A transcriptional complex of Smad3 and β-catenin has been additionally suggested in the context of COL1A1 transcriptional regulation in chronic obstructive pulmonary disease as silencing of β catenin prevented a TGFβ-mediated increase in COL1A1 mRNA and COLα1 (I) levels in a human airway epithelial cell line [56]. Here, TGFB1 is linked to chronic obstructive pulmonary disease.