title: Modulation of transforming growth factor beta signalling pathway genes by transforming growth factor beta in human osteoarthritic chondrocytes: involvement of Sp1 in both early and late response cells to transforming growth factor beta.
abstract: BACKGROUND
  Transforming growth factor beta (TGFβ) plays a central role in morphogenesis, growth, and cell differentiation. This cytokine is particularly important in cartilage where it regulates cell proliferation and extracellular matrix synthesis. While the action of TGFβ on chondrocyte metabolism has been extensively catalogued, the modulation of specific genes that function as mediators of TGFβ signalling is poorly defined. In the current study, elements of the Smad component of the TGFβ intracellular signalling system and TGFβ receptors were characterised in human chondrocytes upon TGFβ1 treatment.
  
  
  METHODS
  Human articular chondrocytes were incubated with TGFβ1. Then, mRNA and protein levels of TGFβ receptors and Smads were analysed by RT-PCR and western blot analysis. The role of specific protein 1 (Sp1) was investigated by gain and loss of function (inhibitor, siRNA, expression vector).
  
  
  RESULTS
  We showed that TGFβ1 regulates mRNA levels of its own receptors, and of Smad3 and Smad7. It modulates TGFβ receptors post-transcriptionally by affecting their mRNA stability, but does not change the Smad-3 and Smad-7 mRNA half-life span, suggesting a potential transcriptional effect on these genes. Moreover, the transcriptional factor Sp1, which is downregulated by TGFβ1, is involved in the repression of both TGFβ receptors but not in the modulation of Smad3 and Smad7. Interestingly, Sp1 ectopic expression permitted also to maintain a similar expression pattern to early response to TGFβ at 24 hours of treatment. It restored the induction of Sox9 and COL2A1 and blocked the late response (repression of aggrecan, induction of COL1A1 and COL10A1).
  
  
  CONCLUSIONS
  These data help to better understand the negative feedback loop in the TGFβ signalling system, and enlighten an interesting role of Sp1 to regulate TGFβ response.
authors.affiliation: Laboratory of Extracellular Matrix and Pathology, Université Caen, IFR ICORE 146, Esplanade de la Paix, 14032 Caen cedex, France. catherine.bauge@unicaen.fr
authors.forename: Catherine
authors.initials: C
authors.lastname: Baugé
authors.forename: Olivier
authors.initials: O
authors.lastname: Cauvard
authors.forename: Sylvain
authors.initials: S
authors.lastname: Leclercq
authors.forename: Philippe
authors.initials: P
authors.lastname: Galéra
authors.forename: Karim
authors.initials: K
authors.lastname: Boumédiene
mesh_terms: D015153:Blotting, Western; D019902:Chondrocytes / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000235:genetics*; D006207:Half-Life; D006801:Humans; D012333:RNA, Messenger / Q000032:analysis; D060888:Real-Time Polymerase Chain Reaction; D018125:Receptors, Transforming Growth Factor beta / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics*; D051900:Smad3 Protein / Q000096:biosynthesis / Q000235:genetics; D051906:Smad7 Protein / Q000096:biosynthesis / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D051900:Smad3 Protein; D051906:Smad7 Protein; D016329:Sp1 Transcription Factor; C508960:TGFB1 protein, human; D053773:Transforming Growth Factor beta1