FIG. 6.

Inhibition of TGF-β-induced and Smad3- or Smad2-dependent transcription by STRAP. (A) Smad3-dependent transcriptional activation of the p3TP promoter is not enhanced by STRAP. HepG2 cells were transiently transfected with p3TP-Lux, Smad3, and increasing amounts of STRAP as indicated. Left, cells were treated with or without TGF-β (100 pM) for 20 h prior to lysis and then analyzed for luciferase activity. Right, TGF-β signaling was initiated by expression of TβR-I(TD). Luciferase activity was normalized to β-galactosidase activity and expressed as the mean ± standard deviation of triplicate measurements from a representative experiment. These experiments were performed four times in triplicate with similar results. (B) STRAP does not cooperate with Smad2 in its transactivation function. This experiment was same as that in panel A except that Smad2 was expressed instead of Smad3.