title: Neu1 sialidase and matrix metalloproteinase-9 cross-talk is essential for Toll-like receptor activation and cellular signaling.
abstract: The signaling pathways of mammalian Toll-like receptors (TLRs) are well characterized, but the precise mechanism(s) by which TLRs are activated upon ligand binding remains poorly defined. Recently, we reported a novel membrane sialidase-controlling mechanism that depends on ligand binding to its TLR to induce mammalian neuraminidase-1 (Neu1) activity, to influence receptor desialylation, and subsequently to induce TLR receptor activation and the production of nitric oxide and proinflammatory cytokines in dendritic and macrophage cells. The α-2,3-sialyl residue of TLR was identified as the specific target for hydrolysis by Neu1. Here, we report a membrane signaling paradigm initiated by endotoxin lipopolysaccharide (LPS) binding to TLR4 to potentiate G protein-coupled receptor (GPCR) signaling via membrane Gα(i) subunit proteins and matrix metalloproteinase-9 (MMP9) activation to induce Neu1. Central to this process is that a Neu1-MMP9 complex is bound to TLR4 on the cell surface of naive macrophage cells. Specific inhibition of MMP9 and GPCR Gα(i)-signaling proteins blocks LPS-induced Neu1 activity and NFκB activation. Silencing MMP9 mRNA using lentivirus MMP9 shRNA transduction or siRNA transfection of macrophage cells and MMP9 knock-out primary macrophage cells significantly reduced Neu1 activity and NFκB activation associated with LPS-treated cells. These findings uncover a molecular organizational signaling platform of a novel Neu1 and MMP9 cross-talk in alliance with TLR4 on the cell surface that is essential for ligand activation of TLRs and subsequent cellular signaling.
authors.affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada.
authors.forename: Samar
authors.initials: S
authors.lastname: Abdulkhalek
authors.forename: Schammim Ray
authors.initials: SR
authors.lastname: Amith
authors.forename: Susan L
authors.initials: SL
authors.lastname: Franchuk
authors.forename: Preethi
authors.initials: P
authors.lastname: Jayanth
authors.forename: Merry
authors.initials: M
authors.lastname: Guo
authors.forename: Trisha
authors.initials: T
authors.lastname: Finlay
authors.forename: Alanna
authors.initials: A
authors.lastname: Gilmour
authors.forename: Christina
authors.initials: C
authors.lastname: Guzzo
authors.forename: Katrina
authors.initials: K
authors.lastname: Gee
authors.forename: Rudi
authors.initials: R
authors.lastname: Beyaert
authors.forename: Myron R
authors.initials: MR
authors.lastname: Szewczuk
mesh_terms: D000818:Animals; D002460:Cell Line; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology; D020780:Matrix Metalloproteinase 9 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D009439:Neuraminidase / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*
chemical_list: D008070:Lipopolysaccharides; D016328:NF-kappa B; D043562:Receptors, G-Protein-Coupled; C495345:TLR4 protein, human; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C486385:NEU1 protein, human; C110128:Neu1 protein, mouse; D009439:Neuraminidase; D020780:Matrix Metalloproteinase 9; C501830:Mmp9 protein, mouse; D019206:GTP-Binding Protein alpha Subunits, Gi-Go