Abstract
Irradiation procedures of the microbeam and the luciferase detection system for p53 gene transcription activity in mouse fibroblast-cultured cells were established for the usage to evaluate low dose rate radiation-induced biological effects. Confluent cells were irradiated by either ion microbeam or broad-ion beam, and the transcription levels of p53 in irradiated cells were observed by this system. In broad beam irradiation of Ne ion from TIARA AVF cyclotron, the particle fluence was approximately one ion per cell. In microbeam irradiation of the same ion, the exact one ion was irradiated at each cross point of orthogonal lattice in a 3 mm square. In broad beam irradiation, the p53 transcription activities had 2-fold increase of control. In microbeam irradiation, the p53 transcription activities reversely decreased to 30-40% of control with increase of number of irradiation cross points of 1-16. The p53 transcription activities decreased with increase of density of ion irradiation in an area. Reduction of the p53 transcription activities in irradiated cell population by the microbeam irradiation, can be explained not by effect of secondary electrons but by bystander effects, because percent of cell population located within the range of secondary electrons in the penumbra around one ion track is corresponding to about 1/10,000 of all cells. Microbeam irradiation of targeting cells may reduce p53 transcription activities in non-irradiated cells by an unknown mechanism through bystander effects. This study was financially supported by Aomori Prefecture, Japan.
