Smad7 Binds to Smurf2 to Form an E3 Ubiquitin Ligase that Targets the TGFβ Receptor for Degradation

• Published in: Molecular cell Vol. 6; no. 6; pp. 1365 - 1375
• Main Authors: Kavsak, Peter, Rasmussen, Richele K., Causing, Carrie G., Bonni, Shirin, Zhu, Haitao, Thomsen, Gerald H., Wrana, Jeffrey L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.2000
• Subjects: Animals; Cell Line; Cysteine Endopeptidases - metabolism; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Down-Regulation - drug effects; Gene Expression Regulation - drug effects; Immunoblotting; Interferon-gamma - pharmacology; Ligases - chemistry; Ligases - metabolism; Lysosomes - metabolism; Macromolecular Substances; Models, Biological; Molecular Sequence Data; Multienzyme Complexes - metabolism; Mutation; Nuclear Proteins - metabolism; Proteasome Endopeptidase Complex; Protein Binding - drug effects; Protein Structure, Tertiary; Protein Transport; Receptors, Transforming Growth Factor beta - metabolism; Recombinant Fusion Proteins; Smad7 Protein; Trans-Activators - genetics; Trans-Activators - metabolism; Transfection; Ubiquitin-Protein Ligases
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/S1097-2765(00)00134-9

Ubiquitin-mediated proteolysis regulates the activity of diverse receptor systems. Here, we identify Smurf2, a C2-WW-HECT domain ubiquitin ligase and show that Smurf2 associates constitutively with Smad7. Smurf2 is nuclear, but binding to Smad7 induces export and recruitment to the activated TGFß receptor, where it causes degradation of receptors and Smad7 via proteasomal and lysosomal pathways. IFNγ, which stimulates expression of Smad7, induces Smad7–Smurf2 complex formation and increases TGFß receptor turnover, which is stabilized by blocking Smad7 or Smurf2 expression. Furthermore, Smad7 mutants that interfere with recruitment of Smurf2 to the receptors are compromised in their inhibitory activity. These studies thus define Smad7 as an adaptor in an E3 ubiquitin–ligase complex that targets the TGFß receptor for degradation.