In vitro response of human dermal fibroblasts to X-irradiation: relationship between radiation-induced clonogenic cell death, chromosome aberrations and markers of proliferative senescence or differentiation

Purpose : To analyse the relationship between radiation-induced clonogenic cell death, chromosome aberrations and markers of proliferative senescence or differentiation. Materials and methods : Plateau-phase human dermal fibroblasts from 18 donors were irradiated with graded doses of 1-6 Gy 200kV X-rays. Cell survival was determined by a colony-forming assay. Markers of differentiation or senescence were: spontaneous and radiation-induced clonal differentiation, which was determined morphologically and by the cellular potential to proliferate in clonal culture, also single-cell g -galactosidase (g -gal) staining at pH 6.0; and the secretion of transforming growth factor- g (TGF- g 1) into the culture medium. Chromosome aberrations were determined as genomic yields of dicentric chromosomes and the excess acentric fragments, scored in Giemsa-stained metaphases, and as partial yields of reciprocal translocations for chromosomes 4, 7 and 9 using the FISH method. Results : A broad spread was found in the shapes of the survival curves, with SF2 ranging from 0.041 - 0.015 to 0.63 - 0.05. Radiation-induced clonal differentiation as well as the secretion of TGF- g 1 was elevated in radiosensitive samples. With respect to chromosome aberrations, a significant correlation was found between clonogenic survival and radiation-induced excess acentric fragments. Conclusions : In the fibroblast cell system, in vitro radiosensitivity is determined not only by processes directly involved in DNA-damage recognition and repair, but also by intracellular signalling cascades, which will lead to differentiation processes.