A role for the adaptor proteins TRAM and TRIF in toll-like receptor 2 signaling

J Biol Chem. 2015 Feb 6;290(6):3209-22. doi: 10.1074/jbc.M114.593426. Epub 2014 Dec 11.

Abstract

Toll-like receptors (TLRs) are involved in sensing invading microbes by host innate immunity. TLR2 recognizes bacterial lipoproteins/lipopeptides, and lipopolysaccharide activates TLR4. TLR2 and TLR4 signal via the Toll/interleukin-1 receptor adaptors MyD88 and MAL, leading to NF-κB activation. TLR4 also utilizes the adaptors TRAM and TRIF, resulting in activation of interferon regulatory factor (IRF) 3. Here, we report a new role for TRAM and TRIF in TLR2 regulation and signaling. Interestingly, we observed that TLR2-mediated induction of the chemokine Ccl5 was impaired in TRAM or TRIF deficient macrophages. Inhibition of endocytosis reduced Ccl5 release, and the data also suggested that TRAM and TLR2 co-localize in early endosomes, supporting the hypothesis that signaling may occur from an intracellular compartment. Ccl5 release following lipoprotein challenge additionally involved the kinase Tbk-1 and Irf3, as well as MyD88 and Irf1. Induction of Interferon-β and Ccl4 by lipoproteins was also partially impaired in cells lacking TRIF cells. Our results show a novel function of TRAM and TRIF in TLR2-mediated signal transduction, and the findings broaden our understanding of how Toll/interleukin-1 receptor adaptor proteins may participate in signaling downstream from TLR2.

Keywords: Innate Immunity; Interferon; Interferon Regulatory Factor (IRF); Macrophage; TIR Domain-containing Adaptor-inducing Interferon-B (TRIF); Toll-like Receptor (TLR); Toll-like Receptor 2 (TLR2); Toll-like Receptor Adaptor Molecule 2.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Vesicular Transport / genetics
  • Adaptor Proteins, Vesicular Transport / metabolism*
  • Animals
  • Cells, Cultured
  • Chemokine CCL4 / genetics
  • Chemokine CCL4 / metabolism
  • Chemokine CCL5 / genetics
  • Chemokine CCL5 / metabolism
  • Endocytosis
  • Endosomes / metabolism
  • HEK293 Cells
  • Humans
  • Interferon Regulatory Factor-1 / genetics
  • Interferon Regulatory Factor-1 / metabolism
  • Interferon Regulatory Factor-3 / genetics
  • Interferon Regulatory Factor-3 / metabolism
  • Interferon-beta / genetics
  • Interferon-beta / metabolism
  • Lipopolysaccharides / pharmacology
  • Macrophages, Peritoneal / metabolism
  • Mice
  • Myeloid Differentiation Factor 88 / genetics
  • Myeloid Differentiation Factor 88 / metabolism
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Receptors, Interleukin / genetics
  • Receptors, Interleukin / metabolism*
  • Signal Transduction*
  • Toll-Like Receptor 2 / agonists
  • Toll-Like Receptor 2 / metabolism*

Substances

  • Adaptor Proteins, Vesicular Transport
  • Chemokine CCL4
  • Chemokine CCL5
  • Interferon Regulatory Factor-1
  • Interferon Regulatory Factor-3
  • Irf1 protein, mouse
  • Irf3 protein, mouse
  • Lipopolysaccharides
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Receptors, Interleukin
  • TICAM-1 protein, mouse
  • TIRP protein, mouse
  • Tlr2 protein, mouse
  • Toll-Like Receptor 2
  • Interferon-beta
  • Tbk1 protein, mouse
  • Protein-Serine-Threonine Kinases