Fig. 4

Acquisition of stemness in vitro using soft agar colony formation and sphere formation assays. a Colony formation rates of all lung cell lines that were incubated under hypoxic conditions were higher than those of cell lines cultured under normoxic conditions. The increased colony formation under hypoxic conditions was reduced after CXCR4 siRNA treatment (scale bar = 500 μm). b Lung cell lines exposed to hypoxic stimuli exhibited increased sphere formation ability compared with that of the normoxic control (scale bar = 500 μm)