A Pseudomonas aeruginosa Type VI Secretion Phospholipase D Effector Targets Both Prokaryotic and Eukaryotic Cells

Abstract

Widely found in animal and plant-associated proteobacteria, type VI secretion systems (T6SSs) are potentially capable of facilitating diverse interactions with eukaryotes and/or other bacteria. Pseudomonas aeruginosa encodes three distinct T6SS haemolysin coregulated protein (Hcp) secretion islands (H1, H2, and H3-T6SS), each involved in different aspects of the bacterium's interaction with other organisms. Here we describe the characterization of a P. aeruginosa H3-T6SS-dependent phospholipase D effector, PldB, and its three tightly linked cognate immunity proteins. PldB targets the periplasm of prokaryotic cells and exerts an antibacterial activity. Surprisingly, PldB also facilitates intracellular invasion of host eukaryotic cells by activation of the PI3K/Akt pathway, revealing it to be a trans-kingdom effector. Our findings imply a potentially widespread T6SS-mediated mechanism, which deploys a single phospholipase effector to influence both prokaryotic cells and eukaryotic hosts.

Salmonella Typhimurium utilizes a T6SS-mediated antibacterial weapon to establish in the host gut

“…T6SSs are versatile systems that deliver toxins into either eukaryotic or prokaryotic cells, or both (10). For example, the Vibrio cholerae Vas and the Pseudomonas aeruginosa H2-T6SS target and kill bacteria but also inject toxins into host cells to prevent phagocytosis or to facilitate invasion, respectively (13)(14)(15)(16)(17)(18). The T6SS is a multiprotein machine that uses a contractile mechanism for toxin secretion (19).…”

Pseudomonas aeruginosa – Pathogenesis and Pathogenic Mechanisms

“…Notably, epithelial cells that were infected with P. aeruginosa mutants (PldA, PldB, H2-T6SS, or H3-T6SS deficient) displayed reduced levels of AKT phosphorylation compared with the wild type strain. Furthermore, PldA and PldB were shown to bind to AKT, and both PldA-AKT and PldB-AKT complexes localized close to the epithelial cell plasma membrane (Jiang, Waterfield, Yang, Yang, & Jin, 2014). These data suggest that PldA and PldB have a central role in the activation of the PI3K-AKT signaling pathway to promote the invasion of epithelial cells by P. aeruginosa.…”

“…Both T6SS effectors, PldA and PldB, can degrade membrane phospholipids, resulting in antibacterial activity. T6SSs, H2-T6SS-dependent PldA and H3-T6SS-dependent PldB, have also been linked to P. aeruginosa immune evasion by promoting internalization into human epithelial cells (Jiang, Waterfield, Yang, Yang, & Jin, 2014). Interestingly, mutations in the catalytic domains of both PldA and PldB reduced P. aeruginosa internalization into epithelial cells, which shows that phospholipase activity is essential for invasion of the mammalian epithelium by P. aeruginosa (Jiang, Waterfield, Yang, Yang, & Jin, 2014).…”

“…Previous works have shown that the internalization of P. aeruginosa is dependent on the activation of the eukaryotic phosphoinositide 3-kinase (PI3K), which results in AKT phosphorylation in presence of phosphatidic acid subsequent actin rearrangement and protrusion formation (Jiang, Waterfield, Yang, Yang, & Jin, 2014;Sana et al, 2012;Kierbel, Gassama-Diagne, Mostov, & Engel, 2005). In addition, PI3K/AKT signaling pathway is crucial to a range of cellular processes including cell growth, proliferation, and programmed cell death (Krachler, Woolery, & Orth, 2011).…”

“…An interest in T6SS has led to its rapid study in P. aeruginosa in term of structure, mechanical function, assembly, and regulation of secretion (Mougous et al, 2006;Ho, Dong, & Mekalanos, 2014). P. aeruginosa T6SS provides defense against other bacteria in the environment (Ho, Dong, & Mekalanos, 2014;Russell, Peterson, & Mougous, 2014) and facilitates interactions with other eukaryotic (Jiang, Waterfield, Yang, Yang, & Jin, 2014). P. aeruginosa encodes three distinct T6SS, which are known as H1-, H2-, and H3-T6SS, each involved in bacterium's interaction with other organisms.…”