To investigate whether YB-1 expression correlates with lung adenocarcinoma progression, the stable YB-1-silenced A549 cells (shYB1-1, shYB1-2) and H1299 cells (shYB1-3, shYB1-4) were generated using two shRNA expressing plasmids (Supplementary Figure 1). The results showed that depletion of YB-1 reduced cell proliferation in both clones (Figure (Figure1A1A and and1B).1B). 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