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Efficient TGF-β Induction of the Smad7 Gene Requires Cooperation between AP-1, Sp1, and Smad Proteins on the Mouse Smad7 Promoter

2000; Elsevier BV; Volume: 275; Issue: 37 Linguagem: Inglês

10.1074/jbc.m002815200

1083-351X

Greger Brodin, Aive Åhgren, Peter ten Dijke, Carl‐Henrik Heldin, Rainer Heuchel,

Genetic factors in colorectal cancer

Sma- and Mad-related protein 7 (Smad7) is an antagonist of transforming growth factor-β (TGF-β) signaling, which has been shown to be induced by TGF-β itself and also by other stimuli. In an effort to understand the molecular mechanisms underlying the transcriptional regulation of the Smad7 gene by TGF-β, we cloned and functionally characterized a mouse genomic DNA fragment encompassing the mouse Smad7 proximal promoter. This region was found to contain a CpG island and to be devoid of a classical TATA box. Cloned upstream of a promoter-lacking luciferase reporter gene, this region conferred robust TGF-β-induced transcription. Point mutations in a palindromic Smad binding element, abolished TGF-β inducibility completely. Through the use of electrophoretic mobility shift assays, we showed the presence of Smad2, Smad3, and Smad4 in complexes binding to the Smad binding element. Interestingly, we also found that point mutation and/or deletion of binding sites for the transcription factors activator protein-1 and Sp1 led to an attenuation of the basal promoter activity, as well as of the TGF-β-mediated induction of Smad7. Taken together, our data imply that Smads, together with activator protein-1 and Sp1 transcription factors, are essential for efficient Smad7 promoter activity.