Smad regulates phosphorylation of ERK1/2 and mTOR activation in podocytes.
A, podocytes were transfected with a mixture of siSmad2 (50 nm) and siSmad3 (50 nm), and expression levels of p-ERK1/2, t-ERK1/2, p-p70S6K, t-p70S6K, t-Smad2, and t-Smad3 were checked by Western blot analysis after TGF-β1 treatment for 6 h. β-actin was used as a loading control. B and C, densitometry analyses of p-ERK1/2 and p-p70S6K from A, respectively (n = 3). D, cells were treated with 50 nm of siSmad4 and TGF-β1 for 6 h. Western blot analysis was performed for p-ERK1/2, t-ERK1/2, p-mTOR, t-mTOR, p-p70S6K, t-p70S6K, Smad4, and β-actin. E and F, densitometry analyses of p-ERK1/2 and p-p70S6K from D, respectively (n = 3). G, Western blot analysis showing that siRNA-mediated individual knockdown of Smad2 or Smad3 (100 nm each) did not recover TGF-β1-induced p-ERK1/2 and p-p70S6K phosphorylation (n = 3). H and I, densitometry analyses of p-ERK1/2 and p-p70S6K from G, respectively. All values are mean ± S.E. *, p < 0.05; **, p < 0.01; ***, p < 0.001; n.s., not significant.