Toll-like Receptor 3-induced Suppression via Binding of Suppressors of Cytokine Signaling 3 to Tyrosine Kinase 2

The Suppressor of cytokine signaling (SOCS) family of negative regulatory proteins are upregulated in response to several cytokines and pathogen-associated molecular patterns (PAMPs), and suppress cellular signaling responses by binding receptor phosphotyrosine residues. Exposure of bone marrow-derived dendritic cells (BMDCs) to 1D8 cells, a murine model of ovarian carcinoma, suppresses their ability to express CD40 and stimulate antigen specific responses in response to PAMPs, and in particular to poly I: C with the upregulated SOCS3 transcript and protein levels. The ectopic expression of SOCS3 in both the macrophage cell line RAW264.7 and BMDCs decreased signaling in response to both poly I:C and IFN. Further, knockdown of SOCS3 transcripts significantly enhanced the responses of RAW264.7 and BMDCs to both poly I: C and IFN. Immunoprecipitation and pull-down studies demonstrate that SOCS3 binds to the IFN receptor TYK2. Since poly I: C triggers autocrine IFN signaling, binding of SOCS3 to TYK2 may thereby suppress the activation of BMDCs by polyI:C and IFN. Thus, elevated levels of SOCS3 in tumor-associated DCs may potentially resist the signals induced by TLR3 ligands and type I interferon to decrease DC activation via binding with IFN receptor TyK2.

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