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Receptor Heterodimerization and Co-Receptor Engagement in TLR2 Activation Induced by MIC1 and MIC4 from Toxoplasma gondii

1
Laboratory of Immunochemistry and Glycobiology, Department of Cell and Molecular Biology and Pathogenic Bioagents, Ribeirão Preto Medical School, University of São Paulo (FMRP/USP), Ribeirão Preto SP 14049-900, Brazil
2
Border Biomedical Research Center (BBRC), Department of Biological Sciences, University of Texas at El Paso (UTEP), El Paso, TX 79968, USA
3
Institute of Medical Biochemistry, Program of Molecular Biology and Biotechnology at Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro RJ 21941-599, Brazil
4
Department of Biology, Faculty of Philosophy, Sciences and Letters at Ribeirão Preto, University of São Paulo USP (FFCLRP/USP), Ribeirão Preto SP 14040-900, Brazil
*
Authors to whom correspondence should be addressed.
Int. J. Mol. Sci. 2019, 20(20), 5001; https://doi.org/10.3390/ijms20205001
Received: 15 August 2019 / Revised: 17 September 2019 / Accepted: 30 September 2019 / Published: 10 October 2019
(This article belongs to the Special Issue The Role of Glycosylation in Host-Microbial Interactions)
The microneme organelles of Toxoplasma gondii tachyzoites release protein complexes (MICs), including one composed of the transmembrane protein MIC6 plus MIC1 and MIC4. In this complex, carbohydrate recognition domains of MIC1 and MIC4 are exposed and interact with terminal sialic acid and galactose residues, respectively, of host cell glycans. Recently, we demonstrated that MIC1 and MIC4 binding to the N-glycans of Toll-like receptor (TLR) 2 and TLR4 on phagocytes triggers cell activation and pro-inflammatory cytokine production. Herein, we investigated the requirement for TLR2 heterodimerization and co-receptors in MIC-induced responses, as well as the signaling molecules involved. We used MICs to stimulate macrophages and HEK293T cells transfected with TLR2 and TLR1 or TLR6, both with or without the co-receptors CD14 and CD36. Then, the cell responses were analyzed, including nuclear factor-kappa B (NF-κB) activation and cytokine production, which showed that (1) only TLR2, among the studied factors, is crucial for MIC-induced cell activation; (2) TLR2 heterodimerization augments, but is not critical for, activation; (3) CD14 and CD36 enhance the response to MIC stimulus; and (4) MICs activate cells through a transforming growth factor beta-activated kinase 1 (TAK1)-, mammalian p38 mitogen-activated protein kinase (p38)-, and NF-κB-dependent pathway. Remarkably, among the studied factors, the interaction of MIC1 and MIC4 with TLR2 N-glycans is sufficient to induce cell activation, which promotes host protection against T. gondii infection. View Full-Text
Keywords: Toxoplasma gondii; microneme proteins; Toll-like receptor 2; TLR co-receptors; TLR heterodimerization; CD14; CD36 Toxoplasma gondii; microneme proteins; Toll-like receptor 2; TLR co-receptors; TLR heterodimerization; CD14; CD36
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Costa Mendonça-Natividade, F.; Duque Lopes, C.; Ricci-Azevedo, R.; Sardinha-Silva, A.; Figueiredo Pinzan, C.; Paiva Alegre-Maller, A.C.; L. Nohara, L.; B. Carneiro, A.; Panunto-Castelo, A.; C. Almeida, I.; Roque-Barreira, M.C. Receptor Heterodimerization and Co-Receptor Engagement in TLR2 Activation Induced by MIC1 and MIC4 from Toxoplasma gondii. Int. J. Mol. Sci. 2019, 20, 5001.

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