Smad7 antagonizes transforming growth factor beta signaling in the nucleus by interfering with functional Smad-DNA complex formation.
Smad7 plays an essential role in the negative-feedback regulation of transforming growth factor beta (TGF-beta) signaling by inhibiting TGF-beta signaling at the receptor level. It can interfere with binding to type I receptors and thus activation of receptor-regulated Smads or recruit the E3 ubiquitin ligase Smurf to receptors and thus target them for degradation. Here, we report that Smad7 is predominantly localized in the nucleus of Hep3B cells. The targeted expression of Smad7 in the nucleus conferred superior inhibitory activity on TGF-beta signaling, as determined by reporter assay in mammalian cells and by its effect on zebrafish embryogenesis. Furthermore, Smad7 repressed Smad3/4-, Smad2/4-, and Smad1/4-enhanced reporter gene expression, indicating that Smad7 can function independently of type I receptors. An oligonucleotide precipitation assay revealed that Smad7 can specifically bind to the Smad-responsive element via its MH2 domain, and DNA-binding activity was further confirmed in vivo with the promoter of PAI-1, a TGF-beta target gene, by chromatin immunoprecipitation. Finally, we provide evidence that Smad7 disrupts the formation of the TGF-beta-induced functional Smad-DNA complex. Our findings suggest that Smad7 inhibits TGF-beta signaling in the nucleus by a novel mechanism.
Zhang
Suping
S
Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China.
Fei
Teng
T
Zhang
Lixia
L
Zhang
Ran
R
Chen
Feng
F
Ning
Yuanheng
Y
Han
Yuna
Y
Feng
Xin-Hua
XH
Meng
Anming
A
Chen
Ye-Guang
YG
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins; D017353:Gene Deletion; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology; D008156:Luciferases / Q000032:analysis / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D015398:Signal Transduction; D051906:Smad7 Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000037:antagonists & inhibitors*
D004268:DNA-Binding Proteins; C497806:SMAD7 protein, human; D051906:Smad7 Protein; D053773:Transforming Growth Factor beta1; D004247:DNA; D008156:Luciferases