Abstract
The radioadaptive response is the induction of cellular resistance to moderate or high doses of radiation by previous exposure to low doses. Treatment with TPA or hydrogen peroxide mimicked X-rays in adaptation when applied at low doses. We have shown that protein kinase C (PKC)-specific inhibitor abolished the adaptive response and that low dose of X-rays induced an alteration in the localization of PKCalpha protein. Although these data suggested that PKCalpha is involved in the radioadaptive response, it has not bee directly proved yet. In this study, we examined the involvement of PKCalpha in the induction of radioadaptive response by using RNAi of PKCalpha to reduce the expression of the protein. We introduced siRNAs into mouse m5S fibroblasts, which target the mouse PKCalpha gene, Prkca. The decrease in the PKCalpha expression was confirmed since both the amount of PKCalpha protein detected by Western blot and the Prkca cDNA quantity analyzed by RT-PCR were reduced. Radioadaptive response in the m5S cells were examined using cells which were pre-treated with low concentration of hydrogen peroxide for 5 hours before the irradiation with 5Gy X-rays, and analyzed the number of micronuclei. The radioadaptive response was suppressed in the cells with reduced amount of PKCalpha protein. In addition, the amount of phosphorylated PKCalpha protein was increased by the treatment with low concentration of hydrogen peroxide, indicating the activation of PKCalpha. These results suggest that the activation of PKCalpha might play an important role in radioadaptive response.
