Ski represses BMP signaling in mammalian cells. (A) Ski
inhibits BMP-induced ALP in W-20-17 cells. W-20-17 cells plated in a
96-well cluster were transfected with increasing amounts of c-ski
as indicated. Twenty-four hours after transfection, the cells were
treated with 250 ng/ml BMP2 for 40 h. ALP was measured by an Elisa
reader and expressed as p-nitrophenol produced in
nmol/min per mg protein. Ski represses BMP-induced transcriptional
activation in W-20-17 (B) and Hep3B (C
and D) cells. W-20-17 and Hep3B cells were cotransfected
with 0.75 μg of 15xGCCG-Luc (B and C)
or Xvent2-Luc (D), 0.5 μg of
constitutive active type I receptors (Alk3* or Alk5*), 0.75 μg of
ski, and 0.15 μg of Smads. Luciferase activity
was measured 48 h later. Alk3*, (Q233D)Alk3; Alk5*, (T204D)Alk5;
S1, Smad1; S4, Smad4.