Abstract
Transcriptional activity of p53-target genes is enhanced by low dose ionizing radiation. However the detailed mechanisms for promoter activation by radiation are not elucidated. One of the reasons is that a reporter vector responsive to radiation has not been developed. Recently plenty of evidences were reported indicating that association of p53 with its recognition sequence of DNA is dependent on the chromatin structure. For instance, it was revealed, by in vitro experiments, that native p53 binds with higher affinity to the chromatin-assembled DNA than to double-stranded oligonucleotides. In vivo DNase I-hypersensitive site analyses showed that p53 recognition sites in the p21, 14-3-3&sigma, and KARP-1 genes are resistant to nuclease digestion even after gene induction by irradiation. We have constructed a reporter vector containing the luciferase gene under the control of the p21 gene promoter by using adeno-associated virus, with which the transgene can be integrated into chromosomes. When the reporter construct was transduced into MCF-7 cells, a remarkably high radiation-response was observed. It was revealed that luciferase expression was significantly induced by 0.5 Gy of X rays. This result indicates that the mechanism for activation of p21 gene promoter by low-dose radiation can be analyzed by use of this vector.
