title: SNAPIN: an endogenous Toll-like receptor ligand in rheumatoid arthritis.
abstract: OBJECTIVE
  The mechanisms contributing to the persistent activation of macrophages in rheumatoid arthritis (RA) are not fully understood. Some studies suggest that endogenous toll-like receptor (TLR) ligands promote the chronic inflammation observed in RA. The objective of this study was to identify endogenous TLR ligands expressed in RA synovial tissue (ST) based on their ability to bind the extracellular domains of TLR2 or TLR4.
  
  
  METHODS
  A yeast two-hybrid cDNA library was constructed from ST obtained by arthroscopy from patients with RA and screened using the extracellular domains of TLR2 and TLR4 as the bait. Interactions between TLRs and Snapin were demonstrated by reciprocal co-immunoprecipitation. ST was examined by histology, and single- and two-colour immunohistochemistry and quantitative reverse transcriptase PCR. Snapin (SNAP - associated protein) expression in macrophages was examined by Western Blot analysis and confocal microscopy. The ability of Snapin to activate through TLR2 was examined.
  
  
  RESULTS
  Employing a yeast two-hybrid system, Snapin was the most frequently identified molecule that interacted with TLR2. These results were confirmed by pull-down of in vitro-expressed Snapin together with TLR2. By immunohistochemistry and quantitative reverse transcriptase PCR, Snapin was highly expressed in RA ST, and it was readily detected in macrophages, where it co-localised in the late endosomes. ST Snapin expression correlated with inflammation and was not disease specific. Finally, Snapin was capable of activating through TLR2.
  
  
  CONCLUSIONS
  These observations identify Snapin as a novel endogenous TLR2 ligand in RA, and thus support a role for persistent TLR2 signalling in the pathogenesis of RA.
authors.affiliation: Department of Medicine, Division of Rheumatology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611-2909, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Shi
authors.forename: QiQuan
authors.initials: Q
authors.lastname: Huang
authors.forename: Paul Peter
authors.initials: PP
authors.lastname: Tak
authors.forename: Margriet J
authors.initials: MJ
authors.lastname: Vervoordeldonk
authors.forename: Chiang-Ching
authors.initials: CC
authors.lastname: Huang
authors.forename: Andrea
authors.initials: A
authors.lastname: Dorfleutner
authors.forename: Christian
authors.initials: C
authors.lastname: Stehlik
authors.forename: Richard M
authors.initials: RM
authors.lastname: Pope
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D015153:Blotting, Western; D011992:Endosomes / Q000378:metabolism / Q000473:pathology; D015870:Gene Expression; D015723:Gene Library; D006801:Humans; D008024:Ligands; D008262:Macrophage Activation; D008264:Macrophages / Q000378:metabolism; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000502:physiology; D013583:Synovial Membrane / Q000378:metabolism* / Q000473:pathology; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D008024:Ligands; C118519:SNAPIN protein, human; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D033921:Vesicular Transport Proteins