p38 inhibition and not MK2 inhibition enhances the secretion of chemokines from TNF-α activated rheumatoid arthritis fibroblast-like synoviocytes

Clin Exp Rheumatol. Jul-Aug 2013;31(4):515-25. Epub 2013 Apr 3.


Objectives: For many years the p38 MAP kinase (MAPK) has been a major anti-inflammatory target for the development of an oral therapy for rheumatoid arthritis (RA). However, disappointing results from Phase II clinical studies suggest that adaptations may occur, which allow escape from blockade of the p38 pathway. In this study we investigated whether p38 inhibition mediated JNK activation represents such an escape mechanism.

Methods: Interaction between the JNK and p38 pathways was studied in TNF-α stimulated THP-1 monocytes, primary macrophages and fibroblast-like synoviocytes from OA and RA patients using pharmacological inhibitors and siRNAs.

Results: TNF-α induced phosphorylation of JNK and c-Jun was sustained by p38 inhibitors in monocytes, primary macrophages and FLS. Upregulation of Mip1α, Mip1β and IL-8 mRNAs and protein were observed upon p38 inhibition. More importantly, inhibition of MK2, the substrate of p38 did not sustain JNK activation upon TNF-α activation and did not elevate Mip1α, Mip1β and IL-8 chemokines as compared to TNF-α alone. In this study, TNF-α or IL-1β induced JNK activation is sustained by p38 inhibition, resulting in enhanced chemokine secretion.

Conclusions: Based on the suggested role of these chemokines in RA pathogenesis, the upregulation of these chemokines may provide an explanation for the lack of efficacy of p38 inhibitors in Phase II. The absence of any effect of MK2 inhibition in our models on this mechanism, while coming with similar efficacy on blocking p38, provides support for further investigations to reveal the potential of MK2 inhibition as a novel treatment of RA.

MeSH terms

  • Arthritis, Rheumatoid / drug therapy*
  • Arthritis, Rheumatoid / enzymology
  • Arthritis, Rheumatoid / immunology
  • Cell Line
  • Chemokines / immunology
  • Chemokines / metabolism*
  • Enzyme Inhibitors / pharmacology*
  • Fibroblasts / cytology
  • Fibroblasts / drug effects*
  • Fibroblasts / metabolism
  • Humans
  • Imidazoles / pharmacology
  • Intracellular Signaling Peptides and Proteins / antagonists & inhibitors*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • MAP Kinase Signaling System / drug effects
  • Monocytes / cytology
  • Naphthalenes / pharmacology
  • Primary Cell Culture
  • Protein Kinase Inhibitors / pharmacology
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Protein-Serine-Threonine Kinases / metabolism
  • Pyrazoles / pharmacology
  • Pyridines / pharmacology
  • Synovial Membrane / cytology
  • Tumor Necrosis Factor-alpha / immunology
  • Tumor Necrosis Factor-alpha / metabolism
  • Up-Regulation / drug effects
  • Up-Regulation / immunology
  • p38 Mitogen-Activated Protein Kinases / antagonists & inhibitors*
  • p38 Mitogen-Activated Protein Kinases / metabolism


  • BIRB 796
  • Chemokines
  • Enzyme Inhibitors
  • Imidazoles
  • Intracellular Signaling Peptides and Proteins
  • Naphthalenes
  • Protein Kinase Inhibitors
  • Pyrazoles
  • Pyridines
  • Tumor Necrosis Factor-alpha
  • MAP-kinase-activated kinase 2
  • Protein-Serine-Threonine Kinases
  • p38 Mitogen-Activated Protein Kinases
  • SB 203580