SMAD3 and lung cancer: As shown in Fig. 6a, c, e and Supplementary Fig. 3, knockdown of TGF-β2 reduced the expression levels of p-Smad2 and p-Smad3 as well as suppressed lung cancer cell growth and proliferation whereas exogenous TGF-β2 elicited the opposite effects, suggesting that TGF-β2 activates Smad signaling and plays an oncogenic role in lung cancer.