p53 -Dependent Adaptive Responses in Human Cells Exposed to Space Radiations

It has been reported that priming irradiation or conditioning irradiation with a low dose of X-rays in the range of 0.02–0.1 Gy induces a p53-dependent adaptive response in mammalian cells. The aim of the present study was to clarify the effect of space radiations on the adaptive response. Two human lymphoblastoid cell lines were used; one cell line bears a wild-type p53 (wt p53) gene, and another cell line bears a mutated p53 (m p53) gene. The cells were frozen during transportation on the space shuttle and while in orbit in the International Space Station freezer for 133 days between November 15, 2008 and March 29, 2009. After the frozen samples were returned to Earth, the cells were cultured for 6 h and then exposed to a challenging X-ray-irradiation (2 Gy). Cellular sensitivity, apoptosis, and chromosome aberrations were scored using dye-exclusion assays, Hoechst33342 staining assays, and chromosomal banding techniques, respectively. In cells exposed to space radiations, adaptive responses such as the induction of radioresistance and the depression of radiation-induced apoptosis and chromosome aberrations were observed in wt p53 cells but not in m p53 cells. These results have confirmed the hypothesis that p53-dependent adaptive responses are apparently induced by space radiations within a specific range of low doses. The cells exhibited this effect owing to space radiations exposure, even though the doses in space were very low.