title: Evidence for TLR4 and FcRγ-CARD9 activation by cholera toxin B subunit and its direct bindings to TREM2 and LMIR5 receptors.
abstract: Cholera toxin (CTX) is a virulent factor of Vibrio cholerae that causes life-threatening diarrheal disease. Its non-toxic subunit CTB has been extensively studied for vaccine delivery. In immune cells, CTB induces a number of signaling molecules related to cellular activation and cytokine production. The mechanisms by which CTB exerts its immunological effects are not understood. We report here the immunological targets of CTB. The unexpected finding that GM1 ganglioside inhibited NF-κB activation in human monocytes stimulated with CTX and agonists of Toll-like receptors (TLR) suggests the possibility of CTX-TLR interaction. Indeed, CTX-induced IL-6 production was substantially reduced in MyD88(-/-) or TLR4(-/-) macrophages. Ectopic expression of TLR4 was required for CTX-induced NF-κB activation in HEK 293 cells. Furthermore, the inflammatory capacity of CTB was lost in the absence of TLR4, adaptor protein FcRγ, or its downstream signaling molecule CARD9. Attempts have been made to identify CTB-binding targets from various C-type lectin and immunoglobulin-like receptors. CTB targeted not only GM1 and TLR4 but also TREM2 and LMIR5/CD300b. CTB-TREM2 interaction initiated signal transduction through adaptor protein DAP12. The binding of CTB inhibited LMIR5 activation induced by its endogenous ligand 3-O-sulfo-β-d-galactosylceramide C24:1. In summary, CTB targets TLR4, FcRγ-CARD9, TREM2, and LMIR5. These findings provide new insights into the immunobiology of cholera toxin.
authors.affiliation: Division of Molecular Immunology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Electronic address: phongsisay@gmail.com.
authors.forename: Vongsavanh
authors.initials: V
authors.lastname: Phongsisay
authors.affiliation: Department of Immunology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Ei'ichi
authors.initials: E
authors.lastname: Iizasa
authors.affiliation: Department of Immunology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Hara
authors.affiliation: Division of Molecular and Cellular Immunoscience, Department of Biomolecular Sciences, Faculty of Medicine, Saga University, Saga, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yoshida
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000276:immunology; D000818:Animals; D001665:Binding Sites; D053468:CARD Signaling Adaptor Proteins / Q000235:genetics / Q000276:immunology*; D002772:Cholera Toxin / Q000494:pharmacology*; D005677:G(M1) Ganglioside / Q000276:immunology / Q000494:pharmacology; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology; D016328:NF-kappa B / Q000235:genetics / Q000276:immunology; D061251:Primary Cell Culture; D011485:Protein Binding; D017452:Receptors, IgG / Q000235:genetics / Q000276:immunology*; D011971:Receptors, Immunologic / Q000235:genetics / Q000276:immunology*; D015398:Signal Transduction; D013433:Sulfoglycosphingolipids / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D053468:CARD Signaling Adaptor Proteins; C513280:Card9 protein, mouse; C527073:LMIR5 protein, mouse; D008562:Membrane Glycoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D017452:Receptors, IgG; D011971:Receptors, Immunologic; D013433:Sulfoglycosphingolipids; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C498716:Trem2 protein, mouse; C484963:Tyrobp protein, mouse; D005677:G(M1) Ganglioside; C084124:I(3)SO3-galactosylceramide; D002772:Cholera Toxin
keywords: Cholera toxin; GM1; Receptor