Ionizing radiation induces a p53-dependent apoptotic mechanism in ARPE-19 cells

Purpose: To investigate the molecular mechanisms for cell growth inhibition or apoptosis in human retinal pigment epithelium (RPE) cells after ionizing radiation. Methods: Cell survival studies, a TdT-mediated dUTP-biotin nick-end labeling (TUNEL) assay, and a caspase-3 immunocytochemical analysis were performed on irradiated ARPE-19 cell cultures at different time periods. Transcriptional levels of p53, p21, Bax, Fas/Fas-L, vascular endothelial growth factor (VEGF), and pigment epithelium-derived growth factor (PEDF) were evaluated by semiquantitative reverse transcriptional polymerase chain reaction. Mutations in the p53 gene were analyzed by DNA sequencing. Protein levels of p53, VEGF, and PEDF were evaluated by Western blot. Results: Cell viability was inversely related to radiation close. TUNEL-positive cells were detected 6 h after radiation exposure. Caspase-3 immunomocytochemical analysis revealed increased immunoreactivity in the TUNEL-positive cells. Levels of p53, p21, and Bax mRNA were greatest at the 2-h postradiation period. VEGF and PEDF mRNA and protein levels were constant. Protein levels of p53 were increased at the 4- and 6-h postradiation period. Conclusions: Ionizing radiation induces apoptosis in normal proliferating RPE cells through p53 activation, without affecting expression of VEGF or PEDF. We documented a molecular basis for explaining the decrease in effectiveness of radiation therapy. particularly, for age-related macular degeneration. In the clinical setting, selection of appropriate radiation therapy methods and the doses for specific diseases need careful evaluation. (C) Japanese Ophthalmological Society 2004.