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

Seong, Jinsil; Pyo, Hong Ryull; Chung, Eun Ji; Kim, Sung Hee; Suh, Chang Ok

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.