Enhanced survival and decreased mutation frequency after photoreactivation of UV damage in rat kangaroo cells

Enhanced repair of cyclobutane pyrimidine dimers and improved UV resistance in photolyase transgenic mice

During evolution, placental mammals appear to have lost cyclobutane pyrimidine dimer (CPD) photolyase, an enzyme that efficiently removes UV-induced CPDs from DNA in a light-dependent manner. As a consequence, they have to rely solely on the more complex, and for this lesion less efficient, nucleotide excision repair pathway. To assess the contribution of poor repair of CPDs to various biological effects of UV, we generated mice expressing a marsupial CPD photolyase transgene. Expression from the ubiquitous beta-actin promoter allowed rapid repair of CPDs in epidermis and dermis. UV-exposed cultured dermal fibroblasts from these mice displayed superior survival when treated with photoreactivating light. Moreover, photoreactivation of CPDs in intact skin dramatically reduced acute UV effects like erythema (sunburn), hyperplasia and apoptosis. Mice expressing the photolyase from keratin 14 promoter photo reactivate CPDs in basal and early differentiating keratinocytes only. Strikingly, in these animals, the anti-apoptotic effect appears to extend to other skin compartments, suggesting the presence of intercellular apoptotic signals. Thus, providing mice with CPD photolyase significantly improves repair and uncovers the biological effects of CPD lesions.

Insect cells and their potential as stabilization barriers for DNA of multiple and single nucleopolyhedroviruses against ultraviolet-B-simulated sunlight inactivation

A cell line from Trichoplusia ni (TN-CL1) infected with the Autographa californica multiple nucleopolyhedrovirus (AcMNPV-HPP) and a cell line from Helicoverpa zea (BCIRL-HZ-AM1) infected with the Helicoverpa zea single nucleopolyhedrovirus (HzSNPV/BrCL2) were subjected to ultraviolet-B (UV-B) irradiation at a predetermined level of exposure that would inactivate greater than 95% of the virus suspended in the liquid. The working hypothesis was that the homologous insect cells would utilize their inherent deoxyribonucleic acid (DNA) repair mechanism(s) to prevent, repair, or at least mitigate the damaging effects of UV-B light on viral DNA synthesis. We attempted to determine this by using infected cells that were subjected to UV-B irradiation at different postinoculation periods under two experimental conditions of exposure: (1) shielded, and (2) nonshielded. Of the two cell lines infected with their respective homologous viruses, the virus from TN-CL1 cells was the least sensitive to UV-B light because the extracellular virus (ECV) and occlusion body (OB) levels of virus-infected TN-CL1 cells were higher than those of the virus-infected BCIRL-HZ-AM1 cells. Production of ECV and OB from both cell lines was lower in the exposed, nonshielded treatment than in the exposed, shielded treatment. However, AcMNPV-HPP was produced in enough quantity to indicate that TN-CL1 might impart a level of protection to the virus against UV light.

Inhibition of RNA and DNA synthesis in UV-irradiated normal human fibroblasts is correlated with pyrimidine (6-4) pyrimidone photoproduct formation

UV-irradiation of living cells results in an inhibition of RNA and DNA synthesis. The purpose of this study was to determine whether specific photoproducts or the total combined yield of lesions were responsible for these effects. Asynchronously dividing human fibroblasts from normal donors were irradiated with UVC (254 nm), broad spectrum UVB (290-320 + nm, Westinghouse FS20 lamp) or narrow spectrum UVB (310-315 nm, Philips TL01 lamp) at fluences which induce known yields of cyclobutane pyrimidine dimers, pyrimidine (6-4) pyrimidone photoproducts or Dewar isomers. DNA synthesis was approximately 3-4 times more sensitive to both UVC and UVB irradiation than RNA synthesis. The immediate inhibition of RNA and DNA synthesis was correlated with (6-4) rather than overall photoproduct formation suggesting that the (6-4) photoproduct is the mediator of these inhibitory effects. In support of this suggestion we found that photoreactivation of cells cultured from the marsupial, mouse Sminthopsis crassicaudata, resulted in removal of 70% of pyrimidine dimers from the overall genome, but had only a slight effect on the recovery of RNA synthesis.

Photoreactivation of ultraviolet radiation-induced release of arachidonic acid from marsupial cells

Exposure of an established marsupial cell line, PtK2 (Potorous tridactylus), to ultraviolet radiation (UVR) from an FS-40 sunlamp (280-400 nm) resulted in a fluence-dependent release of radiolabeled arachidonic acid (AA) from cell membranes. Post-UVR, but not pre-UVR, exposure to photoreactivating light reversed UVR-induced pyrimidine dimers in DNA and suppressed the UVR-induced release of AA. These data indicate that DNA damage contributes to the release of AA from membrane phospholipids.

Photoreactivation of UV damage in cultured Drosophila cells

Cell survival and photoreactivation of 254 nm ultraviolet (UV) light damage in a wild type Drosophila cell line was assayed by colony formation in liquid medium. Fo, Fq, and extrapolation number for the exponential portion of survival curves are 21 J/m2, 3.6 J/m2, and 1.5 for non-photoreactivated cells and 110 J/m2, 11.2 J/m2, and 1.3 for those exposed to photoreactivating light. Maximal photoreactivation occurs at the 100 J/m2 region of the curve. At 10 and 50% survival, 75-80% of the UV damage was photoreactivable.

Kinetics of unscheduled DNA synthesis in UV-irradiated chicken embryo fibroblasts

Unscheduled DNA synthesis induced by 254-nm UV radiation in chicken embryo fibroblasts was examined for 24 h following irradiation, while cells were kept in the dark. The effect on this repair process of a 2-4 h exposure to photoreactivating light immediately after UV was studied. Initial [3H]thymidine incorporation in the light-treated cells was only slightly different from that in cells not exposed to light, but a distinct difference in rate and cumulative amount of unscheduled DNA synthesis was seen several hours after irradiation. By varying the UV dose and the time allowed for photoreactivation, the amount of dimers (determined as sites sensitive to a M. luteus UV-endonuclease) and non-dimers could be changed. The results of these experiments suggest that excision repair of dimers, rather than non-dimer products, is responsible for the unscheduled DNA synthesis seen after UV irradiation.

Cycloheximide-sensitive recovery from 254 nm UV light damage in cultured marsupial cells

Colony-forming ability of Potorous tridactylus-kidney (PtK-2) cells was measured after exposure to 254-nm ultraviolet (UV) light and cycloheximide. Addition of 5 microM cycloheximide after exposure of the cells to UV light greatly decreased cell survival. Maximum effect of the drug was obtained by 24-h exposure after irradiation. The cycloheximide sensitivity of irradiated cells was eliminated if addition of the drug was delayed for 8-10 h after irradiation, or if the cells received photoreactivating light treatment prior to cycloheximide exposure. Thus, a major component of pyrimidine dimer removal may involve a cycloheximide-sensitive mechanism.