Egr-1 inhibits the expression of extracellular matrix genes in chondrocytes by TNFalpha-induced MEK/ERK signalling

Arthritis Res Ther. 2009;11(1):R8. doi: 10.1186/ar2595. Epub 2009 Jan 14.


Introduction: TNFalpha is increased in the synovial fluid of patients with rheumatoid arthritis and osteoarthritis. TNFalpha activates mitogen-activated kinase kinase (MEK)/extracellular regulated kinase (ERK) in chondrocytes; however, the overall functional relevance of MEK/ERK to TNFalpha-regulated gene expression in chondrocytes is unknown.

Methods: Chondrocytes were treated with TNFalpha with or without the MEK1/2 inhibitor U0126 for 24 hours. Microarray analysis and real-time PCR analyses were used to identify genes regulated by TNFalpha in a MEK1/2-dependent fashion. Promoter/reporter, immunoblot, and electrophoretic mobility shift assays were used to identify transcription factors whose activity in response to TNFalpha was MEK1/2 dependent. Decoy oligodeoxynucleotides bearing consensus transcription factor binding sites were introduced into chondrocytes to determine the functionality of our results.

Results: Approximately 20% of the genes regulated by TNFalpha in chondrocytes were sensitive to U0126. Transcript regulation of the cartilage-selective matrix genes Col2a1, Agc1 and Hapln1, and of the matrix metalloproteinase genes Mmp-12 and Mmp-9, were U0126 sensitive--whereas regulation of the inflammatory gene macrophage Csf-1 was U0126 insensitive. TNFalpha-induced regulation of Sox9 and NFkappaB activity was also U0126 insensitive. Conversely, TNFalpha-increased early growth response 1 (Egr-1) DNA binding was U0126 sensitive. Transfection of chondrocytes with cognate Egr-1 oligodeoxynucleotides attenuated the ability of TNFalpha to suppress Col2a1, Agc1 or Hapln1 mRNA expression.

Conclusions: Our results suggest that MEK/ERK and Egr1 are required for TNFalpha-regulated catabolic and anabolic genes of the cartilage extracellular matrix, and hence may represent potential targets for drug intervention in osteoarthritis or rheumatoid arthritis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aggrecans / biosynthesis
  • Aggrecans / genetics
  • Animals
  • Blotting, Western
  • Cartilage / metabolism
  • Cells, Cultured
  • Chondrocytes / drug effects
  • Chondrocytes / metabolism*
  • Collagen Type II / biosynthesis
  • Collagen Type II / genetics
  • Early Growth Response Protein 1 / metabolism*
  • Electrophoretic Mobility Shift Assay
  • Enzyme Inhibitors / pharmacology
  • Extracellular Matrix / genetics*
  • Extracellular Matrix / metabolism
  • Extracellular Matrix Proteins / biosynthesis
  • Extracellular Matrix Proteins / genetics
  • Gene Expression / drug effects
  • Gene Expression / physiology
  • Gene Expression Regulation* / drug effects
  • Gene Expression Regulation* / genetics
  • MAP Kinase Signaling System / drug effects
  • MAP Kinase Signaling System / physiology*
  • Oligonucleotide Array Sequence Analysis
  • Proteoglycans / biosynthesis
  • Proteoglycans / genetics
  • Rats
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / physiology
  • Transfection
  • Tumor Necrosis Factor-alpha / metabolism*


  • Acan protein, rat
  • Aggrecans
  • COL2A1 protein, rat
  • Collagen Type II
  • Early Growth Response Protein 1
  • Egr1 protein, rat
  • Enzyme Inhibitors
  • Extracellular Matrix Proteins
  • Proteoglycans
  • Tumor Necrosis Factor-alpha
  • link protein