Host: The Japan Radiation Research Society
Co-host: City of Kitakyushu, University of Occupational and Environmental Health, Japan
p21WAF1 is transcriptionally induced after exposure to ionizing radiation (IR) through the p53-dependent pathways, and plays critical roles in cell cycle checkpoint regulation. Elucidation of detailed mechanisms for p21WAF1 gene induction after irradiation is an important issue to control the efficacy of cancer radiotherapy in cancer treatment. For this purpose, we here performed a comprehensive analysis of the p21WAF1 gene promoter after irradiation with clinically relevant doses of IR. The sensitive reporter gene assay system by use of recombinant adeno-associated virus vectors was effectively utilized. It was demonstrated that the Oct-1 sites at –1.1 kb, –1.8 kb and –1.75 kb are involved in regulation of the p21WAF1 gene promoter in response to 0.2-2.0 Gy of IR. Constitutive binding of Oct-1 to the sites at –1.1 kb, and –1.75 kb was demonstrated by an electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Functional involvement of Oct-1 was confirmed by use of Oct-1-specific siRNA, which suppressed both the basal and the IR-inducible components of the p21WAF1 gene expression. Furthermore, we found that inducible binding of p53 to the site at –1.4 kb is indispensable for IR responsiveness, although it contains only one and a half repeats of the consensus recognition sequence. Based on the observation that binding of p53 to its canonical recognition sequence at –2.2 kb is constitutive, inducible binding of p53 at –1.4 kb site was suggested to play a major role in IR responsiveness of the p21WAF1 gene.
