FIG. 7.
Smad6 and CtBP are recruited to the Id1 promoter, and they cooperate to repress the BMP-induced Id1 transcription. (A) Smad6 and CtBP coexist on the Id1 promoter. 293T cells were transfected with expression plasmids for Smad1 and Smad6 and treated with BMP2 for 4 h as indicated. (B) Smad6 cooperates with CtBP to inhibit BMP-dependent Id1 induction. P19 cells were transfected with the indicated expression plasmids. BMP2 treatment and the Id1-luciferase assay were done as in Fig. 1B. (C) Overexpression of CtBP has no effects on TGF-β-induced promoter activity. TGF-β-responsive HaCaT cells were transfected with SBE-luc or PAI1-luc, with or without CtBP, and treated with 5 ng of TGF-β per ml for 24 h. The y-axis value represents the induction by TGF-β, i.e., the ratio of Id1 promoter activity in the presence of TGF-β to that in the absence of TGF-β. (D) TSA inhibits the ability of Smad6 to repress BMP-induced Id1 induction. HeLa cells were transfected with the indicated Smad6 expression plasmids and treated with 10 ng of TSA per ml for 18 h. BMP2 treatment and the Id1-luciferase assay were done as in Fig. 1B. RLU, relative light units.