Regulation of β-catenin–p-Smad2 complex formation by extracellular matrices. (A) α3β1 engagement on Ln5 limits the formation of β-catenin–p-Smad2 complex formation. Lysates of TGF-β1–stimulated α3 wt cells from either Fn- or Ln5-coated plates were subject to β-catenin IP followed by p-Smad2 immunoblotting. The β-catenin–p-Smad2 complex formation is only seen with cells plated on Fn and not with Ln5. (B) Ln5 does not limit formation of β-catenin–p-Smad2 complexes in cells unable to engage Ln5 through α3β1 (G163A mutant cells). Lysates of TGF-β1–stimulated G163A mutant cells from either Fn- or Ln5-coated plates were subjected to β-catenin IP followed by p-Smad2 immunoblotting. The β-catenin–p-Smad2 complex formation is seen with cells plated on both Fn and Ln5. (C) α3β1 engagement on Ln5 suppresses TGF-β1–induced α-SMA up-regulation. Up-regulation of α-SMA is suppressed in α3 wt cells plated on Ln5 but not in G163A mutant cells on Ln5. The aforementioned experiments have been performed three times with similar results.