title: Involvement of cell surface TG2 in the aggregation of K562 cells triggered by gluten.
abstract: Gluten-induced aggregation of K562 cells represents an in vitro model reproducing the early steps occurring in the small bowel of celiac patients exposed to gliadin. Despite the clear involvement of TG2 in the activation of the antigen-presenting cells, it is not yet clear in which compartment it occurs. Herein we study the calcium-dependent aggregation of these cells, using either cell-permeable or cell-impermeable TG2 inhibitors. Gluten induces efficient aggregation when calcium is absent in the extracellular environment, while TG2 inhibitors do not restore the full aggregating potential of gluten in the presence of calcium. These findings suggest that TG2 activity is not essential in the cellular aggregation mechanism. We demonstrate that gluten contacts the cells and provokes their aggregation through a mechanism involving the A-gliadin peptide 31-43. This peptide also activates the cell surface associated extracellular TG2 in the absence of calcium. Using a bioinformatics approach, we identify the possible docking sites of this peptide on the open and closed TG2 structures. Peptide docks with the closed TG2 structure near to the GTP/GDP site, by establishing molecular interactions with the same amino acids involved in stabilization of GTP binding. We suggest that it may occur through the displacement of GTP, switching the TG2 structure from the closed to the active open conformation. Furthermore, docking analysis shows peptide binding with the β-sandwich domain of the closed TG2 structure, suggesting that this region could be responsible for the different aggregating effects of gluten shown in the presence or absence of calcium. We deduce from these data a possible mechanism of action by which gluten makes contact with the cell surface, which could have possible implications in the celiac disease onset.
authors.affiliation: Department of Morphology, Surgery and Experimental Medicine, School of Medicine, University of Ferrara, Ferrara, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Feriotto
authors.affiliation: Department of Biomedical Sciences and Surgical Specialties, School of Medicine, University of Ferrara, Via Luigi Borsari 46, 44121, Ferrara, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Calza
authors.affiliation: Department of Biomedical Sciences and Surgical Specialties, School of Medicine, University of Ferrara, Via Luigi Borsari 46, 44121, Ferrara, Italy.
authors.forename: C M
authors.initials: CM
authors.lastname: Bergamini
authors.affiliation: School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, UK.
authors.forename: M
authors.initials: M
authors.lastname: Griffin
authors.affiliation: School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, UK.
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Biology, University "Tor Vergata", Rome, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Beninati
authors.affiliation: Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Ferretti
authors.affiliation: Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Marzola
authors.affiliation: Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Guerrini
authors.affiliation: Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Pagnoni
authors.affiliation: Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Cavazzini
authors.affiliation: Department of Morphology, Surgery and Experimental Medicine, School of Medicine, University of Ferrara, Ferrara, Italy.|LTTA Centre, University of Ferrara, Ferrara, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Casciano
authors.affiliation: Department of Biomedical Sciences and Surgical Specialties, School of Medicine, University of Ferrara, Via Luigi Borsari 46, 44121, Ferrara, Italy. msc@unife.it.
authors.forename: C
authors.identifier: 0000-0002-0029-2205
authors.initials: C
authors.lastname: Mischiati
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002446:Celiac Disease / Q000235:genetics / Q000276:immunology / Q000473:pathology; D002449:Cell Aggregation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D005903:Gliadin / Q000138:chemical synthesis / Q000494:pharmacology*; D005983:Glutens / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D008954:Models, Biological; D062105:Molecular Docking Simulation; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000494:pharmacology*; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D054730:Protein Interaction Domains and Motifs; D011503:Transglutaminases / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D010446:Peptide Fragments; C553138:gliadin peptide (31-43); D006153:Guanosine Diphosphate; D005983:Glutens; D006160:Guanosine Triphosphate; D005903:Gliadin; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; D002118:Calcium
keywords: Agglutination; Gluten; K562 cells; TG2; TG2-inhibitors