title: Loxosceles spider venom induces metalloproteinase mediated cleavage of MCP/CD46 and MHCI and induces protection against C-mediated lysis.
abstract: We have recently shown that sphingomyelinase D toxins from the spider Loxosceles intermedia induce Complement (C) -dependent haemolysis of autologous erythrocytes by the induction of cleavage of cell-surface glycophorins through activation of a membrane-bound metalloproteinase. The aim of this study was to investigate the effects of these toxins on C-regulator expression and the C-resistance of nucleated cells. Cells were incubated with Loxosceles venom/toxins and the expression of C-regulators was assessed by flow cytometry. A reduced expression of membrane co-factor protein (MCP) was observed, while expression of decay-accelerating factor (DAF) and CD59 was not affected. Analysis of other cell-surface molecules showed a reduced expression of major histocompatibility complex I (MHCI). Western blotting showed that a truncated form of MCP was released into the supernatant. Release could be prevented by inhibitors of metalloproteinases of the adamalysin family but not by inhibitors specific for matrix metalloproteinases. Cleavage of MCP was induced close to or within the membrane as demonstrated by the cleavage of transmembrane chimeras of CD59 and MCP. Although the venom/toxins induced a release of MCP, the C-susceptibility was decreased. The mechanism of this induction of resistance may involve a change in membrane fluidity induced by the sphingomyelinase activity of the toxin/venom and/or involvement of membrane-bound proteases. The soluble forms of MCP found in tissues and body under pathological conditions like cancer and autoimmune diseases may be released by a similar mechanism. The identity of the metalloproteinase(s) activated by the spider venom and the role in pathology of Loxoscelism remains to be established.
authors.affiliation: Department of Pharmacology, Therapeutics and Toxicology, University of Wales, College of Medicine, Cardiff, UK. vandenbergcw@cardiff.ac.uk
authors.forename: Carmen W
authors.initials: CW
authors.lastname: Van Den Berg
authors.forename: Rute M Gonçalves
authors.initials: RM
authors.lastname: De Andrade
authors.forename: Fabio C
authors.initials: FC
authors.lastname: Magnoli
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Marchbank
authors.forename: Denise V
authors.initials: DV
authors.lastname: Tambourgi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D003169:Complement Inactivator Proteins / Q000378:metabolism*; D004306:Dose-Response Relationship, Immunologic; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006461:Hemolysis / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors / Q000502:physiology*; D008969:Molecular Sequence Data; D010727:Phosphoric Diester Hydrolases / Q000276:immunology*; D013111:Spider Venoms / Q000276:immunology*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D015703:Antigens, CD; C497857:CD46 protein, human; D003169:Complement Inactivator Proteins; D015395:Histocompatibility Antigens Class I; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins; D013111:Spider Venoms; C055161:loxosceles venom; D010727:Phosphoric Diester Hydrolases; D008666:Metalloendopeptidases