Enhancement of breast cancer cell radiosensitivity by knockdown of HER-2 and TOP2A

Objective To study the individual and combined effects of HER-2 and TOP2A on the radiosensitivity of breast cancer SK-Br-3 cells, and to provide a basis for clinical research. Methods To knock down the expression of HER-2 and TOP2A, the recombinant plasmids expressing HER-2 siRNA or/and TOP2A siRNA were constructed and used to transfect SK-Br-3 cells using Lipofectamine 2000. Western blot was used to evaluate the knockdown efficiency two days later. Flow cytometry and MTT assay were used to evaluate apoptosis and proliferation in cells exposed to radiation, respectively. The expression of apoptosis-and proliferation-related proteins, consisting of caspase-3, Bcl-2, and Ki-67, was determined. The colony-formation assay was used to measure radiosensitivity. Results The breast cancer SK-Br-3 cells with HER-2 or TOP2A knockdown had a higher apoptosis rate and a lower proliferation rate after exposure to radiation. The apoptotic marker, activated caspase-3, had elevated expression, while the anti-apoptotic protein Bcl-2 and the proliferation marker Ki-67 had reduced expression. Knockdown of both HER-2 and TOP2A further promoted apoptosis and inhibited proliferation and colony formation, indicating a synergistic effect of HER-2 and TOP2A. Conclusions Knockdown of HER-2 and TOP2A expression elevates the radiosensitivity and apoptosis rate, and reduces the proliferation rate and colony-formation rate in the breast cancer SK-Br-3 cells. Moreover, there is a synergistic effect between HER-2 and TOP2A. The mechanism is probably related to the proliferation-related protein Ki-67 and the apoptosis pathway involving caspase-3 and Bcl-2. Key words: HER-2 gene; TOP2A gene; SK-Br-3 cell line; Radiosensitivity