Telomere length and radiosensitivity in human fibroblast clones immortalized by ectopic telomerase expression

Telomeres, the ends of eukaryotic chromosomes, have a variable length among individuals and cell types. While studies in telomerase-deficient mice and cells showed an inverse correlation between telomere length and radiosensitivity, it is less clear whether this remains true in telomerase-proficient cells. To gain insight into this topic, we studied radiosensitivity in three telomerase immortalized fibroblast clones derived from the same cell line and characterized by different telomere length. In two clones, cen3tel4 and cen3tel5, the mean terminal restriction fragment length was ~13 and 10 kb, respectively and in the third clone, cen3pci16, it was ~4 kb, which is lower than in senescent fibroblasts. To test radiosensitivity, we determined survival to gamma-rays and the induction of chromosomal aberrations after irradiation. Neither the LD50, the gamma-ray dose that reduces survival to 50%, nor the frequency of aberrations detected in the three cell lines showed an inverse correlation with telomere length. In particular, the cen3pci16 cells, which have very short telomeres, did not show a higher sensitivity to irradiation or a greater frequency of chromosomal abnormalities compared to the other two cell lines. Our results suggest that, in the presence of telomerase activity, short telomeres are stabilized and do not cause an increase in radiosensitivity.