The Listeria monocytogenes Protein InlB Is an Agonist of Mammalian Phosphoinositide 3-Kinase

Abstract

The Gram-positive pathogen Listeria monocytogenes induces its own internalization into some non-phagocytic mammalian cells by stimulating host tyrosine phosphorylation, phosphoinositide (PI) 3-kinase activity, and rearrangements in the actin cytoskeleton. Entry into many cultured cell lines is mediated by the bacterial protein InlB. Here we investigate the role of InlB in regulating mammalian signal transduction and cytoskeletal structure. Treatment of Vero cells with purified InlB caused rapid and transient increases in the lipid products of the PI 3-kinase p85-p110, tyrosine phosphorylation of the mammalian adaptor proteins Gab1, Cbl, and Shc, and association of these proteins with p85. InlB also stimulated large scale changes in the actin cytoskeleton (membrane ruffling), which were PI 3-kinase-dependent. These results identify InlB as the first reported non-mammalian agonist of PI 3-kinase and demonstrate similarities in the signal transduction events elicited by this bacterial protein and known agonists such as epidermal growth factor.Infection of viral, bacterial, or protozoan intracellular pathogens often involves subversion of mammalian signaling pathways. The first step in the life cycle of an intracellular pathogen is internalization by the host cell. While some microbial pathogens are taken up only by professional phagocytes (macrophages or neutrophils), others induce their own uptake ("enter") into cells that are not normally phagocytic, such as epithelial cells underlying mucosal surfaces or endothelial cells inside blood vessels (reviewed in Ref. 1). Entry into non-phagocytic cells can permit traversal of tissue-specific barriers and promote survival of the pathogen by providing access to a nutrient-rich environment that is protected from host antibody or complement.Listeria monocytogenes is a food-borne bacterial pathogen that causes severe illnesses leading to meningitis or abortions in immunocompromised individuals or pregnant women (2).This faculative intracellular pathogen enters into cells that are non-phagocytic, including epithelial cells and hepatocytes. Entry into such cells is likely to play an important role in traversing the intestinal, blood-brain, and placental barriers, and in colonization of the liver (reviewed in Ref. 3).Entry of L. monocytogenes into non-phagocytic cells involves specific bacterial surface proteins that exhibit cell tropism. The bacterial protein InlA (internalin) promotes entry into the intestinal epithelial cell line Caco-2, whereas the protein InlB mediates internalization into several other cultured cell lines, including Vero, HEp-2, HeLa, and some hepatocytes (4 -6). InlB has a role in virulence in the mouse model, as a bacterial mutant (⌬inlB) deleted for the inlB gene is defective in colonization of the liver (4, 5, 7). InlA promotes bacterial entry by interacting with its mammalian receptor, the cell-cell adhesion molecule E-cadherin (8). The mammalian receptor for InlB is not known.Entry of L. monocytogenes requires tyrosine phosphorylation and other sig...

Phosphatidylinositol 3-Kinase Activation and Interaction with Focal Adhesion Kinase in Escherichia coli K1 Invasion of Human Brain Microvascular Endothelial Cells

“…PI3K involvement has been demonstrated in L. monocytogenes invasion of epithelial cells. However, PI3K involvement is independent of FAK in L. monocytogenes invasion of epithelial cells (15). In contrast, our findings indicate the requirement of PI3K interaction with FAK in E. coli K1 invasion of HBMEC.…”

Entry of Listeria monocytogenes in Mammalian Epithelial Cells: An Updated View

“…On the contrary, 10-and 20-fold increases on PI(3,4)P 2 or PI(3,4,5)P 3 levels are detected on infection of Vero cells with L. monocytogenes via the InlB-invasion pathway (Ireton et al 1996). In these cells, activation of type IA PI 3-kinase is promoted by the protein adaptors Gab1, Cbl, and Shc, which are phosphorylated and recruited to the Met cytoplasmic tail, translocating with them the p85 subunit to the L. monocytogenes invasion foci (Ireton et al 1999;Shen et al 2000). Gab1 can also be translocated to the plasma membrane through its pleckstrin homology domain, which binds PI(3,4,5)P 3 (Basar et al 2005) and indirectly boosts type IA PI 3-kinase activity via recruitment of the adaptor protein CrkII (Sun et al 2005;Dokainish et al 2007).…”

The arsenal of virulence factors deployed byListeria monocytogenesto promote its cell infection cycle

“…81,82 Although InlB has several receptors, it is well accepted that Met is the major InlB signaling receptor. InlB has the ability to induce Met autophosphorylation and the recruitment of adaptor proteins, such as Cbl, Shc and Gab1, [83][84][85] that lead to the activation of PI3-kinase 86 and small GTPase Rac1. 87 Upon interaction with Met, InlB induces Met ubiquitination and bacterial internalization via a clathrin-mediated endocytosis mechanism.…”