TGF-β1 responses correlate with α3β1 association with E-cadherin but not Ln5. (A) TGF-β1 responses in primary AECs from wt (left) or α3 conditional null mice (right). wt AECs were cultured on Fn to induce endogenous TGF-β1 activation and were incubated with TGF-β1 receptor kinase inhibitor SB431542 (SB) or DMSO (ctl) for 4 d. α3 conditional AECs were initially cultured on Matrigel/collagen matrices and treated with either adeno-Cre (AdCre) virus or 20 plaque-forming U/cell adeno-GFP control virus. After 96 h, cells were replated on Fn for 4 d. Cell extracts were blotted for various proteins. SB431542 blocks Smad2 phosphorylation and the α-SMA response in wt AECs. Loss of α3 does not affect Smad2 phosphorylation but blocks up-regulation of α-SMA and collagen I. (B) Phase photographs of α3^−/−, α3 wt, H245A, and G163A mutant cells at baseline and after 48-h stimulation with TGF-β1. Videos showing phenotypic change and cell motility of α3 wt and H245A cells after TGF-β1 stimulation are provided (Videos 1 and 2, available). Bar, 50 µm. (C) E-cadherin distribution in α3 wt and H245A mutant cells without and with 48-h TGF-β1 stimulation. Bar, 1 µm. (D) E-cadherin coimmunoprecipitates with wt α3– and G163A-expressing cells but does not coimmunoprecipitate with the H245A mutant. (E) E-cadherin–β-catenin association is not affected by α3β1. The aforementioned experiments have been performed at least three times with similar results.