Fibronectin promotes epithelial mesenchymal transition (EMT) in A549 cells and enhances transforming growth factor (TGF)-β1-induced EMT in human bronchial epithelial cells (HBECs). Human epithelial cells, either alveolar type II A549s (a and b) or primary human bronchial cells (c and d) were plated at equal cell density on PDL or fibronectin-coated dishes and EMT assays performed as described in Materials and Methods. (a and c) Quantitative polymerase chain reaction analysis shows a significant upregulation of collagen I and matrix metalloprotease-2 in A549 cells (a) and HBECs (c) grown on fibronectin compared to PDL in A. In the presence of TGF-β1, fibronectin shows a further significant upregulation of these EMT markers when compared to cells grown on PDL in both cell types. Statistical significance was determined by one-way ANOVA followed by Tukey test; *P < 0.05, **P < 0.01, ***P < 0.001. (b and d) Western-blot analysis shows upregulation of mesenchymal marker proteins and downregulation of epithelial marker proteins in cells on fibronectin as compared to control cells on PDL for both A549 cells (b) and HBECs (d). An antibody against GAPDH was used as loading control.