title: Identification of PDGF-BB binding to thymosin β4 by chemical cross-linking.
abstract: BACKGROUND
  The purpose of our work was to identify unknown interaction partners of thymosin β4 (Tβ4). It was suggested that Tβ4 could be an antifibrotic drug for treatment of liver fibrogenesis, because Tβ4 prevents the platelet-derived growth factor-BB (PDGF-BB)-induced activation of hepatic stellate cells (HSCs). Very little information is available how Tβ4 counteracts the PDGF-BB-induced activation of HSCs. We propose the hypothesis that Tβ4 could bind directly to PDGF-BB and thereby reduce the concentration of free PDGF-BB available for binding to the PDGF-β receptor.
  
  
  METHODS
  To prove our suggestion of a direct interaction between Tβ4 and PDGF-BB, we carried out chemical as well as photochemical cross-linking experiments between the two pure proteins in vitro.
  
  
  RESULTS
  We identified an interaction between Tβ4 and PDGF-BB by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) cross-linking as well as through biotin label transfer using a bifunctional photoactivatable derivative of Tβ4. In an in vitro system, PDGF-BB was identified as the first extracellular partner interacting with Tβ4. This interaction could influence PDGF-BB binding to its receptor and abolish PDGF-BB-related effects.
  
  
  CONCLUSIONS
  Direct interaction of Tβ4 with extracellular factors should be considered as a potential mechanism to explain the pleiotropic effects of β-thymosins.
authors.affiliation: Friedrich-Alexander-University Erlangen-Nuremberg, Institute of Biochemistry , Fahrstr. 17, 91054 Erlangen , Germany +49 9131 85 24187 ; Ewald.Hannappel@fau.de.
authors.forename: Jana
authors.initials: J
authors.lastname: Knop
authors.forename: Christine
authors.initials: C
authors.lastname: App
authors.forename: Thomas
authors.initials: T
authors.lastname: Huff
authors.forename: Federica
authors.initials: F
authors.lastname: Iavarone
authors.forename: Massimo
authors.initials: M
authors.lastname: Castagnola
authors.forename: Ewald
authors.initials: E
authors.lastname: Hannappel
mesh_terms: D000595:Amino Acid Sequence; D000077214:Becaplermin; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003432:Cross-Linking Reagents / Q000737:chemistry; D006801:Humans; D008103:Liver Cirrhosis / Q000188:drug therapy; D008969:Molecular Sequence Data; D011485:Protein Binding; D020574:Proto-Oncogene Proteins c-sis / Q000737:chemistry*; D013947:Thymosin / Q000737:chemistry* / Q000494:pharmacology / Q000627:therapeutic use; D000099201:Thymosin beta(4)
chemical_list: D000077214:Becaplermin; D003432:Cross-Linking Reagents; D020574:Proto-Oncogene Proteins c-sis; D013947:Thymosin; D000099201:Thymosin beta(4)
keywords: biotin label transfer; cross-linking; platelet-derived growth factor; β-thymosin