ABSTRACT
<p><b>OBJECTIVE</b>To investigate the effect of peroxiredoxin I (Prx I) gene silencing on the radiosensitivity of breast carcinoma MCF-7 cell xenograft in nude mice and explore the mechanism.</p><p><b>METHODS</b>MCF-7 cells were transfected with the recombinant plasmids pGPU6-PrxI and pGPU6-HK separately. The pGPU6-PrxI-transfected cells stably expressing Prx I shRNA and pGPU6-HK-transfected cells were inoculated subcutaneously into BALB/c nude mice. After exposure to ionizing radiation (IR) with 6 MV X-ray, the xenografts were harvested for measuring the tumor volume and mass, and the tumor inhibition rates were calculated. Immunohistochemistry was employed for detecting the expressions of Prx I and caspase-3 proteins. The ultrastructural changes of the tumor tissues following the exposure were observed using electron microscopy. Western blotting was used to analyze the expressions of γ-H2AX and Rad51 proteins.</p><p><b>RESULTS</b>Following IR exposure, the pGPU6-Prx I-transfected cell xenograft showed a significantly delayed growth and smaller tumor volume as compared with pGPU6-HK xnegraft, with a tumor inhibition rate reaching 79.76%, significantly higher than that in non-exposed pGPU6-Prx I group (34.92%) and pGPU6-HK+IR group (56.94%) (P<0.05). The pGPU6-Prx I-transfected xenografts showed significantly increased tumor cell apoptosis and necrosis, down-regulated the expressions of Prx I and Rad51 proteins, and up-regulated the expressions of caspase-3 and γ-H2AX proteins; these changes were even more obvious after IR exposure, which caused a decrease of Rad51 protein by 84.8% and an increase in γ-H2AX protein by 5.6 folds compared with those in pGPU6-HK group (P<0.05).</p><p><b>CONCLUSION</b>Prx I gene silencing can significantly enhance the radiosensitivity of breast carcinoma xenograft in nude mice possibly by increasing DNA damage and lowering the capacity of the cells for DNA repair. Prx I may serve as an ideal molecular target for radiosensitization of breast carcinoma.</p>