title: Prolonged tumor necrosis factor α primes fibroblast-like synoviocytes in a gene-specific manner by altering chromatin.
abstract: OBJECTIVE
  During the course of rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) are chronically exposed to an inflammatory milieu. The purpose of this study was to test the hypothesis that prolonged exposure of FLS to tumor necrosis factor α (TNFα) augments inflammatory responses to secondary stimuli (priming effect).
  
  
  METHODS
  FLS obtained from RA patients were exposed to TNFα for 3 days and were then stimulated with interferons (IFNs). Expression of IFN target genes was measured by real-time quantitative reverse transcription-polymerase chain reaction analysis and enzyme-linked immunosorbent assay. Total STAT-1 protein and IFN-mediated STAT-1 activation were evaluated by Western blotting. Total histone levels, histone acetylation, and NF-κB p65 and RNA polymerase II (Pol II) recruitment were measured at the CXCL10 promoter (encodes IFNγ-inducible 10-kd protein [IP-10]) by chromatin immunoprecipitation assays.
  
  
  RESULTS
  Prolonged pre-exposure of FLS to TNFα enhanced the magnitude and extended the kinetics of CXCL10/IP-10, CXCL9, and CXCL11 production upon subsequent IFN stimulation. This phenotype was retained over a period of days, even after the removal of TNFα. Prolonged TNFα exposure decreased histone levels, increased acetylation of the remaining histones, and heightened recruitment of NF-κB p65 and Pol II to the CXCL10 promoter. In parallel, an increase in intracellular STAT-1 led to amplification of IFN-induced STAT-1 activation.
  
  
  CONCLUSIONS
  Our study reveals a novel pathogenic function of TNFα, namely, prolonged and gene-specific priming of FLS for enhanced transcription of inflammatory chemokine genes due to the priming of chromatin, the sustained activation of NF-κB, and the amplification of STAT-1 activation downstream of IFNs. These data also suggest that FLS gain an "inflammatory memory" upon prolonged exposure to TNFα.
authors.affiliation: Hospital for Special Surgery, New York, New York.
authors.forename: Christopher
authors.initials: C
authors.lastname: Sohn
authors.forename: Angela
authors.initials: A
authors.lastname: Lee
authors.forename: Yu
authors.initials: Y
authors.lastname: Qiao
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Loupasakis
authors.forename: Lionel B
authors.initials: LB
authors.lastname: Ivashkiv
authors.forename: George D
authors.initials: GD
authors.lastname: Kalliolias
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D054357:Chemokine CXCL10 / Q000378:metabolism; D054371:Chemokine CXCL11 / Q000378:metabolism; D054370:Chemokine CXCL9 / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism*; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D006657:Histones / Q000378:metabolism*; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism; D013583:Synovial Membrane / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D054357:Chemokine CXCL10; D054371:Chemokine CXCL11; D054370:Chemokine CXCL9; D002843:Chromatin; D006657:Histones; D016328:NF-kappa B; D050794:STAT1 Transcription Factor; D014409:Tumor Necrosis Factor-alpha; D012319:RNA Polymerase II