title: Shiga toxin regulates its entry in a Syk-dependent manner.
abstract: Shiga toxin (Stx) is composed of an A-moiety that inhibits protein synthesis after translocation into the cytosol, and a B-moiety that binds to Gb3 at the cell surface and mediates endocytosis of the toxin. After endocytosis, Stx is transported retrogradely to the endoplasmic reticulum, and then the A-fragment enters the cytosol. In this study, we have investigated whether toxin-induced signaling is involved in its entry. Stx was found to activate Syk and induce rapid tyrosine phosphorylation of several proteins, one protein being clathrin heavy chain. Toxin-induced clathrin phosphorylation required Syk activity, and in cells overexpressing Syk, a complex containing clathrin and Syk could be demonstrated. Depletion of Syk by small interfering RNA, expression of a dominant negative Syk mutant (Syk KD), or treatment with the Syk inhibitor piceatannol inhibited not only Stx-induced clathrin phosphorylation but also endocytosis of the toxin. Also, Golgi transport of Stx was inhibited under all these conditions. In conclusion, our data suggest that Stx regulates its entry into target cells.
authors.affiliation: Department of Biochemistry, Institute for Cancer Research, The Norwegian Radium Hospital, 0310 Oslo, Norway.
authors.forename: Silje Ugland
authors.initials: SU
authors.lastname: Lauvrak
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wälchli
authors.forename: Tore-Geir
authors.initials: TG
authors.lastname: Iversen
authors.forename: Hege Holte
authors.initials: HH
authors.lastname: Slagsvold
authors.forename: Maria Lyngaas
authors.initials: ML
authors.lastname: Torgersen
authors.forename: Bjørn
authors.initials: B
authors.lastname: Spilsberg
authors.forename: Kirsten
authors.initials: K
authors.lastname: Sandvig
mesh_terms: D033922:Clathrin Heavy Chains / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D004789:Enzyme Activation; D019833:Genistein / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D022621:Shiga Toxin / Q000378:metabolism*; D013267:Stilbenes / Q000494:pharmacology; D000072377:Syk Kinase; D014443:Tyrosine / Q000378:metabolism
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D013267:Stilbenes; D033922:Clathrin Heavy Chains; D014443:Tyrosine; C041525:3,3',4,5'-tetrahydroxystilbene; D022621:Shiga Toxin; D019833:Genistein; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase