title: DIP2 disco-interacting protein 2 homolog A (Drosophila) is a candidate receptor for follistatin-related protein/follistatin-like 1--analysis of their binding with TGF-β superfamily proteins.
abstract: Follistatin-related protein (FRP)/follistatin-like 1 (FSTL1) is a member of the follistatin protein family, all of which share a characteristic structure unit found in follistatin, called the FS domain. Developmental studies have suggested that FRP regulates organ tissue formation in embryos. Immunological studies showed that FRP modifies joint inflammation in arthritic disease, and modulates allograft tolerance. However, the principle physiological function of FRP is currently unknown. To address this issue, we cloned four FRP-associated proteins using a two-hybrid cloning method: disco-interacting protein 2 homolog A from Drosophila (DIP2A), CD14, glypican 1 and titin. Only DIP2A was expected to be a membrane receptor protein with intracellular regions. Over-expression of FLAG epitope-tagged DIP2A augmented the suppressive effect of FRP on FBJ murine osteosarcoma viral oncogene homolog (FOS) expression, and the Fab fragment of IgG to FLAG blocked this effect. Knockdown of Dip2a leaded to Fos gene up-regulation, and this was not affected by exogenous FRP. These in vitro experiments confirmed that DIP2A could be a cell-surface receptor protein and mediate a FOS down-regulation signal of FRP. Moreover, molecular interaction analyses using Biacore demonstrated that FRP bound to DIP2A and CD14, and also with proteins of the TGF-β superfamily, i.e. activin, TGF-β, bone morphogenetic protein 2/4 (BMP-2/4), their receptors and follistatin. FRP binding to DIP2A was blocked by CD14, follistatin, activin and BMP-2. FRP blocked the ligand-receptor binding of activin and BMP-2, but integrated itself with that of BMP-4. This multi-specific binding may reflect the broad physiological activity of FRP.
authors.affiliation: Division of Hematology and Immunology, Department of Internal Medicine, Kanazawa Medical University, Ishikawa, Japan. masatana@kanazawa-med.ac.jp
authors.forename: Masao
authors.initials: M
authors.lastname: Tanaka
authors.forename: Kosaku
authors.initials: K
authors.lastname: Murakami
authors.forename: Shoichi
authors.initials: S
authors.lastname: Ozaki
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Imura
authors.forename: Xiao-Peng
authors.initials: XP
authors.lastname: Tong
authors.forename: Takuo
authors.initials: T
authors.lastname: Watanabe
authors.forename: Toshioki
authors.initials: T
authors.lastname: Sawaki
authors.forename: Takafumi
authors.initials: T
authors.lastname: Kawanami
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kawabata
authors.forename: Takao
authors.initials: T
authors.lastname: Fujii
authors.forename: Takashi
authors.initials: T
authors.lastname: Usui
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Masaki
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Fukushima
authors.forename: Zhe-Xiong
authors.initials: ZX
authors.lastname: Jin
authors.forename: Hisanori
authors.initials: H
authors.lastname: Umehara
authors.forename: Tsuneyo
authors.initials: T
authors.lastname: Mimori
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D018076:DNA, Complementary; D038702:Follistatin-Related Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos; D011956:Receptors, Cell Surface; D055411:TGF-beta Superfamily Proteins / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D002352:Carrier Proteins; C481541:DIP2A protein, human; D018076:DNA, Complementary; D038702:Follistatin-Related Proteins; D009687:Nuclear Proteins; D016760:Proto-Oncogene Proteins c-fos; D011956:Receptors, Cell Surface; D055411:TGF-beta Superfamily Proteins