Effect of UHRF1 on radiosensitivity of human breast cancer cells to X-rays and its mechanisms

Objective: To investigate the effect of UHRF1 on the radiosensitivity to x-ray in human breast cancer MDA-MB-231 cells and the underlying mechanisms. Methods: Cell survival was determined by colony formation assay. Cell cycle distribution was measured by flow cytometry. The apoptosis was evaluated by DNA fragmentation assay and Annexin V apoptosis detection kit. Protein expression was analyzed by Western blot, and chromosome aberration (centric rings and dicentrics) were observed by conventional chromosome analysis. Results: A significant decrease of radiosensitivity to X-rays was observed in MDA-MB-231 cells transfected with a full-length of human UHRF1 cDNA (MDA-MB-231/UHRF1) compared with the control cells (MDA-MB-231/parental and MDA-MB-231/Neo), and the D₀ value increased from 2.08 to 3. 17 Gy after UHRF1 transfection. In contrast, a decreased expression of UHRF1 by a specific UHRF1-siRNA significantly decreased cell survival from 41% to 17%. The UHRF1-mediated radioresistance was correlated with a G₂/M arrest, a decreased apoptosis rate, a down-regulation of the pro-apoptotic protein Bax and up-regulation of the DNA damage repair proteins Ku70 and Ku80. Furthermore, chromosomal aberrations (centric rings and dicentrics) by X-ray were less in MDA-MB-231/UHRF1 than those in MDA-MB-231/parental cells and MDA-MB-231/Neo control cells. Conclusion: UHRF1 may be a new target in the radiotherapy of breast cancer via affecting apoptosis and DNA damage repair. (authors)