Figure 4.

Repression of SBE2 × 2-tkluc reporter expression by Ski requires expression of Smad4. Shown is SBE2 × 2-tkluc activity in the TGF-β RII-deficient parental cell line HCT116 (A) and in HCT116 cells lacking Smad4 (B). Cells were transfected with the reporter plus or minus combinations of TGF-β RII, Smad4, and c-Ski as indicated. Cells were transferred to medium containing 0.2% FBS plus or minus 1 ng/ml TGF-β, 20 h after transfection. Luciferase activity was measured 22 h later as described in Materials and Methods. The results shown are averages of two independent experiments performed in duplicate.