To determine the effects of inhibition of YB-1 on proliferation rate, we performed Ki67 immunostaining in lung adenocarcinoma cells. The proliferation rate of the shYB-1 cells was decreased compared to the control cells, as indicated by the significant decrease in the percentage of cells positive for Ki67 (Figure (Figure1C1C and and1D).1D). These data indicated that the depletion of YB-1 repressed the proliferation of lung adenocarcinoma cells.