(J) Validation of SMAD3 inhibitor (SIS3, SMAD3i). Effect of SMAD3i (10µM) on the level of phospho-SMAD3 Ser423/425 in response to TGFβ (2ng/mL, 1hr) (or solvent: HCl 4mM + Bovine serum albumin 1mg/mL) in SKMel28R cells (expressing a high endogenous level of SMAD3 mRNA). Serum starved cells (500,000 per well) were pretreated with SMAD3i 10µM (or control solvent) during 2hr before TGFβ addition. SMAD3 and HSC70 serve as loading control for western-blot experiments. 