SAG and breast cancer: In this study, we tested our working hypothesis that inactivation of SCF E3 ubiquitin ligases by MLN4924, a small molecule inhibitor of NAE [15], would sensitize breast cancer cells to radiation, given the fact that some of SCF E3 components, such as β-TrCP and SAG, were overexpressed in breast cancer cells which was associated with chemo- or radio-resistance [24], [43].