In vitro irradiation is able to cause RET oncogene rearrangement

Elevated risk of thyroid cancers among the atomic bomb survivors as compared to the nonexposed population suggests that some genetic events related to thyroid cancer must be caused by ionizing radiation. Accordingly, inducibility of RET oncogene rearrangements, i.e., the generation of the RET-PTC oncogene, specific for thyroid cancer, was investigated among human undifferentiated thyroid carcinoma cells (8505C), which do not have RET oncogene rearrangement, after 0, 10, 50, and 100 Gy of in vitro X-irradiation by means of reverse transcription polymerase chain reaction. After testing 10(8) cells at each dose point, 3 independent samples obtained with 50 Gy of X-irradiation and 6 independent samples obtained with 100 Gy of X-irradiation showed a rearranged RET oncogene amplified band. No rearranged transcripts were obtained from cells irradiated with 0 or 10 Gy. All of the transcripts were sequenced and found to contain the D10S170 and RET sequence. Interestingly, two types of rearrangements were included in these transcripts: one is specific for thyroid cancer and the other, which contains a 150-base pair insert, is atypical, not usually seen in vivo. This insert was found to be the exon of D10S170. Furthermore, in fibrosarcoma cells (HT1080), X-irradiation also induced RET oncogene rearrangements, which included the same two types of rearrangements observed in the X-irradiated thyroid cells (8505C). These results are in favor of the hypothesis that some radiation-induced thyroid cancers, including those among atomic bomb survivors, might have developed when a growth advantage was obtained through a specific form of RET oncogene rearrangement induced by radiation exposure.