title: Akt phosphorylation in human chondrocytes is regulated by p53R2 in response to mechanical stress.
abstract: OBJECTIVE
  The p53 tumor-suppressor protein p53R2 is activated in response to various stressors that act on cell signaling. When DNA is damaged, phosphorylation of p53 at its Ser 15 residue induces p53R2 production. The role of p53R2 in chondrocytes remains poorly understood. In this study, we evaluated in chondrocytes, p53R2 expression and its regulation in response to mechanical stress. Furthermore, we investigated the function of p53R2 in relation to mechanotransduction.
  
  
  METHODS
  Osteoarthritis (OA) cartilage obtained from total knee replacements and normal cartilage obtained from femoral neck fractures was used to measure p53R2 expression by using immunohistochemistry, western blotting, and real-time polymerase chain reaction (PCR). The OA chondrocytes were subjected to a high magnitude of cyclical tensile strain by using an FX-2000 Flexercell system. Next, sulfated glycosaminoglycan (sGAG) production was quantified in these cells. Protein expression of p53R2, and phosphorylation of Akt, p38MAPK, ERK1/2, and JNK was also detected using western blotting. Moreover, Akt phosphorylation was detected after transfecting the cells with p53R2-specific small interfering RNA (siRNA).
  
  
  RESULTS
  Expression of p53R2 was significantly increased in OA chondrocytes and in chondrocytes after applying 5% tensile strain to the cells. However, Akt phosphorylation was down-regulated in OA chondrocytes after the strain, and was up-regulated after transfection of p53R2. sGAG protein as well as collagen type II and aggrecan mRNA was increased following transfection of p53R2-specific siRNA after 5% tensile strain.
  
  
  CONCLUSIONS
  p53R2 could regulate matrix synthesis via Akt phosphorylation during chondrocyte mechanotransduction. Down-regulation of p53R2 may be a new therapeutic approach in OA therapy.
authors.affiliation: Department of Orthopedic Surgery, Kobe University Graduate School of Medicine, 7-5-2 Kusunokicho, Chuo-ku, Kobe, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kawakita
authors.forename: T
authors.initials: T
authors.lastname: Nishiyama
authors.forename: T
authors.initials: T
authors.lastname: Fujishiro
authors.forename: S
authors.initials: S
authors.lastname: Hayashi
authors.forename: N
authors.initials: N
authors.lastname: Kanzaki
authors.forename: S
authors.initials: S
authors.lastname: Hashimoto
authors.forename: K
authors.initials: K
authors.lastname: Takebe
authors.forename: K
authors.initials: K
authors.lastname: Iwasa
authors.forename: S
authors.initials: S
authors.lastname: Sakata
authors.forename: K
authors.initials: K
authors.lastname: Nishida
authors.forename: R
authors.initials: R
authors.lastname: Kuroda
authors.forename: M
authors.initials: M
authors.lastname: Kurosaka
mesh_terms: D015153:Blotting, Western; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D004260:DNA Repair; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D020370:Osteoarthritis, Knee / Q000235:genetics* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D012264:Ribonucleotide Reductases / Q000096:biosynthesis / Q000235:genetics*; D015398:Signal Transduction; D013314:Stress, Mechanical
chemical_list: D018797:Cell Cycle Proteins; D012333:RNA, Messenger; C405947:RRM2B protein, human; D012264:Ribonucleotide Reductases; D051057:Proto-Oncogene Proteins c-akt