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Identification of MEKK2/3 serine phosphorylation site targeted by the Toll-like receptor and stress pathways

Dongyu Zhang1, Valeria Facchinetti, Xiaofang Wang

  • 1Department of Immunology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030-1903, USA.

The EMBO Journal
|December 20, 2005
PubMed

Insights

Scientists discovered key phosphorylation sites on MEKK2/3, crucial for Toll-like receptor (TLR) and stress signaling. This finding explains how these pathways activate MAP3K signaling, impacting cellular responses like IL-6 production.

Area of Science:

  • Cellular signaling pathways
  • Molecular mechanisms of immune response
  • Protein phosphorylation in signal transduction

Background:

  • Mitogen-activated protein kinase kinase kinase (MAP3K) family members are vital for Toll-like receptor (TLR) and cellular stress responses.
  • The precise molecular mechanisms governing MAP3K activation in these pathways are not fully understood.

Purpose of the Study:

  • To elucidate the regulatory mechanisms of MAP3K activation in TLR and cellular stress signaling.
  • To identify key phosphorylation sites involved in MEKK2 and MEKK3 activation.

Main Methods:

  • Site-directed mutagenesis to create serine-to-alanine mutations in MEKK2 and MEKK3.
  • Generation and application of a phospho-specific antibody against p-MEKK2/3.
  • Stimulation with lipopolysaccharide (LPS) to investigate TLR-mediated signaling.
  • Assessment of interleukin-6 (IL-6) production as a downstream cellular response.

Main Results:

  • Identified serine 519 (MEKK2) and serine 526 (MEKK3) as critical regulatory phosphorylation sites.
  • Mutations at these sites significantly impaired MEKK2/3 activation.
  • Lipopolysaccharide stimulation induced MEKK2/3 phosphorylation at these sites, mediated by TRAF6.
  • This phosphorylation is essential for TLR-induced IL-6 production.
  • MAPK agonists differentially induced this phosphorylation, indicating pathway specificity.

Conclusions:

  • Revealed a novel mechanism for MEKK2/3 activation via TLR and cellular stress pathways.
  • Demonstrated the critical role of specific serine phosphorylation in regulating MAP3K activity and downstream cellular functions.
  • Highlighted the involvement of TRAF6 in TLR-induced MEKK2/3 phosphorylation and IL-6 production.

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