title: CD14 protein acts as an adaptor molecule for the immune recognition of Salmonella curli fibers.
abstract: Amyloids, protein aggregates with a cross β-sheet structure, contribute to inflammation in debilitating disorders, including Alzheimer's disease. Enteric bacteria also produce amyloids, termed curli, contributing to inflammation during infection. It has been demonstrated that curli and β-amyloid are recognized by the immune system via the Toll-like receptor (TLR) 2/TLR1 complex. Here we investigated the role of CD14 in the immune recognition of bacterial amyloids. We used HeLa 57A cells, a human cervical cancer cell line containing a luciferase reporter gene under the control of an NF-κB promoter. When HeLa 57A cells were transiently transfected with combinations of human expression vectors containing genes for TLR2, TLR1, and CD14, membrane-bound CD14 enhanced NF-κB activation through the TLR2/TLR1 complex stimulated with curli fibers or recombinant CsgA, the curli major subunit. Similarly, soluble CD14 augmented the TLR2/TLR1 response to curli fibers in the absence of membrane-bound CD14. We further revealed that IL-6 and nitric oxide production were significantly higher by wild-type (C57BL/6) bone marrow-derived macrophages compared with TLR2-deficient or CD14-deficient bone marrow-derived macrophages when stimulated with curli fibers, recombinant CsgA, or synthetic CsgA peptide, CsgA-R4-5. Binding assays demonstrated that recombinant TLR2, TLR1, and CD14 bound purified curli fibers. Interestingly, CD14-curli interaction was specific to the fibrillar form of the amyloid, as demonstrated by using synthetic CsgA peptides proficient and deficient in fiber formation, respectively. Activation of the TLR2/TLR1/CD14 trimolecular complex by amyloids provides novel insights for innate immunity with implications for amyloid-associated diseases.
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140.
authors.forename: Glenn J
authors.initials: GJ
authors.lastname: Rapsinski
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140.
authors.forename: Tiffanny N
authors.initials: TN
authors.lastname: Newman
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140.
authors.forename: Gertrude O
authors.initials: GO
authors.lastname: Oppong
authors.affiliation: Department of Infectious Diseases and Immunology, Utrecht University, Yalelaan 1, 3584 CL Utrecht, The Netherlands.
authors.forename: Jos P M
authors.initials: JPM
authors.lastname: van Putten
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140. Electronic address: ctukel@temple.edu.
authors.forename: Çagla
authors.initials: Ç
authors.lastname: Tükel
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000276:immunology*; D016207:Cytokines / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D006367:HeLa Cells; D006801:Humans; D007113:Immunity, Innate; D015850:Interleukin-6 / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000378:metabolism; D051194:Toll-Like Receptor 1 / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D016207:Cytokines; D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; D016328:NF-kappa B; D009573:Nitrites; D011994:Recombinant Proteins; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; C077481:Crl protein, Bacteria
keywords: Amyloid; Bacteria; Bacterial Pathogenesis; Biofilm; CD14; Curli; Salmonella; TLR2; Toll-like Receptors (TLR)
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