Knock-down of miR-221 and miR-222 in the radiosensitization of breast cancer cells

Objective To investigate the radiosensitizing effect of knock-down of miR-221 and miR-222 on MCF-7 human breast cancer cells and explore the possible mechanism. Methods Antisense oligo-nucleotides of miR-221 and miR-222( AS-miR-221 and AS-miR-222), mediated by lipofectamine, were transfected to MCF-7 cells to knock down miR-221 and miR-222, Northern blotting was conducted to detect the expression of miR-221 and miR-222 in transfected cells. The cell apoptosis was detected by flow cytome-try and Caspase-3 and Caspase-7 activity assay. Clonogenic assay was used to measure the sensitizing en-hancement ratio. Target genes of miR-221 and miR-222 relevant to radio-sensitivity were searched using bioinformatic analysis . The targeted protein expression was determined by Western blot analysis . Results The expression of miR-221 and miR-222 in the AS-miR-221/222 cells determined by Northern blotting was significantly reduced. Compared with the control group, the cell apoptosis and mitotic cell death after the ra-diation were significantly higher in AS-miR-221/222 cells. The sensitizing enhancement ratio was 1.87. Based on bioinformatic analysis, PTEN was a target gene of miR-221 and miR-222 which could enhance the radiosensitivity of MCF-7 cells. In AS-miR-221/222 cells, the expression of PTEN was up-regulated while pAkt down-regulated. Conclusions AS-miR-221 and AS-miR-222 may enhance the radiosensitivity of MCF-7 breast cancer cells by up-regulating the expression of PTEN. Key words: Cell lines; breast neoplasms; MicroRNA ; Radiosensitivity; PTEN protein