FIGURE 5.

Activin transactivates the human furin promoter in a Smad2- and Smad3-dependent pathway in LβT2 cells. A, cells were transiently transfected with pGL2 or pGL2-furin P1 construct. Transfected cells were then treated with varying doses of activin A (A) or activin B (B) for 24 h. C, LβT2 cells were transiently transfected with pGL2 or pGL2-furin P1 construct and siRNA specific for Smad2 or Smad3 or a nonspecific control siRNA overnight. Transfected cells were then treated with activin A (5 ng/ml) or activin B (20 ng/ml) (D) for 24 h. Luciferase activity was determined and expressed as fold induction relative to the control vector alone. The data are expressed as the means ± S.E. of three independent experiments performed in triplicate. Bars with different letters indicate statistical differences, p < 0.05. E, Western blot analysis was performed the show the specificity and degree of knockdown of phosphorylated and total Smad2 or Smad3 protein by siRNA. Actin was used as a loading control of cell lysates for these immunoblots.