title: Direct interaction between Smad3, APC10, CDH1 and HEF1 in proteasomal degradation of HEF1.
abstract: BACKGROUND
  The Transforming Growth Factor-beta (TGF-beta) regulates myriad cellular events by signaling through members of the Smad family signal transducers. As a key signal transducer of TGF-beta, Smad3 exhibits the property of receptor-activated transcriptional modulator and also the novel ability of regulating the proteasomal degradation of two Smad3 interacting proteins, SnoN and HEF1. It has been shown that Smad3 recruits two types of Ub E3 ligases, Smurf2 and the Anaphase Promoting Complex (APC), to mediate SnoN ubiquitination, thereby enhancing SnoN degradation. The molecular mechanisms underlying Smad3-regulated HEF1 degradation are not well understood. Furthermore, it is not clear how Smad3 recruits the APC complex.
  
  
  RESULTS
  We detected physical interaction between Smad3 and an APC component APC10, as well as the interaction between HEF1 and CDH1, which is the substrate-interacting component within APC. Detailed domain mapping studies revealed distinct subdomains within the MH2 domain of Smad3 for binding to APC10 and HEF1 and suggests the formation of a complex of these four proteins (Smad3, HEF1, APC10 and CDH1). In addition, the protein levels of HEF1 are subjected to the regulation of overexpressed APC10 and CDH1.
  
  
  CONCLUSIONS
  Our data suggests that Smad3 may recruit the APC complex via a direct interaction with the APC subunit APC10 to regulate the ubiquitination and degradation of its interactor HEF1, which is recognized as an ubiquitination substrate by the CDH1 subunit of the APC complex.
authors.affiliation: Benaroya Research Institute at Virginia Mason, 1201 Ninth Avenue, Seattle, WA 98101, USA. claire_nourry@hotmail.com
authors.forename: Claire
authors.initials: C
authors.lastname: Nourry
authors.forename: Lola
authors.initials: L
authors.lastname: Maksumova
authors.forename: Mona
authors.initials: M
authors.lastname: Pang
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Liu
authors.forename: Tongwen
authors.initials: T
authors.lastname: Wang
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing; D064173:Anaphase-Promoting Complex-Cyclosome; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D051900:Smad3 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C099942:NEDD9 protein, human; D010750:Phosphoproteins; D021122:Protein Subunits; D018125:Receptors, Transforming Growth Factor beta; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D046988:Proteasome Endopeptidase Complex