FIGURE 4.

siRNA targeting Smad2 and -3 impairs Tgfβ2 induction of Arf. Shown are representative Western blots (A and B, upper panel) of lysates from wild type MEFs (A) or Arf^lacZ/lacZ MEFs (B) and β-galactosidase assay (β-gal, B, lower panel) in Arf^lacZ/lacZ MEFs treated with Tgfβ2 (T2) or vehicle (V) for 72 (A) or 60 (B) h after transfection with either siRNA control (Scram) or siRNA targeting Smad2 and/or Smad3 as indicated. Western blotting confirms partial knockdown of Smad2. (longer exposure confirming Smad3 knock-down is available as the supplemental figure). β-Galactosidase activity, normalized to expression in respective vehicle, is expressed as the average of three or more replicates from separate experiments. Knockdown of Smad2 or -3 or both significantly decreased β-galactosidase as compared with siRNA control. p < 0.007 for each case (lower panel, *).