Nagilactone E suppresses TGF-β1-induced epithelial-mesenchymal transition, migration and invasion in non-small cell lung cancer cells

Background: Non-small cell lung cancer (NSCLC) is one of the leading causes of cancer-related death around the world. Epithelial-mesenchymal transition (EMT) has been documented to increase motility and invasiveness of cancer cells, which promotes cancer metastasis. Purpose: This study aims to investigate the inhibitory effects and mechanisms of the dinorditerpenoids and norditerpenoids isolated from the seeds of Podocarpus nagi against transforming growth factor (TGF)-beta 1-induced EMT. Methods: A series of dinorditerpenoids and norditerpenoids were isolated from the seeds of P. nagi. Western blot and quantitative real-time PCR assays were performed to determine the expression levels of relative proteins and mRNA, along with immunofluorescence, Smad-binding element (SBE)-luciferase and chromatin immunoprecipitation (ChIP) assays for the mechanism study. Transwell assays were conducted to determine the effect of the compounds on cell migration and invasion. Results: Nagilactone E (NLE) showed the superior inhibitory effect against TGF-beta 1-induced EMT. NLE treatment dramatically inhibited TGF-beta 1-induced expression of EMT markers in A549 cells. Mechanism study indicated that NLE markedly suppressed TGF-beta 1-induced Smad2 and Smad3 activation and nuclear translocation. SBE-luciferase and ChIP assays showed that NLE inhibited the combining of Smad3 to SBE in the promoters of the cell signaling factors. NLE co-treatment attenuated TGF-beta 1-induced up-regulation of the protein and mRNA levels of TGF-beta receptor T beta RI. Furthermore, NLE inhibited TGF-beta 1-stimulated cell migration and invasion, as well as up-regulation of the key signaling proteins related with migration and invasion. Conclusion: NLE inhibited TGF-beta/Smad signaling pathway, thereafter suppressed TGF-beta 1-induced EMT, migration and invasion in NSCLC A549 cells.