Toll-like receptor 9 trafficking and signaling for type I interferons requires PIKfyve activity

Int Immunol. 2015 Sep;27(9):435-45. doi: 10.1093/intimm/dxv021. Epub 2015 Apr 29.


Toll-like receptors (TLRs) traffic to distinct membranes for signaling. TLR7 and TLR9 recognize viral nucleic acids in the endosomes and induce robust anti-viral program. Signaling from these TLRs bifurcate at the level of distinct endosomal compartments, namely VAMP3(+) and LAMP(+) endosomes, to mediate the induction of cytokine and type I interferon (IFN) genes, respectively. The formation of the TLR9 endosome competent for IFNs induction requires AP-3. Phosphoinositides (PIs) mark distinct subcellular membranes and control membrane trafficking. However, their role in TLR trafficking and signaling in different dendritic cell (DC) subsets remains unclear. Here, we examined the role of phosphatidylinositol 3P 5-kinase, PIKfyve, in TLR9 trafficking and signaling. We demonstrate that inhibition of PIKfyve activity preferentially blocks TLR9 signaling for type I IFN induction in FLT3L-bone marrow-derived DCs. By confocal microscopy using RAW264.7 cells, we show that trafficking of both TLR9 and CpG to the LAMP1(+) compartment was blocked by PIKfyve inhibitor treatment, whereas their trafficking to the VAMP3(+) endosome remained intact. Further, AP-3 recruitment to TLR9 endosomes was impaired by PIKfyve inhibition. These data indicate that PIKfyve provides critical PIs necessary for the formation of endosome from which TLR9 signals to induce type I IFNs.

Keywords: TLR9; dendritic cells; innate immunity; intracellular trafficking; signaling; type I IFNs.

Publication types

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

MeSH terms

  • Animals
  • Cell Line
  • Cell Membrane / metabolism
  • DNA-Binding Proteins / metabolism
  • Dendritic Cells / metabolism
  • Endosomes / metabolism
  • Interferon Type I / metabolism*
  • Lysosome-Associated Membrane Glycoproteins / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Protein Transport / physiology
  • Signal Transduction / physiology*
  • Toll-Like Receptor 7 / metabolism
  • Toll-Like Receptor 9 / metabolism*
  • Transcription Factors / metabolism
  • Vesicle-Associated Membrane Protein 3 / metabolism


  • DNA-Binding Proteins
  • Interferon Type I
  • Lamp1 protein, mouse
  • Lysosome-Associated Membrane Glycoproteins
  • Tlr9 protein, mouse
  • Toll-Like Receptor 7
  • Toll-Like Receptor 9
  • Transcription Factors
  • Vesicle-Associated Membrane Protein 3
  • enhancer-binding protein AP-3
  • vesicle-associated membrane protein 3, mouse
  • Phosphatidylinositol 3-Kinases
  • Pikfyve protein, mouse