Transient overexpression of YB-1 protects MM.1s cells from apoptosis induced by treatment with doxorubicin. (A) Western blot analysis of endogenous YB-1 and HA-tagged YB-1 expression in MM.1s cells 48 hours after transient transfection with an expression plasmid for HA-tagged YB-1. Staining of β-actin served as a loading control. (B) MM1.s cells were either transfected with empty pcDNA6 vector as mock control or with a vector encoding HA-tagged YB-1. At 48 hours after transfection, the cells were treated with different concentrations of doxorubicin for another 48 hours. The viable cell fractions were measured by staining with annexin V–FITC/PI. The means and the standard deviations of 3 independent experiments are shown.