Figure 1.

SMAD4 is required for efficient transcription of the COL7A1 promoter and its responsiveness to TGF-β. COS-1 cells were transfected with either the −524COL7A1/CAT or the −456COL7A1/CAT construct of the human COL7A1 promoter, in the absence (−) or in the presence (+) of TGF-β, without (−) or with (+) a Smad4 expression vector. TGF-β (10 ng/ml) was added to the medium 4 h later, and the incubation continued for 40 h. In this and the subsequent figures, cell extracts were assayed for CAT activity with [¹⁴C]chloramphenicol as a substrate by using identical amounts of β-galactosidase activity. The relative CAT activity (mean ± SD) of at least two experiments performed in duplicate is shown in the form of a bar graph.