title: Blocking of interferon regulatory factor 1 reduces tumor necrosis factor α-induced interleukin-18 bioactivity in rheumatoid arthritis synovial fibroblasts by induction of interleukin-18 binding protein a: role of the nuclear interferon regulatory factor 1-NF-κB-c-jun complex.
abstract: OBJECTIVE
  To examine the role of interferon regulatory factor 1 (IRF-1) in tumor necrosis factor α (TNFα)-induced interleukin-18 binding protein a (IL-18BPa) expression in rheumatoid arthritis synovial fibroblasts (RASFs).
  
  
  METHODS
  TNFα-induced IRF-1 expression was assessed by real-time quantitative polymerase chain reaction and Western blotting. The effect of TNFα on IRF-1 was assessed using nuclear and cytoplasmic extracts, Western blots, and immunofluorescence. Chemical inhibitors of NF-κB or MAP kinases were used to analyze the signaling pathways of TNFα-induced IRF-1 expression and IRF-1 nuclear translocation. Control and IRF-1 small interfering RNA (siRNA) were used to analyze the effect of IRF-1 down-regulation on TNFα-induced IL-18BP expression. IL-18BPa expression was assessed by enzyme-linked immunosorbent assay, and IL-18 was assessed at the transcription and bioactivity levels using KG-1 cells.
  
  
  RESULTS
  TNFα induced RASF IRF-1 expression at the messenger RNA and protein levels, with a maximal effect at 2 hours (P < 0.05; n ≥ 3). Furthermore, TNFα induced nuclear translocation of IRF-1, with maximal translocation at 2 hours (∼6 fold-induction) (P < 0.05; n = 4). Blocking of the NF-κB or JNK-2 pathways reduced TNFα-induced IRF-1 nuclear translocation by 35% and 50%, respectively (P < 0.05; n ≥ 4). Using siRNA to knock down IRF-1, we observed reduced IL-18BPa expression. Additionally, IL-18 bioactivity was higher when siRNA was used to knock down IRF-1 expression.
  
  
  CONCLUSIONS
  These results show that IRF-1 is a key regulator of IL-18BPa expression and IL-18 bioactivity in RASFs. Regulation of IRF-1 will be a new therapeutic target in RA.
authors.affiliation: University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Hubert
authors.initials: H
authors.lastname: Marotte
authors.forename: Pei-Suen
authors.initials: PS
authors.lastname: Tsou
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Rabquer
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Pinney
authors.forename: Tatiana
authors.initials: T
authors.lastname: Fedorova
authors.forename: Nalin
authors.initials: N
authors.lastname: Lalwani
authors.forename: Alisa E
authors.initials: AE
authors.lastname: Koch
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D050856:Interferon Regulatory Factor-1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020382:Interleukin-18 / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013583:Synovial Membrane / Q000378:metabolism* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D050856:Interferon Regulatory Factor-1; D020382:Interleukin-18; D016328:NF-kappa B; D016755:Proto-Oncogene Proteins c-jun; D014409:Tumor Necrosis Factor-alpha; C118370:interleukin-18 binding protein