Distinct response of irradiated normal human fibroblasts and their bystander cells to heavy-ion radiation in confluent cultures

Hamada, Nobuyuki*; Iwakawa, Mayumi*; Imadome, Kaori*; Funayama, Tomoo; Sakashita, Tetsuya; Sora, Sakura*; Ni, M.*; Imai, Takashi*; Kobayashi, Yasuhiko

There is significant evidence for radiation-induced bystander effects; however, little information exists on the bystander effect of energetic heavy ions. Here we compared heavy-ion response of irradiated and bystander fibroblasts in confluent cultures. Bystander cells manifested a more transient apoptotic response and delayed p53 phosphorylation than irradiated cells did. More than half of the genes whose expression changed in bystander cells was downregulated, and most of the genes upregulated in irradiated cells were downregulated in bystander cells. The data highlight the distinct response of irradiated and bystander cells.