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

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 IFN? and IL-10 but suppression of pro-inflammatory cytokines (TNF?, 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, GSK3?. Inhibition of PI3K or Akt abrogated the ability of Syk deficiency to enhance IFN? and IL-10 in Syk deficient cells, confirmed by the overexpression of Akt (Myr-Akt) or constitutively active GSK3? (GSK3 S9A). Moreover, neither inhibition of PI3K-Akt signaling nor neutralization of de novo synthesized IFN? could rescue TNF? and IL-6 production in LPS-stimulated Syk deficient cells. Syk deficiency resulted in decreased phosphorylation of IKK? and the NF-?B p65 subunit, further suggesting a divergent influence of Syk on pro- and anti-inflammatory TLR responses. CONCLUSIONS:Syk negatively regulates TLR4-mediated production of IFN? and IL-10 and promotes inflammatory responses in dendritic cells through divergent regulation of downstream PI3K-Akt and NF-?B signaling pathways. GENERAL SIGNIFICANCE:Syk may represent a novel target for manipulating the direction or intensity of the innate response, depending on clinical necessity.

SUBMITTER: Yin H 

PROVIDER: S-EPMC5321715 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature