title: PKC-dependent endocytosis of the Helicobacter pylori vacuolating cytotoxin in primary T lymphocytes.
abstract: Gastric infection by Helicobacter pylori (Hp) is associated with development of gastritis, ulcerations and gastric adenocarcinoma. Production and secretion of the vacuolating cytotoxin (VacA) is an essential Hp virulence factor. VacA is a multifunctional toxin, which exerts immunosuppressive effects on human T lymphocytes via inhibition of cell proliferation and Interleukin-2 (IL-2) signalling. This latter effect of VacA is dependent on the β2-integrin subunit CD18, acting as a receptor for intracellular uptake of VacA. In this study, we investigated the mechanism of endocytosis of VacA into primary human T lymphocytes. A screen with chemical inhibitors for different sets of kinases identified Ser/Thr kinases of the protein kinase C (PKC) family as crucial. Specific inhibitory peptides blocking PKCη or PKCζ-phosphorylating activity, but not PKCα/β specific peptides, resulted in a strong reduction or complete block of VacA uptake. Thus the phosphorylating activity of PKCη and PKCζ is essential for the induction of VacA endocytosis. Furthermore, mimicking of a possible PKC-mediated threonine (T(758)) phosphorylation of the CD18 cytoplasmic tail in resting primary T cells induced VacA endocytosis via activation of the small GTPases Cdc42 and Rac-1. We conclude that VacA is endocytosed into primary T cells via a clathrin-independent pathway.
authors.affiliation: Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: Xaver
authors.initials: X
authors.lastname: Sewald
authors.forename: Luisa
authors.initials: L
authors.lastname: Jiménez-Soto
authors.forename: Rainer
authors.initials: R
authors.lastname: Haas
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D018821:CD18 Antigens / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D002478:Cells, Cultured; D004705:Endocytosis; D005753:Gastric Mucosa / Q000276:immunology / Q000382:microbiology; D006367:HeLa Cells; D016481:Helicobacter Infections / Q000378:metabolism / Q000503:physiopathology; D016480:Helicobacter pylori / Q000378:metabolism / Q000472:pathogenicity*; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism; D019169:Jurkat Cells; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D015398:Signal Transduction; D037521:Virulence Factors; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018821:CD18 Antigens; D007376:Interleukin-2; C074689:VacA protein, Helicobacter pylori; D037521:Virulence Factors; D011493:Protein Kinase C; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein