Syk negatively regulates TLR4-mediated IFNβ and IL-10 production and promotes inflammatory responses in dendritic cells

Biochim Biophys Acta. 2016 Mar;1860(3):588-98. doi: 10.1016/j.bbagen.2015.12.012. Epub 2015 Dec 17.

Abstract

Background: While Syk has been shown to associate with TLR4, the immune consequences of Syk-TLR interactions and related molecular mechanisms are unclear.

Methods: Gain- and loss-of-function approaches were utilized to determine the regulatory function of Syk and elucidate the related molecular mechanisms in TLR4-mediated inflammatory responses. Cytokine production was measured by ELISA and phosphorylation of signaling molecules determined by Western blotting.

Results: Syk deficiency in murine dendritic cells resulted in the enhancement of LPS-induced IFNβ and IL-10 but suppression of pro-inflammatory cytokines (TNFα, IL-6). Deficiency of Syk enhanced the activity of PI3K and elevated the phosphorylation of PI3K and Akt, which in turn, lead to the phospho-inactivation of the downstream, central gatekeeper of the innate response, GSK3β. Inhibition of PI3K or Akt abrogated the ability of Syk deficiency to enhance IFNβ and IL-10 in Syk deficient cells, confirmed by the overexpression of Akt (Myr-Akt) or constitutively active GSK3β (GSK3 S9A). Moreover, neither inhibition of PI3K-Akt signaling nor neutralization of de novo synthesized IFNβ could rescue TNFα and IL-6 production in LPS-stimulated Syk deficient cells. Syk deficiency resulted in decreased phosphorylation of IKKβ and the NF-κB p65 subunit, further suggesting a divergent influence of Syk on pro- and anti-inflammatory TLR responses.

Conclusions: Syk negatively regulates TLR4-mediated production of IFNβ and IL-10 and promotes inflammatory responses in dendritic cells through divergent regulation of downstream PI3K-Akt and NF-κB signaling pathways.

General significance: Syk may represent a novel target for manipulating the direction or intensity of the innate response, depending on clinical necessity.

Keywords: GSK3β; IL-10; Interferon-β; PI3K; Syk; Toll-like receptor 4.

Publication types

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

MeSH terms

  • Animals
  • Cells, Cultured
  • Dendritic Cells / immunology*
  • Glycogen Synthase Kinase 3 / metabolism
  • Glycogen Synthase Kinase 3 beta
  • Inflammation / etiology*
  • Interferon-beta / metabolism*
  • Interferon-gamma / biosynthesis*
  • Interleukin-10 / biosynthesis*
  • Interleukin-6 / biosynthesis
  • Intracellular Signaling Peptides and Proteins / physiology*
  • Mice
  • Mice, Inbred C57BL
  • Phosphatidylinositol 3-Kinases / metabolism
  • Protein-Tyrosine Kinases / physiology*
  • Proto-Oncogene Proteins c-akt / metabolism
  • STAT Transcription Factors / metabolism
  • Syk Kinase
  • Toll-Like Receptor 4 / physiology*
  • Tumor Necrosis Factor-alpha / biosynthesis

Substances

  • IL10 protein, mouse
  • Interleukin-6
  • Intracellular Signaling Peptides and Proteins
  • STAT Transcription Factors
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Tumor Necrosis Factor-alpha
  • Interleukin-10
  • Interferon-beta
  • Interferon-gamma
  • Phosphatidylinositol 3-Kinases
  • Protein-Tyrosine Kinases
  • Syk Kinase
  • Syk protein, mouse
  • Glycogen Synthase Kinase 3 beta
  • Gsk3b protein, mouse
  • Proto-Oncogene Proteins c-akt
  • Glycogen Synthase Kinase 3