A Translocated Effector Required for Bartonella Dissemination from Derma to Blood Safeguards Migratory Host Cells from Damage by Co-translocated Effectors

Abstract

Numerous bacterial pathogens secrete multiple effectors to modulate host cellular functions. These effectors may interfere with each other to efficiently control the infection process. Bartonellae are Gram-negative, facultative intracellular bacteria using a VirB type IV secretion system to translocate a cocktail of Bartonella effector proteins (Beps) into host cells. Based on in vitro infection models we demonstrate here that BepE protects infected migratory cells from injurious effects triggered by BepC and is required for in vivo dissemination of bacteria from the dermal site of inoculation to blood. Human endothelial cells (HUVECs) infected with a ΔbepE mutant of B. henselae (Bhe) displayed a cell fragmentation phenotype resulting from Bep-dependent disturbance of rear edge detachment during migration. A ΔbepCE mutant did not show cell fragmentation, indicating that BepC is critical for triggering this deleterious phenotype. Complementation of ΔbepE with BepEBhe or its homologues from other Bartonella species abolished cell fragmentation. This cyto-protective activity is confined to the C-terminal Bartonella intracellular delivery (BID) domain of BepEBhe (BID2.EBhe). Ectopic expression of BID2.EBhe impeded the disruption of actin stress fibers by Rho Inhibitor 1, indicating that BepE restores normal cell migration via the RhoA signaling pathway, a major regulator of rear edge retraction. An intradermal (i.d.) model for B. tribocorum (Btr) infection in the rat reservoir host mimicking the natural route of infection by blood sucking arthropods allowed demonstrating a vital role for BepE in bacterial dissemination from derma to blood. While the Btr mutant ΔbepDE was abacteremic following i.d. inoculation, complementation with BepEBtr, BepEBhe or BIDs.EBhe restored bacteremia. Given that we observed a similar protective effect of BepEBhe on infected bone marrow-derived dendritic cells migrating through a monolayer of lymphatic endothelial cells we propose that infected dermal dendritic cells may be involved in disseminating Bartonella towards the blood stream in a BepE-dependent manner.

Evolutionary Dynamics of Pathoadaptation Revealed by Three Independent Acquisitions of the VirB/D4 Type IV Secretion System in Bartonella

“…Previous work on Beps of L3 or L4 stayed descriptive regarding the phosphorylation itself and only studied phenotypes that appeared to be unrelated to these motifs (Engel et al. 2011; Okujava et al. 2014).…”

The BID Domain of Type IV Secretion Substrates Forms a Conserved Four-Helix Bundle Topped with a Hook

“…The single BID Structure 25, 203–211, January 3, 2017 domain of BepA binds to host adenylyl cyclase and potentiates GαS-dependent cyclic AMP (cAMP) production, ultimately resulting in inhibition of apoptosis (Pulliainen et al, 2012). The BID domains of BepE are required for normal migration of host cells during infection in vitro and in vivo (Okujava et al, 2014), and those of BepF or BepG trigger actin-dependent uptake of bacterial aggregates into a unique cellular structure known as invasome (Rhomberg et al, 2009; Truttmann et al, 2011). …”

Infections and cardiovascular disease: is Bartonella henselae contributing to this matter?

“…Indeed, in this model, bacteria grow in extracellular aggregates, embedded within collagen matrix, similar to the observations in BP, BA and cat-scratch disease (Chiaraviglio et al, 2010). Bacterial VirB type IV secretion systems (T4SSs) represent crucial pathogenic factors that have contributed to the Bartonella henselae expansion in nature; in fact, T4SSs facilitate adaptation to mammalian hosts (Schmid et al, 2004;Schülein et al, 2001) by translocation of a cocktail of Bartonella effector proteins (Beps) into host cells (Okujava et al, 2014). The ability to survive in these cells helps Bartonella henselae to escape the host immune response, with its lowendotoxic-potency lipopolysaccharide (Zähringer et al, 2004).…”

“…Mechanisms required to infect human erythrocytes and ECs are (i) massive rearrangements of actin cytoskeleton with formation of bacterial aggregates (invasome) (Dehio, 2001); (ii) NFkB-dependent proinflammatory activation, leading to adhesion molecule expression and chemokine secretion (Kempf et al, 2001;Resto-Ruiz et al, 2002); (iii) inhibition of apoptosis (Kirby & Nekorchuk, 2002); (iv) two T4SSs (Trw and VirB) to adapt to a wide range of mammalian hosts, both essential for the interaction with the host but at different stages of the infection cycle (Okujava et al, 2014).…”