The effect of specific photoremoval of UVB induced lesions in DNA repair deficient mice

Abstract

The DNA molecule, in spite of its great biological importance, is constantly under chemical and physical stress, which are capable of generating lesions in this type of molecule. Ultraviolet (UV) irradiation is considered one of our main environmental genotoxic agents, since it can directly induce photolesions in the DNA molecule. These lesions are the Cyclobutane Pyrimidine Dimers (CPDs) and the 6-4PP pyrimidine-pyrimidone photoproducts (6-4PPs). These lesions distort the DNA structure, thereby interfering in essential biological processes, such as DNA replication and RNA transcription. In skin tissue, the photolesions may induce important effects, such as hyperplasia, melanogenesis, inflammation and tumorigenesis. Placental mammals are capable of removing these lesions through the Nucleotide Excision Repair (NER) pathway, which has two subpathways, the Global Genome repair (GG-NER) and the Transcription Coupled repair (TC-NER) pathway. During the student's master's course, we used murine models deficient in the NER or the TC-NER pathway. These mice transgenically expressed either CPD or 6-4PP-photolyases in keratinocytes. Photolyases are enzymes absent in placental mammals, capable of removing photolesions in a specific and direct manner, in a light-dependent process. By using these models, we were able to study the specific effect of each photolesion, since by removing one type of lesion, we can investigate the effect of the remanescent lesions in the genome. We observed that CPD, but not 6-4PP removal is capable of reducing the UVB induced hyperplasia effect in TC-NER deficient mice. When using NER deficient mice, we noted that CPD removal is capable of completely inhibit this effect, while 6-4PP removal managed to reduce it. We also investigated the UVB-induced inflammation process in NER deficient mice. The removal of either CPDs or 6-4PPs were able to reduce and delay the inflammatory response caused by UVB irradiation. However, the removal of neither photolesion was capable of blocking MMP release, a process involved with skin inflammation and wound healing. Considering the results we've obtained so far, the objective of this project is to identify the molecular pathways involved with the shielding effects induced by the removal of CPD or 6-4PP lesions. We also intend to study the pathways related to the other effects caused by the photolesions, such as cell death, melanogenesis and carcinogenesis. In order to perform this study, we will use in vivo and in vitro models, deficient in DNA repair pathways, which allows us to better understand the mechanisms of the effects we observed during the student's master's, and also to obtain data regarding the mutagenicity of each type of lesion through the induction of tumorigenesis induced by UVB irradiation followed by CPD or 6-4PP removal. (AU)