Figure 1.

Response to ionizing radiation of exponentially growing cells. (A) Flow cytometric analysis of HT1080 (□) and HT1080.6TG (•) cells treated with 4 Gy γ-radiation. The number of cells in S phase was determined by BrdUrd incorporation. The number of cells in G₁ and G₂/M phases was estimated from the flow histograms using PI fluorescence. The experiments were repeated at least twice per cell line and the averages are shown. (B) Western blot analysis of p53, p21, and p27 protein levels in control and irradiated cells from each tumor cell line. The levels of these proteins were detected by immunoblotting 4 hr after treatment with 4 Gy γ-rays (+) or following no treatment (−). The membrane was probed for p27 to check for equal loading since its expression does not change in response to radiation.