Abstract
Genomic instability, mutation, cell death, carcinogenesis, and DNA double strand breaks have been considered as a result of radiation exposure. However these responses were observed in unirradiated cells located near by irradiated cells or co-cultured in the same medium. Although the mechanisms of these cellular responses are not clearly understood, these responses were reported as a radiation induced bystander effects. Recent studies indicate that bystander effects are transmitted by gap-junction intercellular communication or by releasing of soluble factors into culture medium.
Human normal fibroblast cells, GM05389, were irradiated with 20Ne7+ (LET = 430 keV/μm) ion beam, by using heavy ion accelerator at TIARA of JAERI-Takasaki. After irradiation, cells (donor cells) were cultured in fresh medium for 24 hours, and then the medium was transferred into other unirradiated cells (recipient cells). After further incubation, chromosomes of recipient cells were observed by using premature chromosome condensation method.
From these analyses, the induction of chromosomal aberrations was clearly observed in recipient cells that were not irradiated directly. In this study, by the addition of drug to prevent the action of DNA-PKcs, an well known enzyme which takes part in repair of DNA double strand break, into donor and recipient cells, the effect of DNA-PK in the bystander effect was also observed.
