REDUCED INDUCTION OF P53 PROTEIN BY GAMMA-IRRADIATION IN ATAXIA-TELANGIECTASIA CELLS WITHOUT CONSTITUTIONAL MUTATIONS IN EXONS 5, 6, 7, AND8 OF THE P53 GENE

Ataxia telangiectasia (AT) is an autosomal recessive disease of childh ood with several phenotypic characteristics. One of the hallmarks of t his syndrome is its hypersensitivity to ionizing radiation, which is b elieved to be due to defects in DNA repair/processing. In addition to radio-resistant DNA synthesis, both fibroblasts and lymphoblastoid cel l lines derived from these patients have been shown to have an impaire d G(1) arrest and prolonged G(2) accumulation of cells indicating a de fect in the regulation of cell cycle after irradiation. Since the (tum or suppressor) p53 protein has been reported to participate in the reg ulation of G, arrest after irradiation, the possibility of p53 gene mu tation and deregulating cell cycle in AT needed to be examined. We use d the PCR amplification and DNA sequencing methods to detect mutations in the hypermutable exons (5-8) of germline p53 in fibroblast cells f rom 3 AT homozygotes. No mutation was found in any of these exons. In order to determine the role of the p53 protein in G, arrest, its level s were measured before and after gamma-irradiation by flow cytometry i n both AT and normal cells. Radiation-induced p53 protein levels in th e AT cells varied from 6 to 60% compared to the normal cells, indicati ng a reduced induction of the protein in AT, These results suggest tha t mutation in the AT gene affects the p53 induction by irradiation and may, thus, alter the cell cycle regulation in the AT patients.