Figure 1.

Radiation induces growth inhibition in repair-deficient cells but not in repair-proficient cells. (A) Exposure to radiation induces growth inhibition followed by delayed cell death in repair-deficient M059J cells (lower panel) but only delayed growth in repair-proficient M059K (upper panel). On day 0, cells were irradiated with 4 Gy and counted on days 0, 1, 3, and 5. Y axis represents the number of viable cell number as measured by trypan blue exclusion. (B) Cell cycle analysis showed that M059J cells were still growth-arrested at the G₂/M phase of the cell cycle after 72 h of radiation, whereas M059K recovered their growth potential, showing a cell cycle distribution comparable to control, vehicle-treated cells. Consistently, cell viability results showed clear recovery in M059K cells but not in M059J cells, suggesting that deficiency in DNA repair due to lack of DNA-PKc function leads to prolonged growth inhibition upon radiation. Error bars represent standard error of the mean (SEM) in A.