IRAK4 kinase activity controls Toll-like receptor-induced inflammation through the transcription factor IRF5 in primary human monocytes

J Biol Chem. 2017 Nov 10;292(45):18689-18698. doi: 10.1074/jbc.M117.796912. Epub 2017 Sep 18.

Abstract

Interleukin-1 receptor-associated kinase 4 (IRAK4) plays a critical role in innate immune signaling by Toll-like receptors (TLRs), and loss of IRAK4 activity in mice and humans increases susceptibility to bacterial infections and causes defects in TLR and IL1 ligand sensing. However, the mechanism by which IRAK4 activity regulates the production of downstream inflammatory cytokines is unclear. Using transcriptomic and biochemical analyses of human monocytes treated with a highly potent and selective inhibitor of IRAK4, we show that IRAK4 kinase activity controls the activation of interferon regulatory factor 5 (IRF5), a transcription factor implicated in the pathogenesis of multiple autoimmune diseases. Following TLR7/8 stimulation by its agonist R848, chemical inhibition of IRAK4 abolished IRF5 translocation to the nucleus and thus prevented IRF5 binding to and activation of the promoters of inflammatory cytokines in human monocytes. We also found that IKKβ, an upstream IRF5 activator, is phosphorylated in response to the agonist-induced TLR signaling. Of note, IRAK4 inhibition blocked IKKβ phosphorylation but did not block the nuclear translocation of NFκB, which was surprising, given the canonical role of IKKβ in phosphorylating IκB to allow NFκB activation. Moreover, pharmacological inhibition of either IKKβ or the serine/threonine protein kinase TAK1 in monocytes blocked TLR-induced cytokine production and IRF5 translocation to the nucleus, but not nuclear translocation of NFκB. Taken together, our data suggest a mechanism by which IRAK4 activity regulates TAK1 and IKKβ activation, leading to the nuclear translocation of IRF5 and induction of inflammatory cytokines in human monocytes.

Keywords: IKKβ; IRAK4; IRF5; NFκB; TAK1; TLR; Toll-like receptor; cytokine; inflammation; interferon regulatory factor.

MeSH terms

  • Active Transport, Cell Nucleus / drug effects
  • Animals
  • Cells, Cultured
  • Computational Biology
  • Cytokines / agonists
  • Cytokines / genetics
  • Cytokines / metabolism
  • Enzyme Activation / drug effects
  • Gene Expression Regulation / drug effects
  • Humans
  • I-kappa B Kinase / antagonists & inhibitors
  • I-kappa B Kinase / chemistry
  • I-kappa B Kinase / metabolism*
  • Interferon Regulatory Factors / agonists
  • Interferon Regulatory Factors / metabolism*
  • Interleukin-1 Receptor-Associated Kinases / antagonists & inhibitors
  • Interleukin-1 Receptor-Associated Kinases / metabolism*
  • MAP Kinase Kinase Kinases / antagonists & inhibitors
  • MAP Kinase Kinase Kinases / chemistry
  • MAP Kinase Kinase Kinases / metabolism
  • Models, Immunological*
  • Monocytes / cytology
  • Monocytes / drug effects
  • Monocytes / immunology
  • Monocytes / metabolism*
  • NF-kappa B / metabolism
  • NF-kappa B p50 Subunit / metabolism
  • Phosphorylation / drug effects
  • Protein Kinase Inhibitors / pharmacology
  • Protein Processing, Post-Translational / drug effects
  • Single-Cell Analysis
  • Toll-Like Receptor 7 / agonists*
  • Toll-Like Receptor 7 / metabolism
  • Toll-Like Receptor 8 / agonists*
  • Toll-Like Receptor 8 / metabolism

Substances

  • Cytokines
  • IRF5 protein, human
  • Interferon Regulatory Factors
  • NF-kappa B
  • NF-kappa B p50 Subunit
  • NFKB1 protein, human
  • Protein Kinase Inhibitors
  • TLR7 protein, human
  • TLR8 protein, human
  • Toll-Like Receptor 7
  • Toll-Like Receptor 8
  • IRAK4 protein, human
  • Interleukin-1 Receptor-Associated Kinases
  • I-kappa B Kinase
  • IKBKB protein, human
  • MAP Kinase Kinase Kinases
  • MAP kinase kinase kinase 7