Legionella RavZ Plays a Role in Preventing Ubiquitin Recruitment to Bacteria-Containing Vacuoles.

Tomoko Kubori,Hiroki Nagai,Xuan T Bui,Andree Hubber

doi:10.3389/fcimb.2017.00384

Abstract

Bacterial pathogens like Salmonella and Legionella establish intracellular niches in host cells known as bacteria-containing vacuoles. In these vacuoles, bacteria can survive and replicate. Ubiquitin-dependent selective autophagy is a host defense mechanism to counteract infection by invading pathogens. The Legionella effector protein RavZ interferes with autophagy by irreversibly deconjugating LC3, an autophagy-related ubiquitin-like protein, from a phosphoglycolipid phosphatidylethanolamine. Using a co-infection system with Salmonella, we show here that Legionella RavZ interferes with ubiquitin recruitment to the Salmonella-containing vacuoles. The inhibitory activity is dependent on the same catalytic residue of RavZ that is involved in LC3 deconjugation. In semi-permeabilized cells infected with Salmonella, external addition of purified RavZ protein, but not of its catalytic mutant, induced removal of ubiquitin associated with Salmonella-containing vacuoles. The RavZ-mediated restriction of ubiquitin recruitment to Salmonella-containing vacuoles took place in the absence of the host system required for LC3 conjugation. These observations suggest the possibility that the targets of RavZ deconjugation activity include not only LC3, but also ubiquitin.

Highlights

Legionella pneumophila is a Gram-negative bacterial pathogen that has a wide variety of eukaryotic hosts, ranging from amoebas to humans (Isberg et al, 2009)
light chain 3 (LC3) Recruitment to Salmonella-Containing Vacuoles Is Inhibited by Co-infecting L. pneumophila
Legionella RavZ is sufficient to inhibit macroautophagy in mammalian cells, but it is not the only determinant preventing LC3 recruitment to Legionella-containing vacuole (LCV) (Choy et al, 2012)

Summary

Introduction

Legionella pneumophila is a Gram-negative bacterial pathogen that has a wide variety of eukaryotic hosts, ranging from amoebas to humans (Isberg et al, 2009). Host phagocytosis normally mediates entry of L. pneumophila into cells. After entry, L. pneumophila remodels the phagosome into a replicative niche, often referred to as a Legionella-containing vacuole (LCV). In order to establish the niche, L. pneumophila translocates ∼300 effector proteins from bacteria into host cells via the specialized Dot/Icm type IV secretion system (T4SS), and by the coordinated function of these effector proteins it modulates a variety of host cellular processes (Ensminger and Isberg, 2009; Isberg et al, 2009; Hubber and Roy, 2010). It was reported that L. pneumophila recruits ubiquitin to LCVs by a process depending on the Dot/Icm T4SS and bacterial protein synthesis (Dorer et al, 2006). L. pneumophila possesses a large array of effector proteins involved in the modulation of the host ubiquitin system

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