity, DNA single strand breaks, and chromosomal aberrations as well as on mutation induced by ultraviolet-B light (UV-B) was investigated in Chinese hamster V-79 cells. Cellular pretreatment with non-toxic levels of 25 microM alpha-tocopherol succinate (vitamin E) for 24 h prior to exposure resulted in a 10-fold increase in cellular levels of alpha-tocopherol. Using a colony-forming assay, this pretreatment decreased the cytotoxicity of UV-B light. However, alkaline elution assays demonstrated that pretreatment with vitamin E did not affect the number of DNA single strand breaks caused by UV-B light. In addition, UV-B exposure produced a dose-dependent induction of chromosomal aberrations and mutations at the HGPRT locus, and neither of these actions of UV-B was influenced by pretreatment with the vitamin. These results suggest that vitamin E protects cells from UV-B-induced cytotoxicity, possibly through its ability to scavenge free radicals. The results also suggest that the extent of genotoxicity induced by UV-B light may not correlate directly with the cytotoxic action of this wavelength region in sunlight.

Non-dimer DNA damage in Chinese hamster V-79 cells exposed to ultraviolet-B light

To understand and characterize non-dimer DNA damage and cytotoxicity induced by ultraviolet-B light (UV-B, 290-320 nm), an alkaline elution technique for analysis of DNA damage was used on Chinese hamster V-79 cells. Ultraviolet-B exposure produced a dose-dependent induction of DNA single strand breaks and DNA-protein crosslinks; however, there was an absence of DNA-DNA interstrand crosslinks. Neither of these types of DNA damage were repaired within a a 24 h incubation of the cells following a single UV-B exposure; rather the damage increased. Using a colony forming assay, we found that UV-B exposure resulted in an increase of cytotoxicity in a dose-dependent fashion. In addition, UV-B exposure inhibited DNA and RNA synthesis. The role of non-dimer DNA damage in the cytotoxicity induced by UV-B is discussed.

Induction of DNA strand breaks and DNA-protein cross-links in normal human skin fibroblasts following exposure to 254 nm UV radiation

Levels of DNA strand breaks and DNA-protein cross-links (DPCs) were measured using the alkaline elution assay in normal human skin fibroblasts irradiated with 0-200 J m-2 of 254 nm UV radiation and incubated for 0-24 h. On incubation, the yields of both single-strand breaks (SSBs) and DPCs increased with similar kinetics and remained elevated. In addition, when SSBs were measured under conditions in which DPCs were not eliminated by treatment with proteinase K, a measurable yield of SSBs could not be detected. Hence, the SSBs that form in the UV-irradiated cells following incubation appear to be associated with the DPCs.

New trends in photobiology. The interaction of UVA radiation with cultured cells

Recent work concerning the interaction of UVA radiation (320-380 nm) with cultured cells is reviewed with particular emphasis on the involvement of cellular oxidative stress in the biological effects of this radiation on eucaryotic cells. Possible chromophores are considered and their role in generation of various oxidant species including hydrogen peroxide, superoxide anion, singlet oxygen and hydroxyl radical. DNA and membranes are discussed as possible targets for the lethal action of long wavelength radiation. Four mechanisms of cellular defence are proposed: (1) DNA repair; (2) antioxidant enzymes; (3) endogenous free radical quenchers; (4) inducible protection.

Effects of UV radiation of cells

UV radiation interacts with mammalian cells in a very complex manner, although DNA appears to be the main chromophore. Recent literature within this field is reviewed. The review is concentrated on the following main topics: Chromophores for UV action, photoproducts in DNA, repair of UV-induced DNA damage, wavelength interactions, inactivation, mutagenesis, transformation and protection mechanisms against UV damage.

DNA-protein crosslinking in normal and solar UV-sensitive ICR 2A frog cell lines exposed to solar UV-radiation

DNA-protein crosslinks (DPC) were measured following exposure to the solar UV wavelengths produced by a fluorescent sunlamp in ICR 2A frog cells and two solar UV-sensitive mutants derived from this cell line. Approx. 5-7 DPC per 10(10) dalton were induced in these cells by either 150 kJ/m2 of sunlamp UV greater than 315 nm plus photoreactivating light (PRL) or 10 kJ/m2 of sunlamp UV greater than 295 nm. The irradiated cells were then incubated for 0-24 h and the level of DPC measured using alkaline elution. It was found for the ICR 2A cells exposed to sunlamp UV greater than 315 nm that the level of DPC increased about 3-fold during a 2-h postirradiation incubation and then decreased. The mutant cell lines also showed an enhancement in the level of DPC following irradiation, although it was much less pronounced and the levels decreased much more rapidly. In a similar fashion, the level of DPC increased in ICR 2A cells exposed to sunlamp UV greater than 295 nm with more than a 5-fold enhancement after a 4-h incubation. Once again, the mutant cell lines showed an increase in the level of DPC that was smaller and more transient than the effect in the ICR 2A cells. These results suggests that this enhancement in DPC may be indicative of a process that plays a role in cellular survival following solar UV-irradiation.