title: Annexin I surface binding sites and their regulation on human fibroblast-like synoviocytes.
abstract: OBJECTIVE
  Annexin I is a glucocorticoid-inducible protein whose expression in rheumatoid synovium and inhibitory actions in animal models of arthritis suggests its involvement in human arthritis. The present study explored the potential for annexin I to mediate its antiinflammatory actions via specific cell-surface binding sites on human fibroblast-like synoviocytes (FLS).
  
  
  METHODS
  Annexin I binding sites on cultured FLS from patients with osteoarthritis (OA) and rheumatoid arthritis (RA) were determined by ligand-binding flow cytometry. Phospholipase A2 (PLA2) activity was determined by arachidonic acid release.
  
  
  RESULTS
  FLS exhibited saturable, concentration-dependent cell-surface annexin I binding, with >99% of the OA FLS exhibiting binding at an annexin I concentration of 10 microM. Annexin I binding of RA FLS was significantly lower than that of OA FLS. FLS annexin I binding sites were not affected by elastase or a specific elastase inhibitor, and elastase release did not differ between RA and OA cells. In contrast, collagenase significantly increased annexin I binding sites on OA FLS and approached a significant effect on RA FLS. Tumor necrosis factor alpha increased annexin I binding sites on OA and RA FLS. Similarly, interleukin-1beta significantly increased annexin I binding on OA FLS; but the increased binding on RA FLS was not significant. Dexamethasone exerted no significant effect on OA or RA FLS annexin I binding sites. Treatment of RA FLS with an annexin I N-terminal peptide significantly inhibited RA FLS PLA2 activity.
  
  
  CONCLUSIONS
  This is the first description of the expression, regulation, and function of cell surface annexin I binding sites on FLS. Reduced annexin I binding sites in RA FLS may impair the sensitivity of certain proinflammatory events to glucocorticoids.
authors.affiliation: Monash Medical Centre, Melbourne, Australia.
authors.forename: A V
authors.initials: AV
authors.lastname: Sampey
authors.forename: P
authors.initials: P
authors.lastname: Hutchinson
authors.forename: E F
authors.initials: EF
authors.lastname: Morand
mesh_terms: D017305:Annexin A1 / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000473:pathology; D001665:Binding Sites / Q000187:drug effects; D017364:Collagenases / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology*; D006801:Humans; D010003:Osteoarthritis / Q000473:pathology; D010196:Pancreatic Elastase / Q000378:metabolism; D013583:Synovial Membrane / Q000166:cytology*
chemical_list: D017305:Annexin A1; D010196:Pancreatic Elastase; D017364:Collagenases