The mutagenic effect of ultraviolet-A1 on human skin demonstrated by sequencing the p53 gene in single keratinocytes

Background. Sun exposure is accepted as the major risk factor for developing skin cancer, the most common cancer in the western world. Ultraviolet-B (UV-B) radiation is considered the causative agent, but recently several findings suggest a role also for ultraviolet-A (UV-A) radiation. Repeated suberythemal doses of ultraviolet-A1 (UV-A1) on healthy human skin induce an increase of p53 immunoreactive cells in epidermis, which may indicate cell cycle arrest and/or occurrence of p53 mutations. Methods: We have investigated the possible mutagenic effect of UV-A1 on skin by sequencing exons 4-11 and adjacent intron sequence of the p53 gene in immunoreactive single cells from three healthy individuals. Previously unexposed buttock skin was irradiated three times a week for 2 weeks with physiological fluences (40 J/cm(2)) of UV-A1. Punch biopsies were taken before and at different time-points after the exposure, and from these single p53 immunoreactive cells were isolated by using laser-assisted microdissection. Results: Three mutations - all being indicative of oxidative damage and most likely related to UV-A exposure were found among the 37 single cells from exposed skin, whereas no mutations were found in the 22 single cells taken before exposure. Conclusions: The findings indicate a mutagenic effect of low-dose UV-A1 on healthy human skin, which further demonstrates the importance of considering UV-A when taking protective measures against skin cancer.