Listeria monocytogenes ActA-mediated escape from autophagic recognition. Nat Cell Biol

Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, 4-6-1, Shirokanedai, Minato-Ku, Tokyo 108-8639, Japan.
Nature Cell Biology (Impact Factor: 19.68). 09/2009; 11(10):1233-40. DOI: 10.1038/ncb1967
Source: PubMed


Autophagy degrades unnecessary organelles and misfolded protein aggregates, as well as cytoplasm-invading bacteria. Nevertheless, the bacteria Listeria monocytogenes efficiently escapes autophagy. We show here that recruitment of the Arp2/3 complex and Ena/VASP, via the bacterial ActA protein, to the bacterial surface disguises the bacteria from autophagic recognition, an activity that is independent of the ability to mediate bacterial motility. L. monocytogenes expressing ActA mutants that lack the ability to recruit the host proteins initially underwent ubiquitylation, followed by recruitment of p62 (also known as SQSTM1) and LC3, before finally undergoing autophagy. The ability of ActA to mediate protection from ubiquitylation was further demonstrated by generating aggregate-prone GFP-ActA-Q79C and GFP-ActA-170(*) chimaeras, consisting of GFP (green fluorescent protein), the ActA protein and segments of polyQ or Golgi membrane protein GCP170 (ref. 6). GFP-ActA-Q79C and GFP-ActA-170(*) formed aggregates in the host cell cytoplasm, however, these ActA-containing aggregates were not targeted for association with ubiquitin and p62. Our findings indicate that ActA-mediated host protein recruitment is a unique bacterial disguise tactic to escape from autophagy.

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Available from: Torsten Hain, Oct 28, 2015
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    • "Although poly-ubiquitination is thought to be the hallmark of protein degradation via the ubiquitin-proteasome system, it also appears to function as a tag for autophagymediated degradation. Indeed, cytosol-invading bacteria have been shown to frequently colocalize with ubiquitinated proteins (Perrin et al., 2004; Collins et al., 2009; Dupont et al., 2009; Yoshikawa et al., 2009; Watson et al., 2012). Possible mechanisms for this bacteriaubiquitin colocalization include the direct ubiquitination of bacteria and the ubiquitination of bacteria-containing endosomes. "
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    • "Peroxisomes may also undergo regulated ubiquitination, and pexophagy was shown to be partially dependent on p62 (Deosaran et al., 2013; Kim et al., 2008). Furthermore, intracellular bacteria, such as Listeria, Shigella, and Salmonella, undergo ubiquitination in response to their escape from endosomes, and p62 was shown to mediate their degradation (Mostowy et al., 2011; Yoshikawa et al., 2009; Zheng et al., 2009). NBR1. "
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    • "Some intracellular bacterial pathogens, such as Salmonella Typhimurium (Birmingham et al., 2006) and Staphylococcus aureus (Schnaith et al., 2007), avoid autophagy by replicating within modified endocytic or autophagic compartments. Other bacterial pathogens, such as Shigella flexneri and Listeria monocytogenes, escape the endocytic pathway and replicate in the cytosol of infected cells, avoiding ubiquitylation by camouflaging their surface with bacterial or host-derived proteins (Dortet et al., 2011; Ogawa et al., 2005; Yoshikawa et al., 2009). Here we provide several lines of evidence that GAS employ a proteolytic mechanism to evade autophagy and replicate in the cytosol of infected cells: (1) genetic deletion of the gene encoding SpeB significantly reduced the intracellular replication of M1T1 5448 ; (2) genetic deletion of the gene encoding SpeB from the M1T1 5448 strain significantly increased the frequency of the recruitment of LC3 to the surface of the intracellular bacteria; (3) expression of SpeB by M6 JRS4 promoted intracellular replication and abolished recruitment of LC3 to the bacterial surface; (4) purified SpeB degrades the ubiq- uitin-LC3 adaptor proteins p62, NDP52, and NBR1; (5) ectopic expression of codon-optimized SpeB in HEp-2 cells reduced the amounts of p62, NDP52, and NBR1; and (6) WT SpeB-expressing strains replicate efficiently in epithelial cells while naturally occurring SpeB-defective strains fail to replicate. "
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    ABSTRACT: Autophagy is reported to be an important innate immune defense against the intracellular bacterial pathogen Group A Streptococcus (GAS). However, the GAS strains examined to date belong to serotypes infrequently associated with human disease. We find that the globally disseminated serotype M1T1 clone of GAS can evade autophagy and replicate efficiently in the cytosol of infected cells. Cytosolic M1T1 GAS (strain 5448), but not M6 GAS (strain JRS4), avoids ubiquitylation and recognition by the host autophagy marker LC3 and ubiquitin-LC3 adaptor proteins NDP52, p62, and NBR1. Expression of SpeB, a streptococcal cysteine protease, is critical for this process, as an isogenic M1T1 ΔspeB mutant is targeted to autophagy and attenuated for intracellular replication. SpeB degrades p62, NDP52, and NBR1 in vitro and within the host cell cytosol. These results uncover a proteolytic mechanism utilized by GAS to escape the host autophagy pathway that may underpin the success of the M1T1 clone.
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