Syk negatively regulates TLR4-mediated IFNβ 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 IFNβ and IL-10 but suppression of pro-inflammatory cytokines (TNFα, IL-6). Deficiency of Syk enhanced 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 of 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.

Proteomic Analysis of HDAC3 Selective Inhibitor in the Regulation of Inflammatory Response of Primary Microglia

“…SH2 domains selectively bind to the phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) of immune receptors, such as MyD88, TRAF6, and TRIF, transmitting initiative signals to downstream pathways. SYK is found to be fundamental for Toll-like receptor signaling pathway and the inhibition of SYK suppresses the release of proinflammatory cytokines [ 25 , 26 ]. In this study, we detected alterations of SYK in protein level but not mRNA level.…”

Pathogens MenTORing Macrophages and Dendritic Cells: Manipulation of mTOR and Cellular Metabolism to Promote Immune Escape

“…Likewise, L. major alters macrophage (BALB/c-derived peritoneal macrophages) CD40 signalosome composition by depleting cholesterol, resulting in the induction of IL-10 production rather than IL-12 [136]. This alteration is regulated by TNF receptor associated factor 6 (TRAF6) and spleen tyrosine kinase (SYK) which both have been shown to regulate mTORC1 signaling, suggesting that mTORC1 signaling is involved in the altered CD40 signalosome composition by L. major [137,138]. Interestingly, cholesterol activates mTORC1 at the lysosomal surface, which indicates that alterations in cholesterol levels elicited by pathogens could, in addition to membrane composition, alter mTORC1 activation [139].…”

Syk inhibitor R406 downregulates inflammation in an in vitro model ofPseudomonas aeruginosainfection

“…Syk involvement in the regulation of signals generated by the engagement of TLR-4 complex by its ligand LPS in human neutrophils and macrophages has also been previously demonstrated (Arndt et al 2004;Ulanova et al 2007;Miller et al 2012), and this mechanism likely operates in our model. Recent studies expanded our understanding of the role of Syk in fine-tuning of cellular responses stimulated by the engagement of innate immune receptors (Aouar et al 2016;Yin et al 2016). For example, it was D r a f t demonstrated that in macrophages and dendritic cells, Syk regulates TNFα exocytosis induced by stimulation of TLR9 by bacterial CpG DNA (Rao et al 2013); such mechanism may potentially be involved in responses of differentiated THP-1 cells to P. aeruginosa.…”