TGF-β isoforms decrease PTEN protein content through differential pathways. A-C) Before treatment with 10 ng/mL recombinant TGF-β isoforms or with vehicle for 24 h, KLE cells were pre-treated with Smad4 siRNA or control (scrambled) siRNA for 24 h (A), 10 μM MEK1/ERK pathway inhibitor PD98059 or vehicle for 1 h (B) or 50 μM PI3-K inhibitor LY294002 or vehicle for 1 h (C). Protein lysates used were identical to the ones used in figure 3. Levels of PTEN protein were determined using western blot. Levels of Smad4 protein, phosphorylated ERK (P-ERK) or phosphorylated Akt (P-Akt) were determined to monitor the efficiency of Smad4 RNAi, MEK/ERK pathway inhibition or PI3-K inhibition, respectively. In all experiments, β-actin was used as a loading control. Graphs represent mean ± SE of three independent experiments. * p < 0.05.