UV effects in "the real world": problems of UV dosimetry in complex organisms

Ultraviolet radiation induces stress in etiolated Landoltia punctata, as evidenced by the presence of alanine, a universal stress signal: a ¹⁵N NMR study

Analysis with (15) N NMR revealed that alanine, a universal cellular stress signal, accumulates in etiolated duckweed plants exposed to 15-min pulsed UV light, but not in the absence of UV irradiation. The addition of 10 mm vitamin C, a radical scavenger, reduced alanine levels to zero, indicating the involvement of free radicals. Free D-alanine was detected in (15) N NMR analysis of the chiral amino acid content, using D-tartaric acid as solvent. The accumulation of D-alanine under stress conditions presents a new perspective on the biochemical processes taking place in prokaryote and eukaryote cells.

UVA, UVB and UVC induce differential response signaling pathways converged on the eIF2α phosphorylation

It is clear that solar UV irradiation is a crucial environmental factor resulting in skin diseases partially through activation of cell signaling toward altered gene expression and reprogrammed protein translation. Such a key translational control mechanism is executed by the eukaryotic initiation factor 2α subunit (eIF2α) and the downstream events provoked by phosphorylation of eIF2α at Ser(51) are clearly understood, but the upstream signaling mechanisms on the eIF2α-Ser(51) phosphorylation responses to different types of UV irradiations, namely UVA, UVB and UVC, are still not well elucidated. Herein, our evidence reveals that UVA, UVB and UVC all induce a dose- and time-dependent phosphorylation of eIF2α-Ser(51) through distinct signaling mechanisms. UVA-induced eIF2α phosphorylation occurs through MAPKs, including ERKs, JNKs and p38 kinase, and phosphatidylinositol (PI)-3 kinase. By contrast, UVB-induced eIF2α phosphorylation is through JNKs and p38 kinase, but not ERKs or PI-3 kinase, whereas UVC-stimulated response to eIF2α phosphorylation is via JNKs alone. Furthermore, we have revealed that ATM is involved in induction of the intracellular responses to UVA and UVB, rather than UVC. These findings demonstrate that wavelength-specific UV irradiations activate differential response signaling pathways converged on the eIF2α phosphorylation. Importantly, we also show evidence that a direct eIF2α kinase PKR is activated though phosphorylation by either RSK1 or MSK1, two downstream kinases of MAPKs/PI-3 kinase-mediated signaling pathways.

Framework for using quantitative PCR as a nonculture based method to estimate virus infectivity

Measuring the efficiency of virus disinfection with quantitative PCR (qPCR) has been criticized as inadequate due to the production of false-positive signals. Such a claim, however, presupposes an understanding of the theoretical qPCR response. Many studies have assumed that the loss in qPCR signal upon disinfection should equal the loss in infectivity, without accounting for the fact that qPCR typically assays only a fraction of the viral genome. This study aimed to develop a theoretical framework to relate viral infectivity with genome damage measured by qPCR. The framework quantified damage to the entire genome based on the qPCR amplification of smaller sections, assuming single-hit inactivation and a Poissonian distribution of damage. The framework was tested and modified using UV(254) inactivation studies with bacteriophage MS2 (culturing and qPCR of approximately half the genome). Genome regions showed heterogeneous sensitivities to UV(254) treatment, thus deviating from the assumption of Poissonian damage. We offered two modifications to account for these deviations and confirmed that the qPCR-based framework accurately estimated virus infectivity. This framework offers the potential to monitor the infectivity of viruses that remain nonculturable (norovirus). While developed for UV(254)-inactivated virus, the framework should apply to any disinfection technique that causes inactivation via single genomic lesions.

Preliminary assessment of the risks associated with solar ultraviolet-A exposure

An approach is proposed to assess the periods of human skin exposure to solar ultraviolet-A (UV-A, 315-400 nm) irradiance in natural conditions that are able to yield doses found to trigger carcinogenesis in laboratory experiments. Weighting functions, adopted to perform such estimate are constructed, allowing for a comparison between environmental and laboratory doses. Furthermore, the impact of stratum corneum (SC) thickness on the studied environmental doses was investigated. Based on laboratory studies, it was found that exposure periods of less than a month, at mid-latitudes, could provide irradiance doses capable of causing tumor formation. The duration of these exposure periods closely depends on the exposure regime, atmospheric conditions and SC thickness. It is believed that the presented evaluations could provide a useful preliminary estimation of the risk associated with environmental UV-A exposure prior to the formulation of the corresponding action spectra and determination of the threshold doses.

Damage to DNA in bacterioplankton: a model of damage by ultraviolet radiation and its repair as influenced by vertical mixing

A model of UV-induced DNA damage in oceanic bacterioplankton was developed and tested against previously published and novel measurements of cyclobutane pyrimidine dimers (CPD) in surface layers of the ocean. The model describes the effects of solar irradiance, wind-forced mixing of bacterioplankton and optical properties of the water on net DNA damage in the water column. The biological part includes the induction of CPD by UV radiation and repair of this damage through photoreactivation and excision. The modeled damage is compared with measured variability of CPD in the ocean: diel variation in natural bacterioplankton communities at the surface and in vertical profiles under different wind conditions (net damage as influenced by repair and mixing); in situ incubation of natural assemblages of bacterioplankton (damage and repair, no mixing); and in situ incubation of DNA solutions (no repair, no mixing). The model predictions are generally consistent with the measurements, showing similar patterns with depth, time and wind speed. A sensitivity analysis assesses the effect on net DNA damage of varying ozone thickness, colored dissolved organic matter concentration, chlorophyll concentration, wind speed and mixed layer depth. Ozone thickness and mixed layer depth are the most important factors affecting net DNA damage in the mixed layer. From the model, the total amplification factor (TAF; a relative measure of the increase of damage associated with a decrease in ozone thickness) for net DNA damage in the euphotic zone is 1.7, as compared with 2.1-2.2 for irradiance weighted for damage to DNA at the surface.