title: The four and a half LIM-only protein 2 (FHL2) activates transforming growth factor β (TGF-β) signaling by regulating ubiquitination of the E3 ligase Arkadia.
abstract: Arkadia is a RING-based ubiquitin ligase that positively regulates TGF-β signaling by targeting several pathway components for ubiquitination and degradation. However, little is known about the mechanisms controlling Arkadia activity. Here we show that the LIM-only protein FHL2 binds and synergistically cooperates with Arkadia to activate Smad3/Smad4-dependent transcription. Knockdown of FHL2 by RNA interference decreases Arkadia level and restricts the amplitude of Arkadia-induced TGF-β target gene responses. We found that Arkadia is ubiquitinated via K63- and K27-linked polyubiquitination. A single mutation at the RING domain that abolishes the E3 activity diminishes Arkadia ubiquitination, indicating that this modification partly involves autocatalytic process. Mutation of seven lysines at the C-terminal region of Arkadia severely impairs ubiquitination through the K27 but not the K63 linkage and slows down the turnover of Arkadia, suggesting that K27-linked polyubiquitination might promote proteolysis-dependent regulation of Arkadia. We show that FHL2 increases the half-life of Arkadia through inhibition of ubiquitin chain assembly on the protein, which provides a molecular basis for functional cooperation between Arkadia and FHL2 in enhancing TGF-β signaling. Our study uncovers a novel regulatory mechanism of Arkadia by ubiquitination and identifies FHL2 as important regulator of Arkadia ubiquitination and TGF-β signal transduction.
authors.affiliation: Key Laboratory of Molecular Virology and Immunology, Institut Pasteur of Shanghai, Chinese Academy of Sciences, Shanghai Institute for Biological Sciences, 225 South Chongqing Road, 200025, Shanghai, China.
authors.forename: Tian
authors.initials: T
authors.lastname: Xia
authors.forename: Laurence
authors.initials: L
authors.lastname: Lévy
authors.forename: Florence
authors.initials: F
authors.lastname: Levillayer
authors.forename: Baosen
authors.initials: B
authors.lastname: Jia
authors.forename: Gaiyun
authors.initials: G
authors.lastname: Li
authors.forename: Christine
authors.initials: C
authors.lastname: Neuveut
authors.forename: Marie-Annick
authors.initials: MA
authors.lastname: Buendia
authors.forename: Ke
authors.initials: K
authors.lastname: Lan
authors.forename: Yu
authors.initials: Y
authors.lastname: Wei
mesh_terms: D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006207:Half-Life; D006801:Humans; D060850:LIM-Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D008156:Luciferases; D051379:Mice; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics* / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism; D054875:Ubiquitination
chemical_list: C105987:FHL2 protein, human; C491382:Fhl2 protein, mouse; D060850:LIM-Homeodomain Proteins; D009124:Muscle Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D025801:Ubiquitin; D008156:Luciferases; C486067:RNF111 protein, human; D044767:Ubiquitin-Protein Ligases