Improved quantitation of DNA-protein crosslinking caused by 405-nm monochromatic near-UV radiation in human cells

Repair of DNA damage induced in systemic lupus erythematosus skin fibroblasts by simulated sunlight

Skin fibroblasts derived from three normal individuals and three patients exhibiting the disease systemic lupus erythematosus (SLE) were exposed to the simulated sunlight produced by a solar simulator. The induction and repair of DNA damage induced by this treatment were examined. The total number of lesions repaired by excision, as well as the removal of pyrimidine dimers and E. coli endonuclease III--sensitive sites did not differ significantly in the three SLE cell strains compared with normal cells. However, abnormalities in the formation and maintenance of DNA-protein crosslinks (DPC) and DNA single-strand breaks (SSB) were found in SLE-4 and SLE-5 following simulated sunlight exposure. In contrast, SLE-3 cells exhibited responses similar to normal cells in reference to SSB and DPC formation. These findings correlate well with the previously determined UV sensitivity of these SLE cell strains.

Principles and practice of DNA filter elution

DNA filter elution assays have proved useful in studies of DNA strand breaks and crosslinks produced in mammalian cells or tissues by a wide variety of carcinogenic and cancer chemotherapeutic agents. The basic types of DNA lesions that can be measured include single and double-strand breaks, interstrand crosslinks and DNA-protein crosslinks. DNA filter elution has also been adapted to the assay of other lesions such as alkali-labile sites and the protein-associated strand breaks of topoisomerase DNA cleavage complexes. The essential concepts and theory of the technique are discussed and the applications of the technique to various types of studies are critically reviewed.

Comparison of initial yields of DNA-to-protein crosslinks and single-strand breaks induced in cultured human cells by far- and near-ultraviolet light, blue light and X-rays

The initial yields of DNA-to-protein crosslinks (dpc) caused by ionizing and nonionizing radiations were compared, with emphasis upon values within the biological dose ranges (D0). Induction of dpc in cold (0-0.5 degrees C) human P3 teratocarcinoma cells was measured by using alkaline elution techniques after exposure to monochromatic UVC (254 nm), UVB (313 nm), UVA (365 and 405 nm), and blue light (434 nm). UVC and UVB light induced detectable numbers (about 100 dpc per cell per D0). Monochromatic UVA radiations produced yields about 8 times higher than UVC or UVB (for 365 nm, about 1500 dpc per cell per D0) Similar results at low doses were obtained for measurements of single-strand breaks induced by the different radiations. The action spectra for dpc were closely similar. The biological significance of these relatively high numbers of DNA lesions caused by environmental nonionizing radiation that readily penetrates into human skin is not understood.

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.

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.

Photosensitized DNA breaks and DNA-to-protein crosslinks induced in human cells by antitumor agent gilvocarcin V

The antitumor agent gilvocarcin V (GV) is photoactivated to a genotoxic form by low fluences of near-ultraviolet radiation. Activation of GV by monochromatic 450-nm radiation causes two specific DNA changes in human P3 cells in culture as shown by alkaline elution techniques: single-strand breaks (i.e., alkali-labile sites plus frank strand scissions) and DNA-to-protein covalent bond crosslinks. When GV is present with the cells during irradiation, the yields of these damages are increased. Fluence and concentration studies show that the induction of both DNA lesions occurs at unusually low concentrations of drug and fluences of radiation. Both breaks and crosslinks are readily detectable after exposure to less than 100 kJ m-2 of 405 nm-radiation at a GV concentration of 7.5 X 10(-9) M. These results indicate a possible potential for use of GV in human tumor photochemotherapy.