The novel E3 ubiquitin ligase Tiul1 associates with TGIF to target Smad2 for degradation

• Published in: The EMBO journal Vol. 23; no. 19; pp. 3780 - 3792
• Main Authors: Seo, Su Ryeon, Lallemand, François, Ferrand, Nathalie, Pessah, Marcia, L'Hoste, Sébastien, Camonis, Jacques, Atfi, Azeddine
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 29.09.2004; Blackwell Publishing Ltd; Nature Publishing Group
• Subjects: Activin Receptors, Type I - metabolism; Amino Acid Sequence; Animals; Cells, Cultured; Cloning, Molecular; Degradation; DNA, Complementary - genetics; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; Humans; Kidney - metabolism; Mice; Molecular Sequence Data; Placenta; Protein Serine-Threonine Kinases; Receptor, Transforming Growth Factor-beta Type I; Receptors, Transforming Growth Factor beta - metabolism; Repressor Proteins - genetics; Repressor Proteins - metabolism; Saccharomyces cerevisiae; Signal Transduction; Smad; Smad2 Protein; Smad7 Protein; TGF-β; TGIF; Tiul1; Trans-Activators - genetics; Trans-Activators - metabolism; Transcription, Genetic; Transforming Growth Factor beta - metabolism; Two-Hybrid System Techniques; Ubiquitin - metabolism; ubiquitin ligase; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism
• ISSN: 0261-4189; 1460-2075
• DOI: 10.1038/sj.emboj.7600398

Ubiquitin‐dependent degradation plays an important role in the negative regulation of TGF‐β signaling. Here, we identify Tiul1 (for TGIF interacting ubiquitin ligase 1), a novel E3 ubiquitin ligase that inhibits TGF‐β signaling by targeting both the activated receptor and Smad2 for degradation. Tiul1 associates constitutively with Smad7 and induces degradation of the activated type I receptor without affecting the expression levels of Smad7. Tiul1 can also interact with Smad2 and the nuclear corepressor TGIF upon activation of TGF‐β signaling. Like Smad7, the steady‐state levels of TGIF are not affected by Tiul1, but the interaction of Tiul1 with TGIF allows this ubiquitin ligase to target Smad2 for degradation. Consistent with this, overexpression of Tiul1 suppressed TGF‐β‐induced growth arrest and transcriptional responses. In addition, silencing of Tiul1 or TGIF genes by siRNA resulted in suppression of the TGF‐β‐dependent degradation of Smad2 and an enhancement of TGF‐β‐mediated gene expression. These results reveal a new role for TGIF as a component of a ubiquitin ligase complex that mediates the degradation of Smad2 in response to TGF‐β signaling.