Expression of the MAPK kinases MKK-4 and MKK-7 in rheumatoid arthritis and their role as key regulators of JNK

Arthritis Rheum. 2003 Sep;48(9):2450-60. doi: 10.1002/art.11228.


Objective: The mitogen-activated protein (MAP) kinase JNK is a key regulator of interleukin-1 (IL-1)-induced collagenase gene expression and joint destruction in arthritis. Two upstream kinases, MKK-4 and MKK-7, have been identified as potential activators of JNK. However, the role of MAP kinase kinases (MAPKKs) and their functional organization within fibroblast-like synoviocytes (FLS) have not been defined. We therefore evaluated the interactions between the various MAP kinase components and determined their subcellular localization.

Methods: MKKs were identified by immunohistochemistry of rheumatoid arthritis (RA) and osteoarthritis (OA) synovium. Western blotting was used to determine the expression of FLS. Immunoprecipitation experiments using antibodies specific for MKK-4, MKK-7, and JNK were performed. Phosphospecific antibodies and immunohistochemistry were used to evaluate the activation state of synovial MKK-4 and MKK-7. Confocal microscopy was used to determine the subcellular location of the kinases.

Results: Immunohistochemistry studies demonstrated abundant MKK-4 and MKK-7 in RA and OA synovium, but the levels of phosphorylated kinases were significantly higher in RA synovium. MKK-4 and MKK-7 were constitutively expressed by cultured RA and OA FLS, and IL-1 stimulation resulted in rapid phosphorylation of both kinases. JNK was detected in MKK-4 and MKK-7 immunoprecipitates. Furthermore, MKK-4 coprecipitated with MKK-7 and vice versa, indicating that the 3 kinases form a stable complex in FLS. Confocal microscopy confirmed that JNK, MKK-4, and MKK-7 colocalized in the cytoplasm, with JNK migrating to the nucleus after IL-1 stimulation. The signal complex containing MKK-4, MKK-7, and JNK was functionally active and able to phosphorylate c-Jun after IL-1 stimulation of FLS.

Conclusion: These studies demonstrate that JNK, MKK-4, and MKK-7 form an active signaling complex in FLS. This novel JNK signalsome is activated in response to IL-1 and migrates to the nucleus. The JNK signalsome represents a new target for therapeutic interventions designed to prevent joint destruction.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Arthritis, Rheumatoid / metabolism*
  • Cell Nucleus / enzymology
  • Fibroblasts / enzymology
  • Humans
  • Interleukin-1 / metabolism
  • JNK Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 4*
  • MAP Kinase Kinase 7
  • Mitogen-Activated Protein Kinase Kinases / biosynthesis
  • Mitogen-Activated Protein Kinase Kinases / metabolism*
  • Mitogen-Activated Protein Kinases / metabolism*
  • Osteoarthritis / metabolism
  • Phosphorylation
  • Signal Transduction / physiology
  • Synovial Membrane / cytology
  • Synovial Membrane / enzymology


  • Interleukin-1
  • JNK Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 4
  • MAP Kinase Kinase 7
  • MAP2K4 protein, human
  • MAP2K7 protein, human
  • Mitogen-Activated Protein Kinase Kinases