DNA photodamage, Repair, Gene Induction and Genotoxicity Following Exposures to 254 nm UV and 8-Methoxypsoralen plus UVA in an Eukaryotic Cell System Dietrich Averbeck* and Simone Averbeck Institut Curie-Section de Recherche, UMR218 du CNRS, LCR n°1 du CEA, Paris, France * To whom correspoondence should be addressed at: Institut Curie-Section de Recherche, UMR218 du CNRS, LCR n°1 du CEA, Paris, France, Phone: 0033 142346695, Fax: 0033 146333016, E-Mail: Averbeck@Curie.fr List of key words: DNA damage-inducible genes, DNA repair, UV irradiation, 8-methoxypsoralen , 1,6-dioxapyrene, double-strand-breaks, Saccharomyces cerevisiae Abbreviations: BER, base excision repair; 3-CPs, 3-carbethoxypsoralen; 1,6-DP, 1,6-dioaxapyrene; 8-MOP, 8-methoxypsopralen; dsb, DNA double-strand breaks; ssb, DNA single- strand breaks; UV, 254 nm UV radiation; UVA, 320-400 nm UV radiation; MA, monoadducts; NER, nucleotide ecision repair; PD, pyrimidine dimers; (6-4) P, pyrimidine(6-4)pyrimidone photoproducts; PFGE, pulse-field gel electrophoresis; PRR, post-replication repair; RR, recombination repair; TCR, transcription-coupled repair; TLR, translesional repair. ABSTRACT In eukaryotic cells the induction and repair of photodamage in DNA has been subject of many studies. We were interested to trace the existing links between these phenomena and the induction of DNA damage inducible genes and photogenotoxicity. Since strong homologies exist between some genes in the yeast Saccharomyces cerevisiae and humans, this organism represents a pertinent eukaryotic model. Comparing the effects of 254 nm UV radiation to that of photosensitizers such as 8-methoxypsoralen (8-MOP) plus UVA and the photodynamic compound 1,6-dioxapyrene (1,6-DP) plus UVA it is clear that different repair pathways are needed for the repair of the photolesions induced. The repair of 8-MOP-DNA photoadducts clearly involves the formation of DNA double-strand breaks (dsb) as repair intermediates, whereas after UV exposure this only occurs at a relatively high density of lesions and is not seen after treatments with 1,6-DP plus UVA. Likewise, the photogenotoxic potential of 8-MOP is higher than that of UV or 1,6-DP. When measuring the induction of the ribonucleotide reductase gene subunit RNR2 in a yeast strain carrying a RNR2-LACZ fusion 254 nm UV and 8-MOP plus UVA were very effective inducers, whereas 1,6-DP plus UVA was ineffective. We hypothesized that the formation of dsb as repair intermediates could be linked to gene induction. In order to study this further, we measured the induction of the RAD51 gene in an RAD51-LACZ fusion wild type strain and in an dsb repair and recombination deficient rad52 mutant. At equal treatment doses and equitoxic doses of UV and 8-MOP plus UVA, gene induction was strong in the wild type but very much reduced in the rad52 mutant. The results suggest that treatments with a high photogenotoxic potential that elicit DNA repair processing with dsb as intermediates are also relatively potent gene inducers. Thus, at least for certain DNA damage inducible genes, the signalling pathways initiated by DNA damage and involving specific repair processing are somewhat linked to the photogenotoxic response.

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