Effect of Small Dose of Radiation on Induction of Apoptosis in Murine Tumors / 대한방사선종양학회지

ABSTRACT

PURPOSE: To investigate the presence of adaptive response by low dose radiation in murine tumors in relation to radiation induced apoptosis as well as related mechanism. MATERIALS AND METHODS: Syngeneic murine tumors, OCa-I and HCa-I, were given 0.05 Gy pretreatment followed by therapeutic dose of 25 Gy radiation. Induction of apoptosis was analyzed for each treatment group. Regulating molecules of apoptosis, p53, Bcl-2, Bax, Bcl-X, were also analyzed by Western blotting. RESULTS: In 0.05 Gy pretreatment group of OCa-I, 25 Gy-induced apoptosis per 1000 cells was 229, which was estimated at 30% lower level than the expected (p<0.05). In contrast, this reduction in radiation induced apoptosis was not seen in HCa-I. In the expression of apoptosis regulating molecules, p53 increased in both tumors in response to radiation. Bcl-2 and Bax did not show significant change in both tumors however, the expression of Bcl-2 surpassed that of Bax in 0.05 Gy pretreatment group of OCa-I. Bcl-X was not expressed in OCa-I. In HCa-I, Bcl-X showed increased expression even with 0.05 Gy. CONCLUSION: Adaptive response by low dose radiation is shown in one murine tumor, OCa-I, in relation to radiation induced apoptosis. Apoptosis regulating molecules including Bcl-2/Bax and Bcl-X, appear to related. This study shows an evidence that adaptive response is present, but not a generalized phenomenon in vivo.