Listeria monocytogenes InlP interacts with afadin and facilitates basement membrane crossing

Abstract

During pregnancy, the placenta protects the fetus against the maternal immune response, as well as bacterial and viral pathogens. Bacterial pathogens that have evolved specific mechanisms of breaching this barrier, such as Listeria monocytogenes, present a unique opportunity for learning how the placenta carries out its protective function. We previously identified the L. monocytogenes protein Internalin P (InlP) as a secreted virulence factor critical for placental infection. Here, we show that InlP, but not the highly similar L. monocytogenes internalin Lmo2027, binds to human afadin (encoded by AF-6), a protein associated with cell-cell junctions. A crystal structure of InlP reveals several unique features, including an extended leucine-rich repeat (LRR) domain with a distinctive Ca2+-binding site. Despite afadin’s involvement in the formation of cell-cell junctions, MDCK epithelial cells expressing InlP displayed a decrease in the magnitude of the traction stresses they could exert on deformable substrates, similar to the decrease in traction exhibited by AF-6 knock-out MDCK cells. L. monocytogenes ΔinlP mutants were deficient in their ability to form actin-rich protrusions from the basal face of polarized epithelial monolayers, a necessary step in the crossing of such monolayers (transcytosis). A similar phenotype was observed for bacteria expressing an internal in-frame deletion in inlP (inlP ΔLRR5) that specifically disrupts its interaction with afadin. However, afadin deletion in the host cells did not rescue the transcytosis defect. We conclude that secreted InlP targets cytosolic afadin to specifically promote L. monocytogenes transcytosis across the basal face of epithelial monolayers, which may contribute to the crossing of the basement membrane during placental infection.

Listeria monocytogenes Exploits Host Caveolin for Cell-to-Cell Spreading

“…One potential explanation may pertain to the L. monocytogenes internalin family of proteins which are involved in several stages of its infection cycle. Cell surface internalin A (InlA) and InlB control initial bacterial invasion into cells (77,78; see also reference 79 for a review), whereas secreted internalin C (InlC) and InlP have been shown to promote bacterial cell-to-cell and cell-to-basement membrane transfer, respectively (80,81). Consequently, future investigations into the L. monocytogenes infection cycle should focus on evaluating whether or not these bacterial components are also involved in the caveolin-mediated engulfment of membrane protrusions.…”

Potential Roles and Functions of Listerial Virulence Factors during Brain Entry

“…Both of them were found to be required for invasion into multiple different cell types, initiating a zipper-type endocytosis [11,30,31]. In addition to InlA and InlB, there are other Inl family members addressed in the literature-for some of them, host cell interaction partners and functions have been described (InlC, InlF, InlK and InlP), while the role of the others is suggested on the basis of available data but not yet fully confirmed (InlH, InlJ and InlL) [19,21,26,[32][33][34][35].…”

Mechanical competition triggered by innate immune signaling drives the collective extrusion of bacterially-infected epithelial cells

“…Similarly, we showed that when L.m. crosses through basement membranes such as those of the placenta, it secretes the InlP toxin which leads to a weakening of the tensional forces between host epithelial cells and their extracellular matrix, thus facilitating apico-basal bacterial spread 4 . Rickettsia parkeri, a bacterial pathogen that undergoes actin based motility like L.m., powers its intracellular spread by reducing intercellular tension between host epithelial cells through secretion of the effector protein Sca4 that disrupts cell-cell junctions 1 .…”

“…The biomechanical interactions between host cells and bacterial pathogens are dictated by both the pathogen and the host. It has been previously shown that there are ways through which intracellular pathogens can manipulate host cell functions, including host cell mechanotransduction, in order to spread more efficiently [1][2][3]…”