Dose-response relationship for radiation-induced mutations at micro- and minisatellite loci in human somatic cells in culture

Abstract

Purpose : The study was designed to determine the dose-response relationship for radiation induction of mutations at mini- and microsatellite loci in human somatic cells. Mutations induced by graded doses of gamma-irradiation were quantified by screening clones derived from single irradiated cells for micro- and minisatellite alterations following irradiation with 1, 2 or 3 Gy. Materials and methods : After irradiation, the moderately radioresistant glioma cell line UVW was seeded at low density into Petri dishes to allow formation of discrete colonies, 100 of which were examined at each dose. All the cells within a colony were presumed to have arisen from a single irradiated cell. Radiation-induced microsatellite alterations were determined at 16 different loci, by PCR amplification and visualization on polyacrylamide gels. Minisatellite alterations were identified at four different minisatellite loci by restriction enzyme digestion and Southern blotting. Results : A dose-response curve for mutation frequency was obtained by analysis of 100 clones, yielding a minisatellite mutation rate of 5.5 X 10 -3 mutations/locus/Gy/cell and a microsatellite mutation rate of 8.75 X 10 -4 mutations/locus/Gy/cell. At microsatellite loci, alterations were predominantly simple loss or gain of repeat units and loss of heterozygosity (LOH). The mutations in minisatellite loci resulted predominantly in LOH and variation in repeat number. The background instability at each locus was determined by analysis of non-irradiated clones. Only 2% and 1% of the micro- and minisatellite loci respectively showed altered bands. Conclusions : This is the first report of a dose-response relationship for radiation-induced micro- and minisatellite mutations in human somatic cells. Described is a sensitive method for analysis of low-dose radiation mutagenesis in somatic cells that may prove to be a useful tool for radiation protection and dosimetry.