title: Indirubin derivatives modulate TGFβ/BMP signaling at different levels and trigger ubiquitin-mediated depletion of nonactivated R-Smads.
abstract: Regulatory Smads (R-Smads), Smad1/5/8 and Smad2/3, are the central mediators of TGFβ and BMP signaling pathways. Here, we screened indirubin derivatives, known kinase inhibitors, and observed strong interference with BMP signaling. We found that indirubin derivative E738 inhibited both TGFβ and BMP pathways through ubiquitin-proteasome-mediated depletion of total R-Smad pools, although phospho-R-Smad levels were initially stabilized by GSK3β and cyclin-dependent kinase inhibition. E738 also enhanced p38 and JNK phosphorylation, involved in Smad-independent TGFβ/BMP signaling. Additionally, using a small siRNA screen, we showed that depletion of ubiquitin proteases USP9x and USP34 significantly reduced total R-Smad levels, mimicking E738 treatment. In fact, both USP9x and USP34 levels were significantly reduced in E738-treated cells. Our findings not only describe the complex activity profile of the indirubin derivative E738, but also reveal a mechanism for controlling TGFβ/BMP signaling, the control of R-Smad protein levels through deubiquitination.
authors.affiliation: Institute of Pharmacy and Molecular Biotechnology, Heidelberg University, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany.
authors.forename: Xinlai
authors.initials: X
authors.lastname: Cheng
authors.forename: Hamed
authors.initials: H
authors.lastname: Alborzinia
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Merz
authors.forename: Herbert
authors.initials: H
authors.lastname: Steinbeisser
authors.forename: Ralf
authors.initials: R
authors.lastname: Mrowka
authors.forename: Catharina
authors.initials: C
authors.lastname: Scholl
authors.forename: Igor
authors.initials: I
authors.lastname: Kitanovic
authors.forename: Gerhard
authors.initials: G
authors.lastname: Eisenbrand
authors.forename: Stefan
authors.initials: S
authors.lastname: Wölfl
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D005347:Fibroblasts / Q000187:drug effects; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D006367:HeLa Cells / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000737:chemistry / Q000494:pharmacology; D019169:Jurkat Cells / Q000187:drug effects; D020935:MAP Kinase Signaling System / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000187:drug effects; D051896:Smad Proteins, Receptor-Regulated / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D043222:Ubiquitin Thiolesterase / Q000378:metabolism; D014981:Xenopus / Q000196:embryology / Q000235:genetics
chemical_list: D019485:Bone Morphogenetic Proteins; C580875:E738 compound; D007211:Indoles; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D051896:Smad Proteins, Receptor-Regulated; D016212:Transforming Growth Factor beta; C506234:USP9X protein, human; D025801:Ubiquitin; D043222:Ubiquitin Thiolesterase; C027185:indirubin