title: Functional relationship between high mobility group A1 (HMGA1) protein and insulin-like growth factor-binding protein 3 (IGFBP-3) in human chondrocytes.
abstract: BACKGROUND
  Insulin-like growth factor I (IGF-I) regulates articular cartilage homeostasis. During osteoarthritis (OA), the anabolic responses of chondrocytes to IGF-I are likely to be prevented by the enhanced production of IGF-binding proteins (IGFBPs), especially IGFBP-3. The aim of this study is to evaluate whether the architectural transcription factor high mobility group A1 (HMGA1) influences IGFBP-3 overexpression in vitro, in cultured chondrocytic cell lines, and ex vivo, in human osteoarthritic cartilage compared to healthy human cartilage controls.
  
  
  METHODS
  Quantitative real-time reverse transcription-PCR (qRT-PCR) was performed to assess the relative transcript levels of HMGA1 and IGFBP-3 in vitro, in the human chondrocytic cell lines T/C-28a4 and C-28/I2. An electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP) and transient transfection assays were performed to investigate the HMGA1-IGFBP-3 gene interaction. Samples of articular cartilage were harvested from osteoarthritic patients and controls and analyzed by qRT-PCR for HMGA1 and IGFBP-3 mRNA levels.
  
  
  RESULTS
  A parallelism between HMGA1 protein levels and IGFBP-3 gene expression has been observed in T/C-28a4 and C-28/I2 cells. The interaction of HMGA1 with the IGFBP-3 gene promoter has been demonstrated by EMSA and ChIP. In transient transfections, IGFBP-3 promoter activity increased in cells overexpressing HMGA1 and decreased in cells pretreated with siRNA detected against HMGA1. IGFBP-3 mRNA expression was higher in cartilage from patients with OA, where the increased expression of IGFBP-3 closely paralleled the increased expression of HMGA1 mRNA.
  
  
  CONCLUSIONS
  Our observations indicate that increased HMGA1 expression in human chondrocytes is associated with increased expression of IGFBP-3. It is tempting to speculate that, through the regulation of IGFBP3 expression, HMGA1 may act as a pathogenetic factor for OA.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Gasparini
authors.forename: Marco
authors.initials: M
authors.lastname: De Gori
authors.forename: Francesco
authors.initials: F
authors.lastname: Paonessa
authors.forename: Eusebio
authors.initials: E
authors.lastname: Chiefari
authors.forename: Antonio
authors.initials: A
authors.lastname: Brunetti
authors.forename: Olimpio
authors.initials: O
authors.lastname: Galasso
mesh_terms: D000368:Aged; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology; D016022:Case-Control Studies; D002460:Cell Line; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005786:Gene Expression Regulation; D025741:HMGA1a Protein / Q000187:drug effects / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D025741:HMGA1a Protein