Open AccessToxoplasma gondii activates a Syk-CARD9-NF-κB signaling axis and gasdermin D-independent release of IL-1β during infection of primary human monocytes
Author(s) -
William Pandori,
Tatiane S. Lima,
Sharmila Mallya,
Tiffany H. Kao,
Lanny Gov,
Melissa B. Lodoen
Publication year - 2019
Publication title -
plos pathogens
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.719
H-Index - 206
eISSN - 1553-7374
pISSN - 1553-7366
DOI - 10.1371/journal.ppat.1007923
Subject(s) - syk , toxoplasma gondii , biology , microbiology and biotechnology , immune system , signal transduction , cytokine , thp1 cell line , immunology , cell culture , antibody , tyrosine kinase , genetics
IL-1β is a potent pro-inflammatory cytokine that promotes immunity and host defense, and its dysregulation is associated with immune pathology. Toxoplasma gondii infection of myeloid cells triggers the production and release of IL-1β; however, the mechanisms regulating this pathway, particularly in human immune cells, are incompletely understood. We have identified a novel pathway of T . gondii induction of IL-1β via a Syk-CARD9-NF-κB signaling axis in primary human peripheral blood monocytes. Syk was rapidly phosphorylated during T . gondii infection of primary monocytes, and inhibiting Syk with the pharmacological inhibitors R406 or entospletinib, or genetic ablation of Syk in THP-1 cells, reduced IL-1β release. Inhibition of Syk in primary cells or deletion of Syk in THP-1 cells decreased parasite-induced IL-1β transcripts and the production of pro-IL-1β. Furthermore, inhibition of PKCδ, CARD9/MALT-1 and IKK reduced p65 phosphorylation and pro-IL-1β production in T . gondii -infected primary monocytes, and genetic knockout of PKCδ or CARD9 in THP-1 cells also reduced pro-IL-1β protein levels and IL-1β release during T . gondii infection, indicating that Syk functions upstream of this NF-κB-dependent signaling pathway for IL-1β transcriptional activation. IL-1β release from T . gondii -infected primary human monocytes required the NLRP3-caspase-1 inflammasome, but interestingly, was independent of gasdermin D (GSDMD) cleavage and pyroptosis. Moreover, GSDMD knockout THP-1 cells released comparable amounts of IL-1β to wild-type THP-1 cells after T . gondii infection. Taken together, our data indicate that T . gondii induces a Syk-CARD9/MALT-1-NF-κB signaling pathway and activation of the NLRP3 inflammasome for the release of IL-1β in a cell death- and GSDMD-independent manner. This research expands our understanding of the molecular basis for human innate immune regulation of inflammation and host defense during parasite infection.