SMAD6 and chronic obstructive pulmonary disease: No differences in the expression of TGF-β1, TGF-β2, TGF-β3, TGF-βRI, TGF-βRII, TGF-βRIII, TGFβ-I/BIGH3, TGIF2, SMAD2, SMAD3, SMAD6, SMAD7, CCN2, LTBP-1, or TRAP-1 were seen in the bronchial epithelia of subjects with COPD compared with nonsmoking control subjects.