|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1990 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1989 : ¥1,800,000 (Direct Cost : ¥1,800,000)
An adaptive response to ionizing radiation was found in cultured mammalian cells, as a phenomenon of a suppressed induction of chromosomal aberrations (micronuclei, SCEs) by challenging doses when cells were conditioned by very low doses. The term, 'radio-adaptive response' (RAR) was proposed for the novel chromosomal response (Mutation Res. 227, 241, 1989). The important characteristics that have emerged in cultured Chinese hamster cells are : 1. Very low doses of beta-rays from tritiated water as well as from tritiated thymidine can induce the RAR. 2. The RAR is dependent on the total dose of the challenging (pretreatment) and the rate at which the doses are given. The RAR can be induced only by a narrow window of challenging doses (cGy level). 3. Gamma-rays can act as ^3 H beta-rays, but thermal neutrons, a high LET radiation, is not effective for induction of the RAR. 4. A 4-h interval is enough for the full expression of the RAR, which decays with the progression of cell proliferation. 5. The RAR is suppressed by an inhibitor of poly (ADP-ribose) polymerase. 6. The RAR can affect clastogenic lesions induced by UV-B, mitomycin C and thermal neutrons (weak), but not by EMS and cisplatin. 7. The RAR is inhibited by cycloheximide, an inhibitor of protein synthesis. 8. Several proteins are synthesized after irradiation with low doses of gamma-rays which can induce the RAR, concurrently with the expression of the RAR. This was revealed by means of 2-D polyacrylamide gel electrophoresis and fluorography. These characteristics suggest that the RAR is an induced chromosmal DNA repair which occurs under a restricted condition, and that the low-dose induced expression of 'RAR genes' is involved in the process of the RAR.