Radiation inhibits protein downregulation by RNA interference and antisense oligodeoxynucleotides in human breast cancer cells.

A lot of efforts have focused on the RNA interference(RNAi) using small interfering RNAs(siRNAs) as a tool to knock down the expression of a target protein, although all of the processes of RNAi has not been clarified yet. It is a potential therapeutic tool. In radiation therapy field, particularly, in fractionated radiation therapy and cures of patients in accidental radiation exposure, treatment with siRNA after irradiation of tissues and cells is expected to be performed in its application. However its efficacy remains unknown. We evaluated effects of radiation on siRNA function. In human breast cancer cells (MCF7), siRNA against PKC delta downregulated PKC delta expression 24 h after treatment. Irradiation with 5Gy inhibited the down-regulation. In the case of the siRNA against PKC alpha as well as PKC delta, radiation also inhibited the down-regulation by the siRNA. Though effects of radiation on transfection efficiency by lipofection was also assessed in the process of siRNA functioning, radiation had no effect on the transfection efficiency. These results suggest that radiation inhibits regulations of siRNA function for downregulation of targeted proteins after the internalization. To understand the mechanism of radiation-induced inhibition of siRNA function, comparative experiments using antisense oligodeoxynucleotides(AS-ODN) were performed. Radiation also inhibited downregulation by AS-ODN against PKC delta. Currently change in internalized RNA degradation after irradiation is under investigation.日本生物物理学会第４４回大会、第５回東アジア生物物理シンポジウ