title: Acute serum amyloid A regulates cytoskeletal rearrangement, cell matrix interactions and promotes cell migration in rheumatoid arthritis.
abstract: OBJECTIVE
  Serum amyloid A (A-SAA) is an acute-phase protein with cytokine-like properties implicated in the pathogenesis of rheumatoid arthritis (RA), atherosclerosis, diabetes and Alzheimer's disease. This study characterises the mechanism of A-SAA-induced cytoskeletal rearrangement and migration in synovial fibroblasts and microvascular endothelial cells (human dermal endothelial cells; HDEC).
  
  
  METHODS
  Immunohistology and immunofluorescence were used to examine αvβ3 and β1-integrins, filamentous actin (F-actin) and focal adhesion expression in rheumatoid arthritis synovial tissue (RAST) and rheumatoid arthritis synovial fibroblast cells (RASFC). A-SAA-induced αvβ3 and β1-integrin binding was measured by adhesion assay. Cytoskeletal rearrangement and ρ-GTPase activation following A-SAA stimulation was examined using dual immunofluorescent staining for F-actin/vinculin staining, pull down assays and immunoblotting for Cdc42 and RhoA. Cell growth, invasion/migration, angiogenesis and actin formation were examined in the presence or absence of specific Rac1 and Cdc42 inhibitors (NSC23766 and 187-1).
  
  
  RESULTS
  αvβ3, β1-integrin and F-actin predominantly localised to vascular endothelium and lining layer cells in RAST, compared with osteoarthritis and normal control synovial tissue. A-SAA significantly increased αvβ3 and β1 binding in RASFC. A-SAA induced cytoskeletal disassembly, loss of focal adhesions and filopodia formation in RASFC and HDEC. A-SAA significantly induced Cdc42 activation but failed to promote RhoA activation in HDEC and synovial fibroblast cells. Blockade of Rac-1 and Cdc42 inhibited A-SAA-induced cell growth, invasion/migration, actin cytoskeletal rearrangement and angiogenesis.
  
  
  CONCLUSIONS
  These data show a novel mechanism for A-SAA-induced cell migrational events in RA mediated via cytoskeletal signalling pathways.
authors.affiliation: Department of Rheumatology, Dublin Academic Medical Centre, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Ireland.
authors.forename: M
authors.initials: M
authors.lastname: Connolly
authors.forename: D J
authors.initials: DJ
authors.lastname: Veale
authors.forename: U
authors.initials: U
authors.lastname: Fearon
mesh_terms: D000199:Actins / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000378:metabolism / Q000473:pathology*; D016022:Case-Control Studies; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000502:physiology; D004730:Endothelium, Vascular / Q000378:metabolism / Q000473:pathology; D005347:Fibroblasts / Q000473:pathology / Q000502:physiology; D020558:GTP Phosphohydrolases / Q000096:biosynthesis; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D016023:Integrins / Q000378:metabolism; D000685:Serum Amyloid A Protein / Q000494:pharmacology / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000199:Actins; D016023:Integrins; D000685:Serum Amyloid A Protein; D020558:GTP Phosphohydrolases