Fig. 4. Effects of L- and S-endoglin on Smad phosphorylation. Mock-, L-Endo- and S-Endo-transfected cells were serum starved for 24 hours before 30 minutes of TGFβ1 treatment. (A) Total protein extracts from control (C) or TGFβ1-treated (T) myoblasts were analyzed by western blot with anti-phospho-Smad1/3 or anti-phospho-Smad2 antibodies; anti-tubulin was used as a loading control. (B) Mock-, L-Endo- and S-Endo-transfected cells were treated with the ALK5 inhibitor SB431542 (SB, 5 µM) 1 hour before treatment with TGFβ1. Total protein extracts from control (C) or TGFβ1-treated (T) myoblasts were analyzed by western blot with anti-phospho-Smad1/3, anti-phospho-Smad2 and anti-tubulin antibodies. A representative blot from three independent experiments is shown.