Fig. 4

Effects of hypoxia and TGF-β1 on the ALDH-positive cell proportion of A549 cell cultures. a Hypoxia, TGF-β1, or the combination of both all led to a higher ALDH-positive proportion. Induction by hypoxia was stronger than that by TGF-β1, and the combination was stronger than either factor alone. *P < 0.05, **P < 0.01, ****P < 0.001. b Hypoxia and TGF-β1 did not cause apoptosis of A549 cells at 24, 36, or 48 h. c Protein expression of the related signaling pathway proteins Notch1, P-Smad2, and P-Smad3 were elevated