Objective     To investigate the effect of silencing peroxiredoxin Ⅰ (PrxⅠ) gene by

RNA interference (RNAi) on the radiosensitivity of breast carcinoma cell line MCF-7 and its mechanism.      Methods     Recombinant plasmid pGPU6-PrxⅠ expressing short hairpin RNA (shRNA) against PrxⅠ and plasmid pGPU6-HK as a negative control were transferred into MCF-7 cells separately. The transfected MCF-7 cells were screened by G418. The mRNA and protein expression levels of PrxⅠ in the transfected MCF-7 cells were detected by RT-PCR and Western blotting. The transfected MCF-7 cells were exposed to 6-MV X ray at a dose of 6 Gy. Forty-eight hours after the radiation (ionizing radiation)

reactive oxygen species (ROS)

cell cycle and cell apoptosis were estimated by flow cytometry. Cell proliferation was detected by MTT assay

and the protein expression levels of Rad51 and γ-H2AX were evaluated by Western blotting. Colony forming efficiency was measured by colony formation assay

and the radiobiological parameters D

o

N

D

q

surviving fraction after 2 Gy (SF

2

) and sensitivity enhancement ratio (SER) were calculated from the cell survival curve.      Results     Two stable MCF cell lines

which carried pGPU6-HK and pGPU6-PrxⅠ separately

were obtained by G418 pressure screening. The cells carrying pGPU6-PrxⅠ had significantly suppressed mRNA and protein expression of PrxⅠ compared with the cells carrying pGPU6-HK (P0.05). Forty-eight hours after 6-Gy X ray radiation

the cells carrying pGPU6-PrxⅠ showed that the ROS level

G

1

phase cell number and cell apoptosis rate were significantly increased

while the cell proliferation capacity and S phase cell number were significantly decreased (P0.05). The Western blot results indicated that after the radiation

the cells carrying pGPU6-PrxⅠ had Rad51 protein expression level decreased by 79.3% but γ-H2AX protein expression level increased by 3.7 times (P0.05). The D

o

N

D

q

and SF

2

of the cells carrying pGPU6-PrxⅠ were 1.354

3.106

1.547 and 0.504

respectively

lower than those of the cel

ls carrying pGPU6-HK. The SER

calculated from SF

2

was 1.353.      Conclusion     RNAi-mediated PrxⅠ gene silencing can significantly enhance the radiosensitivity of breast carcinoma cell line MCF-7. The mechanism may involve the decrease of ROS-scavenging ability

increase of double-stranded DNA damage

and reduction of DNA repair ability in MCF-7 cells. Prx I may be a promising target for tumor radiosensitization.