Low dose radiation effects on the transcription of consensus radiation response genes in primary and immortalized human fibroblast cells

Complete text of publication follows. OBJECTIVE: The linear non-threshold model suggests that tumors might be induced even by low radiation doses. Still, most of the conventional methods are unable to detect damages below 100 mGy. We have studied whether transcriptional responses of consensus radiation response genes can be detected after low dose radiation exposure in directly exposed or bystander primary human fibroblast cells. The short term proliferation capacity of primary fibroblast cells in culture limits their long term application. Therefore we tried to immortalize the cells by the introduction of the human telomerase gene using retroviral vectors. METHODS: Primary human fibroblast cell lines were established from skin biopsies of cancer patients and foreskin samples of young children. To create immortalized cell lines the human telomerase gene was cloned into a retroviral vector. Primary fibroblast cells were transduced and their proliferation capacity studied. To investigate radiation induced transcriptional alterations, cells were irradiated with 60Co γ-rays (0; 0.01; 0,04; 0,1; 2 and 8 Gy) and 2 hours later total cellular RNA was isolated both from directly exposed and bystander cells. Transcriptional alterations were followed in consensus radiation response genes (CDKN1, GADD45, GDF15, IER5, PLK3, TP53INP1) with quantitative real time PCR (Corbett/ SybrGreen). RESULTS: There is an elevated expression of CDKN1, GADD45, GDF15, PLK3, TP53INP1 in the exposed cells. We see only for the PLK3 a dose-dependent increase which manifested also at low doses. It seems this gene is the most sensitive to radiation at low doses. The hTERT-immortalized cells were morphologically identical to the primary cells. the radiation-induced transcriptional profile of immortalized cells were very similar to the primary ones. CONCLUSIONS: hTERT immortalized cells can be used to mimic alterations in primary cells. Low dose irradiation doesn't influence the expression of most of the studied genes. PLK3 might be an efficient marker to estimate individually low dose effects.