Detrimental effects of UV‐B radiation in a xeroderma pigmentosum‐variant cell line

Abstract

DNA polymerase η (pol η), of the Y-family, is well known for its in vitro DNA lesion bypass ability. The most well-characterized lesion bypassed by this polymerase is the cyclobutane pyrimidine dimer (CPD) caused by ultraviolet (UV) light. Historically, cellular and whole-animal models for this area of research have been conducted using UV-C (λ = 100–280 nm) owing to its ability to generate large quantities of CPDs and also the more structurally distorting 6-4 photoproduct. Although UV-C is useful as a laboratory tool, exposure to these wavelengths is generally very low owing to being filtered by stratospheric ozone. We are interested in the more environmentally relevant wavelength range of UV-B (λ = 280–315 nm) for its role in causing cytotoxicity and mutagenesis. We evaluated these endpoints in both a normal human fibroblast control line and a Xeroderma pigmentosum variant cell line in which the POLH gene contains a truncating point mutation, leading to a nonfunctional polymerase. We demonstrate that UV-B has similar but less striking effects compared to UV-C in both its cytotoxic and its mutagenic effects. Analysis of the mutation spectra after a single dose of UV-B shows that a majority of mutations can be attributed to mutagenic bypass of dipyrimidine sequences. However, we do note additional types of mutations with UV-B that are not previously reported after UV-C exposure. We speculate that these differences are attributed to a change in the spectra of photoproduct lesions rather than other lesions caused by oxidative stress.

Minimal Detection of Nuclear Mutations in XP‐V and Normal Cells Treated with Oxidative Stress Inducing Agents

“…Similarly, untreated NHF cells gave a MF value of 0.55 × 10 −5 , with MD (1.65 × 10 −5 ; 3×) and MBL (1.27 × 10 −5 ; 2.4×) again causing very little difference. This is in comparison to our previously published work using environmentally relevant levels of UV-B (10 mJ/cm 2 ) in which the MF of XP-V cells was 25.8 × 10 −5 (26× higher than untreated) and for NHF cells the MF was 8.56 × 10 −5 (15.6× untreated) [18]. In addition, we attempted alternative treatment protocols in an attempt to exacerbate the effects, in case a single, short oxidative stress inducing treatment was insufficient to generate damage/mutations at levels detectable in this assay.…”

“…Abbreviations: CFE, colony forming efficiency; MF, mutation frequency. Data for untreated samples are the same as previously reported [18]. frequency (MF) of 0.98 × 10 −5 .…”

Cooperation and interplay between base and nucleotide excision repair pathways: From DNA lesions to proteins

“…Mutational effects by UVA are typically due to lesions induced by direct DNA absorption (pyrimidine dimers). Most of the published studies have reported C > T changes at dipyrimidine sites (Robert et al, 1996;Ikehata et al, 2003;Agar et al, 2004;Kappes et al, 2006), which is similar to UVC and UVB induced mutagenesis (Brash et al, 1987;Douki et al, 2003;Kappes et al, 2006;Herman et al, 2014). Interestingly, this type of mutation has been detected in nonmelanoma (Giglia-Mari and Sarasin, 2003), as well as, melanoma skin cancers (Greenman et al, 2007;Pleasance et al, 2010).…”

Diagnosis of eight groups of xeroderma pigmentosum by genetic complementation using recombinant adenovirus vectors

“…Exposure of cultured cells to UV irradiation proved that UV‐C (100–280 nm) is more useful than UV‐B (280–315 nm) because of UV‐C's ability to generate large quantities of cyclobutane pyrimidine dimers (CPD) and is also a more structurally distorting 6–4 photoproduct . Herman et al . reported that UV‐B has similar but less striking effects than UV‐C concerning both its cytotoxic and mutagenic effects.…”

“…Exposure of cultured cells to UV irradiation proved that UV-C (100-280 nm) is more useful than UV-B (280-315 nm) because of UV-C's ability to generate large quantities of cyclobutane pyrimidine dimers (CPD) and is also a more structurally distorting 6-4 photoproduct. 30 Herman et al 31 reported that UV-B has similar but less striking effects than UV-C concerning both its cytotoxic and mutagenic effects. In the present study, we aimed to differentiate each XP group by complementation assays using recombinant adenoviruses, and found that both UV-B and UV-C were useful for differentiation of XP groups but UV-C showed a clearer separation between surviving cells after infection of matched recombinant adenoviruses and those of unmatched viruses (Fig.…”