Passage of X-ray-induced immortal, non-transformed phenotype by DNA-mediated transfection

To better understand the molecular basis of X-ray-induced carcinogenesis, the immortalization step of this multistep process was examined. Primary rat embryo cells were X-irradiated in vitro and six clones were isolated. Three of these, one designated X-REF-23, were immortal and non-transformed. Transfection of high molecular weight DNA from rat X-REF-23 cells into primary mouse cells yielded two immortal and non-transformed mouse clones, 1K and 2I. Using a 2.3 kb rat-specific repetitive sequence as probe, 1K and 2I were demonstrated to contain rat DNA. This transfected DNA was not any of the known immortalization-associated proto-oncogenes. DNA from 1K was then transfected into primary mouse cells, with or without co-transfection of pSV2 neo DNA. Six immortal mouse clones were isolated and confirmed to contain rat sequences. In conclusion, the immortal phenotype can be transferred by DNA transfection.