A translocated protein of Bartonella henselae interferes with endocytic uptake of individual bacteria and triggers uptake of large bacterial aggregates via the invasome.
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.
Rhomberg
Thomas A
TA
Focal Area Infection Biology, Biozentrum of the University of Basel, CH-4056 Basel, Switzerland.
Truttmann
Matthias C
MC
Guye
Patrick
P
Ellner
Yvonne
Y
Dehio
Christoph
C
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
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