Abstract
We already reported that low dose-rate radiation induced the gene expression of certain p53 related genes weakly but significantly. In this report, we elucidated that p53 would contribute significantly to molecular response to low dose-rate irradiation as well as to high dose-rate, and found the difference in patterns of p21waf1 gene expression between high and low dose-rate. Method: Human acute lymphoblastic leukemia cell line MOLT-4 and B3 cells, a stable clone derived from MOLT-4 transfected with murine mutant p53, were irradiated with low dose-rate γ-rays at a dose rate of 1.1 mGy/hr. As high dose-rate radiation, we used X-rays at a dose rate of 0.25 Gy/min (150 kV, 5mA, filter: 1.0 mm Al + 0.2 mm Cu). Gene expression was measured by real time reverse transcriptase PCR method. Result: 1) In MOLT-4 cells, the level of p21waf1 gene expression increased up to 1.5-fold by the low dose-rate irradiation, and the level was kept at least for 311 days. 2) In B3 cells in which the function of endogenous p53 was inhibited through a dominant-negative effect, the induction was suppressed. 3) After the low dose-rate irradiation, the level of gene expression decayed more slowly than the case for the irradiation with 0.08 Gy at the high dose-rate which induced p21waf1 to similar extent as the low dose-rate irradiation.
