DNA damage and the bystander response in tumor and normal cells exposed to X-rays.

Monolayer and suspension cultures of tumor (BMG-1, CCRF-CEM), normal (AG1522, HADF, lymphocytes) and ATM-mutant (GM4405) human cells were exposed to X-rays at doses used in radiotherapy (high dose and high dose-rate) or radiological imaging (low dose and low dose-rate). Radiation-induced DNA damage, its persistence, and possible bystander effects were evaluated, based on DNA damage markers (γ-H2AX, p53) and cell-cycle-specific cyclins (cyclin B1 and cyclin D1). Dose-dependent DNA damage and a dose-independent bystander response were seen after exposure to high dose and high dose-rate radiation.