Actin‐based motility allows Listeria monocytogenes to avoid autophagy in the macrophage cytosol

Abstract

Listeria monocytogenes grows in the host cytosol and uses the surface protein ActA to promote actin polymerisation and mediate actin-based motility. ActA, along with two secreted bacterial phospholipases C, also mediates avoidance from autophagy, a degradative process that targets intracellular microbes. Although it is known that ActA prevents autophagic recognition of L. monocytogenes in epithelial cells by masking the bacterial surface with host factors, the relative roles of actin polymerisation and actin-based motility in autophagy avoidance are unclear in macrophages. Using pharmacological inhibition of actin polymerisation and a collection of actA mutants, we found that actin polymerisation prevented the colocalisation of L. monocytogenes with polyubiquitin, the autophagy receptor p62, and the autophagy protein LC3 during macrophage infection. In addition, the ability of L. monocytogenes to stimulate actin polymerisation promoted autophagy avoidance and growth in macrophages in the absence of phospholipases C. Time-lapse microscopy using green fluorescent protein-LC3 macrophages and a probe for filamentous actin showed that bacteria undergoing actin-based motility moved away from LC3-positive membranes. Collectively, these results suggested that although actin polymerisation protects the bacterial surface from autophagic recognition, actin-based motility allows escape of L. monocytogenes from autophagic membranes in the macrophage cytosol.

Evasion of autophagy mediated by Rickettsia surface protein OmpB is critical for virulence

“…OmpB appears to act differently from other pathogen proteins that protect against polyubiquitylation. Form example, the L.monocytogenes surface protein ActA blocks polyubiquitylation by mobilizing the host actin machinery to the bacterial surface, which is required to protect the bacterium from autophagic recognition 11,25,51 . In contrast, OmpB has no effect on host actin mobilization by R. parkeri.…”

“…Several facultative intracellular bacterial pathogens that grow in the host cell cytosol have evolved mechanisms to evade autophagic recognition 9,21,22,23,24 . For example, Listeria monocytogenes uses its surface protein ActA to avoid polyubiquitin coat formation by masking the bacterial surface with components of the host actin machinery 22 and inducing actin polymerization and intracellular motility 11,25 . It remains unclear whether or how other pathogens avoid polyubiquitin coat formation, and what microbial proteins are ubiquitylated by the host.…”

Listeria monocytogenes Virulence, Antimicrobial Resistance and Environmental Persistence: A Review

“…ActA facilitates aggregation in L. monocytogenes through uninterrupted ActA-ActA interactions, is involved in biofilm formation, and mediates intestinal colonization [47]. Results from one study demonstrated that actin-based intracellular motility facilitates the exit of the pathogen from autophagic membranes within the macrophage cytosol [48].…”

Why isListeria monocytogenessuch a potent inducer of CD8+ T‐cells?

“…LLO is necessary to escape from both a primary phagosome and the secondary vacuole that forms upon cell‐to‐cell spread. LLO‐damaged phagosomes and free bacteria in the cytosol are recognised by the host autophagy machinery, but the bacteria secrete two phospholipases C (PlcA/B), and utilise actin‐based motility, that together allow them to bypass autophagy (Cheng, Chen, Engstrom, Portnoy, & Mitchell, ; Mitchell et al, ). Importantly, mutants lacking LLO are incapable of growth in BMMs and are 5‐logs less virulent in mice (Portnoy, Jacks, & Hinrichs, ).…”