Since DA-Raf does not directly affect Smad2/3 signaling but suppresses the TGF-β1-induced non-Smad Ras—ERK pathway, the information obtained in this study might provide ideas to treatment for pulmonary fibrosis without loss of the other important functions of TGF-β1 in maintaining homeostasis. Here, SMAD2 is linked to pulmonary fibrosis.