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Regulation of TLR4 signaling through the TRAF6/sNASP axis by reversible phosphorylation mediated by CK2 and PP4

Feng-Ming Yang1, Hui-Ming Chang2,3,4, Edward T H Yeh5,4

  • 1School of Respiratory Therapy, College of Medicine, Taipei Medical University, Taipei, Taiwan 110301.

Proceedings of the National Academy of Sciences of the United States of America
|November 18, 2021
PubMed

Insights

Protein phosphatase 4 (PP4) acts as a negative regulator in innate immunity. It dephosphorylates somatic nuclear autoantigenic sperm protein (sNASP), thereby inhibiting Toll-like receptor 4 (TLR4)-induced signaling and enhancing sepsis survival.

Area of Science:

  • Immunology
  • Molecular Biology
  • Biochemistry

Background:

  • Toll-like receptors (TLRs) activate innate immunity via complex signaling pathways involving kinases and phosphatases.
  • Somatic nuclear autoantigenic sperm protein (sNASP) binds TNF receptor-associated factor 6 (TRAF6) in resting cells.
  • Upon TLR4 activation, a signaling complex including TRAF6, sNASP, IL-1 receptor-associated kinase 4, and casein kinase 2 (CK2) is formed, with CK2 phosphorylating sNASP.

Purpose of the Study:

  • To identify the specific phosphatase that dephosphorylates sNASP.
  • To elucidate the role of this phosphatase in regulating TLR4-induced innate immune signaling.
  • To investigate the therapeutic potential of modulating this phosphatase activity in infection models.

Main Methods:

  • Biochemical assays to identify sNASP phosphatase activity.
  • Cell-based experiments using ectopic expression and gene silencing of protein phosphatase 4 (PP4).
  • In vivo studies using mouse models of bacterial infection and sepsis, employing recombinant adenovirus for gene delivery.

Main Results:

  • Protein phosphatase 4 (PP4) was identified as the specific phosphatase for sNASP.
  • PP4 dephosphorylates phospho-sNASP (p-sNASP), terminating TRAF6 activation and downstream signaling.
  • Ectopic PP4 expression inhibited pro-inflammatory cytokine production (IL-6, TNF-α) and improved survival in a sepsis model, while PP4 silencing had opposite effects.

Conclusions:

  • PP4 acts as a negative regulator of TLR4-induced innate immunity by modulating the sNASP-TRAF6 interaction.
  • Targeting PP4 offers a potential therapeutic strategy to enhance innate immune responses and combat bacterial infections.
  • The sNASP-TRAF6-PP4 axis represents a novel regulatory mechanism in innate immune signaling.
Keywords:
TRAF6Toll-like receptor 4kinasephosphatasesignaling

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