Evidence for induction of DNA double strand breaks in the bystander response to targeted soft X-rays in CHO cells

Abstract

This study investigated the role of DNA double strand breaks and DNA base damage in radiation-induced bystander responses in Chinese hamster ovary (CHO) cell lines. Two CHO repair deficient clones, xrs5 (DNA double strand break repair deficient) and EM9 (DNA base excision repair deficient) were used in addition to the wild type (CHO). When a single nucleus in the population was targeted with 1Gy, elevated numbers of micronuclei were induced in the neighbouring unirradiated cells in the EM9 and xrs5 cell lines, whereas induction was not observed in CHO. Under these conditions, the surviving fraction in the neighbouring cells was significantly lower in xrs5 than in the other cell lines, showing a higher cell killing effect in xrs5. These results suggest that DNA double strand breaks rather than base damage are caused by factors secreted in the medium from irradiated cells.