Dual Role of the Tyrosine Kinase Syk in Regulation of Toll-Like Receptor Signaling in Plasmacytoid Dendritic Cells

Crosslinking of regulatory immunoreceptors (RR), such as BDCA-2 (CD303) or ILT7 (CD85g), of plasmacytoid dendritic cells (pDCs) efficiently suppresses production of type-I interferon (IFN)-α/β and other cytokines in response to Toll-like receptor (TLR) 7/9 ligands. This cytokine-inhibitory pathway is mediated by spleen tyrosine kinase (Syk) associated with the ITAM-containing adapter of RR. Here we demonstrate by pharmacological targeting of Syk that in addition to the negative regulation of TLR7/9 signaling via RR, Syk also positively regulates the TLR7/9 pathway in human pDCs. Novel highly specific Syk inhibitor AB8779 suppressed IFN-α, TNF-α and IL-6 production induced by TLR7/9 agonists in primary pDCs and in the pDC cell line GEN2.2. Triggering of TLR9 or RR signaling induced a differential kinetics of phosphorylation at Y352 and Y525/526 of Syk and a differential sensitivity to AB8779. Consistent with the different roles of Syk in TLR7/9 and RR signaling, a concentration of AB8779 insufficient to block TLR7/9 signaling still released the block of IFN-α production triggered via the RR pathway, including that induced by hepatitis B and C viruses. Thus, pharmacological targeting of Syk partially restored the main pDC function—IFN-α production. Opposing roles of Syk in TLR7/9 and RR pathways may regulate the innate immune response to weaken inflammation reaction.

[1]  M. Ait-goughoulte,et al.  Early inhibition of hepatocyte innate responses by hepatitis B virus. , 2015, Journal of hepatology.

[2]  M. Colonna,et al.  The multifaceted biology of plasmacytoid dendritic cells , 2015, Nature Reviews Immunology.

[3]  E. Unanue,et al.  Early, transient depletion of plasmacytoid dendritic cells ameliorates autoimmunity in a lupus model , 2014, The Journal of experimental medicine.

[4]  E. Wagner,et al.  Specific roles for dendritic cell subsets during initiation and progression of psoriasis , 2014, EMBO molecular medicine.

[5]  T. Liang,et al.  Specific and Nonhepatotoxic Degradation of Nuclear Hepatitis B Virus cccDNA , 2014, Science.

[6]  Duen-Yi Huang,et al.  The Tyrosine Kinase Syk Differentially Regulates Toll-like Receptor Signaling Downstream of the Adaptor Molecules TRAF6 and TRAF3 , 2013, Science Signaling.

[7]  B. Freedman,et al.  Spleen Tyrosine Kinase (Syk)-dependent Calcium Signals Mediate Efficient CpG-induced Exocytosis of Tumor Necrosis Factor α (TNFα) in Innate Immune Cells* , 2013, The Journal of Biological Chemistry.

[8]  D. Olive,et al.  HCV glycoprotein E2 is a novel BDCA-2 ligand and acts as an inhibitor of IFN production by plasmacytoid dendritic cells. , 2012, Blood.

[9]  J. Blay,et al.  Impaired IFN-α production by plasmacytoid dendritic cells favors regulatory T-cell expansion that may contribute to breast cancer progression. , 2012, Cancer research.

[10]  D. Olive,et al.  Hepatitis C Virus Fails To Activate NF-κB Signaling in Plasmacytoid Dendritic Cells , 2011, Journal of Virology.

[11]  F. Granucci,et al.  CD14 Controls the LPS-Induced Endocytosis of Toll-like Receptor 4 , 2011, Cell.

[12]  P. Hainaut,et al.  Hepatitis B Virus Impairs TLR9 Expression and Function in Plasmacytoid Dendritic Cells , 2011, PloS one.

[13]  R. Schreiber,et al.  Type I interferon is selectively required by dendritic cells for immune rejection of tumors , 2011, The Journal of experimental medicine.

[14]  H. Janssen,et al.  Hepatitis B Virus Lacks Immune Activating Capacity, but Actively Inhibits Plasmacytoid Dendritic Cell Function , 2011, PloS one.

[15]  Christophe Caux,et al.  Impaired Toll-like receptor 7 and 9 signaling: from chronic viral infections to cancer. , 2010, Trends in immunology.

[16]  J. Nunès,et al.  Analysis of Signaling Events by Dynamic Phosphoflow Cytometry , 2009, Science Signaling.

[17]  L. Lanier,et al.  Regulation of TLR7/9 responses in plasmacytoid dendritic cells by BST2 and ILT7 receptor interaction , 2009, The Journal of experimental medicine.

[18]  G. Leone,et al.  Phosphorylation of the activation loop tyrosines is required for sustained Syk signaling and growth factor-independent B-cell proliferation. , 2009, Cellular signalling.

[19]  D. Olive,et al.  Hepatitis C Virus Is a Weak Inducer of Interferon Alpha in Plasmacytoid Dendritic Cells in Comparison with Influenza and Human Herpesvirus Type-1 , 2009, PloS one.

[20]  M. Gilliet,et al.  Plasmacytoid dendritic cells: sensing nucleic acids in viral infection and autoimmune diseases , 2008, Nature Reviews Immunology.

[21]  M. Shiina,et al.  Cell culture–produced hepatitis C virus impairs plasmacytoid dendritic cell function , 2007, Hepatology.

[22]  L. Lanier,et al.  BDCA2/FcɛRIγ Complex Signals through a Novel BCR-Like Pathway in Human Plasmacytoid Dendritic Cells , 2007, PLoS biology.

[23]  A. Fauci,et al.  HIV-1 gp120 inhibits TLR9-mediated activation and IFN-α secretion in plasmacytoid dendritic cells , 2007, Proceedings of the National Academy of Sciences.

[24]  Wei Cao,et al.  Plasmacytoid dendritic cell–specific receptor ILT7–FcɛRIγ inhibits Toll-like receptor–induced interferon production , 2006, The Journal of experimental medicine.

[25]  L. Karlsson,et al.  CpG-induced tyrosine phosphorylation occurs via a TLR9-independent mechanism and is required for cytokine secretion , 2006, The Journal of cell biology.

[26]  J. Plumas,et al.  Virus or TLR Agonists Induce TRAIL-Mediated Cytotoxic Activity of Plasmacytoid Dendritic Cells1 , 2006, The Journal of Immunology.

[27]  S. Akira,et al.  Toll-like Receptor 9–mediated Recognition of Herpes Simplex Virus-2 by Plasmacytoid Dendritic Cells , 2003, The Journal of experimental medicine.

[28]  A. Fauci,et al.  HIV-1 gp120 inhibits TLR9-mediated activation and IFN-{alpha} secretion in plasmacytoid dendritic cells. , 2007, Proceedings of the National Academy of Sciences of the United States of America.

[29]  Wei Cao,et al.  Plasmacytoid dendritic cell-specific receptor ILT7-Fc epsilonRI gamma inhibits Toll-like receptor-induced interferon production , 2006 .