Molecular Mechanisms of Radioadaptive Responses in Human Lymphoblastoid Cells

Purpose : Radioadaptive response (RAR) is one of the biodefensive responses by which cells acquire radioresistance after exposure to low dose radiation. RAR is an important biological phenomenon in regard to the accurate estimation of the low-dose radiation risk. We have previously suggested a distinct molecular mechanism of RAR in terms of mutation from that of chromosomal aberration. In addition, by analyzing the gene expression profile, we have demonstrated that the expression of genes involved in the Ras signaling pathway varies in correlation with induction of RAR. Based on these results, we attempted to identify the genes that function in RAR. Methods : At 3h, 6h, 9h, and 24 h after irradiation with 0.02 Gy of X-rays, total RNAs were purified from the human lymphoblastoid cells (AHH-1) that were unirradiated or irradiated. Then we examined the gene expression by Northern blot analysis or real-time PCR for the genes which we selected as genes potentially related to RAR based on the analysis of the gene expression profile. To generate knockdown cells in which these potential genes are specifically targeted, AHH-1 cells were stably transfected with respective shRNA-expression plasmids. Then, it was analyzed whether RAR could be induced in these knockdown cells. Results : We identified DIDO1, MAPK8IP1 and SOCS3, whose expressions were significantly altered after irradiation with 0.02 Gy by analysis of the gene expression profile. Alteration in expression of these genes was confirmed by Northern blot analysis or real-time PCR. In cells stably transfected with respective shRNA-expression plasmids, it was observed that the knockdown efficiency was up to 68%, 64%, and 71% for DIDO1, MAPK8IP1, and SOCS3, respectively. Relationship of these genes with RAR will be discussed.