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Two mechanistically and temporally distinct NF-kappaB activation pathways in IL-1 signaling

Kohsuke Yamazaki1, Jin Gohda, Atsuhiro Kanayama

  • 1Division of Cellular and Molecular Biology, Department of Cancer Biology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.

Science Signaling
|October 22, 2009
PubMed

Insights

Interleukin-1 (IL-1) activates nuclear factor kappaB (NF-kappaB) via TAK1 and MEKK3. This study reveals cooperative, distinct pathways involving TRAF6 and polyubiquitination, crucial for immune and inflammatory responses.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Signaling

Background:

  • Interleukin-1 (IL-1) is a key mediator of immune and inflammatory responses.
  • Activation of nuclear factor kappaB (NF-kappaB) is a critical downstream event in IL-1 signaling.
  • The roles of transforming growth factor-beta-activated kinase 1 (TAK1) and mitogen-activated protein kinase kinase kinase 3 (MEKK3) in IL-1-induced NF-kappaB activation are established, but their interplay is unclear.

Purpose of the Study:

  • To elucidate the functional and physical interactions between TAK1 and MEKK3 in IL-1-mediated NF-kappaB activation.
  • To investigate the role of polyubiquitination in the formation of signaling complexes involved in IL-1 signaling.
  • To understand the distinct mechanisms and temporal coordination of signaling pathways contributing to sustained NF-kappaB activation.

Main Methods:

  • Co-immunoprecipitation assays to detect protein-protein interactions.
  • Site-directed mutagenesis to identify critical residues for protein function.
  • Ubiquitination assays to analyze polyubiquitination status.
  • Western blotting to assess protein activation and signaling complex formation.

Main Results:

  • TAK1-mediated NF-kappaB activation requires a transient signaling complex containing TRAF6, MEKK3, and TAK1.
  • Lysine 63-linked polyubiquitination of TAK1 at lysine 209, catalyzed by TRAF6 and Ubc13, is essential for complex formation.
  • TRAF6 activates NF-kappaB via MEKK3 independently of TAK1, ensuring continuous NF-kappaB activation for cytokine production.

Conclusions:

  • Cooperative activation of NF-kappaB by two distinct MEKK3-dependent pathways diverging at TRAF6 is critical for immune and inflammatory responses.
  • This intricate signaling network, involving sequential and parallel activation steps, ensures robust and sustained immune cell activation.
  • The findings provide new insights into the molecular mechanisms governing inflammatory signaling and potential therapeutic targets.

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