p300/CBP function in HBZ-mediated activation of Dkk1 expression. (A) Levels of Dkk1 in culture media following siRNA-mediated knockdown of p300/CBP. Acid-precipitated proteins from culture media (upper panel) and 25 μg of cellular lysates (lower panels) from the indicated cell lines were subjected to Western blot analysis using antibodies directed against Dkk1, p300, CBP and β actin, as indicated. (B) Levels of Dkk1 in culture media of cells co-expressing HBZ and p300 polypeptide fragments. A schematic representation of p300 domains and the fragments transfected into HBZ-expressing cells. Domains are denoted according to reference . Acid-precipitated proteins from culture media (upper panel) and 20 μg of cellular lysates (middle panel) were subjected to Western blot analysis using an antibody directed against Dkk1 or the Flag epitope on transfected p300 fragments, as indicated. Acid-precipitated proteins from culture media were also resolved by SDS-PAGE and stained with Coomassie blue (lower panel).