Intracellular Invasion by Orientia tsutsugamushi Is Mediated by Integrin Signaling and Actin Cytoskeleton Rearrangements

Abstract

Orientia tsutsugamushi, the causative agent of scrub typhus, is an obligate intracellular pathogen. Previously, we reported that the 56-kDa type-specific antigen (TSA56), a major outer membrane protein of O. tsutsugamushi, binds to fibronectin and facilitates bacterial entry into the host cell, potentially via an interaction with integrins. Here, we demonstrated that O. tsutsugamushi colocalizes with integrin ␣5␤1 and activates integrin signaling effectors, including focal adhesion kinase, Src kinase, and RhoA GTPase, and also recruits signaling adaptors, such as talin and paxillin, to the site of infection. Inhibition of protein tyrosine kinases or RhoA reduced intracellular invasion. We also observed substantial actin reorganization and membrane protrusions at the sites of infection of nonphagocytic host cells. Finally, we identified a region in the extracellular domain of TSA56 that binds to fibronectin. A peptide containing this region was able to significantly reduce bacterial invasion. Taken together, these results clearly indicate that O. tsutsugamushi exploits integrin-mediated signaling and the actin cytoskeleton for invasion of eukaryotic host cells.Orientia tsutsugamushi, an obligate intracellular organism, is the causative agent of scrub typhus (26), a disease characterized by fever, rash, eschar, pneumonitis, meningitis, and disseminated intravascular coagulation. Scrub typhus can lead to multiorgan failure if it is left untreated, and the mortality rate ranges from 1% to 40% depending on the strain of O. tsutsugamushi (29). Scrub typhus is confined geographically to southeastern Asia and is found in many countries in this region,

Molecular characterization of three major outer membrane proteins, TSA56, TSA47 and TSA22, in Orientia tsutsugamushi

“…6). Previous studies reported that O. tsutsugamushi could bind to host fibronectin and utilize it for internalization via interactions with its outer membrane protein TSA56 (27,28). Our data also confirmed the TSA56 adhesion ability to host cells.…”

“…Recent studies have shown that the scrub typhus pathogen, O. tsutsugamushi, can bind to fibronectin (Fn) via a major antigenic membrane protein, TSA56 (27,28). The ADIII and adjacent C-terminal region of TSA56 was sufficient for Fn interaction and prohibiting Fn-enhanced invasion.…”

“…In the middle of the sequence are three extracellular antigen domains (ADs) and four variable domains (VDs) (27). Previous studies reported that O. tsutsugamushi could bind to host fibronectin and utilize it for internalization via interactions with the outer membrane protein TSA56 (27,28). After adhering to the host cells, O. tsutsugamushi exploits integrin-mediated signaling and rearrangement of the actin cytoskeleton, which mediates phagocytosis in nonphagocytic host cells (29).…”

Invasion of Eukaryotic Cells byBorrelia burgdorferiRequires β1Integrins and Src Kinase Activity

“…Given that several intracellular pathogens utilize Src kinase for internalization and dissemination (16,32,51,61,78,90), we tested whether specific Src family kinase (SFK) inhibitors inhibited B. burgdorferi internalization in vitro. Specifically, Src kinase activity is required for the internalization of Neisseria spp.…”

Active Escape of Orientia tsutsugamushi from Cellular Autophagy

“…These diverse pathological changes in multiple organs are mainly due to focal or disseminated multiorgan vasculitis or perivasculitis of small blood vessels. The bacterium infects several types of nonphagocytic cells, such as endothelial cells and fibroblasts, as well as phagocytic macrophages, polymorphonuclear leukocytes (PMNs), and dendritic cells in vitro and in vivo (17)(18)(19)(20)(21). Previously, it was reported that increased autophagosomes were observed in PMNs after infection with O. tsutsugamushi (22).…”