Overexpression of IRF5 in MCF-7 and MDA-MB-231 cells sensitizes them to DNA damage-induced growth inhibition. A. Endogenous IRF expression was analyzed by Western blot in transformed mammary epithelial cell lines. Levels of β-actin are shown as loading controls. B. Western blot analysis of stable cell lines generated to overexpress retroviral pBIRF5. C. Cell survival was measured in MCF-7 and MDA-MB-231 pBabe cell lines by colony formation assay before and after treatment. Cells were treated with 0.1 or 1 μM Doxorubicin (Dox) or 2, 5 and 10 Gy γ-IR. The number of colonies is plotted on the y-axis as percent of control; 100% represents the number of colonies in empty pBabe control lines. Data are expressed as mean ± SD of three independent experiments performed in duplicate. Statistical significance was determined by comparing the difference between colonies in pBabe versus pBIRF5 cell lines after each treatment; * denotes P < 0.05, ** P < 0.001.