title: Nuclear accumulation of prohibitin 1 in osteoarthritic chondrocytes down-regulates PITX1 expression.
abstract: OBJECTIVE
  To decipher the molecular mechanisms down-regulating PITX1 expression in primary osteoarthritis (OA).
  
  
  METHODS
  The functional activity of different PITX1 promoter regions was assessed by luciferase reporter assay. Tandem mass spectrometry coupled to protein sequencing was performed using nuclear extracts prepared from OA chondrocytes, in order to identify proteins bound to DNA regulatory elements. Expression analyses of selected candidate proteins were performed by real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry methods, using cartilage sections and articular chondrocytes from non-OA control subjects and patients with OA. Gain-of-function and loss-of-function experiments were performed in normal and OA chondrocytes, respectively, to study their effects on PITX1 regulation. The results were validated by real-time RT-PCR and immunohistochemistry in STR/Ort mice, a well-known animal model of OA.
  
  
  RESULTS
  PITX1 promoter analyses led to the identification of prohibitin 1 (PHB1) bound to a distal E2F1 transcription factor site. Aberrant accumulation of PHB1 was detected in the nuclei of OA articular chondrocytes, and overexpression of PHB1 in control cells was sufficient to inhibit endogenous PITX1 expression at the messenger RNA and protein levels. Conversely, knockdown of PHB1 in OA articular chondrocytes resulted in up-regulation of PITX1. Studies of early molecular changes in STR/Ort mice revealed a similar nuclear accumulation of PHB1, which correlated with Pitx1 repression.
  
  
  CONCLUSIONS
  Collectively, these data define an unrecognized role for PHB1 in repressing PITX1 expression in OA chondrocytes.
authors: Sainte-Justine University Hospital Research Center and University of Montreal, Montreal, Quebec, Canada.
authors: Cynthia
authors: C
authors: Picard
authors: Martin
authors: M
authors: Pellicelli
authors: Maryam
authors: M
authors: Taheri
authors: Jean-Francois
authors: JF
authors: Lavoie
authors: Roxanne
authors: R
authors: Doucet
authors: DaShen
authors: D
authors: Wang
authors: Lauriane
authors: L
authors: Bernard
authors: Saadallah
authors: S
authors: Bouhanik
authors: Patrick
authors: P
authors: Lavigne
authors: Alain
authors: A
authors: Moreau
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D016022:Case-Control Studies; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D004195:Disease Models, Animal; D015536:Down-Regulation; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism*; D020370:Osteoarthritis, Knee / Q000235:genetics / Q000378:metabolism; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000091402:Prohibitins; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055815:Young Adult
chemical_list: D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C000717328:PHB protein, human; D051761:Paired Box Transcription Factors; D000091402:Prohibitins; D012097:Repressor Proteins; C101485:homeobox protein PITX1