Forkhead Box Protein H1 (FOXH1)

FAST1 shares with the Xenopus protein the ability to bind to human SMAD2 and to activate an activin response element (ARE). The FAST1-dependent activation of the ARE was completely dependent on endogenous SMAD4 and stimulation by a TGF-beta-like ligand. The FAST1 protein bound to the DNA motif TGT(G/T)(T/G)ATT, an exact copy of which was present within the ARE. A single copy of this motif could activate a reporter in a TGF-beta-dependent fashion, but only when an adjacent SMAD-binding element was present in the construct. These data suggested that responses to TGF-beta family members may be mediated by a DNA-binding complex formed by FAST1, SMAD2, and SMAD4. The predicted protein contains 365 amino acids. The forkhead domain extends from amino acid residues 22 to 129.