title: A translocated protein of Bartonella henselae interferes with endocytic uptake of individual bacteria and triggers uptake of large bacterial aggregates via the invasome.
abstract: Bartonella henselae enters human endothelial cells (ECs) by two alternative routes: either by endocytosis, giving rise to Bartonella-containing vacuoles or by invasome-mediated internalization. Only the latter process depends on the type IV secretion system VirB/VirD4 and involves the formation of cell surface-associated bacterial aggregates, which get engulfed by EC membranes in an F-actin-dependent manner, eventually resulting in their complete internalization. Here, we report that among the VirB/VirD4-translocated effector proteins BepA-BepG only BepG is required for triggering invasome-mediated internalization. Expression of BepG in the Bep-deficient DeltabepA-G mutant restored invasome-mediated internalization. Likewise, ectopic expression of BepG in ECs also restored invasome-mediated internalization of the DeltabepA-G mutant, while no discernable cytoskeletal rearrangements were triggered in uninfected cells. Rather, BepG inhibited endocytic uptake of B. henselae into Bartonella-containing vacuoles and other endocytic processes, that is, invasin-mediated uptake of Yersinia enterocolitica and uptake of inert microspheres. BepG thus triggers invasome-mediated internalization primarily by inhibiting bacterial endocytosis. Bacteria accumulating on the cell surface then induce locally the F-actin rearrangements characteristic for the invasome. These cytoskeletal changes encompass both the rearrangement of pre-existing F-actin fibres and the de novo polymerization of cortical F-actin in the periphery of the invasome by Rac1/Scar1/WAVE- and Cdc42/WASP-dependent pathways that involve the recruitment of the Arp2/3 complex.
authors.affiliation: Focal Area Infection Biology, Biozentrum of the University of Basel, CH-4056 Basel, Switzerland.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Rhomberg
authors.forename: Matthias C
authors.initials: MC
authors.lastname: Truttmann
authors.forename: Patrick
authors.initials: P
authors.lastname: Guye
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Ellner
authors.forename: Christoph
authors.initials: C
authors.lastname: Dehio
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D018416:Bartonella henselae / Q000472:pathogenicity*; D002460:Cell Line; D002478:Cells, Cultured; D004705:Endocytosis; D042783:Endothelial Cells / Q000382:microbiology*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D054884:Host-Pathogen Interactions; D006801:Humans; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology*; D051316:Wiskott-Aldrich Syndrome Protein / Q000378:metabolism; D051300:Wiskott-Aldrich Syndrome Protein Family / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D001426:Bacterial Proteins; C542494:BepG protein, Bartonella henselae; D037521:Virulence Factors; C495767:WAS protein, human; C114864:WASF1 protein, human; D051316:Wiskott-Aldrich Syndrome Protein; D051300:Wiskott-Aldrich Syndrome Protein Family; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein