title: Negative regulation of transforming growth factor-beta (TGF-beta) signaling by WW domain-containing protein 1 (WWP1).
abstract: Smad7 negatively regulates transforming growth factor (TGF)-beta superfamily signaling by binding to activated type I receptors, thereby preventing the phosphorylation of receptor-regulated Smads (R-Smads), as well as by recruiting HECT-type E3 ubiquitin ligases to degrade type I receptors through a ubiquitin-dependent mechanism. To elucidate the regulatory mechanisms of TGF-beta signaling, we searched for novel members of proteins that interact with Smad7 using a yeast two-hybrid system. One of the proteins identified was the WW domain-containing protein 1 (WWP1) that is structurally related to Smad ubiquitin regulatory factors (Smurfs), E3 ubiquitin ligases for Smads and TGF-beta superfamily receptors. Using a TGF-beta-responsive reporter in mammalian cells, we found that WWP1 inhibited transcriptional activities induced by TGF-beta. Similar to Smurfs, WWP1 associated with Smad7 and induced its nuclear export, and enhanced binding of Smad7 to TGF-beta type I receptor to cause ubiquitination and degradation of the receptor. Consistent with these results, WWP1 inhibited phosphorylation of Smad2 induced by TGF-beta. WWP1 thus negatively regulates TGF-beta signaling in cooperation with Smad7. However, unlike Smurfs, WWP1 failed to ubiquitinate R-Smads and SnoN. Importantly, WWP1 and Smurfs were expressed in distinct patterns in human tissues and carcinoma cell lines, suggesting unique pathophysiological roles of WWP1 and Smurfs.
authors.affiliation: Department of Molecular Pathology, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Komuro
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
authors.forename: Masao
authors.initials: M
authors.lastname: Saitoh
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Takao
authors.initials: T
authors.lastname: Yamori
authors.forename: Kohei
authors.initials: K
authors.lastname: Miyazono
authors.forename: Keiji
authors.initials: K
authors.lastname: Miyazawa
mesh_terms: D021581:Active Transport, Cell Nucleus; D030201:Activin Receptors, Type I / Q000502:physiology; D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; C060615:SKIL protein, human; C497782:SMAD2 protein, human; C497806:SMAD7 protein, human; D051899:Smad2 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D025801:Ubiquitin; C471641:SMURF2 protein, human; C471642:WWP1 protein, human; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I