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TLR and TNF-R1 activation of the MKK3/MKK6-p38α axis in macrophages is mediated by TPL-2 kinase

Michael J Pattison1, Olivia Mitchell1, Helen R Flynn2

  • 1The Francis Crick Institute, Immune Signalling Laboratory, Mill Hill Laboratory, London NW7 1AA, U.K.

The Biochemical Journal
|July 13, 2016
PubMed

Insights

Toll-like receptor (TLR) stimulation activates p38α MAP kinase (MAPK) via the IKK/NF-κB1 p105/TPL-2 pathway. This pathway regulates MKK3/6 and p38α activation in macrophages during inflammation.

Area of Science:

  • Immunology
  • Cellular signaling
  • Molecular biology

Background:

  • Toll-like receptor (TLR) stimulation of p38α MAP kinase (MAPK) involves transforming growth factor-β-activated kinase 1 (TAK1) and MAPK kinases (MKKs).
  • Tumour progression locus 2 (TPL-2) is a key kinase in inflammatory signaling pathways.

Purpose of the Study:

  • To investigate the role of TPL-2 catalytic activity in TLR-mediated p38α MAPK activation in macrophages.
  • To elucidate the specific MKKs regulated by TPL-2 and the upstream signaling requirements.

Main Methods:

  • Quantitative mass spectrometry was employed to analyze protein phosphorylation in wild-type and catalytically inactive TPL-2 (Map3k8(D270A/D270A)) macrophages.
  • Stimulation with lipopolysaccharide (LPS), tumor necrosis factor (TNF), Mycobacterium tuberculosis, and Listeria monocytogenes was used to assess signaling pathway activation.

Main Results:

  • TPL-2 kinase activity is essential for phosphorylating the activation loops of MKK3/6, but not MKK4.
  • IκB kinase (IKK) phosphorylation of NF-κB1 p105 is required for MKK3/6 activation, similar to MKK1/2.
  • While LPS-induced p38α activation was only partially reduced due to MKK redundancy, TNF-induced p38α activation was substantially decreased, highlighting MKK3/6's predominant role.

Conclusions:

  • The IKK/NF-κB1 p105/TPL-2 signaling pathway, downstream of TAK1, is critical for regulating MKK3/6 and p38α activation in macrophages during inflammatory responses.
  • TPL-2's catalytic activity is indispensable for MKK3/6 and p38α activation induced by various microbial stimuli.
Keywords:
IKKNF-κB1TLRTPL-2p38tumour necrosis factors

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